bluuebunny/crossref_metadata_2025 huggingface dataset:
Electronic Quantum Effects in Small Particles
Authors: Knight W. D.
Published: July 2002

Theoretical predictions are summarized for the electronic energy levels and magnetic resonance behavior of small metallic particles containing a few thousand atoms or less. Spin pairing in particles containing an even number of electrons is observed by NMR for lithium and aluminum, which follow the orthogonal case. Copper, which follows the symplectic case, appears to exhibit spin orbit coupling of intermediate strength, giving rise to incomplete spin pairing at absolute zero. Observations of odd particle effects are reported for the above metals, and narrow CESR lines for small particles of lithium indicate partial quenching of surface scattering of the conduction electrons. Nuclear spin relaxation measurements on aluminum show effects of superconductor fluctuations. Relaxation measurements in copper are obscured by paramagnetic impurities. Some NMR linewidths appear to result primarily from paramagnetic impurities and RKKY spin density oscillations, which are quenched when spin pairing occurs, with corresponding decrease in linewidth below a critical temperature.
The effect of magnetic fields on substrate temperature and film texture in an rf sputtering system
Authors: Paradis E. L.
Published: July 2002

Data are presented which show that the substrate temperature in a sputtering system can be greatly affected by the shape and strength of an imposed magnetic field. Deposition rate, thickness uniformity, and surface texture of the film are also affected by the fields. A sputtering system is described in which low substrate heating, uniform deposition over a reasonable area, and smooth film growth are simultaneously achieved with a particular magnetic field configuration. The role of the magnetic field is discussed.
Effects of fluorocarbon polymer deposition on the selective etching of SiO2/photoresist in high density plasma
Authors: Chu Changwoong , Ahn Taehyuk , Kim Jisoo , Jeong Sangsup , Moon Jootae
Published: July 2002

A new periodic two-step process composing SiO2 etching with high bias radio frequency (rf) power and fluorocarbon deposition with low bias rf power was studied for the highly selective etching of SiO2 to photoresist (PR). In this experiment, the time scale of each step is longer than the conventional time-modulation technique in order to maximize the protection layer on PR and prevent the etch stop. Many works have focused on the gaseous chemical species especially CF2 radicals for selective surface reaction. However, normally utilizing only the difference of stoichiometric surface reaction, they inherently limit the etching conditions such as dependence on the chemical composition of PR, densities, and impurities of SiO2 layers. And these conventional processes severely suffer reactive ion etching lag or etch stop in high selective etching. The new process utilizes fluorocarbon deposition with low bias rf power to increase the mask selectivity by enhancing the difference between the polymer thickness on the mask and that on the bottom surface of hole. After the etching step, the polymer film remains only on the mask, and then the higher selectivity of SiO2 to PR can be achieved. In this article it has been investigated whether the polymer deposition in the suggested process is governed by aspect ratio of holes, surface temperature, bias rf, and microwave powers. The ratio of the amount of etching to deposition is a very important factor in determining the selectivity. With the process a small and deep contact etching with thin PR is possible without shortage of mask thickness with the mask selectivity improved from 6 to 20. We can also find that the etch rate of this new process does not depend significantly on the aspect ratio.
Investigation of low-pressure elevated-temperature plasma immersion ion implantation of AISI 304 stainless steel
Authors: Tian Xiubo , Chu Paul K.
Published: July 2002

Elevated-temperature plasma immersion ion implantation can be used to improve the surface properties of austenite stainless steels. Unlike previous investigations conducted using radio frequency plasma at a moderate gas pressure (0.1–0.5 Pa), we recently conducted a series of experiments at lower pressure (∼0.06 Pa) utilizing nitrogen plasma sustained by hot filament glow discharge. The implantation voltage was varied from 8 to 25 kV and the sample temperature was kept at 360 °C by adjusting the implantation current density. To elucidate the mechanism and dynamics of the process, the treated samples were characterized by Auger electron spectroscopy and Rutherford backscattering spectrometry. Our experimental results show that surface oxidation is very severe at lower pressure due to higher oxygen partial pressure. It affects the nitrogen profile and diffusion. Since typical plasma immersion ion implanters are not designed for ultrahigh vacuum, the presence of the oxygen in the residual vacuum can give rise to unexpected results, particularly under the elevated-temperature conditions, and it must be controlled properly.
Adsorption of oxygen on ultrathin Cu/Pt(111) films
Authors: Tsay J. S. , Mangen T. , Linden R.-J. , Wandelt K.
Published: July 2002

Adsorption of oxygen on ultrathin Cu/Pt(111) films was studied using Auger electron spectroscopy, low-energy electron diffraction, and quadrupole mass spectroscopy. Comparing the oxygen-saturated copper films, the density of adsorbed oxygen is doubled as the copper coverage is reduced from 2 to 0.4 monolayers. In the submonolayer range, the more edge sites at the copper islands and larger Cu–Cu distances due to pseudomorphic growth provide a higher possibility for the adsorption of oxygen. A different adsorption rate of oxygen was resolved for the exposure of copper films to oxygen. As oxygen starts to incorporate into the film, the adsorption rate decreases. For a film prepared by alternate steps of copper deposition and oxygen adsorption, the oxygen distribution is not homogeneous from sputter profiling measurements. The amount of oxygen at both interfaces is higher than within the film. From the study of the annealing effects for Cu/Pt(111), the onset of diffusion for Cu adatoms into the Pt(111) substrate is slightly influenced by oxygen.
Spectroscopic study of plasma using zirconium tetra-tert-butoxide for the plasma enhanced chemical vapor deposition of zirconium oxide
Authors: Cho Byeong-Ok , Lao Sandy , Sha Lin , Chang Jane P.
Published: July 2002

Plasma enhanced chemical vapor deposition of zirconium oxide using zirconium tetra-tert-butoxide (ZTB) as a metalorganic precursor, Ar as a carrier of the ZTB vapor, and O2 as an oxidant was investigated by using optical emission spectroscopy (OES), Langmuir probe, and x-ray photoelectron spectroscopy (XPS). The electron temperature (Te) and the O2 to Ar flow rate ratio (O2/Ar) were found to dominate the plasma chemistry: the Te determined the maximum Zr and Zr+ emission intensities at an intermediate pressure of 45 mTorr, the high C/C2 emission intensity ratio in the oxygen-rich plasma, and the transition between the dissociation-dominated chemistry at low pressures and the recombination-dominated chemistry at high pressures. The O2/Ar ratio changed the relative abundance of various atomic and diatomic species in the plasma: both ionic and atomic Zr species were depleted with the addition of O2 and a significant amount of ZrO and CO was produced. The O2/Ar ratio and Te determined the concentration ratio of C/O and C2/O in the plasma, the production and dissociation rates of diatomic molecules (C2, CH, CO, and OH), and the degree of decomposition. From XPS, x-ray diffraction, and OES measurements, the deposited ZrO2 was found to be stoichiometric and amorphous at O2/Ar ratios ⩾0.2, and hydrocarbon molecules rather than atomic carbon were more responsible for the carbon incorporation into the film. The carbon content in the film could be controlled by monitoring and varying the OES intensity ratio of C2 at 516.52 nm to O at 777.42 nm.
Reduction of artifacts in temperature programmed desorption measurements of field generated, real-life, powered samples
Authors: Smentkowski V. S. , Linsebigler A. L.
Published: July 2002

Temperature programmed desorption (TPD) is a powerful surface analytical technique used for studies of adsorbate systems when background effects such as desorption from the mounting wires and/or the heater assembly can be minimized. Researchers often use TPD measurements to determine the desorption characteristics of field generated, real-life samples that have been prepared under ambient conditions. Since real-life samples are generated under ambient conditions, the potential for background effects is significantly enhanced. In many cases, background effects and their implications on data analysis are not considered. It will be demonstrated that background effects are very significant for real-life, field generated samples when traditional protocols are used for TPD measurements. We have devised a novel experimental protocol to reduce background effects during TPD measurements of field generated, real-life powdered samples. The novel experimental apparatus and procedures will be described. TPD spectra measured using the new protocol will be compared with spectra measured using traditional protocols.
Contact resistance of focused ion beam deposited platinum and tungsten films to silicon
Authors: DeMarco Anthony J. , Melngailis John
Published: July 2002

Focused ion beam (FIB) techniques are currently being used in industry for circuit repair and rewiring in the prototyping stage. The ability to deposit a conductor directly onto silicon with a good electrical contact using the FIB methods would increase the utility of this technique in repair and circuit function diagnosis. In addition, FIB made contacts may be encountered in microelectromechanical devices (MEMS), and, when combined with FIB direct implantation, may permit local fabrication of transistors [e.g., bipolars and junction field-effect transistors (JFETs)] without conventional, planar techniques. The contact resistance of FIB-deposited platinum and tungsten onto variously doped silicon was investigated. FIB-metal contact to n+ and p+ Si was found to be ohmic after a sintering at 400 °C for 20 min in H2N2 forming gas. Individual contacts were found to vary widely in contact resistance, likely due to nonuniformity in the deposition process. Contacts to lightly doped Si were nonohmic. The contact resistance for Pt contacts to heavily doped Si was found to be on the order of 10−2 Ω cm2, and the contact resistance for W contacts on the order of 10−3 Ω cm2. It is believed that the sintering leads to formation of Pt2Si and PtSi silicides, which may interfere with the metal/semiconductor tunneling contact. Platinum silicides form around 300 °C, at the metal to silicon interface for the platinum contacts. Tungsten silicide, WSi2, forms at 650 °C and is not believed to play a part in the tungsten contact dynamics.
Study of the resist deformation in nanoimprint lithography
Authors: Hirai Yoshihiko , Fujiwara Masaki , Okuno Takahiro , Tanaka Yoshio , Endo Masataka , Irie Sigeo , Nakagawa Kazuo , Sasago Masaru
Published: July 2002

Numerical simulations and experimental studies are carried out to understand the deformation process of thin polymer film in nanoimprint lithography. Deformation of a thin polymer above its glass transition temperature is studied for various imprinting conditions such as the aspect ratios of a mold pattern, initial thickness of the polymer, and imprinting pressure. Cross-sectional profiles of the deformed polymers are simulated by the finite element method based on a rubber elastic model. The results are compared with experimental data. The areal penetration ratio of the polymer into the recessed groove of the mold and residual thickness underneath the mold are quantitatively evaluated. The simulations and the experimental results agree well with each other.
Characterization of a process development tool for ion projection lithography
Authors: Loeschner Hans , Stengl Gerhard , Kaesmaier Rainer , Wolter Andreas
Published: July 2002

This article describes the performance of a process development tool for ion projection lithography (IPL), realized as part of the MEDEA program of the European Union. This system was designed for a 12.5×12.5 mm2 exposure field and 4:1 reduction ratio between the mask and the wafer. The design incorporates several novel concepts, including a negative electrostatic lens at the mask to reduce distortion and field-composable lenses to provide electronic fine alignment of the system. Continuous control of magnification, position offset, distortion, and telecentricity is provided by a real-time feedback system (pattern lock) that monitors the position of reference beamlets traveling in parallel with the integrated circuit image through the ion-optical system. After mechanically aligning the center and tilt of the lenses relative to the optical axis to within 10 μm and 50 μrad, respectively, we achieved 100 nm resolution over the full design field, with 75 nm resolution in local areas within the field. The reduction ratio was within 0.01% of design predictions. We also discuss the experimental plan for further demonstrating the efficacy of IPL for integrated circuit manufacturing far below 100 nm design rules.
Deposition of silicon oxychloride films on chamber walls during Cl2/O2 plasma etching of Si
Authors: Ullal Saurabh J. , Singh Harmeet , Vahedi Vahid , Aydil Eray S.
Published: July 2002

The chemical nature and deposition rate of the silicon oxychloride films deposited on the chamber walls during Cl2/O2 plasma etching of Si were investigated using multiple total internal reflection-Fourier transform infrared spectroscopy. The differences in the infrared spectra of films deposited under different etching conditions were quantified through the Si–O and OSi–Cl absorption band intensities and positions to determine the growth rate and composition of these films. The changes in the film’s deposition rate and composition with rf bias power and O2 flow rate gave insight into the deposition mechanism. Based on our experimental observations, we propose that the silicon oxychloride film is deposited through oxidation of SiClx molecules adsorbed on the reactor walls and suggest a kinetic expression for the film deposition rate. This kinetic expression may also be used judiciously for describing the silicon oxychloride deposition on the sidewalls of etched features in gate etching and shallow trench isolation.
Room temperature magnetism in GaMnP produced by both ion implantation and molecular-beam epitaxy
Authors: Overberg M. E. , Gila B. P. , Thaler G. T. , Abernathy C. R. , Pearton S. J. , Theodoropoulou N. A. , McCarthy K. T. , Arnason S. B. , Hebard A. F. , Chu S. N. G. , Wilson R. G. , Zavada J. M. , Park Y. D.
Published: July 2002

The magnetization of the dilute magnetic alloy GaMnP:C prepared by the implantation of Mn into p-GaP:C or by direct molecular-beam epitaxy is reported. The material implanted to produce a Mn level of 3% produces ferromagnetic behavior that persists up to a temperature of 330 K, while the epitaxially derived material shows evidence of ferromagnetism at a temperature of 300 K. In both cases, no second phases were observed by x-ray diffraction, transmission electron microscopy, or selected area diffraction pattern analysis. A phase diagram of the GaMnP:C system, determined by epitaxial growth, is also reported.
Modeling and simulation of atomic layer deposition at the feature scale
Authors: Gobbert Matthias K. , Prasad Vinay , Cale Timothy S.
Published: July 2002

We present a transient Boltzmann equation based transport and reaction model for atomic layer deposition (ALD) at the feature scale. The transport model has no adjustable parameters. In this article, we focus on the reaction step and the postreaction purge steps of ALD. The heterogeneous chemistry model consists of reversible adsorption of a reactant on a single site, and irreversible reaction of a second gaseous reactant with the adsorbed reactant. We conduct studies on the effect of the kinetic rate parameter associated with the reaction. We provide results for number densities of gaseous species, fluxes to the surface of the feature, and surface coverage of the adsorbing reactant as functions of time. For reasonable reaction rate parameter values, the time scale for gas transport is much smaller than that for reaction and desorption. For these cases, an analytic expression for the time evolution of the surface coverage of the adsorbing reactant provides a good approximation to the solution obtained from the transport and reaction model. The results show that fractional coverage of the adsorbing reactant reduces significantly in the reaction step due to reaction with the gaseous reactant and desorption. Larger values of the reaction rate parameter lead to larger reductions in the fractional coverage during the reaction step. For smaller values of the reaction rate parameter, the decrease in coverage is dominated by desorption. The surface coverage of the adsorbing reactant also decreases during purge steps, due to desorption.
A Study of Thermal Transpiration Using Ultrahigh-Vacuum Techniques
Authors: Edmonds T. , Hobson J. P.
Published: July 2002

The thermal transpiration ratio R=P1/P2 was measured by the absolute method in helium and neon over the pressure range 10−9≤P2≤60 Torr. Cold temperatures were T1=77.4 °K and 232 °K with warm temperature T2=295 °K. An aperture and various tubes were used at the temperature interface. For the aperture Rm=(T1/T2)1/2 was found, as expected, at low pressures but this value was not found, in general, for tubes. The latter case represents a departure from normal assumptions, which are examined in detail. A related conclusion is that the relative method for measuring R is unreliable for tubes at low pressures. It is concluded that a molecule has a greater probability of traversing a tube from the hot end to the cold end than in the opposite direction. It is found that several analytic expressions for R represent the data satisfactorily after suitable choice of constants.
Experimental Conditions for Effective Glow-Discharge Bombardment of Vacuum Deposition Substrates
Authors: Isler W. E. , Bullis L. H.
Published: July 2002

Glow-discharge bombardment is widely used in vacuum practice as the final step in the preparation of substrates prior to the deposition of thin films. Work carried out at these laboratories has shown that the effectiveness of the technique is highly dependent upon the experimental arrangement used. In these experiments, the heating effect upon a glass substrate was taken as a measure of the effectiveness of the bombardment, and a systematic investigation was made of the effects of such parameters as type of discharge, accelerating voltage, electrode size and placement, and residual pressure. The results for direct current (dc) showed that for constant discharge current the heating increased with decreasing pressure and electrode diameter. A maximum was reached at a pressure of 9 mTorr below which, owing to power source limitations, the increase in carrier energy was insufficient to compensate for the decrease in carriers. Grounded-center-tap alternating current (ac) glow discharge, sometimes used for glow-discharge bombardment, was shown to be relatively ineffective as compared with the dc glow discharge.
Deposition rate and substrate temperature effects on the structure and properties of bulk-sputtered OFHC Cu and Cu–O.15 Zr
Authors: Hecht R. J. , Mullaly J. R.
Published: July 2002

Deposition rate and substrate temperature were observed to affect the structure and properties of thick, sputtered OFHC copper and Cu–0.15 Zr deposits. Deposition of OFHC Cu and Cu–0.15 Zr was performed by high-rate sputtering from a cylindrical (hollow) cathode. Bulk deposits varying from 250 to 3700 μ thichnesses were evaluated as to microstructure, surface topography, and fractography. At conditions of low substrate temperature, crystallite size and openness of the structure increased with increasing deposition rate for both materials. At elevated temperatures it was possible to produce an equiaxed, ductile structure of OFHC Cu, but only at low deposition rates. At higher deposition rates open structures resulted having recrystallized, equiaxed grains within large, poorly bonded crystallites. Sputtered Cu–0.15 Zr deposited at basically equivalent conditions, as used for OFHC Cu, exhibited open-type structures for all conditions evaluated. However, lower deposition rates significantly reduced the openness of the structure, as did increasing substrate temperature. The use of a triode discharge to achieve a higher degree of ion bombardment in biasing was effective in generating a dense, non-voided structure of Cu–0.15 Zr.
Factors affecting the initial nucleation of alumina on cemented-carbide substrates in the CVD process
Authors: Johannesson Thomas R. , Lindström Jan N.
Published: July 2002

Alumina nuclei were deposited, using chemical vapor deposition (CVD), under varying process conditions on polished cemented-carbide substrates (WC+TiC, TaC, NbC+Co) for 60 s in order to study the nucleation stage. During the heating up of the substrates the binder of the polished surfaces diffused onto the carbide surfaces. The surface of the WC was thereby converted to η-phase, while no attack on the (Ti,W)C surfaces could be detected. After the short deposition the alumina nuclei were counted. The nucleation was always most dense on the (Ti,W)C grains. The chemical equilibria of the gas for the various process conditions were calculated and supersaturations for the components of the gas and a total one were computed. It was found that the density of nuclei increased with increasing supersaturation of the aluminum chlorides and the total supersaturation. The supersaturation of the oxygen donors, however, did not correlate with the density of nuclei. A dense nucleation is believed to be important for the adherence of the final deposit.
Synthesis of TiC–Ni cermets by the activated reactive evaporation process
Authors: Nimmagadda R. , Bunshah R. F.
Published: July 2002

This investigation is concerned with the deposition of TiC–Ni cermets using the activated reactive evaporation (ARE) process. A Ti–10 Ni alloy rod was evaporated from an electron beam source in the presence of acetylene (C2H2), the vapor species being activated or partially ionized using the ARE proc microhardness, x-ray fluorescence, x-ray imaging for different elements on an electron microprobe analyzer, optical microscopy, and electron microscopy. It has been shown that TiC–Ni cermets can be deposited by the ARE technique, and they are quite hard. When the deposition was made on Ta substrates at high temperatures, it was observed that Ni diffuses into Ta and forms an intermetallic phase near the interface between the substrate and the deposit.
Ultraviolet photoemission and flash-desorption studies of the chemisorption and decomposition of methanol on Ni(111)
Authors: Rubloff G. W. , Demuth J. E.
Published: July 2002

The chemisorption and decomposition of methanol (CH3OH) on Ni(111) has been studied by ultraviolet photoemission spectroscopy (UPS) and flash-deposition mass spectroscopy. The UPS spectra suggest that exposure at ∠80 K produces chemisorbed CH3OH in which the chemisorption interaction affects two molecular orbitals, the oxygen lone-pair oriented perpendicular to the COH plane and an in-plane orbital having mixed lone-pair and σ-bonding character. Upon warming to ∠160 K, some CH3OH desorption occurs and the UPS spectrum changes markedly. Further warming to ∠300 K produces H2 desorption and leaves chemisorbed CO as the final decomposition product on the surface.
Mechanical properties on ion-beam-textured surgical implant alloys
Authors: Weigand A. J.
Published: July 2002

An electron-bombardment Hg ion thruster was used as an ion source to texture surfaces of materials used to make orthopedic and/or dental prostheses or implants. The materials textured include 316 stainless steel, titanium–6% aluminum, 4% vanadium, and cobalt–20% chromium, 15% tungsten. To determine the effect of ion texturing on the ultimate strength and yield strength, stainless steel and Co–Cr–W alloy samples were tensile tested to failure. Three types of samples of both materials were tested. One type was ion textured (the process also heats each sample to 300°C), another type was simply heated to 300°C in an oven, and the third type was untreated. Stress–strain diagrams, 0.2%-offset yield strength data, total elongation data, and area reduction data will be presented. Fatigue specimens of ion-textured and untextured 316 stainless steel and Ti–6% Al–4% V were tested. Included as an ion-textured sample is a Ti–6% Al–4% V sample which was ion machined by means of a Ni screen sputter mask so as to produce an array of 140×140×60-μm-deep pits. A table is presented that compares the fatigue characteristics of ion-textured and untextured samples. Scanning electron microscopy was used to characterize the ion-textured surfaces. An electron-beam microprobe was used to analyze the cross sections of the ion-textured samples.
Surface resonances and the oxidation of single-crystal aluminum
Authors: Bachrach R. Z. , Flodström S. A. , Bauer R. S. , Haström S. B. M. , Chadi D. J.
Published: July 2002

Valence-band photoemission spectra have been studied on single-crystal aluminum faces using polarized sychrotron radiation. New intrinsic and oxygen-related extrinsic surface resonance features are observed within 5 eV of the Fermi level. These surface resonances are correlated with oxygen uptake on the (100), (110), and (111) faces as observed in both valence and core-level spectroscopy. Considerable face dependence to the oxidation is shown. Although aluminum is a free-electron-like metal, its surface behavior on single-crystal faces shows effects due to localized charge.
Abstract: Study of semiconductor surfaces using an atom-probe field ion microscope (1) Hydrogen chemisorption on silicon
Authors: Sakurai Toshio , Tsong T. T. , Culbertson R. J.
Published: July 2002

Semiconductors, particularly silicon, are some of the most important materials in technology today. Surface properties of Si have been intensively investigated by many techniques, such as low-energy electron diffraction (LEED)1,2 and ultraviolet photoemission spectroscopy (UPS).3,4 Most recently Sakurai and Hagstrum have studied surface electronic structures for hydrogen chemisorption on various silicon surfaces using ion neutralization spectroscopy (INS) and UPS.5 Their study suggested the formation of new hydride surface phases, such as SiH5b and SiH3,5c in addition to a well known monohydride phase SiH.5a However this conclusion was drawn without observation of those surface molecules. Here we present a new approach to the study of hydrogen chemisorption on Si surfaces. We applied atom-probe field ion microscopy to observe directly these surface compounds. We have also succeeded in achieving a new atomic resolution of silicon in field ion microscopy.
Chemical trends of Schottky barriers: A reexamination of some basic ideas
Authors: Schlüter M.
Published: July 2002

Fundamental experimental data on metal–semiconductor interfaces are reexamined. It is found that the previously reported abrupt transition in Schottky barrier behavior between covalent and ionic semiconductors is not that clearly defined and diffused by data scattering. Furthermore, the data show no saturation of the linear interface parameter S for S=1. Considering the correct definition of S, it follows that the true Schottky limit can only approximately be described by S and should occur for some value S?2.0–3.0 rather than for exacatly S=1 as previously claimed.
Adatom bonding effects from coverage-dependent angle-resolved photoemission: Ag(001)+Cl
Authors: Weeks S. P. , Rowe J. E.
Published: July 2002

Adatom–adatom interactions and adatom–substrate bonding effects have been studied using coverage-dependent angle-resolved photoemission. Spectra for eight separate coverages, ranging from the clean Ag(001) surface to the saturated c (2×2) ordered chlorine overlayer at ϑ=0.5, were obtained using a multiple-angle parallel detection system, allowing simultaneous collection of photoelectron emission into a 70°×70° solid angle, while maintaining ∠1.5° angular resolution. The angular character and k-space origin of photoemission peaks for the clean surface were determined by comparison with a direct transition model using calculated bulk energy bands. This information was correlated with coverage-dependent attenuation of substrate emission to identify the participation of substrate 5s, 5p, and 4d levels in the chemisorption bond. The measured energy dispersion of adsorbate induced structure provides information on the bonding or antibonding nature of these levels. The k-dependence of Ag 4d-band emission indicates their involvement in indirect adatom–adatom interactions.
Use of SIMS for studies of adsorption on well-defined metal surfaces (1) Combined XPS/LEED/SIMS studies of O2, CO, H2O, and H2 on Ni (100)
Authors: Hopster H. , Brundle C. R.
Published: July 2002

We have investigated the potential of SIMS for providing information on substrate–adsorbate geometry and substrate–adsorbate elemental and chemical composition by studying adsorption on Ni (100) while simultaneously monitoring by XPS and LEED. H2, CO, O2, and H2O were studied. We find no obvious dependence in SIMS ion cluster distributions on specific adsorbate geometry. We find a strong direct dependence on chemical composition. Distinction between molecular and dissociative adsorption of CO and H2O is easy, as is distinction between chemisorbed O and oxide. The ability to detect H is important. Thus low coverages of H on Ni (100) are easily detected, and distinction of O from OH is of great assistance to XPS which cannot distinguish these species on the basis of O(1s) bond energies. We conclude that SIMS is a very useful adjunct to electron spectroscopy but that, at least for the systems we have studied, sputtered ion cluster distributions are not relatable in any simple way to adsorbate–substrate geometry.
Structural determination of the unreconstructed and the reconstructed (110) surfaces of iridium
Authors: Chan C.-M. , Luke K. L. , Van Hove M. A. , Weinberg W. H. , Williams E. D.
Published: July 2002

An Ir(110) – (1×1) surface has been prepared by adsorbing 1/4 monolayer of oxygen at 850 K on a clean, reconstructed (1×2) surface. Good agreement was achieved between theoretical and experimental intensity–voltage (I–V) spectra for a surface model in which the oxygen is randomly and uniformly distributed over the cyrstal surface, and the (1×1) structure is the same as for a clean unreconstructed (1×1) surface with a topmost interlayer spacing of 1.26±0.05 Å. Three different models have been tested for the reconstructed Ir(110) – (1×2) surface, namely, the missing-row model, the paired rows model, and the buckled surface model. Based on the comparison between experimental data (consisting of ten half-order beams and eight integral-order beams) and the theoretical calculations, the mising-row model with a topmost interlayer spacing of 1.22±0.07 Å is the most satisfactory model tested.
Tellurium and selenium selective absorber thin films produced by gas-evaporation methods
Authors: Cocks F. H. , Peterson M. J.
Published: July 2002

The production of Te and Se thin films by evaporation carried out under pressures of argon gas ranging from 1 atm to 0.1 Torr have been studied and the selective absorption characteristics of the resultant Te and Se films determined. Absorptivities (a) in excess of 97% have been observed in Te films deposited in 1 Torr of argon. Absorptivities of gas evaporated Se films did not rise above 60%. Emissivities (e) of Se films were also high, over 20%. Emissivities of Te thin films were less than 10% in most instances. Maximum a/e values of 12:1 were obtained for Te films deposited at an argon pressure of 10 Torr.
Positive electron-beam resist behavior for methacrylonitrile and methyl α-chloroacrylate polymers and copolymers
Authors: Lai J. H. , Helbert J. N. , Cook C. F. , Pittman C. U.
Published: July 2002

The positive electron beam resist exposure characteristics of poly (methacrylonitrile) (PMCN), poly(methyl α-chloroacrylate) (PMCA), and two MCA/MCN copolymers have been obtained using conventional techniques. The 1:1 MCA/MCN copolymer is found to be four to five times more sensitive than PMMA reference under equivalent conditions. PMCN, PMCA, and 2.3:1 MCA/MCN copolymer are also found to be more sensitive than PMMA, but less sensitive than the 1:1 MCA/MCN copolymer. The relatively low observed sensitivities for PMCA and the 2.3:1 MCA/MCN copolymer is attributed to a low Gs/Gx ratio as observed from other studies. PMCN and the 1:1 MCA/MCN copolymer exhibit significantly lower plasma etch rates than PMMA and therefore should be good ’’dry process’’ resists.
Granular aluminum superconducting bolometer as a molecular beam detector
Authors: Cardillo M. J. , Becker G. E. , Kubiak G. D. , Narayanamurti V. , Chin M. A.
Published: July 2002

We have tested a granular aluminum superconducting thin film bolometer as a detector of molecular beams. The bolometer is mounted on a liquid He cryostat and designed to operate in a bakeable UHV scattering chamber. The element is shown to be a sensitve detector of the total thermal energy of the molecular beam flux and if operated in tandem with a mass spectrometer allows the average internal energy to be determined.
Low-energy electron diffraction study of the surface defect structure of Ag (111) epitaxially grown on mica
Authors: Welkie D. G. , Lagally M. G. , Palmer R. L.
Published: July 2002

The use of low-energy electron diffraction (LEED) for the quantitative determination of finite-domain size effects in surfaces and for the separation of domain size effects and strain effects is demonstrated for the first time. Measurements are made of the angular distribution of intensity in diffracted beams observed in LEED from Ag (111) thin film grown epitaxially on mica. The broadening in these beams beyond that due to the finite instrumental resolution is analyzed in terms of three mechanisms limiting the long-range order on the surface: steps, mosaic structure, and strain parallel to the surface. It is demonstrated that no steps exist, and that the considerable broadening that is present is due to mosaic structure rather than strain. The average size of this mosaic structure, as well as the average misorientation of domains, is determined.
Ammonia adsorption on the Pt(111) and Pt(S)-6(111)×(111) surfaces
Authors: Gland J. L. , Kollin E. B.
Published: July 2002

Ammonia adsorption on the Pt(111) and stepped Pt(S)-6(111)×(111) surfaces has been studied using thermal desorption spectroscopy, isotope exchange thermal desorption, and steady-state decomposition measurements. Molecular ammonia adsorbs without dissociation on both the Pt(111) and Pt(S)-6(111)×(111) surfaces below 400 K. Three distinct desorption peaks are observed following adsorption at 90 K. Multilayers of solid ammonia desorb in a narrow peak at 100 K. The weakly chemisorbed high coverage–low temperature form of molecular ammonia desorbs at 150 K with first order kinetics and a heat of desorption of 36 ± 3 kJ/mol (8.6 ± 0.6 kcal/mol). The chemisorbed low coverage–high temperature form of molecular ammonia desorbs in a broad peak in the 170 to 450 K temperature range. A small amount of adsorbed molecular ammonia (<1% of saturation coverage) undergoes isotope exchange with preadsorbed deuterium. These results indicate that exchange occurs via an associative process, probably involving an NH3D type intermediate species. Steady-state ammonia decomposition occurs above 400 K on the Pt (111) surface indicating that dissociative adsorption does occur at elevated temperatures.
Metal–semiconductor interfacial reactions: Ni/Si system
Authors: Cheung N. W. , Grunthaner P. J. , Grunthaner F. J. , Mayer J. W. , Ullrich B. M.
Published: July 2002

Interfacial reactions between Si and deposited metals have been investigated by x-ray photoelectron spectroscopy (XPS) and channeling measurements with MeV 4He ions. This paper is concerned with reactions of Ni deposited at 10−10 Torr on clean Si and with the structure of the interface in the Si/Ni2Si/Ni structure. Both XPS and channeling measurements show that reactions occur where Ni is deposited at 10−10 Torr on Si: Si atoms are displaced from lattice sites, the Ni atoms are in an Si-rich environment, and the Ni/Si interface is graded in composition. Composition gradients are present at both interfaces in the Si/Ni2/Si/Ni system: at the Si/Ni2Si interface Ni atoms are in a more Si-rich environment than that found for Ni in Ni2Si or NiSi and at the Ni/Ni2Si interface Si atoms are in more Ni-rich environment than that found for Si in Ni2Si. In both deposited Ni on Si and the Si/Ni2Si/Ni structures, Ni atoms are found at the tetrahedral interstitial site in Si. For the Ni–Si system, cooling the substrate to ∠100 K slows down the reaction rate. The temperature dependence of the interfacial reactivity indicates the kinetic nature of metal–semiconductor interfaces.
A new method for the batch production of micro-Fresnel zone plates
Authors: Glocker D. , Wiseman R.
Published: July 2002

A new method has been developed for making micro-Fresnel zone plates used in the coded imaging of x rays and α particles produced from laser fusion target implosions. The method allows the fabrication of numerous plating molds from a single master mold, which is particularly useful in α-particle imaging since each target shot requires a new zone plate. A master mold was made in polyimide using reactive ion etching, and a number of silicone rubber replicas were made of the mold. Each replica was then used to produce a number of photoresist final molds into which gold was electroplated. This microfabrication technique has produced high quality 10-μm-thick zone plates having 100 zones and a 5-μm-wide outer zone.
Electron-stimulated desorption in organic molecular solids
Authors: Kelber J. A. , Knotek M. L.
Published: July 2002

Electron-stimulated desorption of H+ from solid cyclohexane, benzene, 1,2,3,–5 tetrafluorobenzene (C6H2F4), and nanofluoroisobutane [(CF3)3CH] and of F+ from solid C6H2F4 and (CF3)3CH are reported. H+ threshold energies are 25(±1)eV, ∼29 eV, 29 (±1) eV, and 27 (±1) eV for cyclohexane, benzene, C6H2F4, and (CF3)3CH, respectively. F+ thresholds are 38 (±1) eV for C6H2F4, and 40 (±1) eV for (CF3)3CH. This behavior is interpreted as being due to desorption from mainly multivalence-hole final states created by decay from single C 2s or F 2s holes. These multihole excitations are localized to the extent that excitations which break C–H bonds do not affect C–F bonds and vice versa. A weak CF+ threshold was observed at ∼40 eV with a large increase in yield at ∼53 eV. A change in slope occurs for the H+ and F+ yields from C6H2F4 near 55 eV and for the H+ and F+ yields from (CF3)3CH near 60 eV. These data, along with the increase in CF+ yield from (CF3)3CH at 53 eV suggest desorption can also occur following more complex multielectron excitations.
Photoemission determination of dipole layer and VB-discontinuity formation during the MBE growth of GaAs on Ge(110)
Authors: Zurcher Peter , Bauer Robert S.
Published: July 2002

Synchrotron radiation-excited soft x-ray photoemission is used to study the heterojunction formation of GaAs on Ge(110) by examining 3d-core levels, the valence band (VB), and the secondary electron distribution cutoff in a photoemission spectrum. Arsenic saturation of the Ge(110) surface prior to MBE growth of GaAs causes a work function increase of 0.26±0.045 eV and a decrease in Ge valence-band maximum (VBM) from the Fermi level by 0.96±0.09 eV. The increase in work function can be explained by the formation of a GeAsx layer. The large VBM decrease is partly due to a band bending of 0.61±0.03 eV and a chemisorption-induced charge transfer reaction. Using two different photoemission methods, the VB discontinuity at the interface is determined to be 0.23±0.08 and 0.26±0.07 eV. This value is different from the one determined for the inverse heterojunction where Ge is deposited on top of GaAs(110) at the same epitaxial growth temperature of 320 °C. The difference in electron affinity between the clean Ge(110) substrate and the GaAs(110) overlayer is Δχ=−0.01±0.08 eV. Therefore, Anderson’s electron affinity rule does not explain the measured VB discontinuity.
GexSi1−x/Si strained-layer superlattice grown by molecular beam epitaxy
Authors: Bean J. C. , Feldman L. C. , Fiory A. T. , Nakahara S. , Robinson I. K.
Published: July 2002

GexSi1−x films are grown on Si by molecular beam epitaxy and analyzed by Nomarski optical interference microscopy, Rutherford ion backscattering and channeling, x-ray diffraction, and transmission electron microscopy. The full range of alloy compositions will grow smoothly on silicon. GexSi1−x films with x≤0.5 can be grown free of dislocations by means of strained-layer epitaxy where lattice mismatch is accommodated by tetragonal strain. Critical thickness and composition values are tabulated for strained-layer growth. Multiple strained layers are combined to form a GexSi1−x/Si strained-layer superlattice.
Vibrational spectroscopy of chemisorbed molecules by infrared emission
Authors: Chiang S. , Tobin R. G. , Richards P. L.
Published: July 2002

The technique of infrared emission spectroscopy has been developed in order to observe vibrational modes of molecules adsorbed on clean, single crystal metal surfaces. A novel apparatus has been constructed which measures the emission from a single crystal sample in thermal equilibrium at room temperature. The apparatus consists of a liquid helium cooled infrared grating spectrometer coupled to an ultrahigh vacuum system equipped with surface preparation and characterization facilities. The system is capable of measuring over the frequency range from 330 to 3000 cm−1 with a resolution of 1 to 15 cm−1. Using this technique, we have measured the linewidths of both the carbon–metal and carbon–oxygen stretching vibrations of monolayer coverage of CO on Ni(100).
Characterization of NBS Standard Reference Material 2135 for sputter depth profile analysis
Authors: Fine Joseph , Navinšek Boris
Published: July 2002

A Ni/Cr multilayered thin-film standard reference material (SRM) for sputter depth profile calibration has been developed jointly by the National Bureau of Standards, the Jozef Stefan Institute, and the American Society for Testing and Materials (ASTM) Committee E-42 on Surface Analysis. This perodically modulated structure can be effectively used to calibrate sputter erosion rates and depth of erosion scales in surface analysis as well as to monitor ion beam stability and to optimize sputtering conditions so as to achieve maximum interface resolution. Characterization results obtained on this first SRM for surface analysis to be issued by NBS indicate that the accuracy of its structure is known to better than 6% and that its sputter profiles are well defined and reproducible. Results of the calibration and compositional analysis of this SRM are presented regarding uniformity and periodicity of thin film layers, absolute film thickness, sputtered interface depth resolution, and relative Ni/Cr sputtering rates and yields. Measurement methods used to characterize this thin-film structure include EN(E) Auger sputter depth profiling, Rutherford backscattering spectrometry, and neutron activation analysis.
Zero stability and calibration results for a group of capacitance diaphragm gages
Authors: Hyland Richard W. , Tilford Charles R.
Published: July 2002

The lowest pressure which may be measured by a capacitance diaphragm gage is established by instabilities in the gage zero. In the systematic study of the stability of 14 different temperature-controlled gages we have observed that most of the instabilities are correlated with changes in room temperature. However, the magnitude of the changes for different gages differed by three orders of magnitude, underscoring the necessity for users to evaluate the stability of their own gages. We also observed small but steady zero drifts which extended over weeks, as well as occasional large, usually discontinuous, zero shifts that were precipitated by fast temperature changes. The most stable gage we observed changed by less than one part per million (ppm) of full range over periods of days; at the other extreme we have observed gages to change by 1000 ppm within an hour. At higher pressures the accuracy of gage readings will be determined in part by the long-term stability of the gage calibration factor. The calibration records for 17 gages, for which we have two or more calibrations separated by intervals on the order of 1 year, show shifts ranging from essentially no change to about 2% with an average value of 0.45%. With one exception, these do not appear as a steady drift with time, but as random shifts between calibrations.
Interaction of metals with model polymer surfaces: Core level photoemission studies
Authors: Sanda P. N. , Bartha J. W. , Clabes J. G. , Jordan J. L. , Feger C. , Silverman B. D. , Ho P. S.
Published: July 2002

Core level photoemission studies have been performed on the in situ interactions of Cr and Cu on two model systems which are related to the pyromellitic dianhydride (PMDA) and oxydianiline (ODA) parts of PMDA–ODA polymide. The model compound which is related to the PMDA constituent is N,N′-diphenylpyromellitimide and the model polymer which is related to the ODA constituent is poly(2,6-dimethylphenylene oxide) (PMPO). Cr evaporation on the PMDA model compound changes the PMDA-related features of the C 1s spectrum, whereas Cu evaporation has comparatively little effect on the PMDA-related features. The results are consistent with Cr bonding with the PMDA part of the related model compound, or fracturing of the carbonyl bonds and/or other bonds contained in the PMDA structure. Cr evaporation on PMPO results in a new peak at lower binding energy without appreciable changes in the shape of the original bands. Cu predominantly affects the peak in the C 1s spectrum of PMPO which originates from carbons in ether linkages.
Infrared reflectance absorbance spectroscopy of coadsorbed CO and H2O on Pt(111) surfaces
Authors: Tornquist W. J. , Griffin G. L.
Published: July 2002

We have used polarization modulated infrared reflectance absorbance spectroscopy (IRRAS) to study the interactions between coadsorbed CO and H2O on Pt(111) surfaces at 150 K. Two types of behavior are observed, depending on CO coverage. For CO coverages greater than θ≊1/2, the vibrational band for linear CO species shifts from 2100 cm−1 for an H2O-free surface to 2095 cm−1 for H2O exposures up to 15 L. For larger H2O exposures a second, broader band appears at around 2080 cm−1. These results indicate that H2O adsorbs in clusters on top of a saturated CO adlayer, without strongly perturbing the CO molecules underneath. In contrast, for CO coverages less than θ≊1/4, adsorption of H2O at 150 K results in the disappearance of the linear CO vibrational band, with its subsequent reappearance upon desorbing the H2O layer. This indicates that for low CO coverages, coadsorbed H2O can displace CO out of its preferred linear coordination mode.
Photon-stimulated ion desorption from condensed SiF4 and SiH4
Authors: Rosenberg R. A.
Published: July 2002

Results of photon-stimulated ion desorption (PSID) experiments on condensed SiF4 and SiH4 are presented. Data on condensed SiF4 are presented in the photon energy range 100–170 eV. The major product is F+. PSID yield spectra are interpreted in terms of excitation of a Si(2p) electron and are compared to previous gas-phase and condensed SiF4 experiments. H+ was found to be the only product desorbing in significant quantities from condensed SiH4 in the photon energy range 15–30 eV. A weak threshold is observed at 16.5 eV and a strong threshold appears at 19 eV. These data are interpreted in terms of excitation of a Si(3s) electron, and comparisons are made to previous electron-stimulated desorption experiments on condensed Si(CH3)4 and Si(111):SiH3.