bluuebunny/crossref_metadata_2025 huggingface dataset:
Chrome mask fabrication with electron-beam-lithographic system
Authors: Ting C. H. , Anderson R. L. , Saiki D. Y. , Kraft A. J.
Published: July 2002

An automated electron-beam-lithographic system, Vector Scan-I, was designed to fabricate devices beyond the optical limit. When the resolution requirement is only moderate, i.e., approximately one micron, VS-1 can be used to fabricate chrome masks for conventional optical processing. VS-1-fabricated chrome masks have better pattern definition and extremely fast turnaround time. Furthermore, the VS-1 electron-beam system can generate pattern sizes from a given design to fit different experimental needs. The capability of accommodating many different designs on a single mask greatly reduces the device fabrication effort. Examples of chrome masks fabricated by the VS-1 electron-beam system will be described. These masks are routinely used for fabricating magnetic bubble devices. Large chips can be obtained by stitching several fields together.
Extrinsic surface states for oxygen chemisorbed on the GaAs (110) surface
Authors: Joannopoulos J. D. , Mele Eugene J.
Published: July 2002

The electronic structure of various configurations of oxygen chemisorbed on GaAs (110) is studied using a localized orbital approach. Recent conflicting interpretations of experimental measurements, concerning the site of chemisorption, are resolved. It is concluded that for low averages, oxygen prefers to chemisorb to the surface arsenics and chemisorbs as an O2 molecule.
Metal–semiconductor surface and interface states on (110) GaAs
Authors: Bachrach R. Z.
Published: July 2002

Photoemission studies have been carried out for aluminum and gallium metal surfaces and metal–GaAs interfaces. Core chemical shifts and valence band changes have been simultaneously investigated with the wide photon energy range available on the 4° beam line at the Stanford Synchrotron Radiation Laboratory. These experiments show that although studies of the individual surfaces provide useful reference information, the separate character of the free surfaces is dominated upon interface formation by chemical changes and bond formation. The studies have shown that, for a simple metal such as aluminum, surface states and charge localization are important on specific crystalline faces. These states can affect the interface that forms between a metal and a semiconductor. For the Ga–GaAs interface investigated as the interface is formed, no Schottky barrier is found for Ga on p-type GaAs. Charge transfer from the surface As atoms to the Ga overlayers occurs, and some As migrates into the overlayer resulting in vacancies at the interface. Valence band changes with Ga coverage show that at least two occupied inteface states arise. These states, at −4.2 and −5.8 eV, fall within the gap in the surface Brillouin zone for projected bulk states. With alumimum an exchange reaction takes place, leaving an interfacial layer of AlAs and a GaAl alloy at the interface.
Limits of composition achievable by ion implantation
Authors: Liau Z. L. , Mayer J. W.
Published: July 2002

In high-dose ion implantation for materials modification, the maximum concentration of the implanted species is determined by ion-induced erosion (sputtering) of the implanted layer. In this review, we consider the influence of preferential sputtering and atomic mixing. The maximum concentration of the implanted species is given roughly by r/S and extends over a depth W where S is the sputtering yield, r is the preferential sputtering factor (1/2≲r≲2) and W is a depth comparable to the ion range. Good agreement between calculation and experiment is found for 150-keV Au implanted into Cu or Fe. Surface conditions, such as oxide layers or carbon films, can alter sputtering yields and can lead to the mixing of surface contaminants throughout the implanted layer. Implantation of species A into a target material AB results in a different concentration limit, but again preferential sputtering and the total sputtering yield set this limit. Calculations for PtSi indicate that the concentration of Si is decreased by implantation of Si for S≳3.
Induced interface interactions in Ti/Si systems by ion implantation
Authors: Wang K. L. , Bacon F. , Reihl R. F.
Published: July 2002

Experimental evidence is presented which suggests ion-bombardment-induced formation of titanium silicide(s) at the interface of ion implanted Ti/Si structures. Titanium films of 1000 to 2000°A were evaporated onto silicon substrates. The structures were implanted with 1×1015 to 2×101714N+ or 11B+ ions/cm2 at beam energies 50–190 keV and at fixed temperatures ranging from −195° to about 25°C. Using Auger electron spectroscopy combined with active ion sputtering, the thickness of the silicide layers was found to vary with implantation temperature, energy, and fluence. Since relatively high temperatures are required for the formation of titanium silicides (∠650°C), it is unlikely that the formation is due to sample heating upon implantation. This was comfirmed by implanting at different beam fluxes and temperatures. The formation mechanism is most likely one of enhanced diffusion and chemical reaction processes during ionic impact, which competes with the recombination of vacancies and self-interstitials, and other capture processes. This mechanism is supported by data from structures implanted at −195°C which showed silicide layers being thicker than those observed for room temperature implants under otherwise identical implant conditions.
Bonding geometry and electronic structure of the chalcogens on Ni(111)
Authors: Capehart T. Weston , Rhodin Thor N.
Published: July 2002

The behavior of oxygen, sulfur, selenium, and tellurium on Ni(111) has been investigated using angular-resolved photoemission, LEED, programmed thermal desorption, and work function measurements. The synthesis of these measurements suggest bonding in a site of C3v symmetry and the existance of three nondegenerate orbitals participating in the nickel–chalcogen bond. Changes which occur in orbital energy levels as the adsorbate is varied from oxygen to tellurium are explained in terms of a tight-binding calculation of chalcogen bonding to a triangular cluster of nickel atoms in a pyramidal configuration.
Study of low coverage adsorption on cleaved (110) InP surfaces using SIMS
Authors: Dowsett M. G. , Parker E. H. C.
Published: July 2002

Recent work on the III–V surfaces has indicated that adsorbate coverages ≲0.01 monolayers can significantly influence the surface electronic structure. The use of secondary ion mass spectrometry (SIMS) to study sorption phenomena on (110) UHV-cleaved surfaces of InP at levels below 0.01 monolayers is reported here. The analyses reveal that significant quantities of adsorbates can accrue on a surface cleaved and stored in UHV, with a very rapid initial contamination of the freshly cleaved surface. For ∠0.1 L exposure to UHV total contaminant coverages ≳10−3 monolayers are observed. The surface chemistry appears complex, with phosphorus oxides being the predominant species. The oxidation is apparently due to a dissociation/adsorption reaction with CO, with the additional possibility of adsorption of volatile phosphorus oxides initially desorbed from the sides of the cleaved boule. The above sorption phenomena are believed to be associated with a relatively small number of highly active surface sites, for example at cleavage steps. Further exposure to UHV up to ∠ 10 L results in partial saturation in the surface contamination coverage. Exposure of this surface to O2 (4×105 L) leads to further oxidation and possible chemisorption of O2 onto P dangling bonds. The SIMS spectra contain evidence for an increasing level of P–In bond breaking with UHV and O2 exposure, and this is associated with contamination-induced surface disorder.
Reconstructing states at the Si–SiO2 interface
Authors: White C. T. , Ngai K. L.
Published: July 2002

There has been a continued interest in the microscopic nature of the Si–SiO2 interface of the thermally oxidized silicon system. Charges and states near the interface often determine the electronic properties of metal–oxide–semiconductor devices, and hence it is of paramount importance to obtain a detailed understanding of the interfacial electronic structure. We have considered the role of interface states in the semiconducting gap arising from threefold coordinated Si atoms as well as strained Si–Si bonds. The obtained reconstructing character of these interface states has interesting implications for the electronic and optical properties of the interface. In particular, within our model one is able to understand qualitatively and semiquantitatively results of many experimental investigations of the Si–SiO interface. These include the amphoteric, metastable character of the interface states, the anomalous hole trapping cross sections and processes at the interface, and the dependence of the shape of the interface density of states on the conductivity type of the silicon substrate.
Metal contacts to silicon and indium-phosphide-cleaved surfaces and the influence of intermediate adsorbed layers
Authors: Williams R. H. , Varma R. R. , Montgomery V.
Published: July 2002

Detailed studies, using a range of experimental techniques, are described of the interfaces formed between metals and the semiconductors silicon and indium phosphide. For contacts between Ag or Au and cleaved (111) Si the existence of thin adlayers of oxygen or chlorine at the interface makes little difference to the magnitude of the Schottky barrier formed, although the adlayers totally change the electronic structure of the free surface. Au, Ag, and Cu contacts on clean (110) surfaces of InP yield good Schottky barriers but exposure of the clean surface to oxygen, air or chlorine prior to deposition of the metal electrodes leads to low apparent barrier contacts at room temperature. Reactive metals such as Al, Fe, and Ni also yield low barrier contacts, at room temperature, when deposited on clean surfaces of InP. These results coupled with studies on other materials cast some doubt about the usefulness of the quantity S, ’’the index of interface behavior’’ often used to describe metal–semiconductor interfaces and on the existence of the much quoted covalent-ionic transition. The present results on InP may be understood in terms of a defect model and details of this model are discussed. The interface electronic properties are dominated by chemical and metallurgical effects.
Voltage dependence of proximity effects in electron beam lithography
Authors: Kyser D. F. , Ting C. H.
Published: July 2002

Intra line and inter line proximity effects and their dependence on beam voltage are explored via computer simulation of electron scattering, energy deposition, and subsequent development in electron-beam lithography processes. For thin resist films (?1 μm) on silicon substrates,the simulation predicts that smaller linewidths and gaps can be achieved without proximity correction at 10 kV, compared to 20 kV. Experimental confirmation of the predictions is presented.
Application of electron beam fabrication to multilevel metal structures
Authors: Kitcher James R.
Published: July 2002

The advantages of direct electron beam fabrication and additive metallization in custom wiring of bipolar LSI logic and array circuits include increased interconnection density, mask elimination, and decreased turn around time on new designs. The application of EL–1, a fixed shape beam, results in image fidelity errors which are corrected by exposure compensation and process modification. PMMA type materials are utilized at 10–20 μC/cm2 for both metal pattern definition and interlevel vias. Multiple coating techniques, new developer systems, and developing controls are presented as important features in the patterning process. The importance of separating image and undercut formation in defining and controlling liftoff structure profiles is pointed out in reviewing various approaches.
Contrast in the electron-beam lithography of substituted aromatic homopolymers and copolymers
Authors: Feit E. D. , Thompson L. F. , Wilkins C. W. , Wurtz M. E. , Doerries E. M. , Stillwagon L. E.
Published: July 2002

The lithographic characteristics of homopolymers and copolymers of substituted styrenes have been determined by electron lithography and compared to polystyrene, which is used as a standard for high contrast among negative resists. Homopolymers, as well as copolymers with glycidyl methacrylate, can be almost equal in contrast to the standard. They are more sensitive than it by at least an order of magnitude. For the homopolymers, the order of contrast among the styrene-substituents is hydrogen?methyl≳chloro∠chloromethy. For copolymers, the order is hydrogen≳chloromethyl≳methyl≳chloro. γ-values, although a familiar index of contrast and an adequate one when comparing families of materials with similar molecular weight distributions, ignore material variations that are significant in thick relief lithography. Preliminary, patterned exposures of three of these substituted styrenes are compared; poly(3-chlorostyrene), poly(vinylbenzyl chloride-co-glycidyl methacrylate). The limiting feature for each was a 2 μm gap of 0.7 μm final thickness. Better resolution is obtained with different features.
1979 LEED analysis of Cu(100)
Authors: Noonan J. R. , Davis H. L.
Published: July 2002

The crystallography of the Cu(100) surface is reexamined by a LEED I–V profile analysis in order to investigate the effects of applying current experimental and computational techniques. The study produces a very small multi-beam reliability factor of 0.068, and it is concluded that the first interlayer spacing of Cu(100) is within 2% of the bulk value. The work also demonstrates that agreement between calculational and experimental I–V profiles can be significantly improved by the simple process of data averaging the experimental profiles which should be symmetrically equivalent.
Modification of elemental incorporation probabilities by ion bombardment during growth of III–V compound and metastable films
Authors: Zilko J. L. , Barnett S. A. , Eltoukhy A. H. , Greene J. E.
Published: July 2002

Low energy ion bombardment of a growing film during vapor phase deposition has been shown to be useful in providing additional control over elemental sticking probabilities. In such a deposition mode, the probability of a given atom being incorporated into the lattice of the growing film is given by σ=φ(1−Γ) where φ is the thermal sticking probability and Γ is the elemental sputtering probability. For low energy (<300 eV) ion bombardment of growing III–V compound films, such as GaSb and InSb, ΓIII=ΓV from the compound phase with no evidence of preferential sputtering. However, under deposition conditions leading to the growth of two phase films, such as Sb to group III flux ratios much greater than or less than unity, bombardment by ions with greater than the threshold sputtering energy always resulted in the preferential removal of the excess species. Thus for the entire range in growth temperatures (50°–500°C) and V/III flux ratios (<1 to ≳10) used in these experiments, stoichiometric films could always be obtained by adjusting the ion bombardment conditions. Temperature dependent Hall measurements were used to determine Sb vacancy concentrations as low as 1016 cm−3 in single-crystal GaSb films grown on (100) GaAs. Finally, ion bombardment during film growth was used to simultaneously alter elemental incorporation probabilities and maintain film stoichiometry in order to grow metastable InSb1−x. pseudobinary alloys with InBi solubilities more than four times larger than the equilibrium value.
Electrochemical measurement of states on oxidized GaAs
Authors: Frese Karl W. , Morrison S. Roy
Published: July 2002

Evidence is presented that a conducting band is present in the anodic oxide of GaAs that lies about 1.0±0.3 eV below the GaAs conduction band. The energy of the level is determined by a new electrochemical technique that in a sense is the reverse of normal electrochemical voltammetric techniques. In normal voltammetry, an unknown energy level of an ion in solution is determined knowing the energy of the source of electrons, but in our new technique, we intentionally add ions of known energy level in the solution and determine, as the unknown, the energy level of the electron source. The energy of the electron source is the conducting band in the anodic oxide. Other evidence that the oxide has a low energy conducting band includes the observation of rectification processes attributable to a Schottky barrier at the interface and the observation that the capacitance calculated from voltage ramp charging curves had values corresponding to the Helmholtz capacitance.
Structural characterization of NbCN thin films
Authors: Skelton E. F. , Wolf S. A. , Francavilla T. L.
Published: July 2002

Reactively sputtered films of NbCxN1−x have been characterized by x-ray diffraction measurements of the unit cell size, mean crystallite dimensions, relative degree of crystallite perfection, and preferred orientation. Large structural variations could be seen in these films which were reproducible functions of the preparation conditions.
XPS study of interface formation of CVD SiO2 on InSb
Authors: Vasquez R. P. , Grunthaner F. J.
Published: July 2002

The interfacial chemistry of CVD SiO2 films deposited on thin native oxides grown on InSb substrates is investigated using x-ray photoemission and chemical depth profiling. The SiO2 films are grown through thermal decomposition of silane in a N2/O2 ambient. The chemical composition of these films is determined through the use of a relatively benign chemical- etching method together with an intensity analysis of the XPS spectra. Absolute peak positions are utilized to determine the different local chemical environments as well as to follow the details of surface potential variations which correlate with the chemical depth profile. Before deposition, the InSb surface is covered by a 15–20 Å native oxide overlayer composed of In2O3 and Sb2O3 in a 3:1 ratio. During deposition of SiO2 on InSb, significant interaction between deposited and native species was found. Reaction of the substrate with oxygen resulted in an In-rich native oxide and 1–2 monolayers of excess elemental Sb at the native-oxide/substrate interface. Incompletely oxidized silane reduced the native oxide, leaving ≲1 monolayer of elemental In at the SiO2/native oxide interface. Etch removal of this thin In-rich layer leads to a change in substrate surface potential of 0.06 eV, corresponding to a net increase in positive charge. The experimental observations are shown to be consistent with simple thermodynamic considerations, and a comparison is made with previous studies of deposited insulators on III–V compound semiconductors.
Interface behavior and crystallographic relationships of aluminum on GaAs(100) surfaces
Authors: Ludeke R. , Landgren G.
Published: July 2002

The degree of covalent bond formation of Al to GaAs at the interface determines both its stability against an exchange reaction with Ga, and the crystallographic relationships between substrate and overgrowths. At elevated temperatures the observed exchange reaction and subsequent interdiffusion of the constituent atoms results in a nonabrupt interface, which facilitates the accommodation of the resulting Al(110) overgrowth. These properties are observed irrespective of the As coverage of the starting GaAs(100) surface. At room temperature, the presence of As on the surface of the GaAs(100)-c(2×8) structure stabilizes the interface against a replacement reaction and constrains the Al to a (110) growth rotate 90° with respect to the high temperature phase. On the predominantly Ga terminated GaAs(100)-(4×6) structure the metallic interfacial bonds permit a lattice matched Al(100)-45° overgrowth to dominate. For this surface a partial replacement reaction is observed beyond a critical overgrowth thickness of ∠1.5 Å and appears in conjunction with the Al nucleation process which invariably occurs for all surfaces and growth conditions. At room temperature, the net energy release during the nucleation process is the determining quantity necessary to overcome the barrier for the exchange reaction. The heat of adsorption of Al on GaAs is not sufficient to trigger the replacement reaction on the GaAs(100) surface, and its high value on the As-stabilized surface inhibits the reaction from occurring.
Formation, growth, and stability of the CdS/CuInSe2 interface
Authors: Kazmerski L. L. , Jamjoum O. , Ireland P. J. , Mickelsen R. A. , Chen W. S.
Published: July 2002

The initial formation and subsequent development of the CdS/CuInSe2 interface are studied. XPS depth-compositional data are used to identify the composition of a interfacial reacted region between the CdS and Cu-ternary layers. Angular-resolved XPS confirm the existence of this transition layer which is a mixed Cu2S–Cu2S binary. Auger transitions in the XPS spectra are used to resolve those compounds. Differences in EELS spectra as a function of CdS growth are also ascribed to the existence of the interface region. The effects of annealing on the integrity of this interface and photovoltaic performance of the device are also presented. Three distinct regimes are identified: (1) T<150 °C. Device and interface properties are stable; (2) 200<T<300 °C. Se and S interdiffusion occurs, with 50%–75% degradation in cell performance; and (3) T≳350 °C. Rapid diffusion of the Cd into the Cu-ternary takes place, destroying junction integrity and causing complete device failure.
Interface electronic structure of Pb on GaAs(001)
Authors: van der Veen J. F. , Smit L. , Larsen P. K. , Neave J. H. , Joyce B. A.
Published: July 2002

The electronic structure of two-dimensional, ordered Pb overlayers in submonolayer coverages on MBE grown GaAs(001) surfaces has been studied by angle-resolved photoemission using synchrotron radiation. A Pb(6s) derived interface state of Δ1 symmetry has been identified in the heteropolar gap of GaAs at an energy of −8.3 eV below the valence-band maximum. Two surface resonances of dangling bond character and of inplane character ( px−py) are located near the top of the valence bands, at −0.4 eV and −2.0 eV, respectively. High resolution studies of Ga(3d), As(3d), and Pb(5d) core levels show that there is no significant chemical interaction between the overlayer and the substrate.
Transparent conducting zinc oxide and indium–tin oxide films prepared by modified reactive planar magnetron sputtering
Authors: Maniv S. , Miner C. J. , Westwood W. D.
Published: July 2002

Transparent conducting layers for liquid crystal displays and plastic substrates must be deposited without significant heating. A planar magnetron sputtering process which provides a suitable combination of resistivity and transparency on unheated substrates has been developed. Transparent conducting films of ZnO and indium tin oxide (ITO) have been deposited by sputtering Zn and In0.9Sn0.1 targets in a planar magnetron system modified to introduce oxygen near the substrate and to reduce the conductance for oxygen to the target. As the oxygen flow rate f2 increased, the dc voltage Va, required to maintain constant sputtering current, first increased and then decreased rapidly as the critical flow rate f2c, at which the target oxidizes, is approached. In the ZnO case, Va had a maximum value of 525 V and was 355 V after the target oxidized; transparent conducting films were obtained at 435 V but the best films were obtained by activating an rf discharge close to the substrate to increase the oxidation rate. These polycrystalline films had a transmittance of 80% and a resistivity of 0.03 Ω cm but their chemical stability was too poor for useful application. In the ITO case, the rf discharge was necessary to obtain transparent conducting films. Even at f2/f2c=0.94, films were opaque in the absence of this extra oxidation mechanism. Films with a transmittance of 79% and a resistivity of 1×10−4 Ω cm were obtained by coupling an rf power of 105 W to the substrate holder, with a substrate self-bias voltage less than 5 V, at f2/f2c=0.77. These films are amorphous and chemically stable. This sputtering process provides a maximum deposition rate of 48 nm/min on unheated substrates and is suitable for fabricating MIM-addressed liquid crystal displays.
Thermal stability of oxide films on Cd0.2  Hg0.8Te: A combined SIMS, AES, and XPS study
Authors: Kaiser U. , Ganschow O. , Wiedmann L. , Benninghoven A.
Published: July 2002

In previous work, the structure of anodic oxide layers on Cd0.2 Hg0.8Te (MCT) has been determined. The stability of these features against heat treatment at 520 K under UHV conditions has been investigated. The layer is thermally decomposed by diffusion of oxygen into the semiconductor. As a consequence, the characteristic structure of the interface is shifted towards the surface, whereas the composition above this structure remains unchanged.
Effects of gaseous oxygen on SIMS analysis of oxygen-isotopes in metal oxides
Authors: Sato Kazunori , Inoue Yasunobu , Ohno Masaaki , Someno Mayumi
Published: July 2002

The influence of an O2 atmosphere on oxygen-isotope analysis by means of secondary ion mass spectrometry (SIMS) was studied in detail using various standard metal oxides enriched with a stable isotope18O. The secondary ion intensities of 16O− and 18O− were examined under different 16O-oxygen pressures and primary Ar+ beam currents. The deviation in the isotope ratio became prominent at an oxygen pressure over about 1×10−4 Pa, and in the sequence of CuO<ZnO<NiO, Co3O4<Cr2O3<TiO2. A decrease in beam current resulted in the enhancement of this oxygen effect. When pure metals such as Cu, Zn, Ni, Co, Cr, and Ti were sputtered in an 16O2 atmosphere, the secondary ion intensities of 16O− changed with oxygen pressures in a similar way to those of 16O− emitted from 18O-oxides consisting of the corresponding metal atoms. It was shown that the oxygen effects among the oxides are closely related to the bonding strength between metal and oxygen atoms; the stronger interaction being responsible for the larger oxygen effects.
Absorption and desorption of hydrogen, deuterium, and tritium for Zr–V–Fe getter
Authors: Ichimura Kenji , Inoue Naoya , Watanabe Kuniaki , Takeuchi Toyosaburo
Published: July 2002

Nonevaporable getters have wide applicability for developing the tritium handling techniques for thermonuclear fusion devices. From this viewpoint, mechanisms of the absorption and desorption of hydrogen isotopes and the isotope effects were investigated for a Zr–V–Fe alloy (St-707) by means of the mass analyzed thermal desorption spectroscopy. It was observed that the absorption rate was proportional to the first power of the pressure, indicating that the rate limiting step is the dissociative adsorption of hydrogen isotopes on the surface. The activation energy was very small, in the order of magnitude of a few tens of calories per mole in a temperature range from −196 to 200 °C. The desorption rate was proportional to the square of the amount of absorption, indicating that the rate limiting step is the associative desorption reaction of hydrogen atoms or ions diffused to the surface from the bulk. The rate constants for hydrogen and deuterium were determined as kd(H2)=(5.3+2.6−1.7)exp[−(28.0±0.7)×103/RT] and kd(D2)=(5.0+2.7−1.7)exp[−(28.6±0.8)×103/RT] in [1/Pa 1 s], respectively, where R is in [cal/mol deg]. With regard to tritium, the rate constant was evaluated as kd(T2)=(5.0+20−4.0)exp[−(29.3±3)×103/RT], however, the frequency factor will have to be corrected by knowing the relative sensitivity factor of the mass spectrometer for tritium (T2).
Modification of the electrochromic response of WO3 thin films by oxygen backfilling
Authors: Sun S.-S. , Holloway P. H.
Published: July 2002

The effect of oxygen backfilling on WO3 electrochromic thin films has been studied. Previously it was shown that O2 backfilling reduced the corrosion rate in H2SO4. In this phase of the study it has been shown that O2 backfilling also affects the EC response. For example, the coloration speed and optical efficiency were decreased while bleaching speed and self-erasure rate were increased. The current injection during coloration was found to be controlled by the same mechanism as the films without backfilling (i.e., WO3 resistivity and Helmholtz double layer). However, the magnitude of the current passed was lowered due to increased film resistivity from backfilling. The optical absorption maximum remained unchanged while the thermal hopping energy increased with oxygen backfilling. These observations suggest that a decreased density of optically active absorption centers resulted in the lower optical efficiency.
High resolution sputter depth profiling of implantation structures in Si by low energy SNMS
Authors: Oechsner H. , Paulus H. , Beckmann P.
Published: July 2002

The potentialities of the direct bombardment mode of secondary neutral mass spectrometry (SNMS) for depth profile analysis are discussed. In particular the achievement of extremely high depth resolution by using ion bombarding energies on the order of only 102 eV is emphasized. Low energy SNMS is applied for depth profiling of implantation profiles of As and P in Si. The range parameters obtained from the measured profiles are compared with theoretical values. By means of the high depth resolution, detailed structures in the unannealed implantation profiles are quantitatively determined and partially explained by the presence of residual surface oxides.
A transmission electron microscopy study of rf- and dc-magnetron-sputtered thin film chromium and chromium–platinum coatings
Authors: Fishkis M. R. , Sisson R. D. , Biederman R. R.
Published: July 2002

Microstructural features of sputtered chromium and chromium-50 wt.% platinum thin films on carbon substrates are presented. Films produced by rf sputtering and dc magnetron sputtering are compared using analytical electron microscopy techniques. All rf-sputtered films are uniform in chemistry and thickness and are amorphous. The chromium film became crystalline with a grain size of less than 100 Å after a 320 °C heat treatment for 1 h. The chromium-50 wt. % platinum film remained amorphous after the same heat treatment. The as-sputtered dc magnetron chromium film was crystalline.
Plasma sprayed WC–Co coatings: Influence of spray conditions (atmospheric and low pressure plasma spraying) on the crystal structure, porosity, and hardness
Authors: Vinayo M. E. , Kassabji F. , Guyonnet J. , Fauchais P.
Published: July 2002

Ten WC–Co (12, 17, and 20 wt.% Co) powders manufactured by different techniques (sintering, atomization, coating) were studied. Both open atmosphere Ar–H2 plasma spraying and controlled atmosphere Ar–He chamber plasma spraying were performed. Pressures of 60, 150, 400, and 700 Torr were employed. To optimize controlled atmosphere spray conditions, particles splatted on glass slides rapidly traversing the jet at different distances from the nozzle exit were studied. The melting conditions were determined as a function of the plasma power level, the particle composition, and structure for particles with the same size distribution. Crystal structure analysis showed a strong decomposition of the carbides when sprayed in open atmosphere. Less decomposition occurred in the coated or atomized particles. The decomposition was reduced and coating density increased by reduced pressure spraying. The best results were obtained at 60 Torr. The hardness depended on the cobalt content, the degree of decomposition and on the density of the coatings.
The anodic vacuum arc. I. Basic construction and phenomenology
Authors: Ehrich H.
Published: July 2002

A new type of vacuum arc is described, the anodic vacuum arc at low currents. This arc discharge is ignited in vacuum and generates a pure metal vapor plasma by evaporating anodic material, which continuously sustains the discharge. By proper construction of the electrodes a steady arc can be maintained at low currents (20–40 A). Basic electrode phenomena are the formation of cathode and anode spots. Metallic coatings produced by means of the anodic vacuum arc show promising features: the coatings are homogeneous, the deposition rates are high (8 nm/s for a 0.7-kW Al arc), and the thermal stress of the substrates being coated is low.
Ordered phases and phase transitions of cesium on the Cu(111) surface
Authors: Fan W. C. , Ignatiev A.
Published: July 2002

Low-energy electron diffraction (LEED) experiments have been carried out to study the ordered phases and phase transitions of cesium on the Cu(111) surface in the temperature region between 80 and 450 K. The cesium on the 80-K surface forms an orientationally ordered incommensurate structure (IS) at coverage θ>0.12. The overlayer lattice parameter of the IS phase decreases continuously with coverage until a Cs–Cs spacing 7% smaller than in bulk cesium is reached. By increasing the temperature, the IS phase undergoes several transitions as a function of coverage: (i) a better ordered phase at 135 K, (ii) a disordered phase through an intermediate phase (‘‘hexatic’’ phase) at θ<0.21 or without the intermediate phase at θ>0.21, and (iii) a (2×2) phase at θ>0.25 and T≊260 K and a (6×6) phase at T≊355 K. The cesium on the surface also forms an antisymmetrical metallic domain phase and a coexisting phase of ( (4)/(3) (3)1/2× (4)/(3) (3)1/2)-R30° and (2×2).
Explosive crystallization in zirconium/silicon multilayers
Authors: Wickersham C. E. , Poole J. E.
Published: July 2002

Explosive crystallization (EC) in multilayer films of zirconium and silicon with periods ranging from 7.4 to 29.4 nm and total film thickness ranging from 0.4 to 10 μm has been studied and found to depend strongly upon both the total film thickness and the multilayer period. The optimum multilayer period for EC in Zr/Si multilayer films, where the ratio of the Zr and Si layer thickness is 0.583 (stoichiometric ZrSi2), is 20 nm. Films sputter deposited with this structure exhibited EC at room temperature with a total film thickness of only 0.45 μm (∼50 times thinner than amorphous Ge). The variation in the propensity of Zr/Si films to undergo EC is found to depend upon the number of interfacial layers per unit volume. A model is developed which accurately describes the observed variation in EC behavior with multilayer period. An 18% increase in film density accompanies the EC transformation in Zr/Si multilayer films. This large density change places the resulting ZrSi2 film in a high tensile stress condition.
Radio-frequency sputter deposition of boron nitride based thin films
Authors: Mitterer C. , Rödhammer P. , Störi H. , Jeglitsch F.
Published: July 2002

Thin films (≊2 μm) of boron nitride, titanium boron nitride, and titanium aluminum boron nitride have been grown on molybdenum, niobium, and cemented carbide substrates employing nonreactive as well as reactive rf magnetron sputter deposition from either a BN, a TiN-BN, or a TiN–AlN–BN target. Substrates have been rf biased, with dc potentials up to −200 V. By means of nonreactive sputtering mixed-phase structures with dominant phases B48B2N2 (using a BN target), or B48B2N2 and hexagonal Ti–B–N (using a TiN–BN or a TiN–AlN–BN target) are formed. Reactive deposition leads to the existence of hexagonal BN in all deposition modes. In the cases of Ti–B–N and Ti–Al–B–N films this phase is accompanied by fcc Ti–B–N. SEM cross sections revealed very fine grained to fracture-amorphous film structures. Hardness measurements gave the following maximum HV 0.02 values: B–N films 2800, Ti–B–N films 2750, and Ti–Al–B–N films 1650.
Current–voltage characteristics of silicon measured with the scanning tunneling microscope in air
Authors: Jahanmir J. , West P. E. , Young A. , Rhodin T. N.
Published: July 2002

A scanning tunneling microscope, operated in air, is utilized to measure the current–voltage (I–V) curves of silicon samples with differently prepared thin layers of oxide. We report measurements on as-prepared (mechanically and chemically polished by the manufacturer) wafers and on wafers with a thin layer of thermal oxide. The I–V measurements on the silicon sample with the thermal oxide were dominated by surface states. In contrast, band bending was observed on the ‘‘as-prepared’’ silicon samples. The difference between the results were related to the nature of the thin film of oxide on the surface. The forward bias I–V characteristics, for the as-prepared samples, are compared with the behavior predicted by the metal–insulator–semiconductor theory. In these measurements, larger than expected tip-to-sample spacings are observed. This is attributed to the presence of a layer of contamination between the tip and sample.
Stress dependence of reactively sputtered aluminum nitride thin films on sputtering parameters
Authors: Huffman G. L. , Fahnline D. E. , Messier R. , Pilione L. J.
Published: July 2002

Aluminum nitride thin films (∼5000 Å) were deposited by reactively sputtering an aluminum target in a dc magnetron system. The stress and crystallographic orientation associated with these films were found to depend on the total sputtering pressure and the N2 partial flow rate in the sputtering mixture. A pressure range was found to exist between 3.00 and 3.75 mTorr where the film stress was in transition between compression and tension. At total sputtering pressures outside this transition range the pressure determined the type of film stress, while at total sputtering pressures within the transition range the N2 partial flow rate played an important role. Film stress was determined qualitatively by substrate curvature, while x-ray diffraction was used to observe changes in the crystallographic orientation of the films.
Scanning tunneling microscopy of rough surfaces
Authors: Denley D. R.
Published: July 2002

When the high resolution capability of scanning tunneling microscopy (STM) is coupled with digital data acquisition, it is possible to get quantitative information on surface texture. This capability has been used for surface roughness measurement, and searching for fractal behavior. The peak altitude method of measurement of surface roughness is illustrated for evaporated gold films and the dependence of roughness on deposition temperature and annealing time is described. By using algorithms for scale dependent measurement of surface area, the existence of fractal morphology is investigated. This method is used to contrast the behavior of the fracture of steel vs epoxy resin. The results on gold films show a clear trend for which the roughness, as well as the experimental deviance of the roughness, is found to be minimal for evaporation at 300 °C. The limitations of STM for roughness measurement are discussed. The steel fracture surfaces were similar on length scales studied, but were highly variable over the studied surfaces. A fractal dimension was determined, and this value was compared to fractal dimensions determined previously by lower-resolution techniques. On the other hand, the resin fracture did not fit well with the expected behavior of either a geometric surface, or that of a self-similar surface.
Interaction of copper with a vapor deposited polyimide film
Authors: Mack R. G. , Grossman E. , Unertl W. N.
Published: July 2002

The interaction of copper with a vapor deposited film of PMDA-ODA polyimide was studied using x-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM). Copper was evaporated onto the polyimide surface to a total thickness estimated to be about five atomic layers. The copper initially interacts with the planar imide ring—the nitrogen XPS signal is preferentially attenuated, some copper is oxidized, and the carbonyl XPS intensities are altered. We find no evidence for chemical interaction with the ODA part of the polyimide. Heating the copper covered surface leads to redistribution of copper, probably below the surface as reported in earlier studies. STM images of the heated surfaces show that substantial surface roughening has occurred.
Evidence of SiOx suboxides at Ar ion etched silica surfaces
Authors: Paparazzo E. , Fanfoni M. , Quaresima C. , Perfetti P.
Published: July 2002

X-ray photoelectron spectroscopy (XPS), Auger spectroscopy, and synchrotron radiation (SR) photoemission are used for studying composition changes induced by 1–8 keV Ar ions on silica surfaces. When recorded at normal electron emission, both XPS and Auger spectra show that SiOx phases (0<x<2) form for Ar energies higher than 2 keV. The presence of these species is also disclosed by the silicon Auger parameters. The 0/Si atomic ratio, calculated by quantitative XPS analysis, drops well below two for impact energies ≥5 keV. SR photoemission and angular dependent XPS results, obtained at depth resolutions in the range 4–10 Å, show that photoemission techniques possess a chemical capability for discriminating between SiOx suboxides and silica, which is comparable with that achievable by Auger Si LVV spectra.
Deoxyribonucleic acid structures visualized by scanning tunneling microscopy
Authors: Bendixen C. , Besenbacher F. , Lægsgaard E. , Stensgaard I. , Thomsen B. , Westergaard O.
Published: July 2002

The capability of the scanning tunneling microscope (STM) to produce atomic-resolution images makes it a powerful tool in both basic and applied science. The main application of STM has been for the analysis of structural features and electronic properties of a wide spectrum of metals and semiconductors, while only a few biological items have been investigated. With a STM operating in air at ambient pressure, we present images showing the molecular structure of naked DNA. High-resolution topographic images of linear DNA fragments reveal structures with a periodicity of ∼38±6 Å and a width of 28±4 Å, consistent with the molecular dimensions of the helical repeat of double-stranded DNA. In addition, the supreme resolving power of the STM permits visualization of the major and minor grooves.
Infrared-laser interferometric thermometry: A nonintrusive technique for measuring semiconductor wafer temperatures
Authors: Donnelly V. M. , McCaulley J. A.
Published: July 2002

We report an optical, interferometric technique for measuring the temperature of semiconductor substrates during heating or cooling, which is applicable in vacuum. The technique circumvents many of the problems associated with thermocouple or pyrometer measurements. A low-power infrared (IR) laser (e.g., λ=1.15-μm He–Ne laser) having an energy below the band gap is directed at a wafer that is polished on both sides, where either reflected or transmitted laser light is detected by a photodiode. Interference results between reflections off the front and back surfaces of the wafer. As the temperature of the wafer is either increased or decreased, the temperature dependence of the refractive index, along with a smaller contribution from thermal expansion, causes the optical path within the wafer to change by λ/2n (i.e., a full interference cycle) for every ∼3 K for a typical Si, GaAs, or InP wafer thickness of 500 μm. Consequently, temperature changes of ±0.2 K are easily detected. This technique, has been used between room temperature and 600 °C on GaAs substrates in a low-pressure metal-organic chemical vapor deposition (MOCVD) system, and in an ultrahigh vacuum thermal desorption experiment. This method can be used well below room temperature, as well as at temperatures above 650 °C with the optimum choice in laser wavelength. Application of this method to other processes such as molecular beam epitaxy (MBE), reactive ion etching, and rapid thermal processing should be straightforward. We also describe a refinement of the method for measuring the sign, as well as magnitude of temperature changes for typical, slightly tapered wafers during heating or cooling cycles. In this case the reflected laser beam contains a series of parallel lines that move toward the thinner end of the region probed by the laser beam as the temperature increases. Sensing the direction that these spatial interference fringes move can be used to determine whether the sample is heating or cooling.
The growth of Ag films on Si(100)
Authors: Brodde A. , Badt D. , Tosch St. , Neddermeyer H.
Published: July 2002

Room temperature condensation of Ag films on Si(100) in the submonolayer and monolayer range has been studied by means of voltage-dependent scanning tunneling microscopy and in some cases by scanning tunneling spectroscopy (STM). The uncovered Si(100) substrate showed various kinds of local atomic structures, which influence the growth behavior of the Ag films. Short heating of Si(100) produced a 2×1 reconstruction with a comparably small number of defects. Extensive heating increased the number of defects and finally led to ordering of defects and formation of a 2×8 reconstruction showing weak 1/8 and strong 1/2 order low-energy electron diffraction (LEED) beams. In the submonolayer range Ag condenses in row-like structures along the dimer rows of the substrate (i.e., vertical to the dimer direction). The Ag atoms are repelled from the Si defect sites. For a large number of defects (e.g., for a 2×8 reconstructed substrate) 1 ML Ag does not cover completely the substrate surface but already starts with the growth of three-dimensional Ag islands. The Stranski–Krastanov growth mode of the system Ag/Si (100) (interface+island formation) has therefore been convincingly established. The interaction between the Ag atoms in the interface layer and the Si substrate is remarkably weak. We reproducibly observed current instabilities near Ag sites and distinct diffusion processes of the Ag atoms during the STM measurements.
Sputtered neutrals mass spectrometry of organic molecules using multiphoton postionization
Authors: Terhorst M. , Kampwerth G. , Niehuis E. , Benninghoven A.
Published: July 2002

Multiphoton postionization of sputtered neutral molecules has been investigated by high-resolution time-of-flight mass spectrometry. The desorption of the molecular species is induced by a pulsed 10 keV Ar+-ion beam with primary-ion dose densities below 1013 PI/cm2. For postionization an excimer laser at 193 nm wavelength or a tunable dye laser operating between 240 and 300 nm are used. In systematic investigations fragment patterns and useful yields of the commonly occurring amino acids were investigated. With λ=193 nm nearly all of them could successfully be identified by their (M-45) fragment which corresponds to the loss of the carboxyl group. The photoion yield varied over nearly two orders of magnitude for different amino acids. The aromatic ones could also be postionized at longer wavelengths (260–300 nm). Ion yields and fragment patterns critically depend on energy deposition of both the sputter process and the multiphoton absorption. This can be seen by comparison with gas-phase ionization of evaporated molecules and by the dependence of the ionization signal on the laser power density. In contrast to the postionization of sputtered atoms the ionization of sputtered molecules is not characterized by strong spectral features and only a poor degree of ionization selectivity can be achieved. In general, the results demonstrate that the combination of ion-beam sputtering and multiphoton postionization offers great potential not only in element analysis, but also in surface analysis of organic materials.
A novel source design for molecular beam machines
Authors: Weber Peter M. , Stanks J. , Thantu N. , Hellmer Roland
Published: July 2002

We describe the performance of a molecular beam machine with a recently introduced wide range turbomolecular pump as a source pump. In comparison to large diffusion pumps the turbo pump has a small pumping speed, which leads to the formation of a weak, partially penetrable barrel shock surrounding the free jet expansion. Collisions of background gas molecules that penetrate the shock with seed gas molecules were found to reduce the density of the seeded molecules in the skimmed molecular beam by about 20%. For many experiments this attenuation can be tolerated, so that full advantage of wide range turbo pumps can be taken.