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Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films

Issue 6 • Date Nov 1986

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Displaying Results 1 - 25 of 136
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • First principles investigation of chemisorption of moderately heavy atoms on semiconductor surfaces—bromine on silicon

    Page(s): 2441 - 2446
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    Self‐consistent field Hartree–Fock cluster investigations have been carried out for bromine atoms chemisorbed on Si (111) surface using 5, 14, and 27 atom clusters. For the first two clusters, both all‐electron and pseudopotential procedures have been used and the total energy curves as a function of adatom position have been found to compare very well. The third cluster has been studied by the pseudopotential procedure alone. For the five‐atom cluster which corresponds to the SiH3Br molecule, the Si–Br bond distance and 79Br quadrupole coupling constant (e2qQ) are obtained as 2.20 Å and 355.4 MHz, respectively, in very good agreement with the experimental values from microwave measurements of 2.21 Å and 346 MHz. For the surface chemisorbed system, we have studied the location of the bromine atom, the local density of states (LDOS), the frequencies and amplitudes of the Si–Br vibrations and the 79Br quadrupole coupling constant. The calculated Si–Br bond distance of 2.23 Å agrees very well with two experimental values of (2.22±0.01) and (2.17±0.04) Å available in the literature. For the vibrational amplitude, satisfactory agreement is found with the available result for Br on germanium surface. It is hoped that experimental data will become available in the future to test our predictions for the other properties. In particular, it would be desirable to have UPS data to compare with the interesting trends found in the LDOS curves in going from fluorine to chlorine to bromine and quadrupole interaction data to verify the significant decrease in e2qQ in going from the molecule to the surface‐adsorbed system. View full abstract»

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  • Hydrogen isotope sorption and recovery by a nonevaporable getter combined with a chemical compressor material

    Page(s): 2447 - 2451
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    Due to the spreading use of hydrogen isotopes in many advanced fields of physics such as nuclear fusion, there is an increasing interest in devices able to sorb, store, and release these gases safely and controllably. In some cases there is also the requirement to purify the gas during the same adsorption–desorption process. A way to obtain this is to use a nonevaporable getter, which is able to sorb H2 isotopes reversibly and permanently sorb active gases, combined with a chemical compressor material (usually U). The present investigation refers particularly to a combination of getter materials with chemical compressors based on La–Ni–Al and Zr–Fe–V alloys. The nonevaporable getter sorbs H2 isotopes in the temperature range of 20–400 °C, at low pressures, and in a second stage, on heating, releases these gases at higher pressures allowing sorption by the chemical compressor at room temperature. Subsequent heating (200–400 °C) of the compressor provides a hydrogen isotope source at a substantially constant pressure of around 1 atm. The characteristics of these compressor alloys in terms of isotope equilibrium pressure, physical–chemical properties, and their use at defined pressures and temperatures are discussed, together with anticipated practical operation modes. View full abstract»

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  • Surface processes leading to carbon contamination of photochemically deposited copper films

    Page(s): 2452 - 2458
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    Copper films exhibiting periodic microstructure have been grown by photolytic decomposition of bis‐(1,1,1,5,5,5‐hexafluoropentanedionate) copper (II) [Cu(hfac)2] and its ethanolate using ultraviolet light. The composition of the films has been analyzed by Auger spectroscopy as a function of cell temperature, precursor, mode of illumination (pulsed or continuous), and light intensity at nearly constant wavelength. The results show that the concentration of the principal contaminant of the films, carbon, is a function of cw light intensity. Addition of ethanol in the form of Cu(hfac)2(ethanol) also has a profound effect on carbon incorporation. Although the elements O and F are a large component of the gas phase copper complex, they are essentially absent from the films under all conditions. These data, when combined with high‐resolution analysis of the periodic structures on the films, provide information on surface photochemical and thermal processes likely to be important during film growth. They also allow a general comparison to be made between homogeneous and heterogeneous decomposition of Cu(hfac)2. View full abstract»

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  • An x‐ray photoelectron spectroscopy study of poly(methylmethacrylate) and poly(α‐methylstyrene) surfaces irradiated by excimer lasers

    Page(s): 2459 - 2462
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    X‐ray photoelectron spectroscopy (XPS) has been used to study the surface composition of poly(methylmethacrylate) (PMMA) and poly(α‐methylstyrene) (α‐MePS) following excimer laser irradiation at 193 nm. For fluence levels between 50 and 300 mJ/cm2, no surface compositional changes were observed after irradiation of PMMA. However, α‐MePS samples showed a decrease in aromatic character following irradiation, as indicated by the decrease in pi–pi* intensity in the C 1s region. View full abstract»

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  • A correlation of Auger electron spectroscopy, x‐ray photoelectron spectroscopy, and Rutherford backscattering spectrometry measurements on sputter‐deposited titanium nitride thin films

    Page(s): 2463 - 2469
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    Auger and electron spectroscopy for chemical analysis (ESCA) data of TiNx were analyzed as a function of film composition as established by Rutherford backscattering spectrometry (RBS). The overlap of the N(KVV) and Ti(LMM) Auger transitions necessitated the assessment of two methods previously proposed for the derivative spectra. These results were compared with peak height and peak area measurements (after background subtraction) of the well‐separated N(1s) and Ti(2p) ESCA photoemissions. Neither the Auger nor the ESCA N/Ti intensity ratios scaled linearly with the N/Ti compositional ratios determined by RBS, especially for low nitrogen content. This behavior most likely results from ion‐bombardment‐induced losses of nitrogen in those phases with dissolved nitrogen rather than from an increased satellite emission in the Ti(2p) spectra from the near‐stoichiometric nitride. In terms of precision and analysis speed, the Auger peak‐to‐peak quantification methods are preferred over ESCA quantification. In the near‐stoichiometric phase (N/Ti≊1), RBS analysis shows higher sensitivity to nitrogen compositional changes than either ESCA or Auger. View full abstract»

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  • Surface analyses of the CdSe0.65Te0.35/aqueous polysulfide interface in relation to its photoelectrochemical properties

    Page(s): 2470 - 2476
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    The photocorrosion of n‐Cd(Se,Te) electrodes, in potassium and cesium polysulfide solutions, is investigated by x‐ray photoelectron spectroscopy and Auger electron spectrometry. It is shown that Se and Te are exchanged with sulfur from the solution during photocorrosion, possibly via two separate mechanisms: (a) preferential bleaching of tellurium from the crystal matrix, and (b) uniform photocorrosion of the crystal as a whole. Photocurrent spectrum measurements which are presented suggest that a graded band gap is formed when tellurium is preferentially bleached out of the original Cd(Se,Te) crystal. It is shown that cesium is present on the electrode surface which may explain the negative shift of the flat band potential, i.e., increased open circuit voltage of the photoelectrochemical cell. This suggests that the cesium treatment could be used to increase the open circuit voltage of photovoltaic cells. View full abstract»

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  • The influence of substrate temperature on the optical losses of ZnS film

    Page(s): 2477 - 2481
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    Loss measurements in waveguide thin films are shown to exhibit a sensitive optical probe of surface and volume losses and thus of film quality. The high accuracy and sensitivity of this device was exploited for assessing the role of substrate temperature on the optical performance of ZnS films. In general, film losses tend to increase with substrate temperature. However, broad optima in losses are observed at 200 and 250 °C. A correlation between film structure and scatter losses as measured by the integrating sphere method with results of losses obtained from waveguide mode technique is discussed. This correlation leads to more reliable interpretation of the influence of substrate temperature on the losses of ZnS film. View full abstract»

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  • Surface morphology of chemical vapor deposition grown Ge on Ge substrates

    Page(s): 2482 - 2491
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    Geometrically defined Ge structures, projecting out from Ge surfaces deposited by a GeH4–He system on (100) Ge substrates, all oriented in the same direction and having a similar shape, are observed using scanning electron microscopy. They indicate the existence of an epitaxial layer–substrate relationship. Under the same growth conditions, but at short deposition periods, these projections are isolated, but as the growth time increases their lateral dimensions increase, the average distance between them decreases, and coalescence occurs. They are identified as local overgrowth, which yields a rough surface, and their origin is attributed to surface and deposition conditions. Morphometric measurements made by an image analyzer have shown the time dependence of these progressive changes. View full abstract»

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  • The determination of amorphous layer thickness in ion implanted silicon using secondary ion mass spectrometry

    Page(s): 2492 - 2498
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    Secondary ion mass spectrometry has been used to study boron‐doped Si[100] that was rendered amorphous by the implantation of 75As. Using oxygen bombardment and negative secondary ion detection, all secondary ion species show a shift in ion energy of greater than 2 eV upon sputtering through the amorphous layer and into the underlying crystalline silicon. After regrowth of the same specimens by rapid thermal annealing, the secondary ion energy shift occurs significantly deeper, at approximately the p–n junction. In both specimens, the energy shift was shown to be due to bombardment‐induced specimen charging. Thus, the thickness of the amorphous layer in the as‐implanted specimen can be determined by profiling with a narrow secondary ion energy window. Mechanisms for this effect are discussed. View full abstract»

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  • Properties of a‐Si,Ge:H,F alloys prepared by rf glow discharge in an ultrahigh vacuum reactor

    Page(s): 2499 - 2504
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    a‐Si1-xGex H,F alloys with the Ge concentration x ranging from 0 to 1 have been prepared by the rf glow discharge decomposition of SiF4, GeF4, and H2 gas mixtures. An ultrahigh vacuum deposition system has been designed and constructed for the preparation of these alloys. The stainless‐steel deposition chamber has Cu gasket‐sealed flanges, is turbomolecular pumped, and reaches a base pressure below 10-7 Torr (10-5 Pa). This deposition system incorporates a load lock which permits short pump‐down cycles and which may reduce impurity contamination of the films. The system is described in detail. Compositional, structural, optical, and electronic properties of alloy films made with this system are reported. View full abstract»

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  • Radio frequency‐plasma oxidation of fine‐grained Pb‐alloy films formed by codeposition at 90 K

    Page(s): 2505 - 2509
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    Oxidation characteristics of fine‐grained (30–50 nm) Pb‐alloy film formed by the codeposition of Pb, In, and Au onto a liquid‐nitrogen‐cooled substrate (∼90 K) were studied in comparison with conventional film of 200 nm grain size formed by the sequential deposition of Au, Pb, and In at room temperature. The oxidized films were examined by Auger electron spectroscopy as well as x‐ray photoelectron spectroscopy and ellipsometry, and the normal tunneling resistance of Josephson junctions fabricated using the above films as base electrodes was measured. The thermal oxides formed on the fine‐grained and conventional films are identical. Rf‐plasma oxidation with these thermal oxides also present results in oxides of identical structure and thickness. In the absence of the thermal oxides, rf‐plasma oxidation of the fine‐grained film leads to In‐rich oxides of smaller thickness compared to the conventional films. It seems reasonable to attribute these results to the difference in grain sizes, i.e., the smaller‐grained films offer the In more available paths to diffuse through the alloy film. When the thermal oxides are present, rf‐plasma oxidation rate is reduced such that the difference in the diffusion rate of In through the alloy film is not evident and identical oxide structure and thickness are obtained. View full abstract»

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  • Self‐positioned thin Pb‐alloy base electrode Josephson junction

    Page(s): 2510 - 2514
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    A self‐positioned thin (SPOT) Pb‐alloy base electrode Josephson junction is developed. In this junction, a 50‐nm thick Pb‐alloy base electrode is restricted within the junction region on an Nb underlayer using a self‐alignment technique. The grain size reduction and the base electrode area restriction greatly improve thermal cycling stability, where the thermal cycling tests of 4000 proposed junctions (5×5 μm2) showed no failures after 4000 cycles. In addition, the elimination of insulator layer stress on the Pb‐alloy base electrode rectifies the problem of size effect on current density. The Nb underlayers also serve to isolate the Pb‐alloy base electrodes from the resistors. View full abstract»

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  • Aluminum alloy ultrahigh vacuum system for molecular beam epitaxy

    Page(s): 2515 - 2519
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    As a research project for aluminum alloy molecular beam epitaxy systems, a large aluminum alloy chamber with a special surface finish was constructed. Its outgassing rate and ultimate pressure were measured. The special surface finish was analyzed using Auger electron spectroscopy. The oxide layer on the aluminum alloy was about 40 Å thick. The outgassing rate before baking was measured as 10-11 Torr l/s cm2, and the rate after baking (150 °C, 24 h) was 3×10-13 Torr l/s cm2. This value is approximately one to two orders of magnitude lower than that of a stainless‐steel chamber, such as SUS 304. The ultimate pressure was 7×10-11 Torr when pumped with a turbomolecular pump and an ion pump. With addition of the newly developed titanium sublimation pump, the ultimate pressure was 6×10-12 Torr (6.5×10-12 mbar). This ultimate pressure is very low for a large aluminum alloy vacuum chamber. Ceramic coating of SiO2 using a spark discharge in a silicate solution on aluminum alloy was not corroded by gallium. This ceramic treatment was suitable for an ultrahigh vacuum. View full abstract»

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  • Data analysis for particle balance studies on the axially symmetric divertor experiment

    Page(s): 2520 - 2525
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    Throughput of H2 or D2 fueling gas during and after a plasma discharge is a strongly time‐dependent quantity. Various data, such as divertor pressure and integral fueling rate, are used in a computer routine to investigate the particle balance on the axially symmetric divertor experiment (ASDEX). It is seen that the dominant portion of the gas required to fuel the plasma is reversibly pumped by the walls. This is due to the dissociation of molecules and subsequent strong wall adsorption of the resulting atoms. The amount of gas lost to the wall increases with plasma density. After the discharge most of the gas is released depending somewhat on the preconditioning of the walls by previous discharges and the time interval in between discharges. View full abstract»

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  • A three‐point‐pressure method for measuring the gas‐flow rate through a conducting pipe

    Page(s): 2526 - 2530
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    A new method for measuring the gas‐flow rate through an outgassing pipe has been introduced, in which the pressures at three different points in the pipe are measured to calculate the real gas‐flow rate. This method was applied to measuring the flow rate of nitrogen through a pipe. The gas‐flow rates calculated using three pressures were compared with those calculated using two pressures under the same condition. The method based on three pressures gave real rates which were higher than those based on two pressures, especially in lower pressure regions, thus indicating the presence of outgassing. View full abstract»

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  • An extended core‐hole Hamiltonian for a combined study of electron stimulated desorption and photoemission

    Page(s): 2533 - 2536
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    Recent developments (two‐hole states) in electron stimulated desorption (ESD) from adsorption systems involving d bands are incorporated into an extended valence‐hole model Hamiltonian which includes explicitly a short‐range Coulomb interaction between adsorbate and substrate. This allows a combined study of photoemission and ESD from the same model. A novel relaxation effect of the metal surface (different from surface plasmon screening) may have a strong effect on the intra‐adsorbate relaxation due to the valence hole and, therefore, on adsorbate–substrate charge transfer processes. View full abstract»

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  • TiN high temperature diffusion barrier for copper‐gasketed stainless‐steel flanges

    Page(s): 2537 - 2538
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    Klystrons manufactured at the Stanford Linear Accelerator Center are typically baked at temperatures of 550 °C for times as long as 200 h. During these long bakeouts the copper‐gasketed type 304 stainless steel flange joints (seven in all) diffusion bond so intimately that the flanges can be separated only with a jacking fixture, and copper is left on the sealing surfaces. Removal of this copper necessitates the use of abrasive materials, which can result in contamination of the klystron body and compromise its reuse. We report on the use of 50 and 150 Å TiN thin films as a diffusion barrier between the Cu gasket and the stainless‐steel flange. View full abstract»

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  • Evaluation of sputter ion plated CoCrAlY and NiCrAlTi coatings for gas turbines

    Page(s): 2557 - 2564
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    This paper highlights the potential of a simple dc sputtering process to deposit the complex MCrAlY overlay compositions onto the hot end components of gas turbines. Particular advantages of sputter ion plating technology include good control of coating composition, no need to rotate the components to be coated, and deposition in a clean environment. The effect of peening on coating microstructure and the subsequent oxidation behavior of the coating has been examined for a range of MCrAlY compositions. Peening serves to eliminate leader defects from the surface layers by compaction of the coating and also affects the oxide‐growth mechanisms. The surface roughness of the sputter ion plating coatings, both as deposited and after glass bead peening, increases with that of the substrate and compares favorably with published values for electron beam evaporated coatings. For coatings tested between 1020 °C and room temperature in a heat treated and peened condition, fatigue cracks occurred after 100–150 cycles, while for peened and heat treated coatings, the time to crack initiation was extended to 800 cycles. Results from engine endurance trials are also summarized. View full abstract»

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  • Titanium distribution in multilayer oxide scales on oxidized INCOLOY 800H

    Page(s): 2565 - 2570
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    Different samples of INCOLOY 800H were exposed up to 950 °C and 10 000 h to a gas atmosphere simulating exposure to steam reforming methane process gas. The results indicated the predominant role of titanium in the formation of the main reaction products. The influence of titanium could be described by the following modifications of the primary oxide phases: (1) changing the lattice parameters of Cr2O3 by small amounts of Ti, (2) formation of solid solution of the spinels MnCr2O4 and Mn2TiO4, and (3) existence of an additional Ti containing phase of ilmenite type. Furthermore, it was observed that (1) manganese was practically insoluble in the Cr2O3 and (2) after long annealing time manganese was lost. View full abstract»

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  • Structure and 700 °C hot corrosion behavior of chromium modified platinum–aluminide coatings

    Page(s): 2571 - 2576
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    It is well known that the addition of chromium to coatings on nickel‐base superalloys improves the hot corrosion resistance of the coating. Recognizing this advantage, the low‐temperature (700 °C) hot corrosion (LTHC) testing of chromium modified platinum aluminides was initiated in order to determine whether combined additions of Cr and Pt were even more beneficial. The substrates chosen were IN100 and IN738, two commercially used nickel‐base superalloys. It was found that the structure of the chromium modified platinum–aluminide coating was dependent on the sequence of modifying element addition. The optimum coating for LTHC resistance was obtained by the Cr–Pt–Al deposition sequence which resulted in a coating with a continuous PtAl2 layer on the surface backed up with a fairly high level of Cr and Pt. View full abstract»

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  • The oxidation behavior of some FeCrAlY, FeCrAl, and yttrium ion‐implanted FeCrAl alloys compared and contrasted

    Page(s): 2577 - 2582
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    The 1050 °C oxidation behavior of an iron–25 wt. % chromium–4 wt. % aluminum alloy modified by yttrium additions was studied. Yttrium was added to this alloy in the form of (1) a metallic addition; (2) an ion implant; and (3) as yttrium sulfide. In agreement with other investigators, metallic yttrium additions effected thin, essentially flat adherent scales. As compared with the base line alloy without any yttrium, implantation did improve the resistance of the scale to cracking. However, highly convoluted scales resulted with the yttrium implants. When yttrium was added as the sulfide, scales were produced similar to those found when no yttrium was added to the alloy. For the base line alloy without yttrium additions, aluminum oxide protrusions (or pegs) developed at the base of the alumina scales. Despite this, the scales were clearly cracked and poorly adherent. In the yttrium‐containing alloy, indigenous sulfur was present in the form of precipitates associated with yttrium. View full abstract»

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  • High‐temperature behavior of different coatings in high‐performance gas turbines and in laboratory tests

    Page(s): 2583 - 2592
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    Turbine blades of advanced engines are often subject to a surface attack caused by oxidation or hot corrosion. Typical features of the different modes of high‐temperature surface attack are presented using results of failure analysis of turbine parts and of laboratory experiments. At very high temperatures, interactions take place between the coatings, which are indispensable in this temperature range, and the base metal. Some examples are described that have been gained from cyclic oxidation tests with a nickel‐base single‐crystal alloy and different types of coatings. The development of a broad diffusion zone and the depletion of β phase of the coatings indicate that interdiffusion plays an important role in determining the coating life. In a particular temperature range platelike phases precipitate in the matrix close to the coating. Kirkendall porosity, which frequently occurs at the coating substrate interface at very high temperatures, can markedly reduce the adhesive strength. The behavior of coated parts under mechanical loading is influenced by the coating–substrate combination. Some examples are shown describing creep and thermal fatigue properties of coated components. View full abstract»

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Aims & Scope

The Journal of Vacuum Science and Technology A is devoted to reports of original research, review articles, and Critical Review articles.

Full Aims & Scope

Meet Our Editors

Editor
G. Lucovsky
North Carolina State University