bluuebunny/crossref_metadata_2025 huggingface dataset:
Scanning tunneling microscopy of cubic silicon carbide surfaces
Authors: Zheng N. J. , Knipping U. , Tsong I. S. T. , Petuskey W. T. , Kong H. S. , Davis R. F.
Published: July 2002

Surface topographies of n-type β-SiC single crystals epitaxially grown by chemical vapor deposition on Si(100) and Si substrates inclined at 4° off (100) toward (011) were imaged by a scanning tunneling microscope. The images suggest that smooth surfaces can be achieved by epitaxial growth on the 4°-off substrates. Oxidation of the β-SiC surfaces followed by chemical etching to remove the oxide layer also tend to produce smooth surfaces.
Radio-frequency coupling to plasmas
Authors: Colestock P. L.
Published: July 2002

A survey of the physics associated with coupling rf power to plasmas is given with emphasis on methods of analysis relevant to applications in the fields of plasma production, processing, and fusion research. The significance of resonant versus nonresonant coupling methods is discussed and specific applications are described where these phenomena dominate the coupling physics.
A study of graphite and intercalated graphite by scanning tunneling microscopy
Authors: Gauthier S. , Rousset S. , Klein J. , Sacks W. , Belin M.
Published: July 2002

The surface of some intercalated compounds of graphite has been investigated by scanning tunneling microscopy. The images obtained on two acceptor compounds generally reveal a graphitic structure with the same range of corrugation as on graphite. On the contrary, the surface of one donor compound looks quite different from graphite. These observations are in agreement with a recently proposed model [M. Lagües, D. Marchand, and C. Frétigny, Solid State Commun. 59, 583 (1986)].
Inverse photoemission and resonant photoemission characterization of semimagnetic semiconductors
Authors: Wall A. , Franciosi A. , Gao Y. , Weaver J. H. , Tsai M.-H. , Dow J. D. , Kasowski R. V.
Published: July 2002

The new magnetotransport and magneto-optical properties of the semimagnetic Cd1−xMnxTe semiconductor alloy series depend critically on the nature of the Mn-derived d states. We examine here the electronic structure of these alloys with a combination of inverse photoemission spectroscopy, core-level photoemission line-shape analysis, valence-band resonant photoemission, and local density pseudofunction theory. The spectroscopic data reflect the local Mn–Te coordination and are in remarkable agreement with our one-electron calculations. We see no evidence of Mn-derived d states in the gap, and observe an experimental d↑–d↓ exchange splitting of 8.4±0.4 eV, i.e., almost twice as large as expected from earlier theoretical estimates. The ground-state configuration of Mn in the solid is primarily (d↑)(s↑)(p↑), and the super-exchange interaction has an important role in determining the stability of such a configuration relative to (d↑)5s2.
Low hydrogen content silicon nitride deposited at low temperature by novel remote plasma technique
Authors: Hattangady S.V. , Fountain G. G. , Rudder R. A. , Markunas R. J.
Published: July 2002

A novel remote plasma deposition technique has been used to deposit low hydrogen content silicon nitride at a temperature of 300 °C. This technique uses a remote noble gas discharge to excite nitrogen and silane species which are introduced downstream, out of the plasma region. Optical emission spectroscopy indicates that the downstream interaction creates excited molecular nitrogen with little evidence of atomic nitrogen. Infrared spectroscopy has been used to qualify the hydrogen content in these films. The etch rate in buffered HF of these films is as low as (1)/(20) that of thermal oxide. A surface reaction model for hydrogen removal is proposed. In that model the hydrogen incorporation is controlled by the arrival rate of SiHx species (i.e., the growth rate) and the desorption of NHx groups from the film surface. Electrical results indicate that the fixed charge density in the nitride films is in the low 1011 cm−2 and the interface state density is in the upper 1011 cm−2 eV−1 range. The current–voltage characteristics under ramped bias show no ledges and sustain a current density of 4.6×10−4 A cm−2 at a field of 4.2 MV cm−1. Their analysis shows that conduction is through Poole–Frenkel transport (bulk-trap limited) as in conventional chemical vapor deposited Si3N4. Furthermore, a trilayer oxide–nitride–oxide structure on silicon has been fabricated with no hysteresis observed on capacitance–voltage measurements and a (3–5)×1010 cm−2 eV−1 interface state density.
The adsorption and decomposition of formic acid on Ni(111): The identification of formic anhydride by vibrational spectroscopy
Authors: Erley W. , Sander D.
Published: July 2002

The adsorption and decomposition of formic acid (HCOOH) on a Ni(111) surface has been examined using thermal desorption spectroscopy (TDS), electron energy-loss spectroscopy (EELS), and reflection–absorption infrared spectroscopy (RAIRS). At 90 K several adsorption states above monolayer coverage are detected. Hydrogen bonding of HCOOH is indicated by strongly red-shifted OH stretching modes. The first layer, possibly consisting of adsorbed HCOOH dimers, is dehydrated above 250 K and forms a stable surface intermediate. Further heating leads to the known autocatalytic decomposition of the surfaces species and produces extremely sharp TDS peaks of CO2 and H2 . Above 360 K only CO is left on the surface. After forming the stable surface intermediate using DCOOH, modes at 776, 1267, 1329, 2181, and 2199 cm−1 are observed by RAIRS. The latter two modes, which are not resolved by EELS, are interpreted as the symmetric and antisymmetric CD stretching modes of the surface intermediate. Consequently, whereas most vibrational studies on other surfaces favor a formate ion (HCOO) as stable surface intermediate, we propose a formic anhydride on the Ni(111) surface. The modes observed at 1323 and 1267 cm−1 are interpreted as symmetric and asymmetric CO stretching modes. The existence of a formic anhydride intermediate is finally confirmed by an experiment using a mixture of HCOOH and DCOOH: The RAIRS spectra show the presence of all three different kinds of intermediates which are (HCO)2 O, (DCO)2 O, and HCO–O–DCO.
High-porosity coated getter
Authors: Giorgi E. , Ferrario B. , Boffito C.
Published: July 2002

The importance of nonevaporable getters is recognized by the increasing number of various applications in vacuum technology. To meet some specific requirements of certain applications (e.g., special vacuum tubes) a nonevaporable getter layer (from a few tens to 100 μm or more) having high porosity (50%–60%) and very good gas sorption and mechanical characteristics has been developed. The special method used for the preparation of these getters produces gettering surfaces on conductive substrates of many different preformed shapes (very thin strips, cylinders, wires, etc.). This allows accomodation of the getters in special or restricted spaces. These results are reached by depositing on the substrates a mixture of powdered Ti (or Zr) and a nonevaporable getter alloy of the types: Zr–Fe–V or Zr–Al. The getter material is then partially sintered to obtain a good mechanical stability, keeping a relatively high porosity. The present paper describes the characteristics of the recently developed high-porosity coated getters in terms of their physical features (porosity, mechanical behavior in different working conditions, such as high H2 gas load, etc.) and sorption performances for some main gases under different activation conditions (from 300 to ∼750 °C), also making some comparisons with an evaporated Ti layer.
Evidence of anomalous behavior in low-n-type mercury cadmium telluride induced by extended defects
Authors: Pelliciari B. , Destefanis G. L. , Di Cioccio L.
Published: July 2002

Suitable improvements of our liquid phase epitaxy (LPE) growth process enable us to obtain excellent quality p-type as-grown mercury cadmium telluride (MCT) epilayers, well adapted to high-performance photovoltaic (PV) detector technology. Although our technology only needs undoped p-type MCT as starting material, we also convert a lot of these epilayers to n type to check their electrical properties in view of two fundamental problems: anomalies of electrical behavior and residual doping level. After n-type annealing, most of our LPE layers have a classical behavior versus temperature even under a high magnetic field value of 10 000 G: at 77 K, values of n77d =2×1014 cm−3 and μ77 =105 cm2  V−1  s−1 and at 27 K n27d =2×1014 cm−3 and μ27 =2 to 3×105 cm2 V−1  s−1 are routinely obtained, for a cutoff wavelength of 6.3 μm (as given by IR transmission at room temperature); this corresponds to a cutoff wavelength of 10.6 μm at 77 K, as measured on our PV diodes.

Transmission electron microscopy (TEM) observations show that these layers are defect-free and this is confirmed by x-ray topography which shows only the misfit dislocation pattern. However, some samples have an anomalous behavior featured by a ‘‘kink’’ on the mobility curve between 100 and 77 K, the nd value being in the low-1014 range. TEM observations show in this case the presence of dislocations, the density of which is directly correlated to a more or less significant kink on the mobility curve; also, the aspect of the x-ray topography changes from a sharp misfit structure (low density of loops) to a mixed structure (higher density of loops). If this density of loops is still increased, the x-ray topography becomes hazy and the Hall-effect measurement indicates the epilayer to be p type even after an n-type annealing. These loops are assumed to generate doping microinhomogeneities responsible for anomalous Hall-effect behavior. So, extended defects have to be avoided to achieve high-quality MCT material; a way to reach this goal is to grow buffered structures, the electrical properties of which are presented together with TEM observations.
Variation in GaAs surface oxide desorption temperature as a function of shuttered aluminum oven temperature
Authors: Kuhn K. J. , Pubanz G. A.
Published: July 2002

A variation in the thermal desorption temperature of surface oxides as a function of shuttered aluminum oven temperature has been observed for GaAs substrate material prepared for molecular-beam epitaxy (MBE) using two different wet-etch processes. A novel temperature calibration technique was developed to determine the absolute thermal desorption temperature. The observed thermal desorption temperature with a cool shuttered aluminum oven displayed no variation and was consistent with the currently accepted value of 582 °C. However, experimental results indicate that the thermal desorption temperature with a hot shuttered aluminum oven is substantially greater (630–650 °C) than the currently accepted value. It is suggested that aluminum species present on the shutter desorb and react with the surface gallium oxide to form a more refractory surface oxide.
Magneto-optical properties of a small-gap HgTe/CdTe superlattice
Authors: Wagner R. J. , Perez J. M. , Meyer J. R. , Han Jeong W. , Cook J. W. , Schetzina J. F.
Published: July 2002

Far-infrared magneto-optical experiments have been performed on a p-type HgTe/CdTe superlattice with a small effective band gap. The angular dependence of the hole cyclotron resonance spectra reveals that the effective mass is two orders of magnitude heavier in the growth direction than transverse to it. These results provide evidence for a large valence-band offset. In addition, a tentative identification of hole spin resonance has been made. Evidence is presented which shows that the superlattice band structure can be substantially modified by the application of modest magnetic fields.
Temperature-dependent photoemission study of the HgTe–CdTe valence-band discontinuity
Authors: Sporken R. , Sivananthan S. , Faurie J. P. , Ehlers D. H. , Fraxedas J. , Ley L. , Pireaux J. J. , Caudano R.
Published: July 2002

We have studied the temperature dependence of the CdTe–HgTe valence-band discontinuity with x-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). The samples have been cooled at 110 K for the XPS experiments and at 50 K for UPS. At room temperature, we measure a valence-band discontinuity of 0.35±0.05 eV, in agreement with previous photoemission results. The valence-band discontinuity is found to change by only a few millivolts between room temperature and 50 K, with an estimated uncertainty of ∼60 meV.
Reactions at the interface of metal/HgCdTe oxide
Authors: Lau W. M. , Hui K. C. , Hill I. R. , He J.-W. , Norton P. R. , Scholes R.
Published: July 2002

The interfacial reactions between metals and the anodic oxide of mercury cadmium telluride (MCT) have been studied by polar-angle-dependent x-ray photoelectron spectroscopy. It was found that the deposition of thin metal films (<2 nm) of indium, platinum, and gold reduced the oxidized tellurium of the MCT oxide at the interface. The spectral results show that indium is more reactive than platinum and gold, but the latter two metals still cause similar interfacial interactions. In the study of the reaction mechanism, depositions of indium and gold by direct evaporation ruled out the possibility that the observed interfacial reactions are caused by energetic particles arriving at the surface during sputter deposition. Metal deposition on MCT oxide which was separated from the MCT substrate also ruled out the possibility of metal diffusion through pinholes in the oxide. It is possible that the condensation of metal causes the breaking of tellurium–oxygen bonds and thereby initializes the interfacial reactions.
Tritium release from a codeposited layer of carbon and tritium during air exposure
Authors: Causey R. A. , Chrisman W. L. , Hsu W. L. , Anderl R. , Wishard B.
Published: July 2002

In fusion reactors containing large quantities of graphite, one of the principal processes causing the retention of tritium in the torus is codeposition of eroded carbon with the tritium. When tritium operations begin in the Tokamak Fusion Test Reactor (TFTR) and eventually in the Compact Ignition Tokamak (CIT), this process will result in a significant in-vessel inventory of tritium. If there is an accidental loss of vacuum for the torus resulting in air entering the vacuum vessel, much of this tritium could be released. Experiments on the stability of similar tritium/carbon films in air, nitrogen, and helium have been performed at Sandia, Livermore using the Tritium Plasma Experiment (TPX) along with an ionization chamber/tritiated water collection system provided by the Idaho National Engineering Laboratory. Results show that tritium is released primarily in a form removed by a glycol bubbler, presumably tritiated water, at room temperature, and that the release rate is increased significantly by heating. Additional experiments were performed using deuterium in the Laser Plasma Materials Experiment (LAMPE) at Sandia, Livermore where 200-nm-thick codeposited films were produced. Long-term monitoring of the deuterium remaining in these films indicated that the amount was still decreasing after 300 days in air. The results of all of these experiments emphasize the need to minimize the amount of tritium in these layers through glow-discharge cleaning or some other technique.
Process modeling of reactive sputtering
Authors: Berg S. , Blom H.-O. , Moradi M. , Nender C. , Larsson T.
Published: July 2002

Reactive sputtering is a very complex and nonlinear process. There are many parameters involved. Normally it is not possible to vary a single parameter independently of the others. It is therefore very difficult to characterize the process based on experimental observations. A better understanding of the reactive sputtering mechanism is needed. We have suggested a simple model for the reactive sputtering process. This model is primarily based on well-known gas kinetics, transferred to this application. With this model it is possible to theoretically predict different processing conditions and actually study the influence of a change in an individual parameter value. The results may then be used to predict optimal experimental conditions. With this technique it is also possible to study means of affecting the well-known hysteresis effect. This article is specially devoted to explain the width of the hysteresis region and how it is affected by the sputtering intensity. Experimental results are presented that support the validity of the proposed model. It was found that the hysteresis width increases in proportion to the rf power fed to the sputtering target. It is thus not possible to eliminate the hysteresis effect by any kind of variation of the sputtering intensity.The effect of the hysteresis effect on the composition limitation of the deposited films will also be described.
Heteroepitaxy of 76Ge films on GaAs by direct deposition from a low-energy ion beam
Authors: Haynes T. E. , Zuhr R. A. , Pennycook S. J. , Larson B. C. , Appleton B. R.
Published: July 2002

Germanium thin films have been deposited on GaAs substrates by direct deposition from a 40-eV 76 Ge+ ion beam. The effectiveness of in situ surface treatments and the relationship of deposition temperature to the quality of epitaxy have been examined. Single-crystal, epitaxially oriented Ge layers were grown at temperatures from 270 to 410 °C. Ion channeling measurements on these layers showed excellent minimum yields. Transmission electron microscopy revealed a uniform distribution of small dislocation loops (diameter <10 nm) in the Ge film and a band of buried dislocation loops in the GaAs substrate. The defect characteristics were temperature dependent such that the average loop size in the epitaxial films decreased with temperature but the total damage density increased when the deposition temperature was lower than 410 °C. Formation of these dislocation loops is ascribed to the coalescence of migrating interstitials which originate as low-energy recoils near the growing surface.
Phase transformations induced by rapid thermal annealing in Ti–Si and W–Si alloys
Authors: Nava F. , D’Amico A. , Bearzotti A.
Published: July 2002

The crystallization of amorphous TiSi2 coevaporated and WSi2.4 chemical vapor deposited thin films was performed by tungsten lamp annealing system at various temperatures and time. A typical annealing process was composed of a fast heating at a constant rate of ∼83 °C/ s up to the required temperature, followed by a fast cooling step to room temperature. A metastable form of TiSi2 (base-centered orthorhombic) and of WSi2 (hexagonal) is formed first and the entire amorphous layer is consumed before this phase undergoes a polymorphic transformation to face-centered-orthorhombic TiSi2 and to tetragonal WSi2, respectively, at higher temperatures. The temperature of transformations are found well correlated with those measured in furnace annealing processes, with typical heating rates varying from 1 to 50 °C/min, and reported in an Ozawa’s plot (logarithm of the heating rate versus reciprocal of the temperature of transformation) to evaluate the activation energies of the aforesaid transformations. These latter ones were investigated in this work using room-temperature sheet resistance measurements and the x-ray diffraction technique. In the face-centered-orthorhombic TiSi2 and tetragonal WSi2 phases, when fully annealed, the resistivities are 14 and 56 μΩ cm at room temperature, respectively.
Adsorption of liquid crystals imaged using scanning tunneling microscopy
Authors: McMaster T. J. , Carr H. , Miles M. J. , Cairns P. , Morris V. J.
Published: July 2002

Scanning tunneling microscopy has been used to obtain images of the surface conformations of 4-n-octyl-4′-cyano-biphenyl, a room-temperature smectic liquid crystal. Working in air and using the constant-current mode, it has been possible to resolve both the aliphatic and aromatic parts of the molecule, and to observe individual benzene rings. Two previously unreported structures have been observed: an overlapping bilayer of layer spacing 37 Å, and a densely packed monolayer of spacing 24 Å. Periodic dislocations in the molecular packing have also been observed. Surface forces and intermolecular interactions are discussed as factors which could lead to these observed structures.
X-ray photoelectron spectroscopy/Ar+ ion profile study of thin oxide layers on InP
Authors: Thurgate S. M. , Erickson N. E.
Published: July 2002

The effect of incremental ion bombardment on the surface layers of an aqua regia etched InP sample was studied by monitoring the components of the In 3d5/2 and O 1s x-ray photoelectron spectroscopy (XPS) lines as the sample was bombarded with low energy (1 keV) Ar+ ions. The changes in the stoichiometry of the surface produced large shifts in the position of the In 3d and O 1s lines that were not paralleled by shifts in the P 2p line. Analysis of these shifts indicated that the surface was covered with a mixture of indium hydroxide and indium phosphate, with the phosphate closer to the InP substrate. It is proposed that this layer structure is due to differences in the dissolution rates of the oxidation products in the acid etch and the effect of the distilled water rinse. It may be possible to alter the composition of such oxides by carefully tailoring the etch conditions to optimize the kinetics for the particular oxide phase required. The analysis of the XPS lines also showed that the InP substrate was damaged at very low ion doses, and finally decomposed by the ion beam. When the ion ‘‘cleaned’’ sample was exposed to oxygen, a different oxide system was produced which consisted largely of In2O3 and InPO4 [or In(PO3 )x]. This model of the oxidized surface of InP is consistent with other measurements and we conclude that ion milling together with XPS and careful curve fitting can be used to find the nature of the thin oxides on InP.
Principles in design and microfabrication of variable-capacitance side-drive motors
Authors: Mehregany Mehran , Bart Stephen F. , Tavrow Lee S. , Lang Jeffrey H. , Senturia Stephen D.
Published: July 2002

This paper presents a detailed discussion of the critical issues it the design and fabrication of polysilicon, rotary, variable-capacitance, side-drive, electric micromotors. Three different side-drive motor architectures with stator pole number to rotor pole number ratios of 3:1; 3:2, and 2:1 are considered. For each architecture, output torque characteristics of typical microfabricated motors are simulated using two-dimensional finite-element solutions in the plane of the substrate. The 3:2 design is shown to provide superior torque coverage with higher minimum torque values as compared to the other two designs. An examination of the contribution of the axial fringing fields shows that, for typical micromotors, the rotor–stator capacitance is more directly a function of the rotor–stator thickness and not of the vertical rotor–stator pole-face overlap. Furthermore, since the rotor–stator capacitance is not very sensitive to a vertical offset between the rotor and the stator, electric forces tending to vertically align the rotor to the stator are significantly smaller than would be predicted from a simple parallel-plate capacitance calculation. A standard and a localized oxidation of silicon (LOCOS)-based side-drive micromotor fabrication process are described. The standard process is used as a case study to provide a detailed discussion of practical issues that need to be considered in the development of a polysilicon surface-micromachined motor fabrication process. Specific motor design examples are described and a brief history of our experimental findings is presented. Typical 3:2 micromotors have been operated with bipolar excitations as low as 37 V across 1.5 μm gaps and at speeds as high as 15 000 rpm.
Scanning tunneling microscopy study of initial stages of silicon molecular beam epitaxy
Authors: Hoeven A. J. , Dijkkamp D. , Lenssinck J. M. , van Loenen E. J.
Published: July 2002

Initial stages of Si molecular beam epitaxy on vicinal Si(001) substrates were investigated using scanning tunneling microscopy. It was found that at temperatures around 750 K first a preferential growth of one type of terrace occurs, leading to the formation of a single-domain surface. During continued growth both step flow and nucleation of islands occur. Disordered areas can block the step flow and antiphase disorder offers preferential nucleation sites.
Optical second-harmonic generation study of Si and Ge deposition on Si(001)
Authors: Hollering R. W. J. , Hoeven A. J. , Lenssinck J. M.
Published: July 2002

Using optical second-harmonic generation, the deposition of Si and Ge on Si(001) under ultrahigh vacuum conditions has been studied, in real time. For both Si and Ge deposition at room temperature, a strong initial decrease in second-harmonic intensity has been found, showing that the technique is very sensitive to the surface electronic structure of Si(001), and that growth at this temperature destroys the long-range order. During continued deposition of Ge the second-harmonic intensity increases again, leading to a maximum at a coverage of one monolayer (ML). This is interpreted as being due to the buildup of a dipolar layer at the Si–Ge interface. For deposition at temperatures around 750 K the disorder-induced intensity decrease vanishes, whereas the formation of a dipole layer at the Si–Ge interface again induces a maximum in second-harmonic intensity at a coverage of 1 ML.
Novel semiconductors and heterostructures
Authors: Coon D. D.
Published: July 2002

Molecular beam epitaxy and metalorganic chemical vapor deposition in conjunction with modulated doping continue to contribute new classes of electronic and optoelectronic materials and devices. Recent advances include new heterostructure infrared detectors which exploit the flexibility of growth techniques to tailor detector response to particular wavelengths out to 12 μ and beyond. These detectors utilize intraband transitions in quantum wells and superlattices. They can be implemented in widegap materials like AlxGa1−xAs/GaAs with fewer materials problems than narrow gap materials like HgxCd1−xTe. Quantitatively predictable spectral response has resulted from improved understanding of device physics issues, including the analysis of electron–electron exchange interactions in doped quantum wells. Progress has also been made in quantitative analysis of the effects of interface roughness on electronic states in quantum wells. These recent advances are important not only for detectors, but also for ultrahigh speed electronic devices employing resonant tunneling in heterostructures.
Epitaxial growth of Al(100) on Si(100) by gas-temperature-controlled chemical vapor deposition
Authors: Sekiguchi A. , Kobayashi T. , Hosokawa N. , Asamaki T.
Published: July 2002

Epitaxial Al(100) film was deposited on Si(100) by low-pressure chemical vapor deposition with the use of tri-isobutylaluminum (TIBA) at the substrate temperature of 380–400 °C with the deposition rate of 400 nm/min. For the epitaxial film growth, it was concluded that preheating the TIBA gas just before the incidence onto the substrate was very important (gas-temperature-controlling). The specular reflectance of the 1-μm-thick aluminum film on silicon substrate was the same level as that of the sputtered film. The x-ray diffraction peak was very narrow and only Al(100) orientation was observed. The transmission electron diffraction (TED) patterns of Al(100) films showed clear spots. Using disilane, we could suppress the diffusion of substrate silicon into the aluminum film.
A study of modified polyimide surfaces as related to adhesion
Authors: Flitsch R. , Shih D-Y.
Published: July 2002

Surfaces of fully imidized pyromellitic, dianhydride–oxydianiline (PMDA-ODA) based polyimide films have been studied after argon ion-beam bombardment or treatment with either oxygen or nitrogen plasmas. The treated surfaces were characterized by x-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and surface energy measurements. The XPS spectrum of the C1s level showed that intensity related to carbonyl and imide ring structure decreases while that related to carbon-to-carbon bonding increases with argon ion bombardment. Oxygen plasma treatment resulted in an increase by a factor of two in the atomic concentration of oxygen and a decrease of carbon concentration. Polycarbonate and/or peroxy type carbon–oxygen structures were formed as indicated by the C1s level. Treatment with a nitrogen plasma caused an increase in the atomic percent of nitrogen by a factor of three, a decrease in carbon and no change in the oxygen. The N1s level was resolved into three peaks that are assigned in part to imide and nitrile moieties. All of the modified polyimide surfaces show significant improvement in adhesion to a overcoated chromium film. This enhancement in adhesion is attributed to the increased surface energy and number of bonding sites. Surface topography studies by SEM show the relative smoothness of the surface is reduced slightly after ion bombardment and plasma treatments.
Initial stages of heterojunction formation: Si on GaAs(111)
Authors: González M. L. , Soria F. , Alonso M.
Published: July 2002

Si/GaAs(111) interfaces grown at 300, 573, and 773 K on both polar surfaces have been studied by Auger electron spectroscopy (AES), low-energy electron diffraction (LEED), energy-loss spectra (ELS), and work function measurements. In both polar faces Si deposits up to 8 monolayers (ML) onto a room temperature substrate result in disordered and abrupt Si interfaces. At 573 and 773 K the first Si ML grows pseudomorphically with the substrate occupying first the vacancy and defect sites of the top Ga surface layer, followed by the remaining sites. The second and subsequent monolayers have the atom density of the bulk Si crystal. A surface segregation of up to 1 ML of Ga and As atoms at 773 K occurs by diffusion through the interface of about 0.65 nm thickness. The observed decrease of the work function in the submonolayer coverage range is explained by variations in the ionization energy due to positive-outwards surface dipoles created by Si adsorption on defect sites with a charge tranfer to the As atoms of 0.12 e0 per Si atom and polarizability of 4.3×10−22 cm3 at 300 K. These values indicate the strong interaction that the Si atoms encounter at the Ga defect sites.
Controlled modification of heterojunction band lineups by diffusive intralayers
Authors: McKinley J. T. , Hwu Y. , Rioux D. , Terrasi A. , Zanini F. , Margaritondo G. , Debska U. , Furdyna J. K.
Published: July 2002

We explore the effects of ultrathin Au intralayers at the interfaces of the lattice-matched heterojunctions ZnSe–Ge and GaP–Si, and compare them to earlier results with Al intralayers. Au intralayers do not chemically react with the semiconductors and diffuse strongly into both sides of the junction, whereas Al intralayers react and remain localized to the interface. Not only do the intralayer metals diffuse differently, but they cause the semiconductor components to interdiffuse differently. Comparison gives insight concerning interface-localized effects on the valence band discontinuity.
Epitaxial growth of Cu films on Si by ionized cluster beam deposition
Authors: Sosnowski Marek , Usui Hiroaki , Yamada Isao
Published: July 2002

The growth of Cu films deposited by ICB method on Si(111) and Si(100) has been studied. Depositions were made in ultra high vacuum with substrates at near room temperature. The film growth was analyzed by in situ RED and XPS measurements. Channeling, x-ray diffraction, Auger spectroscopy, and scanning ion microscopy measurements were made outside the deposition chamber. The growth of Cu films on Si(111) was initially two dimensional followed above ten monolayers by the appearance of three-dimensional structures. 100 nm thick films had quite uniform crystal structure with epitaxial relation to the substrate. No intermixing or silicide formation at the interface was seen. Ion acceleration improved the smoothness of the film surface but had no appreciable effect on the film structure or interface. By contrast, in deposition on Si(100) ion acceleration strongly influenced the film structure and intermixing at the interface. Smooth films were obtained at acceleration voltage of 3 kV and higher while more disordered structure with strongly intermixed interface was observed at lower acceleration voltages. It was found that the effect of ion bombardment during film growth strongly depends on the substrate crystallographic orientation.
Low temperature interdiffusion in the HgCdTe/CdTe system, studied at near-atomic resolution
Authors: Kim Y. , Ourmazd A. , Feldman R. D.
Published: July 2002

By combining chemical lattice imaging and vector pattern recognition we determine, as a function of annealing temperature, the composition of individual atomic planes across each HgCdTe/CdTe interface of a multiquantum well stack. The resultant composition profiles, which directly reveal the chemical change across each interface at near atomic resolution, are analyzed in terms of linear and nonlinear diffusion theory, to deduce the interdiffusion coefficient and its activation energy. We find the interdiffusion coefficient to be nonlinear, and a sensitive function of the interface depth beneath the surface.
Surface termination of epitaxial NiAl on GaAs(001) by x-ray photoelectron diffraction
Authors: Chambers S. A.
Published: July 2002

The surface termination of molecular-beam epitaxy (MBE)-grown NiAl on GaAs(001) has been examined by means of high-energy x-ray photoelectron diffraction. Scanned-angle x-ray photoelectron diffraction measurements of Ni 3p and Al 2p photoemission intensities were made at select polar and azimuthal angles and compared with single scattering calculations involving different surface terminations. R-factor analysis was employed to quantify the level of agreement between theory and experiment. Azimuthal angular distributions at shallow polar angles are very similar in appearance for Ni 3p and Al 2p photoemission intensities. In addition, the R factors are consistently lower for Ni 3p angular distributions when a Ni-terminated surface is modeled, while an Al-terminated surface structure yields lower R factors for Al 2p scans. In light of the short range, localized sensitivity of the photoelectron diffraction probe, these results are best understood as evidence for a mixed surface termination. Indeed, R-factors averaged over the two core levels as a function of composition in the surface layer show broad, shallow minima at intermediate composition for azimuthal scans near grazing emission. This analysis gives strong qualitative support for the presence of a mixed surface termination.
Adsorption geometry and overlayer morphology in the formation of interfaces between metals and (110) III–V surfaces
Authors: Stevens K. , Soonckindt L. , Kahn A.
Published: July 2002

Interfaces formed between metals (In, Ag) and cleaved (110) surfaces of III–V compound semiconductors (GaSb, GaAs) held at low temperature are studied with low-energy electron diffraction and electron energy-loss spectroscopy. We consider the unrelaxation of the semiconductor surface structure by the metal adatoms, the adsorption sites on the surface and their implications for semiconductor band bending. The results are discussed in light of recent scanning tunneling microscopy measurements on metal/semiconductor interfaces and tight binding calculations of preferential adsorption sites.
Growth and characterization of silicon nitride films produced by remote microwave plasma chemical vapor deposition
Authors: Landheer D. , Skinner N. G. , Jackman T. E. , Thompson D. A. , Simmons J. G. , Stevanovic D. V. , Khatamian D.
Published: July 2002

Films of silicon nitride have been grown in an ultrahigh vacuum system by the reaction of silane with nitrogen remotely excited in a microwave plasma at pressures in the range 0.1–0.9 Torr with substrate temperatures in the range 70–350 °C. Growth rates have been determined as a function of silane–nitrogen flow ratio, pressure, microwave power, and substrate temperature in order to give some insight into the growth mechanism. Results indicate that the rate of film deposition is governed by the arrival rate of active nitrogen species at the surface. The films have been characterized by 15N nuclear reaction profiling and Rutherford backscattering analysis to determine the hydrogen, silicon, and nitrogen contents. Hydrogen contents are comparable to those obtained with parallel-plate plasma enhanced chemical vapor deposition reactors while near stoichiometric, nitrogen rich films can be obtained over a wide range of deposition parameters. Floating double probe measurements used to obtain the electron temperatures and ion densities verify that substrate bombardment by charged or energetic particles is not a factor in the growth of these films.
Thermal stress-induced and electromigration-induced void-open failures in Al and Al–Cu fine lines
Authors: Kwok T. , Chan K. K. , Chan H. , Simko J.
Published: July 2002

Thermal stress-induced and electromigration-induced void-open failures in Al and Al–Cu fine lines have been studied. The extra thermal stress induced by temperature cycling shortens the electromigration lifetime of both Al and Al–Cu fine lines by more than an order of magnitude. Our data indicate that there is a ∼15% reduction in the electromigration resistance of Al fine lines without visual damage after temperature cycling, which may be caused by the subtle structure damage. Our results also show that the addition of Cu in Al fine lines improves the resistance to thermal stress-induced failures, probably by the suppression of grain boundary sliding and migration.
Observation of the initial stages of growth of hydrogenated amorphous carbon films by scanning tunneling microscopy
Authors: Vandentop G. J. , Nascente P. A. P. , Kawasaki M. , Ogletree D. F. , Somorjai G. A. , Salmeron M.
Published: July 2002

Scanning tunneling microscopy was used to investigate the initial stages of growth of hydrogenated amorphous carbon (a-C:H) films. The films were deposited on highly oriented pyrolytic graphite and silicon substrates both on the powered (negatively self-biased) and grounded electrodes from a methane rf plasma (13.56 MHz) at 68–70 mTorr and room temperature. On graphite substrates, films formed at the powered electrode were observed to nucleate in clusters ∼50 Å in diameter. Cluster density increased with deposition time, while cluster size remained relatively constant. The atomic structure of individual clusters was resolved and found to be amorphous, containing areas of both five- and sixfold rings in a disordered matrix. No long-range order was observed. The C–H bonding in these clusters was observed by high-resolution electron-energy-loss spectroscopy. Films formed on graphite substrates placed at the grounded electrode produced very noisy images due to an unstable tunneling gap, indicative of the material’s poor electrical conductivity. On silicon substrates placed at the powered electrode, cluster formation was not observed, and the films formed were measured to be flat to within 3-Å rms. The clusters formed on graphite at the powered electrode may be initiated by nucleation sites created by high-energy ion bombardment. Due to the higher reactivity of silicon, growth onto these substrates proceeds without the requirement of ion bombardment nucleation sites, thus the more homogeneous growth on silicon.
Vibrational excitation processes in molecular discharges
Authors: O’Neill James A.
Published: July 2002

Infrared (IR) spectroscopy has been used to examine the vibrational excitation processes in a pure N20 discharge. An infrared imaging camera was used to characterize the distribution of vibrationally excited species in the plasma through measurements of the profile of the IR plasma emission at 4.7 μm. These results show that the distribution of IR intensity is peaked in the center of the plasma, unlike that for visible emission which is greatest at the plasma sheaths. In addition, a high-resolution IR diode laser absorption probe was used to characterize rotational and vibrational temperatures in the plasma. While rotational heating is minimal under low power conditions vibrational temperatures are significantly higher and depended on the vibrational manifold under examination. Vibrational lifetime measurements in a modulated rf plasma illustrate that diffusion plays a significant role in the redistribution of long-lived vibrationally excited species. The chemical implications of elevated vibrational excitation in semiconductor process plasmas is also discussed.
Comparison of low temperature polysilicon crystal growth on low cost substrates
Authors: Czubatyj W. , Beglau D. , Chao B. S. , Gonzalez-Hernandez J. , Pawlik D. A. , Klersy P. , Jablonski D. , Himmler R.
Published: July 2002

We have investigated the growth of silicon polycrystals from deposited amorphous films on several different substrates. Using Raman spectroscopy, x-ray diffraction, transmission electron microscopy, and optical microscopy, we find that substrate choice affects crystallite size, preferential orientation, and growth rate. In addition, it is shown that large high quality crystals can be grown on low cost glasses.
Ion beam oxidation of GaAs: The role of ion energy
Authors: Vancauwenberghe O. , Herbots N. , Manoharan H. , Ahrens M.
Published: July 2002

In this work, room temperature oxidation of GaAs was investigated using ion beam oxidation (IBO). In IBO, an ion beam is used to introduce oxygen athermally into the substrate, in this case GaAs. GaAs bonds are broken upon collision with the ions, making gallium and arsenic atoms readily available to react with the oxygen species. Ion beam oxidation of GaAs at room temperature was studied as a function of oxygen ion energy between 500 and 8 keV. The ion beam oxidized GaAs was characterized in situ by Auger electron spectroscopy (AES) and ex situ with x-ray photoelectron spectroscopy (XPS) for accurate determination of the film chemical composition. Below 1 keV, a thin oxide film is formed: it is composed of Ga2O3 and As2O3 with almost no metallic arsenic, and presents insulating properties. As the ion energy increases, preferential sputtering of As and decomposition of As2O3 increase and prevent formation of an insulating film. No damage was detected by Rutherford backscattering spectrometry (RBS) combined with ion channeling, in the substrate subjected to IBO below 1 keV.
X-ray absorption study of diamond films grown by chemical vapor deposition
Authors: Yang X.-Q. , Ruckman M. W. , Skotheim T. A. , den Boer M. , Zheng Yu , Badzian A. R. , Badzian T. , Messier R. , Srivatsa A. R.
Published: July 2002

Carbon k-edge x-ray absorption fine structure (XAFS) is used to study the structure and bonding of chemical vapor deposition (CVD) grown diamond and diamond-like carbon films. Diamond films grown at 875 °C on silicon using a 1% CH4 /H2 mixture have near-edge spectra resembling type 1(a) natural diamond. The k-edges of the diamond-like films grown by electron cyclotron resonance CVD at 200 °C using 10−4 Torr of CH4 show a broad main peak lacking the sharp structure of graphite or diamond. Comparing the near edges of the CVD diamond film with other carbon compounds (i.e., graphite) and the CVD diamond film, the diamond-like film shows a strong π* feature at 285 eV indicative of sp2 bonded carbon and a feature at 289 eV, the σ*(C–H) resonance indicating C–H bonds. The relatively weak extended x-ray absorption fine structure (EXAFS) shows that the diamond-like carbon film is highly disordered on an atomic level.
Reactive sputtering of molybdenum-oxide gradient-index filters
Authors: Jankowski A. F. , Schrawyer L. R. , Perry P. L.
Published: July 2002

Molybdenum-oxide gradient-index films are produced by reactive sputter deposition. A molybdenum metal target is sputtered continuously with an argon–oxygen gas mixture. For each target power used, a reproducible oxide composition and corresponding refractive index result. Repetitive variation of applied target power is used to produce a structure composed of discrete layers of preselected stoichiometry. The systematic control of a single process parameter, target power, simplifies the fabrication of molybdenum-oxide rugate filters.
Contrasts in the reactions of sulfur from different sources with GaAs surfaces
Authors: Mokler S. M. , Watson P. R.
Published: July 2002

We have studied S2 and H2S adsorption on the GaAs(100) surface using low-energy electron diffraction (LEED), Auger electron spectroscopy (AES), and thermal desorption spectroscopy (TDS). We find that sulfur adsorption onto this surface proceeds to a much greater extent in the case of S2, involving amounts corresponding to several monolayers. A corrosion reaction probably occurs leading to the desorption of both disulfides and monosulfides of Ga and As. H2S adsorption is initially rapid, but sulfur uptake proceeds to an extent of only (1)/(5) the amount of S2. While GaH and AsH3 desorb at 100 °C, only the monosulfides desorb on heating from a surface saturated with H2S. The loss of the hydrides plays a role in removing defects from the surface, and may contribute to the lowering of the Schottky barrier height seen by others.
Low-voltage scanning electron microscopy: A surface sensitive technique
Authors: Katnani A. D. , Hurban S. , Rands B.
Published: July 2002

The advancements in electron optics have made it possible to cover a wide electron energy range without significant degradation in the imaging quality of a scanning electron microscope. The secondary electron emission and the surface sensitivity are enhanced when using low voltages. The addition of an energy dispersive x-ray spectrometer with a thin window allows the detection of low energy emission lines, thus making the technique comparable, or at least complementary to surface techniques such as Auger electron and x-ray photoelectron spectroscopies. In this paper, aspects of low-voltage SEM are discussed and factors affecting the secondary electron images are examined. The surface sensitivity is evaluated and is compared to Auger electron spectroscopy. Study cases from the printed circuit board manufacturing area are presented.
Surface analysis studies of copper chemical vapor deposition from 1,5-cyclooctadiene-copper(I)-hexafluoroacetylacetonate
Authors: Cohen Susan L. , Liehr Michael , Kasi Srinandan
Published: July 2002

The chemical vapor deposition of Cu from the 1,5-cyclooctadiene copper(I) hexafluoroacetylacetonate (COD-Cu-hfac) precursor has been studied using x-ray photoelectron spectroscopy, high-resolution electron energy-loss spectroscopy, and in situ reactor growth. Cu films are reproducibly grown on a Ag seed layer with resistivities of 2.0–2.4 μΩ cm with a deposition rate of 30–80 Å/min at 180 °C. After deposition, the surface of the Cu is covered by some adsorbed precursor fragments and residual hydrocarbon. Upon heating in vacuum, the precursor desorbs leaving behind about 3–5 Å carbon. Incorporation of carbon, oxygen, and fluorine into the bulk of the Cu films is limited to 1% or less. The reactive sticking coefficient of the COD-Cu-hfac molecule during deposition is estimated to be ∼ 1 × 10−3 at 180 °C. Cu grows somewhat selectively on metal relative to oxide surfaces at 180 °C. Room temperature adsorption of the precursor on Ag leads to dissociation of the molecule and loss of the COD ligand. The stoichiometry of the surface complex corresponds to Cu(I)-hfac. Heating the surface to ≳170 °C leads to desorption of the surface hfac ligand. This is consistent with a bimolecular disproportionation reaction in which 2 Cu(I)-hfac species react to form a volatile Cu(hfac)2 complex and a reduced Cu atom.