bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of Mirco-Machine Moving with Glucose and Hydrogen Peroxide
Authors: Yamazaki Keitaro , Kaneko Shingo , Tanabe Toyokazu , Gunji Takao , Matsumoto Futoshi
Published: February 2020

We are developing the micro-machine moving by converting chemical energy to mechanical energy to apply the micro-machine to drug delivery system. Our micro-machines were fabricated with two steps. In the first step, Au metal was electrochemically deposited on a Ag wire, following by the chemical dissolution of the Ag wire in strong acidic solution. In second step, inner walls of the cylinder of Au metal obtained with the dissolution process were used for fixing the glucose oxidase and catalase, that work in pair to convert chemical energy of glucose to mechanical energy of O2 gas formation, by adsorbing them with layer-by-layer method using polymer material (Fig. 1). The O2 gas formation becomes driving force of the micro-machine. We made two type of micro-machine with metal and polymer cylinders (Fig. 2). The time courses of metal cylinder type of micro-machine were monitored for 1 min (Fig. 3). When the enzyme of catalase was fixed on the inner wall of the metal cylinder, the micro-machines moved actively by the formation of O2 bubbles with oxidation of H2O2 on catalase. In the solution in the absence of H2O2, the micro-machine did not move except for slight movement due to natural convection of the solution. In order to remove the bubbles of O2 from the inner wall of the metal cylinder and to increase the moving rate of the micro-machine, a surfactant of TritonX-100 was added to the test solution where the micro-machines are moving. In addition, the micro-machine moved to the source of H2O2 (Fig. 4(a)), that is the micro-machine go up the gradient of H2O2 concentration. In the photographs of Fig.4, the injection points of H2O2 were located in the left side of the photographs. On the other hand, the micro-machine which was not modified with catalase did not move(b). Therefore, the moving direction of the micro-machines that we designed can be controlled by the gradient of chemical materials that produce the O2 bubbles by converting chemical energy to mechanical energy.

Figure 1
The Role of Pre Hydrogen Flow in Nucleation of Graphene on Silicon Nitride
Authors: Park Segeun , Kang Doyeon , Roh Yonghan
Published: February 2020

Graphene has been considered as one of most attractive materials in nano-scaled electronic devices. Graphene film has been mainly grown on many metal (eg., Ni , Cu, Fe) by chemical vapor deposition (CVD) process and transferred on dielectric substrate. However, the complicated transfer techniques for metal-catalyzed graphene inevitably have resulted in wrinkles, holes, and metal etching residues. Thus, there is a substantial need to develop a scalable method for reliable production of large-area graphene directly on insulating substrates.

 We synthesized the nucleation of graphene on silicon nitride (Si3N4) substrate and report the influence of pre hydrogen flow during CVD process on silicon nitride which is the stable dielectric and suitable for carbon diffusion barrier. Test wafer was cleaned in 10:1 HF solution and nucleation of graphene was synthesized by CVD process using CH4, Ar, H2gas at 1000°C.

 We evaluated the graphene nucleation with and without pre hydrogen flow on silicon nitride film as shown in Fig.1. Although amorphous carbon cluster was formed on silicon nitride without pre hydrogen flow as shown in Fig. 2(a), Raman shift peak related graphene was obtained with pre hydrogen flow condition as shown in Fig. 2(b). It is assumed that hydrogen ions are bonded with silicon atom on silicon nitride surface during pre hydrogen process and then chemisorptions of carbon precursors on the H-terminated surface are easily made. Fig.3 shows the role of hydrogen [1]. To synthesize the graphene film on silicon nitride, it is essential to be terminated with hydrogen at silicon nitride surface.

Reference

[1] Jae-Hyun Lee et al, “Wafer-Scale Growth of Single-Crystal Monolayer Graphene on Reusable Hydrogen-Terminated Germanium”, Science, Vol. 344, 2014

Figure 1
Focused Ion Beam Milling Technique for Plan-View TEM Sampling of DRAM Capacitor
Authors: Lee Sungho , Kang Jonghyuk , Yang Cheol-Woong
Published: February 2020

As the semiconductor device feature size becomes smaller, the aspect ratio of DRAM capacitor gets higher. The higher the height of capacitor, the more storage node bent. Therefore, we adopt the Mechanically Enhanced Storage node for virtually unlimited Height (MESH) [1] process to prevent storage node’s bending nowadays. Nevertheless, the bending failure still exists, and thus we need to make a sample for physical failure analysis (PFA). Normally PFA needs a site specific transmission electron microscopy (TEM) sample which is vertically cross-sectioned by using focused ion beam (FIB) , but sometimes a plan-view TEM sample is also required to clarify the exact cause of failure.

 Figure 1-(a) shows the vertical TEM result of two bits failure caused by DRAM storage node’s bending. In the conventional plan-view TEM sampling process, the target height for plan-view TEM sampling is marked with ‘l’ shape marker [2] after realizing the height of node bridge as shown in figure 1-(b). It is important to know the end point during FIB milling [3]. And then, the top (red area) and bottom (yellow area) parts are removed to get the plan-view TEM sample. Figure 1-(c) is a TEM image after this plan-view TEM sampling process. The nodes do not stand in a line as you see in figure 1-(c). The nodes seem to move during the 3rd step milling (mill a bottom part) because of the void between nodes. The node may fall off a TEM thin foil sample in the worst case. In order to overcome this problem, we add a carbon deposition step right after the 2nd step of the top part milling as shown in figure 2-(a). As a result, we are able to get a plan-view TEM image where the nodes stand in a line as shown in figure 2-(b). Four major steps are,

Step 1 : ‘1’ shape marking at the target height

Step 2 : milling a top part of capacitor

Step 3 : carbon deposition to fill the space between nodes

Step 4 : milling a bottom part of capacitor

 We adopted this modified milling method to the TEM sampling of a real failure case and obtained a PFA result of a 2 bit failure using plan-view TEM image as shown in figure 2-(c). The new modified milling method turned out to be very effective and can be adopted in a mass production.

References

[1] D. Kim, J. Kim, M. Huh, Y. Hwang, J. Park, D. Han, D. Kim, M. Cho, B. Lee and H. Hwang, in Electron Devices Meeting, 2004. IEDM Technical Digest. IEEE International, p. 69 (2004).

[2] Moon-Yee Wang, S.X. Lee, S. Peri, “The Effect of FIB Technology on Design Methodology”, Circuits and Systems, 1993, 725-728 vol1.

[3] S. Lee, C.-W. Yang, T. J. Park, J. K. Kim, J. H. Ahn, J. Choi and G. Y. Song, in Meeting Abstracts, p. 1608 (2014).

Figure 1
Reaction Energies for Electrode Surface Atom Insertion into R-H Bonds and Their Dependence on Electrode Potential: Application to Pt(111)
Authors: Zhao Meng , Anderson Alfred B.
Published: February 2020

Electrochemistry is not ordinarily expected to be a tool for measuring bond strengths.  Our work shows how to determine R─H bond strengths from reversible potentials, U
rev, for outer sphere and surface oxidation reactions:

R-Haq ⇌ Raq + H+
aq + e-    (1)

and

R-Hads ⇌ Rads + H+
aq + e-  (2)

The electrode considered for this work is the close-packed Pt(111) surface.

The R─H oxidation reactions addressed are those that occur during ethanol oxidation at the anode in a fuel cell.  The reversible potentials for the reactions taking place on the electrode surface are significant to understanding the mechanism of the 12 electron oxidation reactions and the limitations of platinum as an electrocatalyst. They were determined previously for reaction (2). However, there is another mechanism for an R─H bond oxidation, and that is dissociation of the bond on the surface by metal atom insertion or by H atom abstraction prior to aqueous proton formation. Our work addresses the insertion mechanism.

We show that R─H bond strengths in R─Haq and R─Hads are functions of reversible potentials for their oxidations. We find that underpotential deposited (UPD) hydrogen on Pt(111) electrodes makes the R─Hads bond strengths zero for reactions that have reversible potentials in the range from 0.0 V (vs. SHE) to 0.35 V (vs. SHE). For R─Hads reactions with reversible potentials in the double layer region (U
rev > 0.35 V), the dissociation bond strengths are greater than zero and increase linearly with increasing reversible potentials. When the reversible potentials of R─Hads oxidation are above the double layer potential region (U
rev > 0.6 V), Oads and OHads form which block R-Hads dissociation. The R-Hads dissociation is also blocked in the potential region of H2 evolution(U
rev < 0.0 V).
Fabrication of Ag-Deposited Silicon Nanoparticles for a Lithium Ion Battery Anode Prepared By Alkaline Immersion Plating
Authors: Sugawara Yu , Arai Susumu
Published: February 2020

INTRODUCTION

Lithium ion batteries (LIBs) with greater       energy density are required for use in energy-demanding applications such as electric cars and electronic devices. Silicon is an attractive candidate anode material for use in LIBs due to its high theoretical capacity (4200 mAh/g) compared to carbon (372 mAh/g) currently used in commercially available lithium ion batteries.

The commercial use of Si-based powders in anodes remains hindered by the low electrical conductivity of silicon and its huge volume change during lithiation and delithiation.

Many studies have been conducted to alleviate the pulverization of silicon during the charge/discharge process and to increase the conductivity of silicon materials. Recently, several approaches for synthesizing 3D porous Si-based anode materials that exhibit good cycling characteristics have been developed. Several approaches employ a wet-chemical etching process using hydrofluoric acid (HF) and silver nitrate (AgNO3). The fabrication process consists of two steps. First, Ag is deposited on silicon nanoparticles using HF and AgNO3. Subsequently, the particles are immersed into HF and hydrogen peroxide (H2O2), resulting in the generation of 3D porous silicon nanoparticles. However, HF is a dangerous chemical and thus a process not requiring HF for the fabrication of Ag-deposited silicon particles is required.1,2,3)

Herein, we present Ag-deposited silicon nanoparticles

fabricated using an alkaline method and describe their charge/discharge properties as a LIB anode material.

EXPERIMENTAL

We used planetary ball milling silicon nanoparticles. An immersion plating bath containing 2 g/L Si, 0.005 M AgNO3 and 0.010 M EDTA-2Na was prepared, and KOH was then added to adjust to pH 9~12. The silicon nanoparticles were dispersed using ultrasonic irradiation for 30 min. The reaction was conducted in a water bath to maintain the temperature at 25, 30 40, 50, 60, 70, 80°C, respectively for 2 hours. The silicon nanoparticles were then collected on a filter by suction filtration and dried in vacuum at 110 °C for 2 hours.

The microstructures of the samples were observed using field-emission scanning electron microscopy (FE-SEM) and scanning-transmission electron microscopy (STEM). Charge-discharge cycle tests of the prepared samples were performed. A coin cell (Model CR2032) was used as the test cell and lithium metal foil was used as the counter electrode. The cut-off potentials for the charge/discharge processes were 0.02 V and 1.5 V (vs. Li/Li+).

RESULTS AND DISCUSSION

Ag-deposited silicon nanoparticles were fabricated using an alkaline immersion plating method in the absence of HF.

REFERENCES

1)       Jung-In Lee, Soojin Park Nano Energy (2013) 2, 146-152

2)       Satoshi Uchida, Megumi Mihashi, Masaki Yamagata, Masashi Ishikawa, Journal of Power Sources 273 (2015) 118-122

3)       Chunli Li, Ping Zhang, Zhiyu Jiang Electrochemica Acta 161 (2015) 408-412

Figure 1
The Study of Abnormal Degradation in High-Voltage P-Type Mosfets with N+ Polysilicon Gate during AC Stress
Authors: Lee Dongjun , Lee Changsub , Hur Sunghoi , Song Duheon , Choi Byoungdeog
Published: February 2020

We investigated the degradation characteristics of High-voltage (HV) P-type Metal-oxide-semiconductor field effect transistors (P-MOSFETs) during negatively AC stress. The threshold voltage is shifted by degradation during the highly-negative gate bias, and the performance of transistors is degraded. In HV P-MOSFET with N+ polysilicon gate, there are two kinds of degradations during AC stress. One is the early degradation by Negative Bias Temperature Instability (NBTI), and the other is abnormal and drastic degradation after NBTI. To understand this abnormal degradation, we measured two samples with different gate materials such as N+ and P+ polycrystalline silicon and compared their degradation chracteristics. Thus we noticed that the abnormal degradation occurs only with N+ polysilicon gate in spite of lower oxide E-field. In this work, we studied the chracteristics of abnormal degradation and discussed a suitable mechanism of this phenomenon.
Improved Performance and Stability of Ni-Free Anode Materials for Intermediate Temperature-Solid Oxide Fuel Cells
Authors: Jo Soo-Yeon , Park Jun-Young
Published: February 2020

Solid oxide fuel cells (SOFCs), which convert the chemical energy to electrical energy through electrochemical processes, have been considered as highly promising power generation devices, because they have numerous advantages, such as high conversion efficiency, low greenhouse gas emission, multi-fuel capability and high tolerance to fuel impurities. These days, the most commonly used anode materials are Ni-based cermets due to their excellent electrocatalytic properties for fuel oxidation. However, Ni-based cermets suffer chemical and physical performance degradations caused by the carbon deposition when hydrocarbon gases use as the anode fuel. Furthermore, Ni-based cermets are exposed to the severe mechanical stresses under the fuel starvation condition due to the volume expansion of the anode by the Ni oxidation to NiO. Hence in order to resolve these reliability issues of the Ni-based cermet anode, more durable Ni-free anode materials with good electrocatalytic properties are developed. Among these, (La,Sr)(Cr,Mn)O3-
δ (LSCM) materials have considered as an alternative of Ni-based cermet anode because of high stability under H2 and CH4 conditions. However, LSCM shows low electrocatalytic activity for fuel oxidation because of its low ionic and electronic conductivity. Hence, various materials are doped to LSCM to improve electrocatalytic activity and thus resulting in improving the SOFC performance with high stability.

References

[1] A. Atkinson, S. Barnett, R.J. Gorte, J.T.S. Irvine, A.J. McEvoy, M. Mogensen, S.C. Singhal, J. Vohs. Nat. Mater. 3 (2004) 17.

[2] S. Tao, J.T.S. Irvine. J. Electrochem. Soc. 151 (2004) A252.

[3] J. Pena-Martinez, D. Marrero-Lopez, J.C. Ruiz-Morales, C. Savaniu, P. Nunez, J.T.S. Irvine. Chem. Mater. 18 (2006) 1001.

[4] E. Lay, L. Dessemond, G. Gauthier. J. Power Sources 221 (2013) 149.

[5] X. Zhu, Z. Lü, B. Wei, Y. Zhang, M. Liu, X. Huang, W. Su. J. Electrochem. Soc. 157 (2010) B691.

Keywords:
solid oxide fuel cells, anode, carbon deposition, mechanical stress, electrocatalysts, fuel starvation condition.
Specimen Preparation Method to Dual-Axis TEM Analysis Technique
Authors: Park Sang Gul , Lee Sungho
Published: February 2020

We usually do Physical Failure Analysis (PFA) to visualize the failure in the semiconductor process. First, we find the site-specific target (or failed cell). And then, we should do de-processing which contains lapping and chemical etch. As the semiconductor gets more complex and multi-layer, we should do multi-de-processing steps. If the failure has the oxide-material, we cannot know the cause of failure. Because the oxide can be removed by Hydrogen Fluoride (HF) chemical, which means the failure will be gone during de-processing step. We should use Focused Ion Beam (FIB) which can make a thin sample to exclude chemical step. High-resolution analytical tools such as Transmission Electron Microscopy (TEM) have become indispensable in PFA. We make a Dual-Axis TEM (DAT) method for PFA. We make a Plan-view TEM (PTEM) sample with FIB first, we can find an exact location of failure through the first step. And then, we make cross-sectional TEM (XTEM) sample with a site-specific target in PTEM sample. Below summarizes the four major steps and its precautions;

1. Making a Planar lamella by FIB

2. Observing a PTEM specimen with TEM

(Precaution : zone axis should be adjusted exactly)

3. Making a cross-section lamella by FIB

(Precaution : Protection layer should be deposited on both sides)

4. Observing a XTEM specimen with TEM

We propose DAT method to improve the problem of artifact in de-processing step. The TEM result with DAT method is shown in figure 4. We can know the exact location of failure with observing a PTEM sample. We can know the cause of failure with observing a XTEM sample. Moreover, we can analysis the chemical and physical information through DAT method. This method is very effective and has a high success rate in analysis.

REFERENCE

 

[1] A.E.M. De Veirman, “3-Dimensional’ TEM silicon-device analysis by combining plan-view and FIB sample preparation”, Materials Science and Engineering: B, 102(1-3), pp. 63-69, 2003.

 [2] Jon C. Lee, David Su, J.H. Chuang, “A Novel Application of the FIB Lift-out Technique for 3-D TEM Analysis”, Microelectronics Reliability Asset, 41(9-11), pp. 1551-1556, 2001.

Figure 1
Surface Functionalized Carbon Nanofiber Supports for Alkaline ORR Catalysts
Authors: Huang Wenjiao , Ahlfield John M. , Kohl Paul A , Zhang Xinsheng
Published: February 2020

Fuel cells are attractive because they provide clean and efficient energy for stationary and portable applications. Among the various types of fuel cells, the proton-exchange membrane fuel cells (PEMFC) have a high energy density and a fast start-up, but the cost of noble-metal catalysts and perfluorinated membranes is high. Anion-exchange membrane fuel cells (AEMFC) are attractive because they have enhanced the oxygen reduction and methanol oxidation kinetics at high pH, which makes the use of non-noble catalysts possible.

Carbon nanofibers (CNFs) have outstanding structural, mechanical and electrical properties, and are widely used as catalyst supports in fuel cells. CNFs are also considered to be good material for the oxygen reduction reaction catalysts in alkaline fuel cells because of their high surface area, thermal stability and electrical conductivity.

In this work, we use CNFs as the support for fuel cell catalysts in hybrid fuel cells, which combine alkaline and acidic conditions at the different electrodes. Functional groups were added onto the CNFs, including carboxyl groups (CNF-OX), carbonyl groups (CNF-CO), hydroxyl groups (CNF-OH) and nitrogen-containing groups (CNF-ON). In previous studies, they were tested them in half-cell experiments and it was found that the catalysts supported on CNF-ON have high ORR activity. The CNF-ON electrodes can change the ORR from the two-electron pathway to the four-electron pathway. Pt/CNFs have been tested in hybrid fuel cell and compared with Pt/C.
C-Doped TiO2-B Nanowires Derived from TiC As an Anode Materials for Lithium Ion Batteries with High Rate Performance
Authors: Goriparti Subrahmanyam , Zaccaria Remo Proietti , Capiglia Claudio
Published: February 2020

In the recent past nanostructured materials have been attracting much interest owing to their physical and chemical characteristics, which make them extremely suitable for a number of applications. In particular, one of the most promising applications is their use as electrode materials for rechargeable lithium ion batteries (LIB)1-2.

Among the anode materials, Titanium dioxide (TiO2) has been deeply investigated for lithium intercalation/de-intercalation due to high rate capability, very good reversible capacity,  low volume expansion ( <2% ) upon cycling and furthermore lost cost, high abundant and very safe lithium reaction potential ~ 1.5 V vs Li/Li+, owing to these characteristics, TiO2 anodes have been considered to target in EVs and HEVs application1-3. Recently, the various polymorphs of TiO2 (anatase, rutle, brookite and bronze) have been explored as efficient anodes for LIB3. In particular, TiO2-Bronze (TiO2-B) has been receiving significant interest due to its theoretical  capacity of 335 mAh g-1. Importantly, TiO2-B manifests the major advantages of fast charging-discharging through a pseudo-capacitive mechanism in addition to the bulk diffusion, whereas other polymorphs of TiO2 mostly show intercalation of Li-ion through bulk diffusion controlled mechanism3. However, the low electronic conductivity and low rate of Li-ion diffusivity of TiO2 are key issues for a high rate capable anode. To overcome these issues, we report synthesis of carbon-doped TiO2-B nanowires by facile and inexpensive method without using external carbon source. The carbon doping was verified by UV–visible and X-ray photoelectron spectroscopy and further structure and morphology was investigated with X-ray diffraction, Raman spectroscopy and Scanning and Transmission microscopies. The electrochemical performances of the C doped and undoped TiO2-B nanowires were tested by galvanostatic charge/discharge cycling, cyclic voltammetry, and electrochemical impedance spectroscopy. This novel C-doped materials presented high capacities and higher rate capability in electrochemical cycling experiments with respective to undoped material. This is attributed to the reduction of Li-ion diffusion path lengths along with improving electrical conductivity of TiO2-B nanowires. The electrochemical experiments demonstrated that C-TiO2-B nanowires electrodes exhibited superior lithium storage capacity of  ~306 mAh g-1 at current rate of 0.1C as well as excellent rate ability of  ~160 mAh g-1even at high current rate of 10C after 1000 cycle in lithium-ion batteries.

References:

S.Goriparti, E. Miele, F. D. Angelis, E.D. Fabrizio, R. P. Zaccaria, C. Capiglia, J. Power Sources, 257 (2014) 421

G. Zhu, Y. G. Wang and Y. Y.  Xia, Energy Environ. Sci., 5 (2012) 6652

A. G. Dylla, G. Henkelman and K. J. Stevenson, Acc. Chem. Res, 46 (2013) 1104

Figure 1
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).
Carbon Nanomaterials Doped with Sulfur for ORR in Alkaline Media
Authors: Montiel-Macias Elizabeth , Balbuena Perla B , Gauvin Raynald , Rosado Gabriel , Verde Gomez Ysmael
Published: February 2020

Fuell cells are recognized as an attractive alternative for clean energy generation. However, their commercialization has been limited by the high cost of their components. Platinum supported on carbon (Pt/C) has been considered a conventional electrocatalyst due to their high electroactivity. However, recent researches works have shown that the free platinum electrocatalyst such as nanostructured carbons doped with heteroatoms (e. g. B, P, N and S) have similar electrocatalytic activities that Pt/C for oxygen reduction reaction (ORR) in alkaline media. This work present the behavior for ORR in alkaline media of nanomaterials based on carbon doped with sulfur. The materials were prepared using a modified chemical vapor deposition method. Toluene and thiophene was used as carbon and sulfur source, respectively, while ferrocene was used as growing agent. Nanocarbons morphology and textural properties are investigated by high resolution transmission and scanning microscopy, X Ray diffraction and Raman spectroscopy. Electrochemical analysis was evaluated using cyclic voltammetry (CV) and rotating disk electrode (RDE) in 0.1 M KOH media.
Carbon Coated MoO2 Deposited through an Economical Polymer-Assited Solution Method on Nickel Foam As Anodes for Lithium-Ion Batteries
Authors: Patterson Brian , Luo Hongmei
Published: February 2020

Increasing energy demands requires improvements in energy storage devices which in turn necessitates the investigation of new materials implemented in lithium-ion batteries (LIBs). Molybdate based compounds such as MoO2 and MoS2 have been determined as a promising anode material for LIBs due to its high theoretical capacity. Taking MoO2 as an example, it can accept four Li ions during the charge and discharge processes, corresponding to a high theoretical capacity of 838 mAh/g. Most of molybdate based compounds have been prepared by non-economic and lab methods such as the hydrothermal method. A polymer deposition method which has been developed by our lab has advantages over previous methods due to its low cost and scalability. Carbon coated oxides on an electrode support can be created directly through this method without any additional binders and conductive materials. In this report, a carbon coating of molybdate oxide was successfully coated on the nickel foam, and the electrode exhibited superior capacity, high rate capability and cycle performance in LIBs. The carbon left from the decomposition of polymers is an effective binder between metal oxides and the nickel foam. The good performances of these electrodes could be attributed to intimate contact between the active material and the nickel foam, the porosity of the current collector, and the network structure of the active materials.
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.
Finish.
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.