Proceedings ofWorkshop on Semiconductor
Materials and Detectors,
November 19, 2013,
The University of Toledo, OH, USA

Jointly held by

Dr. Toru Aoki laboratory of
Graduate School of Informatics,(Faculty of Informatics)
at Shizuoka University&
Nanotechnology and MEMS Laboratory of
MIME Department at the University ofToledoEdited by: Dr. Ahalapitiya H. Jayatissa of the University of Toledo
and Dr. Toru Aoki of Shizuoka University

Proceedings of Workshop on Semiconductor Materials and Detectors, November 19, 2013, Toledo, OH, USA

Introduction
This workshop will cover current research topics of Toru Aoki Laboratory at
Shizuoka University and Nanotechnology and MEMS laboratory of MIME Department at
the University of Toledo. The topics covered include electronic materials, nanomaterials,
neutron and other radiation detectors. These materials have numerous applications inother fields such as, electronics, biotechnology, energy harvesting and sustainability ofenvironments. The importance of semiconductor materials and device technology has
been well documented by both industrial and academic communities worldwide. It isbelieved that breakthroughs in these fields will create more opportunities in safety aspects
in nuclear power industries and security.
The workshop is intended to provide a exchange of ideas between two universities.
Also, this activity support Japanese students to see US universities and researchlaboratories. The primary objectives of this workshop are to:1) Facilitate interaction between students from Shizuoka University and the
University of Toledo related to the fields of development and application ofmaterials, with a special emphasis on sensors;(2) Provide graduate students and undergraduate students with a forum to actively
engage in research discussions, and professional development; and(3) Create opportunities for the cultural exchange activities of both institutions.
This workshop will include one plenary speech on engineering ethics and contributed
presentations. The plenary session has five presentations in the field of electronics
materials, nonmaterial's, and characterization methods. These topics address timely andimportant issues around the globe.
The workshop provides opportunities for senior undergraduate students, graduate
students and professors to actively engage in research discussions, and professional
development. We hope participants will enjoy the technical program of this conference.

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Proceedings of Workshop on Semiconductor Materials and Detectors, November 19, 2013, Toledo, OH, USA

Program Schedule
November 19 (Tuesday),Room # 4000 MIME Conference Room

10.00 am - 10.30 am

Introduction of Workshop
Dr. A. H. Jayatissa and Dr. A. H. Aoki
Dr. A. H. Jayatissa
Evaluation of Semiconductor Radiation Detector

10.30 am - 11.00 am

High-Contrast K-Edge CT by CdTe Photon Counting Detector

9.30 am - 10.00 am
Session Chair

11.00 am - 11.30 am
11.30 am - 12.00 am

Direction detection of radioisotope using a semiconductor radiation detector
Low exposure CT using a photon counting detector

12.0 am - 1.00 am

Lunch Speech, Engineering Ethics
Dr. Douglas Oliver, PhD, JD

Session Chair

Dr/ Toru Aoki

1.00 am - 1.30 pm

BGaN Semiconductor Neutron Detector

2.30 pm - 3.00 pm

Aqueous Hydrothermal Synthesis and Charaterization of Pyrite (FeS2)
Nanoparticles
Effects of Laser Irradiation on Optical, Structural and Gas Sensing Properties of
Sputtered ZnO Thin Films
Polypyrrole/Graphene Nanocomposite Synthesis and Conductivity Study

3.00 pm - 3.30 pm

Experimental Study on Thin Film Cu2ZnSnS4 Deposition by Spin Coating

1.30 pm - 2.0 pm
2.00 pm - 2.30 pm

3.30 pm - 4.00 pm
4.00 pm - 4.20 pm

Estimation of thickness of ultra-thin materials by optical measurements
Concluding Remarks: Dr. Toru Aoki
Acknowledgements: Dr. A. H. Jayatissa

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Proceedings of Workshop on Semiconductor Materials and Detectors, November 19, 2013, Toledo, OH, USA

Table of Content
Page

1. Evaluation of Semiconductor Radiation Detector
Hisaya Nakagawa, Hisashi Morii, Hidenoori Mimura, and Toru Aoki

5

2. High-Contrast K-Edge CT by CdTe Photon Counting Detector
Kanichi. Ashitomi, Yukino. Imura, Hidenori. Mimura, Toru. Aoki

8

3. BGaN Semiconductor Neutron Detector
Masaki Nakamura, Katsuhiro Atsumi, and Takayuki Nakano
Hidenori Mimura, Toru Aoki

12

4. Low exposure CT using a photon counting detector
Ryudai Hatanaka, Kanichi Ashitomi, Yukino Imura, Hidenori Mimura, Toru Aoki

14

5.

Direction detection of radioisotope using a semiconductor radiation detector
Takuto Sanada , Toru Aoki , Hidenori Mimura, and Hisashi Morii17

6. Aqueous Hydrothermal Synthesis and Charaterization of Pyrite (FeS2) Nanoparticles
Zhengqi Shi and Ahalapitiya H. Jayatissa

20

7. Effects of Laser Irradiation on Optical, Structural and Gas Sensing Properties of
Sputtered ZnO Thin Films
Yue Hou and Ahalapitiya H. Jayatissa

24

8. Polypyrrole/Graphene Nanocomposite Synthesis and Conductivity Study
Weiling Wang and Ahalapitiya H. Jayatissa

28

9.

Experimental Study on Thin Film Cu2ZnSnS4 Deposition by Spin Coating
Mahdi Rajabpour, Zhengqi Shi and Ahalapitiya H. Jayatissa

433

Proceedings of Workshop on Semiconductor Materials and Detectors, November 19, 2013, Toledo, OH, USA

Evaluation of Semiconductor Radiation Detector
Hisaya Nakagawaa, Hisashi Moriib, Hidenoori Mimurab and Toru AokibaFaculty of Informatics, Shizuoka University, Japan, cs10066@s.inf.shizuoka.ac.jp,bResearch Institute of electronics, Shizuoka University, Japan,

ABSTRACT:In this study, we compared the characteristic of CdTe, CdZnTe and TlBr. In physical property and simulation,
CdTe, CdZnTe, TlBr semiconductors have high detection efficiency for gamma-ray and X-ray. In current-voltage
characteristic and capacitance-voltage characteristic, CdTe and CdZnTe semiconductors have schottky junction and
TlBr has ohmic contact. In gamma-ray spectral measurement, the total absorption peak of CdTe is appeared
sufficient. But that of CdZnTe and TlBr was not enough.

Key words: Semiconductor radiation detector, Thallium Bromide (TlBr), Cadmium Telluride (CdTe),
Cadmium Zinc Telluride (CdZnTe)(7.56g/cm3) and wide band gap energy (2.68eV). In
the semiconductor, the larger the atomic number anddensity are important for the high detection efficiency.
And the wider band gap energy is for the less thermal
noise. Table 1 shows physical property ofsemiconductor materials.

I. Introduction
At present, the small X-ray tube and accelerator(about 1MeV) were developed and made practicable.
The social infrastructure, containers which cannot betransmitted X-ray can become measured. However
detectors have low sensitivity and low energy
resolution.
We use CdTe semiconductor radiation detector.
The thick CdTe is necessary to detect high energy.
CdTe have weak point to increase leakage current
when increase of thickness. We use CdZnTe which
can inhibit leakage current even if it is thick. Also,
detector which made heavy material to detect for highenergy. We can use TlBr which is heavier than CdTe.
In this study, we compared the characteristic of CdTe,
CdZnTe, and TlBr with the aim of creating
semiconductor radiation detector which has highsensitivity and high energy resolution for high energy
at room temperature.

Table1
Physical property of semiconductor
AtomicBand gap
Density
NumberEnergy(g/cm3)
(eV)
CdTe
5.85
1.44
48，52
CdZnTe5.81
1.6
48，30，52
TlBr
7.56
2.68
81，35

III. Simulation
The simulation was performed by Electron
Gamma Shower version 5 (EGS5) of High Energy
Accelerator Research Organization. EGS5 is Monte
Carlo particle transport calculation simulator. The sizeof all detectors was 10mm×10mm×0.5mm. And
radiation source was 137Cs source. Fig 1 shows theresults of simulation. All detectors were shown
662keV the full energy peak. Therefore, they havehigh detection extraction for X-ray and gamma-ray inthe simulation.

II. Physical property
Semiconductors used as semiconductor radiation
detectors are Si or Ge. Si detector has low atomic
number (14) and low density (2.33g/cm3). Therefore,
this is not suitable for the detection of high energy Xray and gamma-ray. Ge detector has high atomic
number (32) and high density (5.33g/cm3). But, it low
band gap energy (0.72eV) material. Therefore it has
weak point that it is necessary to be cool. CdTe hashigh atomic number (Cd:48 Te:52), high density(5.85g/cm3) and wide band gap energy (1.44eV).
CdZnTe is crystal growth with Zn. Its average atomic
number and density hardly change CdTe. However its
band gap energy is slightly bigger than CdTe. TlBr
has high atomic number (Tl:81 Br:35), high density

IV. Evaluation of electrical characteristic
Semiconductor is required charge transportationand extraction. In order to extract, there is a need as
small as possible leakage current. And the size of
depletion layer is also important. There are notincluded in the results of simulation. We researched

5Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USAleakage current by current-voltage characteristic anddepletion layer by capacitance-voltage characteristic.

IV-1. Current-voltage characteristic
Semiconductor which has ohmic contact follow
ohmic law, when it was applied voltage.
Semiconductor which has schottky junction starts toflow current above a certain voltage when it wasapplied forward current. When it was applied reverse
bias, current flow very low in the ideal. But current
flow it in actually. Current-voltage characteristic wasmeasured by Semiconductor Parameter Analyzer(Hewlett Packard 4155B). Fig 2 shows currentvoltage characteristic obtained from CdTe, CdZnTeand TlBr. Bias voltage applied from -100V to 100V atroom temperature. In the TlBr's measurement, since
the relationship between applied voltage and current is
proportional connection, it has ohmic contact. The
result of CdTe and CdZnTe, they have a schottky
junction. And when they were applied reverse bias,
the leakage current of CdTe is bigger than that of
CdZnTe. Because the band gap energy of CdTe isnarrower than that of CdZnTe.

Fig.1 Simulation of the 137Cs (a)Result of CdTe (b)Result of
CdZnTe (c)Result of TlBr

Fig.2 Current-voltage characteristic of CdTe, CdZnTe andTlBr

IV-2. Capacitance-voltage Characteristic
All detectors were performed capacitance-voltage
characteristic to compare depletion layer spread when
it was applied bias voltage. Capacitance-voltage
characteristic was measured by Precision Impedance
Analyzer (Agilent Technologies 4294A). Fig 3 shows
capacitance-voltage characteristic obtained from
CdTe, CdZnTe and TlBr. Bias voltage was applied
from -40V to 40V at room temperature in dark room.
In the result of this measurement, we cannot obtain
results to discuss enough because of small capacity.
But CdTe and CdZnTe semiconductors show
dependent on voltage. TlBr semiconductor does notshow dependent on voltage. Therefore, we can say
CdTe and CdZnTe have schottky junction and TlBr
has ohmic contact in conjunction with current-voltage
characteristic.

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Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USA

Fig 4. Gamma-ray spectral measurement of 137Cs (a) Result of CdTe(b) Result of CdZnTe (c) Result of TlBr

Fig3. Capacitance-voltage characteristic of CdTe

V. Gamma-ray spectral measurement

Gamma-ray energy of 137Cs spectra wasmeasured to evaluate the spectral characteristic ofdetections at the room temperature. The output signal
from the amplifier were observed and recorded bymulti-channel analyzer. When CdTe and CdZnTe
were measured, bias voltage was applied 400V andshaping time was 0.5µs. When TlBr was measured,bias voltage was applied 100V and shaping time was
6.0µs. Fig 4 show gamma-ray spectral measurement
obtained from CdTe, CdZnTe and TlBr. The fullenergy peak of CdTe is appeared sufficient. But thatof CdZnTe was small, and that of TlBr was notappeared.

VI. Conclution
In physical property and simulation, we foundthat detection efficiency of CdTe, CdZnTe, TlBr
semiconductor for gamma-ray and X-ray is high. In
current-voltage characteristic and capacitance-voltage
characteristic, CdTe and CdZnTe semiconductor haveschottky junction and TlBr has ohmic contact. And
when CdTe and CdZnTe compared, the leakage
current of CdZnTe is smaller than that of CdTe. In
gamma-ray spectral measurement, the total absorption
peak of CdTe was appeared sufficient. But that of
CdZnTe was small, and that of TlBr was not appeared.
In conclusion, three detectors was high detection
efficiency in the theoretical value. However, thedetectors were shown excellent results in themeasured value. We think that these results are theproblem which is crystalline.
References[1] Tadayuki
Takahashi ， Kazuhiro
Nakazawa
CdTe/CdZnTe handotai wo mochiita gammasen
kensyutuki to utyuu kannsokuhe no oyo (Application to
space observation and gamma-ray detector)[2] Fumihiko Hirose(2013) Handotai debaisu no yoten(Pointofsemiconductor
device)http://fhirose.yz.yamagatau.ac.jp/(Accessed2013.11.01)

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Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USA

High-Contrast K-Edge CT by CdTe Photon Counting Detector
Kanichi. Ashitomi1,2,*, Yukino. Imura1, Hidenori. Mimura1, Toru. Aoki1,2

1Research Institute of Electronics, Shizuoka University, Hamamatsu, Japan
Graduate School of Informatics, Shizuoka University, Hamamatsu, Japan2

3-5-1, Johoku, Naka-ku, Hamamatsu City, Shizuoka 432-8011, Japan
TEL&FAX: +81-53-478-1319*
e-mail: ashitomi@nvrc.rie.shizuoka.ac.jp
ABSTRACT:
X-ray are used in Medical treatment field as Roentgenogram, X-ray CT, PET and so on. It is potentially demanded
for using low dose X-ray for human body. We conducted K-edge CT with photon-counting detector using cadmium
telluride(CdTe) and made extracted images of Iodine which is used for contrast media at blood vessel inangiography. Though there are some noise on the others part as low dose X-ray, we can see blood vessel clearly. We
can make higher contrast CT images of iodine by using high energy resolution.

Key words: low dose, k-edge, photon-counting, cadmium telluride1.

energy band width for K-edge CT. Using narrower
energy band width for K-edge CT makes higher
contrast.

Introduction

Low dose X-ray imaging has been demanded on Xray photography and X-ray computed tomography(X-ray CT), etc for medical care scene[1].
Angiography which uses contrast media is useful tosee blood vessel clearly, though there is noise on theothers part in low dose X-ray imaging. K-edge CT
use feature of K-edge and information of X-ray
energy for subtraction[2][3]. We can extract Iodine ofblood vessel by K-edge CT and see it more clearly.
We obtained information of X-ray energy by photon
counting detector. We used information of X-ray
energy for subtraction. We used CdTe semiconductor
detector with high energy resolution. We discussed
energy band width and over lapping energy band forK-edge CT. Energy band width and over 0lapping
affect contrast of subtracted images. Two points
above and below K-edge is the best of energy band
width for K-edge CT. So, broad energy band widthcontaining linear part of spectrum of X-ray and overlapping energy band makes low contrast because it is
low for difference of amount of X-ray counts for two
CT images. Then, we try to use strict band width for
K-edge CT. As CdTe semiconductor detector has
high energy resolution, we can use strict X-ray

2.

K-Edge CT

We carried out K-edge radiography using iodinebased contrast media. The iodine contrast
media(30mg/ml) put into a hole in an acrylic vessel
and it was measured by X-ray CT with the CdTe
detector using photon counting method(X-ray tube
voltage:150kV, current 8uA). K-edge energy is a
specific property of X-ray energy of each material.
The X-ray attenuation coefficient for a material has
discontinuous relation below and above K-edgeenergy. K-edge of iodine is 33.2keV. Since the X-ray
attenuation coefficient for bones and muscles don’t
have K-edge at 33.2keV, we can see large differenceof image of iodine in two CT images used data below
and above K-edge without bones and muscles image.
Then, we extracted iodine image by subtraction ofthese two CT images.
Our detector has high energy resolution(~1keV).
Therefore, we found out the optimum width for thehighest contrast of iodine CT image. In the result, thecontrast ratio of this photon counting CT system is8

Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USA
1:11(acryl : iodine). The contrast ratio of estimatedsystem which has low energy resolution(~16keV) is
1:4. Our system improves the contrast ratio ofsubtraction of iodine CT image.

3.

Experiment

We carried out X-ray CT and got information of Xray energy. Fig.2 shows an illustration of theexperiment system. X-ray tube voltage is 150kV. Xray tube current is 8uA. X-ray detector is CdTe
detector (X-123, amptek)

4.

Result and Discussion

We can see large difference of image of iodine in
two CT images(bandwidth 4keV)(fig.3) used data
below(low energy) and above(high energy) K-edge.
Fig.4 shows profiles of both two CT images. Red line
is for profile of CT image used high energy band,
blue line is for low energy band. CT values of part of
Iodine are difference between two CT image. Then,we extracted iodine image by subtraction of thesetwo CT images(fig.5).

Fig.2 : The experiment system

Fig.3 : CT images of a) below and b) above K-edge energy of I

Fig.4 : Profiles of CT images of below and above K-edge

Fig.1 : Mass absorption coefficient of iodine, bone and muscle[4]Fig.5 : The image of the subtraction of both CT image

Fig.6 shows result and comparison of subtraction
images of three previous methods. Previous method
A : Using overlapped X-ray energy data for
subtraction. It is assumed to use two X-ray tubes.
Previous method B : Using X-ray energy data beyond
K-edge for subtraction. It is assumed to use low

Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USA

Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USA
resolution detector. Method C : Proposed method.
Using X-ray data which is cut strictly for subtraction.
Fig.7 shows profiles of three methods. The graphshows proposed method C and method B is higher
contrast than method A at part of Iodine. Pixel value
at part of acryl of Method C is nearer 0 than method
B. This indicates part of acryl of subtracted image bymethod C is disappeared and we can see only part of
Iodine.
Fig.8 is variation of subtracted images by using
some energy bandwidth. Part of acryl of image isdisappeared further as getting narrower and narrower
the energy band width for subtraction. And, we cansee the part of Iodine more clearly. Fig.9 shows thatusing narrower energy band for subtraction makes
higher contrast. Pixel value of part of acryl is nearer 0
that is pixel value of air. Pixel value of part of Iodine
is farther from 0. Fig.10 shows that the narrower
energy band width we use for subtraction, the nearer
0 pixel value of part of acryl and - Fig.11 shows – thefarther pixel value of part of Iodine from 0 which isthe pixel value of air.

Fig.6 : Comparison of three methods

Fig.7 : Profiles of A(Previous method 1), B(Previous method 2)
and C(Proposed method)

Fig.8 : Variation of subtracted image by using some energy
bandwidth

Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USA

Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USA

Fig.10 : Pixel value at part of acryl

Fig.9 : Profiles of four images
Fig.11 : Pixel value at part of Iodine

5.

Conclusion

We discussed effects of using energy band widthand over lapping data of X-ray for K-edge CT.
Using narrower energy band width for K-edge CT ishigher contrast.

Acknowledgments: This work was supported by
grants from Keiryo Research
Foundation, Promotion and Mutual Aid CorporationforPrivate Schools of Japan, Japan Science andTechnology
Agency (JST), New Energy and Industrial
Technology
Reference[1] Ryo Matsushita, Eiichi Sato, Yutaka Yanbe, Hiraku
Chiba, Tomoko Maeda, Osahiko Hagiwara, Hiroshi
Matsukiyo, Akihiro Osawa, Toshiyuki Enomoto, Manabu
Watanabe,Shinya Kusachi, Shigehiro Sato, Akira Ogawa,Using strict energy band data for K-edge CT makes
higher contrast than over lapping data.
andJun
Onagawa,“Low-Dose-Rate
Computed
Tomography System Utilizing 25 mm/s-Scan Silicon X-ray
Diode and Its Application to Iodine K-Edge Imaging Using
Filtered Bremsstrahlung Photons”, JJAP-52-042202 (2013).
[2] Manabu Watanabe, Eiichi Sato, Purkhet Abderyim,
Hiroshi Matsukiyo, Akihiro Osawa, Toshiyuki Enomoto,
Jiro Nagao, Seiichiro Nomiya, Keitaro Hitom e, Akira
Ogawa, Shigehiro Sato, Toshio Ichimaru, ” Energydiscriminating K-edge x-ray computed tomographysystem”, Proc. of SPIE Vol. 7080 70800B-5(2008).
[3] Eiichi Sato, Purkhe Abderyim, Hiroshi Matsukiyo,
Akihiro Osawa, Toshiyuki Enomoto, Manabu Watanabe,
Jiro Nagao, Seichiro Nomiya, Keitaro Hitom, Akira Ogawa,Shigehiro Sato, Toshio Ichimaru, “Energy-discriminating
x-ray camera utilizing a cadmium telluride detector”, Proc.
of SPIE Vol. 7079 70790Z-5(2008).
[4]”denno
nyumonsho”,
http://www.mb.ccnw.ne.jp/sfujii/satuei/satuei06.html

Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USA

Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USA

BGaN Semiconductor Neutron Detector
Masaki Nakamuraa, Katsuhiro Atsumib, and Takayuki Nakanob
Hidenori Mimurac, Toru Aokia ,caFaculty of Informatics, Shizuoka University, Japan, cs10069@s.inf.shizuoka.ac.jp,bFaculty of Engineering, Shizuoka University, Japan,cResearch Institute of Electronics, Shizuoka University, Japan,

ABSTRACT:This paper proposes novel neutron detector used by BGaN semiconductor. The principle of this detector is detection
the α-ray due to GaN that is released as a result of nuclear reactions that arising catching neutron by boron. We
showed creating α-ray detector and neutron has detected by BGaN.

Key words: Semiconductor, Boron, Gallium Nitride (GaN), Boron Gallium Nitride (BGaN)
1. Introduction
There is demand on various occasions the neutron
detector, for example, security sector, medical sector,
and industrial sector, and so on. The neutron
detectors that are currently mainly used are 3He
neutron detector and scintillator neutron detector.
There are advantages and disadvantages to each ofthese detectors. The 3He neutron detector has anadvantage that high sensitivity for neutron and can beseparated the neutron and γ-ray.
However,disadvantage of 3He is fewer. The Scintillator neutron
detector has quick response, but there is a drawback
difficult to separate the neutron and γ-ray. Therefore
we tried to develop a detector with a performance
like redeeming of the two detectors. Namely our goal
is development high sensitivity detector for neutron
with low sensitivity for γ-ray instead of 3He detector.

2. Materials

Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USA

The Second International Conference on Materials, Energy and Environments (ICMEE),
August 08-09, 2013, Yokohama, Japan

Fig. 2 The output current of GaN was measured with α-ray and/or γ-ray

First, the material that we have focused wasboron. As shown Figure 1, boron can capture neutron
than almost materials. However, neutrons do not haveelectric charge and boron has no chargetransportation characteristics. We considered thattrying to utilize α-ray that caused by the (n, α)
reaction when boron caught a neutron. If the α-ray isdetected by semiconductor, we can confirm thedetection of neutron indirectly. The semiconductor
have focused was GaN. The major reason forchoosing a GaN semiconductor is its high carriertransportation properties proven as a blue LED. In
addition, GaN has a good factor of low sensitivity of
γ-ray. We aim to create a neutron detector that is
possible to achieve the goal using BGaN combines
boron converter and GaN semiconductor.

3. Experiments
We conducted on experiments whether detect theFig. 3 The detected signal of a neutron by BGaN detector

neutron based on this principle. One is related to GaN,
we have to the performance of high sensitivity of αray, low sensitivity of γ-ray. The experimental
method is irradiated to GaN with α-ray and γ-ray, toascertain the current amount severally. As a radiation

Fig. 1 Thermal neutron and X-ray mass attenuation coefficients for the elements

Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USA

The Second International Conference on Materials, Energy and Environments (ICMEE),
August 08-09, 2013, Yokohama, Japan
source, we use 241Am. For BGaN, we have toascertain it can detect the neutron. The experimental
method is irradiated to BGaN with neutron, toascertain whether currents flowing. We use 252Cf as
neutron source.

experimental result on BGaN. This figure shows thatneutrons could be detected by suggested mechanism.

4. Results and Discussion

We studied the neutron detector using asemiconductor. Boron and GaN is proposed asconverter, and as base material. Experimental results
were shown that GaN can be detected to separate theα-ray and γ-ray and BGaN can be detected neutron.
The suggested neutron detection mechanism isrealized using BGaN. We would like to improve thisdetector hereafter.

Figure 2 shows the experimental results on GaN.
From this figure, the current was almost unchanged
compared no irradiation with γ-ray irradiation. The
current when irradiated with α-ray is increased
significantly compared with no irradiation. Fromthese results, GaN is low sensitivity for γ-ray andhigh sensitivity for α-ray. Figure 3 shows the

5. Conclusion

Low exposure CT using a photon counting detector
Ryudai Hatanaka, Kanichi Ashitomi, Yukino Imura, Hidenori Mimura, Toru Aoki
Faculty of Informatics, Research Institute of Electronics, Shizuoka University,
3-5-1 Jouhoku, Naka-ku, Hamamatsu, Shizuoka 432-8011, Japanhatanaka@nvrc.rie.shizuoka.ac.jp

ABSTRACT:
In order to evaluate the performance of photon counting detector, we get CT scan image the acrylic phantom as an
object in practice. From the experimental results, we found that clear image is obtained by increasing the number ofsteps than the scan time, and also found that amount of exposure is reduced considerably compared to conventional
detector.

Key words: 4 keywords can be given. All letters are lower case. word files only. PDF files cannot be
accepted.
1. INTRODUCTION
The Computer Tomography(CT) is essential inmodern medical field. The advantage of CT is there
are many, such as clear image represented by the CT
value, reduction of inspection time, and so on. On theother hand, the patient is inevitable exposure to someextent in order to determine that the material exactly,
make a image quality improvement. For this reason,
one of the challenges is that of how to achieve a CT of
low exposure in any way.

In this paper, we rated the performance of thephoton counting detector is expected to be one way toachieve low radiation CT.
The advantage of using a photon counting
detector are varied. One of the advantage, afterscanning CT image, we can calculate the requiredparts by selecting the energy band. If you scan at least
once, It is possible to determine the substance bychecking the energy band. Therefore, we do not haveto scan many times. In addition, the detector canmeasure the X-ray photons by converting directly to

Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USA

The Second International Conference on Materials, Energy and Environments (ICMEE),
August 08-09, 2013, Yokohama, Japan
charge, this is also one of the advantages. For thisreason, the image quality and the energy resolution is
improved. As a result, it is possible to reduce theirradiation dose.
Object of this experiment is to evaluate theperformance of the photon counting detector in order
to compare the performance of a conventional
detector.
We used the Cadmium Telluride(CdTe)
semiconductor detectors as a photon counting detector.
CdTe is substance absorption and radiation detection
efficiency is high. Also, it is a substance there is no
aging.

II. Experimental Methodology``

Fig. 1 Arrangement plan`

In order to evaluate the performance of thedetector, we got CT scan in practice.
We used acrylic phantom as an object, X-ray
tube(x-ray150: Hamamatsu Photonics) and a
detector(X-123 CdTe type radiation detector) in the
CT scan.
We arranged to be a straight line in the order of
X-ray tube, an object and a detector.
At this time, the X-ray tube and the object, theobject and the detector were placed so that distance ofthem is 40cm straight line (Figure 1). And, when thesubject was placed on a rotating stage is rotated 360
degrees, we were measured two cases of step 36 or 72
the rotation step. Further, we have cases divided into
three types of 0.1, 0.25, 0.5 seconds each scan time
per step.
We used acrylic phantom as an object, X-ray
absorption rate of the phantom is similar to that of thehuman body. We filled with water and an aqueous
iodine solution of 30g / L as a contrast agent,respectively, two holes that are open to the phantom.
Specification for the phantom is shown in Figure 2.
Voltage and current of the X-ray tube was set
150kV, 8µA respectively.
In this paper, amount of exposure is represented
by "current of the X-ray tube (mA) × total irradiation
time (s)". Thus, amount of exposure is "0.008 × (scantime per step × number of steps)".
After the experiment, I confirmed amount of
exposure and contrast of the CT value, which is thequality of the image.

Fig. 2 Specification of phantom

III. Result and Discussion
CT image of the result was shown in Figure 3
and 4.
And we showed the image profile which was
expressed as CT values the dotted line of the CT
image in Figure 5 and 6.
(Note, in the part of the 0.5 second and 72 steps
which is an image of figure 4, artifact of the streak
can be seen for the deficiencies. But please ignored
because it is not the intention in this experiment.)
When we compare the CT images of the resultsof each, we found that the larger the number of steps,
the more artifacts are reduced. In particular, it can beseen that the noise is reduced when compare theresults of the image profile which is shown in Figures
5 and 6. Further, the contrast of the iodine portion islarger in the case of 72 steps.
For the CT scan time, there was no change that
affects the image quality significantly in any numberof steps.

Fig. 3 Scan results in the case of 36 steps

Fig. 4 Scan results in the case of 72 steps

Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USA

The Second International Conference on Materials, Energy and Environments (ICMEE),
August 08-09, 2013, Yokohama, Japan
Amount of exposure when using a
conventional detector is 500 ~ 1000mA ・ sapproximately, Thus we found that is suppressed
exposure appreciable in the results of Figure 3 and 4.
But, the image in the case of 72 steps, It is not thecrisp image quality enough for use as a medical,
Therefore, it is necessary to increase the image
quality to the same extent as conventional detector byincreasing the number of steps further. On the other
hand, about the CT scan time, since there has been nochange in image quality in 0.5 seconds is the longest
and 0.1 seconds is the shortest, it was found that it
can be scanned in a short time more.

[2]

[3]

[4]

[5]
[6]

Sept.
2013.
<http://www.daiyukai.or.jp/recruit/article/index.php>
X-ray CT (X-ray computed tomography) - ATOMICA
-.
22
Sept.
2013.
<http://www.rist.or.jp/atomica/data/dat_detail.php?Tit
le_Key=08-02-01-02>
B [28]What do you see in the image examination of
the brain?| | Brain |Cardiovascular this andthat|National Cardiovascular Information Service([28］nou no gazoukensa de nani ga wakaru?). 22
Sept.
2013.
<http://www.ncvc.go.jp/cvdinfo/pamphlet/brain/pamph28.html>
About
X-ray,
ultrasound,CT,
MRI(rentogen,tyouonpa,CT,MRI ni tuite). 22 Sept.
2013.
<http://www002.upp.sonet.ne.jp/andouiin/kennsa.html>
MCA infarct with CT perfusion | Image |Radiopaedia.org.
22
Sept.
2013.
<http://radiopaedia.org/images/889549>
What is CdTe - acrorad(CdTe toha - acrorad). 22 Sept.
2013. <http://www.acrorad.co.jp/cdte.html>

Fig. 5 Image profile in the case of 36 steps

Fig. 6 Image profile in the case of 72 steps

IV. Conclusions
In the future, we will adjust the image quality by
setting more number of steps and short scan time.
Then, we're going to scan to be the image quality thatis adjusted in both detectors and to compare theexposure of both.
In the end, we want to achieve low exposure CT
by indicating the superiority of the photon counting
detector performance from this comparison.

V. References[1] Diagnostic imaging article collection|Social care
corporation Daiyukai|Official site (gazoushindan
kijishu | shakaiiryouhojin daiyukai | koushikisaito). 22

Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USA

The Second International Conference on Materials, Energy and Environments (ICMEE),
August 08-09, 2013, Yokohama, Japan

Direction detection of radioisotope using
a semiconductor radiation detector
Takuto Sanadaa , Toru Aokia,b , Hidenori Mimurab, and Hisashi MoriicaFaculty of Informatics, Shizuoka University, Japan, cs10049@s.inf.shizuoka.ac.jp,bResearch Institute of Electronics, Shizuoka University, Japan,c
ANSeeN, Japan

ABSTRACT:In Fukushima of Japan, a large amount of radiation material was released outside of the nuclear power plant by theearthquake occurred in March 2011, and effect on crops and people are concerned. On the other hand, radiation is
not visible, decontamination work is rough going. Therefore we did locating of the radioisotope using the directional
dependence of the CdTe detector with high energy resolution. The experimental results showed a difference insensitivity due to the incident direction of radiation, but not sufficient, we found to be necessary to devise toimprove the dependence.
contaminated and conventional radiation detector does
not have the ability to identify the location of the
1. Introduction
radioactive material, to detect points of high doses
Tokyo Electric Power Company Fukushima Daiichi
called "hot spots" is not easy. Therefore in order tonuclear power plant was severely damaged by the
improve the efficiency of the decontamination work,
Tohoku-pacific ocean earthquake and tsunami
we propose the development of hot spots detection
occurred in 2011 and fell into a serious situation thatsystem using the directional dependence of
release a large amount of radioactive material to thesemiconductor detectors with high energy resolution.
exterior of the plant. In order to remove theradioactive material, a hard decontamination work is
2. Prior research
being continued even today. Since the wide range is

Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USA

Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USA
On the relationship between the half-life, cesium isparticularly concerned the long term effect in theradioactive materials released in an accident at the
Fukushima Daiichi nuclear power plant. Gamma
camera is an apparatus for performing position
location of a substance that emits γ-rays as cesium.
There are mainly two types of gamma camera.

energy deposition and the number of γ-ray reacted at
the detector inside by detecting current flowing due tothe incident radiation with high reverse bias.
Semiconductor detectors with Ge and Si have beencommercialized mainly, however we use CdTe
detector that has high effective atomic number andcan also be operated at room temperature.

2.1. Compton camera

3.2. Incident directional dependence

Compton camera is a device that utilizes the Compton
scattering, which is one of the interaction of thesubstance with γ-rays and consists of absorption
material for causing the photoelectric absorption andscattering material for causing the Compton scattering.
It use the information of scattering, absorption
position and the scattering angle calculated from thescattered energy to locate the γ-ray source, thenproject it on the image taken by camera to visualize
the position of the radioactive material. This device isefficiency because it uses individual γ-ray entered thedetector and it is also excellent in removing thebackground by forming an image by focusing theenergy range. System is complex to analyze vast
number of data of channels. Therefore the camera waslarge and costly immediately after the earthquake, butthey are improving in recent years.

Distance the radiation passes through crystal before
leaving it depends sensitively on the shape of thecrystal, location of the incident, and angle ofincidence. In addition, the effective area of thedetector for receiving the incident radiation varies
with the angle of incidence. For performing
measurements targeting γ-ray source, it is necessary toconsider the effect of the interaction of the substancewith γ-rays, i.e. photoelectric effect, compton
scattering, electron pair production. However, γ-ray
emitted from 137Cs doesn't cause electron pair
production because it does not exceed the thresholdvalue of electron pair production. So, we can't expect
to take advantage of this reaction. Photoelectric effct
is just absorption reaction, however compton
scattering, which can change the direction of travel ofthe photon clearly affects the sensitivity of thedetector. Angle differential cross-section of Compton
scattering is given by the formula of Klein-Nishina.

2.2. Pinhole typeThe gamma camera based on this method, theshielding material surrounding the detector functions
as a collimator and background subtraction. In order
to identify the position of γ-rays source from thepositional relationship between the window and thedetector that has absorbed γ-rays, the incident$\gamma$-rays are limited to those that go straight tothe window from the radioactive material. This device
needs heavy shielding material such as lead to prevent$\gamma$-ray from being incident except thosepassed the window. Therefore this camera is tooheavy to carry for decontamination workers.

3. Theory
In this study, we are taking advantage of thecharacteristics of the radiation detector that sensitivity
varies with the angle of incidence of the radiation andattempt to develop a system for performing position
location of radioactive isotope. Semiconductor
detector has higher energy resolution than other solid
detector, so we selected it.

⎧
dσ 1 2
1
α2 ⎫
2
= r
+
+
1
cos
θ
⎨
⎬
dΣ 2 {1 + α }2 ⎩
1+α ⎭

α=

(1)

hv
(1 − cos θ )m0 c 2

Where hv is the energy of photon, m0 c

2

is restmass of the electron, and r is the classical radius of theelectron. We have applied the equation (1) withrespect to photons that the energy is 662KeV, andshow the relationship between the differential
scattering cross-section and photons scattered per unit
solid angle at Fig. 1.

3.1. γ-ray detection with semiconductor
detectorThrough the reaction of the detector, γ-rays can beraised to the conduction band the number of electrons
according to their energy. Since the detector is asemiconductor diode, it is possible to measure theProceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USA

Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USAfrom the detector was amplified by pre-amplifier (type5102, manufactured by CLEAR-PULSE). We
measured 137Cs installed at the distance of 20cm
from the detector. The detector was reverse-biased for
500 V, and the measurement time was 70 minutes.
The detector was fixed on the stage and is controlled
within 0.01 degrees by stage controller.
Measurements were performed in each case incident
angle was 0 degrees, 30 degrees, 45 degrees, 60
degrees, and 90 degrees with the detector surface.

5. Results and discussion

Fig.1 Differential cross section of photn
In this energy, most of Compton scattering is aforward scattering that scattering angle is less than 90
degrees. Practically, it must be taken into account the
influence of Doppler broadening effects due to themomentum of the electrons in atoms, and multiple
scattering in the crystal. In parallel with theexperiment, we perform a simulation using theelectron and photon transport calculation code jointly
developed by the University of Michigan, Stanford
University, and the High Energy Accelerator Researchand Development Organization to reveal the effect of
the interaction of photons and atoms give thedirectional dependence.

4. Experiment
We measured the 137Cs using Schottky CdTe
detector (manufactured by Acrorad Co.Ltd.). The
detector holds titanium and indium electrode on theanode and platinum electrode on the cathode and thesize of detector is 10×10×0.5mm. Electrical signal

Fig. 2 is an energy spectrum of the each angle ofincidence, and comparison of the spectrum was
performed in order to clarify the differences between
each angle. Gross of the total absorption
peak(662KeV) showed a maximum value, 8877, and aminimum value, 7361, at 60 and 90 degrees,
respectively. Detection efficiency of the total
absorption reaction to the total number of detected
was maximum at 60 degrees. Peaks of the 200KeV
peaks and 33KeV was confirmed that the count isdecreased as the incident angle is gradually increased
from 0 degrees. On the other hand, there was little
difference by incident angle in compton scattering
section.
Maximum detection efficiency was observed when
the angle of incidence was 60 degrees, probably
because it was optimum conditions in this experimentwith respect to the effective area of the detector andthe distance γ-ray passes through. Difference ofCompton scattering was hardly observed, we must
devise methods for increasing the dependency. The
peak of 200KeV is observed only in the case ofmeasuring 137Cs with CdTe detector and well reflects
the incident angle.

Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USA

Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USA

Fig.2 Energy spectrum of each angle
However, this peak has unknown cause ofgeneration and is not reproduced in the simulation.
Therefore we must clarify the cause to utilize the peak.

the other hand, we will also plant to check theexperimental data and the theoretical value obtainedby simulation.

6. Summary

References

Obtained directional dependence was not enough inthis experiment, then we plan to use the collimatorand compton scattering material in addition to the
CdTe detector to improve directional dependence. On[1]Tadayuki Takahashi, Shinichirou Takeda, Shin
Watanabe, Visualization of diffusion situation ofradiation material by Compton camera, Journal of the
Physical Society of Japan Vol.68, 2013, pp382-386

Aqueous Hydrothermal Synthesis and Charaterization of Pyrite (FeS2)
Nanoparticles
Zhengqi Shi and Ahalapitiya.H.Jayatissa
Nanotechnology and MEMS Laboratory, Department of Mechanical, Industrial, and Manufacturing
Engineering, University of Toledo, Toledo, OH 43606, USA, Corresponding Author: ajayati@utnet.utoledo.edu

ABSTRACT:
Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USA

The Second International Conference on Materials, Energy and Environments (ICMEE),
August 08-09, 2013, Yokohama, JapanFeS2 nano-particles was successfully synthesized by a simple, low-temperature aqueous hydrothermal reaction
and annealed in 450 oC for 30 min. The microstructure and electrical properties were determined. The X-ray
diffraction (XRD) pattern indicated pure pyrite phase of the annealed powder and a small average grain size of 29.47
nm. The Scanning Electron Microscope (SEM) study displayed a larger grain size at same magnitude and indicatedhigher crystal growth rate than thermal sulfuration approach. Resistance dependence on temperature was studied andthe result follows Arrhenius equation with a small activation energy (29.27 meV) and small resistance of the powder(~101 Ω)

Key words: pyrite; hydrothermal; characterization
1. INTRODUCTION
Pyrite (FeS2) was separated widely and known
as one of the most common mineral[1]. Its
composition are also among most abundant elements
on earth. Pyrite has a cubic FCC crystal structure like
NaCl: the S22- were located as Cl- while Fe2+ stay at
positions for Na+. However, another possible
structure for FeS2 is marcasite. The difference is thearrangement of S22- around iron ions[2]. Due to thehigh absorption coefficient (~105 cm-1, twomagnitude higher than Si)[3] and similar band gap
energy (0.95 eV) as poly-silicon (1.1 eV), FeS2 isconsidered as an alternative candidate for thin film
solar cell application[4].
Various synthesis approaches for pyrite powders
and thin films have been developed including metalorganic chemical vapor deposition (MOCVD)[5-8],
thin-film thermal sulfuration of pre-deposited films[912],electro-deposition[13]andsolution-based
methods[14-19]. For MOCVD, thermal sulfuration andelectrodeposition, those relative costly process wereusually multi-steps including thermal annealing undersulfur atmosphere to obtain enough S atoms for
pyrite FeS2. Moreover, those two approaches
indicated the pyrite phase may be stable only above
450oC since almost all FeS2 films were treated never
below 450oC in conventional synthesis[5]. The
solution-based approaches could serve as costeffective process but most of the reaction wereaccomplished under high temperature or longreaction periods[14,18]. In addition, some works weredone even with hazardous solvents[16,17]. Those facts
limited the development of solution-based approach.
In this work, an simple, low-temperature aqueoushydrothermal approach is applied to synthesize purephase pyrite. A short annealing at 450oC was followed
to investigate the .approximate crystal growth. The
reaction conditions required to synthesize iron pyrite
nano-particles, microstructure and electrical propertiesof the FeS2 powders were all discussed.

II. Experimental
A hydrothermal approach was applied for thesynthesis of iron pyrite nano-particles. In a typicalapproach, 5 mmol Ferrous Sulfate Crystal(FeSO4·7H2O, certified ACS, Fisher Scientific), 20
mmol Ammonium Thiosulfate ((NH4)2S2O3, 99%,
Alfa Aesar) were separately dissolved completely
with DI water. Then these two solutions were mixed
together and sonicated for 15 min. After thesonication, the total solution was sent into thealuminum pressure cooker (model No.921,
Wisconsin aluminum foundry). This pressure cooker
was filled with DI water up to 1/4 of its total capacity.
After the preheating at 550oC for 1h, the internalpressure reached the designed 15 psi. Then thehydrothermal reaction started and continued for 9h at
500oC. The dark precipitate was later retrieved byfiltration and washed with DI water for 5 times andethanol for 1 time. To observe the crystal growth, theroom-temp dried precipitate was annealed in nitrogenat 450oC for 30 min.
An X-ray diffractometer (PANalytical X’Pert
Pro MPD) with Cu Kα radiation was applied toindicate the crystal structure of FeS2 powder. The
scanning range was from 2θ=20o--70o with λ=1.5418
Å. To investigate the surface morphology, a vacuum
deposition on clean glass substrate was applied. The
surface morphology of the as-deposited FeS2 thinfilm was then observed with a scanning electron
microscopy (SEM, JEOL 6100). In order to test theelectrical properties of FeS2 powder, small amount of
powder (1 mm thickness) was sealed in a glass tube
(7.9 mm internal diameter) with its two ends fixedtightly with graphite electrodes. The tube was buriedin oil and the whole system was heated on hotplate in
air. The electrode was connected to an electronic
resistance meter (Keithley 2420 model) to collect theresistance response between 25oC and 140oC

III. Results and Discussion
The black powders after short annealing under
450oC, 30 min was characterized by powder X-ray
Diffraction. The relative pattern was shown in Fig.1.
After comparison with JCPDS 01-071-1680, thepeaks are clearly referred to a pure cubic pyrite
structure and match with the reference in both thepeak position and ratio of intensity. Relative planes
for all peaks are labeled in Fig.1 and the mostdominant peak indicated (200) planes. However,since (113) and (102) also own high intensity peaks,

Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USA

Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USA
it’s hard to justify the preferential growth direction ofthis iron pyrite powder.
In order to estimate the average grain size of thisannealed powder, Scherrer equation shown below
was applied with β as the full width of half maximumof the first several high intensive peaks and k is aconstant of 0.9:

τ=

32.99
37.10
56.20

0.26
0.28
0.34

(200)
(102)
(113)

31.99
29.93
26.49
29.47

kλ
β cos θFig.2 SEM morphology of the annealed FeS2
Fig.1 X-ray Diffraction Patterns of annealed
FeS2 particles
The corresponding calculation was shown in
Table.1 below. The results indicated an average grain
size of 29.47 nm. To verify this calculation, a SEM
measurement was applied to analyze the grain size
and microstructure of this annealed iron pyrite nanoparticles. Fig.2 indicated a small and uniformly
distributed FeS2 particles. The average grain size
could be roughly observed approximately as 50 nm,
which demonstrated the previous estimation was notaccurate enough. Moreover, a highly crystal growthrate of the iron pyrite can be estimated after
comparison with long-time annealing from L.Meng etal[10]. This could be another advantage ofhydrothermal synthesis. Also, the particles are mostly
close-packed and very few holes could be observed.
However, some unexpected large particles also occur
in Fig.2 (lighter, larger patterns). This is inferred astungsten sulfide since tungsten boat was applied in
the thermal vacuum film deposition. Few particles of
WS2 may formed during deposition and finally occur
in the final thin film.

Fig.3 shows the relationship of logarithm onreciprocal of resistivity to the reciprocal of
temperature. The result indicates this annealed FeS2
nano-particles has a semiconductor behavior. Thisdependence was linearly fitted and the fitting curve
could be described via Arrhenius equation:σ = σ 0 exp(−

∆Eo
)
kT

where σ, k, T means conductivity, Boltzmann
constant and temperature, respectively. During themeasurement, the oil temperature was between room
temperature (25oC) and 140oC. From the result, theactivation energy of the annealed FeS2 powder can becalculated and the value was 29.27 meV, whichmatches well with N.Berry et al.[8] (31 meV and 29
meV) shown as the inserted plot in Fig.3. Moreover,the small resistance of FeS2 powder (~101 Ω)
indicated great conductivity of this material.

Table.1 Calculation of average grain size of
annealed FeS2 powder, data in lower right corner was
the average of the three grain sizes above.
2θ
(deg.)

FWHM(deg.)

Planes (hkl)

GrainSize (nm)Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USA

Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USA
Fig.3 Arrhenius plot of resistance versus temperature.
Insert plot shows the similar plot from N.Berry et al[8]IV. Conclusions
Pyrite nano-particles was synthesized via onestep aqueous hydrothermal approach. The XRD
pattern indicates a single pure pyrite phase after shortannealing under 450oC for 30 min. No preferential
growth direction was observed. The grain size wasestimated via Scherrer equation from three major
peaks and the result was 29.47 nm. However, further
SEM morphology observation resulted in a higher
average grain size around 50 nm, which indicated ahigher crystal growth rate than thermal sulfuration oniron thin film. Resistivity dependence on temperature
was measured and the result follows the Arrhenius
equation. The resistance of FeS2 powder was aroundseveral ohm scale. The activation energy wascalculated as 29.27 meV.
Acknowledgments:
This work was supported by a grant (ECS0928440) from the National Science Foundation(NSF) of USA.
References[1] Eun Jung Kim, Bill Batchelor, Synthesis andcharacterization of pyrite (FeS2) using microwave
irradiation, Materials Research Bulletin 44 (2009) 15531558.
[2]I.Uhlig, R.Szargan, H.W.Nesbitt, K.Laajalehto, Surface
States and Reactivity of Pyrite and Marcasite, Applied
Surface Science 179 (2001) 222-229.
[3]A.Ennaoui, S.Fiechter, C.Pettenkofer, N.Alonso-Vante,
K.Bilker, M.Bronold, C.H6pfner, H.Tributsch, Iron
Disulfide for Solar Energy Conversion, Solar Energy
Materials and Solar Cells 29 (1993) 289-370.
[4]Wadia, Cyrus; Wu, Yue; Gul, Sheraz; Volkman, Steven;
Guo, Jinghua; Alivisatos, A. Paul, Surfactant-Assisted
Hydrothermal Synthesis of Single phase Pyrite FeS2
Nanocrystals, Chemistry of Materials 2009, 21, 2568-2570.
[5]A.Ennaoui, S.Fiechter, W. Jaegermann, H.Tributch,
Photoelectrochemistry of Highly Quantum Efficient Single‐Crystalline n ‐ FeS2 (Pyrite), Journal of
Electrochemical Society, 1986 volume 133, issue 1, 97-106.
[6]Ben Meester, Liesbeth Reijnen, Albert Goossens, Joop
Schoonman, Synthesis of Pyrite (FeS2) Thin Films by
Low-Pressure MOCVD, Chem. Vap. Deposition 2000, 6,
No. 3.

[7]J.Oertel, K. Ellmer, W. Bohne, J. Röhrich, H. Tributsch,
Growth of n-type polycrystalline pyrite (FeS2) films bymetalorganic chemical vapour deposition and theirelectrical characterization, Journal of Crystal Growth
198/199 (1999) 1205-1210.
[8]Nicholas Berry, Ming Cheng, Craig L. Perkins, Moritz
Limpinsel, John C. Hemminger, Matt Law, AtmosphericPressure Chemical Vapor Deposition of Iron Pyrite Thin
Films, Advanced Energy Materials 2012, 2, 1124–1135.
[9]C.de las Heras, I.J.Ferrer, C.Sánchez, Pyrite thin films:
Improvements in their optical and electrical properties byannealing at different temperatures in a sulfur atmosphere,
Journal of Applied Physics. 74(7), 1 Oct. 1993.
[10] L.Meng, Y.H.Liu, L.Tian, Structural, optical andelectrical properties of polycrystalline pyrite (FeS2) films
obtained by thermal sulfuration of iron films, Journal of
Crystal Growth 253 (2003) 530-538.
[11]N.Hamdadou, A.Khelil, J.C.Bernède, Pyrite FeS2 films
obtained by sulphuration of iron pre-deposited films,
Materials Chemistry and Physics 78 (2003) 591-601.
[12]R.J.Soukup, P.Prabukanthan, N.J.Ianno, A.Sarkar,
C.A.Kamler, D.G.Sekora, Formation of pyrite (FeS2) thinfilms by thermal sulfurization of dc magnetron sputterediron, Journal of Vacuum Science and Technology A 29(1),Jan/Feb 2011.
[13]Youzhong Dong , Yufeng Zheng, Xiaogang Zhang, He
Duan, Yanfei Sun, Yanhua Chen, FeS2 (pyrite) electrodeposition thin films and study of growth mechanism,
Science in China Ser. E Engineering and Materials Science
2005 Vol.48 No.6 601611 601.
[14]D. Wei, K. Osseo-Asare, Aqueous synthesis of finely
divided pyrite particles, Colloids and Surfaces A:
Physicochemical and Engineering Aspects Volume 121,
Issue 1, 10 March 1997, Pages 27–36.
[15]S.Kar, S.K.Mandal, D.Das, S.Chaudhuri, Wet chemical
synthesis of iron pyrite and characterization by Mössbauer
spectroscopy, Materials Letters 58 (2004) 2886-2889.
[16]J.Puthussery, S.Seefeld, N.Barry, M.Gibbs, M.Law,
Colloidal Iron Pyrite (FeS2) Nanocrystal Inks for Thin-Film
Photovoltaics, Journal of the American Chemical Society.
2011, 133, 716-719.
[17]Su-Ching Hsiao, Chih-Ming Hsu, Szu-Ying Chen, YuHsun Perng, Yu-Lun Chueh, Lih-Juann Chen, Lih-Hsin
Chou, Facile synthesis and characterization of hightemperature phase FeS2 pyrite nanocrystals, Materials
Letters Volume 75, 15 May 2012, Pages 152–154.
[18]A. Moradi Golsheikh, N.M.Huang, H.N.Lim, C.H.Chia,
I. Harrison, M.R.Muhamad, One-pot hydrothermal
synthesis and characterization of FeS2 (pyrite)/graphene
nanocomposite, Chemical Engineering Journal Volume 218,
15 February 2013, Pages 276–284.
[19]Xiaoqing Qiu, Min Liu, Toru Hayashi, Masahiro
Miyauchi, Kazuhito Hashimoto, Solution-based synthesisof pyrite films with enhanced photocurrent generation,
Chem. Commun., 2013, 49, 1232-1234.

Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USA

Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USA

Effects of Laser Irradiation on Optical, Structural and Gas Sensing Propertiesof Sputtered ZnO Thin Films
Yue Hou and Ahalapitiya H. Jayatissa*
Nanotechnology and MEMS Laboratory, Mechanical, Industrial and Manufacturing Engineering (MIME)
Department, The University of Toledo, OH 43606, USA.
*Corresponding author: Ahalapatiya H. Jayatissa
E-Mail: ajayati@utnet.utoledo.edu

ABSTRACT
Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USA

Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USA
The effect of laser irradiation on the optical, structural and gas sensing properties of Al-doped ZnO thin films withdifferent laser power was investigated. Al-doped ZnO thin films were deposited by rf magnetron sputtering on glass
substrate. The Al-doped ZnO thin film exhibits higher optical transparency in the visible region after laser
irradiation treatment. At the same time, the laser irradiation results in a broadening of optical band gap. All the Aldoped ZnO thin films show a c-axis preferred orientation. The peak intensity decreased with high laser power
irradiation. The grain size of Al-doped ZnO thin films continuously decreased with increasing laser power. The gas
sensing behavior was investigated for H2 under different concentrations in air. The results indicate that the sensor
characteristics such as sensing response, response and recovery time can be significantly improved by optimizing
the laser power.

Key words: Al-doped ZnO, rf magnetron sputtering, laser irradiation, gas sensor
1. INTRODUCTION
Zinc oxide (ZnO) a well-known semiconducting
material and has attracted a great deal of attention due
to its versatile properties and large application
potentials. ZnO has been used in many applications
such as surface acoustic wave devices (SAW), thinfilm transistors, varistors and gas sensors [1-4].
Undoped ZnO generally possesses high resistancewhich is a barrier for energy saving. Impurity doping
is an effective way to achieve high conductivity of
ZnO. ZnO can be doped with a wide variety of
impurity ions such as Al, Sn, Mn and Sb. Amongthem, Al as one of the group III elements with anionic radius of 0.072 nm is one of the best candidate.
Many researchers have reported the high conductivityof Al-doped ZnO (AZO) [5,6]. In recent years, laser
irradiation has emerged as a novel heat treatment
method due to its local and rapid thermal heating
ability. Compared with convention furnace heating,laser beam heats a small local area rather than thewhole system. Therefore, it is worthwhile toinvestigate the effect of laser irradiation on the thinfilm properties. In this study, the rf magnetron
sputtered AZO thin films were irradiated by a pulsed
laser with a wavelength of 532 nm under different
laser power. The influences of laser irradiation on the
optical, electrical and gas sensing properties of AZO
thin films were investigated as a function of laser
power.

2. EXPERIMENTS
Al-doped ZnO films were deposited on glass
substrates by an rf magnetron sputtering system using
a metallic AZO (2wt% Al2O3, 98wt% ZnO) target
with 99.9% purity of 50.8 mm diameter and 6.35 mm
thick. The target to the substrate distance was 40 mm
and was kept fixed. The vacuum chamber was first
evacuated to 2 x 10-6 Torr using a cryopump. The
magnetron sputtering was carried out in a mixture ofoxygen and argon (99.999%, O2/Ar: 1/1) by supplying
rf power at a frequency of 13.56 MHz and the rf
power was 100 W. The introduced high-purity gas
mixture raised the pressure in the chamber anddeposition pressure was around 5.3 x 10-3 Torr. The
films were deposited for 10 min without heating thesubstrate. Before the deposition, the target was presputtered for a few minutes to remove the possible
contamination on the surface. The films were
deposited on alkali free glass substrates. The glass
substrate was first rinsed thoroughly with detergent
and then washed completely with deionized water andacetone to remove the dust particles and organic
residuals. After the deposition, the as-deposited films
were annealed in a tube furnace at 550oC for 3 h in theair.
The laser irradiation was carried out by a pulsed
laser system (Quantronix Osprey-532-5-0) with awavelength of 532 nm. The deposited sample wasdivided into three pieces and two of which were
subjected to laser irradiation with different laser
power. The laser beam diameter was about 80 µm,
and the incident laser power was varied from 268 to
735 mW. The as-deposited films, laser-irradiatedfilms with 268 mW and laser-irradiated films with
735 mW were designated as sample-1, sample-2 andsample-3, respectively.
In this study, the microstructure was investigatedby X-ray diffraction (PANalytical X’Pert Pro MPD)
using Cu Kα radiation source. The scanning range
was from 2θ = 25o to 45o with λ = 1.5418 Å. The
average grain size D was estimated based on Scherrer
equation, which is given by D = Kλ/(βcosθ), where K
is a constant, β is the full width at the half maximum(FWHM) of the XRD peak. The optical transmittance
was investigated in the wavelength range of 300 –1000 nm using an UV/Vis spectrophotometer(SHIMADZU UV-1650PC). The gas sensing
behavior was tested in a homemade device. The
configuration of the system was given in our previous
paper [7]. Finger-patterned Au electrodes weredeveloped on the sample surface by opticallithography. The samples were mounted in the glasschamber. The operating temperature was constantly
monitoredbyathermocouple.
Different
concentrations of target gases were introduced into thechamber with 100 ccm constant airflow.

Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USA

Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USA
3. RESULTS AND DISCUSSIONS
3. 1 OPTICAL PROPERTIES

Fig. 2 X-ray diffraction pattern of AZO thin films.
Fig. 1. Optical transmittance spectra of AZO thinfilms.
Figure 1 shows the optical transmittance spectraof as-deposited and laser-irradiated AZO thin films.
All the thin films exhibited an average transmission ofhigher than 85% in the visible region with a very
sharp fundamental absorption edge. The hightransparency implies that all the thin films have goodstructural homogeneity and crystallinity. It is seen thatsample-2 showed slightly higher transparency thanthat of sample-1. The transparency increased withfurther increase of the laser power to 735 mW(sample-3). The inset of Fig. 1 shows thetransmittance in the wavelength range of 330 to 390
nm. A shift of absorption threshold was observed.
This feature indicated the shrinkage of optical
bandgap. This phenomenon may be attributed to boththe stress relaxed and the increase of oxygen
vacancies or interstitial ZnO atoms during laser
irradiation treatment [8].

3. 2 Structural properties

Figure 2 shows the X-ray diffraction pattern ofas-deposited and laser-irradiated AZO thin films in
the range of 2θ = 25o to 45o. Only one prominent
peak was observed at round 2 θ = 34.4ocorresponding to the (002) plane. It indicated that thefilms had a preferential orientation along the c-axis
normal to the substrate surface. The phenomenon may
be attributed to the nature of the grains that it tends togrow along the lowest surface energy plane. It is also
observed that the (002) peak of sample-2 became
strong and broad compared to that of sample-1.
However, the (002) peak deteriorated with further
increase of laser power. Table 1 shows the FWHMs,
position and average grains of (002) peak for asdeposited and laser-irradiated AZO thin films. It isseen that the laser irradiation broadened the peak andincreased the FWHM values as increasing laser power.
According to Table 1, the average grain size
decreased from 13.17 to 6.68 nm with increasing laser
power from 0 to 735 mW.
TABLE ITHE FWHMS, POSITION AND AVERAGE GRAIN SIZEFOR AS-DEPOSITED AND LASER-IRRADIATED AZOTHIN FILMS.
Sample #Sample-1

FWHM(Deg.)
0.66

Position(Deg.)
34.13

Average grain size
(nm)
13.17

Sample-2

1.09

34.04

8.97

Sample-3

1.3

33.93

6.68

Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USA

Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USA
3. 3 GAS SENSING BEHAVIOR
The gas sensing behavior of as-deposited andlaser-irradiated AZO thin films were examined at an
operatingtemperatureof
135oC.
Variousconcentrations of H2 were introduced into thechamber. The gas response S of gas sensor was
defined as S = [(Ra – Rg)x100%]/Ra, where Ra is theresistance of the sensor in air and Rg is the resistanceof the sensor in H2-air mixture gas.

Figure 4 shows the response and recovery
characteristics of all the AZO sensors. It is seen that
all the AZO sensors responded immediately to H2 as it
introduced into the chamber. All the sensors reached
70% of its saturation sensing response in tens ofseconds and saturated in minutes. It is worthwhile tonotice that the as-deposited AZO sensor (sample-1)
did not recovery to the original baseline after
exposing to H2. However, all the laser-irradiated AZO
sensors recovered to the original baseline. Moreover,the laser-irradiated AZO sensors (sample-2 and 3)
showed much shorter recovery time than that of asdeposited AZO sensors (sample-1).

4. Conclusions

Fig. 3 Variation of sensing response as a function of
H2 concentration for AZO sensors.
Figure 3 shows the dependence of sensing
response versus H2 concentration ranging from 1000
to 2500 ppm for all the AZO sensors. It is seen thatthe sensing response increased with the increase of H2
concentration. The sensing response of sample-2
increased significant compared with that of sample-1.
However, sample-3 showed a decrease in sensing
response compared with that of sample-1. The result
indicates that the sensing response of sputtered AZO
sensors enhanced by laser irradiation with optimum
laser power. Further increase of laser power over the
optimum power level resulted in a decrease in sensing
response.

Fig. 4. Dynamic response and recovery of AZO
sensors.

Al-doped ZnO thin films deposited by rf
magnetron sputtering have been post treated by laser
irradiation with different laser power. The optical,
structural and gas sensing behavior of laser-irradiatedZnO thin films were investigated as a function of laser
power. The optical transparency increased after laser
irradiation. The absorption edge continuously shiftedwith increasing laser power. The XRD peaks
broadened after laser irradiation. The grain size of the
AZO thin film decreased as the increase of laser
power. The gas sensor performance indicated that thesensing response was improved significantly with
optimum laser power. Furthermore, the response andrecovery time shortened after laser irradiation
treatment.
Acknowledgment: This research was supported by
grants (Grant number: 0933069 and 0928440) from
National Science Foundation (NSF), USA.
References[1] V.K. Varadan, V.V. Varadan, H. Subramanian, Sens.
Actuators A 90 (2001) 7–19.
[2] T. Soga (Ed.), Nanostructured Materials for Solar
Energy Conversion (2006) Amsterdam.
[3] U. Ozgur, Y.I. Alivov, C. Liu, A. Teke, M.A.
Reshchikov, S. Dogan, V. Avrutin, S.J. Choand, H.
Morkoc, Journal of Applied Physics 98 (2005)
041301.
[4] D.L. DeVoe, Sens. Actuators A 88 (2001) 263–272.
[5] K. Lin, Y. Chen, K. Chou, Solution derived Al-doped
zinc oxide films: doping effect, microstructure andelectrical property, J Sol-Gel Sci Technol 49 (2009)238-242.
[6] H. Zhou, D. Yi, Z. Yu, L. Xiao, J. Li, Preparation ofaluminum doped zinc oxide films and the study of
their microstructure, electrical and optical properties,Thin Solid Films 515 (2007) 6909-6914.
[7] Y. Hou, A.M. Soleimanpour, A.H. Jayatissa, Low
resistive aluminum doped nanocrystalline zinc oxide
for reducing gas sensor application via sol–gel process,Sensor Actuat. B-Chem. 177 (2013) 761-769.

Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USA

Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USA[8] R. Hong, C. Wei, H. Bo, Z. Fan, J. Shao, Influence of
CO2 laser irradiation on the structure andphotoluminescence of zinc oxide thin films, Thin
Solid Films 485 (2005) 262-266.

Polypyrrole/Graphene Nanocomposite Synthesis and Conductivity Study
Weiling Wang and Ahalapitiya H. Jayattisaa
Nanotechnology and MEMS Laboratory
Mechanical, Industrial, and Manufacturing Engineering Department
The University of Toledo, OH 43607, USA
Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USA

Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USAaCorresponding author. Email Address: ajayati@utnet.utoledo.edu.

ABSTRACT:
A conductive nanocomposite consists of polypyrrole and graphene was formed by one step in-situ
polymerization. The mixture of graphene isopropanol dispersion and pyrrole monomers was doped withhydrochloride, and oxidized by ammonia pursulfate (APS). A black liquid ink was obtained after
centrifuging and dividing the resultant, which was brush-deposited on glass slides to form ananocomposite film. XRD was used to characterize the composition of this nanocomposite. The electrontransport mechanism of this nanocomposite was studied. The temperature dependence of conductivity
could be described by Arrhenius equation. Graphene fillers was found to contribute to conductivity
negatively because it causes the increase in disorder. O2 plasma treatment was conducted and found tohave the potential to reduce activation energy.
Key words: polypyrrole, graphene, nanocomposite, conductivity, electron transport
I. Introduction
Graphene is a single layer of carbon atoms
arranged in a honeycomb lattice. Single-layer
graphene is a unique two dimensional material,of which the π-bands are responsible for charge
carrier transport[1]. Since its discovery in 2004,
numerous research has been carried on this kindof material. It has been proved to have superior
electric conductivity, thermal conductivity andmechanical strength [2-5]. It has huge potential
to be applied in solar cell[6] and display[7] astransparent electrodes, in high frequency
transistor[8, 9] and highly sensitive sensor[10,11] as functional materials. It also could beapplied in composite materials as fillers [12, 13].
Polypyrrole (PPy) is an insulator, but its
oxidized derivatives are good electricalconductors. After oxidization (doping), thedouble bonds of which could form transport pathfor charge carriers. Charge carriers transport on
the backbone of polymer chain, and there issome crosslinking of polymer chains and charge
carriers have to hop between the polymer chains,
so it is described as "quasi unidirectional" vs.
one-dimensional[14]. Since it will expand
during charging and sensitive to humidity andsome gas, it is widely used an artificial muscle
and biochemical sensor [15-18]. Nanocomposite
consists of graphene nanoplatelets andpolypyrrole has been studied recently as well,which is reported to have potential to be used insupercapacitors [12, 19, 20].
Graphene could be obtained by many ways, suchas CVD, reduced graphene oxide, direct
exfoliation. Direct exfoliation is used in thisstudy. The main reason is because its final
product is dispersion, which could be mixed
with pyrrole monomers directly. Pyrrole could
be polymerized by chemical oxidization andelectrochemical
oxidization.
Chemicaloxidization is chosen in this study to get a liquid
dispersion directly, and the oxidize agent isammonia persulfate (APS). A nanocomposite
consists of graphene nanoplatelets andpolypyrrole
using
one
step
in-situpolymerization has been formed in this study.
The effect of graphene concentration on
conductivity has been investigated and reported.
The electron transport mechanism of thisnanocomposite has been studied.
II. Experimental
Pyrrole monomers were purchased from Alfa
Aesar with purity of 98+%. Ammonia persulfate(ASP) was purchased from Sigma-Aldrich.
Graphite was purchased from Alfa Aesar withsize of -20+80 mesh and purity of 99.9%.
Graphene was purchased from Cheap Tubes.
Hydrochloride was purchased from Alfa Aesar.
All chemicals were used as received.
Graphene dispersions with different
concentration were prepared. In a beaker 3 g ofgraphite was mixed with 60 mL isopropanol,and the mixture was sonicated for 90 min. Aftersetting the mixture aside for 1 hour, upperdispersion was collected, which is the originalgraphene dispersion. Graphene dispersion withhigher concentration (three times of the original)
was obtained by evaporating graphene

Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USA

Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USA
isopropanol at 60 °C in a petri dish to one thirdof its original volume and sonicated the resultant
for 60 min. To get higher concentration ofgraphene, 0.05 g of purchased graphene powder
was dispersed in 2 mL of isopropanol bysonication for 60 min.
In a beaker 2 mL of graphene dispersion
was mixed with 0.03 M of pyrrole monomers,
and the mixture was sonicated for 30 min. Aftersonication, it was put in ice bath for 10 min topre-condition the mixture. One drop of HCl wasadded into the mixture while sonicating the
mixture in ice bath, and 2 mL of pre-conditioned
ammonia persulfate with concentration of 0.66
mM/mL was added in during sonication drop
wisely. Reaction lasted for 3 hours, during
which ice bath sonication was continued through.
Resultant liquid mixture was centrifuged at 1500
rpm for 2 minutes. After centrifuge the liquid
will be divided into two parts as shown in Fig. 1.
Black polypyrrole-graphene ink floated on top,
clear nonreacted pyrrole monomers were
cumulated at bottom. By using a pipette, the ink
on top was collected and put in a container inrefrigerator. A control group is prepared bymixing polypyrrole fine powder with purchasedgraphene in isopropanol directly by sonicatingfor 60 min in order to verify the advantage of insitu polymerization. Resultant inks withdifferent composition were deposited on glass
slides using a brush on hot plate. Glass slides
were heated on a hot plate at 40 °C. The ink was
deposited on glass slides layer by layer. Total
five layers were deposited on each glass slide,with an average thickness of 0.003 mm.

Figure 1 Illusion of synthesis procedure ofpolypyrrole/graphene ink

III. Results and Discussion

After deposition, in-situ polymerization samples
were washed by methanol and deionized waterand dried. XRD images were taken for samplesof pure polypyrrole (PPy), polypyrrole withoriginalgraphene
dispersion(PPy-Gr),
polypyrrole with condensed graphene dispersion(PPy-3Gr), polypyrrole with purchased graphene
nanoplatelets (PPy-B-Gr), and direct mixture ofpolypyrrole powder and purchased graphene
nanoplatelets, the graphene concentration ofeach sample were listed in Table 1. From Fig. 2,
the peak indicating graphene nanoplatelets at
26.6º is not strong for PPy-Gr, PPy-3Gr and
PPy-B-Gr, while is pretty pronounced for
DirectMix-PPy-B-Gr. Since the graphene
concentration for the PPy-B-Gr is 10%, which issimilar to the concentration of DirectMix-PPyB-Gr (10%), this could be explained by thatduring polymerization, polypyrrole was formeda polymer layer surrounding graphene
nanoplatelets.

Figure 2 X-ray diffraction patterns ofpolypyrrole/graphene nanocomposites withdifferent concentration of graphene
TABLE ICONDUCTIVITY OF FILMSAMPLESWITH
DIFFERENT
GRAPHENE CONCENTRATION
SampleConductivity(s/m) at 298 K

ppy
ppy-Grppy-3Gr
ppy-B-Gr
DirectMix-Ppy-B-Gr

4.08
3.61
3.60
1.61
-

Graphene
Concentration
(wt%)
0
0.09%
0.27%
10%
10%

Conductivity of graphene/polypyrrole film wasevaluated by two probe methods. Two parallel
aluminum electrodes with rectangular shaped
space between them were deposited on samples

Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USA

Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USA
by physical vapor deposition. Table 1 shows thatas graphene concentration increase, theconductivity of nanocomposite decreased. Thatsuggested the existence of graphene inpolypyrrole didn't contribute to the charge
carriers
transport
positivelyinthenanocomposite film. Conducting polymers could
be seen as one-dimensional conducting chains,which have backbones of contiguous sp2
hybridized carbon centers forming a conducting
path. Disorder and one-dimensionality ofpolypyrrole lead to localization of the electron
wave functions[14, 21]. Conductivity decreasein Table 1 suggested that during polymerization,
graphene introduced more disorder and defects.
That is supported by the surface morphology in
Figure 3. With a much higher concentration ofgraphene, the PPy-B-Gr sample has a muchrougher surface than pure PPy and PPy-3Gr.

maybe due to oxidation during plasma treatmentcompleted the undoped path in polymer chain.

a

10 µm

b

The
temperaturedependenceofconductivity of this nanocomposite was studied.
Figure 4 shows the ln(σ) vs.T-1 curves of sample
PPy, PPy-Gr and PPy-B-Gr. The temperaturedependence of all the samples could be
described by Arrhenius equation:

10 µm

c

where,
is conductivity,
is dependent onmaterial, kB is Boltzmann constant, T istemperature, and Ea could be seen as activationenergy needed for the carrier to hop or diffuse
from one polymer chain to another. From Figure
4, the negative coefficient shows semiconductor
behavior of this nanocomposite. There is notmuch difference in the calculated activationenergy for each sample, which indicates that thedominant electron transport mechanism is thesame as polypyrrole, and the energy need bycharge carriers to hop between polymer chains is
not effected by graphene.
Figure 5 shows O2 plasma treatment effecton surface conductivity. Trend of O2 Plasma
treatment reduced the activation energy isobservable, however not very pronounced. That

10 µm
Figure 3 Optical microscopic images ofsample (a) PPy, (b) PPy-3Gr, (c) PPy-B-Gr.

Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USA

Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USA
Reference

Figure 4 ln(σ) vs. T-1 curves for sample PPy,
PPy-Gr and PPy-B-Gr.

Figure 5 ln(σ) vs. T-1 curves for sample PPy,
PPy with O2 plasma treatment, PPy-Gr, and
PPy-Gr with O2 plasma treatment.

IV. Conclusion
A synthesis method of graphene/polypyrrole
nanocomposite ink was demonstrated. Sinceboth polypyrrole and graphene are not soluble
and fusible, compare to direct mix solution, insitu polymerization ink could produce a filmwith better integrity, and the ink could be
deposited as conventional ink. Conductivity ofpolypyrrole/graphene
nanocomposite
film
formed by this ink has been studied. Compare topolypyrrole,graphene
contributes
toconductivity negatively. O2 plasma treatment isfound to increase the conductivity and reduced
the activation energy a little bit. Temperaturedependence of conductivity was studied, and thedominant electron transport mechanism ofnanocomposite is the same as PPy, and noteffected by graphene fillers.

[1] Novoselov KS, Geim AK, Morozov SV, Jiang D,
Katsnelson MI, Grigorieva IV, et al. Two-dimensional
gas of massless Dirac fermions in graphene. Nature.
2005;438:197-200.
[2] Balandin AA, Ghosh S, Bao W, Calizo I, Teweldebrhan
D, Miao F, et al. Superior Thermal Conductivity ofSingle-Layer Graphene. Nano letters. 2008;8:902-7.
[3] Das Sarma S, Adam S, Hwang EH, Rossi E. Electronictransport in two-dimensional graphene. Reviews ofModern Physics. 2011;83:407-70.
[4] Du X, Skachko I, Barker A, Andrei EY. Approachingballistic transport in suspended graphene. Nature
nanotechnology. 2008;3:491-5.
[5] Lee C, Wei X, Kysar JW, Hone J. Measurement of theelastic properties and intrinsic strength of monolayer
graphene. Science. 2008;321:385-8.
[6] Zhang DW, Li XD, Li HB, Chen S, Sun Z, Yin XJ, et al.
Graphene-based counter electrode for dye-sensitizedsolar cells. Carbon. 2011;49:5382-8.
[7] Bae S, Kim H, Lee Y, Xu X, Park JS, Zheng Y, et al.
Roll-to-roll production of 30-inch graphene films fortransparent electrodes. Nature nanotechnology.
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[8] Dimitrakopoulos C, Lin Y-M, Grill A, Farmer DB,
Freitag M, Sun Y, et al. Wafer-scale epitaxial
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and Nanometer Structures. 2010;28:985.
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Kaner RB, et al. Graphene-like nano-sheets for surface
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[11] Zhao J, Zhang G-Y, Shi D-X. Review of graphenebased strain sensors. Chinese Physics B.
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Electrochemical performance of a graphenepolypyrrole nanocomposite as a supercapacitor
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Herrera-Alonso M, Piner RD, et al. Functionalizedgraphene sheets for polymer nanocomposites. Nature
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and inhomogeneous metallic state in conducting
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[15] Ateh DD, Navsaria HA, Vadgama P. Polypyrrolebased conducting polymers and interactions withbiological tissues. Journal of the Royal Society,
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[16] Hernandez SC, Chaudhuri D, Chen W, Myung NV,
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Electrochemical sensors based on conducting

Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USA

Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USApolymer—polypyrrole.
Electrochimica
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Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USA

Experimental Study on Thin Film Cu2ZnSnS4 Deposition by Spin Coating
Mahdi Rajabpour, Zhengqi Shi and Ahalapitiya H. Jayatissaa
Nanotechnology and MEMS Laboratory, Department of Mechanical, Industrial and Manufacturing Engineering(MIME), University of Toledo, Ohio, USAa
Ahalapitiya.Jayatissa@UToledo.edu

ABSTRACTThis paper reports a simple approach to synthesis Cu2ZnSnS4 (CZTS) thin film over the glass substrate by spin
coating. A precursor solution of inorganic salts of Cu (II) and Zn (II) and Sn(II) along with thiourea in methanol was
prepared at room temperature. Drying of deposited layers was carried out through two different procedures followedby an annealing at 500oC temperature for 2 h in N2. The X-Ray Diffraction (XRD) results confirmed partiallyformation of CZTS crystal, while there was still considerable amount of oxides inclusions in the films. However,oxidation largely reduced by drying films in N2.
Keywords: CZTS, Thin film coating, solar cell

I. INTRODUCTION
There is a growing research interest in synthesisof Cu2ZnSnS4 (CZTS) as a serious alternative of
CIGS for next generation of solar cells. Containing
only nontoxic earth abundant elements, CZTS is a Ptype semiconductor with kesterite crystal structureand desired electrical and optical properties (tunableband gap energy and optical absorption coefficient),
which all together introduce it theoretically as quite
ideal material for absorber layer in a solar unit.[1-3]Considering this promising prospective, several
efforts have been done to synthesis CZTS(Se) inform of powder or deposited layer. Different methods
have already proposed for CZTS production,
including vacuum based approach (Sputtering,thermal evaporation) and Non-vacuum approach(mainly solution based methods).[4-6] Regarding
drawbacks in vacuum based techniques (expensive,
need for high vacuum and complicated apparatus)
there is a common intention towards developing
facile, inexpensive and robust non vacuum methods
to synthesis CZTS material.[6]Following solution-based approach, several
research groups could successfully synthesis andemploy CZTS(Se) powder/film to fabricate a solar
cell device. Sun et all[7] have dip-coated CZTSSe thinfilm over Glass substrate using fully dissolved CZTS
precursor
solution.
Preparing
solutionofthioacetamide and salt chlorides of Cu(I), Zn(II),
Sn(IV) in a proper solvent (Ethanol andMonoethanolamine (MEA)), film layers depositedand annealed at 480oC for 30 min under Se vapor. A
solar unit device with such a synthesized material asabsorber layer has shown efficiency of 5.36% . Guo
et al[8] have implemented hot-injection method alongwith knife coating to achieve densely packed
CZTSSe thin film. Taking cupper-poor/zinc- richapproach, salt (acetylacetonate) solution of Cu(II),Zn(II) and Sn(IV) in Oleyamine (solvent) heatedgently at 130oC for 30 min under Ar purge.
Increasing reaction temperature to 225oC, solution of
S-Oleyamin injected to the flask and heated for 30
min. Resulted nanoparticle crystals used for knife
coating over glass substrate and then annealed at
500oC for 20 min in Se vapor. They have reported anefficiency of 7.2% for a solar cell unit using thisabsorber layer. In an another attempt, Schnabel et al[9]have adopted blade coating method to make CZTSSe
absorber layer for a solar cell with cell efficiency of
7.5%. Precursor mixture prepared via dissolving
metal salts and thiourea in solvent (dymethylesolfuxid) at room temperature. Deposited film driedin N2 at 300oC for 1 min, followed by final annealingin Se atmosphere at 540oC for 6 min. Among allreported CZTS(Se) based fabricated solar cell, avacuum-free hydrazine solution based synthesized
CZTSSe, developed by IBM, achieved highest record
efficiency of 11.1%. Making a proper precursor
solution of Cu(I), Zn(II), Sn(II) in hydrazine, thinfilm spin coated over the substrate, followed byannealing on hot plate (at 540oC) under S
atmosphere.[10]Some other groups mainly concentrated oversynthesis and characterization of CZTS(Se) powders
and nanoparticles through solution based methods.
As a simple inexpensive synthesis technique using
non toxic solvent, Hydrothermal route has recently
considered a potential method to make CZTS(Se)powder.
Wang et al[11] have reported hydrothermal
synthesis of CZTS nano crystal powder with band
gap of 1.7 eV. Reaction precursor, mixture of salt
chlorides of Cu(I), Zn and Sn(IV) and Thiourea(concentration ratio 2:1:1:4) in DI water, heated indifferent reaction conditions (time-temperature)

Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USA

Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USA
inside an autoclave, with best results achieved at
200oC for 30 h. Using similar salts and thiourea withconcentration ratio of (2:1:1:12), Hsu et al[12] haveclaimed to obtain pure CZTS powder, with band gapof 1.45 eV, by heating rich sulfur precursor at 180oC
for 72 h inside an autoclave. Kush et al[13] have
employed Na2S as sulfur source for DI water based
precursor with chloride salts of Cu(II), Zn(II) andSn(II) and concentration ratio of 2:1:1:4. Reaction
completed via heating precursor solution at 180oC for
18 h, resulted in formation of CZTS nano crystal
powder (aggregated particles) with band gap energy
1.75 eV. In another attempt similar to Kush[13] studies,
Liu et al[14] have dissolved stochiometric ratio of
Cu(II), Zn(II) and Sn(II) elements (using chloride salt
and other proper salts) and Thiourea in a solution of
DI water and Ethylenediamine (stabilizer andchelating agent). Heating precursor at 180oC for 24 h,
CZTS nano crystal particles with band gap energy of
1.47 eV have claimed to be achieved. In a similar
research work by this group, it is shown that
increasing reaction time from 6 h to 48 h, the final
CZTS particle size will increase from 3 nm to 10.5
nm. [15]
Here we report a simple approach to spin coat a
CZTS thin film on the glass substrate using aprecursor mixture of metal salts and chalchogenide inmethanol. Coated samples was dried in the same
temperature but different atmosphere and thenannealed at 500oC for 2 h in N2. A conclusion over
XRD result was finally provided.

II. EXPERIMENTAL DETAILSTo prepare precursor solution, 5 mmol ofcupric(II)Nitrate (Cu(No3)2.2.5H2O Fisher Scientific),
2.5
mmol
of
Zinc(II)Nitrate.Hegzahydrate(Zn(No3)2.6H2O Fisher Scientific), 2.5 mmol ofTin(II)-ethylhexanoate (SIGMA 95%), 10 mmol ofthiourea (CH2SNH2, Fisher Scientific) and 80 ml of
Methanol (purity 98%) were chosen. Dissolving
metal salts and thiourea in methanol (20 mmol) in
separate beakers, metal salt solutions mixed together
and stirred for 20 min to obtain a clear blue-green
solution. In next step, thiourea solution added to thecurrent metals solution, the mixture stirred for 15 min.
Following addition of thiourea, white gel colloidal
precipitated in remaining transparent colorlesssolvent. The obtained precursor employed to spincoated over two samples (precisely cleaned glass
substrates (1x1 cm2)) with different drying
procedures.
For the first sample, proper amount of mixture
were dropped on the substrate and film layer
deposited through spin coating at 500 RPM for 20 s,
followed by intermittent drying over hot plate
substrate at 230oC for 3 min. Over drying, color of

deposited layer changes from white to dark black.
Repeating this procedure for 20 times, a thin film
deposited over the substrate.
For the sample two, deposition procedure was thesame as first sample, except for drying stage, wherein the second sample each deposited layer dried atroom temperature in air without heating. Final coatedsample was then dried at 230oC for 1 h in N2.
To improve film crystal structure, both samples
were annealed at 500oC for 2 h in N2 flow, and thencooled down to room temperature very slowly.

III. RESULTS AND DISCUSSIONS
X-Ray diffractometer (PANalytical X’Pert Pro
MPD), with Cu Kα radiation was employed tomeasure XRD patterns of both coated samples.
Regarding XRD results, first sample was seemed to
be a combination of SnO2 (score 80), ZnS (score 54)
and CZTS (score 27) (Fig. 1), while the second
sample mainly consisted of SnO2 (score 85) and
CZTS (score 72) (Fig. 2). Moreover, main peak insample one belonged to SnO2, while CZTS
represented the main peak in sample two, which
verified formation of higher amount of CZTS insecond sample. These results indicated that synthesis
of CZTS in sample two was more successful thansample one, which mainly could be attributed toapplying different drying stage. In sample one, eachdeposited layer was dried in air at relatively hightemperature, leading to oxidation of Sn elements ofprecursor, while in sample two, N2 atmosphere tosomehow prevented precursor from oxidation.
Therefore more oxides were expected to present infinal layer in sample one than sample two. In addition,
annealing the samples in high temperature wasanother probable source of oxidation. Despite using
ultra high purity N2 as protection atmosphere inannealing, very few amount of oxygen could be stillavailable in the atmosphere, probably high enough tooxidize part of film in high temperature during
annealing.
However, as XRD pattern of CZTS crystal issimilar to some binary compounds like ZnS, Cu2SnS4
and Cu2S, further examination like Raman
Spectroscopy is required to precisely identify crystal
structure of coated film.

IV.CONCLUSION
Synthesis and coating of CZTS thin film wasstudied in this paper. Using XRD pattern of crystal
structures, two different films were compared fromsynthesis point of view. It was revealed that oxidation
prevention is a crucial stage in making film, both infilm drying and annealing stages. Moreover it was
shown that more synthesis tuning was needed toreach pure CZTS film

Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USA

Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USA

Fig. 1: XRD pattern of CZTS film dried (each layer) at 230oC for 3 min on hot plate in air (Sample one).

Fig. 2: XRD pattern of CZTS film dried at 230 oC for 1 h in N2 (sample two).

Proceedings of Workshop on Semiconductor based Detectors, November 19, 2013, Toledo, OH, USA
University of Toledo
primarily supports the conference (Grant No. ECS0928440).

V.Acknowledgment:

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