bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fast Sensitive Ultra-Low Power Micro Thermal Conductivity Gas Sensor
Authors: Mahdavifar Alireza , Hesketh Peter , Findlay Melvin W , Stetter Joseph R 
Published: February 2020

Abstract

A miniature, ultra-low power, sensitive, microbridge-based thermal conductivity gas sensor has been developed. The batch fabrication of the sensors was realized by CMOS compatible processes and surface micromachining techniques. Doped polysilicon was used as the structural material of the suspended sensing element with critical dimension of 500 nm.
To understand the design of the sensors, a model of the suspended element was simulated in COMSOL that couples electrical and thermal physics together and includes minimal simplifications. Modeling results coincide with experimental data in predicting resistance changes. The sensor was tested with nitrogen, carbon dioxide, helium and methane.
An electronic circuit was developed to measure very fine changes in the signal output and to keep the signal to noise ratio such that ppm detection is possible, while exciting the sensor at minimal power levels. The sensor was able to detect ppm levels of helium, methane, or carbon dioxide in nitrogen at room temperature. The sensor can make a measurement in less than 2 ms consuming only 5 nJ or power per reading.
The transient as well as steady state response was investigated as potential indicator of gas thermal capacity; as thermal conductivity and thermal capacity are independent properties of a gas, this new approach may enable MicroTCD sensors to make detections in gas mixtures by thermal analysis [1].
[1]U.S. Patent 8,426,932 B2, April 23, 2013, Apparatus and Method for Microfabricated Multidimensional Sensors and Sensing Systems, Joseph R. Stetter.
Direct CVD Growth of High Quality Single Layer Graphene on Dielectric Substrates
Authors: Choi Hee Cheul 
Published: February 2020

Many applications of graphene especially for the fabrication of electrical devices require physical placement of graphene on dielectric substrates. Several strategies developed for the graphene device fabrication include 1) mechanical exfoliation of graphene on a dielectric substrate followed by fabrication, 2) graphene growth on metal catalysts by chemical vapor deposition (CVD) process followed by transferring it onto dielectric substrates and fabrication, 3) dispersion of reduced graphene oxides (RGOs) on dielectric substrates followed by fabrication, etc. To utilize the intrinsic high charge carrier mobility of graphene, however, a direct synthesis of graphene by CVD on dielectric substrates is highly demanding. In this presentation, I will introduce our recent experimental results demonstrating successful direct growth of graphene on various dielectric substrates, such as hexagonal boron nitride (h-BN), sapphire, quartz, and amorphous SiO2/Si, thus excluding complex transfer process to secure the quality of graphene by excluding impurities that are accompanied during the transfer process. The detailed growth mechanism involved in graphene nucleation and growth propagation on various substrates will be also discussed.

References

1. Kim, H.; Son, Y.; Park, C.; Cho, J.; Choi, H. C. Angew. Chem. Int. Ed.
2013, 52, 5997-6001. Catalyst-free Direct Growth of a Single to a Few Layers of Graphene on a Germanium Nanowire for the Anode Material of a Lithium Battery
2. Song, H. J.; Son, M.; Park, C.; Lim, H.; Levendorf, M. P.; Tsen, A. W.; Park, J.; Choi, H. C. Nanoscale
2012, 4, 3050-3054. Large scale metal-free synthesis of graphene on sapphire and transfer-free device fabrication.
3. Son, M.; Lim, H.; Hong, M.; Choi, H. C. Nanoscale,
2011, 3, 3089-3093. Direct Growth of Graphene Pad on Exfoliated Hexagonal Boron Nitride Surface.
Pushing the Limits of Plasmonic Nanoantenna Design Using New Materials and Nanofabrication Tools
Authors: Muskens Otto L. 
Published: February 2020

Plasmonic nanoantennas are of interest for their capacity of controlling light on the nanoscale [1]. In particular, precise control of plasmonic near-field interactions on sub-nanometer scales is of interest for achieving strongly enhanced local fields as well as for exploring the fundamental limits of nonlocal and quantum plasmonic effect [2]. Such applications require pushing the limits of nanofabrication to new levels of precision and control.
Helium ion microscopy (HIM) is a surface imaging technique which involves scanning a helium ion beam across a sample surface and forming an image from secondary electron emission which is similar to an SEM. The larger mass and therefore smaller de Broglie wavelength of a helium ion compared to that of an electron enables the HIM to focus the charged beam to a smaller spot on a sample. The latest commercially available version of the HIM are rated at an edge resolution of 0.35nm[3]. The helium ion microscope is also a patterning tool which can be used to pattern resist like electron beam lithography or can be used for direct writing on a substrate like a focused ion beam.
In our recent work, we have demonstrated the ultrafine control of milling partial antenna gaps and narrow conducting bridges with nanometer precision using a helium ion beam microscope (HIM) [4]. A conducting bridge of nanometer height is found sufficient to shift the antenna from the capacitive to conductive coupling regime, in agree with the circuit theory.
In addition to new fabrication tools, we are developing new materials systems to combine plasmonics in electrically and optically controlled environments. I will present recent results showing how we can use new hybrid nonlinearities to achieve tunable and reconfigurable plasmonic devices.

[1] Novotny, L.; van Hulst, N. Nat. Photonics 2011, (5) 83-90

[2] Savage, K. J.; Hawkeye, M. M.; Esteban, R.; Borisov, A. G.; Aizpurua, J.; Baumberg, J. J. Nature 2012, (491) 574-577.

[3] Bell, D. C.; Lemme, M. C.; Stern, L. A.; Williams, J. R. and Marcus, C. M. 2009 Nanotechnology (20) 455301

[4] Wang, Y.; Abb, M.; Boden, S. A.; Aizpurua, J.; de Groot, C. H.; Muskens, O. L. Nano Lett. 2013, 13(11), 5647-5653

Figure 1 (left panel) Illustration showing analogy between radiowave antenna and plasmonic nanoantenna. Bottom: SEM image of antenna fabricated using e-beam lithography. (right panel) SEM image showing nano-gap obtained by helium ion beam milling.
Ovonic Threshold Switching Selection Device Based on Chalcogenide ZnTe for Cross-Point ReRAM Device
Authors: Kim Youngjae , Min Yoonki , Lee Jimin , Sohn Hyunchul 
Published: February 2020

Cross-point array structure has attracted increasing attention for high-density ReRAM, owing to the development of ReRAM with promising scalability. Cross-point array of only resistors(1R) cannot function because of sneak current through unselected devices, which can be reduced by integrating resistive memory elements with bidirectional nonlinear selection devices(1S1R). Namely, the high value of Kw in ON states, which is the writing current @ Vwrite / the current @ 1/2Vwrite, was required in cross-point ReRAM memory industry.
In this study, the high current density non-linear IV curve of Ovonic threshold switching(OTS) selection device based on Chalcogenide ZnTe was shown and the ALD HfO2 switching device has the linear properties of ON states and the compliance current of 100uA. In 1S1R unit cells based on ZnTe OTS selection device of low off current (< 400nA) and HfO2 switching device, excellent non-linear characteristics of ON states such as Kw of 522, Kr (reading current @Vread / current @ 1/2Vread) of 1430 and on/off ratio of 43 were shown. OTS behaviors with ZnTe film thickness, device area and annealing temperatures were investigated. Initial current during electro-forming process was decreased but OTS characteristics were not changed with increasing ZnTe thickness and decreasing device area. Initial current in electro-forming process and OTS characteristics at annealing temperature of below 200°C was not changed, but initial current and off current was rapidly increased and threshold voltage (Vth) in OTS was decreased at above 250°C because of Te diffusion in ZnTe film. To suppress the diffusion of Te atoms, the reactive N2during deposition which can improve the thermal stability of the chalcogenide glass was performed. And chemical compositions of ZnTe thin films were analyzed by Rutherford backscattering spectrometry(RBS). Also, crystallinity as a function of annealing temperature was investigated by Raman spectroscopy, X-ray diffraction (XRD) and plan-view transmission electron microscopy (TEM).
Synthesis of MoS2 Thin Film
Authors: Mun Jihun , Kim Dongbin , Shin Yonghyeon , Yun Juyoung , Kang Sangwoo , Kim Taesung 
Published: February 2020

The two dimensional materials such as graphene, and thin films of transition metal dichalcogenides are became alternative and attracted for use in next generation nanoelectronic devices due to their planar nature and mechanical flexibility. Especially, graphene is promising and most widely studied two-dimensional material for use in flexible and transparent devices. Despite of all these excellent electrical properties, it is difficult to fabricate on/off and logic devices using grapheme because of zero band gap. In contrast, molybdenum disulfide (MoS2) has the band gap between 1.2 and 1.8 eV as a function of the number of layers (band gap of monolayer MoS2is 1.8eV) (K. F. Mak, et al., 2010).
Many researchers have been used various methods such as mechanical exfoliation (B. Radisavljevic, et al., 2011), sulfurization (Y. Zhan, et al., 2012), chemical vapor deposition (CVD)(Y. H. Lee, et al., 2012; Y. Shi, et al., 2012) to grow MoS2 thin film. In the case of mechanical exfoliation, excellent electrical properties were shown. However, there is limitation of mass production. CVD method is a typical method and there are many reports. However, the method for large area MoS2growth on dielectric substrate at the relatively low temperature is not reported.
In this work, we successfully have grown a few layer MoS2 thin film (Fig. 1) on a SiO2 substrate using molybdenum hexacarbonyl (Mo(CO)6) and hydrogen disulfide (H2S) by a CVD method. The large area MoS2 thin film was grown by optimization of the Mo and S precursor ratio and growth conditions such as process pressure and temperature. The properties of the films were analyzed using atomic force microscope (AFM), transmission electron microscope (TEM), and Raman spectroscopy.

References

K. F. Mak, C. Lee, J. Hone, J. Shan, and T. F. Heinz, Atomically thin MoS2: a new direct-gap semiconductor, Phys. Rev. Lett., 105, 136805 (2010).
B. Radisavljevic, A. Radenovic, J. Brivio, V. Giacometti, and A. Kis, Single-layer MoS2 transistors, nature nanotechnology, 6, 147-150 (2011).
Y. Zhan, Z. Liu, S. Najmaei, P. M. Ajayan, and J. Lou, Large-Arae Vapor-Phase Growth and Characterization of MoS2 Atomic Layers on a SiO2 substrate, small, 8, 7, 966-971 (2012).
Y. H. Lee, X. Q. Zhang, W. Zhang, M. T. Chang, C. T. Lin, K. D. Chang, Y. C. Yu, J. T. Wang, C. S. Chang, L. J. Li, and T. W. Lin, Synthesis of Large-Area MoS2 Atomic Layers with Chemical Vapor Deposition, Advanced Materials, 24, 17, 2320-2325 (2012).
Y. Ishikawa and K. Kawakami, Structure and Infrared Spectroscopy of Group 6 Transition-Metal Carbonyls in the Gas Phase: DFT Studies on M(CO)n (M = Cr, Mo, and W; n = 6, 5, 4, and 3), J. Phys. Chem. A, 111, 9940-9944 (2007)
W. K. Hofmann, Thin films of molybdenum and tungsten disulphides by metal organic chemical vapour deposition, J. Mater. Sci., 23, 11, 3981-3986 (1988)
Novel Cholesterol Sensor Based on Ultra-Low Detection Limit Hydrogen Peroxide Sensor
Authors: Chu Chia Ho , Fang Kuan Chung , Hsu Chen-Pin , Kang Yen-Wen , Fang Jung-Ying , Hsu Chia-Hsien , Huang Yu-Fen , Chen Chih-Chen , Li Sheng-Shian , Yeh J. Andrew , Yao Da-Jeng , Wang Yu-Lin 
Published: February 2020

Hydrogen peroxide attracts a great interest due to its important role in food, pharmaceutical, and clinical applications. Hydrogen peroxide is also a by-product in many enzyme catalytic reactions, such as glucose oxidase, lactate oxidase, cholesterol oxidase, alcohol oxidase, urate oxidase, aldehyde oxidase, and oxalate oxidase, which are implemented to detect glucose, lactic acid, cholesterol, ethanol, urea, formaldehyde, and oxalate, respectively. These biomolecules are significant markers in many biologically metabolic reactions. In our study, we present a cholesterol sensor based on a high sensitivity hydrogen peroxide sensor with ultra-low detection limit. The sensor can directly test the sample and only need very small amount of sample. And because of the simple structural design and fabrication, the sensor can be used as a cheap, efficient, and portable sensor system.
The HRP-modified resistive sensors based on n-alkylated polyaniline(PANI) detect hydrogen peroxide in solution with very high sensitivity, ultra-low limit, and short response time. The sensitivity is higher than that of other sensing methods, such as electrochemical sensors or transistor sensors. The detection limit of PANI sensor is 0.7 nM. It is three orders smaller than that of other common methods with detection limit around 1 μM. To the best of our knowledge, it is the lowest detection limit that has ever been reported. And we combine the hydrogen peroxide sensor with cholesterol oxidase to build up the cholesterol sensor.
In our study, the PANI layer and gold electrodes were deposited on silicon nitride substrate, and the PANI was applied to fabricate a thin film between two electrodes. Then the PANI layer was sultonated by propane sultone and modified with HRP. After that, the device was combined with dialysis membrane which was modified with cholesterol oxidase. During the measurement, the sensor was operated at 100mV and different concentrations of cholesterol PBS solutions (pH=7.0) were dropped on it. The cholesterol reacted with the cholesterol oxidase and created hydrogen peroxide on the PANI thin film (Figure 1).
The current change was measured when the hydrogen peroxide reacted with the HRP immobilized PANI thin film. According to regular cholesterol level in human blood, we tested the cholesterol solution from 100 mg/dl to 400 mg/dl ,and we get a very good linear result (Figure 2).
In summary, the cholesterol sensor can provide a more exact cholesterol concentration detection. The simple process for the sensor fabrication also allows the sensor to be cheap, disposable and combinable with other sensors to build up sensing system.
This work was partially supported by National Science Council grant (No.99B20495A & 101-2221-E-007-102-MY3) and by the research grant (100N2049E1) at National Tsing Hua University.
CMOS Inverters and P-N Junction Diodes Based on Transition Metal Dichalcogenide Monolayers
Authors: Takenobu Taishi 
Published: February 2020

The atomically thickness and emerging large bandgap of two dimensional transition metal dichalcogenides (TMDCs) offer a high degree of electrostatic control than those of bulk forms, which provide potential applications to electronics and optoelectronics. Recent progresses of exfoliated-TMDC-based n-type or p-type transistors allow widespread device applications such as circuits, diodes and sensors [1]. However, limited sample size and efficient carrier doping system are still remained, which consequently hamper the practical utility of TMDCs for complementary devices. Towards further advances, establishing scalable preparation techniques of various TMDCs and controlling their electronic properties are highly required. One of the most powerful methods to modulate the carrier density of semiconductors is electrostatic doping by using electrolyte to form electric double layer [2]. The huge specific capacitance of electric double layer transistors (EDLTs) enables the strong depletion of donor carriers and the continuous band filling, resulting in tuning material polarities.
In this study, we fabricated ion-gel-gated EDLTs using large-area TMDC monolayers, MoS2, MoSe2 and WSe2, grown by chemical vapor deposition [3-6]. The Fermi level of TMDCs can be continuously shifted by applying gate voltage, and we can induce both hole and electron transport in these devices. The hole mobility of WSe2 can be enhanced up to 90 cm2/Vs at high carrier density of 1014 cm-2, whereas the MoS2 showed electron mobility of 60 cm2/Vs. By combining MoS2 and WSe2, we demonstrated complementary logic inverters, which yielded extremely high voltage gain of 110 that is the highest value in atomically thin 2D materials. We also introduce unique techniques to form stable pn junctions in ambipolar TMDC EDLTs and investigate its optoelectronic properties.
[1] Q. H. Wang, et al., Nat. Nanotechnol. 7, 699 (2012).
[2] J. T. Ye, et al., Science. 338, 1193 (2012).
[3] J. Pu, L.-J. Li, T. Takenobu, et al., Nano Lett. 12, 4013 (2012).
[4] J.-K. Huang, T. Takenobu, L.-J. Li, et al., ACS Nano. 8, 923 (2014).
[5] J. Pu, L.-J. Li, T. Takenobu, et al., Appl. Phys. Lett., 103, 23505 (2013).
[6] J. Pu, L.-J. Li and T. Takenobu, Phys. Chem. Chem. Phys., 10.1039/C3CP55270E (2014).
Optical Properties and Defect Formation in Gallium Phosphide/Gallium Nitrogen Phosphide Core/Shell Nanowires
Authors: Dobrovolsky A. , Stehr J E , Kuang Y J , Sukrittanon S , Tu C W , Chen W M , Buyanova I A 
Published: February 2020

III-V semiconductor nanowires (NWs) have recently attracted increasing attention due to their potential applications in optoelectronic and photonic devices. Among all III-V compounds, GaP-based materials have the smallest lattice mismatch to Si are, therefore, among the best candidates for growth of III-V core/shell NWs on silicon. Adding a small amount of N in GaP allows one to further minimize this mismatch and also leads to transformation of the band gap character from an indirect one in GaP to a direct-like one in the GaNP alloys, leading to improvements in efficiency of light emission.
In this work we evaluate radiative efficiency of novel GaP/GaNP core/shell NWs grown on Si substrates by using comprehensive optical characterization techniques, including cw- and time-resolved photoluminescence (PL) spectroscopies and optically detected magnetic resonance (ODMR). Superior optical quality of the structures is demonstrated from the observation of intense PL emission from a single NW at room temperature (RT). This emission is concluded to originate from radiative transitions within N-related localized states, based on the results from the temperature dependent cw- and time-resolved PL studies. In spite of the high optical quality, the RT carrier lifetime in the structures is still found to be governed by non-radiative recombination processes as evident from the results of the time-resolved PL measurements. ODMR studies identified a defect complex involving a P atom at its core as a non-radiative recombination center in the GaNP shell, most likely located at the GaP/GaNP interface.
Compound Semiconductor Nanowires for Optoelectronic Device Applications
Authors: Tan Hoe 
Published: February 2020

The excitement of nanowire research is due to the unique electronic and optical properties of these nanostructures. Both axial and radial heterostructure nanowires have been proposed as nano-building blocks for the next generation devices, which are expected to revolutionise our technological world. The unique properties stem from their large surface area-to-volume ratio, very high aspect ratio, and carrier and photon confinement in two dimensions. These nanowires are usually grown by the so-called vapor-liquid-solid mechanism, which relies on a metal nanoparticle to catalyze and seed the growth. An alternative technique to grow the nanowires is by selective area growth technique, where a dielectric mask is first patterned on the substrate prior to growth.
In this talk, I will present an overview of compound semiconductor nanowire research activities at The Australian National University. The optical and structural properties of binary and ternary III-V nanowires including GaAs, InGaAs, InP and GaAsSb nanowires grown by metal-organic vapour phase epitaxy will be presented. Various issues such as tapering of the nanowires, compositional non-uniformity along nanowires, crystal structure, carrier lifetime and polarization effect will be discussed. I will also present our results of III-V nanowires grown on Si substrate which are of great interests for the integration of nano-optoelectronic devices on Si platforms. Our results of enhancing the quantum efficiency of nanowires by using plasmonics are promising to improve the performance of nanowire devices. Finally, the results from our nanowire lasers and solar cells will be presented.
Solution Processed Oxide Thin Film Transistors
Authors: Avis Christophe , Jang Jin 
Published: February 2020

We have developed thin-film-transistors (TFTs) manufactured by a solution processing of the gate insulators and the active material. Oxide insulators, such as aluminum oxide, hafnium oxide, or zirconium doped aluminum oxide represent a method to achieve high performance and low power consuming TFTs. Along with amorphous indium gallium zinc oxide ( a-IGZO), other oxide semiconductors have been studied. Solution processing offers the opportunity to test various materials quickly with low capital investment. We studied poly-crystalline materials, such as indium oxide (In2O3), and tin oxide (SnO2), or amorphous oxides such as indium zinc tin oxide (IZTO).
We have developed inket-printed TFTs at the maximum process temperature of 300oC. Inkjet-printed polycrystalline InOx TFTs have mobilities of 60cm2/Vs, and were used in unipolar inverters. SnOx TFTs, show a dependence on the solution concentration, and the mobility can reach ~70cm2/Vs. On the other hand, amorphous IZTO TFTs showed the highest mobility of ~100cm2/Vs by the careful control of the inkjet process.

References

C. Avis and J. Jang, J. Mater. Chem., 21, 10649-10652, 2011
C. Avis and J. Jang, Jap.
J. Appl. Phys., 2011, 50, 01BG03, 2011
C. Avis and Jin Jang, Electrochem. Solid-State Lett., 4, J9-J11, , 2011
Y. G. Kim, C. Avis and J. Jang, ECS Solid-State Lett., 1, Q23-Q25, 2012
C. Avis, Y. G. Kim, and J. Jang, J. Mater. Chem., 22, 17415–17420, 2012
Y. G. Kim, C. Avis, and J. Jang, J. Disp. Tech., accepted, 2014
Figure 1: transfer characteristics of IZTO TFT.