bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of Proton Irradiation on DC Performance and Reliability of Circular-Shaped AlGaN/GaN High Electron Mobility Transistors
Authors: Xi Y. Y. , Hwang Ya-Hsi , Hsieh Yueh-Ling , Li Shun , Ren Fan , Pearton Stephen J. , Patrick Erin , Law Mark E , Yang Gwangseok , Kim Hong-Yeol , Kim Jihyun , Baca Albert G. , Allerman Andrew A. , Sanchez Carlos 
Published: February 2020

AlGaN/GaN High Electron Mobility Transistors (HEMTs) show great promise for applications such as military radar and satellite-based communications systems. Circular devices, with smaller junction areas and higher effective gate width/gate length, are better suited for high power, high frequency application. Since the circular devices have been shown to improve the device performance, the effect of radiation on their reliability is an important topic. There are many studies characterizing the performance under proton, neutron, and electron irradiations for rectangular AlGaN/GaN HEMTs. However, the studies for circular-shaped devices are limited. In this work, we report the effect of proton irradiation on circular-based AlGaN/GaN HEMT. DC performance, breakdown voltage, and gate lag measurement were done to characterize the devices.
AlGaN/GaN HEMT heterostructures were grown on c-plane sapphire by molecular beam epitaxy (MBE). The layer structure included a thin AlGaN nucleation layer followed with a 2 µm thick undoped GaN buffer topped by a 25 nm thick unintentionally doped Al0.28GaN layer. Mesa isolation was achieved by using an inductively coupled plasma system with Ar/Cl2-based discharges. The Ohmic contacts were formed by lifting-off e-beam evaporated Ti (200 Å)/Al (1000 Å)/Ni (400 Å)/Au (800 Å). Gates with the dimension of 1.5 µm × 314 µm were defined by lift-off of e-beam deposited Ni/Au metallization. The contacts were annealed at 850°C for 45 s under a flowing N2 ambient in Heatpulse 610T system. The final step was deposition of e-beam evaporated Ti/Au (300 Å/1200 Å) interconnection contacts. Devices were exposed to protons with 5 MeV and different doses of 2×1014 proton/cm2. The device DC performance was characterized using an HP 4156 parameter analyzer. The breakdown voltage was conducted with a Tektronix 370A curve tracer. FLOODS TCAD finite-element solver was used to simulate the electrical field around the gate edge to confirm the experimental result.
As shown in Figure 1, drain current IVs, IDSS, decreased from 454 to 398 mA/mm after irradiation with a proton dose of 2×1014 cm-2. Moreover, resistance between source and drain increased and extrinsic transconductance decreased after irradiation. However, the drain breakdown voltage increased from 150 to 230 V. The improvement of the breakdown voltage was due to the reduction of electric field at the edge of the gate, caused by the defects generated by proton irradiation at AlGaN/GaN interface, which was confirmed with simulation, as shown in Figure 2.
Both gate and drain pulse measurements were also performed to verify the introductions of implanted defects into the HMET structure, which will be discussed in the talk.
Impact of Annealing on Contact Formation and Stability of IGZO TFTs
Authors: Mudgal Tarun , Walsh Nathaniel , Manley Robert G. , Hirschman Karl D 
Published: February 2020

Oxide semiconductors are candidate materials to replace amorphous silicon in thin-film transistors (TFTs) for LCD and OLED backplanes where the demand on performance is increasing. Indium-Gallium-Zinc-Oxide (IGZO) has shown promise because it exhibits high electron mobility and can utilize the existing fabrication infrastructure for flat-panel display manufacturing. However the acceptance of IGZO requires exceptional uniformity and stability in device performance. The necessity to anneal sputtered IGZO for improved device operation has been widely established; however the temperature, gas ambient, and process integration details vary.
In this work, bottom-gate top-contact TFTs are fabricated using sputtered IGZO. Molybdenum and aluminum were investigated as contact metals which defined the working source/drain electrodes. Annealing processes applied either before or after metal deposition were investigated. Annealing was done at 400 °C in various gas ambients including air, oxygen, nitrogen, forming gas (5% H2 in N2) and vacuum. Channel passivation materials including SiO2 and Al2O3 were also investigated. The annealing ambient and arrangement of process steps were found to have a significant influence on the contact behavior and the uniformity and stability of electrical characteristics. These details have a significant impact on circuit operation, which will be discussed along with results of test circuits including inverters and ring oscillators.
Effect of Waveforms of Applied Voltage on CO2 Reforming of CH4 in an Atmospheric Plasma Reaction
Authors: Nguyen Duc Ba , Lee Won Gyu 
Published: February 2020

CO2 reforming of CH4 to syngas has been the subject of great interest because two greenhouse gases are consumed and several valuable products can be produced. The products, such as ammonia, methanol, acetic acid, dimethyl ether, synthetic gasoline, and so on, can be used as the basic materials for other chemical reactions. Recently and traditionally, a catalytic method, a plasma method and a combined catalytic and plasma method have been employed for the reaction of CO2 reforming of CH4.
Reaction with a catalyst is still considered an attractive method. However, the high temperature operation required for this method increases its cost. Also, the continuous formation and deposition of carbon black on the catalyst surface leads to the deactivation of the catalyst, which is the main disadvantage of this method. As an effective approach, a plasma method was suggested as a dry method of reforming methane without the concern about the formation of carbon black. Several plasma systems have been employed for CO2 reforming of CH4, such as thermal plasma, corona discharge, arc discharge and dielectric barrier discharge (DBD). Among the plasma systems, reaction by DBD has produced a relatively low degree of conversion of feed gases and selectivity of products. Therefore, many research groups have researched ways to improve the efficiency of reaction by DBD. Several research groups presented that CO2-CH4 reforming could be improved by a pulse type power supply. It was reported that the reaction by a DBD reactor was enhanced using a pulsed plasma, while the pulse width was not effective to enhance the conversion of reactants.
In this study, CO2 reforming of CH4 to syngas was performed by an atmospheric dielectric barrier discharge reactor immersed in an electrically insulating oil bath. For comparison of the effects of applied voltage waveforms on the reaction, two kinds of waveforms, namely, sinusoidal and pulse, were supplied to the plasma reactor for CO2 reforming of CH4. Several parameters such as reaction time and applied voltage were evaluated for the conversion of reactants, the selectivity of products, and energy efficiency for both waveforms of applied voltage.
Photoelectrochemical Analysis of Nanostructured Titanium Oxide Conjugated to Organic Molecules for Hydrogen Evolution
Authors: Giraldo Manuel Louis , Shepard Cathrine , Sakthivel Tamil Selvan , Saraf Shashank , Gupta Ankur , Leuenberger Michael , Seal Sudipta 
Published: February 2020

Photocatalytic water splitting using TiO2 for hydrogen applications has been limited by its inability to absorb wavelengths within the visible light range. TiO2 covalently linked with folic acid (FA) by the linker molecule 3-aminopropyl)-diethoxy-methylsilane (APTMS) has shown to exhibit photoluminescence under visible light [1]. In this study, functionalized TiO2 was used as a photocatalyst for water oxidation which was measured using a photoelectrode setup. In order to measure the photoelectric current generated by the catalyst chronoamperometry techniques were employed. In addition, the Butler-Volmer equation was used to model the relationship between the quasi-fermi energy of electron photocarriers, current density, and the ultimately the hydrogen evolution rate.
Experimentation focused on comparing the volume of hydrogen evolution induced by three different photocatalysts: commercially available TiO2 (P25), sol-gel prepared TiO2, and functionalized sol-gel prepared TiO2. P25 was used for a comparison with TiO2 and TiO2 functionalized layers. The photochemical cell configuration allowed for the efficient reduction of electron-hole pair recombination and separated hydrogen and oxygen evolution.
Platinum was placed in the acid solution as a cathode (counter electrode) and the nanostructured coatings on stainless steel were placed in the basic solution as an anode (working electrode). The two cells were separated by a nafion 211 cation exchange membrane film and a xenon lamp was directed at the anode through a quartz window in the plexiglass cell. The anode was connected to the cathode using a stainless steel wire which allowed various external bias voltages to be applied to the system. The voltages applied to the system were critical in calculating the hydrogen evolution rates.

Figure 1: Chronoamperometric comparison of P25, TiO2 , TiO2-APTMS-FA at .55 V

1. Turkowski, V., et al., Linker-Induced Anomalous Emission of Organic-Molecule Conjugated Metal-Oxide Nanoparticles. ACS Nano, 2012. 6(6): p. 4854-4863.
Effect of H-Bonding on the Electrochemistry of a p-Phenylenediamine-Based Urea. Competition Between Another Urea and a Cyclic Diamide Guest
Authors: Pham An T. , Clare Laurie A. , Woods Jessica E. , Smith Diane K. 
Published: February 2020

In previous work done by our group, we reported the observation of strong oxidation-based redox dependent hydrogen bonding between an electroactive urea 1-phenyl-3-(p-N,N-dimethylaminophenyl)urea U(H)H and a cyclic diamide 1,4-dimethylpiperizine-2,3-dione (PZD) in methylene chloride.1Large negative shifts in the apparent, reversible one electron oxidation of U(H)H are observed upon addition of PZD, consistent with strong H-bonding of PZD to the radical cation of U(H)H.
However, with further study of U(H)H and similar molecules, it is clear that the electrochemistry and the mechanism is not as straightforward as once believed. Instead of undergoing a simple one electron oxidation, a variety of data now suggests that U(H)H actually undergoes a two electron oxidation to the quinoidal form with transfer of a proton to another U(H)H, which deactivates the second U(H)H. Thus the overall process corresponds to one electron per urea. Because acetonitrile is more polar than methylene chloride, it can better solvate the quinoidal urea and the protonated, unoxidized urea to prevent them from hydrogen bonding to each other. In contrast, stronger H-bonding between the quinoidal urea and the protonated, unoxidized urea is expected in the less polar solvent, methylene chloride and we believe this is what facilitates the observed reversible electrochemistry.
In the current study we are re-investigating the addition of PZD to U(H)H in light of our better understanding of the electrochemistry of U(H)H by itself. According to our new NMR titration data, PZD is H-bonded to U(H)H even without oxidation, which is consistent with our previous study. The binding constants, K, measured in different electrolyte solutions between PZD and U(H)H show that there is an electrolyte effect. In the NMR titration experiment without electrolyte, due to the solvent effect, PZD is more strongly H-bonded to U(H)H in the less polar solvent CH2Cl2 than in CH3CN (K in CH2Cl2 = 60.4 M−
1and K in CH3CN = 17.8 M−
1). With a large anion electrolyte, NBu4B(C6F5)4 in CH2Cl2 , the binding constant is greater (K = 95.9 M−
1) than with a small anion electrolyte, NBu4PF6 in CH2Cl2 (K = 48.6 M−
1). This is consistent with the larger potential shift observed with the addition of PZD in NBu4B(C6F5)4 in CH2Cl2 solution relative to NBu4PF6 in CH2Cl2. This suggests that the smaller PF6−ion may be competing with PZD for the binding site.
Re-examination of the cyclic voltammetry of U(H)H suggests the same overall reaction, 2e− oxidation of half the urea with proton transfer to the other half, is occurring with or without PZD present. However, the peak potentials are affected by the presence of PZD indicating the overall reaction is facilitated by PZD.
1. Jessica E. Woods, Yu Ge, and Diane K. Smith, Journal of the American Chemical Society
2008
130 (31), 10070-10071.
Formation and Mathematical Modeling of Electrical Field Distribution within TiO2 Nanotube Arrays
Authors: Zhao Ying , Hoivik Nils , Wang Kaiying 
Published: February 2020

Self-ordered TiO2 nanotubes fabricated by electrochemical anodization have received considerable attention due to its unique nanostructure as well as potential applications. The nanotubes can be implemented on solar cells and gas sensors owing to its photoelectrical properties, and on water splitting/ hydrogen production and CO2 conversion from photocatalytic point of view.
However, the formation mechanism of the hexagonal nanotubes is still being developed and none has been worked out a really quantitative form that would correctly yield numerical figures. According to a number of previous theoretical models, the formation of the pores is resulted from the competition of the oxidation (TiO2 membrane growth process: TiO2+6F-+4H+→TiF6
2-+2H2O) and dissolution (hollow nanotube formation process: Ti+2H2O/2OH-→TiO2+4H+/2H++4e). In order to get better understanding on these two simultaneous processes, the evolution of electrical field distributes on the working electrode are crucial factors for nanotube initialization and formation.
In this paper, self-ordered TiO2 nanotube arrays were fabricated by electrochemical anodization. A high-purity titanium foil (Purity of 99.7%, size of 20 mm × 10 mm × 0.5 mm) were used as anode after surface degreasing by acetone and ultra-sonication, and surface washing and drying with de-ionized water and nitrogen. The experimental set-up is shown in fig 1a. The anodic oxidation process was conducted at 50V for 4 hours in electrolytes with composition of NH4F (0.5 wt%)/ glycol/ H2O (3.0 vol%). A platinum wire (Purity 99.9%, diameter ~ 0.25mm and length ~ 20 mm) was used as cathode in this process. A representative SEM (Scanning Electron Microscope) image of TiO2 nanotube structure is shown Fig.1b. We further implemented this experimental data into COMSOL simulation to verify the effects of nano-sized structures on electrical field distribution. The mathematical simulations were carried out with identical spacious geometry at micro and nano size level respectively. Fig. 2a shows the mathematical modeling of electrical distribution on assumed microtubes with diameter of 3 µm, length of 4 µm and gaps between tubes of 2 µm; Fig. 2b displays the simulated electrical distribution, which are fitted into the experimental data: 100nm in diameters (approximately) and 1µm in length, 50nm in gaps. Comparing the two mathematical simulations, it is concluded that the size of the structure plays a significant role on both the amplitude and the direction of the surface electrical field distribution.
In summary, formations of TiO2 nanottubes have been studied by electrochemical anodization. Mathematical simulations have been performed at micro and nano scale for simulating possible electrical distribution on the TiO2 tubes. The parameters of boundary condition are closely related to electrical distribution and can be distorted due to the dimensional effect between two neighboring structures.
Combined Dot Sensors in the Domain of Food, Pharmaceutical and Biological Areas
Authors: VAN Staden Jacobus Frederick , Stefan-van Staden Raluca Ioana 
Published: February 2020

Combined dot sensors are new tools in sensors' technology. Different scenarios regarding the innovation, development, design, behaviour, implementation and application of dot sensors will be outlined. They were designed for food, pharmaceutical or biological analysis. Food additives such as colorants and ascorbic acid were determined directly from food and beverages, sildenafil citrate in pharmaceutical formulations and dopamine from pharmaceutical and biological samples. The working dot sensors were based on diamond or carbon paste modified with different porphyrin base or metal-porphyrin complexes. Different electrochemical techniques such as, differential pulse voltammetry (DPV) were used for the assay of the samples. The lower limits of detection obtained allowed the assay of these analytes at levels that do not need preconcentration of the samples.
Acknowledgements
The present work was supported by the Romanian National Programme
PN II, Ideas, Contract Nr. 100/27.10.2011.
Enantioanalysis of S-Ketoprofen Using Potentiometric and SPR Sensors
Authors: Stefan-van Staden Raluca Ioana , VAN Staden Jacobus Frederick , Bokretsion Rahel Girmai , Aboul-Enein Hassan Y. 
Published: February 2020

Ten enantioselective, potentiometric and SPR sensors based on carbon paste and gold impregnated with alpha-, betta-, carboxymethyl-betta-(as sodium salt), 2-hydroxyl-3-trimethylammoniopropyl -betta-(as chloride salt) and gamma-cyclodextrins, were proposed as a chiral selectors for assay of S-ketoprofen raw materials and in its pharmaceutical formulation Ketoflam capsule. The best response was obtained when betta-cyclodextrin was used for the electrode design. The sensors showed very low detection limits (of 10-8 to 10-9 magnitude orders). Stability constants values were also recorded for the interaction between S-ketoprofen and chiral selectors using SPR method.
Acknowledgements This work was supported by UEFISCDI PNII Program Ideas 2011-2014, Contract nr. 123/05.10.2011 and by ERC-like-3/07.2012 program.
Simulation and Experimental Investigation of a SAW Sensor Containing a Microcavity Array in the Delay Path
Authors: Sankaranarayanan Subramanian , Bhethanabotla Venkat , Richardson Mandek 
Published: February 2020

Summary
An integrated experimental and theoretical study was carried out to modify the delay path of a SAW device to include an array of cavities having square cross-sectional areas (microcavities). Our results show significant reduction in insertion loss and improved sensitivity to viscous loading. Trends dependent on the device geometry were elucidated through finite element modeling. It is found that devices having microcavities optimized for a particular substrate and wave mode improve sensor characteristics. Using results from the simulations as a basis, we fabricated devices on ST-X Quartz that support shear-horizontally polarized waves. A standard SAW delay-line and a SAW device containing microcavities were compared by measuring insertion loss and determining the sensitivity to changing glycerol concentrations. Our experimental results agree well with simulations and introduce delay path modification in the form of microcavities as an effective way to improve SAW sensing performance.
Motivation
Surface Acoustic Wave (SAW) devices can be used as direct, label free biosensors that monitor the interaction between a receptor and its target in real time through changes in the properties of the traveling wave (i.e., frequency, phase, and amplitude)1 . An ideal biosensor will be selective to the species of interest, robust, have high sensitivity and consume a small amount of power. It is common when dealing with SAW sensors to have high insertion losses. Several approaches have been utilized which includes the incorporation of reflective gratings, grooves and corrugated surfaces, and the application of a waveguide material to remedy this problem. Decreasing the amount of power consumed will limit the amount of heat generated that can adversely affect protein activity and increasing sensitivity will allow the detection of antigens at clinically relevant concentrations.
Results
In this study, we compare finite-element simulations and experiments on SAW devices whose delay path has been modified to include an array of microcavities. Two different substrates commonly used in biosensors were studied, ST-Quartz and 36° YX -LiTaO3. From simulations, we find that microcavities optimized for a particular substrate and wave mode scatter the incident wave causing constructive interference while acting as a waveguide limiting its penetration into the bulk. This results in a decrease in insertion loss as well as a shift in the center frequency, attenuation of higher frequency modes, and increased out of band rejection. The insertion loss of fabricated devices was measured using an Agilent 8753 ES network analyzer. A decrease in insertion loss and a positive shift in center frequency shown experimentally are in agreement with simulated results.
Nanotechnology Based Cell-All Phone-Sensors for Extended Network Chemical Sensing
Authors: Li Jing 
Published: February 2020

Today’s chemical sensing networks work effectively to cover limited and specific physical area and environments with significant cost and overhead. In order to greatly expand coverage and realize greater WMD protection for the nation, a revolutionary breakthrough that provides for a much larger and lower cost sensing distributed network is required. In order to practice this idea, US department of homeland security, HSARPA program made a call for Cell-All Ubiquitous Biological and Chemical Sensing.
NASA Ames Research Center responded to the call and won the proposal award. The work presented here is a first ever complete intelligent network chemical sensing system with 1) a compact, low-cost, low-power, high-speed nanosensor array-based detector integrated with 2) a smartphone for detection of chemical threats and transmit the sensor data via cellphone communication system to 3) a network cloud for centralizing the chemical sensing information from multiple phone-sensors from various locations.
At NASAARC, we have developed miniaturized sensing modules that can connect with an iPhone for chemical detection using carbon nanotubes (CNT) based nanostructure materials. Our devices possess high sensitivity (ppmv - ppbv), fast response (in sec), high selectivity, low power (5mW without sampling fan and 27mW with sampling fan), and very small size like a postage stamp, and they have been demonstrated for integration with an iPhone for chemical sensing of ppm concentration level of carbon monoxide, and ammonia in Windex and chlorine gas in Bleach.
The prototype-sensing module can be easily connected with an iPhone. Software has been developed to control the sensor chip for chemical detection; to collect and process sensor data, to display the chemical identification and associated concentration, and the sensor response in real time on the iPhone screen, and to transmit sensor data via 3G and/or Wi-Fi to a central location – an Internet server, to build a wider range of sensing network.
An effective cell phone-based chemical detection network will take advantage of both the standalone computing capability of modern cellular phones and the ability to aggregate sensor data over the cellular network for distributed processing or to a centralized processing location. This chemical detection network expands the coverage and realizes greater protection for the nation from hazardous chemical attack.
Note: This work is funded by DHS HSARPA Cell_All Program.