bluuebunny/crossref_metadata_2025 huggingface dataset:
Sample manipulator employing a gas-thermal switch designed for high pressure experiments in an ultrahigh vacuum apparatus
Authors: Sneh Ofer , George Steven M.
Published: July 2002

A sample manipulator with a gas-thermal switch was designed for high pressure surface science experiments in an ultrahigh vacuum (UHV) apparatus. The gas-thermal switch coupled the sample mount to the cryostat using helium gas. When helium gas was present and the thermal switch was on, the cooling time constant was τ∼2.6 min. When the helium gas was evacuated, the sample mount was isolated and could be easily warmed to room temperature in ∼5 min using a small ceramic heater. The sample manipulator was built to be part of an internal high pressure chamber. The internal high pressure chamber could obtain pressures as high as 100 Torr with only small pressure excursions of ΔP≊1–2×10−10 Torr in the UHV chamber. Recovery back to UHV conditions occurred only minutes after high pressure experiments with gases or condensable materials such as H2O. This note details the rationale and mechanical design of this sample manipulator with a gas-thermal switch for high pressure experiments in an UHV apparatus.
Chemical vapor deposition of aluminum from dimethylaluminumhydride (DMAH): Characteristics of DMAH vaporization and Al growth kinetics
Authors: Kondoh Eiichi , Ohta Tomohiro
Published: July 2002

The metallization process for the chemical vapor deposition of aluminum from dimethylaluminumhydride [(Al(CH3)2H, DMAH)] has received considerable attention. In this article, the authors discuss the vaporization of DMAH, Al deposition kinetics, selective growth, and film properties. Although DMAH has extremely high viscosity (about 4000 cP), it was found by metering the DMAH flow rate that DMAH can be vaporized while maintaining a high efficiency of 80%–100 % of the theoretical flow rate, even with the conventional bubbling method. The film growth rate followed the Arrhenius law at lower temperatures (<250–270 °C, depending on the partial pressure of DMAH). The maximum growth rate attained was about 1160 nm/min at 350 °C. In the surface-reaction-controlled region, Al was deposited selectively on metal substrates. The origin of selectivity is discussed from the viewpoint of surface chemical conditions. The Al deposition rate was independent of the deposition area, which is discussed in terms of the supply and consumption balance of Al.
Excimer laser ablation mass spectrometry of inorganic solids: Chemical, matrix, and sampling effects on polyatomic ion yields
Authors: Gibson John K.
Published: July 2002

Positive ions formed directly by excimer laser ablation in vacuum of several lanthanide (Ln) and transition metal solid materials—including Ln2O3, Ln2S3, LnF3, Ta2O5, ZrO2, TiO, and TiO2—were identified by time-of-flight mass spectrometry. Variations in ion yields were investigated as a function of the composition of the precursor material, laser irradiance, and ion sampling delay after ablation. The compositions of the observed polyatomic ions reflected the distinctive chemistries of the metal constituents, but the ion yield distributions were not generally indicative of the particular chemical/valence constitution of the target material. For example, the yield of CeO+ relative to Ce+ was substantially greater from the trivalent cerium oxide, Ce2(WO4)3(s), than from tetravalent CeO2(s). Observed ion distributions apparently reflected the chemical composition of the ablation plume and the degree of gas-phase recombination therein. The observed abundances of polyatomic ions were found to correlate well with their estimated bond strengths. Further obscuring the chemical composition of the progenitor, minor changes in ablation, and sampling parameters—especially irradiance and sampling delay—were often manifested as significant variations in relative ion intensities.
Modeling of water outgassing from metal surfaces (III)
Authors: Li Minxu , Dylla H. F.
Published: July 2002

A model of water adsorption on metal oxide layers and water outgassing from metal surfaces has been developed. The oxide layer is assumed to have porous structure and a pore length (l) distribution of 1/l2. Numerical evaluation shows that the quantity of water adsorbed is logarithmic with time within a certain time range as experimentally observed. The outgassing rate from surfaces with adsorbed water distributed uniformly on the inner surfaces of individual pores is shown analytically to be inversely proportional to time. This result is consistent with frequently observed pumpdown curves.
A study of the interaction between thermally deposited aluminum films and fluoropolymer substrates
Authors: Du Yuezhong , Gardella Joseph A.
Published: July 2002

Aluminum was thermally deposited onto fluoropolymer substrates. The effects of interfacial reaction of aluminum with several fluoropolymeric substrates were investigated. These included PFA (poly[tetrafluoroethylene-co-perfluoro(alkoxy vinyl ether)]), FEP (poly(tetrafluoroethylene-co-hexa- fluoropropylene), and hydroxylated FEP (m-FEP). The hydroxyl modification was prepared by a previously developed radio frequency glow discharge (RFGD) method. X-ray photoelectron spectroscopy (XPS) studies of thin (∼30 Å) Al deposited samples showed the formation of new fluorine-containing species, due to fluorine diffusion into the Al overlayers. Auger and XPS depth profiles of samples with thick (∼200 Å) Al overlayers also suggested the diffusion of fluorine and the formation of Al fluorides at the interface. The RFGD modification process prior to the Al deposition was performed to investigate potential adhesion of Al to the substrates. This is envisioned as a reaction between Al and RFGD introduced oxygen. The resulting Al/oxide interface limits the diffusion of fluorine.
Structural study of the growth of thin Cu films on Ru(0001) by low-energy alkali ion scattering
Authors: Shen Y. G. , O’Connor D. J. , Yao J. , van Zee H. , Roberts R. H. , MacDonald R. J. , Wandelt K.
Published: July 2002

The surface structure of thin Cu films on Ru(0001) has been studied by low-energy Li+ ion scattering, Auger electron spectroscopy, and low-energy electron diffraction. It was found that Cu grew layer-by-layer for the first two layers. Experimental results obtained by analyzing the incident angle dependence associated with shadowing of Ru by Cu confirmed that the first overlayer Cu was in a normal registry position, i.e., there was a continuation of the hexagonal close-packed stacking sequence. The second overlayer Cu was also determined to be in registry along the long azimuth (one of three possible domains) by analyzing the shadowing critical angles for the second overlayer Cu focusing onto the first overlayer Cu. The structure of the Cu thin films up to 6 monolayers has been probed by measuring the incident and azimuthal angle dependences. The results were consistent with an epitaxial Cu(111) structure by comparing with the results of standard Cu(111), although some distortion was observed.
Surface phase transformations in the Ni/Si(111) system observed in real time using low-energy electron microscopy
Authors: Bennett P. A. , Lee M. Y. , Parikh S. A. , Wurm K. , Phaneuf R. J.
Published: July 2002

Submonolayer Ni deposits quenched from above 840 °C produce an ‘‘impurity stabilized’’ 1×1 phase, which scanning tunnel microscope observations reveal to be a 1×1 lattice gas of ring clusters (RCs) together with Si adatoms in local 2×2 domains. We call this phase 1×1-RC. Real time low-energy electron microscopy observations show the following: terraces are covered with the 1×1-RC phase except for narrow strips of 7×7 along the top side of bilayer steps. The strip width decreases with increasing Ni coverage and increasing quench rate. Slow cooling results in clean 7×7 only. Depositing Ni at 700 °C causes the 1×1-RC phase to expand, consuming 7×7. At 720 °C, the 1×1-RC phase mixes with 7×7 to cover the terraces uniformly. Depositing at 500 °C instead causes formation of NiSi2 islands in a matrix of clean 7×7. These reactions are summarized in terms of a temperature versus coverage phase formation diagram.
Sputter deposition of yttria-stabilized zirconia onto a porous Au substrate
Authors: Jankowski A. F. , Hayes J. P.
Published: July 2002

Process issues key to thin-film/solid–oxide fuel cells include the deposition of defect-free electrolyte layers on porous electrodes, gas transport through the porous conducting electrodes, and sufficient structural integrity for stack assembly and temperature cycling. This study addresses the method of electrolyte layer deposition. Our initial approach uses a porous metal substrate to permit measurement of the electrolyte performance as well as provide a pore size similar to conventional cermet electrodes. The sputter deposition of Au under controlled process parameters provides the porous substrate. An optimum choice for the electrolyte material is yttria-stabilized zirconia (YSZ). Our focus is to evaluate the process parameters of rf sputtering a YSZ target to densely coat the porous (Au) substrate. A high sputter gas pressure of Argon facilitates filling surface voids of the porous substrate leading to the formation of a defect-free layer of cubic YSZ as examined with electron microscopy techniques.
Plasma-induced damage of GaAs during etching of refractory metal contacts
Authors: Shul R. J. , Lovejoy M. L. , Baca A. G. , Zolper J. C. , Rieger D. J. , Hafich M. J. , Corless R. F. , Vartuli C. B.
Published: July 2002

The effect of plasma-induced damage on the majority carrier transport properties of p-type GaAs has been studied by monitoring changes in sheet resistance (Rs) of thin conducting layers under various plasma conditions including etch conditions for refractory metal contacts. Rs determined from transmission line measurements are used to evaluate plasma-induced damage for electron cyclotron resonance (ECR) and reactive ion etch (RIE) conditions by varying the thickness and doping of epitaxial layers. Damage depths calculated from Rs data show a strong dependence on doping levels. This can be explained by a plasma-damage-induced trap density profile which tails off into the sample. Consistent trends have been observed where Rs increases with increasing dc bias, increasing microwave power, and decreasing pressure, thus showing Rs increases as either the ion energy or ion flux increases. The lowest plasma-induced damage observed in this study occurs with ECR at low microwave power and no rf biasing. Under rf-bias conditions, samples exposed to the ECR (1 mTorr total pressure) show more damage than those exposed to the RIE (8 mTorr total pressure) at comparable dc bias. We have also observed Rs dependence on ECR plasma chemistry where Rs is lower in SF6/Ar plasmas than Ar and N2 plasmas possibly related to interactions of F or S atoms with the GaAs surface. Moderate anneal temperatures (200–500 °C) have shown significant Rs recovery.
Contact potential measurements of hard disk drive surfaces in humid environments
Authors: Zanoria Elmer S. , Danyluk Steven , Zharin Anatoly L. , Bhatia C. Singh
Published: July 2002

Contact potential difference (CPD) experiments were conducted by the vibrating probe (Kelvin) method on humidity-exposed hard disk drive surfaces. The measurements were made at various locations along the circumference of a wear track caused by the sliding contact with a spherical silicon pin, operated in a pin-on-disk configuration. The load on the pin, rotational speed of the disk, and the humidity were controlled. The CPD signals varied along the wear track and the magnitude of the CPD change increased with the load from 29 to 98 mN at a fixed relative humidity. The CPD signals also increased linearly with relative humidity ranging from 30% to 70% as the normal load was fixed at 29 and 49 mN. The CPD signal appears to saturate at a load of 98 mN where the relative humidity is 50% and higher.
High resolution digital Auger database of true spectra for Auger electron spectroscopy intensities
Authors: Seah M. P. , Gilmore I. S.
Published: July 2002

An outline is presented of a new high resolution digital Auger database including most of the nonradioactive elements with wide scan spectra from 20 to 2500 eV at 1 eV intervals and details of the peaks at 0.1 eV intervals. These details are recorded at 0.25 eV resolution. These spectra have all instrumental contributions effectively removed. The database also contains measurements for many oxides. By using a new Auger electron spectrometer calibration system (shortly to become generally available) these data are presented as true spectra with an intensity scale of sr−1 eV−1. By convolution with the measured instrument response function these data may be made to simulate the measurements on any analytical spectrometer or, conversely, any instrument (without faults) may be calibrated to produce equivalent absolute spectra. Predictions of theoretical Auger electron intensities, based on Gryzinski’s cross section, Shimizu’s backscattering factor, and Tanuma et al.’s relations for the inelastic mean free path, summed to allow for Coster–Kronig transitions, are compared with the experimental measurements after the backgrounds have been removed. Both theory and experiment, here, have no arbitrary fitting parameters and are expressed on the absolute intensity scale in units of sr−1. Agreement is achieved for the first time.
Comparison of submicron particle analysis by Auger electron spectroscopy, time-of-flight secondary ion mass spectrometry, and secondary electron microscopy with energy dispersive x-ray spectroscopy
Authors: Childs Kenton D. , Narum David , LaVanier Lori A. , Lindley Patricia M. , Schueler Bruno W. , Mulholland George , Diebold Alain C.
Published: July 2002

Particulate contamination can result in a significant yield loss during semiconductor device fabrication. As device design rule dimensions decrease the critical defect size also decreases, resulting in the need to analyze smaller defects. Current manufacturing requirements include analysis of sub-0.5-μm defects, with analysis of sub-0.1-μm defects expected in the near future. This article investigates the particle analysis capabilities of Auger electron spectroscopy, time-of-flight secondary ion mass spectrometry, and energy dispersive x-ray spectroscopy during scanning electron microscopy (SEM/EDS). In order to evaluate each method carefully, a standard set of samples was prepared and analyzed. These samples consist of 0.5-, 0.3-, and 0.1-μm Al and Al2O3 deposited on 1-in. Si wafers. Although all the methods observed an Al signal, a semiquantitative gauge of capability based on the relative strengths of particle versus substrate signal is provided. The dependence of the sample-to-substrate signal on primary electron energy is examined for both EDS and Auger analyses. The ability to distinguish metallic Al particles from Al oxide particles for the three techniques is also discussed.
Pulsed plasma deposition of chromium oxide/chromium-cermet coatings
Authors: Gall D. , Gampp R. , Lang H. P. , Oelhafen P.
Published: July 2002

A novel radio frequency magnetron sputtering method for the deposition of composite films which consist of chromium oxide and chromium (Cr2O3/Cr-cermet) is presented. As an extension to conventional reactive sputtering of a Cr target in an argon and oxygen atmosphere the oxygen flow into the process chamber is switched periodically on and off. This leads to an oscillating oxygen partial pressure during the sputtering process and an alternating deposition of metallic chromium and chromium oxide. In situ x-ray and ultraviolet photoelectron spectroscopy are used to monitor the oxidation state of chromium at the film surface and to study the chemical interactions between adjacent layers. Ex situ x-ray diffraction analysis reveals the multilayered and nanocrystalline structure of the deposited films. The overall chromium and chromium oxide concentration is estimated from the optical constants n and k determined by reflectance and transmission measurements in the wavelength range between 400 and 2200 nm.
Production of nanometric particles in radio frequency glow discharges in mixtures of silane and methane
Authors: Bertran E. , Costa J. , Viera G. , Zhang R. Q.
Published: July 2002

The formation of silicon particles in rf glow discharges has attracted attention due to their effect as a contaminant during film deposition or etching. However, silicon and silicon alloy powders produced by plasma-enhanced chemical vapor deposition (PECVD) are promising new materials for sintering ceramics, for making nanoscale filters, or for supporting catalytic surfaces. Common characteristics of these powders are their high purity and the easy control of their stoichiometry through the composition of the precursor gas mixture. Plasma parameters also influence their structure. Nanometric powders of silicon–carbon alloys exhibiting microstructural properties such as large hydrogen content and high surface/volume ratio have been produced in a PECVD reactor using mixtures of silane and methane at low pressure (<1 Torr) and low frequency square-wave modulated rf power (13.56 MHz). The a-Si1−xCx:H powders were obtained from different precursor gas mixtures, from R=0.05 to R=9, where R=[SiH4]/([SiH4]+[CH4]). The structure of the a-Si1−xCx:H powder was analyzed by several techniques. The particles appeared agglomerated, with a wide size distribution between 5 and 100 nm. The silane/methane gas mixture determined the vibrational features of these powders in the infrared. Silicon–hydrogen groups were present for every gas composition, whereas carbon–hydrogen and silicon–carbon bonds appeared in methane-rich mixtures (R<0.6). The thermal desorption of hydrogen revealed two main evolutions at about 375 and 660 °C that were ascribed to hydrogen bonded to silicon and carbon, respectively. The estimated hydrogen atom concentration in the sample was about 50%.
Near-field scanning optical microscope for microelectronic materials and devices
Authors: Duncan Walter M.
Published: July 2002

We have developed a near-field scanning optical microscope (NSOM) with spectroscopic capability for application to advanced microelectronic materials and devices. Combining NSOM with spectroscopic analysis provides chemical information on thin films and defects with ultrahigh spatial resolution. Several microelectronic systems, InGaAs/InAlAs/GaAs epitaxial layers, partially fabricated SiO2/Si complementary metal–oxide semiconductor structures, and bulk samples of GaP and diamond, were examined in this work as vehicles to elucidate NSOM imaging modes. Reflected intensity contrast in NSOM provides images of defect networks in InGaAs/InAlAs/GaAs epitaxial layers and shows thickness variations in SiO2 films on Si. Fluorescence and Raman scattering modes are examined for chemically identifying materials and defects.
Formation of an in situ diffusion barrier while diffusing aluminum through boron-enriched nickel
Authors: Peterman D. J.
Published: July 2002

A coating process is described in which a boron-doped nickel layer is first deposited onto a substrate and is then overcoated with aluminum. This duplex coating is annealed such that a nickel aluminide coating is formed on top of a boron-based diffusion barrier. During a low temperature anneal, the boron, which had been evenly distributed throughout the Ni layer, becomes concentrated in a remnant Ni layer which is located between the substrate and a NiAl overlayer. During a high temperature anneal on Ti-alloy substrates, Ti borides are formed. This study reveals two stages in which diffusion is inhibited. First, diffusion is inhibited by the boron-enriched nickel layer. Second, diffusion is arrested by a titanium diboride diffusion barrier. Results of electron and ion spectroscopies are used to illustrate the nature and effectiveness of the diffusion barrier when applied to various Ti-alloy substrates. In this application, it is shown that the diffusion of Ti, V, and Mn, into the NiAl layer is inhibited. Anticipated benefits of this barrier, when employed with oxidation protection coatings, are discussed.
Growth mechanism of cubic boron nitride thin films by ion beam assist sputter deposition
Authors: Park K. S. , Lee D. Y. , Kim K. J. , Moon D. W.
Published: July 2002

Cubic boron nitride (c-BN) thin films were successfully grown on Si(100) substrates by dual ion beam sputter deposition and the growth mechanism was studied with angle resolved in situ x-ray photoelectron spectroscopy (XPS) analysis. Boron was sputter deposited by 1 keV argon ions from a boron target and simultaneously bombarded with low energy nitrogen and argon ions mixture. Through Fourier transform infrared absorption spectroscopy (FTIR) and in situ XPS experiment, the optimum conditions for the c-BN growth such as the substrate temperature, the assist ion current density and the ion energy were determined to be 460 °C, 60 μA/cm2 and 350 eV, respectively. Angle resolved in situ XPS analysis showed that the 1.2±0.2 nm surface layer of the c-BN film is always in the hexagonal boron nitride (h-BN) phase, which clearly shows that c-BN phase grows by the transformation from the initially formed h-BN phase by low energy ion bombardment. Cross-sectional high resolution transmission electron microscopy (TEM) images show that the BN thin films on Si has a sequential layered structure which consists of an initial amorphous BN (a-BN) layer (∼4 nm), a transitional h-BN layer (∼5 nm), and a main c-BN layer. The transformation of the h-BN to the c-BN phase and the unusual sequential layered structure were discussed in view of the compressive stress model.
Numerical study of the effects of reactor geometry on a chlorine plasma helicon etch reactor
Authors: Font Gabriel I. , Boyd Iain D.
Published: July 2002

The flow field inside a helicon plasma etch reactor is simulated using a direct-simulation Monte Carlo method for a chlorine feed gas flow. Computations for the gas discharge are carried out modeling the ions and neutrals as particles and imposing the electrons as a background condition conforming to experimental measurements. The neutrals and ions are then allowed to interact with the background electrons and relax to a steady state. The resulting plasma is primarily composed of chlorine atoms and ions. The plasma flow is compared for three separate nozzle locations. The flow field, in the presence of the plasma, is found to be affected minimally by the nozzle location. A nozzle location is identified which maximizes flux to the wafer.
Temperature and concentration effects on ozone ashing of photoresist
Authors: Gardner W. L. , Baddorf A. P. , Holber W. M.
Published: July 2002

Photoresist removal was studied using single-crystal silicon samples mounted on a ceramic heater in an UHV compatible chamber. The photoresist-coated sample was exposed to an ozone-oxygen mixture at atmospheric pressure and at a flow rate of 4 s ℓ/min. Resist removal rate was measured using in situ laser interferometry. The removal rate was found to be a linear function of ozone concentration with a slope of 0.82 nm/s/unit mass fraction at a substrate temperature of 200 °C. The linearity is consistent with a simple chemical rate model. Typical photoresist removal rates at a mass density fraction ozone concentration of 0.09 ranged from 2.5 to 13 nm/s for substrate temperatures ranging from 150 to 300 °C, respectively. These rates are comparable with those observed by others. Over this temperature range, removal rates follow standard Arrhenius behavior from which an activation energy of 5.2 kcal/mol was determined. This value is similar to the known activation energy of 6.0 kcal/mol for the thermal dissociation of ozone leading us to conclude that thermal dissociation is the rate limiting step in the process. Our result is also significantly lower than reported previously and may be more accurate since the substantial shrinkage of photoresist with temperature was accounted for in these results. Additionally, the combination of concentration and temperature information is shown to lead to an effective chemical reaction rate constant for the removal of photoresist with ozone.
Scanning tunneling spectroscopy of Fe/W(110) using iron covered probe tips
Authors: Bode M. , Pascal R. , Wiesendanger R.
Published: July 2002

We have used iron covered tungsten probe tips to study the electronic structure of thin films of Fe on a W(110) substrate by means of scanning tunneling spectroscopy. In contrast to earlier experiments which were performed with tungsten tips we have found a minimum in the differential conductivity dI/dV at submonolayer Fe coverage just above the Fermi level. At a coverage of 1.3 ML a pronounced peak is measured above Fe islands of the second layer approximately 0.9 eV above the Fermi level, i.e., in the empty sample states. This empty state peak was found to be extremely sensitive to contamination from the residual gas which is also known to influence the magnetic state of the second layer islands.
Scanning tunneling microscopy studies of strain relaxation and misfit dislocations in InAs layers grown on GaAs(110) and GaAs(111)A
Authors: Belk J. G. , Sudijono J. L. , Yamaguchi H. , Zhang X. M. , Pashley D. W. , McConville C. F. , Jones T. S. , Joyce B. A.
Published: July 2002

Strain relaxation during the growth of InAs thin films on GaAs substrates by molecular beam epitaxy has been studied by scanning tunneling microscopy (STM). A two-dimensional growth mode operates for InAs layers grown on both GaAs(110) and GaAs(111)A. Detailed STM profiles of the InAs surfaces reveal small relaxation phenomena that are related to the presence of misfit dislocations at the buried heterointerface. The origin of these surface features is discussed, and their utility in studying the relaxation of strained semiconductor thin films is demonstrated.
Unit cell layer-by-layer heteroepitaxy of BaO thin films at temperatures as low as 20 °C
Authors: Ohnishi T. , Yoshimoto M. , Lee G. H. , Maeda T. , Koinuma H.
Published: July 2002

BaO thin films were grown epitaxially on the ultrasmooth SrTiO3 (001) substrate at temperatures ranging from 20 to 600 °C by laser molecular beam epitaxy. The film surface was characterized by in situ reflection high energy electron diffraction (RHEED) and ex situ atomic force microscopy (AFM). RHEED intensity oscillation at the specular beam spot could be clearly observed during the film growth in all the temperature range. The oscillation period corresponded well with the growth unit of biatomic (BaO)2 layer, indicating a unit cell layer-by-layer manner of the growth. AFM analysis also proved the two-dimensional biatomic layer-by-layer growth.
Hard boron–suboxide-based films deposited in a sputter-sourced, high-density plasma deposition system
Authors: Doughty C. , Gorbatkin S. M. , Tsui T. Y. , Pharr G. M. , Medlin D. L.
Published: July 2002

Boron–suboxide-based thin films have been deposited on Si in an electron cyclotron resonance microwave plasma using a radio frequency (rf) magnetron as a source of boron. Variations of the oxygen fraction in the deposition ambient and of the rf bias applied to the substrate were related to film tribology. The best films have hardnesses of ∼28 GPa and moduli of ∼240 GPa and were deposited in oxygen fractions <1% at substrate temperatures <350 °C. The films contain 4%–15% O and ∼15% C, with carbon originating from the sputter target. They are amorphous and have surface roughnesses of ∼0.2 nm. Boron–oxide films may form a self-generating lubricating layer of B(OH)3 in ambient atmosphere. Compositional depth profiling of these films reveals an oxygen-enriched surface of ∼10 nm thickness. Initial nanoscratch test results indicate that these films fail at high critical loads and have low friction coefficients relative to other hard coatings.
Interactions of evaporated aluminum atoms with polyaniline films: An x-ray photoelectron spectroscopic study
Authors: Lim S. L. , Tan K. L. , Kang E. T.
Published: July 2002

X-ray photoelectron spectroscopy was employed for the in situ study of the interactions between thermally deposited Al atoms and polyaniline films of different intrinsic oxidation states. Quantitative changes in the N 1s core-level line shape, the evolution of the Al 2p core-level spectra, and the changes in surface stoichiometry of these films throughout the Al deposition process were carefully tracked. Although the nitrogen sites appear to be more attractive to the incoming Al atoms and the emeraldine and nigraniline films undergo an apparent decrease in intrinsic oxidation state ([=N–]/[–NH–] ratio) as a result of Al deposition, there is no direct interaction between the two species, and the adsorbed oxygen from the bulk of the polymer film plays a dominant role in the interfacial interactions between the polymer and the metal.
Magnetoresistance of NiMnSb-based multilayers and spin valves
Authors: Caballero J. A. , Park Y. D. , Childress J. R. , Bass J. , Chiang W.-C. , Reilly A. C. , Pratt W. P. , Petroff F.
Published: July 2002

We report magnetic and magnetoresistance (MR) measurements in the current-in-plane (CIP) and current-perpendicular-to-the-plane (CPP) geometries of multilayers and spin-valve structures based on the predicted half-metallic (100% spin-polarized) ferromagnetic Heusler alloy NiMnSb. Multilayers of the form [NiMnSb/Cu]×10, as well as a trilayer spin valve of the form [NiMnSb/Cu/Y] (Y=Ni80Fe20 and NiMnSb/FeMn) have been grown using a low-rate, low-pressure sputtering deposition technique. The multilayers do not show evidence of antiferromagnetic coupling between the NiMnSb layers, and the measured CPP magnetoresistance is 4.5% at 4.2 K. NiMnSb/Cu/NiFe spin valves and NiMnSb/Cu/NiMnSb/FeMn quasispin-valves adopt more closely antiparallel alignments of adjacent magnetic layer magnetizations, and CPP MR ratios as high as 7.2% are measured at 4.2 K. Although these CPP MRs are larger than the CIP MRs for similar samples, the largest CPP MR observed is still smaller than expected for a 100% spin-polarized material.
Cubic boron nitride thin film deposition by unbalanced magnetron sputtering and dc pulsed substrate biasing
Authors: Otaño-Rivera Wilfredo , Pilione Lawrence J. , Zapien Juan A. , Messier Russell
Published: July 2002

Boron nitride (BN) thin films were deposited by unbalanced magnetron sputtering. An asymmetric bipolar pulsed dc power supply was used to bias the substrate with a 218 kHz signal. BN was deposited at different negative bias voltages and films with over 80% of the zinc-blende cubic phase, as measured by Fourier transform infrared (FTIR) spectroscopy, were obtained. For a given set of deposition conditions a window of maximum negative bias voltage was defined inside which the cubic phase is stabilized. This negative bias voltage was used to derive the momentum imparted to the growing film per arriving boron atom, and it is shown that a threshold value for the formation of the cubic phase (cBN) is consistent with previous results using ion beam assisted deposition. Several films were deposited on aluminum nitride and diamond thin films previously deposited on crystalline silicon in order to study the effect of the substrate on the stabilization of the cBN phase. A twofold reduction in the full width at half maximum (FWHM) of the 1060 cm−1 FTIR peak is obtained for films deposited on diamond, which is indicative of better ordering of the B–N cubic bonding. At high negative bias voltages the FWHM increases toward the value for BN films deposited onto crystalline silicon which is expected since the greater energetic bombardment produces excessive damage to the film.
In situ observation of gas-source molecular beam epitaxy of silicon and germanium on Si(001)
Authors: Goldfarb I. , Owen J. H. G. , Bowler D. R. , Goringe C. M. , Hayden P. T. , Miki K. , Pettifor D. G. , Briggs G. A. D.
Published: July 2002

We have observed the development of the surfaces during gas-source growth of silicon and germanium in an elevated temperature ultrahigh vacuum scanning tunneling microscopy (STM), with near-atomic resolution under a range of temperature and flux, which are the two dominant parameters, and applied atomistic modeling to the structures seen by STM to enable us to give confident interpretation of the results. A key role in the growth of silicon and germanium on Si(001) from disilane and germane, respectively, is played by the surface hydrogen. The growth of germanium follows a similar path to that of silicon for the first few monolayers, after which the strain becomes relieved by periodic trenches, and eventually by a combination of faceted pits and clusters, both of which nucleate heterogeneously at surface defects. Understanding these processes is crucial to controlling the self-assembled Ge/Si quantum structures.
Surface and intergallery catalytic properties of Cu(II)-exchanged hectorite: A scanning force microscope study
Authors: Porter Timothy L. , Manygoats Kevin , Bradley Michelle , Eastman Michael P. , Reynolds Benjamin P. , Votava Amy E. , Hagerman Michael E.
Published: July 2002

Many layered silicate clay minerals such as hectorite readily adsorb or intercalate organic species. Surface or intergallery structural effects, electric fields, or charged particles may then facilitate polymerization or other reactions, resulting in novel inorganic/organic host–guest composite systems. We have studied the interaction of Cu(II)-exchanged hectorite with the polar monomer aniline, nonpolar styrene, and the amino acid glycine. Hectorite is known to readily intercalate aniline into its intergallery regions, where spontaneous polymerization occurs, resulting in nearly two-dimensional sheets of the conducting polymer polyaniline. In addition, aniline vapor is spontaneously polymerized on the surface of Cu(II)-exchanged hectorite, due to the presence of micro-pore sites on the silicate surface where oxidizing Cu2+ cations are available. For the nonpolar styrene molecule, little or no intercalation occurs. Surface polymerization of styrene is observed for long, intense exposures to the monomer in solution. Cu(II)-exchanged hectorite was also exposed to the amino acid glycine and subjected to alternate cycles of heating and wetting. Concentration and condensation of the amino acid into short glycine oligomers was observed. These reactions were seen to occur only at surface step edges and micro-pore sites. Polymerization of biological molecules on the surface of clay minerals under simulated prebiotic conditions may help to explain the emergence of these more complex molecules on the early Earth.
Bonding nature between oxygen and sodium on Si(113) surface
Authors: Hwang Chan-Cuk , An Ki-Seok , Park Rae-Jun , Kim Jeong-Seon , Lee Ju-Bong , Park Chong-Yun , Kimura Akio , Kakizaki Akito
Published: July 2002

We have investigated the bonding nature between oxygen and sodium on Si(113) surfaces using photoemission spectroscopy. It was found that the modified Auger parameter decreased drastically from about 2065.4 to 2062.4 eV upon oxidation of 1 monolayer Na/Si(113) surface at room temperature. The modified Auger parameter for O2/Na/Si(113) surface at room temperature was comparable to that for the typical sodium oxides, such as Na2O2 and Na2O, having ionic bonding character between oxygen and sodium. These results suggest that the bonding nature between oxygen and sodium on Si(113) surface at room temperature be ionic. O 1s spectra taken from O2/Na/Si(113) surface showed two oxygen components, which means that there are two bonding sites of oxygen at room temperature. The lower binding energy component of O 1s core level peaks, depended on sodium coverage at room temperature, was observed at binding energy between those of Na2O2 and Na2O, and decreased with increasing sodium coverage at low temperature. The concentration ratio [ρ(Na)/ρ(O bonded to Na)] is about 1 from simple calculation. These results suggest that the lower binding energy component comes from oxygen being at the interface between sodium and silicon substrate, forming Si–O–Na bridge configuration.
Measurement and control of sticking probability of H2O on stainless steel surfaces
Authors: Shiokawa Yoshiro , Ichikawa Masakazu
Published: July 2002

A unique method to measure the sticking probability of H2O in chemical adsorption has been developed. It uses molecular beam detection in which a mass filter with differential pumping can only detect H2O released from the sample surface. First, the amount of the dose is measured from reflected H2O during its irradiation to a sample surface. Next, the amount of adsorption is measured from released H2O by heating the sample. The sticking probability of H2O is obtained through the ratio of these amounts. The measurement limit at one Langmuir dose is 1×10−4. Error may be expected to be within 100%. We apply this method to an SUS304 surface to measure the dependence on the amount of adsorption. This suggests that there are two kinds of adsorption sites.
Effects of CdCl2 treatment on the recrystallization and electro-optical properties of CdTe thin films
Authors: Moutinho H. R. , Al-Jassim M. M. , Levi D. H. , Dippo P. C. , Kazmerski L. L.
Published: July 2002

The effects of CdCl2 processing on the physical and electro-optical properties of CdTe were evaluated for thin films produced by physical vapor deposition and close-spaced sublimation (CSS). Two substrates (CdS and Indium–tin–oxide) were used with the physical vapor deposition (PVD) films specifically to isolate the effects of the Cd(SxTe1−x) alloy formed during the treatment of films deposited on CdS. The samples were analyzed by x-ray diffraction (XRD), atomic force microscopy (AFM), and photoluminescence. The observed changes in microstructure were caused by recrystallization, which consisted of the nucleation and development of a new CdTe structure and subsequent grain growth. Nevertheless, for these processes to take place, it was necessary that enough lattice-strain energy was available in the films. For this reason, PVD films did recrystallize, while CSS films did not. For the first time, recrystallization was observed directly in AFM images of CdTe films and confirmed by XRD analysis, which indicated the existence of two lattice parameters in PVD samples treated at 350 °C. For samples treated at 400 °C, the CdCl2 treatment improved the minority-carrier lifetime of the films by more than one order of magnitude. This improvement was attributed to the elimination of deep defect levels within the band gap of the CdTe films as a result of the treatment. The sulfur diffusion into CdTe films deposited on CdS, during the CdCl2 treatment at 400 °C, strongly affected the defect structure.
Electrical characterization of the p-Hg1−xZnxTe interface after anodic sulfidization treatments
Authors: Rousière O. , Lemoine D. , Quémerais A. , Granger R. , Rolland S. , Triboulet R.
Published: July 2002

We have investigated the p-Hg1−xZnxTe interface, with x in the range of 0.19–0.23, after electrochemical treatments with Na2S in ethylene glycol using admittance spectroscopy of metal–insulator–semiconductor structures made on these passivated surfaces. Native sulfide layers are characterized from angle-resolved x-ray photoelectron spectroscopy measurements and are constituted mainly by ZnS. The surface roughness is ascertained by atomic force microscopy. Free carriers densities and the degree of compensation for the semiconductor are deduced from capacitance measurements: the method is based on a numerical analysis of the normalized capacitance measured at high frequency as a function of the bias voltage. The positive fixed charge density in the native sulfide layer is found to be in the range of 1010–1011 cm−2 as deduced by the shift in the C–V characteristics. C–V plots show a very small hysteresis effect at 77 K, resulting in a low density of slow surface states (∼1×1010 cm−2). The energy distribution of fast interface states is calculated in two ways from capacitance and conductance measurements. The conductance method shows a higher sensitivity. A broad U-shape distribution is obtained for the different samples studied, with a reproducible minimum density of about a few 1010 eV−1 cm−2. The best passivation conditions are obtained with a constant current density of about 100 μA cm−2 and a sulfidization duration of ∼15 min. The time constant of the interface traps is deduced from the energy loss peak and leads to an estimation of their capture cross section. All these results show that a very high interface quality can be obtained on p-Hg1−xZnxTe in a reproducible way by anodic sulfidization.
Surface composition and morphology of polyimidesiloxane copolymers with short polydimethylsiloxane segments studied by electron spectroscopy for chemical analysis and time-of-flight secondary ion mass spectrometry
Authors: Zhao Jin , Rojstaczer Sergio R. , Gardella Joseph A.
Published: July 2002

A series of polyimidesiloxane (SIM) copolymers, based on α,ω-aminopropylpoly- (dimethylsiloxane) (PDMS), 2,2-bis(4-[4-aminophenoxyl]phenyl)propane and 4,4′- oxydiphthalicanhydride was synthesized in our laboratories. The effects of siloxane segment length (dimethylsiloxane repeat units=1, 2, 3, 4, 5, and 9) and PDMS bulk content (1–30 wt %) on the surface composition and free surface morphology of the copolymers were investigated. Experimentally, angle-dependent electron spectroscopy for chemical analysis (ESCA) was used to acquire composition information of the copolymer surface at various sampling depths. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) was used to describe ion formation mechanism of bulk SIM copolymers with variation of bulk composition or structure. In all cases, PDMS was segregated to the topmost 100 Å of the air (free) surface of ∼75 μm thick film, even with short siloxane segments and low PDMS contents. Angle-dependent ESCA measurements show that the dominant factor in defining the surface composition of these copolymers is not bulk composition, but in fact siloxane segment length. With the same PDMS content, a longer siloxane segment gives a surface richer in siloxane. For a given siloxane segment length, varying PDMS content does not significantly change the surface composition. TOF-SIMS measurements of bulk copolymers simulated by solvent-cast thin films show that a longer siloxane segment gives higher relative ion yields of fragment ions from siloxane versus imide segments even with the same 10 wt % PDMS content in the copolymers. For a given average siloxane segment length of 9 dimethylsiloxane repeat units, a higher PDMS content in the copolymers yields higher relative yields of fragment ions formed from siloxane versus imide segments.
Formation of nanocrystalline NiCr–N films by reactive dc magnetron sputtering
Authors: Musil J. , Regent F.
Published: July 2002

The article reports on structure and hardness of NiCr–N films prepared by dc reactive magnetron sputtering of NiCr (80/20 wt. %) target in a mixture of Ar and N2 on glass and 15 330 steel substrates at room temperature using a round planar magnetron of diameter 75 mm. It was found that while pure NiCr films are polycrystalline, an addition of nitrogen into the film reduces a grain size d and makes it possible to form nanocrystalline NiCr–N films. The hardness HV of the NiCr–N film increases with decreasing grain size d but only down to about 7 nm. For grains smaller than 7 nm the hardness HV decreases.
Particle generation in W–Ti deposition
Authors: Lo Chi-Fung , Gilman Paul
Published: July 2002

This study reports the influence of sputter target density, microstructure and second phase precipitation on the particle performance in W 10 wt % Ti target sputtered thin films. By controlling the sintering process, a variety of W–Ti alloy sputtering target structures were prepared. These targets were sputtered using a physical vapor deposition process. Observations of the sputtered target surfaces reveal that the brittle redeposited nodules generate in the low erosion zone and around voids in the target material. The nodules together with the precipitated tungsten in the Ti-rich phase are most likely the particle sources.
Smoothing of polycrystalline Cu(In,Ga)(Se,S)2 thin films by low-energy ion-beam etching
Authors: Frost F. , Lippold G. , Otte K. , Hirsch D. , Schindler A. , Bigl F.
Published: July 2002

We present a study of the smoothing process of polycrystalline CuInS2 and CuGaSe2 thin films using ion-beam etching with low-energy nitrogen ions. The evolution of the surface roughness and morphology have been studied by atomic force microscopy with respect to the ion-beam angle of incidence and the ion dose. Raman scattering and photoluminescence spectroscopy were applied to investigate the surface damage induced by the ion-beam etching process. A drastic reduction of the surface roughness for both materials has been observed for ion-beam angles of incidence larger than 70° with increasing ion doses without significant surface damage. Using this technique the initial root-mean-square roughness of, e.g., CuGaSe2 of about 87 nm could be decreased to about 25 nm. Roughness analysis over different spatial wavelength regions by using the power spectral density reveals that smoothing occurs for all spatial wavelengths. Hence, ion-beam etching with nitrogen is a suitable method to polish polycrystalline CuInS2 and CuGaSe2 thin films for surface analysis techniques and depth profiling.
Cobalt sputtering target and sputter deposition of Co thin films for cobalt silicide metallization
Authors: Zhang Hao , Poole John , Eller Rick , Keefe Mark
Published: July 2002

CoSi 2 is considered an alternative to TiSi2 for use as a contact in ultralarge scale integration due to its low resistivity, excellent chemical stability and lower formation temperature. Sputter deposition of Co thin films is one of the crucial steps in the cobalt salicide (a self-aligned silicide) process. One major problem with sputter deposition of Co thin films is that Co is a ferromagnetic material and is difficult to sputter. The dc magnetic field transmitted through a ferromagnetic material from one side to another is called the pass-through flux (PTF). In this study, the effects of target PTF and sputtering process parameters such as Ar pressure and sputtering power on the sputter process were studied. Co targets with PTF% of 65% (high PTF), 53% (medium PTF) and 32% (low PTF) were sputter tested. The sputter deposition rate, I–V characteristics, film sheet resistance and film uniformity were measured under various sputter conditions. The study indicated that, in magnetron sputtering of Co, a high magnetic flux intensity could be obtained by using a high PTF target that allowed maximum magnetic flux to permeate through the target. The I–V characteristics of different PTF targets followed the typical I=KVn relationship of dc planar magnetron sputtering. The exponents in the equation, n, increased with increasing target PTF%, indicating the sputtering impedance decreased with increasing target PTF%. The target with the highest PTF% demonstrated the best performance and film uniformity. Rapid thermal processing (RTP) was carried out to form cobalt silicides at temperatures between 300 and 850 °C in Ar atmosphere for various times. The sheet resistance of the Co and cobalt silicide films produced was monitored by a four-point probe before and after the RTP. The sheet resistance decreased significantly after annealing at 600 and 700 °C due to formation of CoSi2, which has lower resistivity. The significant increase in sheet resistance after annealing at 400 and 500 °C was attributed to formation of the CoSi phase. For the 16 nm thick Co film, a sheet resistance of 3.2 Ω/sq was obtained after RTP at 600 and 700 °C.
Fast electronic transport in organic molecular solids?
Authors: Karl N. , Kraft K.-H. , Marktanner J. , Münch M. , Schatz F. , Stehle R. , Uhde H.-M.
Published: July 2002

Starting from the question, what fast electronic transport is based on, and why organic materials in general are more problematic in this respect than typical inorganic ones, methods are introduced that allow to measure the principal material property charge carrier mobility. Some representative experimental results are presented which prove that mobilities around 1–10 cm2/V s can be achieved at room temperature, and more than 100 cm2/V s at low temperature—but only if chemical purity and structural order can be brought to a very high level.