Nanoscience and Nanotechnology Commons^™

Study On The Surface States Of Zinc Sulfide Thin Film Doped With Erbium And Their Effect On The Relaxation Luminance, Yujiang Wang, Zhaohong Liu, Zhenxiang Chen

Journal of Electrochemistry

X-ray photoelectron spectrum and characteristics of the capacity, versus thevoltage of the thin film devices are measured to study the surface states of the zinc sulfide thin film.The transient electroluminescence excited by pulses shows the relaxation luminance peaks during anon-exponential decay process of the characteristic transitions activated by Er³⁺ in the ZnS directcurrent thin film electroluminescence (DCTFEL) devices.The surface structures of ZnS:Cu, Cl, Erfilm with the absorption of oxygen, and the effect of the surface states on the relaxation luminance ofthe devices are discussed.

The Influnce Of Conjugated Π Bond In Promoter Molecule On The Direct Electrochemical Reaction Of Cytochrome C, Xiaogang Qu, Tianhong Lu, Shaojun Dong

Journal of Electrochemistry

The promoter effect of thiophene with only one-functional group on the directelectrochemical reaction of cytochrome c was compared with that of tetrahydrothiophene in this report. It was found that thiophene is a good promoter. But tetrahydrothiophene could not facilitate the directelectrochemistry of cytochrome c although this compound is very similar to thiophene in str uctureexcept for conjugated π bond. This demonstrated that the conjugated π bond in thiophene plays animportant role for the acceleration of the direct electrochemistry of cytochrome c.

Effect Of Symmetric Alternating Current On Cathode Surface Before Iron Deposition, Xintan Hu

Journal of Electrochemistry

The composition and thickness of active film formed on the surface of cathode made of low carbon steel after treated by symmetric alternating current (SAC) in ferris chloride bathis studied,and the interfacial morphology of the iron deposit and the substrate is also examined. The results show that the active film, which a thickness of 20～25nm can be obtained under SAC densityof about 7 A·dm^-2 ,so that the adherent iron deposit can be achieved on the active film. The effect of SAC on cathode surface is discussed in detail.

Method Of Making Quasicrystal Alloy Powder, Protectivecoatings And Articles, Jeffrey E. Shield, Alan I. Goldman, Iver E. Anderson, Timothy W. Ellis, R. William Mccallum, Daniel J. Sordelet

Department of Mechanical and Materials Engineering: Faculty Publications

A method of making quasicrystalline alloy particulates wherein an alloy is superheated and the meltis atomized to form generally spherical alloy particulates free of mechanical fracture and exhibiting a predominantly quasicrystalline in the atomized condition structure. The particulates can be plasma sprayed to form a coating or consolidated to form an article of manufacture.

A Sutface-Enhanced Raman Spectroscopic Study On The Inhibition Mechanism Of Bmat On Stainless Steel In Hydrochloric Acid Solutions, Yinghua Zha, Baoming Wei, Zhongqun Tian, Changjian Lin

Journal of Electrochemistry

The absorbtion of some nitrogen and sulfur compounds such as BMAT on 18-8stainless steel (SS) in 0.5% HCl were investigated by surface enhanced Raman scattering (SERS) spectroscopy. The SERS spectra of BMAT adsorbed on SS were measured using a SS electro deposited with discontinuous silvet micro-islands. The results show that the inhibitor, BMAT, is chemisorbed on the SS surface through the N atom. Under the influence of π-electron interaction, BMAT can be adsorbed on SS surface at an angle. The allyls in BMAT molecules play the role of steric hindrance in the inhibition effect.

Incorporation Of Zn In Gaas During Organometallic Vapor Phase Epitaxy Growth Compared To Equilibrium, W. Reichert, C.Y. Chen, W.M. Li, Jeffrey E. Shield, R.M. Cohen, D.S. Simons, P.H. Chi

Nebraska Center for Materials and Nanoscience: Faculty Publications

The zinc concentration measured after organometallic vapor phase epitaxy (GMVPE) growth on (100)-oriented GaAs at 700 °C has been compared to the zinc concentration measured after in-diffusion under near-equilibrium conditions. During diffusion, the concentration of Zn 20 nm below the surface was found to vary with P_Zn^1/2, as expected for bulk solid-vapor equilibrium. During growth, the concentration of Zn varied linearly with P_Zn up to a maximum value which was found to correspond to the solubility limit set by second phase formation, e.g., growth of Zn₃As₂. Although large differences were observed between …

Transient Photocurrent Behavior Of Multiple Quantum Well Gaas/AlXGa(1-X)As Electrode, Liu Yao, Xurui Xiao, Yuan Lin, Yiping Zeng, Dianzhao Sun, Haiqun Zheng

Journal of Electrochemistry

Transient photocurrents induced by short light pulses at lattice-matched multiplequantum well (MQW)GaAs/Al_0.3)Ga_0.7 As electrodes were studied in the 1 ×10^-2 mol·dm^-3 ferrocene([Fc⁰]/[Fc⁺]=9/1)-0.1 mol·dm^-3 tetrabutylammonium tetrafluoroborate acetonitrile solutionin order to examine the relaxation photoprocesses and to evaluate kinetic parameters of superlattice electrodes.

GaAs/Al_0.3Ca_0.7 As MQW electrode consisting of 10 periods with each of GaAs well (5.3 nm) and Al_0.3Ga_0.7. As barrier (10 nm) showed two pronounced and well-resolved peak structures located at 1.503 eV and 1.699 eV in the photocurrent spectrum, corresponding to the …

Atomic And Molecular-Perspectives In Electrochemical Interfaces, Zhaowu Tian

Journal of Electrochemistry

The following recent studies on the atomic and molecular-perspectives at electrochemical interfaces using Raman, IR, STM and quantum chemical methed by electrochemistry group in Xiamen University are briefly reviewed. 1.Orientation, charge transfer and bonding of adsorbed molecules. 2. Adsorption effect, electrode potential effect and adatom effect on the electron populations and strength of intramolec ular bonds of the adsorbed molecules. 3. Detailed classification into various types (e. g., competitive, chemically inductive, physical inductive etc.) of coadsorption on electrodes according to the above-mentioned effects.  4. Single crystal face structure effect and adatom effect on the kinetics and the mechanisms of electrocatalytic …

Self Assembly Via Layer By Layer Surface Reaction On Gold Electrodes And The Electrochcmical Characterization, Xiandui Dong, Juntao Lu, Chuanxin Cha

Journal of Electrochemistry

The self-assembled monolayers,which were built by spontaneous adsorption of ω-carboxylic acid thiols on gold surface,were used as substrate for further modification through later bylayer amide surface reactions. At each stage of modification,the gold surface was characterizedelectochemieally. The results demonstrated that the strategies of layer by layer self assembly is ofsignificant potential for fabrieating functionalized ultrathin layers.

Study Of Electrochemical Properties Of Ni(Oh)2/Niooh With Spectroscopic Ellipsometry, Shengtao Zhang, Zongqing Huang

Journal of Electrochemistry

Electrochemical reactions of Ni(OH)₂ /NiOOH system were studied by using in-situ spectroscopic ellipsometry and the conventional electrochemical metheds. By fitting data from ellipsometric measurements, a transformation medel of the surface film was obtained for cathedic and anodic processes. The results indicated that the transformation medel after cobalt implantation almost remained the same as that before cobalt implantation, but the electrochemical properties were affected obviously by implantation of cobalt.

The Electrode Process Of Y(Ⅲ) On Copper Electrode And Its Surface Metallizing, Chungen Zhou, Shuzhen Duan

Journal of Electrochemistry

The reduction of yttrium ion on copper electrode in NaCl-KCl-YCl₃ molten saltshas been investigated. The results indicate that the formation of intermetallic compounds is occuredbefore the metallic yttrium to be formed. The formation of intermetallic compounds is controlled bythe process of which yttrium atoms are diffusing into copper electrode. The kinetic characters todiffusion of yttrium atoms were also discussed.

Characterization Of Piezoceramic Crosses With Large Range Scanning Capability And Applications For Low Temperature Scanning Tunneling Microscopy, J. A. Helfrich, Shireen Adenwalla, J. B. Ketterson, G. A. Zhitomirsky

Shireen Adenwalla Papers

We have developed a large amplitude piezoceramic scanner which should have numerous applications. Scanning tunneling microscopy (STM) and other scanning probe microscopies predominantly use piezoceramics for the scanning elements. Similarly adaptive optics, high resolution lithography, and micromanipulators are other examples of research which regularly utilize piezoceramic scanners. We present a new geometry for a piezoceramic scanner which allows for both high resolution (~nanometers) and large amplitude (~400 µm) displacements. The cross-shaped geometry makes it possible to produce extremely long pieces with very high tolerances. We have shown its effectiveness by using it as the major component of a low temperature …

Nmr And Nqr Study Of The Electronic And Structural Properties Of Al-Cu-Fe And Al-Cu-Ru Quasicrystals, A. Shastri, F. Borsa, D.R. Torgeson, Jeffrey E. Shield, A.I. Goldman

Nebraska Center for Materials and Nanoscience: Faculty Publications

²⁷ Al and ^63.65Cu NMR measurements are reported for powder samples of stable Al-Cu-Fe and Al-Cu-Ru icosahedral quasicrystals and their crystalline approximants, and for an Al-Pd-Mn singlegrain quasicrystal. Furthermore, ²⁷Al NQR spectra at 4.2 K have been observed in the Al-Cu-Fe and Al-Cu-Ru samples. From the quadrupole-perturbed NMR spectra at different magnetic fields, and from the zero-field NQR spectra, a wide distribution of local electric-field gradient (EFG) tensor components and principal-axis-system orientations was found at the Al site. A model EFG calculation based on a 1/1 Al-Cu-Fe approximant was successful in explaining the observed NQR spectra. The average …

Resonant Tunneling Through Quantum Dot Arrays, Guanlong Chen, Gerhard Klimeck, Supriyo Datta, Guanhua Chen, William A. Goddard Iii

Birck and NCN Publications

We apply the Hubbard Hamiltonian to describe quantum-dot arrays weakly coupled to two contacts. Exact diagonalization is used to calculate the eigenstates of the arrays containing up to six dots and the linear-response conductance is then calculated as a function of the Fermi energy. In the atomic limit the conductance peaks form two distinct groups separated by the intradot Coulomb repulsion, while in the band limit the peaks occur in pairs. The crossover is studied. A finite interdot repulsion is found to cause interesting rearrangements in the conductance spectrum.

Conductance Spectroscopy In Coupled Quantum Dots, Gerhard Klimeck, Guanlong Chen, Supriyo Datta

Birck and NCN Publications

We investigate the linear-response conductance through a pair of coupled quantum dots. The conductance spectrum under ideal conditions is shown to consist of two sets of twin peaks whose locations and amplitudes are determined by the interdot coupling and the intradot charging. We will show that the qualitative features of the spectrum survive against experimental nonidealities such as (1) detuning of the individual dots, (2) interdot charging, (3) inelastic scattering, and (4) multiple lateral states. The effect of higher lateral states depends strongly on the nature of the interaction potential, screening lengths, and exchange terms, but the lowest set of …

Rate Equations For The Phonon Peak In Resonant-Tunneling Structures, Roger Lake, Gerhard Klimeck, J. P. Anantram, Supriyo Datta

Birck and NCN Publications

The ratio of the phonon peak current to the main peak current in double-barrier resonant-tunneling structures is significantly enhanced by barrier asymmetry. Previously, using the Keldysh formalism, we derived analytical expressions, valid in the zero-temperature, high-bias regime, which explained this eftect. We now provide analytical expressions valid for finite temperature and bias obtained from (i) an intuitive derivation using a rate equation approach and (ii) a more general derivation using the Keldysh formalism. The results of the two difFerent approaches are shown to be essentially identical for the ex- perimental device parameters. The finite temperature expressions shed light on the …

Rate Equations From The Keldysh Formalism Applied To The Phonon Peak In Resonant-Tunneling Diodes, Roger Lake, Gerhard Klimeck, Supriyo Datta

Birck and NCN Publications

Starting from the Keldysh formalism, general analytical expressions are derived for the current and the occupation of the well in the presence of inelastic scattering, both at the main peak and at the pho- non peak. These expressions are then evaluated from a continuous coordinate representation of a double-barrier potential profile and also from a tight-binding model of a weakly coupled central site. The resulting expressions are similar, and the analytical expressions derived from the continuous coordi- nate representation compare well with the results obtained from numerical simulations. The analytical expressions and the numerical results show that unlike the main …

Icosahedral Phase Stabilities In Al-Cu-Ru Alloys, Jeffrey E. Shield, C. Hoppe, R.W. Mccallum, A.I. Goldman, K.F. Kelton, P.C. Gibbons

Nebraska Center for Materials and Nanoscience: Faculty Publications

By examining a wide region of the Al-Cu-Ru phase diagram, a thorough analysis of the compositional and thermal stability of the icosahedral phase has been completed. The primary solidification product of rapid solidification was a topologically and chemically disordered icosahedral phase with an extensive compositional region. Crystallization through exothermic events of the as-solidified materials produced crystalline phases, without the formation of the face-centered-icosahedral (FCI) phase. However, the FCI phase does form at higher temperatures through an endothermic reaction, indicating that it is a stable phase of the system, but only at elevated temperatures. Of the alloys studied, the FCI phase …

Laser Bandwidth-Induced Fluctuations In The Intensity Transmitted By A Fabry-Perot Interferometer, Gerhard Klimeck, Daniel Elliott, M. Hamilton

Birck and NCN Publications

We have measured the power spectrum of the intensity Auctuations of light transmitted by a Fabry- Perot interferometer when the input field is the real Gaussian field. The real Gaussian field is a field characterized by real, random (Gaussian) amplitude Auctuations. The bandwidth of the real Gaussian field was varied, taking on values less than that of the interferometer, as well as greater. Comparisons of the measured spectra with calculated spectra are quite satisfactory. Of special interest is a feature in the spectra centered at the laser-interferometer detuning frequency.

Diffraction Studies On Ni-Co And Ni-Cr Alloy Thin Films, A. R. Sethuraman, R. J. De Angelis, P. J. Reucroft

Nebraska Center for Materials and Nanoscience: Faculty Publications

Alloy films of Ni-Co and Ni-Cr of compositional ratios 1:1, 1:3, and 3:1 deposited by vapor deposition were studied by Transmission Electron Microscopy (TEM) and X-Ray Diffraction (XRD). Results of TEM analysis on the Ni-Co alloy films indicated that the films were face-centered cubic (fee) in structure. XRD results confirmed the TEM observations. TEM analysis of Ni-Cr alloy films showed that the films were bodycentered cubic (bec) in structure. With increase in the Cr content more than 25%, the material contained a higher fraction of an amorphous phase. XRD studies provide limited information owing to the quasi-amorphous structure of the …

Automating Tolerance Synthesis: A Framework And Tools, Stephen C.-Y. Lu, Robert G. Wilhelm

Department of Mechanical and Materials Engineering: Faculty Publications

This paper describes CASCADE-T—a new approach to tolerance synthesis that uses a complete representation of the conditional tolerance relations that exist between features of a part under design. Conditional tolerances are automatically determined from functional requirements and shape information. Tolerance primitives based on the virtual boundary requirements approach to tolerance representation are composed to form more complex tolerance relationships. Artificial intelligence techniques, including a constraint network, frame-based system, and dependency tracking are used to support flexible and detailed computation for tolerance analysis and synthesis.

Nondestructive Detection Of An Undeserable Metallic Phase, T1, During Processing Of Alumnum-L Thumalloys, Otto Buck, David J. Bracci, David C. Jiles, Lisa J.H. Brasche, Jeffrey E. Shield, Leonard S. Chumbley

Department of Mechanical and Materials Engineering: Faculty Publications

A method is disclosed for detecting the T1 phase in aluminum-lithium alloys through simultaneous measurement of conductivity and hardness. In employing eddy current to measure conductivity, when the eddy current decreases with aging of the alloy, while the hardness of the material continues to increase, the presence of the T1 phase may be detected.

Microcomputer Based Digital Image Processing System Developed To Count And Size Laser-Generated Small Particle Images, K. D. Ahlers, D. R. Alexander

Department of Mechanical and Materials Engineering: Faculty Publications

A microcomputer-based digital image processing system has been developed to count and size laser-generated small particle images. Processing rates of 5 to 600 frames per minute were achieved by utilizing a real-time digital image processor. Particles from 7 to 700 µm in the plane of focus were counted and sized. A major emphasis in this work was to determine the basic problems and limitations involved with using a digital image processing scheme to accurately size particles. Areas that were investigated include the effect of the threshold level on measured particle size, particle boundary diffraction gray-level gradients, and geometric nonlinearities introduced …