bluuebunny/crossref_metadata_2025_split huggingface dataset:
GaN Based Ethanol Sensor
Authors: Jung Sunwoo , Baik Kwang Hyeon , Bai Seoung Jai , Jang Soohwan 
Published: February 2020

Ethanol is one of most common aliphatic alcohol, which is used in chemical, biomedical, and food industry including alcoholic beverage. In recent, there are growing demands for the ethanol gas sensor to detect early spoilage of carbohydrate food, and this kind of sensors are to be employed in consumer electronics including refrigerators and mobile devices. Electrochemical, optical, potentiometric, polymer, and semiconductor sensors have been developed for fast and accurate detection of ethanol. Among the various detection methods, semiconductor based sensor can be operated at low power consumption in compact size. So far now, metal oxide semiconductors such as SnO2, Fe2O3, CuO, and ZnO are researched mostly.
GaN based material is very suitable for gas sensors, and has many superior material properties to oxide semiconductors. Wide bandgap of GaN enable devices to be operated at high temperature and harsh radiative environment, and mechanical and chemical robustness of GaN ensures reliability and durability of the device. Many types of GaN based gas sensing devices including Schottky diodes, metal oxide semiconductor (MOS) diodes, GaN nanowires and AlGaN/GaN high electron mobility transistors (HEMTs) which employ specific sensing material as a catalytic active layer have been developed for prompt and sensitive detection of target gas. Specially, AlGaN/GaN HEMT structure with 2 dimensional electron gas (2-DEG) channel induced by piezoelectric and spontaneous polarization at the interface between the AlGaN and GaN layers shows highly sensitive current changes to surface charges created by catalytic reaction of target gas on the specific active sensing layer. Typically, field effect transistors with higher drain current exhibit better responsivity of gas detection. With 30 % Al concentration in AlGaN layer, 5~10 times higher channel sheet electron densities are obtained compared to GaAs or InP HEMTs.
In this study, AlGaN/GaN HEMT based Schottky diode ethanol sensor using silver as a sensing material was fabricated, and the response of the device to ethanol gas was investigated. The diode showed current reduction in ethanol ambient due to the increase of Shottky barrier height at 250oC, and fast reliable repeatability to cyclic exposures of various concentrations of ethanol gas.
Low-Temperature Aluminum-Aluminum Wafer Bonding
Authors: Rebhan Bernhard , Hinterreiter Andreas , Malik Nishant , Schjølberg-Henriksen Kari , Dragoi Viorel , Hingerl Kurt 
Published: February 2020

Thermo-compression wafer bonding is a key technology for the wafer-level production of hermetically sealed cavities, which are essential for the functioning of many microelectromechanical systems (MEMS). Aluminum, with its low material price, high thermal and electrical conductivities and its complementary metal oxide semiconductor (CMOS) compatibility, is a promising candidate for the fabrication of CMOS-MEMS, in which the sensor/actuator part is bonded to the electrical circuit. The chemically highly stable oxide layer on the Al surface cannot be removed by conventional methods. It acts as a thin diffusion barrier layer between the two aluminum metallization layers, and therefore inhibits successful low temperature Al-Al wafer bonding. So far, effective Al-Al wafer bonding has required extreme processing temperatures of >300°C and high contact pressures. Typically, 450°C-550°C led to bonded Al-Al wafers with incorporated alumina (Al2O2) precipitates and reasonable bonding quality. By using the EVG®580 ComBond®system, in which the aluminum oxide is first removed physically, followed by bonding of the two metallization layers – both performed in a high vacuum cluster – for the first time successful Al-Al wafer bonding was feasible at a temperature of 100°C.
In the present work, the microstructure of structured and unstructured aluminum films on silicon substrates was characterized by atomic force microscopy (AFM) and transmission electron microscopy (TEM). C-mode scanning acoustic microscopy (C-SAM), TEM and energy dispersive x-ray spectroscopy (EDXS) interface studies of Al-Al wafer pairs bonded with this novel method revealed oxide-free, atomic contact and grain growth across the original interface. Further, the bond strength was characterized based on dicing yield and pull tests.
(Invited) MEMS Capping By Anodic Bonding of Evaporated Glass Thin Films
Authors: Hansen Ulli , Maus Simon , Gyenge Oliver , Hu Xiaodong 
Published: February 2020

Anodic bonding is a widely used MEMS process to join silicon and glass wafers. It has been utilized for many years in a large variety of devices and is valued for its possibility to create highly reliable and strong bonds at rather robust process parameters – e.g. not demanding extremely perfect surface conditions as in fusion bonding. However, the limitation in the choice of bond partners (typically borosilicate glass like Pyrex or Borofloat33 to silicon) and the rather harsh processing conditions (temperatures around 400°C and typical voltages of 600-1000V) has restricted the use of this process.
Extensive research has been done over the years to adapt the process conditions in order to enable anodic bonding at lower temperatures and voltages and reach a higher compatibility of the process. The quality of the anodic bond is characterized by the charge (alkaline ion content) moved in the glass substrate and the ability of the glass to form covalent bonds with the silicon wafer. It can be observed that the bonding result is mainly an interaction on three process parameters: temperature, voltage, and process time with a clear dependence on the surface roughness of the bond partners. In bulk anodic wafer bonding it is not p ossible to reduce all three of these parameters and receive a satisfactory result. In order to enhance the compatibility of the anodic bonding process, the limitation of bulk silicon glass bonding needs to be overcome. Work has been reported on replacing the bulk glass wafers by thinner glass structures e.g. formed on a silicon wafer by polishing a previously anodically bonded glass substrate to a thickness of 20-50µm to achieve a kind of glass film. Other approaches include sputtering of borosilicate glass and the evaporation of this glass type, which is the focus of this contribution. On part of the silicon wafer, anodic bonding has be verified to work with different metalization layers, esp. aluminum coatings. Our contribution gives an overview on the possibilities of bonding with evaporated glass thin films to silicon and aluminum structures, and it applications in e.g. MEMS capping or pressure sensors. We investigate the influence of the process parameters of the glass deposition on the bonding result and present concepts for enhancing the compatibility of the anodic bonding process using evaporated glass thin films.
Cooling Rate Dependent High Substitutional Sn Concentration (>10%) in GeSn Crystals on Insulator by Pulsed Laser-Annealing
Authors: Moto Kenta , Matsumura Ryo , Sadoh Taizoh , Ikenoue Hiroshi , Miyao Masanobu 
Published: February 2020

Introduction

Crystalline GeSn thin-films on insulator with high substitutional Sn concentration (>10%) are deseired to realize high-speed thin film transistors. However, thermal equilibrium solid-solubility of Sn in Ge is only 1%. To solve this problem, we examined non-thermal equilibrium crystallization of amorphous-GeSn (a-GeSn) by pulsed laser-annealing (PLA). In the present study, we focus on the influence of pulse number on crystallization of a-GeSn by PLA.

Experimental Procedure

In the experiment, a-Ge1-xSnx (0≦x≦0.2) films (thickness: 100 nm) were prepared on quartz substrates by a molecular beam deposition technique. These samples were irradiated with a pulsed laser (wavelength: 248 nm, pulse duration: 80 ns, repetition rate: 100 Hz, fluence: ~140 mJ/cm2, pulse number: 1-200 shot). The laser-annealed regions were analyzed by Nomarski microscopy, Raman scattering spectroscopy, and transmission electron microscopy (TEM). Cooling rate after PLA was estimated by in-situ optical reflectivity measurements.

Results and Discussion

Figure 1(a) shows Raman spectra of Ge0.95Sn0.05 samples after PLA (laser flunence: 140 mJ/cm2) with various pulse numbers. In all spectra, sharp peaks due to Ge-Ge bonding in crystalline GeSn are observed. Thus, GeSn has been crystallized for all pulse numbers, which was confirmed by TEM observation. Substitutional Sn concentration in the grown layers is investigated from the difference of Ge-Ge Raman peak positions between GeSn samples and a crystalline Ge substrate [1]. Pulse number dependence of substitutional Sn concentration is shown in Fig. 1(b). Substitutional Sn concentration increases with decreasing pulse number, and GeSn crystals with very high substitutional Sn concentration (~13%) has been realized for the sample (initial Sn concentration: 20%) with a single shot. These results suggest that non-thermal equilibrium conditions are enhanced by lower pulse number. To explore non-thermal equilibrium growth by modulating pulse number, cooling rate after PLA is estimated by in-situ optical reflectivity measurements, as shown in Fig. 2(a). Reflectivity at 10th and 100th shots as a function of time is shown in the inset of Fig. 2(b). From the decreasing curve of reflectivity, time constants of cooling processes are estimated, which are summarized in Fig. 2(b). Interestingly, substitutional Sn concentration increases with decreasing time constant. The detailed physics will be discussed in the presentation.

References

[1] V. R. D’Costa, J. Tolle, R. Roucka, C.D. Poweleit, J. Kouvetakis, J. Menendez: Solid State Communications 144, 240 (2007).

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(Invited) Vertical Channel Amorphous Indium Gallium Zinc Oxide Thin Film Transistors
Authors: Shieh Han-Ping D. , Chauhan Ram Narayan , Chuang Kang-Ju , Tiwari Nidhi 
Published: February 2020

Vertical channel thin film transistors (VTFTs) are proposed as an effective approach to reduce driving voltage and power consumption for achieving high speed and high resolution displays. VTFTs with amorphous silicon (a-Si) technology have severe problems related to low on/off current ratio (Ion/off), high drain-leakage current, and absence of saturation behavior at high drain voltages. In this concern, thin gate insulator plays a key role to result well behaved a-Si VTFT characteristics such as clear saturation behavior at high drain voltage, low leakage current and good device performance with high Ion/off. However, poor mobility and contact resistance due to space charge limited current a-Si VTFT become increasingly noticeable, when the channel length is scaled down to nanometer dimensions. In contrast, the oxide semiconductor can be scaled to a very short channel without deteriorating the device performances. Considering that oxide semiconductors have large-area compatible processes, it will be better to find a method for achieving low driving voltages with conventional optical lithography machines used for large area display panels. In this talk, we will review the state of art of the vertical TFTs and explore the major fabrication issues. In addition, we will examine amorphous indium gallium zinc oxide (a-IGZO) vertical channel TFT fabricated at low temperature to evaluate the impact of gate dielectric on electric characteristics of the vertical vis-à-vis planar TFTs. VTFTs employing vertical amorphous a-IGZO channel of 500 nm have been fabricated without additional photolithography process. The various issues related to the improved device performance will be addressed.

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(Invited) Nanoscale III-Vs on Oxides and Metals - a Route Towards Low-Cost, High-Performance Electronic and Photonic Devices on Non-Traditional Substrates
Authors: Kapadia Rehan 
Published: February 2020

Pushing the boundaries of electron devices—from transistors to photovoltaics—demands complete control over device architectures and material systems. However, traditional growth and fabrication techniques often fall short when optimal design calls for non-planar geometries or integration of non-epitaxial material systems. Thus, in the past decade, a variety of techniques for X-on-Y growth/integration have been explored. In particular, nanostructures grown via the vapor-liquid-solid (VLS) technique have been studied heavily, demonstrating excellent device performance with the possibility of integrating single crystalline materials with non-epitaxial substrates. However, the stringent restrictions on growth geometry due to the traditional VLS growth mode limits the devices architectures that may be grown and fabricated. Here, a novel method for substrate-agnostic growth of arbitrary geometry III-V materials will be presented as a route towards high performance optoelectronic devices.
The direct growth of optoelectronic quality III-V semiconductors on non-epitaxial substrates will be discussed. Structures with geometries varying from the micro/nanoscale single crystalline islands to ultra-large grain polycrystalline thin films may be grown via a thin-film vapor-liquid-solid (TF-VLS) technique. By careful control over nucleation position and shape of III-V semiconductors, arbitrarily shaped single-crystalline islands may be grown on non-epitaxial substrates. First, the general method for this growth will be discussed, illustrating how different structures and geometries may be obtained. Next electronic and optoelectronic characterization of the grown materials will be presented, showing that films display excellent optoelectronic characteristics. Finally, devices fabricated from the grown material will be shown, illustrating that high-performance devices may be obtained without utilizing costly lattice matched substrates.
(Invited) Bottom-up Growth of Fully Transparent Indium Tin Oxide Nanowire Layers for Enhanced Light Output for Light Emitting Devices
Authors: O'Dwyer Colm 
Published: February 2020

The development of optically transparent and mechanically flexible electronic circuitry is an essential step in the effort to develop next-generation display technologies which will undoubtedly have to address so-called ‘see-through’ and conformable products. In view of the inherent limitations of silicon-based electronic circuits and the demand for portable display and communication products, the development of high performance transparent devices is the focus of much activity. With the addition of branched and cross-wired structures to assemblies of nanorods and nanowires, the potential for synthesizing materials with interesting electrical, optical, and mechanical properties is even greater. As the most important transparent conducting oxide, tin-doped indium oxide has found a wide range of applications in photovoltaics, smart windows, organic light-emitting diodes, and flat-panel displays.
The ability to realize fully transparent and conductive arrays of indium tin oxide nanowires grown as dedicated, uniform contact layers is demonstrated here to exhibit such dual functionality. The growth method mimics that of standard epitaxial growth regimes for known device architectures, allowing a one-step bottom-up method of both device and epitaxial nanowire layer fabrication. Large area nanowire arrays of various morphologies, self-catalysed and seeded during molecular beam epitaxy (MBE) are shown. We detail this new molecular beam epitaxial growth method; control of the nucleation, crystal growth direction, nanowire shape, density, conductivity and transparency is possible without necessitating neither a heterogeneous metal catalyst nor predefined placement of nanowire seeding. The electronic and photonic properties of branched nanostructured arrays are optimized for application as fully transparent contacts in the visible to near-infra red region for silicon-based light emitting devices (LEDs).

References

C. M. Eliason and M. D. Shawkey, Optics Express, 22 A642 (2014).

C. O’Dwyer, M. Szachowicz, G. Visimberga, V. Lavayen, S. B. Newcomb and C. M. S. Torres, Nat. Nanotech., 4, 239 (2009).

C. O'Dwyer and C. M. S. Torres, Front. Physics, 1, 18 (2013).

M. Osiak, W. Khunsin, E. Armstrong, T. Kennedy, C. M. S. Torres, K. M. Ryan and C. O’Dwyer, Nanotechnology, 24, 065401 (2013).

M. Osiak, E. Armstrong, T. Kennedy, C. M. S. Torres, K. M. Ryan and C. O’Dwyer, ACS Appl. Mater. Interfaces, 5, 8195 (2013).

P. D. C. King, T. D. Veal, J. Phys.
23, 334214 (2011).

J. Q. Xi, M. F. Schubert, J. K. Kim, E. F. Schubert, M. Chen, S. Y. Lin, W. Liu and J. A. Smart, Nature Photonics, 1, 176 (2007).

M.L. Kuo, Y.S. Kim, Mei-Li Hsieh and Shawn-Yu Lin, Nano Lett.
11, 476 (2011).
(Invited) Active Fe-Oxide on Iron Phosphorus Trichalcogenides (FePS3) Nanosheets Surface for Highly Efficient Electrocatalytic Oxygen Evolution
Authors: Song Bo 
Published: February 2020

Active Fe-Oxide on Iron Phosphorus Trichalcogenides (FePS3) Nanosheets Surface for Highly Efficient Electrocatalytic Oxygen Evolution

Ying Yin,1 Jiecai Han,1 and Bo Song2,
*

1Centre for Composite Materials and Structures, Harbin Institute of Technology, Harbin 150080, China

2Academy of Fundamental and Interdisciplinary Sciences, Harbin Institute of Technology, Harbin 150080, China
Efficient and cost-effective oxygen evolution reaction (OER) electrocatalysts is of great importance for sustainable energy conversion technologies. Fe-based electrocatalysts have been intensively investigated because of their promising activity and earth abundance. However, the OER efficiency for most of the developed Fe-based electrocatalysts has been intrinsically limited due to their poor active site exposure yield. Herein, we report active Fe-oxide on FePS3 nanosheets as an efficient OER electrocatalyst for the first time. Benefiting from their atomic-thick structure and optimized electronic structure, the FePS3 nanosheets with Fe-oxide surface realize an improved OER activity compared with bulk FePS3. Our finding suggests that transition MPS3 (M = transition metal) nanosheets could serve as a new group of OER electrocatalysts with excellent property.
*Corresponding Author: songbo@hit.edu.cn
(Invited) Study on the Role of Thermal Stress on Prismatic Slip of Dislocations in 4H-SiC Crystals Grown by PVT Method
Authors: Guo Jianqiu , Yang Yu , Goue Ouloide Yannick , Raghothamachar Balaji , Dudley Michael 
Published: February 2020

Recent advances made towards the improvement of the quality of 4H silicon carbide (4H-SiC) have enabled many successful applications in the power device industry. Nevertheless, there is still a great interest in understanding the formation mechanism of crystal defects such as dislocations as well as their behavior during crystal growth.
While basal plane slip is most frequently observed in 4H-SiC crystals grown by PVT method, prismatic slip of dislocations has also been reported before. [1] The glide of threading edge dislocations (TEDs) on the prismatic planes ({1-100}), for example, leaves long segments of prismatic dislocations in their wake, some of which, if adopting enough screw component, become screw type dislocations. On one hand, these screw dislocations can cross-slip onto the basal planes, generating more BPDs in the substrate crystals. On the other hand, the existence of screw BPDs segments with Burgers vector 1/3[11-20] in the substrate will be harmful for the quality of epilayers since such dislocations, if intersecting with substrate surface, will replicate into the epilayer without conversion to TEDs.
In this study, we have observed three types of straight prismatic dislocation segments in a commercial wafer. These are three different types of dislocations with either screw or mixed characters and are formed by the prismatic slip of different types of TEDs with Burgers vectors and line directions along one of the three 1/3<11-20> directions. The three types of prismatic dislocations are each distributed non-uniformly in the wafer. We believe this non-uniformity is a result of the resolved shear stress distribution caused by the radial temperature gradient in the growing crystal boule, since TEDs only start gliding on the prismatic planes in regions where the critical resolved shear stress is reached. From thermal model simulation, we obtained the distributions of the resolved shear stress for all three types of prismatic dislocations by assuming an appropriate profile for the radial temperature variation. Based on these results, a simulated map can be generated to predict the spatial distributions of prismatic dislocations in the wafer. The map is then compared with X-ray topographic images and correlation is found between the two. It is shown that the prismatic dislocations are mainly distributed on the periphery of the boule and the exact distribution of each type depends highly on the difference in radial temperature profile.
[1] Huanhuan Wang, Shayan Byrappa ,Fangzhen Wu, Balaji Raghothamachar, Michael Dudley, Edward Sanchez, Darren Hansen, Roman Drachev, Stephan G. Mueller, Mark J. Loboda, Materials Science Forum Vols. 717-720 (2012) pp327

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Monocrystalline Ni12P5 Hollow Spheres with Ultrahigh Specific Surface Area As Advanced Electrocatalysts for the Hydrogen Evolution Reaction
Authors: Chang Jinfa , Li Songtao , Li Guoqiang , Liang Liang , Ge Junjie , Liu Changpeng , Xing Wei 
Published: February 2020

Hydrogen is an ideal energy carrier with an energy density of 140 MJ kg-1 and water as its final product, which is considered as an ideal candidate for the replacement of fossil fuels.1 To date, most H2 is produced today through nickel-catalyzed conversion of CH4 to H2 and CO followed by a water gas shift reaction to yield H2 and CO2. However, this approach is based on unsustainable fossil energy and discharges greenhouse gas. Water is an ideal source for H2 production as it is carbon-free, plentiful and almost costless. Water electrolysis, with only H2 and O2 as the final product, is a highly promising route in environmental benign H2 generation.2, 3 Although the ultimate goal is to couple hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) to an integrated efficient device for whole water electrolysis, one of the most crucial issues that must be solved is the development of highly efficient and durable catalysts for water oxidation and reduction.3

In this study, monocrystalline Ni12P5 hollow spheres with ultrahigh specific surface area (222.5 m-2 g-1) were prepared by a water-in-oil microemulsion method (Figure 1). The over potential required for 10, 20 50 and 100 mA cm-2 current densities are 144, 173, 225 and 277 mV in strong acidic solution with a Tafel slope of only 45 mV dec-1, ranking among the most active nonprecious HER catalysts. Moreover, the monocrystalline Ni12P5 hollow spheres catalyst exhibited a highly active and stable performance during a 3,000 cycling tests through cyclic voltammetry and a 12 hour duration chronopotentiometry test. The results indicate the highly promising application potential of the monocrystalline Ni12P5 hollow spheres catalysts in hydrogen generation to replace Pt. These promising features make Ni12P5 hollow spheres ideal candidates for the next generation HER catalysts. These catalysts with novel monocrystalline structure can be extended to electrochemical applications in various fields, such as supercapacitors, fuel cells, batteries and electrochemical sensors, and so on.
Figure 1. The illustration of synthesis procedure for the Ni12P5 hollow spheres and the water electrolysis behavior of the catalysts.

Acknowledgments

This work is supported by the Strategic priority research program of CAS (Grant No. XDA09030104), the Jilin Province Science and Technology Development Program (Grant No. 20130206068GX, 20140203012SF, 20160622037JC) and the Recruitment Program of Foreign Experts (Grant No. WQ20122200077).

References

1. X. Zou and Y. Zhang, Chem. Soc. Rev., 2015, 44, 5148-5180.
2. M. G. Walter, E. L. Warren, J. R. McKone, S. W. Boettcher, E. A. S. Qixi Mi and N. S. Lewis, Chem. Rev., 2010, 110, 6446–6473.
3. S. D. Ebbesen, S. H. Jensen, A. Hauch and M. B. Mogensen, Chem. Rev., 2014, 114, 10697-10734.

Figure 1