bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental and analytical studies on mechanical behavior of knife-edge-type metal-seal flange for fusion vacuum sealing
Authors: Kitamura K. , Itoh K. , Uchida T. , Kondoh M. , Obara K. , Nakamura K. , Murakami Y.
Published: July 2002

Mechanical behavior of a knife-edge-type metal-seal flange system was examined on the variations of the displacement between the flanges and reaction forces of the tightening bolts during load steps such as tightening the bolts, setting up a transverse weight load on the flange surface and 300 °C baking and cool down. These were compared with a thermo-elasto-plastic finite element method structural analysis. Good agreement was obtained for both the flange deformation and reaction forces of the bolts and copper gasket between experimental and analytical results. Effects of the transverse load by a dummy weight mounted at the flange surface on the changes of reaction force of the bolts and on gasket deformation were considered to be negligibly small in the view of vacuum seal characteristics. The application of Inconel Belleville spring washers between bolt heads and flange surface was confirmed to be quite effective for the suppression of the bolt force looseness and gasket relaxation due to cyclic heating and cooling of the knife-edge-type metal-seal flange system.
Real-time scanning microprobe reflection high-energy electron diffraction observations of III–V growth during molecular-beam epitaxy
Authors: Isu T. , Morishita Y. , Goto S. , Nomura Y. , Katayama Y.
Published: July 2002

Scanning microprobe reflection high-energy electron diffraction is a powerful technique to investigate the growth mechanism through microscopic surface observations during molecular-beam epitaxy (MBE) or metalorganic MBE. The Ga droplet formation and annihilation were observed in real time during GaAs growth with an alternative source supply. Droplets with a round shape whose diameter was the order of a micrometer were formed when only Ga was supplied over an amount of monolayer of GaAs on the surface. They were annihilated when As was supplied to grow a GaAs layer. At high substrate temperatures, the droplets on the vicinal GaAs surface moved upward to atomic steps before its annihilation. Anomalous features of droplet formation were observed during AlAs growth with an alternative source supply on the GaAs substrate. This is interpreted by the intermixing between Al and Ga atoms on the surface during growth. Indium droplets were also observed during InAs MBE growth at high temperatures, which were revealed to be the origin of the InAs hillocks.
Comparison of intrinsic and extrinsic carbon doping sources for GaAs and AlGaAs grown by metalorganic molecular beam epitaxy
Authors: Abernathy C. R. , Pearton S. J. , Ren F. , Hobson W. S. , Wisk P. W.
Published: July 2002

p-type doping due to incorporation of carbon acceptors has proven to be extremely valuable for fabrication of various III–V device structures. In general, gaseous sources have proven to be more successful than elemental sources, with trimethylgallium and halocarbons such as carbon tetrachloride being the most commonly used intrinsic and extrinsic sources respectively. While both sources are capable of supplying carbon to the growth front, their behavior at the substrate surface is significantly different. This article will discuss how these differences affect the utility of each source for doping of various materials during growth by metalorganic molecular beam epitaxy. In particular, practical considerations such as interfacial abruptness, undesirable uptake of other impurities (i.e., hydrogen or chlorine), dependence of growth rate on dopant concentration, and incorporation efficiency will be presented.
Interface structure of Ge/Si(111) during solid-phase epitaxy studied by medium-energy ion scattering
Authors: Sumitomo K. , Nishioka T. , Shimizu N. , Shinoda Y. , Ogino T.
Published: July 2002

The interface structure between a Ge thin film and Si(111) substrate during solid-phase epitaxy of Ge is studied by medium-energy ion scattering. Intermixing within the bilayer between the two-dimensional Ge layer with the critical thickness of 4 monolayers (ML) and the Si substrate occurs at 550 °C and above. The intermixing advances into deeper layers with annealing at higher temperatures, and Si atoms from the substrate migrate to the uppermost surface above 770 °C. When Ge is deposited, in excess of the critical thickness, three-dimensional islands form on the two-dimensional layer with a thickness of 4 ML before intermixing between Ge and Si layers begins. Atomic displacement is observed in both the Ge film and the substrate near the interface. The substrate is compressed vertically about 1.2%. However, the strain caused by the lattice mismatch between Ge and Si is relaxed by intermixing, so atomic displacement is partially restored.
Nondestructive and quantitative depth profiling analysis of ion bombarded Ta2O5 surfaces by medium energy ion scattering spectroscopy
Authors: Lee J. C. , Chung C. S. , Kang H. J. , Kim Y. P. , Kim H. K. , Moon D. W.
Published: July 2002

Ion beam sputtering has been widely used for sputter depth profiling with x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). However, the problem of surface compositional change due to ion bombardment remains to be understood and solved. So far sputtering processes have been usually studied by surface analysis tools such as XPS, AES, and secondary-ion mass spectrometry which use the sputtering process again. In this work, the altered surface layer of amorphous Ta2O5 thin films due to Ar+ ion bombardment was depth profiled nondestructively and quantitatively for the first time by medium energy ion spectroscopy (MEIS) as a function of the ion incidence angle and the ion dose with a depth resolution of better than 1.0 nm. The MEIS spectrum showed that the preferential sputtering of oxygen atoms developed with the ion dose and saturated in the ion dose of 3.1×1016 ions/cm2. The Ta mole fraction at the surface increased from 0.29 up to 0.42±0.03 at the saturation ion dose under normal incident 3 keV Ar+ ion bombardment, which corresponds to the stoichiometry of TaO1.4±0.2. The oxygen depletion depth was 2.6±0.8 nm at the saturation dose. The Ta concentration and the oxygen depleted depth decreased with the ion incidence angle. The MEIS experimental results were consistent with XPS results. These MEIS analysis results were compared with Monte Carlo simulation results and good agreement was obtained when both the sputtering and the ion beam induced diffusion were considered.
Effect of substrate bias on the properties of diamondlike carbon films deposited using unbalanced magnetron sputtering
Authors: Seo Soon-Cheon , Ingram David C. , Richardson Hugh H.
Published: July 2002

Diamondlike carbon (DLC) films were deposited using unbalanced planar circular magnetron sputtering of a graphite target with argon as the support gas. The properties of the DLC films were studied as functions of the applied negative substrate bias voltage, 50–200 V, and argon gas pressure, 2–6 mTorr. The hydrogen content was measured by elastic recoil spectroscopy and impurity content was measured by Rutherford backscattering spectroscopy; the physical thickness was measured by mechanical profilometry. For the first time films with densities as high at 3 g/cm3 have been made by this technique. The hydrogen content in the films is 12–16 at. % and 20–32 at. % for an argon gas pressure of 2 and 6 mTorr, respectively. As the bias voltage increases, the hydrogen content decreases. The transmission electron diffraction of the films indicated that they are amorphous. The bonding structure, optical property, and optical band gap were determined by Fourier transform infrared (FTIR) spectroscopy, and ultraviolet-visible spectroscopy. FTIR spectra from DLC films deposited at 6 mTorr display the C–H stretching absorptions centered around 2900 cm−1 with a bonding configuration of sp3/sp2-C:H at 2920, 2860, and 3012 cm−1, as well as the deformation peaks of sp3C–CH3 at 1450 and 1370 cm−1. The decreasing ratio of sp3CH2 to sp3CH1 in the C–H stretching region indicates a decrease in hydrogen content with bias voltage.
Growth of thin Ti films on Si(111)-(7×7) surfaces
Authors: Saleh Adli A. , Peterson L. D.
Published: July 2002

A study of the room-temperature growth of ultrathin Ti films [up to 7 monolayers (ML)] on clean and atomically flat Si(111)-(7×7) surfaces using Auger electron spectroscopy and low-energy electron diffraction (LEED) is presented. The variations in the Auger signal due to Si L2,3VV with binding energy of 92 eV are used to model the growth morphology of this system. These measurements indicate the growth of an initial disordered and continuous Ti film of up to 1.6 ML in thickness where the LEED pattern completely disappears and the Si Auger signal is strongly attenuated. As more Ti is deposited, this is followed by the disintegration of the continuous film and the formation of an intermixed Ti/Si film. This is evidenced by a change in the slope of the Auger signal time plot, and the reappearance of the LEED pattern. The modification in the overlayer composition for films thicker than 1.6 ML is confirmed by a change in the Si L2,3VV Auger peak that resembles the peak shape due to TiSi2.
X-ray photoelectron study of the reactive ion etching of SixGe1−x alloys in SF6 plasmas
Authors: Peignon M. C. , Cardinaud Ch. , Turban G. , Charles C. , Boswell R. W.
Published: July 2002

Reactive ion etching of SixGe1−x alloys (0≤x≤100%) deposited on silicon wafers using the electron-beam evaporation technique was investigated in a low pressure fluorine-based plasma (SF6). The etch rates of the SixGe1−x alloys increase with the Ge content of the alloy but are constantly lower than the etch rates expected from independent etching mechanisms of Ge and Si atoms in the alloys. Analysis of the reactive layer on the surface of the alloys before and after etching was performed in situ by x-ray photoelectron spectroscopy (XPS). The reactive layer on the etched alloys consists of silicon, germanium, fluorine, and sulfur atoms. Fluorinated Ge (GeFn) and Si (SiFn) species, known to be precursors in the formation of the GeF4 and SiF4 etch products, are identified. A precise analysis of the sulfides of Ge (GeSn) and of Si (SiSn) present on the surface revealed a strong difference between sulfur–germanium and sulfur–silicon interactions by the detection of mostly GeS2 and SiS species. A sulfur-rich reactive layer is measured on the surface of the germanium-rich alloys, whereas a fluorine-rich layer exists on the surface of the silicon-rich alloys. Still, the sulfur-rich reactive layer exists over a large range of alloy stoichiometry (0≤x≤80%) with an increase of GeS2 density as a function of Si content in the alloy. The XPS analysis showed no enrichment of Ge or Si in the reactive layer compared to the substrate, suggesting equal etch rates of Ge and Si atoms of the alloy.
Preparation of crystalline beta barium borate (β-BaB2O4) thin films by opposed-targets magnetron sputtering
Authors: Liao H. B. , Xiao R. F. , Yu P. , Wong G. K. L. , Zheng J. Q.
Published: July 2002

Crystalline beta barium borate (β-BaB2O4) thin films have been successfully prepared in situ on several kinds of substrates by using opposed-targets magnetron sputtering. The crystallinity of these films is highly dependent on the deposition temperature. Crystalline films start to form at 500 °C and gradually become c-axis aligned as the temperature is increased. At 700 °C the film grown on sapphire substrates shows hundred-micrometer-sized domain structures with a single (006) x-ray diffraction peak normal to the film surface. For a linearly polarized fundamental beam incident along the surface normal, the second harmonic intensity exhibits a sixfold azimuthal pattern with a d22 second harmonic coefficient of 1.2 pm/V.
A novel tilt assembly for ultrahigh vacuum XYZ-rotary manipulators
Authors: Labanda J. G. C. , Barnett S. A.
Published: July 2002

A novel sample tilt assembly was developed for ultrahigh vacuum XYZ-rotary manipulators which have the sample surface normal on the manipulator rotation axis. With conventional tilt mechanisms, sample azimuth and tilt angle cannot be varied independently since the rotation motion is about the manipulator axis, not the tilted sample normal. The present design allows sample tilt of ±10° and independent 360° rotation about the tilted sample surface normal.
Slow laser deposition of high quality ErBa2Cu3O7−x thin films
Authors: Del Vecchio A. , Tapfer L. , Berling D. , Loegel B. , Leggieri G. , Luches A. , Acquaviva S.
Published: July 2002

High quality ErBa2Cu3O7−x thin films were grown by reactive laser deposition on yttria-stabilized zirconia substrate. The structural and electrical properties of the samples were investigated by x-ray double-crystal diffractometry, texture analysis and reciprocal space mapping, and resistivity measurements, respectively. The best films were obtained by using high substrate temperature combined with a low fluence and low laser repetition rate. In these conditions the deposition rate results were very low, namely <0.25 Å/s. We found that in this case we can grow films with a very high degree of crystalline perfection. Preliminary results show that this process promotes the fabrication of very thick films (thickness ≳500 nm) which are highly c-axis oriented.
Photochemistry of O2 on Ag(110) using picosecond ultraviolet laser pulses
Authors: Erkkila V. J. , Hoffbauer M. A. , White J. M.
Published: July 2002

Surface second-harmonic generation (SHG) was used to study the photochemical reaction of O2 with Ag(110) using ∼6 ps laser pulses. A clean well-ordered Ag(110) surface produces a strong SHG signal at 580 nm. The SHG signal measured in real time during O2 exposure is sensitive to submonolayer coverages of O2 and to the subsequent exposure of this system to picosecond ultraviolet laser pulses. Upon O2 adsorption at 130 and 200 K, the signal decreases by more than a factor of 2 at saturation coverage. Langmuir adsorption kinetics are used to fit the O2 dosage curves relating the decrease in SHG intensity to the oxygen coverage. Subsequent exposure of the surface dosed at 130 K to 290 nm light of the same pulse width also produces a change in the second-harmonic response. Combined with surface SHG temperature programmed desorption measurements, these results are correlated to the photochemical reaction taking place on the surface in which chemisorbed O2 photodissociates and photodesorbs. The results of the surface photochemical reaction initiated by picosecond UV pulses are compared to those previously studied using continuous wave radiation and are found to have similar overall behavior while possibly showing some new features.
Morphology and growth mode of Al films deposited by chemical vapor deposition from dimethylethylamine alane on GaAs(001)2×4 surfaces
Authors: Venkateswaran N. , Karpov I. , Gladfelter W. , Franciosi A.
Published: July 2002

We investigated the initial stages of growth of Al films fabricated by chemical vapor deposition at 100 °C on GaAs(001)2×4 surfaces using the molecular precursor dimethylethylamine alane. In situ reflection high energy electron diffraction and scanning tunneling microscopy and spectroscopy, as well as ex situ atomic and lateral force microscopy, were employed for morphological analysis. Film growth was found to occur in the Volmer–Weber mode and involve islands with remarkably low z-aspect ratio (∼1:16). Scanning tunneling spectroscopy data on some of these islands in the early stages of growth suggest the formation of an AlAs interface phase.
High transmittance–low resistivity ZnO:Ga films by laser ablation
Authors: Hirata G. A. , McKittrick J. , Siqueiros J. , Lopez O. A. , Cheeks T. , Contreras O. , Yi J. Y.
Published: July 2002

High transmittance, low resistivity, and c-axis highly oriented ZnO:Ga thin films on glass were obtained by laser ablation at different deposition temperatures. The surface morphology, crystalline structure, and optical and electrical properties were found to depend directly on substrate temperature. From optical and electrical analyses we observed that the optical transmittance, carrier concentration, and optical energy gap of the ZnO:Ga transparent conductive oxides increased when the deposition temperature is raised from 150 to 300 °C. Films grown on 300 °C substrates showed a low resistivity value of 3.6×10−4 Ω cm, a carrier concentration of 8.7×1020 cm−3, a band gap of 3.81 eV, and a visible transmission of 85%. These films were deposited with an excimer (KrF) laser beam of λ=248 nm operated under optimized conditions of 2.7 mJ/cm2 energy density and 30 Hz repetition rate.
Sputter deposited piezoelectric fiber coatings for acousto-optic modulators
Authors: Fox G. R. , Muller C. A. P. , Setter N. , Ky N. H. , Limberger H. G.
Published: July 2002

All-fiber optical phase modulators were fabricated by coating standard telecommunication optical fibers with thin films of piezoelectric ZnO. Piezoelectric optical fiber coatings of PbZrxTi1−xO3(PZT) were also produced, and the actuation capability necessary for making optical fiber modulators is demonstrated. Both the ZnO and the PZT fiber coatings were deposited by reactive direct current magnetron sputtering of metal targets. The geometry of the sputtering system, fiber rotation, and reactive sputtering processes that result in sufficiently high deposition rates for deposition of axially symmetric coatings between 0.5 and 7 μm thick were studied. Two types of piezoelectric fiber optic modulator structures, Cr/Au/ZnO/Cr/Au and Ti/Pt/PZT/Au, are currently being investigated. Results on crystalline phase formation, microstructure, and piezoelectric and optical behavior of the coated optical fiber devices are presented. Impedance and phase angle measurements are used to demonstrate how device geometry affects the resonance response of ZnO coated devices. Interferometric measurements have shown that the ZnO-based modulators can produce optical phase shifts as high as 0.70 rad when the modulator is driven at the 196.5 MHz fiber radial resonance.
Evidence for the appearance of carbon-rich layer at the interface of SiC film/Si substrate
Authors: Sonoda Nobuo , Sun Yong , Miyasato Tatsuro
Published: July 2002

A porous carbon-rich layer with the thickness in submicron order is found to form at the interface between polycrystalline cubic SiC film and (100) Si substrate during the film growth using a reactive hydrogen plasma sputtering of ceramic SiC target. The appearance of the porous carbon-rich layer at the interface is due to an indiffusion of carbon atoms through the growing SiC film, and is related to the existence of a hollow voids at the interface. The results obtained in the present study suggest that the indiffusion of carbon atoms through the film may result SiC film growth at the interface.
Application of plasma enhanced chemical vapor deposition silicon nitride as a double layer antireflection coating and passivation layer for polysilicon solar cells
Authors: Winderbaum S. , Yun F. , Reinhold O.
Published: July 2002

Reflection losses in passivated emitter solar cell polycrystalline silicon solar cells have been reduced by the application of a double layer antireflection coating of plasma enhanced chemical vapor deposition silicon nitride (PECVD SixNyHz). The layer was deposited in a single wafer parallel plate reactor powered by a 13.56 MHz rf power supply using SiH4 and NH3 as the reactive gases. The layers deposited had refractive indexes of 2.50 and 1.95 at HeNe wavelength and thicknesses of 42.5 and 64.5 nanometers (nm), respectively. The overall reflectance measured in the wavelength range between 350 and 1150 nm was 8.5%. The extinction coefficient of the high refractive index film showed a significant increase in absorption for short wavelengths. However, the improvement in current collection was higher than expected from the overall reflectance and absorption of the film. Short circuit current was increased by 49% and open circuit voltage increased by 3.3% when compared with uncoated cells. These results imply a passivation effect which increases the open circuit voltage beyond the value expected solely from the current collection addition.
Characterization of fluorinated tetra ethyl ortho silicate oxide films deposited in a low pressure plasma enhanced chemical vapor deposition reactor
Authors: Weise M. T. , Selbrede S. C. , Arias L. J. , Carl D.
Published: July 2002

Fluorinated silicon dioxide films were deposited in a commercial plasma enhanced chemical vapor deposition reactor using tetra ethyl ortho silicate (TEOS), oxygen, and C2F6. The depositions were carried out using dual rf frequency power at low pressure, 500–750 mTorr. Film properties were investigated as a function of rf power, pressure, gas flows, and wafer temperature. Fluorine content, refractive index, stress, and deposition rate are among the film properties studied. Special attention was paid to the stability of these properties in air, in boiling water, and after subsequent annealing. The base line TEOS process is unusual in that high compressive stress values can be achieved, up to about 300 MPa. It was thought that this high initial stress would lead to improved stability at higher fluorine concentration. Film stress was found to be quite compressive, even at high fluorine concentration. Good film stability was observed for fluorine concentrations up to 10% (Si–F/Si–O peak ratio). Refractive indices as low as 1.40 were measured. This work demonstrates that a stable, production-quality, fluorinated oxide film can be deposited in this reactor.
Luminescence from GaAs(100) surface excited by a scanning tunneling microscope
Authors: Chizhov Ilya , Lee Geunseop , Willis Roy F. , Lubyshev Dmitry , Miller David L.
Published: July 2002

We have measured luminescence of atomically clean GaAs(100) samples induced by a scanning tunneling microscope (STM) under ultrahigh vacuum (UHV) conditions. GaAs(100) samples were grown by molecular beam epitaxy and capped with a thick arsenic overlayer to protect the surface during transfer through ambient atmosphere to the UHV STM chamber equipped with a light collection system. The luminescence arises from the radiative recombination of the excited carriers across the band gap induced by the tunneling current. Maps of luminescence as a function of lateral position of the STM tip (photon maps) have been recorded. Arsenic related features of the size of ∼20 nm appear as dark areas in the photon maps indicating increased local nonradiative recombination. Photon maps acquired at positive and negative sample bias show significant differences in contrast. Mechanisms responsible for the STM excited luminescence and contrast observed in the photon maps are discussed.
Influence of electrostatic forces on the investigation of dopant atoms in layered semiconductors by scanning tunneling microscopy/spectroscopy and atomic force microscopy
Authors: Schlaf R. , Louder D. , Nelson M. W. , Parkinson B. A.
Published: July 2002

Investigation of the atomic scale topography and electronic structure of dopant sites in semiconductor materials is a promising application of scanning probe microscopies. Dopants have been imaged with scanning tunneling microscopy (STM) on and near the surface of conventional semiconductor materials as well as on layered compounds. On both kinds of materials, dopants are detected as either protrusions or depressions in the STM image. The comparison of the measured heights between the materials shows that the values on layered materials are considerably larger than those on the conventional (three-dimensional) semiconductors. We interpret this as the influence of dopant induced electrostatic forces between the tip and sample leading to a structural deformation of the surface around dopant atoms. In order to investigate the influence of electrostatic forces, we performed STM measurements on p-type MoS2 at different bias voltages. The bias dependence of the images indicates the presence of electrostatic forces and demonstrates the influence of screening due to the surrounding electron density. Additional measurements with current imaging tunneling spectroscopy show that changes in the density of states at dopant sites plays only a minor role and cannot account for the large protrusions observed. Atomic force microscopy measurements, with an applied dc voltage between cantilever and sample, also confirm the role of electrostatic forces since voltage dependent changes in the topograpy were observed.
High-resolution algorithm for quantitative elemental depth profiling by angle-resolved x-ray photoelectron spectroscopy
Authors: Williams John M. , Beebe Thomas P.
Published: July 2002

We have developed an algorithm for analysis of angle-resolved x-ray photoelectron spectra that allows quantitative depth profiling of the surface elemental composition with atomic depth resolution. This method has nondestructively yielded valuable new information about adsorbate bonding and conformation for several of the chemical systems listed below, permitting adsorbate modeling at the atomic level. The computation implements a profile-smoothing search and gives error limits on the profiles. The method is capable of computing at least six simultaneous elemental profiles, is robust to as much as 10% experimental error, and performs well even under unfavorable conditions such as patchy overlayers, complex organic adsorbates (such as DNA), and trace elemental quantities (<10%). The depth profiles obtained for Cu on Ru(0001), SiO2 on Ag(111), and for sulfur-modified DNA, Cl(CH2)3SH, and cystamine adsorbed onto Au(111), show close correspondence to scale molecular models and to expected stoichiometries for the surface composition.
Secondary ion mass spectrometry study of silicon surface preparation and the polystyrene/silicon interface
Authors: Strzhemechny Y. M. , Schwarz S. A. , Schachter J. , Rafailovich M. H. , Sokolov J.
Published: July 2002

Secondary ion mass spectrometry (SIMS) is now routinely employed to obtain depth profiles in polymer films on silicon substrates, where diffusion, segregation, and ordering of deuterated polymer blend components are typically examined with a depth resolution of less than 100 Å. In some cases, diffusion or segregation behavior near the silicon surface is influenced by the extent of surface oxidation. There is also the potential for remnant moisture at the polymer/silicon interface to influence the redistribution of blend components. The effect of standard wet chemical wafer cleaning procedures on the polystyrene/silicon interface is investigated here. Deuterated solutions are employed to allow detection of remnant moisture from the cleaning/etching steps, and to indicate the extent of hydrogen termination at the polystyrene/silicon interface. Implant standards and deuterated polystyrene blends are employed to quantify the detected interfacial contaminants. The SIMS data indicate that the surface is effectively terminated by approximately one monolayer of hydrogen after an HF etch step, and by a thin oxide layer after an HCl/peroxide etch, in accord with numerous studies. There is no evidence of remnant moisture. Interfacial deuterium and oxygen are stable under 190 °C anneals. The absence of CD− secondary ions at the interface indicates that the interfacial deuterium does not become associated with adjacent polystyrene chains. Low levels of fluorine are also monitored, and the integrated fluorine concentration at the polystyrene/silicon interface is less than 0.01 monolayers of coverage.
Surface smoothing with energetic cluster beams
Authors: Insepov Z. , Yamada I. , Sosnowski M.
Published: July 2002

Impacts of energetic clusters, consisting of hundreds or thousands of atoms on a solid surface, have some remarkable effects, one of which is surface smoothing. To understand its mechanism, we have examined the results of molecular dynamics (MDs) simulations of cluster collisions with a solid which revealed that cluster impacts form craters on the surface and that ejected atoms have a significant lateral momentum component (parallel to the surface). It is postulated that these energetic atoms which are not in thermal equilibrium with the surface are responsible for rapid surface diffusion and consequently the surface smoothing. A new model of surface smoothing by energetic clusters has been developed. The model is based on nonlinear dynamics of a surface profile described by the noisy Kuramoto–Sivashinsky equation. A Monte Carlo procedure is used for simulating cluster impacts by distributing on a surface craters whose volume is defined by MDs simulations. The results of calculations show a qualitative agreement with experimental data on smoothing of Cu surface with 20 kV Ar clusters of 1000 atoms.
Direct calculation of metal–oxide–semiconductor field effect transistor high frequency noise parameters
Authors: Chen C. H. , Deen M. J.
Published: July 2002

This article presents, for the first time, a method to directly calculate the noise parameters (minimum noise figure NFmin, equivalent noise resistance Rn, and optimized source resistance Ropt and reactance Xopt) of metal–oxide–semiconductor field effect transistors based on the HSPICE level 3 model because all the model parameters are available from the manufacturer of our device-under-test. All physically based high frequency noise sources, thermal noise from the channel, gate, source and drain resistances, induced gate noise, and the correlation among them, are considered, and the impact of gate resistance and induced gate noise on the noise parameters is studied. The method of direct calculation of noise parameters can be applied to any sophisticated small-signal device model.
Self-organized quantum dots and quantum dot lasers (invited)
Authors: Ishikawa H. , Shoji H. , Nakata Y. , Mukai K. , Sugawara M. , Egawa M. , Otsuka N. , Sugiyama Y. , Futatsugi T. , Yokoyama N.
Published: July 2002

The growth and characterization of two types of self-organized quantum dots, Stranski-Krastanow (S-K) mode grown quantum dots and atomic layer epitaxy (ALE) grown quantum dots, are described. In the S-K mode growth, molecular beam epitaxy has been used. Multilayer stacked structures have been fabricated. S-K mode grown quantum dots showed the ground state photoluminescence (PL) emission wavelength of 1.14 μm and the full width at half maximum of the emission linewidth of 80 meV. ALE mode grown quantum dots are fabricated using metalorganic chemical vapor deposition. A smaller PL linewidth of 40 meV, indicating a higher uniformity in the size and composition of quantum dots, and a room temperature emission at 1.3 μm were obtained. Continuous wave lasing at the ground state at room temperature was achieved with a S-K mode grown quantum dot laser owing to the high dot density enabled by the stacked dot layer structure. Because of the low density of dots, lasing was at 80 K at the higher order sublevel in ALE grown quantum dot lasers. Based on these experimental results, we discuss the key issues involved in these fabrication technologies and the carrier dynamics to achieve the ideal performance for quantum dot lasers.
Growth of GaS on GaAs (100) surfaces using the [(tBu)GaS]4 molecular precursor in ultrahigh vacuum
Authors: Yi S. I. , Chung C.-H. , Weinberg W. H.
Published: July 2002

The growth of a GaS film on both GaAs (100)-(2×4) and -(4×2) surfaces using a directional beam of [(tBu)GaS]4 has been studied in ultrahigh vacuum with high-resolution electron energy loss spectroscopy, Auger electron spectroscopy, low-energy electron diffraction (LEED), and temperature programmed desorption. At a surface temperature of 650 K, the growth of a GaS film with no measurable carbon contamination was observed. Upon adsorption of a monolayer of GaS, the surface forms a (2×1) reconstruction. Upon further adsorption, as a multilayer of GaS film was deposited, a (1×1) LEED pattern was observed. The resulting film had a S to Ga ratio identical to that grown via metal organic chemical vapor deposition and exhibited a vibrational mode at 350 cm−1 which is attributed to the cubic phase GaS phonon mode. Upon annealing a surface, which was exposed to [(tBu)GaS]4 at a surface temperature of 100 K, desorption of isobutylene and hydrogen was observed at a temperature of 650 K. In agreement with this, hydrocarbon vibrational mode intensities corresponding to the t-butyl ligands began to rapidly decrease at 600 K and disappeared completely by 650 K. This suggests that β-hydride elimination is the dominant mechanism for t-butyl ligand detachment at the growth temperature of ∼650 K.
Spatially-averaged model for plasma etch processes: Comparison of different approaches to electron kinetics
Authors: Ahlrichs P. , Riedel U. , Warnatz J.
Published: July 2002

A well stirred reactor model determines spatially averaged species composition in a plasma etch reactor by solving conservation equations for species, mass, and electron energy distribution function (EEDF). The reactor is characterized by a chamber volume, surface area, mass flow, pressure, power deposition, and composition of the feed gas. The well stirred reactor model is increasingly common in the literature due to its low requirement of computer resources for detailed chemical kinetics calculations. In such plasma etch models, assumptions on the EEDF, which are needed to determine reaction rate coefficients for electron impact reactions, are crucial for a prediction of steady state conditions. In this article we focus on a comparison for three different levels of sophistication with regard to the electron energy distribution function: obtaining the EEDF from a fully coupled solution of species equations and the Boltzmann equation, pre-computing and tabulating the EEDF for typical reactor conditions, and assuming a Maxwellian EEDF. The influence of these modeling assumptions on the steady state conditions of the reactor is examined by various parametric studies for a chlorine plasma. The results clearly indicate limitations of the two simplified approaches to electron kinetics. To summarize, in this article we show the feasibility of a zero-dimensional model which predicts steady state reactor conditions from a fully coupled solution of Boltzmann and species equations.
PbTiO
3
buffer layer effects on the structural and electrical properties of Pb(Zr, Ti)O3 thin films grown by sputtering on silicon substrates
Authors: Velu G. , Haccart T. , Jaber B. , Rèmiens D.
Published: July 2002

Pb(Zr, Ti)O 3 (PZT) thin films have been grown on Si/SiO2 and Si/SiO2/Ti/Pt substrates by rf magnetron sputtering and the effects of PbTiO3 (PT) buffer layers to the structural and electrical properties of PZT films were studied. The PT buffer layers were grown in situ (without postannealing) with thicknesses ranging from 100 to 1200 Å. The PT layer orientation can be adjusted by the deposition temperature. The PZT films with a composition near the morphotropic phase (54/46) were deposited at room temperature followed by a conventional postannealing treatment. The disappearance of cracks in PZT films deposited on Si/SiO2/PT substrates indicates the role of the buffer layer as a stress absorber. By using a PT buffer layer it was possible to control the PZT films’ orientation. Polycrystalline PZT films without a buffer layer changed to highly (100) or (111) oriented films, depending on the preferred orientation of the buffer layer. The influence of the buffer layer thickness and the PZT films’ orientation on the electrical properties was also investigated.
Nitridation of vacuum evaporated molybdenum films in H2/N2 mixtures
Authors: Amazawa Takao , Oikawa Hideo
Published: July 2002

The nitridation behavior of molybdenum (Mo) films has been studied in relation to the crystal structure of the films. Vacuum evaporated Mo films are nitrided to form γ-Mo2N by annealing in H2/N2 mixtures in the temperature region of 400–900 °C. The temperature region becomes narrow with increasing H2/N2 flow ratio, and the Mo films are not nitrided by annealing in only nitrogen. These results are interpreted as caused by the reaction process involving hydrogen reduction of molybdenum oxide followed by direct nitridation of Mo. During annealing, the Mo films show uniform nitrogen distribution throughout the film and the nitrogen content increases with increasing annealing time. This behavior is well explained by the grain-boundary nitridation model in which each columnar grain of a Mo film is nitrided from the periphery to the center of the grain.
Heterogeneous reactions of NO2 on NaCl and Al2O3 particles
Authors: Goodman A. L. , Miller T. M. , Grassian V. H.
Published: July 2002

In this study, heterogeneous reactions of NO2 on NaCl and Al2O3 particles, two different types of particles present in the Earth’s atmosphere, are compared. Transmission Fourier-transform infrared spectroscopy and diffuse reflectance UV/Vis spectroscopy are used to characterize gas-phase and adsorbed products following reaction with NO2. For Al2O3 particles, two adsorbed species have been identified. At low NO2 pressures, adsorbed nitrite is formed whereas at higher NO2 pressures, nitrate is present on the surface of the aluminum oxide particles. For NaCl particles, adsorbed nitrate forms at all NO2 pressures. Kinetic measurements show that nitrate formation on sodium chloride is second order in NO2 pressure, in agreement with previous studies, whereas nitrate formation on aluminum oxide is first order in NO2 pressure. The potential importance of heterogeneous reactions of NO2 with these particles in the atmosphere is discussed.
Effect of postplasma treatment on characteristics of electron cyclotron resonance chemical vapor deposition SiOF films
Authors: Lee Seoghyeong , Park Jong-Wan
Published: July 2002

The effects of the postplasma treatment on the dielectric properties and reliability of F-doped silicon oxide (SiOF) thin films were investigated. The postplasma treatment of the SiOF films was carried in terms of plasma treated radio frequency (rf) bias power. As the plasma treated rf bias power increased, the chemical properties of plasma treated SiOF films tended to resemble those of thermal oxide as a result of both the reduction of the Si–F bond in the films and the increment of film density. The density of the film varied with the applied rf bias power; 1.927 g/cm3 for 0 W and 2.113 g/cm3 for 150 W, which were lower than those of the thermally grown silicon oxide by about 15% and 7%, respectively. As the plasma treated rf bias power increased, increases in both dielectric constant from 3.14 to 3.43 and the breakdown field strength from 3.5 to 8 MV/cm were determined for the postplasma treated SiOF films. Fourier transform infrared results also showed the intensity reduction of both the H–OH peak at about 3400 cm−1 and the Si–OH peak at about 3650 cm−1 with increasing the rf bias power. Therefore, both surface oxidation and densification resulting from O2 plasma treatment seemed to play a major role in making the SiOF films a very attractive material for ultralarge scale integrated intermetal dielectrics.
High temperature pinning properties of IrMn versus FeMn in spin valves
Authors: Tondra Mark , Wang Dexin
Published: July 2002

The antiferromagnetic pinning properties of IrMn and FeMn have been observed as a function of temperature by building spin valve samples with the structure NiFeCo/CoFe/Cu/CoFe/NiFeCo/(IrMn or FeMn) and measuring their magnetoresistive properties. The pinning strength was evaluated in terms of the break field, defined as the field applied in the direction opposite to the magnetization of the pinned layer at which the pinned layer switches. At room temperature, the break fields for both the IrMn and FeMn samples were about 250 Oe. But with increasing temperature, the break field for samples pinned with IrMn held up considerably better than for those pinned with FeMn. Specifically, the pinning of the FeMn spin valves was gone at 150 °C while the pinning of the IrMn spin valves persisted to temperatures above 225 °C. The IrMn spin valves performed as well as the FeMn spin valves in terms of magnetoresistance and lithographic process compatibility.
Plasma polymerization of fluorine alloyed amorphous carbon coatings
Authors: Vanhulsel A. , Dekempeneer E. , Smeets J. , Celis J.-P.
Published: July 2002

This article reports on the deposition conditions and characterization of plasma polymerized fluorocarbon coatings grown by an inductively coupled radio frequency plasma source, using CH4 and CF4 as precursor gases. SiH4, H2, or Ar were further added to the plasma to investigate their influence on the coating properties. The coatings were characterized by x-ray photoelectron spectroscopy to determine the surface and bulk composition and combined with Fourier-transform infrared spectroscopy to reveal the structure of the coatings. The mechanical properties (hardness and Young’s modulus) were measured by nano-indentation. The surface energy was obtained by contact angle measurements with two different liquids. By varying the deposition conditions, it was possible to adjust separately the polar and dispersive part of the surface energy. With the appropriate feed gases and process parameters, we were able to deposit coatings with surface energies as low as 14 mN/m. A low polar component of the surface energy corresponds to a high fluorine, CF3 and CF2 content at the surface of the coatings. The maximum contact angle achieved was 113°. By adding H2 to the plasma, it is possible to minimize the polar component and maximize the dispersive component of the surface energy to obtain a relatively hard (3 GPa) coating with a hydrophobic nature [contact angle (H2O)=90°].
Proposal of atom/molecule switching devices
Authors: Wada Yasuo
Published: July 2002

In this article very fast [more than tera (1012) Hz] and very small (less than a few nm) devices, atom relay transistors (ART) and molecular single electron switching transistors (MOSES) are proposed and the progress of the research towards the verification of these ideas is reported. These devices are anticipated to supersede the metal-oxide-semiconductor field effect transistor for future information processing. Atom/molecule manipulation technology using the scanning tunneling microscope (STM) would be the key factor in achieving these devices. The basic technology developments toward the realization of ART and MOSES are reported, including a beam assisted scanning tunneling microscope for insulator observation, needle formation and tip imaging for atomic-scale evaluation of the STM tip apex, a micromachine STM for single molecule manipulation and atom wire fabrication technology development on a silicon (100) hydrogen terminated surface.
Fabrication of nanometer size photoresist wire patterns with a silver nanocrystal shadowmask
Authors: Choi S. H. , Wang K. L. , Leung M. S. , Stupian G. W. , Presser N. , Chung S. W. , Markovich G. , Kim S. H. , Heath J. R.
Published: July 2002

In this article, we present a new method for fabricating precisely defined nanometer scale photoresist wire patterns. The Langmuir technique was utilized to form high aspect ratio lamellae, or wire patterns, of Ag nanocrystals at the air/water interface, and these patterns were transferred onto resist-coated substrates as a Langmuir–Schaeffer film and as a shadowmask. The wire patterns were transferred to the photoresist material by spatially selective electron beam exposure on the Ag nanocrystal wire shadowmask. Monte Carlo simulation was done to estimate the electron stopping power for the Ag nanocrystal shadowmask at low voltage.
Proximity x-ray lithography of siloxane and polymer films containing benzyl chloride functional groups
Authors: Dressick W. J. , Dulcey C. S. , Brandow S. L. , Witschi H. , Neeley P. F.
Published: July 2002

Silicon wafers coated with films of (p-chloromethyl)phenyl-trichlorosilane or spun coated polyvinyl benzyl chloride were exposed at the University of Wisconsin synchrotron x-ray source using 0.9385 nm radiation (800 MeV) at doses ranging from 50 to 1500 mJ/cm2. Exposure resulted in changes to the surface energy and chemical reactivity of the films. The loss of chlorine and formation of oxidized carbon photoproducts upon exposure was followed as a function of dose using x-ray photoelectron spectroscopy. A corresponding change in surface energy, as monitored by static water contact angle, was also observed. The selective chemical grafting (reductive amination) of amine ligands to the portions of the siloxane and polymer films which have been exposed to proximity x rays definitively establishes the formation of surface aldehyde or ketone groups as an important photochemical pathway. The resulting surface amine was used to covalently bind either a fluorescent tag or a colloidal Pd (II) nanoparticle capable of initiating the selective deposition of electroless Ni in the irradiated regions of the film.
Deposition of copper by using self-sputtering
Authors: Fu Jianming , Ding Peijun , Dorleans Fernand , Xu Zheng , Chen Fusen
Published: July 2002

A magnetron sputtering source using sustained self-sputtering has been developed for uniform deposition of copper on large wafers (200 mm in diameter). Usually, Ar gas is used in sputter deposition. In sustained self-sputtering, no Ar gas was used for deposition, the sputtered Cu atoms were ionized in the magnetron plasma, and some Cu ions were accelerated to sputter more Cu atoms out of the target. In this work, the magnetron was optimized to allow sustained self-sputter deposition of Cu on 200 mm wafers with reasonable power (9–12 kW). When sputtering a target of 325 mm in diameter, the minimum power density to sustain plasma without using Ar gas was found to be 10.8 W/cm2. This was much lower than the threshold power density reported in the literature. A chamber employing a large spacing between the target and wafer (16 cm) was used. The resulting deposition rate was about 320 nm/min, when a 12 kW of dc power was applied. The standard deviation in film thickness was less than 2.5% in our limited experiments. The pressure during sputtering was less than 4×10−4 Pa. In comparison with Ar sputtering at an Ar pressure of 0.13 Pa, the bottom coverage, defined by the ratio of film thickness on the trench bottom to the film thickness on the open field area, was increased by about 20% by using sustained self-sputtering. The bottom coverage can be further increased when the throw distance is increased. However, we did not observe significant enhancement of bottom coverage by applying dc and rf biases to the wafer during sustained self-sputtering, although about 20% of Cu species arriving at the wafers was ionized.