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

Issue 2 • Date Mar 1988

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Displaying Results 1 - 25 of 91
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Ion mixing of Al2O3 and Al films on SiO2

    Page(s): 185 - 192
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    The influence of ion implantation on the interfacial chemistry, morphology, and adhesion of Al and Al2 O3 films on SiO2 was examined. The specimens were implanted with varying doses of 131 Xe+ and 84 Kr+ at different substrate temperatures (2×1016 Xe cm-2 at 130 °C, 1×1017 Kr cm-2 at 70 °C, and 1×1017 Kr cm-2 at 350 °C). These implanted specimens were compared to Al/SiO2 and Al2 O3 /SiO2 specimens vacuum annealed at 600 and 1000 °C, respectively. Unlike thermal processing, ion implantation induced substantial interfacial mixing and adhesion enhancement in both the Al2 O3 /SiO2 and Al/SiO2 specimens. Interfacial mixing and adhesion enhancement increased with ion dose. The adhesion increases (3–25×) were attributed primarily to interfacial Si–O–Al bonding. Interfacial bonding (adhesion enhancement) was promoted most extensively by implants which produced glassy interfacial mixtures. Implants that induced crystallization, resulting in phase separation, produced less extensive interfacial bonding. The 131 Xe+ and 84 Kr+ implants resulted in bubble, void, dendrite, and crack formation. Characterization was performed using Auger electron spectroscopy, x‐ray photoelectron spectroscopy, scanning electron microscopy, and x‐ray diffraction. Film adhesion was examined using a scratch test. View full abstract»

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  • Interaction of atomic hydrogen with cleaved InP. I. The adsorption stage

    Page(s): 193 - 198
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    The interaction of atomic hydrogen with the (110) face of InP, prepared by cleavage under ultrahigh vacuum, has been studied by Auger electron spectroscopy, electron energy‐loss spectroscopy, low‐energy electron diffraction, and photoemission yield spectroscopy. The interaction occurs in two stages: first, an adsorption of H, then a decomposition of the substrate. The adsorption stage is characterized by the covalent bonding of, most likely, one H atom per surface unit cell which induces a change in the surface reconstruction of the substrate, the surface unit mesh remaining 1×1. A hydrogen‐induced surface state band, about 0.26 eV wide, is observed around 0.06 eV below the valence‐band edge. Upon H adsorption, the Fermi level gets pinned in the gap at about 0.4 eV below the conduction‐band edge on both n‐ and p‐type samples, while the ionization energy decreases, the decrease reaching 0.35 eV at saturation. View full abstract»

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  • Interaction of atomic hydrogen with cleaved InP. II. The decomposition stage

    Page(s): 199 - 203
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    Auger electron spectroscopy, electron energy‐loss spectroscopy, low‐energy electron diffraction, and photoemission yield spectroscopy have been used to study the interaction of atomic hydrogen with cleaved InP(110) upon heavy hydrogenation. Beyond the initial adsorption stage, the substrate dissociates into In metal and possibly two hydrogenated compounds of P, among which most likely phosphine PH3, which remain adsorbed on the surface. This interaction stage is characterized by the existence of the ‘‘black hole’’ phenomenon in photoemission yield spectroscopy, i.e., the complete disappearance of the photoemission signal at 5.3 and ∼5 eV, photon energies specific of the adsorbed species. The hydrogenated compounds desorb upon heating at 525 °C leaving a surface close to its H‐adsorbed state. From there on, the properties of the surface can by cycled by, alternately, introducing a new heavy dose of H and annealing. View full abstract»

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  • Oxygen effect on secondary ion emission of impurities in GaAs

    Page(s): 204 - 209
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    To investigate quantitatively the effect of oxygen on the ion yields in secondary ion mass spectrometry (SIMS) analysis of impurities in GaAs, oxygen‐implanted GaAs crystals were prepared. Oxygen‐induced ion yield enhancement was demonstrated by the SIMS analysis of these oxygen‐implanted GaAs crystals. B, Cr, Cu, and Mn in these crystals were found to have impurity ion yields 50 times larger than those without oxygen under Ar+ bombardment. The ion yield enhancement of impurities by oxygen has been interpreted by treating ion yields as a function of oxygen fraction, i.e., probability of occupying the adjacent site to the impurities by oxygen atoms. For oxygen fractions, the local thermodynamic equilibrium calculations were carried out to obtain T parameters which enable the impurity ion yields to be estimated only by ionization potentials if the oxygen fraction is given. View full abstract»

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  • Evidence for oxygen underlayer formation at near‐liquid‐nitrogen temperatures on Zr(0001)

    Page(s): 210 - 212
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    When a clean Zr(0001) crystal is exposed to oxygen at 82 K, the work function initially decreases by ∼250 mV for an exposure of 0.7 to 0.8 L. Annealing this surface to ∼550 K produces a further decrease in work function of ∼300 mV, and a ‘‘(2×2)‐like’’ low‐energy electron diffraction pattern is observed. The initial decrease in work function upon oxygen adsorption at 82 K is believed to be due to oxygen incorporation into the Zr lattice. View full abstract»

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  • Secondary ion mass spectrometry depth profiling of Mo/SiO2/Si structural samples

    Page(s): 213 - 216
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    This report describes the influence of surface roughness resulting from the Mo film sputter process on oxygen profiles of the thin SiO2 interlayer in an Mo/SiO2/Si structural sample. The sputter‐induced surface roughness causes expansion of oxygen profiles. The expansion increases as the Mo grain size increases. This is why the original surface roughness of an Mo film deposited on an SiO2 surface is almost all proportional to Mo grain size (20–300 nm) and why the sputter‐induced surface roughness is developed by the original Mo surface roughness. The relation between sputter‐induced inexactness resulting from the Mo film sputter process and an expanded oxygen profile of the thin SiO2 interlayer is obtained. The Mo grain size is controlled by postdeposition heat treatment (800–1100 °C). View full abstract»

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  • Morphological and structural features of Cu seed cones

    Page(s): 217 - 222
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    Morphologies and structures of surface cones formed on polycrystalline Cu targets seeded with Mo were surveyed by means of high‐resolution electron microscopy. The sputtering of the target with a focused Ar+‐ion beam generated Cu cones having diversified configurations and crystalline states, obviously reflecting an intricate mechanism of cone evolution. Some of the cones observed were characterized by an amorphouslike structure, commonly grown at the apex areas, and Mo was never detected from coned areas. These findings strongly suggest that the role of Mo seeds was to nucleate cones, and that the direct supply of sputtered Cu atoms to the cone nucleation sites interplayed with the ion‐etching process so as to develop the nucleated cones. View full abstract»

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  • Current–voltage relations in magnetrons

    Page(s): 223 - 229
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    The current–voltage relationship in a magnetron plasma appears to be strongly dependent on the dynamics of the sputtered particle–gas atom interaction. Large fluxes of energetic (several eV) sputtered atoms from the cathode heat the gas in the near cathode region, resulting in a significant reduction in the local gas density as a function of discharge current (and hence particle flux). This reduction in gas density results in a lower rate of ion formation, and hence a more resistive plasma. Thus, the rate of voltage increase with current in a magnetron is related to the magnitude of the gas density rarefaction, which is dependent on the cathode sputter yield, sputtered atom energy, the cross section for sputtered atom–gas collisions, the molecular velocity of the gas, and the gas density. A model has been developed which describes the observed rate of voltage increase in a magnetron as a function of this thermalization process. View full abstract»

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  • Characterization and thermal desorption spectroscopy study on a new, low outgassing material surface for improved ultrahigh vacuum uses

    Page(s): 230 - 234
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    The surface of an austenitic stainless steel doped with N, B, and Ce (SUS304‐NBCe), which was covered with thin BN precipitated layers, has been characterized using Auger electron spectroscopy (AES), Fourier transform infrared, transmission electron microscopy, transmission electron diffraction (TED), and reflection high‐energy electron diffraction (RHEED) techniques. Thermal desorption spectroscopy method was also applied for evaluating its outgassing nature. AES spectra obtained from the BN precipitated layers coincided well with those of a hexagonal BN even in fine structures of B(KLL) and N(KLL) Auger transitions. RHEED and TED patterns obtained from them showed that the structure of the BN layer was hexagonal and that the c axis preferred to be parallel to the surface normal. That is to say, the basal plane of the hexagonal BN, which is more inert to adsorption than other planes are, preferred to cover the surface. The outgassing nature of the above surface has been measured and compared with two other types of stainless‐steel surfaces such as an electropolished surface and a S segregated one. Among the three, the amount of desorbed gases from the BN covered surface was the lowest on heating up to 800 °C. The potential of the BN precipitated surface for UHV vessels with low outgassing is pointed out. View full abstract»

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  • Proposal for a sensitive leak test telescope

    Page(s): 235 - 237
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    A proposal for an in‐vessel movable leak sensor, called a leak test telescope, is described for leak localization inside two of the largest thermonuclear fusion devices (TFTR and JET). To improve sensitivity and source identification beyond the present state of the art, a differential sensor head employing two actively pumping collimators, a continuously rotating shutter, and a quadrupole mass spectrometer as sensor is proposed. With the use of phase‐lock signal processing this detector should be capable of detecting a leak of 1×10-6 Torr l/s from a distance of 0.5 m in a typical fusion environment with backgrounds ≫1×10-7 Torr deuterium–tritium. View full abstract»

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  • Rotary pump backstreaming: An analytical appraisal of practical results and the factors affecting them

    Page(s): 238 - 242
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    Useful data on the backstreaming of vapors from oil sealed rotary pumps have been obtained by a number of workers using quartz‐crystal microbalance techniques. The interpretation of results obtained using this method is complicated by the heterogeneous nature of the pump fluids, arising mainly from degradation of oil in the pump mechanism, and by the large vapor pumping speed of the cold finger on which the quartz crystal is mounted. The work described here attempts to separate the factors involved and to quantify their effects. The results obtained support a proposed model of the vapor atmosphere of which the most significant feature is the limited production rate of degraded oil products. It is shown that the significance of backstreaming rates, measured using a cooled quartz crystal, is strongly dependent on the experimental arrangement. View full abstract»

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  • Reactively sputtered TeOx thin films for optical recording systems

    Page(s): 243 - 245
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    Tellurium suboxide (TeOx ) thin films have been obtained by rf reactive sputtering deposition by using a Te target and an Ar–O2 gas mixture. Different samples were prepared by changing both the rf power (80–200 W) and the oxygen concentration in the sputtering gas. The transmissivity and the reflectivity of these films change markedly by thermal treatment at critical temperatures in the range 120–150 °C. This property makes these films suitable for optical disk recording with a low‐output power laser diode. View full abstract»

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  • Studies of superconductors using a low‐temperature, high‐field scanning tunneling microscope

    Page(s): 259 - 262
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    We have developed a scanning tunneling microscope (STM) capable of operating at temperatures as low as 0.4 K and fields as high as 8 T. We have used this STM to study the energy gap of the high‐Tc superconductors La–Sr–Cu–O and Y–Ba–Cu–O. We find that the reduced gap for these oxide superconductors falls in the range 3≪2Δ/kBTc≪7, for polycrystalline, single‐crystal, and thin‐film samples. We have also simultaneously imaged the surface topography and superconducting energy gap for thin films of the granular superconductor NbN. We occasionally see regions with smaller best‐fit gaps that correlate with surface topographical features, but have been unable so far to image flux vortices. View full abstract»

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  • Detection of vortex motion in a type‐II superconductor by tunneling

    Page(s): 263 - 265
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    A tunnel junction with adjustable barrier width was made using superconducting electrodes, one of which was a niobium tip and the other a niobium sheet. Quasiparticle tunneling characteristics with normal‐state resistances of the order of 102 to 105 Ω could be obtained. When operating in the constant current mode a clearly visible modulation of the gap voltage was observed associated with the passing of vortices across the junction. While these observations indicate the possibility of scanning tunneling microscopy of vortices at rest, we report here on local investigations of vortex motion using constant tip position. The gap modulation signal was analyzed using its autocorrelation function. View full abstract»

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  • Atomic force microscopy using optical interferometry

    Page(s): 266 - 270
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    An atomic force microscope using optical interferometry as the lever detection method is presented. Topographic images of graphite with 50‐Å lateral resolution have been obtained using repulsive contact forces. Images of the graphite surface showing the atomic periodicity were also recorded; in this case, the image contrast does not represent surface topography, but rather variations in the lateral frictional force on the tip. Images using attractive electrostatic forces to map topographic features are shown. The instrument has also been operated as a scanning tunneling microscope while simultaneously measuring the contact force between the tip and a graphite surface. View full abstract»

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  • Atomic resolution with the atomic force microscope on conductors and nonconductors

    Page(s): 271 - 274
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    The atomic force microscope (AFM) has achieved atomic resolution on nonconducting as well as electrically conducting surfaces, opening a new class of materials to atomically resolved surface imaging. Images of boron nitride (a nonconductor) reveal that AFM can distinguish different atomic species. AFM images of molybdenum disulfide and graphite are also presented. Graphite AFM images appear identical to images obtained by scanning tunneling microscopy (STM), although AFM and STM probably respond to different atomic sites on the graphite surface. Microfabrication procedures for constructing low‐mass force‐sensing cantilevers are discussed. View full abstract»

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  • Atomic force microscopy: General aspects and application to insulators

    Page(s): 275 - 278
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    Atomic force microscopy (AFM) has been proposed to map the force of interaction between the sample and a sharp tip. For the first time atomic resolution imaging of nonconducting surfaces is possible. Our aim is to apply the atomic force microscope to a variety of materials. We have realized two designs with different approach mechanisms. The force sensing lever is prepared from a piece of metal foil which is electrochemically etched at one end to form a sharp tip. Two different modes of measurement are discussed. Lateral resolution of 2.5 Å has been obtained on noncrystalline quartz. Images of LiF and of optical lenses are presented. View full abstract»

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  • Application of atomic force microscopy to magnetic materials

    Page(s): 279 - 282
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    A new method of imaging the surface on a submicron scale is described and the observation of magnetic domain walls presented. Measurements in air on Co–Ni recording media and rapidly quenched Fe–Nd–B are shown. A resolution of better than 10 nm is achieved. This magnetic microscope is based on the idea of measuring magnetic forces with the recently developed atomic force microscope (AFM). Forces acting on a tip are recorded by the measurement of the deflection of a lever to which this tip is attached. The lever is made from a metallic foil with an integrated, electrochemically etched tip. Different measurement modes of the magnetic microscope are described. The images obtained by the AFM using a para‐ and ferromagnetic force sensor and by the STM are compared. Furthermore, results are compared with previous studies by the scanning electron microscope with polarization analysis and the Lorentz electron microscope. Finally, a concept is presented by which magnetic, topographic, and chemical information is simultaneously acquirable. View full abstract»

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  • Scanning tunneling microscopy and atomic force microscopy of the liquid–solid interface

    Page(s): 283 - 286
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    The liquid–solid interface is important not only for science, but also for technology. Scanning tunnel microscopes (STM’s) and atomic force microscopes (AFM’s) can image and even manipulate solids covered with liquids. An image of a line 75 nm long and 5 nm wide drawn with an STM on a liquid‐covered Au(111) surface demonstrates the potential for manipulating surfaces. Images of a Pt film demonstrate the ability of STM’s to find new features by zooming from large‐area scans down to the atomic scale. Finally, an AFM image of a liquid‐covered graphite surface demonstrates atomic resolution. View full abstract»

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  • Atomic resolution atomic force microscopy of graphite and the ‘‘native oxide’’ on silicon

    Page(s): 287 - 290
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    An atomic force microscope (AFM) can image surfaces of conductors, insulators, and even organic materials. Images of highly oriented pyrolytic graphite show atomic structure with a corrugation height of 0.03 nm. Images of the ‘‘native oxide’’ layer grown in ambient pressure on a (111) facet on a (100) silicon wafer show steps. Images of the native oxide layer on a (111) silicon wafer show features 0.6 nm apart and aligned with the silicon substrate. The images shown here were obtained with an instrument that can also operate as a scanning tunneling microscope (STM); it is an AFM/STM. View full abstract»

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  • Experimental study of forces between a tunnel tip and the graphite surface

    Page(s): 293 - 295
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    Forces between a scanning tunneling microscope (STM) tip and graphite surface are studied in air by use of a cantilever beam as the conducting tip holder and another tunnel tip as a detector for the deflection of the beam. The results show that the STM tip usually operates under the strong repulsive force. The measured force changes according to the topographic corrugations in the standard topographic mode: however, the change is not observed in the current‐imaging mode. 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