Correlation of stress and atomic-scale surface roughness evolution during intermittent homoepitaxial growth of (111)-oriented Ag and Cu

Stress evolution during intermittent homoepitaxial growth of (111)-oriented Cu and Ag thin films has been studied. A tensile stress change is observed when growth is stopped, but the change is reversed when growth is resumed. Reflection high energy electron diffraction analysis of the atomic scale surface roughness during intermittent growth demonstrates a strong correlation between the surface structure and reversible stress evolution. The results are discussed in terms of an evolving surface defect population.     

Effect of the Radiation Power Density on the Sensitivity of a Diamond Detector

This paper presents the results of an experimental study of the sensitivity of a detector made of natural diamond of the IIa type as a function of the power density of the radiation of a pulsed xenon lamp. It has been shown that the sensitivity of the detector depends on the power density of the xenon lamp radiation and equals about (1–6)·10^–4 A/W. A monotonic decrease in sensitivity of the detector during a radiation pulse has been detected. The minimum resistance of the diamond crystal with an irradiated face of area 3 mm², placed 7 mm away from the axis of the xenon lamp, was 300 , which corresponds to a specific conductivity of 2.2 ^–1·m^–1.     

Analysis of HRTEM images for carbon nanostructure quantification

Image processing algorithms have been developed to extract fringe length, tortuosity and separation from high resolution transmission electron microscopy images. To validate the separation algorithm, a comparison is made between the image-based fringe separation and that obtained by analysis of X-ray diffraction data for a progressively heat-treated carbon black. Agreement is favorable. To illustrate the utility of the analysis parameters for a range of carbon nanostructures, analysis is applied to a series of pyrolytically prepared carbon soots – qualitatively described as containing amorphous, graphitic or fullerenic nanostructure. For all processing, the intermediate image, in the form of a skeletonized binary image of the original high resolution transmission electron micrograph, is shown and found to accurately reflect the nanostructural organization within the carbon as visually observed. Statistical results for each analysis parameter, extracted from the binary images, are presented in the form of histograms and quantitatively distinguish the different carbon nanostructures.     

Organometallic complexes as hole-transporting materials in organic light-emitting diodes

The use of metal complexes fac-tris(1-phenylpyrazolato-N,C(2)('))cobalt(III) [fac-Co(ppz)(3)], fac-tris(2-phenylpyridinato-N,C(2)(') cobalt(III) [fac-Co(ppy)(3)], and [tris[2-((pyrrole-2-ylmethylidene)amino)ethyl]amine]gallium(III) [Ga(pma)] as materials for hole-transporting layers (HTL) in organic light-emitting diodes (OLEDs) is reported. Co(ppz)(3) and Co(ppy)(3) were prepared by following literature procedures and isolated as mixtures of facial (fac) and meridional (mer) isomers. The more stable fac isomers were separated from the unstable mer forms via column chromatography and thermal gradient sublimation. Crystals of fac-Co(ppz)(3) are monoclinic, space group P2(1)/c, with a = 13.6121(12) A, b = 15.5600(12) A, c = 22.9603(17) A, beta = 100.5 degrees, V = 4781.3(7) A(3), and Z = 8. [Tris[2-((pyrrol-2-ylmethylidene)amino)ethyl]amine]gallium [Ga(pma)] was prepared by the reaction of gallium(III) nitrate with the pmaH(3) ligand precursor in methanol. Ga(pma) crystallizes in the cubic space group I3d with cell parameters a = 20.2377(4) A, b = 20.2377(4) A, c = 20.2377(4) A, beta = 90.0 degrees, V = 8288.6(3) A(3), and Z = 16. These cobalt and gallium complexes are pale colored to colorless solids, with optical energy gaps ranging 2.6-3.36 eV. A two-layer HTL/ETL (ETL = electron-transporting layer) device structure using fac-Co(ppz)(3) and fac-Co(ppy)(3) as the HTL does not give efficient electroluminescence. However, the introduction of a thin layer of a hole-transporting material (N,N'-bis(1-naphthyl)-N,N'-diphenylbenzidine, NPD) as an energy "stair-step" and electron/exciton-blocker dramatically improves the device performance. Both fac-Co(ppz)(3) and fac-Co(ppy)(3) devices give external quantum efficiencies higher than 1.0%, with brightness 5000 and 7000 Cd/m(2) at 10 V, respectively. Ga(pma) also functions as an efficient interface layer, giving device performances very similar to those of analogous devices using NPD as the interface layer. Stability tests have been carried out for Co(ppz)(3)/NPD/Alq(3) and Co(ppy)(3)/NPD/Alq(3) devices. While fac-Co(ppy)(3) gave stable OLEDs, the fac-Co(ppz)(3)-based devices had very short lifetimes. On the basis of the experimental results of chemical oxidation of fac-Co(ppz)(3), the major cause for the fast decay of the fac-Co(ppz)(3) device is proposed to be the decomposition of fac-Co(ppz)(3)(+) in the HTL layer during the device operation.     

Improved convergence in block copolymer self-consistent field theory by Anderson mixing

A modification to real space polymeric self-consistent field theory algorithms that greatly improves the convergence properties is presented. The method is based on Anderson mixing [D. G. Anderson, J. Assoc. Comput. Mach. 12, 547 (1965)], and each iteration computed takes negligibly longer to perform than with other methods, but the number of iterations required to reach a high accuracy solution is greatly reduced. No a priori knowledge of possible phases is required to apply this method. We apply our approach to a standard diblock copolymer melt, and demonstrate iteration reductions of more than a factor of 5 in some cases.     

Improving resolution for channel-format chip-based electrophoresis with electrochemical array detection

Resolution in channel electrophoresis has been improved by means of the addition of a surfactant to the running buffer and minimization of the channel internal height and sampling capillary internal diameter. Micellar electrokinetic channel chromatography with electrochemical detection has been applied to the separation of several cationic catecholamines and has been used to continuously monitor a dynamic system of dopamine, norepinephrine, and epinephrine. Resolution was also enhanced by coupling small internal-diameter (5 microm) sampling capillaries with sub-micrometer internal-height separation channels. The improvements in resolution offered by these methods will extend the applicability of channel electrophoresis with electrochemical detection to more complex samples while permitting sample volumes in the nL range to be probed.     

Protein microarray scanning in label-free format by Kelvin nanoprobe

Surface-immobilized protein species deposited in the microarray format have been detected by time-of-flight secondary ion mass spectrometry and by scanning Kelvin nanoprobe. The former method was used to examine the nature of protein deposition on amine-coated glass slides and gold substrates in preparation for Kelvin measurements. Both gallium and SF(5)(+) ion sources were employed to produce positive and negative ion spectra of amino acids and polypeptides. Scanning Kelvin technology has been used to detect antibody-antigen interactions in a label-free protocol through measurement of the surface potential of the biochemical pair on indium tin oxide, amine-treated slides and gold substrates. The results show that good inter-spot reproducibility can be achieved and that deposited areas can be examined for homogeneity at 100 nm resolution. This work represents the first report on surface potential detection in protein microarray technology.     

Broadband sound propagation in shallow water and geoacoustic inversion

Part of an experiment to test a measurement package in a shallow water region in the Gulf of Mexico was designed to gather broadband acoustic data suitable for inversion to estimate seabed geoacoustic parameters. Continuous wave tow acoustic signals at multiple frequencies and broadband impulsive source signals were recorded on a horizontal line array in a high-noise environment. Simulated annealing with a normal mode forward propagation model is utilized to invert for a geoacoustic representation of the seabed. Several inversions are made from different data samples of two light bulb implosions, the measured sound speed profiles at the HLA and at the positions of the light bulb deployments, and for two different cost functions. The different cost functions, measured sound speed profiles, and measured time series result in different inverted geoacoustic profiles from which transmission loss is generated for comparison with measurements. On the basis of physical consistency and from the comparison of the transmission loss and time series, a best estimate geoacoustic profile is selected and compared to those obtained from previously reported inversions. Uncertainties in the sound speed profile are shown to affect the uncertainties of the estimated seabed parameters.     

A combined 14N/27Al nuclear magnetic resonance and powder X-ray diffraction study of impurity phases in beta-sialon ceramics

Beta-sialons are ceramic phases occurring in the SiO(2)-Si(3)N(4)-AlN-Al(2)O(3) system. A series of samples with differing compositions has been investigated by magic-angle spinning nuclear magnetic resonance (NMR) spectroscopy and powder X-ray diffraction (XRD). Although the constituent nitrogen nuclei occupy positions of low symmetry in the beta-sialon structure, 14N NMR spectra could be recorded for the samples examined. The origin of the 14N signal could be traced to the presence of an aluminium nitride (AlN) impurity phase with the help of 27Al NMR and XRD results. Similarly, the existence of Al(2)O(3) grains could be readily detected for a number of samples. Thus, the combination of 14N and 27Al NMR is shown to be an especially effective tool in identifying and characterizing impurity phases in sialon ceramics, complementing the results obtained from standard XRD analysis.     

Effects of applied DC/AC fields in electrical fixing process with SBN:60

We present experimental investigations of electrical fixing techniques in Ce:SBN:60. The effect of crystal fatigue on the diffraction efficiency of electrically fixed photorefractive gratings is studied. We observed that applying an ac field to the crystal eliminated crystal fatigue and improved diffraction efficiency. A controllable diffraction efficiency of a photorefractive grating is presented. A reproducible diffraction efficiency of up to 75% is obtained using a write-reveal grating technique with high-voltage pulses of opposite polarity. We also show that the diffraction efficiency can be controlled by varying the intensity of the writing beams incident to the crystal during the recording process. A method of determining the hysteresis loop using the domain-fixing technique is proposed. The dependence of the diffraction efficiency on the direction of the applied electric field while writing the hologram is studied. Our experiments show that, during writing, when the electric field is applied opposite to the c axis the grating can be successfully revealed with both positive and negative dc voltages. However, when the grating is written with a field parallel to the c axis, the grating can be revealed only with a field applied in the opposite direction. Received: 28 October 2002 / Revised version: 28 February 2003 / Published online: 14 May 2003 RID="*" ID="*"Corresponding author. Fax: +1-812/872-6167, E-mail: azad.siahmakoun@rose-hulman.edu