bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis of Lanthanum Telluride Thin Films By Electrodeposition from Ionic Liquids
Authors: Snow Yitzhak , Pounds Tyler D. , Farias Stephen L. , Cammarata Robert C. 
Published: February 2020

Thermoelectric devices allow for conversion between electrical and thermal energy and have a great deal of potential as both cooling devices and alternative energy sources. Currently they are limited by their low efficiency, and so are only used in very specialized applications. Some potential materials for use in high temperature thermoelectric devices include rare earth telluride compounds. One such material is bulk lanthanum telluride, La3-xTe4, 0 ≤ x ≤ 1/3, which was found to have a ZT greater than unity at temperatures near 1000 C [1]. Lanthanum is already commonly used in many industrial applications, including as lanthanum hydride in the cathode of nickel metal hydride batteries [2].
Nanostructured materials have been shown to have a higher thermoelectric efficiency relative to bulk materials due to the enhancement of phonon scattering through quantum confinement [3]. This has generated a great deal of interest in low-dimensional and nanostructured thermoelectric devices. Since lanthanum telluride is usually made by ball milling, the creation of complex nanostructures or thin films with traditional methods is difficult.
We have developed a technique to electrochemically deposit lanthanum telluride thin films from an ionic liquid at low temperatures (approximately 70 C). The films were deposited on noble metal substrates from 1-ethyl-3-methylimidazolium bromide ionic liquid based electrolytes containing to 0.05 M to 0.25 M lanthanum nitrate and 0.025M (HTeO2)+. The ratios of lanthanum to tellurium in the deposited films were determined by relative concentrations of the anions and cations in the electrolyte. The technique used for the deposition of these thin films could ultimately be used in the synthesis of nanostructured lanthanum telluride. This electrochemical method promises to be simpler, less expensive, and more efficient than current techniques.
1. A. May, J-P. Fleurial and G. J. Snyder, Phys. Rev. B, 78, 125205 (2008).
2. T. Sakai et al., J. Less-Common Met., 161, 193-202 (1990).
3. L. D. Hicks and M. S. Dresselhaus, Phys. Rev. B, 47, 12727 (1993).
Effect of Br2 Complexation on a Hydrogen-Bromine Flow Battery Performance
Authors: Dowd Regis Paul , Zeets Michael , Nguyen Trung Van 
Published: February 2020

Hydrogen-bromine flow batteries offer a viable solution for storing energy from the electrical grid or directly from renewable energy sources such as wind and solar due to its high roundtrip efficiency and relatively low cost. During charge, a hydrogen-bromine flow battery stores energy in the form of hydrogen (H2) and bromine (Br2). During discharge, hydrobromic acid (HBr) is produced. One of the major issues with the hydrogen-bromine flow battery system is the difficulty of safely storing bromine. Bromine has a high vapor pressure and is both toxic and very corrosive.
Past research has shown that complexing Br2 with organic molecules is an effective way to reduce the amount of free bromine in the solution, thus reducing its vapor pressure and corrosivity. For example, Eustace demonstrated how quarternary ammonium salts could be complexed with bromine in zinc-bromine flow batteries.2 Kosek et al previously studied the complexation of bromine using polyethylene glycol (PEG).3 Kosek et al performed kinetic studies of PEG-1000 in concentration ranges of 1-5M and temperatures of 24-43oC, observing the highest dissociation rates occurred at 3M HBr and room temperature.3 Cho et al demonstrated high performance of a hydrogen-bromine flow battery using high surface area porous carbon electrodes for the bromine reaction.1 Other research conducted by Kosek et al and Masud et al demonstrates high performance and good stability (compared to Pt) when using non-Platinum catalysts at the hydrogen electrode such as rhodium sulfide or ruthenium/iridium at the hydrogen electrode.3,4

In this study, we will use different types of complexing agents at various concentrations to determine the most suitable conditions for reducing the concentration of free bromine while also maintaining high bromine electroactivity. Electrochemical measurement techniques using a rotating disc electrode will be used to acquire the kinetic reaction parameters of interest, including the exchange current density and charge transfer coefficients. The effect of using complexing agents in the HBr/Br2 electrolyte will then be tested in an actual fuel cell to obtain polarization curves. This information is expected to determine the viability of using a complexing agent in an actual hydrogen-bromine fuel cell system in order to reduce the concentration of free Br2 while also enabling high performance.
References:

K.T. Cho, P. Ridgway, A.Z. Weber, S. Haussener, V. Battaglia, and V. Srinivasan, J. Electrochem. Soc., 159, 11 (2012).

D.J. Eustace, J. Electrochem. Soc., 127, 3 (1980).

J.A. Kosek and A.B. LaConti, Investigation of Bromine Complexed Hydrogen/Bromine Regenerative Fuel Cells for Portable Electric Power, General Electric Final Report to U.S. Army Mobility Equipment Research and Development Command, Sept 1984.

J. Masud, T.V. Nguyen, N. Singh, E. McFarland, M. Ikenberry, K. Hohn, C.-J. Pan, and B.-J. Hwang, J. Electrochem. Soc., 162 (4), F455 (2015).
Composite Polymer Electrolyte Containing Core-Shell Structured SiO2(Li+) Particles for Suppressing Lithium Dendrite Growth and Improving High Temperature Cycling Stability of LiNi0.5Mn1.5O4
Authors: Shin Won-Kyung , Park Se-Mi , Kim Dong-Won 
Published: February 2020

The most widely used electrolyte for lithium-ion batteries is lithium hexafluorophosphate (LiPF6) in a mixture of organic carbonate solvents due to its high conductivity, good electrochemical stability and acceptable cycle performance at low temperatures [1]. However, the use of liquid electrolytes in lithium batteries has many drawbacks, such as high flammability of organic solvents, possibility of leakage and poor thermal stability [2, 3]. Among the potential electrolytes for lithium batteries, polymer electrolyte has received considerable attention due to high ionic conductivity and superior thermal safety with no electrolyte leakage [4]. However, polymer hosts lose their mechanical strength when they are plasticized with liquid electrolyte solution, leading to serious problems in terms of cycle life and safety [5]. In this study, in order to obtain polymer electrolytes with enhanced mechanical strength and good electrochemical properties, core-shell structured SiO2 nanoparticles containing poly(lithium acrylate) in the shell were synthesized. They were used as functional fillers in preparing composite polymer electrolytes for suppressing lithium dendrite growth and preventing HF generation in the electrolyte. The composite polymer electrolytes prepared with SiO2(Li+) particles exhibited high ionic conductivity, good thermal stability and favorable interfacial characteristics. The lithium metal polymer cells composed of lithium metal negative electrode and LiNi0.5Mn1.5O4 positive electrode are assembled and their cycling performances are evaluated. The cells assembled with the composite polymer electrolyte exhibited superior cycling performance both at ambient temperatures and at elevated temperature.

References

1. K. Xu, Chem. Rev., 104, 4303 (2004).
2. S.E. Sloop, J.B. Kerr, K. Kinoshita, J. Power Sources, 119-121, 330 (2003).
3. G. Nagasubramanian, K. Fenton, Electrochim. Acta, 101, 3 (2013).
4. M. Yang, J. Hou, Membranes, 2, 367 (2012).
5. E. Quartarone, P. Mustarelli, Chem. Soc. Rev., 40, 2525 (2011).
Engineering Optical Properties of Nanorods Fabricated By Physical Vapor Deposition
Authors: Uddin Md Aman , Pasaogullari Ugur 
Published: February 2020

Nanorod arrays fabricated by physical vapor deposition (PVD) have many technological applications due to its flexibility in changing morphology and structure of the materials. Tailoring the nanorod structures, optical properties of the materials can be manipulated.
There is a dependency of nanorod length as well as surface area in light absorbance of silver nanorod arrays. The long and high surface area nanorod arrays provide more space for light to couple with surface plasma and more propagation space to scatter and attenuate light intensity resulting lower reflectance. Changing the size and the length of the nanorods, surface plasma resonance wavelength (SPRW) can be tuned as shown in figure 1 for aluminum nanorods. With the increase of the nanorod length, absorbance increases and SPRW shifts from 248nm to 255nm. These nanorods are fabricated at a deposition angle of 86.5˚ and operating pressure of 1×10-5Torr. Controlling the operating pressure and the substrate temperature, smaller nanorods can be fabricated and tuned to SPRW. Moreover, engineering the nanostructures, optical properties can be further manipulated. Figure 2 shows zigzag nanowalls of Silicon on diffraction gratings. These nanowalls can be used to confine light at a certain wavelength with well-defined spacing between nanowalls and number of zigzags.

Acknowledgements

The authors gratefully acknowledge financial support from the National Science Foundation (CBET-0748063).

Figure 1
Analysis of a Four H-Bond Array Using Cyclic Voltammetry: Introducing a New Redox Center to Strengthen Dimerization
Authors: Tamashiro Bryan T. , Smith Diane K. 
Published: February 2020

Hydrogen bonding arrays are useful building blocks for supramolecular chemistry due to their strong hydrogen bond interactions that can form dimers. The strength of the H-bond interactions can be perturbed by applying an external stimuli, in this case electron transfer. Recently, our group has modified Meijer’s four H-bond ureidopyrimidinone (UPy) array1 to make it electroactive by adding a dimethylaminophenyl group. The modified structure forms strong H-bond interactions in CH2Cl2, creating a dimer that can undergo a reversible 2e-oxidation, followed by an irreversible oxidation at more positive potentials. The latter results in the break-up of the dimer due to electrostatic repulsion.
For this study, we aim to modify another four H-bond Upy array by introducing a methyl pyridinium redox center as shown below. We hypothesize that this array will prefer the tautomer that presents an ADAD H-bond motif in the starting oxidation state. This motif will form a dimer with relatively weak H-bond interactions due to electrostatic repulsions and also unfavorable secondary H-bond interactions. Upon 2e- reduction, where 1e- is gained for each methyl pyridinium redox center, the H-bond strength should increase due to the loss of repulsive charges and also allows the nitrogen to become a stronger hydrogen acceptor. Since the resulting nitrogen is now a better H-acceptor, there is a possibility of intermolecular proton transfer which will induce the tautomer to have an AADD motif that will further strengthen the H-bonds by favorable secondary H-bond interactions.
1. Beijer, F.H.; Sijbesma, R.P.; Kooijman, H.; Spek, A.L.; Meijer, E.W. J. Am. Chem. Soc., 1998, 120 (27), pp 6761–6769.

Figure 1
Effect of Etchant Composition on Surface Morphology of GaAs during Anisotropic Chemical Etching
Authors: Asoh Hidetaka , Ono Sachiko , Ito Daiki 
Published: February 2020

Micro-/nanostructures formed on semiconductor substrates have been applied in various devices such as electronic devices and biosensors. In particular, III-V semiconductors (e.g., GaAs, GaN, and InP) have received a great attention for realizing future generation optoelectronic devices owing to their excellent optical and electrical properties including high electron mobility and a direct band gap. Recently, we have reported the fabrication of ordered pore arrays, pillar arrays, and nanowire arrays with a high-aspect-ratio in n-type GaAs (111) B substrate by a combination of anodic etching and subsequent chemical etching [1–3]. The controlled GaAs micro-/nanostructures have potential technological and scientific applications in optoelectronics and chemical sensors that require ordered patterns, high device densities, and high surface-to-volume ratios. In this study, we investigated the effects of etchant composition on the orientation-dependent surface morphology of GaAs during anisotropic chemical etching using various types of etchants.
p-type GaAs (111) B was mainly used as a substrate. To control the reactive sites during chemical etching, the photoresist layer with the honeycomb-like openings of 3 μm periodicity was applied as a mask, as described in our previous report [1]. The GaAs substrates coated with a photoresist mask were immersed in various types of etchants consisted of acid (H2SO4, H3PO4, HF) and oxidant (KMnO4
, H2O2) at 20°C. When a mixture of 2 mol dm−3 H2SO4 and 0.05 mol dm−3 KMnO4 was used as an etchant, etch pits having curved bottom and hexagonal aperture were formed (Fig. 1a). The diameter and depth of pits were 1.7 µm and 0.6 µm, respectively. Although pore diameter increased with increasing etching time from 30 s to 150 s, the profile shape of etch pits was not clear (Fig. 1b). However, when KMnO4 concentration increased to 0.2 mol dm−3, anisotropic etching proceeded obviously, resulting in the formation of pit arrays with equilateral-triangular aperture depending on crystal plane of {100} (Fig. 1c). On the other hand, shallow etch pits with hexagonal aperture were formed by chemical etching for 30 s using 0.05 mol dm−3 H2O2 as an oxidant instead of KMnO4 (Fig. 1d). With further chemical etching for 300 s, the diameter of etch pit increased causing lateral etching (Fig. 1e). However, the obtained etch pits were shallower than that of pits formed using KMnO4 of the same concentration despite longtime etching. These results indicate that etching rates for each crystal plane are strongly affected by the type and concentration of oxidants. Correlation between the etchant composition and orientation-dependent surface morphology of GaAs after chemical etching will be discussed in detail.
[1] H. Asoh, S. Kotaka and S. Ono, Electrochem. Commun., 13, 458–461 (2011).
[2] S. Ono, S. Kotaka and H. Asoh, Electrochim. Acta, 110, 393–401 (2013).
[3] H. Asoh, S. Kotaka and S. Ono, Mater. Res. Express,
1 045002 (2014).

Figure 1
Opaque White Anodic Oxide Film Formed on Aluminum
Authors: Kurihara Ayaka , Asoh Hidetaka , Ono Sachiko 
Published: February 2020

Anodic porous alumina film, which is formed by anodizing of aluminum in an appropriate acidic solution, has been studied on the protection or design of aluminum surfaces owing to commercial applications. The appearance and surface quality of aluminum products (e.g., architectural materials, electronic devices) are key points as with surface properties such as a corrosion resistance, hardness and wear resistance. Although dyeing, painting and electrolytic coloring are well known as industrial methods to provide color variation for aluminum surface, integral coloring, which produces color by anodizing step itself without use any pigment or metallic salt, is also applied in terms of the simplicity and production cost. In our previous work, it was reported that alumina films with irregular porous structure formed in Ematal bath or chromic acid showed opaque white appearance [1, 2]. Irregular porous structure in the direction of pore depth, which contained branching, curving and distortion of pores in anodic alumina, produced the roughening of the metal-oxide interface and made the appearance of the film more opaque [1, 2]. However, Ematal bath containing expensive potassium titanium oxalate deteriorates easily. In terms of reduction of environmental burdens, it is required to avoid using harmful chemical compound such as chromic acid. Under such background, we studied a low-cost alternative anodizing method to form opaque white oxide film. In addition, we also investigated in detail the relation between the appearance and porous structure of oxide film.
Anodizing was conducted using high purity (99.99 %) aluminum sheets in various electrolytes (phosphoric acid, sulfuric acid, critic acid, and Ematal bath). Whiteness of the obtained samples was evaluated by spectrophotometry (KONICA MINOLTA, CM-5) based on standard of American Society for Testing Materials (ASTM E313-73).
When anodizing was carried out in phosphoric acid at 60 °C at a constant current density of 200 Am−2, anodized specimen indicated whiteness value of 39. Surface appearance was gray in color. The aluminum specimen anodized in Ematal bath showed whitish appearance compared with that treated in phosphoric acid. Whiteness value of aluminum specimens anodized in Ematal bath increased from 35 to 47 with increasing final arrival voltage from 150 V to 350 V during constant current anodizing. On the other hand, whiteness value increased effectively using two-step anodizing; long first anodizing and short second anodizing were conducted in phosphoric acid and subsequently Ematal bath. Under optimized conditions, whiteness value increased to 58. The more increase of the thickness of total oxide film and barrier layer and the degree of branching, the more white appearance indicated. Thus, it is confirmed that the appearance of anodized specimen was strongly affected by these factors.
[1] S. Ono, S. Chiaki, T. Sato; J. Met.
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Soc. Jpn., 26, (10), 456-460 (1975).
[2] S. Ono, T. Sato; J. Met.
Finish. Soc. Jpn., 31, (3), 134-139 (1980).
Influence of Focused Electron Beam on Electrical Characterization of Advanced Mosfets
Authors: Kang Jonghyuk , Lee Sungho , Choi Byoungdeog 
Published: February 2020

The focused electron beam based inspection instruments such as Scanning Electron Microscope (SEM) have become widespread in the semiconductor manufacturing and failure analysis of scaled devices. Also, nano-probing systems with SEM guidance have become important in the failure analysis area to evaluate the localized device in the actual LSI [1]. However, electron beam leads to device degradation [2] and its damage are increasing with the scaling. As CMOS scaling is going to be sub-10nm regime [3], electron beam damages are becoming critical issue in performing electrical characterization at the contact level in integrated devices using nano-probe technique. To avoid the electron damage, the acceleration voltage should be lower. However, the lower acceleration voltage of electron beam leads to lower resolution of image created by SEM guidance.
In this work, we evaluated NMOS FinFET in SRAM cells manufactured in a 10nm CMOS process with Atomic Force Microscopy (AFM) based nano-probing system. AFM based nano-probing system has no electron beam damage because it uses topography image created by AFM instead of SEM for guidance at contact level [4]. After deprocessing the samples to the contact level, we irradiated electron beams to samples to investigate a dependency of the device characteristics on electron beam acceleration voltage. Compared to a non-exposed reference transistor, the exposure of electron beam on the target transistor lead to significant changes on device characteristics such as saturation current (IDS), sub-threshold voltage (VTH) and sub-threshold swing (S). This might be due to trapped charges in the gate oxide and interface state [5]. Our studies show that it is critical to avoid electron beam exposure before electrical device characterizations are carried out at the contact level using nano-probe system since electron beam induced device parameter changes are not negligible in the failure analysis of sub-10nm devices.
References
[1] S. Ikeda, Y. Yoshida, K. Ishibashi, Y. Mitsui, Electron Devices, IEEE Transactions on, 50 (2003) 1270-1276.
[2] K. Nakamae, H. Fujioka, K. Ura, Journal of Applied Physics, 52 (1981) 1306-1308.
[3] K. Okano, T. Izumida, H. Kawasaki, A. Kaneko, A. Yagishita, T. Kanemura, M. Kondo, S. Ito, N. Aoki, K. Miyano, Electron Devices Meeting, 2005. IEDM Technical Digest. IEEE International, IEEE2005, pp. 721-724.
[4] R. Mulder, S. Subramanian, T. Chrastecky, INTERNATIONAL SYMPOSIUM FOR TESTING AND FAILURE ANALYSIS, ASM International; 2006, pp. 503.
[5] S. Shabde, A. Bhattacharyya, R.S. Kao, R.S. Muller, Solid-state electronics, 31 (1988) 1603-1610.
Analysis of Shunt Currents and Associated Corrosion of Bipolar Plates in PEM Fuel Cells
Authors: Lvovich Vadim , Bennett William , Hoberecht Mark 
Published: February 2020

Proton exchange membrane (PEM) fuel cells are being developed for future NASA missions. These fuel cells use a bipolar construction, with internal manifolds to conduct product water and coolant water. The wetted surfaces of the manifolds present large voltage gradients across the product water and coolant water passages, which can induce water electrolysis in the manifolds of full-scale stacks. As such, shunt currents lead to parasitic power losses and corrosion of the fuel cell metal surfaces; therefore, it is important to understand and characterize the effects of shunt currents. The circuit analog models provide an approximation of the shunt currents, limited by the estimation of the charge transfer resistance. As such, the methods should be used cautiously.
Shunt currents are influenced by cell voltage, cell number, manifold ohmic resistance, product water/coolant purity, and the charge transfer resistance of bipolar plate surfaces to electrolysis. In this work, electrochemical characterizations were performed to estimate these characteristics under relevant operating conditions. A numerical solution of the shunt currents is presented, and the distribution of corrosion and hydrogen evolution are described. The same calculations would apply to PEM electrolyzers used for hydrogen and oxygen production. With some adjustment, similar calculations may also be applied to other electrochemical system with common electrolyte channels, such as flow-batteries and other devices where an electrolyte manifold experiences voltage gradients.