bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of test bed system for high melting temperature alloy fabrication and mass spectroscopy analysis of liquid metal ion beam source
Authors: Higuchi-Rusli R. H. , Corelli J. C. , Steckl A. J. , Cadien K. C.
Published: July 2002

Recent advances in microlithography with focused ion beam (FIB) systems for submicron integrated circuit fabrication, and the important role of liquid metal ion source (LMIS) in FIB systems to produce a stable ion beam current of selected specie, require a test bed system capable of testing, analyzing, and fabricating a variety of alloy sources. Most fabrication of alloy sources require a contaminant-free environment, therefore wetting and fabricating of the alloy for LMIS must be carried out in high vacuum at a pressure of 10−7 Torr or lower. The development of a high-vacuum LMIS test bed system capable of fabricating high melting temperature alloys for FIB system as well as testing the sources are described in detail. The mass spectra of remelted alloys of Cu3P, Pd73B27, and Pt58B42 show no nitrogen or oxygen contamination during alloy fabrication process.
Plasma enhanced chemical vapor deposition of polycrystalline diamond and diamondlike films
Authors: Vitkavage D. J. , Rudder R. A. , Fountain G. G. , Markunas R. J.
Published: July 2002

Polycrystalline diamond and diamondlike films have been deposited using a variant of plasma enhanced chemical vapor deposition where excited He atoms flowing downstream from an intense plasma region interact with CH4 molecules. Unlike conventional diamond chemical vapor deposition where pressures in excess of 20 Torr and kilowatts of power are forwarded into the plasma, typical deposition pressures and rf power are below 10 mTorr and 100 W, respectively. The results obtained here reflect gas–solid phase interactions of CHx radicals and H atoms with the substrate. The concentration of CH4 is too low and the residence time of CH4 is too short in the reactor to allow any gas phase polymerization to occur. Energy-loss spectroscopy (1.0–40.0 eV), x-ray photoelectron spectroscopy, Raman spectroscopy, and reflection high-energy electron diffraction have been used to characterize the films.
Rotary pump backstreaming: An analytical appraisal of practical results and the factors affecting them
Authors: Laurenson L. , Hickman Sara , Livesey R. G.
Published: July 2002

Useful data on the backstreaming of vapors from oil sealed rotary pumps have been obtained by a number of workers using quartz-crystal microbalance techniques. The interpretation of results obtained using this method is complicated by the heterogeneous nature of the pump fluids, arising mainly from degradation of oil in the pump mechanism, and by the large vapor pumping speed of the cold finger on which the quartz crystal is mounted. The work described here attempts to separate the factors involved and to quantify their effects. The results obtained support a proposed model of the vapor atmosphere of which the most significant feature is the limited production rate of degraded oil products. It is shown that the significance of backstreaming rates, measured using a cooled quartz crystal, is strongly dependent on the experimental arrangement.
A simple ultrahigh vacuum compatible sample cooling system
Authors: Chaban E. E. , Citrin P. H. , Sette F.
Published: July 2002

A simple and inexpensive system is described for obtaining efficient and rapid cooldown of samples studied in ultrahigh vacuum. In most cases the design is easily adaptable to existing sample manipulators without sacrificing other desirable features.
Measurements of electron temperature in a capacitively coupled plasma using emission spectroscopy
Authors: Felts J. , Lopata E.
Published: July 2002

Measurements using the derived calculation scheme to determine the electron temperature from optical emission spectroscopy are presented. The electron temperature was measured using both optical emission spectroscopy and Langmuir probes with our computer based system. The computer allowed us to make both measurements and do the calculations on line in a reasonable amount of time. Because of the accuracy of our emission spectrometer, we made several Langmuir probe measurements for each emission spectrum taken. We first determined that the optically measured electron temperature and Langmuir probe measured electron temperature were following the same trend with variations in the process variables. In addition to varying process variables, we also determined the effect of adding an additional gas to the discharge. The results presented verify that our optically determined electron temperature is valid in this case.
A time resolved study of velocity distributions in pulsed molecular beams
Authors: Eldridge Benjamin N. , Yu Ming L.
Published: July 2002

We have studied with 12-μs resolution the time evolution of the characteristic flow velocity and parallel temperature of a supersonic gas jet produced by a commercial pulsed valve. The gases studied were H2, He, Ne, O2, Ar, and a seed mixture of 5% O2 in He. The gases were supplied to the pulsed valve at 100- and 1000-Torr inlet pressure. Our results indicate that the time required to reach an equilibrium flow condition is essentially independent of the gas species used, but is a function of the inlet pressure. Furthermore, the static Mach number obtained in the expansion is found to deviate from that predicted for a cw expansion with the same nozzle Knudsen number Kn0 with increasing inlet pressure. This leads to the conclusion that the effective diameter Deff through which the gas expands is a function of inlet pressure, and that the observed equilibration time is in fact the time required for the valve opening to reach this effective value. The results obtained should be applicable to any pulsed valve with similar mechanical bandwidth and gas passage geometry.
Tritium removal from noble gas streams
Authors: Shmayda W. T. , Kherani N. P. , Heics A. G.
Published: July 2002

A process loop to remove tritium from a flowing helium stream in a single pass has been constructed and commissioned. Inventories injected into the loop range from 1 GBq–28 TBq. Concentrations within the stream entering the loop range from 40 MBq/m3 to 15 TBq/m3 . The tritium is removed from the stream by gettering on uranium beds. Residual concentrations leaving these beds are removed with zirconium–iron getter beds. Purification factors of 10 for the uranium beds and a minimum of 19 400 for the zirconium–iron bed have been measured. This paper describes the process loop and the performance of the getter beds during one 28-TBq injection.
Sputtering yield and radiation damage by neutral beam bombardment
Authors: Mizutani Tatsumi , Nishimatsu Shigeru
Published: July 2002

To clarify the difference between ion beam etching and neutral beam etching, a low-energy (100–1000 eV) Ne0 neutral beam obtained by charge exchange reaction has been used to bombard Cu, Si, and SiO2 surfaces. The sputtering yields of Cu and Si by Ne0 have been found to be the same as those by Ne+. The sputtering yield of SiO2 by Ne0 is slightly smaller than that by Ne+. It is believed that electronic sputtering mechanisms play only a small role in the sputtering of these materials at these low ion energies. C–V measurements show that the amount of radiation damage caused by Ne0 neutral beam bombardment of the SiO2/Si structure is significantly less than that by a Ne+ ion beam. When the Ne+ dosage increases, the flat-band voltage shift increases and the thin SiO2 films on Si eventually break down. In Ne0 neutral bombardment, the flat-band voltage shift saturates with increasing dosage and no breakdown of SiO2 occurs. It is assumed that, in neutral beam bombardment, the surface potential of SiO2 is limited by secondary emission of charged particles whose energies are at most 10–20 eV and the resulting surface potential is not large enough to cause dielectric breakdown.
Gas utilization in the Tokamak Fusion Test Reactor neutral beam injectors
Authors: Kamperschroer J. H. , Gammel G. M. , Kugel H. W. , Grisham L. R. , Stevenson T. N. , von Halle A. , Williams M. D. , Jones T. T. C.
Published: July 2002

Measurements of gas utilization were performed using hydrogen and deuterium beams in the Tokamak Fusion Test Reactor (TFTR) neutral beam test beamline to study the feasibility of operating tritium beams with existing ion sources under conditions of minimal tritium consumption. (i) It was found that the fraction of gas molecules introduced into the TFTR long-pulse ion sources that are converted to extracted ions (i.e., the ion source gas efficiency) was higher than with previous short-pulse sources. Gas efficiencies were studied over the range 33%–55%, and its effect on neutralization of the extracted ions was studied. At the high end of the gas efficiency range, the neutral fraction of the beam fell below that predicted from room-temperature molecular gas flow (similar to observations at the Joint European Torus). (ii) Beam isotope change studies were performed. No extracted hydrogen ions were observed in the first deuterium beam following a working gas change from H2 to D2. There was no arc conditioning or gas injection preceding the first beam extraction attempt. (iii) Experiments were also performed to determine the reliability of ion source operation during the long waiting periods between pulses that are anticipated during tritium operation. It was found that an ion source conditioned to 120 kV could produce a clean beam pulse after a waiting period of 14 h by preceding the beam extraction with several acceleration voltage/filament warm-up pulses. It can be concluded that the operation of up to six ion sources on tritium gas should be compatible with on-site inventory restrictions established for D–T, Q=1 experiments on TFTR.
Quantitative Auger electron spectroscopy of TiSiy: Peak height, line-shape, and sputtering yield analyses
Authors: Galuska A. A. , Wallace W. O.
Published: July 2002

The Auger electron spectroscopy (AES) peak heights, sputtering yields, and line shapes of well-characterized TiSiy films were examined. Analysis of AES peak-to-peak heights showed that the total correction factor (KT) used for quantification varied linearly by a factor of 10 as the mole fraction of Si (XSi) changes from 0 to 1. The KT variation was attributed primarily to preferential sputtering although line-shape variations also had some effect. The line shapes of the derivative SiLVV and TiLVV spectra were examined as a function of XSi. The TiLVV line shape did not change significantly with composition. However, the characteristic features (peak height, peak width, skewdness, etc.) of the SiLVV line shape were shown to vary linearly with silicide composition. The average sputtering rates and yields of the titanium silicides were shown to vary by a factor of 2 as XSi varies from 0 to 1. The average sputtering yields of the silicides varied linearly with composition while the sputtering rates did not. The use of peak height, line-shape, and sputtering yield calibration lines for quantitative concentration and depth determinations is discussed.
A broad-beam electron cyclotron resonance ion source for sputtering etching and deposition of material
Authors: Ghanbari E. , Trigor I. , Nguyen T.
Published: July 2002

A broad-beam electron cyclotron resonance ion source for sputtering etching and deposition of material has been designed and constructed. The source uses a 1-kW magnetron at 2.45 GHz and can operate at an argon gas pressure of <0.1 Pa (7.5×10−4 Torr). Plasma ion density of 0.45 to 1×1012 cm−3 and electron temperatures of 7.5 to 11 eV have been obtained. Based on these results and the free fall ion diffusion theory, the calculated ion current density in the source varies from 15 to 30 mA/cm2. The source is also capable of producing a uniform ion beam current density of 0.5 to 1.5 mA/cm2 using an array of grids at an energy range of 100 to 1000 V. The ion beam uniformity varies between ±3% and ±5% across 76–140 mm diameter of the extracted ion beam. Of particular note are the long lifetime and ease of operation.
The role of oxygen in chemical vapor deposition nucleation barriers of triisobutylaluminum on silicon
Authors: Mantell David A.
Published: July 2002

The nucleation of chemical vapor deposition (CVD) using triisobutylaluminum (TIBA) on Si(100) surfaces is observed in situ with x-ray photoelectron spectroscopy. Oxygen from oxide on the silicon inhibits the rate of nucleation by reacting with adsorbed TIBA and forming a thin layer of oxidized organometallic. This layer blocks active adsorption sites and prevents further deposition. On a surface without oxide, the TIBA molecules decompose liberating aluminum that can migrate and nucleate into islands opening sites for further adsorption and film growth. Thus the barrier to nucleation on oxide surfaces makes selected area CVD possible with TIBA.
An x-ray photoelectron spectroscopy study of water removal from beryllium at 160 K: Evidence for ion beam induced oxidation
Authors: Lindquist John M. , George Patricia M.
Published: July 2002

We present data for the ion beam removal of H2O from beryllium at 160 K. The removal rate of H2O from beryllium is qualitatively slower than that from copper. Evidence from x-ray photoelectron spectroscopic measurements indicates the ion beam causes surface oxidation up to a point where the oxide thickness prohibits further reaction. The mechanism for this ion beam induced surface oxidation is discussed and points toward H2O bond breakage by the ion beam as a significant contributing factor.
Interaction of alkali-metal overlayers with oxygen
Authors: Hrbek J. , Xu G.-Q. , Sham T. K. , Shek M. L.
Published: July 2002

The interaction of oxygen with alkali metals (Li, Na, K, and Cs) was studied with valence and core-level photoemission (PE) using synchrotron radiation and by multiple mass thermal desorption (TDS). During a stepwise coadsorption of oxygen at 80 K, an increase in the emission intensity, a linewidth broadening, and a negative binding-energy shift of alkali-metal core levels is observed. Two stages of oxygen adsorption are identified in PE and TDS. In the low O2 exposure range, an oxide species is formed; at higher exposures, peroxide and superoxide species are observed in Na, K, and Cs. The potassium–oxygen interaction is discussed in detail.
The effect of electron transmission function on calculated Auger sensitivity factors
Authors: Mroczkowski Susan J.
Published: July 2002

It has been shown previously that calculated sensitivity factors can be used in some cases for quantification of Auger electron spectroscopy data. Internal calibration had been recommended for accurate quantification of transitions with energy <200 eV. In this study, the effect of various electron transmission functions on calculated Auger electron spectroscopy sensitivity factors is investigated. Spectrometer resolution and its relation to intrinsic peak width are also discussed. The transmission function-corrected calculated sensitivity factors are compared to several available empirical handbook sensitivity factors. There is now improved reliability on the use of calculated values for the quantification of transitions at the lower end of the energy spectrum. When conductive, high-purity standards are routinely available, calculated and experimental sensitivity factors correlate well. There is a considerable difference when high-purity standards are not available as in the light element and lanthanide series. If accurate quantification is required and internal standards are not available, the Auger electron emission current should be correlated to the area under the peak for Auger spectra taken in the direct mode rather than peak-to-peak height measurements in the derivative mode.
Reduction of noise amplification in processing noise containing data using global approximation based on spline functions
Authors: Sasse A. G. B. M. , Wormeester H. , van Silfhout A.
Published: July 2002

One of the main problems in the analysis of measured spectra is how to reduce the influence of noise in data processing. We show a deconvolution, a differentiation, and a Fourier transform algorithm that can be run on a small computer (64K random access memory) which suffers less from noise than commonly used routines. This objective is achieved by implementing spline based functions in mathematical operations to obtain global approximation properties in our routines. The convenient behavior and the pleasant mathematical character of splines makes it possible to perform these mathematical operations on large data input in a reasonable computing time on a small computer system. Some examples of the performance of a differentiation, deconvolution, and Fourier transform routine are shown.
Low-retardance fused-quartz window for real-time optical applications in ultrahigh vacuum
Authors: Studna A. A. , Aspnes D. E. , Florez L. T. , Wilkens B. J. , Harbison J. P. , Ryan R. E.
Published: July 2002

We describe a low-strain, Suprasil quartz window assembly for ultrahigh vacuum applications that require high transmittance and/or low retardance over a wide spectral range. The assembly mounts on a 2 (3)/(4) in. Conflat flange. The window can be heated externally to 400 °C to remove typical molecular-beam-epitaxy growth deposits, thereby eliminating a major source of inaccuracy in optical pyrometry and allowing high-light fluences to be transmitted with minimal attenuation. Retardations at 459 nm (2.5 eV) of four unmounted Bellcore windows ranged from 0.05° to 0.3° while retardations of properly mounted windows were <0.5°. These retardations could be reduced an order of magnitude by applying small counterstresses, thereby allowing highly accurate real-time growth data to be obtained by polarization-sensitive optical techniques such as reflectance-difference spectroscopy or spectroellipsometry.
Imaging and analysis of surfaces with high spatial resolution
Authors: Cowley J. M.
Published: July 2002

New electron microscopes designed to operate with specimens prepared, treated, characterized, and observed in an ultrahigh vacuum environment, provide several techniques for the study of surfaces with atomic or near-atomic resolution. The method of profile imaging allows the best attainable resolution (1.6 Å) to be applied to determine surface atom positions and atomic motions may be recorded at television rates. Reflection electron microscopy is sensitive to fractions of a monolayer of foreign atoms on a surface and shows atom-high surface steps with good contrast. Reflection electron energy loss spectroscopy, under surfaces resonance diffraction conditions is sensitive to the composition of surface monolayers. Microdiffraction allows structure analysis of subnanometer particles or crystal defect regions. Spectroscopic analysis or imaging with secondary or Auger electrons provides nanometer resolution on variations of surface composition.
Scanning tunneling microscopy of ion impacts on semiconductor surfaces
Authors: Wilson I. H. , Zheng N. J. , Knipping U. , Tsong I. S. T.
Published: July 2002

The effects of individual ion impacts on the surfaces of two semiconductors Si(100) and PbS(100) were studied by scanning tunneling microscopy (STM). As+ and Ge+ ions ranging in energies from 20 keV to 1 MeV were implanted into Si(100) through a SiO2 layer. STM was performed after removal of the SiO2 by HF etching. Kr+ ions of 8 keV bombarded freshly cleaved PbS(100) surfaces at 45° incidence. Atomically resolved STM images of the impact zone were obtained in this case. Low ion doses ∼1011 cm−2 were used throughout to avoid overlap of cascades. Surface features observed by STM include craters, structural disorder, and surface print defects. There is a 1:1 correlation between the number of ion impacts and the number of craters. The mean crater diameter correlates with the lateral extent of nuclear energy deposition at the surface.
The determination of structure in small supported metal particles by scanning transmission electron diffraction
Authors: Poppa H. , Moorhead R. D. , Avalos-Borja M.
Published: July 2002

The crystallographic structure of small Pd particles formed during the earliest stages of vapor deposition onto refractory oxide supports was studied by energy filtered in situ UHV scanning transmission electron diffraction (STED). Although only the average structure of particles can be obtained by this high-precision, large area diffraction technique, its main advantage over high-resolution transmission electron microscopy (TEM) is the drastic reduction of radiation damage effects. On-line processed experimental diffraction data were compared to calculated elastic diffraction intensities and radial distribution functions obtained by Fourier transformation. The results show conclusive evidence that small Pd clusters of less than about 2 nm size prefer non-fcc icosahedral packaging over the standard fcc structure, which confirms earlier theoretical predictions for minimum energy cluster configurations. Standard fcc structures always dominate in later stages of growth with increasing particle size.
Low-temperature pulsed plasma deposition. II. The production of novel amorphous compounds of germanium in thin film
Authors: Scarsbrook G. , Llewellyn I. P. , Heinecke R. A.
Published: July 2002

Recently a new process for the room-temperature, low-pressure, deposition of thin films has been published, which uses pulsed radio-frequency discharges of very high power levels. Here, we describe the use of the process for the deposition of amorphous compounds containing germanium, sulfur, and phosphorus. The deposited compounds, many of which cannot be readily deposited using any other method, are shown to have useful properties as infrared coatings and as compound semiconductors with band gaps extending into the visible spectrum. The stability of the deposited compounds on exposure to high temperatures and on exposure to moisture is found to correlate with deposition conditions and compound stoichiometry, and the use of these materials under adverse environmental conditions is discussed.
The topography of isolated molecules of copper–phthalocyanine adsorbed on GaAs(110)
Authors: Möller R. , Coenen R. , Esslinger A. , Koslowski B.
Published: July 2002

Single molecules of Cu–phthallocyanine (CuPc) have been investigated on a GaAs (110) substrate under UHV conditions. Prior to the measurement, a tunneling experiment on a silver substrate covered with about one monolayer of CuPc was performed. By this procedure a few molecules are transferred to the tunneling tip. When tunneling on GaAs some of these molecules can be redeposited on the freshly cleaved (110) surface. The ring structure and the fourfold symmetry of the molecule can be clearly recognized on the atomic flat surface of GaAs. In a few cases, a deep dip in the middle of the molecule is visible.
Atomic structure of alkali metal overlayers on the Si(001) surface
Authors: Batra Inder P.
Published: July 2002

We have calculated the atomic structure of alkali metals overlayers on Si(001) at two different coverages. It is concluded that at 1/2 monolayer coverage, the quasihexagonal site proposed by Levine is favorable if the lattice is allowed to relax. The long bridge site along the dimerization direction is somewhat less stable. Although the top site above one of the dimer forming Si atoms is found to be energetically unfavorable at the coverages investigated, an asymmetric buckling of the surface does lead to a substantial lowering of the total energy. These findings are discussed in the context of recent scanning tunneling microscopy observations. At the monolayer coverage, our calculations predict a puckered structure. It is also shown that the 2×1 reconstruction is stable at least up to 1 monolayer coverage of alkali metals. The implications of the 2×3 low-energy electron diffraction structure for adsorption sites are briefly discussed.
Characterization of the Pd/a-Al2O3 supported cluster system
Authors: Marks F. A. , Lindau I. , Browning R.
Published: July 2002

Palladium deposits supported on amorphous alumina were prepared in ultrahigh vacuum and studied using transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and energy loss spectroscopy (ELS). The growth of clusters with deposition time was followed using TEM. The XPS, AES, and TEM results support a consistent model for the distribution of palladium on the alumina substrate, with the amount of material within the clusters accounting for the majority of the palladium deposited. The combined results of XPS, ELS, and TEM indicate that the deposit growth with deposition time can be tentatively separated into the following size regimes: monolayer islands, ‘‘small’’ clusters and metallic three-dimensional clusters. The size-dependent XPS Pd 3d binding energy shifts are analyzed within the initial-state-final-state framework. Component fitting of the Pd 3d spectra is consistent with assigning one of the components to the layer of interfacial Pd atoms.
Confirmation of an exception to the ‘‘general rule’’ of surface relaxations
Authors: Noonan J. R. , Davis H. L.
Published: July 2002

Low-energy electron diffraction (LEED) I–V spectra for Al(111) have been remeasured and analyzed to resolve a conflict concerning interlayer relaxations that are induced by the creation of the surface. Previous measurements of the Al(111) surface relaxations generally report a small expansion of the first interplanar spacing with respect to the bulk spacing. Several recent theories not only predict a contraction, but also that an expansion is not even possible with the formalism used. A large database of I–V measurements at room temperature and at 160 K has been compared to a very extensive set of calculated spectra. It was determined that the surface was expanded, Δd12=+1.7±0.3%, Δd23=+0.5±0.7%. Importantly, the analysis has also identified surface-enhanced thermal motions and no temperature dependence for the static interplanar relaxation within an accuracy of 0.007 Å.
CF4/O2 plasma etching and surface modification of polyimide films: Time-dependent surface fluorination and fluorination model
Authors: Scott P. M. , Matienzo L. J. , Babu S. V.
Published: July 2002

The interaction of CF4/O2 plasma mixtures with polyimide pyromellitic dianhydride–oxydianiline (PMDA-ODA) films is a complex process. In this investigation, the reactions of PMDA-ODA with a gas mixture containing 90% CF4/10% O2, as a function of treatment time, are studied with x-ray photoelectron spectroscopy (XPS). Curve fitting of the resulting spectra yields the distribution of CFx species formed during reaction. A detailed reaction mechanism of F atom addition to PMDA-ODA is constructed on a simplified monomer unit. The experimental results fitted to the proposed model yield apparent reaction rate constants and the time dependent concentration of unstable surface species in the reaction zone.
Photoemission study of the CdS/CdTe(110) interface
Authors: Engelhardt M. A. , Niles D. W. , Höchst H.
Published: July 2002

The formation and electronic interface properties of CdS grown by molecular beam epitaxy (MBE) on CdTe(110) substrates was studied by angle-resolved synchrotron radiation photoemission spectroscopy (ARPES) and reflection high-energy electron diffraction (RHEED). Core level intensity measurements from the CdTe substrate as well as from the CdS overlayer indicate the epitaxial two-dimensional deposition of zinc blende CdS films. The analysis of core and valence band spectra of the heterostructure shows that the interface is nonreactive and atomically abrupt. The CdS valence band is offset by ΔEv=−0.65 eV with respect to the Γ15v-point of CdTe. Using the band gap of cubic CdS, which is close to that of the thermodynamic stable wurtzite structured CdS of Eg=2.42 eV, the conduction band offset at the CdS/CdTe(110) interface is determined to be ΔEc=0.21 eV.
Properties of reactively sputtered NbN films
Authors: Westra K. L. , Brett M. J. , Vaneldik J. F.
Published: July 2002

The variation of the properties of niobium nitride (NbN) thin films as a function of argon partial pressure and nitrogen flow were studied. The films were deposited by dc reactive planar magnetron sputtering onto unheated substrates. All of the films were superconducting and had the B1, face-centered cubic crystal structure. A number of films deposited at argon partial pressures of 5 and 7 mTorr had superconducting critical temperatures (Tc ) of 15.6 K and grain sizes of 100–120 nm. The film morphology showed a zone 1 to zone T transition as the argon partial pressure was decreased from 12 to 5 mTorr. Films deposited below 5 mTorr exhibited excessive tensile stress (>1.9×109 N/m2) and delaminated from the substrate.
A comparison of HgCdTe metalorganic chemical vapor deposition films on lattice matched CdZnTe and CdTeSe substrates
Authors: Bevan M. J. , Doyle N. J. , Greggi J. , Snyder D.
Published: July 2002

Epitaxial layers of Hg1−xCdxTe have been grown by metalorganic chemical vapor deposition (MOCVD) with the interdiffused multilayer process using diethyltelluride and diisopropyltelluride. Both double crystal x-ray diffraction and cross-sectional transmission electron microscopy have confirmed that the crystal quality is limited by that of the lattice matched substrates, CdZnTe and CdTeSe. The (100)-oriented epilayers are free of twinning and have the lowest values of rocking curve widths reported for MOCVD HgCdTe. Growth on (211)B CdZnTe has been explored to avoid both twinning and pyramidal defects in HgCdTe.
Partial pressures of Hg and Te2 over (Hg1−xZnx)1−yTey solid solutions
Authors: Chen Kuo-Tong , Sha Yi-Gao , Brebrick Robert F.
Published: July 2002

The partial pressures of mercury PHg and of diatomic tellurium P2 have been determined from the optical density of the vapor phase coexisting with HgTe–ZnTe solid solutions containing 10, 20, 30, 50, and 70 mol % ZnTe. The optical density was measured between 250 and 750 nm, the maximum temperature range covered was 300 to 791 °C. The predominant vapor species is PHg, even for the Te-saturated state. Only PHg was measurable for the metal-saturated state. The maximum value was measured for 50 mol % ZnTe and is 34 atm at 727 °C. At temperatures up to about 500 °C, PHg is very nearly the same for all of the metal-saturated samples studied. For the Te-saturated state, both PHg and P2 were measured. A plot of log PHg against 1000/T is a straight line at low temperatures and at a given temperature, PHg is higher the smaller the mol % ZnTe in the solid solution. The chemical potential of HgTe in the solid solutions is derived from the data and compared to that in HgTe–CdTe.
Point defects with lattice distortion in CdTe and HgCdTe
Authors: Schick J. T. , Morgan-Pond C. G.
Published: July 2002

Results of self-consistent, tight-binding supercell calculations of electronic defect levels and relaxation about defects for As, Sb, and Te interstitials in CdTe and for the Hg vacancy in HgTe are presented. Trends in the localized defect levels and the relaxation of the lattice seen for these defects and for Cd, Hg, and In interstitials, from previous calculations,1 are discussed. Te interstitials are found to have the largest lattice relaxation of these interstitials in their preferred tetrahedral positions. This may help explain the tendency for excess Te to condense into second-phase inclusions. It is also suggested that a strain-mediated interaction between Te interstitials and cation vacancies may promote the creation of Te antisites in Te-rich HgCdTe.
Interfacial chemistry of metals on CdTe and ZnTe (110)
Authors: Wahi A. K. , Carey G. P. , Miyano K. , Chiang T. T. , Lindau I. , Spicer W. E.
Published: July 2002

We consider interfacial chemistry and band bending behavior for Al, In, Ag, and Pt overlayers on vacuum-cleaved p-CdTe and p-ZnTe (110) in a comparative study using ultraviolet photoelectron spectroscopy and x-ray photoelectron spectroscopy. A range of metal–substrate reactivities have been considered: Al reacts strongly with Te, Ag moderately, and In minimally, with no evidence seen for In reaction on ZnTe. Pt exhibits strong alloying behavior with both Cd and Zn. These results for the binaries are compared to metal/HgCdTe interface formation. We find that Hg loss can significantly influence the extent of reaction and/or intermixing for these overlayers, with resulting disruption either inhibiting or facilitating chemical interaction. Reaction and intermixing for Al, Ag, and Pt overlayers on CdTe and ZnTe indicate these interfaces are not ideal. The possible role of defects at these four metal/CdTe and metal/ZnTe interfaces is considered, and provides a consistent explanation for the final Fermi level positions observed.
The interface state study of TaSix/GaAs Schottky barrier
Authors: Kao C. H. , Huang F. S. , Chen Jiann-Ruey
Published: July 2002

Tantalum silicide films on GaAs exhibit high temperature stability. While the Schottky diodes of TaSix/GaAs (x=0.6 and 2) show good I–V characteristic curves. The interface state both of TaSi2/GaAs and Ta5Si3/GaAs under various annealing conditions were investigated by I–V, C−2 versus V, deep-level transient spectroscopy (DLTS), Auger electron spectroscopy (AES), multifrequency capacitance analysis (MCA), and G–V techniques. The silicon diffusion into GaAs was found in Si-rich sample after furnace annealing at 700 °C for 20 min. This diffusion gives the shallow trap states near the interface edge, while their energies can be estimated from the MCA data. The gallium out-diffusion into TaSix (x=0.6 and 2) was found with an interfacial layer formed after rapid thermal annealing (RTA). Card and Rhoderick’s model (MIS model) was adopted to explain the data obtained from the above electrical measurements, and found that the ideality factor, the barrier height, the frequency dependence on capacitance and conductance, and the carrier concentration profile are consistent to each other.
The role of ion-assisted deposition in the formation of diamond-like carbon films
Authors: Aisenberg Sol
Published: July 2002

The recent interest in diamond-like carbon (DLC) and its special properties and applications has resulted in attempts to deposit such films at greater rates and over larger areas. It is necessary that the new methods retain the special properties of the DLC material. The purity and structure of the films will be discussed from the point of view of high kinetic energy of the atoms on the surface and the additional kinetic energy supplied to the film by ion-assisted deposition through the simultaneous bombardment by 40–200 eV argon ions.
Simulation of scanning tunneling microscope image based on electronic states of surface/tip system
Authors: Kobayashi Katsuyoshi , Tsukada Masaru
Published: July 2002

Scanning tunneling microscope images of graphite are calculated taking into account microscopic electronic structure of tip. As a model tip with [111] protrusion, a W10 cluster is used. Electronic states of surface and tip are calculated non-empirically and are combined to obtain the tunnel current. When all the tip levels contribute to tunneling, normal images of graphite are obtained, which change from triangular to honeycomb lattice by increasing the bias. In the case that special tip levels are active in tunneling, anomalous images such as linear-chain type are obtained. It is shown that anomalous images are not necessarily multitip effect. By varying the applied bias, conductance spectrum is also calculated and is compared with experimental one.
New versatile room-temperature field ion scanning tunneling microscopy
Authors: Sakurai Toshi , Hashizume T. , Hasegawa Y. , Kamiya I. , Sano N. , Yokoyama K. , Tanaka H. , Sumita I. , Hyodo S.
Published: July 2002

We have designed and developed a series of room-temperature field ion scanning tunneling microscopes (RT FI-STMs). The great advantages of the RT FI-STM are (1) almost simultaneous use of both the STM mode and FIM mode is possible without wasting machine time and thermal drift; (2) inspection and manipulation of a STM tip in situ in the STM system can be performed and, thus, each tip can be used over several months, maintaining a desired atomic resolution; and (3) a well-characterized tip ensures a very high (∼100%) success rate in STM imaging with a known resolution. Several examples are given.
Studies on the properties of zirconia films prepared by direct current reactive magnetron sputtering
Authors: Suhail M. H. , Rao G. Mohan , Mohan S.
Published: July 2002

This paper deals with the preparation of zirconia films by direct current reactive magnetron sputtering. The films were annealed in ambient atmosphere at temperatures ranging from 300 to 850 °C. The as deposited films were found to be amorphous and a crystalline structure developed at 400 °C. The refractive index and extinction coefficient were found to be 1.93 and 0.5×10−3 at 600 nm for the as deposited films and they changed to 1.71 and 2.5×10−3 on annealing at 850 °C. The optical constants were found to be constant in the wavelength region beyond 400 nm, below which dispersion was observed.
Reduction of water in inorganic spin on glass
Authors: Ito Shinichi , Homma Yoshio , Sasaki Eiji
Published: July 2002

Water absorption characteristics of an inorganic spin on glass (SOG) are investigated. The weight of inorganic SOG film baked at 200 °C is about 35% retained water. Baking the SOG film at 200 °C and then at 450 °C in N2 for 30 min leaves 20% water in the film. Oxygen plasma treatments such as ashing or sputter etching on 450 °C-baked SOG films generally decrease the water content in the film. These treatments decrease the chemically adsorbed water, but increase the physically adsorbed water. We surmise that the energetic particles in the plasma eliminate the -OH group and at the same time deform the Si–O–Si framework structure, both resulting in water adsorption at the surface layer of the SOG film (physically adsorbed water). An oxygen plasma treatment in a parallel electrode reactor using a graphite susceptor drastically decreases the water content in the SOG film and reduces water adsorption during immersion in water. This treatment is called reactive glass stabilization (RGS). It is also found that the incorporation of organic material, which reduces the SOG water adsorption, is enhanced by the immersion of the RGS-treated SOG film in organic solutions.
Work function variations of the Ag/GaSb (110) interface at room and low temperature
Authors: Bonnet J. J. , Doukkali A.
Published: July 2002

The first stages of the interface formed between Ag and cleaved (110) surfaces of GaSb are investigated at room (RT) and low temperature (LT≤140 K) by using the method of the vibrating capacitor. Surface photovoltage measurements are used to get informations about band bending and affinity variations. Ag depositions are made in the 10−4–1 Å range. The results are in good agreement with those obtained in the 10−2–1 Å range common to our results and ultraviolet photoemission spectroscopy (UPS) measurements. We discuss here more particularly LT results and set up different state distributions which could explain the experimental curves. Our analysis suggests that at the very beginning of the Ag deposition two successive acceptor–donor pairs are formed, followed by a more intricate system of states before reaching the monolayer. The reduction in clustering observed at LT by other methods has been a key to interpret the formation of these states. Eventually we propose a model to explain the evolution of the states involved at LT.
Photoemission investigation of compound semiconductor monodisperse clusters
Authors: Tobin J. G. , Colvin V. L. , Alivisatos A. P.
Published: July 2002

We have used synchrotron radiation photoemission to probe the valence and core level electronic structure of compound-semiconductor monodisperse clusters (nanocrystals). These clusters exhibited a 10% or less variation relative to the mean diameter and were attached to the metal substrates via alkane chains. Direct evidence of gap broadening due to size variation in CdS clusters was observed. The novel utilization of alkane chain attachment is the key to eliminating the otherwise debilitating problem of sample charging, as occurs with powders. The quality of sample preparation was confirmed by other methods such as transmission electron microscopy, Raman scattering, and x-ray diffraction. This work provides a direct link between photoemission studies of expitaxial ultrathin films of compound semiconductors, the photon-spectroscopy measurements of cluster powders and the existing theories of quantum confinement in reduced dimensionality structures.
Microstructure of sputter-deposited Al–Cu–Si films
Authors: Shimamura Hideaki , Yajima Akira , Yoneoka Yuji , Kobayashi Shigeru
Published: July 2002

The microstructure of Al–3 wt. % Cu–1.5 wt. % Si and Al–0.5 wt. % Cu–1.0 wt. % Si films was analyzed with respect to crystal grain orientation and grain size distribution before and after annealing at 475 °C for 30 min. Films were deposited at various substrate temperatures using load-lock magnetron sputtering systems. Crystal orientation was analyzed by Kikuchi line patterns in 20 individual grains with respect to the substrate surface in each sample. Crystal grain size distributions were analyzed in high-Cu content films deposited under no-heat, 140 and 280 °C predeposition conditions. θ-CuAl2 precipitates were found in the as-deposited 280 °C sample at the triple points of the grain boundary. This sample showed the largest orientation dispersion. This phenomenon was not affected by annealing. Stable θ-phase precipitates formed at the grain boundaries during deposition were thought to impede the coalescence of grains resulting in a low degree of preferred orientation. Thin (0.1 μm) Al–0.5 wt. % Cu–1.0 wt. % Si films were deposited onto a MoSi2 underlayer at low substrate temperature and heated, followed by an additional 0.9 μm deposition. Samples treated in this manner exhibited a high degree of crystal orientation. It was found that crystal orientation in the initial stage of deposition is one of the major determinants in the final crystal orientation of films.
Surface characterization of carbon-supported iron catalysts for carbon monoxide hydrogenation: Influence of catalyst distribution and coal minerals
Authors: Schwar J. , Jahn P. W. , Wiedmann L. , Benninghoven A.
Published: July 2002

The iron catalysed carbon monoxide hydrogenation (Fischer–Tropsch synthesis) has been studied by on-line combination of a chemical microreactor working under technical conditions with surface analytical methods (photoelectron spectroscopy, secondary ion and thermal desorption mass spectrometry, ion scattering spectroscopy, electron and x-ray microscopy). In contrast to other sample preparation methods, deposition of Fe(CO)5 onto carbon substrates leads to a surface shell with highly dispersed iron particles. Metallic iron, which is the most important species in the reaction, is formed by reduction of the samples in H2 atmosphere at elevated temperature. A reduction time of 16 h is required to achieve complete reduction of residual FeO at the interface between iron and the carbon support. The activity and selectivity of the catalyst is mainly determined by the existence of a mobile potassium phase which segregates to the surface. A high potassium concentration shifts the selectivity towards long chains, a low concentration lowers the total activity. Degradation of the catalyst during the reaction mainly occurs by two processes: the gradual oxidation of metallic iron to FeO and sintering of iron to larger particles. Iron oxidation can be reversed by reactivation in H2. Sintering cannot be prevented completely, but seems to be delayed by a high Al content in the carbon substrate.
Microscopic x-ray photoelectron spectroscopy using a focused soft x-ray beam
Authors: Ninomiya Ken , Hirai Yasuharu , Momose Atsushi , Aoki Sadao , Suzuki Keizo
Published: July 2002

An axisymmetric Wolter type mirror is used in a synchrotron radiation beamline to focus 150 eV soft x rays for microscopic x-ray photoelectron spectroscopy (XPS). The focusing characteristics are evaluated for x-ray source sizes of 1 mm, 200 and 120 μm in diameter. In this evaluation, the Si(2p) photoelectrons from a Si sample are counted while a knife edge is scanned across the focal point of the mirror. The lateral resolution is 2 μm by the 25%–75% criterion, and 4 μm by the full width at half-maximum definition in the beam intensity profile. The Wolter type mirror is expected to provide microscopic XPS techniques with micrometer to sub-micrometer resolution.
Variable angle spectroscopic ellipsometry studies of oriented phthalocyanine films
Authors: Debe M. K. , Field D. R.
Published: July 2002

Thin films of metal-free phthalocyanine (H2Pc), vapor deposited onto sputtered copper substrates, are characterized using a fully automated Woollam variable angle spectroscopic ellipsometer. Data from over a dozen H2Pc films in the thickness range of 1000 to 1140 Å were acquired over a 4000–8000 Å wavelength range in 100 Å steps, and 45°–79° incidence angle range in 2° steps. Two classes of H2Pc films were formed, uniaxially oriented with the molecular stacking b axis in either a standing or surface-parallel configuration, by carrying out the deposition at two different substrate temperatures and deposition rates. Reflection absorption infrared spectroscopy was used to verify the different orientations. It is observed that the three dimensional plots of the ellipsometric parameters Δ and Ψ versus wavelength and incidence angle have different characteristic shapes for the two classes of oriented films, implying anisotropic dielectric functions. Using a multilayer optical modeling code capable of treating fully anisotropic films, we attempt to determine the in-plane and out-of-plane optical constants for each of these ‘‘orthogonally’’ oriented film types. Significant differences in the optical constant spectral solutions are found for the two classes when treated with isotropic film models, but convergent solutions of the direct anisotropic regression analyses have not been found. However, due to the high degree of uniaxial ordering in the two film classes, it is possible to extract approximate solutions to the parallel and perpendicular optical constants taken with respect to the crystalline b axis.
The use of secondary ion mass spectrometry to investigate copolymer enhanced adhesion between immiscible polymers
Authors: Deline V. R. , Brown H. R. , Char K.
Published: July 2002

The interfacial adhesion between immiscible polymers (homopolymers) is usually weak, but it can be strengthened with the addition of a diblock copolymer where one block is miscible with one homopolymer and the other block is miscible with the other homopolymer. A diblock copolymer consists of one polymer chain chemically linked at one end to another polymer chain. Secondary ion mass spectrometry (SIMS) is used to measure the copolymer organization at the joining interface, to measure the extent of intermixing between the copolymer blocks and the adjoining homopolymers and to determine the location of the copolymer blocks after the joint is fractured. The SIMS results provide unique and valuable information on the function of the copolymer to enhance the adhesion between the immiscible homopolymers.
Secondary ion mass spectrometry analysis of aluminum films: Relative sensitivity factors and analytical considerations
Authors: Stevie F. A. , Kahora P. M. , Cochran G. W.
Published: July 2002

Relative sensitivity factors (RSFs) have been measured for 20 elements in sputter deposited aluminum films using oxygen and cesium primary beams. E+, EAl+, EO+, and EAl O+ (where E is the element) were monitored for oxygen bombardment, and E−, EAl−, ECs−, and EAl Cs− for cesium bombardment. The results follow the RSF patterns observed for other matrices. Depth resolution degradation due to nonuniform sputtering of aluminum was examined. Oxygen bombardment produced smoother craters than cesium bombardment; sputtering rate and aluminum deposition temperature were also found to affect crater topography. The effect of surface oxygen on depth profiles has also been studied.