Physical Chemistry Commons^™

Chemical And Electronic Structure Of Surfaces And Interfaces In Compound Semiconductors, Sujitra Pookpanratana

UNLV Theses, Dissertations, Professional Papers, and Capstones

The interface formation between two different materials is important in applications for optoelectronic devices. Often, the success or performance of these devices is dependent on the formation of these heterojunctions. In this work, the surface and interfaces in such materials for optoelectronic devices are investigated by a suite of X-ray analytical techniques including X-ray photoelectron (XPS), X-ray excited Auger electron (XAES), and X-ray emission (XES) spectroscopies to provide novel insight.

For the group III-nitrides (e.g., AlxGa1-xN) used in many light emitting devices, a significant challenge exists to form an Ohmic contact. The electron affinities and band gaps of GaN and …

Ab Initio Search For Novel Bxhy Building Blocks With Potential For Hydrogen Storage, Jared K. Olson

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

On-board hydrogen storage presents a challenging barrier to the use of hydrogen as an energy source because the performance of current storage materials falls short of platform requirements. Because boron is one of the lightest chemical elements that can form strong covalent bonds with hydrogen, it provides an excellent opportunity to design new lightweight materials on the basis of novel boron hydride building blocks. Realizing this potential requires an understanding of the electronic structure, chemical bonding, and stability of neutral and anionic B_xH_y clusters with variable stoichiometry. While a large number of boron hydride compounds are known, …

Characteristics And Stability Of Oxide Films On Plutonium Surfaces, Harry Guillermo García Flores

Department of Chemistry: Dissertations, Theses, and Student Research

The oxidation of plutonium (Pu) metal continues to be an area of considerable activity. The reaction characteristics have significant implications for production use, storage, and disposition of this radiological material. Developing an accurate physical model of the structures, oxidation states, and oxygen concentration gradients present during oxidation are essential to understanding this process. Traditionally, the stable oxides of Pu have been thought to be plutonium sesquioxide (Pu₂O₃, O/Pu = 1.5, Pu³⁺) and plutonium dioxide (PuO₂, O/Pu = 2.0, Pu⁴⁺), existing in a layered structure on Pu metal. Many of the …

Synthesis And Catalytic Activity Of Nanostructured Cerium Oxide, Neil J. Lawrence

Department of Chemistry: Dissertations, Theses, and Student Research

Cerium oxide (ceria, CeO_2-x where x is 0 to 0.5) has been one of the most widely used heterogeneous catalysts particularly in three way catalytic converters. Most of the catalytic traits can be attributed to two properties of ceria: first, the high mobility and storage capacity of oxygen within the lattice; second, the ease with which cerium changes between Ce³⁺ and Ce⁴⁺ states. These properties, combined with the abundance of cerium on earth, make ceria a low-cost highly effective alternative to noble metal catalysts. Recent research has been focused on the nanoscale properties of ceria.

The effect …

The Roles Of The Width Of Gas/Liquid/Solid Three-Phase Boundary Zone Of Dispersion Water Films In Atmospheric Corrosion Of Metals, Wang Jia, Jing Jiang

Journal of Electrochemistry

The roles of TPB(Three-Phase Boundary) width in the corrosion processes of metals under dispersed water films were investigated by electrochemical techniques combined with contact angle measurement.It is found that both cathodic limiting current density and corrosion current density linearly increases with increasing the TPB width,confirming the important role of TPB width in gas/liquid/solid multiphase corrosion systems.Based on above results,the effect of water film thickness on atmospheric corrosion rate was quantitatively evaluated by the TPB width.

Research On Nafion/Sio_2 Composite Membrane In All Vanadium Redox Flow Battery, Dong-Dong Liu, Mao-Cai Lin, Tao Guan, Qing-Chun Yu

Journal of Electrochemistry

The Nafion117/SiO2 composite membrane was prepared by sol-gel method.The results showed that,during composite membrane preparation process,the ratio of MeOH and TEOS did not affect the penetration rate of VO2+ basically,however,the lowest permeability of 427×10-9cm2/s in the membrane was achieved while hydrolysis time was 10 min and natural drying for 24 h after hydrolysis,which reduced by 52 times than that in Nafion117 membrane.The SEM tests proved that SiO2 grains grew bigger in the composite membrane during the natural drying,and most of the holes in Nafion117 were filled.Single cell test showed the battery power efficiency was improved by 2.7 %.

Electrodeposition Of Lead Dioxide From Dluoroborate Solutions, Chun-Mei Kong, Yong-Ming Tang, Wen-Zhong Yang, Xiao-Yuan Yang

Journal of Electrochemistry

The PbO2 anodes were prepared on platinum from fluoroborate media and its doped solutions by electrodeposition technique.Elecchemical and pysicochemical properties of these PbO2 films were studied by cyclic voltammetry methods,XRD and SEM.The results showed that the presence of BF4-increased PbO2 electrodeposition rate;the prepared lead dioxide consisted of β-PbO2;the preferential orientation of crystals and surface morphology were affected a lot by doping F-and Fe3+.The FB/F-Fe-PbO2 electrode exhibited regular-shaped layers with compact morphology.Furthermore,increasing current density also change the preferential orientation of PbO2 crystals.

Electrochemical Performance Of Zinc Tetra (Trifluoroethoxy) Phthalocyaninate In Aqueous And Nonaqueous Solvents, Xiao-Shan Wu, Li-Ying Huang, Jin-Que Zhang, Shan-Lan Zhu

Journal of Electrochemistry

The cyclic voltammetric performance of ZnPcF in N,N-dimethylformaide(DMF),dimethyl sulfoxide(DMSO) solution and phosphate buffer solutions(PBS) has been examined.The results showed that four pairs of redox peaks appeared in nonaqueous solvents,and the values of half-wave redox potential were 0.558 V,-0.761 V,-1.034 V,-1.417 V,respectively,exhibiting four quasi-reversible phthalocyanine ligand based one-electron transfers.In PBS only two redox peaks were observed and the values of half-wave redox potential were-0.885 V,-1.104 V,exhibiting irreversible behavior characteristics.Comparing to the zinc phthalocyanine(unsubstitute ZnPc),introducing electron-withdrawing groups-trifluoroethoxyl to the peripheral sites of the phthalocyanines shifts the redox processes of the complex toward positive potentials.

Eis Study On The Change Of Resistance And Water Absorption During The Failure Graduation Of Inorganic Zinc-Rich/Epoxy/Aliphatic Polyurethane Composite Coatings, Shao-Ping He, Jin-Ping Xiong, Yu-Ming Tang, Yu Zuo

Journal of Electrochemistry

The failure process of inorganic zinc-rich/micaceous iron oxide epoxy/aliphatic polyurethane composite coatings in 3.5% NaCl solution under ultraviolet radiation(UV) was studied with Electrochemical Impedance Spectroscopy(EIS).The result shows that the protective property of the coating was enhanced with the increase of total coating thickness,but the degree of improvement reduced gradully as the coating thickness increased.The shielding effect of the micaceous iron oxide epoxy was mainly reflected in the initial period of the service process,while in later period the coating performance largely depended on the zinc-rich primer.The change of the water uptake in the composite coating presented a 'three-stage' characteristic.The thinner the …

Electrochemical Detection For The Corrosion Of Reinforcing Steel In Concrete During Immersion And Drying Cycles, Bing-Li Jia, Fa-He Cao, An-Na Chen, Jian-Qing Zhang

Journal of Electrochemistry

The corrosion behavior of reinforcing steel in concrete under dry-wet cycle condition has been studied by electrochemical noise(EN) compared with the electrochemical impedance spectroscopy(EIS),SEM micrographs and EDS.The statistical method has been employed to analyze the EN data of reinforcing steel in concrete,which revealed three different corrosion stages of reinforcing steel in concrete,including the dissolution of the passive film,the active corrosion and the cumulation of corrosion product.The wavelet transform has also been employed,which indicated that steel in concrete with pH 1 is associated with uniform corrosion,while steel in concrete with pH 3 and pH 7 are associated with localized corrosion,such as …

Study Of The 11-Ferrocenylalkanethiol Redox-Induced Structure Changes By Flow-Injection Electrochemical Surface Plasmon Resonance, Xiu-Juan Xiao, Yong-Hui He, Juan Xiang, Bin Ren

Journal of Electrochemistry

Redox-induced orientation changes of self-assembled monolayers(SAMs) of 11-ferrocenylundecanethiol(FcC11SH) were studied by the flow-injection electrochemical surface plasmon resonance(FI-EC-SPR).Results indicated that there existed two mechanisms concerning the redox-induced structure change of the self-assembled monolayer of ferrocenylalkanethiols:the electrostatic repulsion between the positively charged surface and the ferricenium cation and that among the cations led to a decrease in the tilt angle of the alkanethiol chain;upon Fc oxidation,the Fc group rotated from a tilted conformation to a position where the cyclpentyldiene plane became perpendicular to the electrode.

Study On Aluminum Foils For Aluminum Electrolytic Capacitor, Hui-Zhong Tan, Guo-Qing Qian, Wen-Bao Wang, Lan Sun, Chang-Jian Lin

Journal of Electrochemistry

Scanning electron microscopy(SEM),X-ray diffraction(XRD),weight-loss method and electrochemical testing method were employed to study the chemical compositions and corrosion behaviors of hard foil and soft foil.The results showed that the surface morphology,chemical composition and crystal structure of hard foil and soft foil are different.It is found from electrochemical tests that the soft foil is suitable to the corrosion under low acidity conditions,which provides the base for developing the corrosion techniques under low acidity conditions.

Electrochemical Behaviors Of Organic Coating/Matal Substrate Under Simulated Deep Sea Environment Partⅰ.Effects Of Seawater Pressure On Transportation Behavior Of Water Through Coating And Coating′S Protective Performance, Bin Liu, Zhi-Gang Fang, Tao Wang, Hong-Bin Wang

Journal of Electrochemistry

By means of electrochemical impedance spectroscopy(EIS),the electrochemical behaviors of organic coating/metal substrate were studied under simulated deep sea environment in the laboratory.Effects of seawater pressure on the transportation behavior of water through coating and the protective performance of coating were analyzed.The experimental results showed that,compared to normal pressured seawater,there were different impedance characteristics of coating in 3.5 MPa pressured seawater.The main observations were that high seawater pressure accelerated the process of water uptake and invalidation of coating,increased water absorption,and lowered the anti-corrosion property of coating.

Photoelectrochemical Properties Of N,S,And Cl Modified Nano Tio_2 Thin Films, Hong Yun, Chang-Jian Lin, Jing Li, Rong-Gui Du

Journal of Electrochemistry

The nitrogen(N),sulfur(S) and chlorine(Cl) modified nano TiO2 thin films were prepared by adding Ti(O-n-Bu)4 as the precursor into concentrated HNO3,H2SO4 and HCl Solutions,respectively,on different substrates in a sol-gel process.The photoelectrochemical performances of N,S and Cl modified nano TiO2 thin films have been studied by UV-vis(DRS),photocurrent curves,EIS and OCP-time curves.N-modified TiO2 nano films show better surface structure,which helps to improve the quantum efficiency of nano TiO2 thin films.

Initial Stage Of Atmospheric Corrosion Of Ndfeb(M35) In A Simulated Marine Atmosphere, Chun-Ling Li, Yuan-Tai Ma, Ying Li, Fu-Hui Wang

Journal of Electrochemistry

This study detailed the atmospheric corrosion behaviour of sintered NdFeB(M35) in a simulated marine atmosphere with 80% relative humidity(RH).The dissolution and subsequent reaction of NaCl particles cause the attack of NdFeB.The corrosion presented three representative types:if the electrolyte covered magnetic phase and Nd-rich phase,the Nd-rich phase was corroded firstly due to galvanic effect;if the electrolyte covered magnetic phase,magnetic phase was corroded along the grain boundary;if the electrolyte located near the position of defects,corrosion progressed along with the defect because of low concentration of oxygen inside the defect.With corrosion progressing,local corrosion areas were mutually connected,with Nd-rich phase and grain boundary being …

Hydrothermal Reduction Synthesis Of Lifepo_4 And Its Electrochemical Performance, Hong-Li Zou, Guang-Hui Zhang, Pei-Kang Shen

Journal of Electrochemistry

The cathode materials of LiFePO4 were prepared via a hydrothermal reduction method using FeCl3 as Fe source and iron as a reducing agent.The results showed that ferric salt could be reduced to ferrous salt completely under the hydrothermal condition and pure-phase LiFePO4 was obtained based on the test results of XRD and FTIR.Carbon-coated LiFePO4 was synthesized by pyrolysisng glucose at high temperature.The morphologies of pure LiFePO4 displayed cluster-like while the LiFePO4/C displayed sphere-like particles.The electrochemical test showed that the LiFePO4/C had good rate performance,while LiFePO4 delivered much lower discharge capacity.

Corrosion Electrochemical Behavior Of Am60 Magnesium Alloys In Automobile Engine Coolants, Ling-Jie Li, Sha Wang, Yin Xiao, Jun Lan, Jing-Lei Lei, Sheng-Tao Zhang, Fu-Sheng Pan

Journal of Electrochemistry

The polarization measurements and electrochemical impedance spectroscopy(EIS) were used to study the corrosion electrochemical behavior of AM60 magnesium alloys in three kinds of commercial coolants for automobile engine.Results show that the tested commercial coolants are slightly corrosive to AM60 magnesium alloys and their corrosivity varies from coolant to coolant.The coolant C is the least corrosive among the studied commercial coolants and the coolant A is more corrosive than the coolant B and C.The coolant C appears to be the most promising coolant for automobile engine made by magnesium alloys.The coolant resistivity plays an important role in the corrosion of AM60 …

The Sol-Gel Synthesis And Electrochemical Performance Of Li_3v_2(Po_4)_3/C Cathode Material For Lithium Ion Battery, Li-Ying Liu, Lian Chen, Hai-Yan Zhang, Yu-Chun Zhai

Journal of Electrochemistry

Li3V2(PO4)3/C was synthesized by sol-gel method with citric acid as chelate and C sources.Physical and electrochemical performances of as-prepared materials were characterized through XRD,SEM and galvanostatic charge-discharge tests,etc.The results showed that products produced by calcining at 800 ℃ for 12 h had a single phase crystal structure and relatively small particle sizes with uniform distribution.At 0.1 C,0.5 C and 1 C,the initial specific discharge capacities were 153.0,143.1 and 130.6 mAh·g-1,respectively,and capacity efficiencies were 93.1%,85.4% and 77.3% after 50 cycles,respectively.Charge efficiencies were all above 80% and discharge voltages were higher.

Effect Of Cldh On Rebar Corrosion Behavior In Chloride Contaminated Neutral Pore Solutions, Yu-Ming Tang, Le Niu, Yu Zuo

Journal of Electrochemistry

The effect of calcined LDH-MgAl-CO3 on rebar corrosion behavior in chloride ion contaminated neutral concrete pore solutions was investigated in this paper.Corrosion potentials of rebars in pore solutions after treatment with CLDH were higher than before treatment.According to polarization tests,passivated region of rebars in pore solutions after treatment with CLDH was found apparently instead of activation.EIS tests showed that CLDH made the impedance of specimens increase.The measurements of pH and chloride ion concentration after treatment indicated that / of pore solutions decreased by 4～5 magnitude orders.

Preparation And Characterization Of The Silane-Phosphonic Acid Composite Passivation Coating For Electrogalvanized Steel, Yong Guan, Jian-Guo Liu, Chuan-Wei Yan

Journal of Electrochemistry

A new silane-phosphonic acid composite passivation coating process has been developed for the protection of electrogalvanized steel based on N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane(AAPTMS),γ-(2,3-epoxypropoxy)propyltrimethoxy-silane(GPTMS) and 1-hydroxy ethylidene-1,1-diphosphonic acid(HEDP).The results of X-ray photoelectron spectroscopy(XPS),Fourier transform infrared spectroscopy(FTIR),potentiodynamic polarization scan,electrochemical impedance spectroscopy(EIS) and neutral salt spray(NSS) tests indicated that the major structure of the prepared silane-phosphonic acid composite passivation coating consisted mainly of Si—O—Si and Si—O—P bonds.The area of white rust was not more than 5% of the total panal after 120 h NSS test,which could be compared favourably with the chromate colour passivation coating.However,the corrosion reaction on the anode of the silane-phosphonic acid composite passivation …

Study On Preparing Technology And Corrosion Resistance Of Ti/Zr Based Chromium-Free Chemical Conversion Coating On Zinc Electroplating Layer, Yong Guan, Jian-Guo Liu, Chuan-Wei Yan

Journal of Electrochemistry

In this paper,we obtained environmental-friendly chromium-free chemical conversion coating on the non-cyanide alkaline zinc electroplating layer by employing the optimized Ti/Zr based conversion technique.At the same time,the performances of the Ti/Zr based conversion coating were compared with chromate colour passivation coating.The corrosion resistances of the conversion coatings were investigated by using neutral salt spray(NSS) test,potentiodynamic polarization and electrochemical impedance spectroscopy(EIS).The results showed that the white rust appeared after 96 hours when the NSS test was performed on the Ti/Zr based conversion coating,which was close to the corrosion resistance rating of chromate colour passivation coating.Compared with the chromate passivation coating,the Ti/Zr …

Comparative Studies On The Deterioration Process Of Organic Coatings Under Immersed And Cyclic Wet-Dry Conditions By Eis, Yu-Nan Li, Jia Wang, Wei Zhang

Journal of Electrochemistry

Under the immersed and wet-dry cyclic conditions,the deterioration processes of the organic coatings on carbon steel surface have been comparatively studied by using electrochemical techniques.The wet-dry cycles were carried out in the alternating conditions of 12 h by immersing in a 3.5% sodium chloride solution and drying at 25 ℃ and 50% RH.Coating resistance,Rf,coating capacitance,Cf,and double layer capacitance,Cd,were monitored continuously and separately under above two conditions.The percentages of the intenfacial active area,Aw,were estimated from the obtained double layer capacitance,Cd.According to the EIS characteristics,the entire deterioration processes under above two mentioned conditions can be divided into three main stages,consisting of the …

Effects Of Solvents And Electrolyte Salts On The Electrochemical Reduction Of Oxygen In Non-Aqueous Electrolytes, Yan-Yan Tian, Wei Wu, Jun Gao, Yong Yang

Journal of Electrochemistry

The electrochemical reduction processes of oxygen in different non-aqueous solvents such as acetonitrile(MeCN),propylene carbonate(PC) and their mixtures were investigated by cyclic voltammetry method.The results indicated a one electron reduction of oxygen to O2-occured in these systems as a first step reduction,no matter whether in tetrabutylammonium hexafluorophosphate(TBAPF6)/MeCN or TBAPF6/PC electrolyte.However,the CV curves in 0.1 mol·L-1 TBAPF6/MeCN showed a couple of reversible redox peaks,indicating that the reduction process of oxygen was irreversible in the 0.1 mol·L-1 TBAPF6/PC electrolyte.In the PC-based electrolyte,the reduction current peak reduced largely and the oxidation peak of O2-almost disappeared as compared to that of the former electrolytes.The possible …

Electroless Deposition And Characterization Of Nickel Coating In Lead-And Cadmium-Free Bath, Fang-Zu Yang, Ming-Hui Chen, Xia-Jing Huang, Zhong-Qun Tian, Shao-Min Zhou

Journal of Electrochemistry

Technology of electroless nickel deposition in lead-and cadmium-free bath was developed.Coating′s morphology,composition,structure and electrochemical activity were characterized by SEM,EDS,XRD and electrochemical methods.The results showed that,the deposition rate of nickel in self-catalysing was 22.4 μm·h-1,which was increased by the increase of bath temperature and pH value.The effect of sodium hypophosphite on deposition rate was much more remarkable compared with nickel sulfate.The obtained nickel coating was 7.8% in phosphor weight content,having compact and neat surface morphology,amorphous structure,and good electrochemical corrosion resistance in sodium chloride solution.

Systematic Approach To Electrostatically Induced 2d Crystallization Of Nanoparticles At Liquid Interfaces, Sumit Kewalramani, Suntao Wang, Yuan Lin, Huong Giang Nguyen, Qian Wang, Masafumi Fukuto, Lin Yang

Faculty Publications

We report an experimental demonstration of a strategy for inducing two-dimensional (2D)crystallization of charged nanoparticles on oppositely charged fluid interfaces. This strategy aims to maximize the interfacial adsorption of nanoparticles, and hence their lateral packing density, by utilizing a combination of weakly charged particles and a high surface charge density on the planar interface. In order to test this approach, we investigated the assembly of cowpea mosaic virus (CPMV) on positively charged lipid monolayers at the aqueous solution surface, by means of in situX-ray scattering measurements at the liquid–vapor interface. Theassembly was studied as a function of the solution …

Vibrationally Promoted Electron Emission At A Metal Surface: Electron Kinetic Energy Distributions, Jerry L. Larue, Tim Schäfer, Daniel Matsiev, Luis Velarde, N. Hendrick Nahler, Daniel J. Auerbach, Alec M. Wodtke

Biology, Chemistry, and Environmental Sciences Faculty Articles and Research

We report the first direct measurement of the kinetic energy of exoelectrons produced by collisions of vibrationally excited molecules with a low work function metal surface exhibiting electron excitations of 64% (most probable) and 95% (maximum) of the initial vibrational energy. This remarkable efficiency for vibrational-to-electronic energy transfer is in good agreement with previous results suggesting the coupling of multiple vibrational quanta to a single electron.

Some Features Of The Concentration Oscillations In The Phenylacetylene Oxidative Carbonylation Reaction (In Russian), Sergey N. Gorodsky

Sergey N. Gorodsky

Some modes of concentration oscillations in the homogeneous system KI-PdI2-CO-O2-CH3OH are described in this paper.

Jahn-Teller Coupling And Fragmentation After Core-Shell Excitation Ini Cf4 Investigated By Partial-Ion-Yield Spectroscopy, Renaud Guillemin, Wayne C. Stolte, Maria Novella Piancastelli, Dennis W. Lindle

Chemistry and Biochemistry Faculty Research

We investigate fragmentation processes induced by core-level photoexcitation in CF4 at both the carbon and fluorine K edges by means of partial-ion-yield spectroscopy. The molecule CF₄ is a textbook example of systems in which Jahn-Teller coupling strongly manifests itself in the photoabsorption spectrum. Spectral features related to Jahn-Teller and quasi-Jahn-Teller splitting are observed, and important differences in the fragmentation pathways are revealed depending on the symmetries of the core-excited states. We interpret these experimental observations on the grounds of symmetry lowering from the Td to the C3v point group as well as preferential orientation with respect …

Synthesis And Cyclic Voltammetry Of A2e, Elizabeth White, Willa Harper

Student Scholarship – Chemistry

As aging occurs, great exposure to light leads to the build-up of fluorescent materials called lipofuscin in the retinal pigment epithelial cells. This accumulation of lipofuscin is correlated to the progression of age related macular degeneration and other retinal dystrophies. No cure for macular degeneration has been found, so lipofuscin is of great interest. The lipofuscin has been associated with an increase in radiation intake and a loss of photoreceptors in the retina. The compound A2E is being studied in this project because it is frequently found in the lipofuscin. The goal of this project is to further characterize A2E …

Site-Specific Photocatalytic Splitting Of Methanol On Tio2(110), Chuanyao Zhou, Zefeng Ren, Shijing Tan, Zhibo Ma, Xinchun Mao, Dongxu Dai, Hongjun Fan, Xueming Yang, Jerry L. Larue, Russell Cooper, Alec M. Wodtke, Zhou Wang, Zhenyu Li, Bing Wang, Jinlong Yang, Jianguo Hou

Biology, Chemistry, and Environmental Sciences Faculty Articles and Research

Clean hydrogen production is highly desirable for future energy needs, making the understanding of molecular-level phenomena underlying photocatalytic hydrogen production both fundamentally and practically important. Water splitting on pure TiO₂ is inefficient, however, adding sacrificial methanol could significantly enhance the photocatalyzed H₂ production. Therefore, understanding the photochemistry of methanol on TiO₂ at the molecular level could provide important insights to its photocatalytic activity. Here, we report the first clear evidence of photocatalyzed splitting of methanol on TiO₂ derived from time-dependent two-photon photoemission (TD-2PPE) results in combination with scanning tunneling microscopy (STM). STM tip induced molecular manipulation …