bluuebunny/crossref_metadata_2025 huggingface dataset:
Novel Solar Cells Using Carbon Materials
Authors: Shapter Joe George , Tune Daniel , Flavel Ben , Krupke Ralph
Published: February 2020

Due to the high cost of silicon photovoltaics there is currently great interest in finding alternative semiconductor materials for light harvesting devices. Single walled carbon nanotubes are an allotrope of carbon having unique electrical and optical properties and are promising as future photovoltaic materials. It is thus important to investigate methods of exploiting their properties in photovoltaic devices. Ironically, one way to do this is to combine them with a relatively well understood model semiconductor such as silicon. Nanotube-silicon heterojunction solar cells are a recent photovoltaic architecture with demonstrated power conversion efficiencies of up to 14 % that may in part exploit the photoactivity of carbon nanotubes.

Silicon solar cell devices fabricated with a thin film of the conductive polymer, polyaniline, have been reported but these devices can suffer from poor performance due to the limited lateral current carrying capacity of very thin polymer films. This talk will focus on hybrid solar cell devices of a thin film of polyaniline deposited on silicon and covered by a single walled carbon nanotube film are fabricated and characterised. These hybrid devices combine the conformal coverage given by the polymer and the excellent electrical properties of single walled carbon nanotube films and significantly outperform either of their component counterparts. Treatment of the silicon and carbon nanotubes with hydrofluoric acid and the strong oxidiser, thionyl chloride, leads to a significant improvement in performance.
Hybird Heterojunction and Photoelectrochemistry Solar Cell Based on Silicon and Graphene Woven Fabrics (GWFs)
Authors: Li Xiao
Published: February 2020

Crystalline silicon based solar cells have drawn tremendous interest in the photovoltaic market. A facile route to obtain GWFs was reported lately by simply replacing copper with copper meshes substrate in chemical vapor deposition. In addition to its extraordinary electromechanical performance, GWFs also has an alternative application as transparent electrodes as well as graphene film in heterojunction solar cell with Si. Although its conductivity may be fade to graphene film, GWFs surely has better light transparency property because of its cross ribbon structures. This structure was also beneficial to embed other materials, such as liquid electrolyte and other conductive polymers for energy harvesting. Recently, solid state electrolyte has attracted a lot of attention due to its great potential in assembling of flexible nanodevices.

In this paper, we proposed a hybrid heterojunction and photoelectrochemistry solar cell based on Si and GWFs. GWFs not only served as the transparent layer for charge collection and transport, but played an important role as p-type layer to form heterojunction with Si. In addition, particular configuration of woven fabrics with empty space between meshes facilitated the filling up of acidic solid state electrolyte. HNO3 solid state electrolyte significantly boosted the efficiency by comprehensively improving the open circuit voltage, short circuit current density and fill factor by simply spin-coating on GWFs-Si solar cell. The role of HNO3 solid state electrolyte was discussed in detail. Different models were designed to confirm the hybrid function existed in the solar cell and we can prove that heterojunction junction and photoelectrochemistry function worked synergistically. By accommodating the density of HNO3 solid state electrolyte, the power conversion efficiency could reach up to 11.03%, which was really encouraging. Subsequent experiment convinced H3PO4solid state electrolyte also had positive effect to enhance power conversion efficiency. By adopting solid state electrolyte, we stood a chance to assemble flexible solar cells by precisely controlling the thickness of Si and maintain the cell efficiency at the same time, which extends the application area of GWFs-Si solar cell to flexible field.

Fig. (a) Optical image of the solar cell (b) schematic diagram of the solar cell
Structure Analysis of C60(CF3)10 Isomers
Authors: Bukovsky Eric V , Larson Bryon , Strauss Steven H. , Boltalina Olga , Popov Alexey A
Published: February 2020

The molecular structures and solid state packing of molecules are crucial to the performance of organic electronic materials, in devices, in terms of charge mobility in the solid state, charge transfer at interfaces, and electrochemical stability. Few studies have been able to compare such a large number of C60X
n
isomers to ascertain the effects that addition patterns have on physiochemical properties of molecules and domains of molecules. We have now synthesized and characterized 27 isomers of C60(CF3)10, including 11 by single crystal X-ray crystallography, six of these are reported for the first time. This represents the greatest number of fullerene or fullerene derivatives/isomers of any kind that have been structurally characterized. Our primary interest in this particular series of fullerene isomers is their variation in reduction potentials and electron affinities that stem from their respective addition patterns since all isomers have the same number of electron withdrawing CF3 groups. Correlations between molecular structure, packing efficiency (density), and electronic properties will be discussed.

References

1. I. E. Kareev; S. F. Lebedkin; S. M. Miller; O. P. Anderson; S. H. Strauss; O. V. Boltalina, Acta Cryst., E62, o1498 (2006).

2. A. A. Popov; I. E. Kareev; N. B. Shustova; E. B. Stukalin; S. F. Lebedkin; K. Seppelt; S. H. Strauss; O. V. Boltalina; L. Dunsch, J. Am. Chem. Soc., 129, 11551 (2007).

3. I. E. Kareev; S. F. Lebedkin; A. A. Popov; S. M. Miller; O. P. Anderson; S. H. Strauss; O. V. Boltalina, Acta Cryst. E62, o1501, (2006).

4. N. B. Shustova,; D. V. Peryshkov; A. A. Popov; O. V. Boltalina; S. H. Strauss, Acta Cryst. E63, o3129 (2007).

5. I. E. Kareev; A. A. Popov; I. V. Kuvychko; N. B. Shustova; S. F. Lebedkin; V. P. Bubnov; O. P. Anderson; K. Seppelt; S. H. Strauss; O. V. Boltalina, J. Am. Chem. Soc., 130, 13471 (2008).

6. B. W. Larson; E.V. Bukovsky; I. V. Kuvychko; Y. Chen; A. A. Popov; O. V. Boltalina; S. H. Strauss, Manuscript in progress
Exfoliated Graphene and Ensembles with Photoactive Electron Donors for Diverse Applications
Authors: Tagmatarchis Nikos
Published: February 2020

Exfoliation of graphite in a liquid phase is a top down approach to produce graphene sheets suitable for further functionalization.1 Organic solvents were screened in parallel with sonication conditions (time and power) in the search for new and more efficient strategies toward exfoliated graphene. We will present that stable dispersions of graphene can be formed especially in o-dichlorobenzene and N-methyl pyrrolidine.2 However, careful spectroscopic examination by X-ray photoelectron spectroscopy (XPS), IR and Raman revealed the presence of defects on the graphene skeleton in the form of oxygen-based functionalities.3 Moreover, we will show that the number and nature of the species introduced onto the graphene lattice can be evaluated by high-resolution XPS and we will reveal how the sonication conditions applied critically affect the quality of the so-produced graphene.3 In the following step, we will present the immobilization of photoactive electron donors, such as porphyrins and others, onto graphene via non-covalent means (supramolecularly), toward the formation of novel electron donor-acceptor systems.4 Finally, solid evidence for the immediate utilization of these graphene-based ensembles as photocatalysts for the removal of dyes from wastewater and water splitting for hydrogen production will be given.5

Acknowledgments

Partial financial support from GSRT/ESPA 2007-2013 through action “Postdoctoral support” project GRAPHCELL PE5(2126) as well as GSRT and the EC through the European Fund for Regional Development, NSRF 2007-2013 action “Development of Research Centers – ΚΡΗΠΙΣ”, project “New Multifunctional Nanostructured Materials and Devices – POLYNANO” is acknowledged.

References

S. P. Economopoulos, N. Tagmatarchis, Chem. Eur. J. 2013, 19, 12930.

T. Skaltsas, N. Karousis, H. J. Yan, C. R. Wang, S. Pispas, N. Tagmatarchis, J. Mater. Chem. 2012, 22, 21507.

T. Skaltsas, X. Ke, C. Bittencourt, N. Tagmatarchis, J. Phys. Chem. C
2013,
117, 23272.

T. Skaltsas, S. Pispas, N. Tagmatarchis, Chem. Eur. J. 2013, 19, 9286.

T. Skaltsas, N. Karousis, N. Tagmatarchis, Submitted, 2013.
Synthesis, Characterization and Electrochemical Investigation of Phthalocyanine Compounds Bearing Fluorine Functionality
Authors: Arslanoglu Yasin , Gokceoren Argun T , Hamuryudan Esin
Published: February 2020

Peripherally substituted symmetrical phthalocyanine derivatives have the potential to use in a wide range of high technology applications, such as in catalysis, in photodynamic therapy, in electrochromic display devices, and as a molecular electronics, or magnetic devices. Phthalocyanines possess an extended π-conjugated electron system which permits π stacking between planar macrocycles. Adding substituents to the periphery of the macrocycles increases their solubility since these substituents increase the distance between the stacked phthalocyanines and enable their solvation. The phthalocyanine complexes are also electrochemically precious complexes due to their excellent electrochemical behaviors. It is well known that the different functionalities changes the features of the MPc complexes, thus electrochemical properties of these complexes should be investigated for possible applications. [1-3]

We present here the syntheses of tetra-substituted fluorine containing biphenyl-malonic ester groups bearing phthalocyanine derivatives with different central metal atoms and investigation of their electrochemical behaviors. All synthesized novel phthalocyanine compounds have been characterized by using their elemental analyses, FT-IR, UV-Vis, 1H NMR, 13C NMR and mass spectroscopic methods. The electrochemical activity of phthalocyanine derivatives were also evaluated from the current–voltage curves obtained by cyclic and differential pulse voltammetric methods.

REFERENCES

1-
A. Koca, Y. Arslanoğlu, E. J Electroanal Chem, 616 (2008), pp. 107–116

2- N.B. Mckeown, B. Dunn, J.W. Goodby, A.R. West (Eds.), Phthalocyanine materials: synthesis, structure and function, Cambridge University Press, Cambridge (1998)

3- H.S. Nalwa, J.S. Shirk, C.C. Leznoff, A.B.P. Lever (Eds.), Phthalocyanines: properties and applications, VCH Publishers Inc, New York (1996), pp. 79–181.
(Invited) Octadecylphosphonic Acid Self-Assembled Monolayers in Low Voltage Electrowetting-on-Dielectric Systems
Authors: Mibus Marcel , Hu Xiaoyu , Knospe Carl , Reed Michael L. , Zangari Giovanni
Published: February 2020

Electrowetting-on-dielectric (EWOD) is a useful phenomenon in which the apparent contact angle of a conductive liquid upon a dielectric-coated electrode changes in response to an applied electric voltage. Large electrowetting effects can be achieved when the dielectric film has small thickness, large permittivity, and high breakdown field strength [1]. EWOD is the fundamental building block to numerous devices: displays, lens, and electronic paper [2]. The use of self-assembled monolayers (SAMs) has the potential to drastically reduce voltage requirements for contact angle change, when used in conjunction with a high breakdown field strength layer.

We studied self-assembled monolayers on anodic aluminum oxide. The monolayer films are formed using various solvents, immersion times, and formation temperatures. Characterization used contact angles and AFM to assess the quality of the films. Contact angles were studied in both a static and a dynamic configuration to assess the SAMs ability to serve as a hydrophobic layer for EWOD systems.

Static contact angles are measured optically through a Ramé-Hart goniometer system, allowing full electrowetting characterization, such as in Figure 1. The three regions shown are low voltage EWOD, which is modeled according to the Lippman – Young (LY) curve at low voltage: cos(θ) = cos(θ0) + cV2/2γ; where c is capacitance, V is applied voltage, γ is the gas-liquid interface tension, and θ0is the equilibrium angle. This is followed by a saturation region, giving a limiting angle below which an increase in electric field has no effect. Finally, at high field the monolayer desorbs causing a large drop in wetting angle.

Dynamic contact angles describe three phase boundary motion giving “advancing” and “receding” contact angles, with their difference defining the contact angle hysteresis (CAH). The measurements are made using the Wihelmy plate method and a Krüss tensiometer; the technique consists in dipping the plate in the liquid electrolyte, measuring the force as a function of the immersion depth. CAH gives an insight into the homogeneity of the SAM films, since any discontinuity in the SAM may obstruct the drop movement; this is observed in the saturation region of Figure 1. Additionally, the raw force-depth data from the tensiometer system show how the contact angle changes across the sample and through repeated cycles, as shown in Figure 2. The deviation from a linear behavior during immersion and emersion (Figure 2) suggests the presence of inhomogeneities in the SAM; the lines in fact smooth out for SAMs formed at higher immersion time.

References

[1] F. Mugele and J.-C. Baret, “Electrowetting: from basics to applications,” J. Phys. Condens. Matter, vol. 17, no. 28, pp. R705–R774, Jul. 2005.

[2] R. Shamai, D. Andelman, B. Berge, and R. Hayes, “Water, electricity, and between… On electrowetting and its applications,” Soft Matter, vol. 4, no. 1, p. 38, 2008.
The Improvement of FN Degradation in 3-Dimension TR
Authors: Ha Sung Yeob , Park Se Geun , Kim Shin Deuk , Kim Hyun Chul , Lee Kyu Pil , Jung Il Sub
Published: February 2020

As Transistor length shrink, many unexpected short channel effects occur under 20nm size. Among these short channel effects, this paper explains about reliability problem of FN degradation and its improvement in 3-Dimension Transistor. The graph of Fig.1 demonstrates that there was threshold voltage(Vth) shift after reliability test(High voltage, High temperature, Long time condition). Of course, the original black curve must be maintained its value despite of reliability stress. This phenomenon caused serious reliability problem in the device.

Above all the easiest method to solve this problem was that we increased the thickness of the oxide. However this method had serious demerit that we must endured the current decrease [1]. Therefore the following two methods were considered for solving this problem.

The first method was that we changed the profile of FIN to reduce the leakage current. The electric fields were crowded at the sharp point and degradation could occur well in Fig.2 (a) profile-1. Therefore we made the sharp point be rounded like Fig.2 (b) profile-2 by changing FIN shape. This was good solution to protect charge converging on cusp and to reduce FN degradation. In the graph of Fig.4 we could confirm that profile-2 was better than profile-1. However this method must be applied carefully in device because it generated side effects that were caused by decreased margin of Gate to Active isolation.

The second method was that we reduced fixed charges generation by adjusting the grain size of metal gate. The grain size of metal gate was more lager after all integration than just deposition status. This grain growth acted as (+) charge formation factor in the condition of reliability stress. In other words, at the interface of Si and metal gate the following reaction happened lively (TiN + SiO2 -> TiON + SiO+ ). Therefore we must reduce the grain growth to improve the FN degradation. We knew that the grain size was changed by temperature of TiN deposition through many experiments [2]. In Fig.3 (a), the grain size grew approximately 0.8nm per 30 degrees of TiN deposition temperature. As the TiN deposition temperature increased, gap of grain growth became smaller than low temperature status. It noted that the grain size after all integration is almost same as the grain size of just deposition status like Fig.3 (b) which is real grain TEM image in condition of 660°C.

In conclusion, to confirm enhancement we verified the result of FIN profile optimization and TiN deposition temperature experiment by measuring Vth shift. In Fig.4, Vth shift and residual stress became smaller and smaller as we applied improvement condition.

References

[1] Fundamentals of Modern VLSI Devices, by Yuan Taur and Tak H.Ning

[2] Hsyi-En Cheng, Wen-Jen Lee, C.-M. Hsu, Thin Solid Films Volume 485, Issues 1–2, 1 August 2005, Pages 59–65
(Invited) Challenges in Contact Technologies for Planar/Non-Planar Si Technologies
Authors: Adusumilli Praneet , Alptekin Emre , Breil Nicolas
Published: February 2020

The transition from 2D planar devices to 3D devices that is underway in the semiconductor industry has significant implications for parasitic resistance & capacitance of CMOS devices. This talk will focus on challenges in contact technologies as we make this transition.

Increases in the width of the channel per foot print and the simultaneous scaling of gate pitch have accelerated the shrink in effective contact area per channel width and has elevated the importance of contact length for formation of low resistance contacts.

Additionally, scaling of gate pitch is leading to new concerns about device yield and defectivity - such as shorts between interconnect contacts due to increase in contact critical dimensions post patterning. This has put renewed focus on anisotropic cleans and other surface preparation techniques. A nominal increase in contact critical dimensions while beneficial for parasitic resistance has a capacitance penalty and this trade off needs to be carefully managed.

Furthermore, an increase in material and process integration complexity adds to the challenge of engineering the specific contact resistivity of the contact metal/source-drain interface. For example, the impact of down stream thermal processing on dopant activation in the source-drain regions needs particular attention.

Finally, the contribution from interconnect metallization to the overall parasitic resistance is on the rise and needs to be mitigated.
Investigation of Na2/3Ni1/3Ti2/3O2 as Novel Bi-Functional Electrode Material for Non-Aqueous, Room Temperature Na-Ion Batteries
Authors: Shanmugam Rengarajan , Lai Wei
Published: February 2020

Developing long life, low-cost energy storage solutions based on earth abundant minerals is crucial for renewable energy sources, smart electric grid networks, portable electronics and automotive sector. Na-ion batteries, engineered to operate under ambient conditions with non-aqueous electrolytes, offer much promise in that they do not have resource constraints1and by selecting appropriate materials they can be fabricated into high voltage electrochemical cells, similar to Li-ion chemistry.

The objective of the current work is to study the electrochemical properties of a new oxide material with the composition Na2/3Ni1/3Ti2/3O2 (SNTL)2 as a “bi-functional” intercalation-type electrode for Na-ion battery applications. The presence of two transition metals in this layered oxide enables us to activate two redox couples (Ni2+/3+ and Ti4+/3+) of different species in the same material and thereby provides the opportunity to use it as anode or cathode depending on the potential window. This approach of making both electrodes (anode and cathode) using the same material can simplify electrode design and potentially reduce manufacturing costs for commercial applications.

The solid state synthesis conditions of SNTL have been optimized to make phase-pure oxide with minimal particle size as shown in Figure 1a and Figure 1b.

Galvanostatic cycling shows that up to 50% of sodium ions can be removed reversibly by oxidizing nickel from 2+ to higher oxidation state without any significant capacity loss. This contributes to a sloping voltage profile in the range of 3-4.2 V (Figure 1c) with solid solution-type mechanism involving no phase transitions.

Sodium insertion into pristine SNTL, due to its sodium deficient nature, activates the Ti4+/3+ redox couple. This leads to again a sloping voltage profile with an average voltage of 0.7 V vs. Na/Na+ as shown in Figure 1d. The reaction has been confirmed to be of solid solution-type using ex-situ XRD measurements. Thus, SNTL can be used to fabricate 3V intercalation-based Na-ion batteries.

Wet chemistry-based synthetic routes (sol gel) are being currently explored to reduce the particle size, decrease the diffusion length scale of electrons and thereby improve the electrochemical performance under higher currents. Fabrication and testing of solid state batteries using SNTL material as active electrodes (anode and cathode) and Na3Zr2P1Si2O12 material (NASICON)3as fast sodium conducting solid electrolyte is also currently under progress.

References

1. M.D.Slater, D. Kim, E. Lee, C.S. Johnson, Sodium-Ion Batteries, Advanced Functional Materials, 2013, 8, 947-958

2. Y.J. Shin, M.Y. Yi, Preparation and structural properties of layer-type oxides NaxNix/2Ti1-x/2O2, Solid State Ionics, 2000, 132, 131-141

3. Goodenough JB, Hong HYP, Kafalas JA., Fast Na+-Ion transport in skeleton structures. Mater Res Bull 1976, 11(2), 203-220
Organic Redox Active Molecular Engineer for NRF
Authors: Zhang Lu , Huang Jinhua , Vaughey John T , Burrell Anthony K.
Published: February 2020

Abstract:

Non-aquoes redox flow battery is a unique energy storage technology. Unlike traditional battery systems, the active energy storage material is in mobile phase and could basically be stored anywhere separately. This gives a lot of flexibility in terms of capacity, power and safety control, making it an idea candidate for large scale stationary energy storage application.

Material development for this technology is crucial for possible implementation. Molecular engineer of organic redox active molecules could lead to tunable physical and electrochemical properties, including solubility in organic solvents, molecular mobility, redox potential, and electrochemical reversibility, which are key factors to energy storage applications. Specifically, one family of dimethoxybezene based organic molecules will be discussed in this talk. Dimethoxybezene based molecules have drawn increasing attentions due to their excellent electrochemical activities, especially as redox shuttle additives and possible non-aqueous flow battery catholytes, which both require redox active molecules to be the key functional components. Due to the organic synthesis feasibility, structural improvements could be conducted to intentionally tune the physical or electrochemical properties of dimethoxybezene. For instance, ANL-2 was developed with improved solubility in carbonate based electrolytes and excellent overcharge performance as redox shuttle additive. The success of ANL-2 was based on the previous attempts using various design strategies to improve the solubility of DDB, including asymmetric ANL-1, and DBMOEB (1,4-di-tert-butyl-2,5-bis(2-methoxyethoxy)methoxy-benzene). Other examples are ANL-3 and ANL-4 molecules, with focus on increasing the redox potentials. ANL-3 is able to provide 4.8 V vs Li/Li+ overcharge protection, highest ever reported in the literature. ANL-4, on the other hand, exhibited 4.5 V vs Li/Li+ redox potential and good electrochemical reversibility.
A Quinone-Based Flow Battery for Large-Scale Electrochemical Energy Storage
Authors: Huskinson Brian , Marshak Michael P. , Gerhardt Michael R. , Aziz Michael J.
Published: February 2020

We report results from an aqueous quinone-bromine redox flow battery in which the negative electrode is a substituted quinone/hydroquinone couple and the positive electrode is bromine/hydrobromic acid. The redox active materials, which can be very inexpensive, contain no metals. Consequently, the cell appears to be a very attractive candidate for inexpensive, large-scale electrical energy storage.

We will report the performance of a small flow battery based on this couple.
Hybrid Organic and Inorganic Redox Active Components for Non-Aqueous Redox Flow Batteries
Authors: Liu Tianbiao , Wang Wei , Wei Xiaoliang , Li Bin , Nie Zimin , Chen Baowei , Sprenkle Vincent
Published: February 2020

Redox flow battery (RFB), as one of the most promising technologies for large-scale stationary energy storage up to MW (power) or MWh (energy), has attracted increasingly attentions from both academic and industrial research groups.1RFB is characteristic of many attractive advantages including decoupling of energy storage and power output, exceptional design flexibility, excellent scalability and modularity, long service life, high efficiency, etc. These technic merits make

RFB a well-suitable choice to stabilize the power grid and overcome the intermittency of renewable energy sources (solar, wind and hydroelectricity etc.).2 Traditional aqueous RFB (ARFB), although with a number of technic advantages, is primarily limited by low energy density due to the narrow operation voltage confined by water electrolysis and low concentrations of redox components. To circumvent the limitations of the ARFB system, we have initiated research on non-aqueous redox flow battery (NARFB) employing redox active organic3and hybrid organic/inorganic molecules as flowable electrode materials.

In this presentation, we will report our new results on synthetically design and modification of advanced redox active organometallic complexes in order to optimize operating redox potentials and increase concentrations (i.e. volumetric energy density). Electrochemical performance of the new electrode materials for NARFB will be discussed to highlight research and development of NARFB at PNNL and address future research directions.

References:

Z. Yang, J. Zhang, M. C. W. Kintner-Meyer, X. Lu, D. Choi, J. P. Lemmon and J. Liu, Chemical Reviews, 2011, 111, 3577-3613.

W. Wang, Q. Luo, B. Li, X. Wei, L. Li and Z. Yang, Advanced Functional Materials, 2013, 23, 970-986.

W. Wang, W. Xu, L. Cosimbescu, D. Choi, L. Li, Z. Yang, Chemical
Communications, 48, 6669-6671 (2012).

Acknowledgment

We acknowledge financial supportfrom the U.S. Department of Energy’s (DOE’s) Office of Electricity Delivery and Energy Reliability (OE) (under Contract No. 57558). Pacific Northwest National Laboratory is operated by Battelle for the U.S. Department of Energy.
(Invited) Flexible 3-Dimensional Graphene Foam-Based NO2 Gas Sensors
Authors: Lee Chongmin , Kim Byung-Jae , Kim JiHyun
Published: February 2020

Graphene has attracted much attention due to its great optical and electronic properties. Since indium-tin-oxide which is common transparent-conductive-layer in GaN-based light-emitting diodes (LEDs) has reached its limitation, many researchers have focused on the applications of graphene as transparent-conductive-layer in optoelectronic devices, for instances LEDs and solar-cells. Especially, the exceptional transmittance in UV (ultra-violet) and IR (infra-red) spectral ranges opens a new possibility for the graphene to be integrated with UV-LEDs. However, the high sheet resistance of the graphene is still an issue in its implementations. The methods to improve the sheet resistance and the stability by a chemical doping method will be discussed.
(Invited) Effect of Annealing on Electronic Carrier Transport Properties of Gamma-Irradiated AlGaN/GaN High Electron Mobility Transistors
Authors: Yadav Anupama , Schwarz Casey , Shatkhin Max , Wang Luther , Flitsiyan Elena , Chernyak Leonid , Liu Lu , Hwang Y.H. , Ren Fan , Pearton Stephen J. , Lubomirsky Igor
Published: February 2020

AlGaN/GaN High Electron Mobility Transistors (HEMTs) are the most advanced electronic nitride devices to be used at high temperatures and in harshly radiated environments. A clear understanding of radiation effects on these devices is essential in order to predict their behavior in space and terrestrial applications including military, nuclear and high energy physics. Only a limited amount of insight exists into the behavior of III-N based junction transistor after exposure to gamma irradiation. Investigation of gamma-irradiated device properties will provide important information about the defects in semiconductor heterostructures. Therefore, it is important to understand how defects are created by gamma-rays and how they can be healed by annealing. Here we present the impact of gamma-irradiation on AlGaN/GaN heterostructures fundamental properties including carrier transport and recombination. We also report the effect of annealing at 200o C over 25 min on gamma-irradiated samples through monitoring of minority carrier diffusion length using Electron Beam Induced Current (EBIC) method.

We found the relationship between dose, diffusion length and its activation energy after gamma-irradiation and after annealing treatment. Temperature dependent EBIC measurements yielded a decrease in diffusion length with corresponding increase in activation energy after the gamma-irradiation.The increase in activation energy is likely an indication of the creation of deeper gamma irradiation induced defect traps due to nitrogen vacancies. These deep traps reduce the carrier concentration and mobility and increase the activation energy related to carrier recombination. It is evident from our results that annealing of HEMTs that were gamma-irradiated with moderate dose leads to the recovery (depending on dose) of minority carrier diffusion length. The recovery is also reflected in the activation energy returning to its pre-irradiated value. The level of recovery of gamma-irradiated devices after annealing treatment depends on the dose of irradiation. Increase in diffusion length after annealing had been attributed to a reduction in point defects (nitrogen vacancies) induced in AlGaN/GaN by gamma-irradiation.
Theoretical Screening of Novel Host Oxide Materials Suitable for Eu2+ Doped Yellow and Red Luminescence Phosphor
Authors: Takaba HIromitsu , Matsui Ryota
Published: February 2020

Theoretical screening of host materials suitable for Eu2+ doped phosphor applicable to light emitting diodes was carried by using computational chemistry techniques and crystal structure database. It is well known that an energy level of Eu 4f and 5d orbitals are shifted by the interaction with host crystals that causes a significant spread of Eu 5d orbital. Hence, a control of emission properties of phosphors would be possible by selecting a suitable host material. In this study, emission wavelength and efficiency for more than 8000 oxide structures, almost which are not well investigated as a host structure for Eu2+, were screened by our original prediction method. We reported that there is the relationship between crystal structure and emission colors of Eu2+ doped phosphors, and a quantitative structure-property relationship (QSPR) was applied to reveal it. Developed QSPR model is confirmed to predict the emission wavelength of phosphors we investigated. Our suggested method for the estimation of emission efficiency of Eu2+-doped phosphors is based on the structural information. We defined an alkaline-earth network (ANet) to represent the magnitude of the interaction of alkaline earth atoms with Eu2+ atoms in the host crystal. ANet shows an inversely relationship to an internal quantum efficiency, which supports that ANet is a good index for searching a high efficient Eu2+-doped phosphors qualitatively. It is noted that they are estimated only from the structural information of host materials. In this paper, the prediction methods of emission properties were applied to explore novel host structures for Eu2+ doped phosphors applicable for LED. For more than 8000 oxide crystal candidates for host structure, are screening. Several oxide structure suitable for Eu2+ doped phosphor for LED are suggested.
(Invited) Advances in Silicon Nanophotonics
Authors: Franzó Giorgia , Irrera Alessia , Miritello Maria , Boninelli Simona , Iacona Fabio , Priolo Francesco
Published: February 2020

Silicon nanophotonics is emerging as a new platform for the integration of photonic and electronic devices. Several examples of recent efforts on monolithic light sources based on silicon nanostructures will be presented and discussed. In particular it will be shown that silicon-on-insulator (SOI) is emerging as an interesting photonic material. The first electrically pumped silicon-on-insulator nano light source, tunable around 1300-1600nm range and operating at room temperature will be presented. H-related optically active defects are properly introduced into silicon enhancing the electrically driven emission in a photonic crystal nanocavity device. A narrow (Δλ = 0.5 nm) emission line with the highest spectral power density ever reported from any silicon emitter will indeed be presented. Alternatively Er ions are introduced into the nanocavity showing an enhanced emission at 1500 nm with potentials for a population inversion and laser action. Group-IV semiconductor nanowires (NWs) are also attracting interest among the scientific community as building blocks for a wide range of future nanoscaled devices. We show that metal-assisted chemical etching is a powerful technique to obtain nanometer-size high density and low-cost Si NWs with high and controllable aspect ratio. NWs obtained by this technique have exactly the same structure and doping properties of the substrate and present quantum confinement effects. We will show that luminescence is very efficient (in the order of the percent) and tunable with NWs size according to quantum confinement. Light emitting devices based on Si NWs have also been realised, showing the efficient electroluminescence emission at room temperature under low voltage excitation. The relevance and the perspectives of the reported results opening the route towards novel applications of Si nanostructures in photonics will be discussed.
Luminescent Electrochromic Device Based on a Biohybrid Electrolyte Doped with a Mixture of Potassium Triflate and a Europium β-diketonate Complex
Authors: Fernandes Mariana , Botas A. M. P. , Leones R. , Pereira S , Silva M. M. , Ferreira Rute Sa , Carlos Luis D , Fortunato Elvira , Rego Rosa , de Zea Bermudez V.
Published: February 2020

The “mixed cation” approach, which basically involves the use of two guest salts instead of a single one, is an attractive procedure that usually results in a significant increase of the ionic conductivity of polymer electrolytes (PEs). Recently, the sol-gel process [1] was successfully combined with the “mixed cation” effect to produce novel luminescent and ion conducting biohybrid electrolytes composed of a di-urethane cross-linked poly(e-caprolactone) (PCL(530)/siloxane hybrid network and a mixture of lithium and europium triflates, with application in electrochromic devices (ECDs) [2].

To enhance the quantum efficiency of these electrolytes, while preserving acceptable levels of ionic conductivity, we have decided in the present work to replace europium triflate by several europium b-diketonate complexes and to include other alkaline metal triflate salts [3,4]. In a previous study we concluded that adding lanthanide aquocomplexes incorporating b-diketonate ligands to d-PCL(530)/siloxane matrix is of interest as it yields an effective protecting cage that efficiently encapsulates the emitting centers and reduces luminescence quenching [5].

The structure, morphology and thermal stability of the new electrolyte systems have been characterized. ECDs have been built with optimized electrolyte samples and their performance has been analyzed by means of UV/VIS and chronoamperometric measurements.

[1] C. J. Brinker, G. W. Scherer, Sol-gel Science: The Physics and Chemistry of Sol-Gel Processing, Academic Press, San Diego, CA, 1990.

[2] M. Fernandes, S. S. Nobre, L. C. Rodrigues, A. Gonçalves, R. Rego, M. C. Oliveira, R. A. S. Ferreira, E. Fortunato, M. M. Silva, L. D. Carlos, V. de Zea Bermudez, ACS Appl. Mater.
Interfaces, 3, 2011, 2953.

[3] S. C. Nunes, V. de Zea Bermudez, M. M. Silva, M. J. Smith, D. Ostrovskii, R. A. S. Ferreira, L. D. Carlos, J. Rocha, A. Gonçalves, E. Fortunato, J. Mater. Chem., 17, 2007,4239.

[4] M. Fernandes, L. C. Rodrigues, R. A. S. Ferreira, A. Gonçalves, E. Fortunato, M. M. Silva, M. J. Smith, L. D. Carlos, V. de Zea Bermudez; Solid State Ionics, 204-205, 2011, 129.

[5] M. Fernandes, V. de Zea Bermudez, R. A. Sá Ferreira, L. D. Carlos, A. Charas, J. Morgado, M. M. Silva, M. J. Smith, Chem.Mater. 19, 2007, 3892.
Electromigration in Passivated Gold Interconnects for GaAs Devices
Authors: Kilgore Steve
Published: February 2020

Electromigration in metal interconnects is the most pernicious failure mechanism in semiconductor integrated circuits (ICs). Early electromigration investigations were primarily focused on aluminum interconnects for silicon-based ICs. An alternative metallization compatible with gallium arsenide (GaAs) was required in the development of high powered radio frequency (RF) compound semiconductor devices operating at higher current densities and elevated temperatures. Gold-based metallization was implemented on GaAs devices because it uniquely forms a very low resistance ohmic contact and gold interconnects have superior electrical and thermal conductivity properties. Gold (Au) was also believed to have improved resistance to electromigration due to its higher melting temperature, yet electromigration reliability data on passivated Au interconnects is scarce and inadequate in the literature.

Electromigration lifetimes of large quantities of passivated electroplated Au interconnects were measured utilizing high resolution in-situ resistance monitoring equipment. Application of moderate accelerated stress conditions with a current density limited to 2 MA/cm2and oven temperatures in the range of 300°C to 375°C avoided electrical overstress and severe Joule-heated temperature gradients. Temperature coefficients of resistance (TCRs) were measured to determine accurate Joule-heated Au interconnect film temperatures.

A failure criterion of 50% resistance degradation was selected to prevent thermal runaway and catastrophic metal ruptures that are problematic of open circuit failure tests. Test structure design was optimized to reduce resistance variation and facilitate failure analysis. Characterization of the Au microstructure yielded a median grain size of 0.91 µm. All Au lifetime distributions followed log-normal distributions and Black’s model was found to be applicable. An activation energy of 0.80 ± 0.05 eV was measured from constant current electromigration tests at multiple temperatures. A current density exponent of 1.91 was extracted from multiple current densities at a constant temperature. Electromigration-induced void morphology along with these model parameters indicated grain boundary diffusion is dominant and the void nucleation mechanism controlled the failure time.
Reflectance Studies in Silicon Nanowires Grown By Electroless Etching
Authors: Velez Victor H. , Mertens Robert George , Sundaram Kalpathy B
Published: February 2020

One of the major energy loss mechanisms of solar cells is optical reflection. Utilization of nanostructures in solar cells may eliminate the need for antireflective coating [1]. The antireflective nature of Silicon nanowires (SiNW’s) revealed by their black color and dull appearances have drawn the attention of researchers [2]. Highly oriented SiNWs arrays prepared by electroless etching method can significantly suppress light reflection across a broad spectrum. Reflectivity studies on these show a significantly decrease in optical reflectivity down to 1.3% for 10 µm long SiNWs arrays [3]. Electroless etching is a top-down technique for growing SiNWs and does not need costly and expensive equipment to grow SiNWs as bottom-up methods usually do.

The electroless process begins with the cleaning of silicon substrates. They were cleaned in acetone, methanol and deionized water, then blow-dried with N2. They are dipped in hydrofluoric acid (HF) 49% solution for 1 min to remove any remaining oxide.

The silicon (Si) wafers are dipped for 45 minutes at room temperature in an electroless solution prepared in a petri dish containing silver nitrate (AgNO3) and hydrofluoric acid (HF) [4].

The substrates are dipped and galvanic reactions disperse silver ions on their surface, losing silicon as SiF6. As a consequence of this etching process, the removal of Si via Ag ions results in vertically aligned arrays of SiNWs covered with silver dendrites. Varying the heights of the SiNWs(fig. 1). changes their optical reflectance. A target optical reflection would be 0.8.

Fig 1. Cross sectional SEM images of the vertically standing Si NW arrays obtained by electroless etching.

REFERENCES

[1] Jin-Young Jung, Han-DonUm, Sang-WonJee, Kwang-TaePark, JinHoBang, Jung-HoLee, “Optimal design for antireflective Si nanowire solar cells,” Solar Energy Materials & Solar Cells, 2013.

[2] Baris Ozdemir, Mustafa Kulakci, Rasit Turan and Husnu Emrah Unalan, “Effect of electroless etching parameters on

the growth and reflection properties of

silicon nanowires,” IOP Science, 2011.

[3] Hua Bao and Xiulin Ruan, "Optical absorption enhancement in disordered

vertical silicon nanowire

arrays for photovoltaic applications," OPTICS LETTERS, 2010.

[4] R. G. Mertens and K. B. Sundaram, “Recession and Characterization of Patterned Nanowires Grown by Electroless Etching of Silicon”. ECS Journal of Solid state Science and Technology, 2012.
Synthesis of Cu-in Alloy (CuIn and Cu2In) Nanoparticles in Aqueous Solution for the Application of CIGS Solar Cell
Authors: Takahashi Hideyuki , Fujiki Hironari , Yokoyama Shun , Tohji Kazuyuki
Published: February 2020

Many researchers have vigorously studied to develop the low cost solar cells with high efficiency. Among the various solar cells, it is well known that CIGS (Cu(In,Ga)Se2) type solar cell shows attractive performances, nevertheless it can be produced lower cost than Si solar cell. These CIGS type solar cell is synthesized by gas phase method. However, since vaporizing temperature of four elements is extremely different, productivity under the gas phase is relatively low, which read the large amount of waste of resources. Thus, to decreasing the cost of CIGS type solar cell, synthesis method with high recovery rate should be developed.

On the other hand, it is also well known that liquid phase reduction methods can be produced the nano materials with high recovery rate. Among the various liquid phase methods, we reported that well crystallized and uniform alloy nanoparticles, such as Pd20Te7, can be synthesized by restrict controlling the homogenization of metallic complexes in the aqueous solution which reading the control of reduction rate, under the room temperature [1]. However, ternary, or more, alloy nano materials with uniform structure can not be synthesized until now, because of difficulty of controlling these conditions.

Therefore, in this study, the relationship between copper and/or indium complex condition in the aqueous phase and its reduction potentials was evaluated.

Amine-based and/or carboxyl-based complexing reagent, were used for the complex reagents. Condition of metallic complexes in the aqueous solution can be restricted to homogenized species by utilizing the theoretical calculation method using the critical stability constants. Detailed calculation procedure was summarized in Ref. 1. Reduction potential of Cu (and/or In) complexes was measured, and synthesized materials were analyzed by XRD.

Calculation was performed for various system, such as the Cu-NO3-OH-glycine system (dissolution of Cu(NO3)2 and glycine). The ratio of each species was Cu : NO3 : malic acid =1 : 2 : 3. Horizontal and vertical axis shows the pH and abundance ratio (%), respectively. As the result, copper complex was successfully restricted to single species, [(Cu2+)(Gly)2], at the pH range over 6. As the same manner, various copper complexes were adjusted at pH10.

By using the reduction potential decided by using CV (cyclic voltammetry), relationship between stability constants of complex reagents and reduction potential were summarized.

It become clear that correlation between reduction potential and stability constants showed the linearly interaction. Moreover, it became apparent that, in order to synthesize CuIn alloy, amine-based complexing reagent which have large stability constants will be needed.

This work was supported by the Grant-in-Aid for Challenging Exploratory Research (No. 25550085).

References: [1]H. Takahashi, et.,al; Applied Catalysis A: General 392, 80-85 (2011)
Plasma Assisted Preparation of PAN-Based Carbon Fiber
Authors: Dong Qi , Cho Hyoung J. , Lu Chunyuan , Park YeongMin , Kim TaeGyu
Published: February 2020

Carbon fibers’ capabilities could be affected critical on stabilization which were attributed to its manufacturing process. In this study, hydrogen-oxygen gas plasma assisted stabilization (PAS) was utilized for facilitating the oxidation reaction of the PAN-based precursor fibers in variant oxygen gas ratio. While oxygen gas, including in the gas ingredients, consists from 8 sccm, 10 sccm to 12 sccm. A carbonization reaction was carried on under nitrogen gas plasma. All of the involving plasma was generated via plasma-enhanced chemical vapor deposition (PECVD). The effect on preparation of carbon fibers by plasma assist was analyzed using SEM, FT-IR, DSC, and XRD. The tensile strength, modulus and apparent crystallite orientation of carbon fibers were preferential to those conventional preparation precursor fibers. Results of experimental applications of plasma assisted preparation procedure is given to illustrate the carbon fiber manufacturing.

Kerword: carbon fibers, plasma assisted preparation, variant gas ratio, carbon fiber manufacturing
Benzene Adsorption on (110) Surfaces of Transition Metals: Role of Van Der Waals Interaction and Substrate
Authors: Matos Jeronimo , Yildirim Handan , Kara Abdelkader
Published: February 2020

The characteristics of Benzene adsorption on metals and their alloy surfaces, and the interface features have been the subject of many experimental and theoretical studies. With the availability of the new vdW functionals, we revisit this organic molecule/metal system to assess the influence of vdW interactions on the adsorption as well as to examine the performance of these vdW functionals. We will present the adsorption geometries, adsorption energies and heights, the characteristics of interface electronic structure, and the charge transfer for Benzene adsorption on the (110) surfaces of seven transition metals; Au, Ag, Cu, Pd, Pt, Rh, and Ni. The calculations are carried out using PBE and vdW-DF family functionals implemented in the VASP package. We will provide comparisons with the available experimental and theoretical studies on the adsorption geometries and energies, and the effect introduced by varying surface chemistries. We will also provide comparisons with the recent study for Benzene adsorption on the (111) surfaces of the same metal substrates [1].

[1] H. Yildirim, T. Greber, and A. Kara J. Phys. Chem. C 2013, 117, 20572.

This work is funded by the U.S. Department of Energy Basic Energy Science under Contract No DE-FG02-11ER16243