bluuebunny/crossref_metadata_2025 huggingface dataset:
A Novel Technique to Measure the Magnitude and Direction of Flow in a Tube
Authors: Robinson Allen L. , Sextro Richard G.
Published: July 2002

This paper describes a novel in-line sensor that measures the magnitude and direction of gas flow in a tube. The sensor possesses a unique set of performance characteristics: low detection limit, little resistance to flow, and directional sensitivity. The sensor consists of two hot wire anemometers mounted in a U-shaped tube. Differences in the signals between the two hot wires under low velocity conditions are used to determine the direction of the flow. Calibration curves of flow rate versus measured velocity are used to determine the magnitude of the flow. The sensor has applications in systems that are characterized by naturally driven oscillating flows. [S0098-2202(00)02701-2]
Pumping Characteristics of a Herringbone-Grooved Journal Bearing Functioning as a Viscous Vacuum Pump
Authors: Yoshimoto S. , Ito Y. , Takahashi A.
Published: July 2002

A laser scanner motor with low power and high speed has been developed. This scanner motor uses a herringbone-grooved journal bearing which functions as a viscous vacuum pump. The windage power loss of a polygon mirror is reduced, since the air inside the pump housing is pumped out by herringbone-grooved viscous vacuum action. In this paper, the theoretical pumping characteristic of this bearing is investigated, using the narrow-groove theory and accounting for first-order slip flow. The effects of various design parameters on the pumping characteristics are discussed. Optimum geometric design parameters were found to obtain the minimum inner chamber pressure of the housing. The theoretical predictions considering slip flow effects are in good agreement with experimental measurements. [S0742-4787(00)01801-4]
On the Influence of Thermal Properties on Wear Resistance of Rubbing Metals at Elevated Temperatures
Authors: Abdel-Aal Hisham A.
Published: July 2002

This paper studies the effects of the heat dissipation capacity of a rubbing material on wear resistance at high temperatures. These effects are studied with a special focus on the dilatation of the thermal energy in sliding. These results suggest a connection between wear transition and the change in the heat dissipation capacity of a rubbing material. The nature of change in the thermal properties before and after the transition influences the thermal environment within the contacting layers. This controls the kinetics of oxide formation and thereby controls wear. Thermal dilatation is a super position of three functions that represent the competing effects of the room temperature thermal properties and their respective variation with temperature. Whence, the change in the thermal properties bears on dilatation. The possible relation between thermal dilatation and protective oxide formation is studied by examining the fretting wear data for two alloys—a Ni-based alloy and a Co-based alloy. The results indicate a strong correlation between the formation of protective oxides and the change in the thermal dilatation of the examined alloys with temperature. Moreover, examination of the wear data suggests that a critical ratio between the effects of the conductivity and those of the effusivity has to be established for favorable wear resistance. This ratio reflects on the intrinsic ability of the material to sustain an oxidative reaction of a controlled rate. So that, the protective glaze oxide layers are formed in a rate that is approximately equal to the rate of oxide layer breakdown. Whence, continuous compensation for the removed oxide layer (self-repairing oxides) is established. [S0742-4787(00)00903-6]
Clean, As-terminated n-type GaAs by XPS
Authors: Chambers S. A. , Loebs V. A.
Published: July 2002

Specimens were prepared by growing a 1 μm thick n-type (4 × 1017 / cm3 Si) GaAs buffer layer on GaAs(001) in a Varian Gen-II MBE chamber, followed by As capping with As4 for transfer through the air. After entry into the preparation chamber associated with the XPS system, the As cap was desorbed by annealing for 5 min at 450°C in ultrahigh vacuum. The resulting surfaces were As terminated and free of contaminants, as judged by XPS, and exhibited a clear, sharp c(2 × 8)/(2 × 4) LEED pattern.
Gold Mg K
α XPS Spectra from the Physical Electronics Model 5400 Spectrometer
Authors: Mansour A. N.
Published: July 2002

Gold spectra were measured with the Physical Electronics Model 5400 x-ray photoelectron spectrometer using unmonochromatized Mg Kα x rays and two pass energy settings corresponding to anaylzer energy resolutions of 1.34 and 0.54 eV. The specimen was a high purity gold foil that was sputter-cleaned by 3 keV Ar ions. We present the survey spectrum (binding energy range of 0–1100 eV) measured at an analyzer energy resolution of 1.34 eV. Multiplexes of the Au 4f (80–100 eV), Au 4d (325–365 eV), Au 4p3/2 (535–565 eV), and valence band region (−5–20 eV) were measured at an analyzer energy resolution of 0.54 eV.
High Resolution Photoemission Study of the Spin-Dependent Band Structure of Permalloy and Ni
Authors: Altmann K. N. , Petrovykh D. Y. , Himpsel F. J.
Published: July 2002

High resolution, angular-resolved photoemission is used in a comparison of the energy bands of permalloy (Ni0.8Fe0.2) and single crystal Ni. The nickel was cleaned with a combination of Ar-ion bombardment and annealing. The permalloy was grown epitaxially on the clean single crystal Ni surface to minimize lattice mismatch. The magnetically split bands at the Fermi level that are responsible for spin-dependent transport are resolved in both systems. In addition, spectra are shown demonstrating both “s,p” and d bands in Ni.
Strain relaxation of InGaAs by lateral oxidation of AlAs
Authors: Mathis S. K. , Chavarkar P. , Andrews A. M. , Mishra U. K. , Speck J. S.
Published: July 2002

Strained InGaAs layers grown on AlAs/GaAs have been shown to relax when the AlAs is laterally oxidized. A detailed microscopy study is reported of the InGaAs structure before and after oxidation. Plan-view transmission electron microscopy (TEM) reveals that the misfit dislocation density in the InGaAs/AlAs interface is reduced by 30 times after lateral oxidation. The mechanism proposed for this reduction is the oxidation of the InGaAs interface, including the core regions of the misfit dislocations. Threading dislocation densities in the InGaAs are not measurable by TEM either before or after oxidation for optimized In0.20Ga0.80As and In0.30Ga0.70As layers. Two possible strain relaxation mechanisms are examined: (i) the compressive strain in the InGaAs is relaxed by a tensile stress developing during oxidation in the cap layer; and (ii) the stress is relaxed by the threading dislocation motion in the cap layer during oxidation. The removal of misfit dislocations reduces the likelihood of threading dislocation blocking, which prevents threading dislocations from moving across misfit dislocations.
GaInAsP grown on GaAs substrate by solid source molecular beam epitaxy with a valve phosphorous cracker cell
Authors: Zhang D. H. , Wang X. Z. , Zheng H. Q. , Shi W. , Yoon S. F. , Kam C. H.
Published: July 2002

GaInAsP epilayers grown on GaAs substrate by solid source molecular beam epitaxy with a valve phosphorous cracker cell at varied arsenic beam equivalent pressure ratio, fAs/(fAs+fP), were investigated. It is found that the InGaAsP/GaAs can be easily grown with the solid sources, and the incorporation rate of arsenic is higher than that of phosphorous and varies with arsenic to phosphorous beam equivalent pressure (BEP) ratio, fAs/(fAs+fP). The lattice mismatch, Δa/as, varies from negative to positive linearly with BEP ratio and follows a polynomial expression with arsenic composition. GaP-, InP-, GaAs-, and InAs-like LO modes are observed in all samples and shift as expected. The GaP- and InP-like TO mode is observed in most of the samples while the GaAs-like TO mode is observed only in the sample with an arsenic composition of 0.96. Photoluminescence measurements reveal that the luminescence peak energy of the materials does not change significantly at high arsenic composition but increases drastically with the decrease of arsenic composition. The full width at half maximum is found to be the largest in the sample with peak energy of 1.78 eV due likely to cluster formation. All samples studied show smooth surfaces.
Anisotropic strain in (100) ZnSe epilayers grown on lattice mismatched substrates
Authors: Yang Z. , Sou I. K. , Chen Y. H.
Published: July 2002

We show that part of the reflectance difference resonance near the E0 energy of ZnSe is due to the anisotropic in-plane strain in the ZnSe thin films, as films grown on three distinctly different substrates, GaAs, GaP, and ZnS, all show the resonance at the same energy. Such anisotropic strain induced resonance is predicted and also observed near the E1/E1+Δ1 energies in ZnSe grown on GaAs. The theory also predicts that there should be no resonance due to strain at the E0+Δ0 energy, which is consistent with experiments. The strain anisotropy is rather independent of the ZnSe layer thickness, or whether the film is strain relaxed. For ZnSe films with large lattice mismatch with substrates, the resonance at the E1/E1+Δ1 energies is absent, very likely due to the poor crystalline quality of the 20 nm or so surface layer.
Electrical properties of self-organized nanostructures of alkanethiol-encapsulated gold particles
Authors: Huang Shujuan , Tsutsui Gen , Sakaue Hiroyuki , Shingubara Shoso , Takahagi Takayuki
Published: July 2002

In this article, we present the fabrication and electrical characterization of nanostructures made of alkanethiol-encapsulated gold particles. We fabricated ordered close-packed monolayer and multilayer structures of encapsulated gold particles using a self-organization process. Room-temperature electrical properties of these nanostructures were studied by using a conductive atomic force microscope. In both cases of monolayer and multilayer structures, the current suppression around zero bias was observed for 9-nm-diameter gold particles. However, it was not observed for 20-nm-diameter particles. This suggests that the Coulomb blockade has occurred in the case of 9-nm-diameter particles. Moreover, the current–voltage properties of multilayer structures demonstrate a nearly linear relation between the Coulomb gap Vg and the number of layers NL, which is in good agreement with the theory of single-electron tunneling in a tunnel-junction array. These electrical properties suggest that an alkanethiol shell on gold particles can serve as a stable tunnel barrier. As a consequence, the proposed method for fabricating quantum dot structures is very useful for developing nanoelectronic devices.
Outgassing of photoresists in extreme ultraviolet lithography
Authors: Chauhan Maharshi M. , Nealey Paul F.
Published: July 2002

The outgassing characteristics of 100 nm thick films of several commercial photoresists were investigated during and after exposure to lithographically relevant doses of extreme ultraviolet lithography radiation. Three positive tone and two negative tone chemically amplified deep ultraviolet resists were evaluated that are commercially available. The amount and chemical composition of the outgassed species was determined by quartz crystal microbalance and quadrupole mass spectrometry. Outgassed species identified were products from acid catalyzed or photochemical cleavage reactions involving protecting groups, and products from the decomposition of photoacid generator molecules. t-butyl ester protected positive resist based on tetra polymers of methacrylates (IBM version 2.1) outgassed during exposure, and t-butoxy carbonyl protected positive resist based on polyhydroxystyrene (APEX-E) outgassed during and after exposure. Outgassing from t-butyl ester positive resist based on an ESCAP type polymer (UV6) and from negative resists (SAL 605 and NTS-4A4) was below detection limits in our experiments.
All-metal ultrahigh vacuum optical fiber feedthrough
Authors: Miller D. L. , Moshegov N. T.
Published: July 2002

We describe the design and performance of an inexpensive bakeable ultrahigh vacuum-compatible metal-sealed optical fiber feedthrough. A machined aluminum plug replaces the forward ferrule of an otherwise unmodified Swagelok stainless steel compression fitting to make a seal to seven parallel aluminum-jacketed quartz optical fibers. We have found this design to be leak tight to 10−9 cm3/min helium after baking repeatedly to 250 °C. The feedthrough my be disassembled by removing the fiber-and-plug assembly and then reassembled without creating leaks.
“p-on-n” Si interband tunnel diode grown by molecular beam epitaxy
Authors: Hobart K. D. , Thompson P. E. , Rommel S. L. , Dillon T. E. , Berger P. R. , Simons D. S. , Chi P. H.
Published: July 2002

Si interband tunnel diodes have been successfully fabricated by molecular beam epitaxy and room temperature peak-to-valley current ratios of 1.7 have been achieved. The diodes consist of opposing n- and p-type δ-doped injectors separated by an intrinsic Si spacer. A “p-on-n” configuration was achieved for the first time using a novel low temperature growth technique that exploits the strong surface segregation behavior of Sb, the n-type dopant, to produce sharp delta-doped profiles adjacent to the intrinsic Si spacer.
Thermal oxides of In0.5Ga0.5P and In0.5Al0.5P
Authors: Pulver Daryl , Wilmsen Carl W. , Niles David , Kee Ron
Published: July 2002

An investigation of the chemical composition of wet thermal oxides grown on In0.5Ga0.5P and In0.5Al0.5P is reported. The oxides were grown in the temperature range 500–650 °C. An estimate of the expected oxide composition was obtained by the construction of three-dimensional phase diagrams of the In–Ga–P–O and In–Al–P–O systems. These diagrams indicate that under thermodynamic equilibrium, the oxide layers should be composed primarily of mixtures of InPO4 and GaPO4 on In0.5Ga0.5P and InPO4 and AlPO4 on In0.5Al0.5P. X-ray photoemission spectroscopy (XPS) sputter profiles were used to determine the distribution of elements in the oxide layers and to identify the chemical compounds. The binding energy shifts observed in the XPS data suggests that the oxides are composed primarily of metal phosphates with low concentrations of the metal trioxides. At lower growth temperatures, the oxides composition is uniform with depth, but there is an increasing depletion of In near the substrate interface as the growth temperature increases.
Use of angle resolved x-ray photoelectron spectroscopy for determination of depth and thickness of compound layer structures
Authors: Spruytte S. , Coldren C. , Harris J. , Pantelidis D. , Lee H.-J. , Bravman J. , Kelly M.
Published: July 2002

A new graphical technique has been developed to characterize complex layered structures by angle resolved x-ray photoelectron spectroscopy. The technique enables estimation of layer composition, layer thickness, and depth of all the layers in a multilayer structure within a region up to several electron escape depths from the surface by measuring at two different escape angles with respect to the surface. These data are fit by the graphical technique to provide a layer depth profile. The technique requires making assumptions. The resulting limitations of the technique are discussed. We have tested the technique on a layer structure consisting of silicon, silicon dioxide, and platinum and have compared the results to a transmission electron microscope image. We also demonstrate this analysis technique for a GaAs/AlAs layer structure grown by molecular beam epitaxy.
Low temperature metalorganic chemical vapor deposition of conformal silver coatings for applications in high aspect ratio structures
Authors: Eisenbraun Eric T. , Klaver Arjen , Patel Zubin , Nuesca Guillermo , Kaloyeros Alain E.
Published: July 2002

A low temperature metalorganic chemical vapor deposition process has been developed for the growth of conformal silver coatings for applications in reflective mirror arrays, computer chip metallization, and superconducting wire and cable technologies. The process employed the silver source precursor Ag(COD)hfac, where COD=1,5-cyclooctadiene and hfac=1,1,1,5,5,5-hexafluoro 2,4-pentanedionate. Silver films were deposited at wafer temperature, source temperature, and processing pressure in the range of, respectively, 160–240 °C, 80–150 °C, and 0.5–5 Torr. Experiments were carried out in the presence of either argon or hydrogen as coreactant. The resulting films were characterized by Rutherford backscattering spectrometry, x-ray photoelectron spectroscopy, x-ray diffraction, and cross-section scanning electron microscopy. These investigations indicated that the silver films were pure, highly specular, and exhibited excellent conformality in 180 nm wide trench structures with 7:1 aspect ratio.
Fabrication of gated cathode structures using an in situ grown vertically aligned carbon nanofiber as a field emission element
Authors: Guillorn M. A. , Simpson M. L. , Bordonaro G. J. , Merkulov V. I. , Baylor L. R. , Lowndes D. H.
Published: July 2002

Vertically aligned carbon nanofibers (VACNFs) are extremely promising cathode materials for microfabricated field emission devices, due to their low threshold field to initiate electron emission, inherent stability, and ruggedness, and relative ease of fabrication at moderate growth temperatures. We report on a process for fabricating gated cathode structures that uses a single in situ grown carbon nanofiber as a field emission element. The electrostatic gating structure was fabricated using a combination of traditional micro- and nanofabrication techniques. High-resolution electron beam lithography was used to define the first layer of features consisting of catalyst sites for VACNF growth and alignment marks for subsequent photolithography steps. Following metallization of these features, plasma enhanced chemical vapor deposition (PECVD) was used to deposit a 1-μm-thick interlayer dielectric. Photolithography was then used to expose the gate electrode pattern consisting of 1 μm apertures aligned to the buried catalyst sites. After metallizing the electrode pattern the structures were reactive ion etched until the buried catalyst sites were released. To complete the devices, a novel PECVD process using a dc acetylene/ammonia/helium plasma was used to grow single VACNFs inside the electrostatic gating structures. The issues associated with the fabrication of these devices are discussed along with their potential applications.
Electrical properties of Pd-based ohmic contact to p-GaN
Authors: Kim Dae-Woo , Bae Jun Cheol , Kim Woo Jin , Baik Hong Koo , Lee Sung-Man
Published: July 2002

We have investigated the ohmic contact formation mechanism of Pd-based ohmic contacts to Mg-doped p-GaN grown by metalorganic chemical-vapor deposition. To examine room-temperature ohmic behavior, various metal contact systems were deposited and current–voltage measurements were carried out. In spite of the large theoretical Schottky barrier height between Pd and p-GaN, Pd-based contacts showed perfect ohmic characteristic even before annealing. According to the results of synchrotron x-ray radiation, the Pd (111) layer grew epitaxially on GaN (0001) surfaces with Pd[11̄0]∥GaN[112̄0]. The closed-packed atomic planes of the Pd film were quite well ordered in surface normal direction, as well as in the in-plane direction. The effective Schottky barrier height of Au/Pd/Mg/Pd/p-GaN was 0.47 eV, which was estimated by the Norde method. This discrepancy between the theoretical barrier height and the measured one may be due to the epitaxial growth of Pd contact metal.
Surface acoustic wave investigation by ultrahigh vacuum scanning tunneling microscopy
Authors: Voigt P. U. , Krauß S. , Chilla E. , Koch R.
Published: July 2002

The scanning acoustic tunneling microscope is based on the conventional scanning tunneling microscope and extends its topography-mapping capability to the investigation of both amplitude and phase of surface acoustic waves (SAWs) with frequencies in the MHz range. The mechanical oscillation of the surface induced by the SAW modulates the tunneling current. By adding a sinusoidal high frequency signal to the dc tip voltage this ac tunneling current signal is mixed down to an easily detectable low frequency signal. Here, we report the first ultrahigh vacuum (UHV)-compatible version of this technique including provision for sample transfer and in situ surface preparation. Since both signal-to-noise ratio and spatial resolution are significantly enhanced in UHV, acoustic oscillations of topography features can be investigated on the nanoscale. At present, SAW frequencies up to 400 MHz have been successfully fed into the UHV system.
Surfactant-mediated growth and characterization of Ge(211)/Si(211) heterostructures grown by molecular beam epitaxy
Authors: Tari S. , Brill G. , Sivananthan S. , Floyd M. , Smith David J.
Published: July 2002

We report the characterization of thin and thick Ge layers grown by molecular beam epitaxy on Si(211) substrates with and without As deposition prior to Ge growth. The role of the As surfactant, as well as the dependence of the overall layer quality on the Ge growth rates and growth temperatures has been studied. The Ge layer growth was monitored in situ by reflection high-energy electron diffraction, and the Ge/Si heterostructures were characterized ex situ by Raman spectroscopy, x-ray diffraction, and cross-sectional transmission electron microscopy. The results indicate that the growth mode is altered significantly by saturating the Si surface with a monolayer of As prior to initiation of Ge growth. Although Ge–Si interdiffusion and alloy formation on the Si(211) surface are dramatically reduced by nucleating Ge on Si with the aid of a surfactant, they are not completely suppressed. A structural model for initiation of the surfactant-mediated growth is briefly discussed.
Interfacial chemistry of the Sr/SiOxNy/Si(100) nanostructure
Authors: Kirsch P. D. , Ekerdt J. G.
Published: July 2002

The interfacial chemistry of a strontium/silicon oxynitride (SiOxNy)/silicon(100) nanostructure was investigated with x-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS) to determine if SiOxNy can serve as a barrier for the strontium titanate high-k dielectric. The structure consisted of 19 Å (5 ML) of Sr on a 10 Å SiOxNy barrier layer on a Si(100) substrate. Both XPS and SIMS results suggest that strontium oxide (SrO) and silicon dioxide (SiO2) at the Sr/SiOxNy interface form strontium silicate even at 300 K. The kinetics of this reaction were accelerated by heating the structure in a stepwise fashion to 1000 K. After the 500 K anneal, the SrO and SiO2 XPS chemical states attenuate leaving predominantly two silicate phases. Annealing the nanostructure to 1000 K tested the barrier capability of the 10 Å SiOxNy layer to Sr diffusion. SIMS Sr+, SrSi+, SrSiO+, and Sr2N+ signals reveal that Sr containing species do not significantly penetrate below the N≡Si3 bonds characteristic of SiOxNy. Comparison of 10 Å SiO2 and 10 Å SiOxNy confirms that the N≡Si3 bonds are the key to the barrier properties. Without N atoms, the SrSiO+ signal increased by a factor of 3.6 and penetrated 26 Å deeper into the Si substrate after a 900 K anneal. These results show that N atoms in the barrier layer retard Sr diffusion and silicate formation. Comparison of Ba and Sr on SiOxNy suggests that Ba is more likely to form silicide, whereas Sr is more likely to form silicate.
New phase formation of Gd2O3 films on GaAs(100)
Authors: Kortan A. R. , Hong M. , Kwo J. , Mannaerts J. P. , Krajewski J. J. , Kopylov N. , Steiner C. , Bolliger B. , Erbudak M.
Published: July 2002

A fluorite-related phase of Gd2O3, with a tetragonal unit cell of a=5.65 Å and c=5.37 Å, was attained in this study. The new phase was found either in a thin Gd2O3 film (∼18 Å), which was epitaxially grown on GaAs(100), or in a disordered (by mild Ne+-ion sputtering) and recrystallized (by UHV annealing) thin cubic α-Gd2O3 film. The structural characteristics of the new oxide films were studied using in situ reflection high-energy electron diffraction, secondary-electron imaging, and single-crystal x-ray diffraction.
Deposition of diamond films at low pressure in a planar large-area microwave surface wave plasma source
Authors: Yeh W. Y. , Hwang J. , Wu T. J. , Guan W. J. , Kou C. S. , Chang H.
Published: July 2002

In this study a planar large-area microwave plasma source is used to grow diamond films at low gas pressure. This plasma source is based on the excitation of plasma surface waves so that overdense plasmas can be generated. Above all, this plasma source is easy to scale up. For admixture of CH4/H2 gas, radical information and characteristics of the plasma are carefully characterized at low pressure. Some features different from those at high pressure are observed. A three-step process for diamond growth in the planar microwave plasma chemical vapor deposition system has been developed. High nucleation density can be achieved as a result. At a low pressure of 0.2 Torr, diamond films can be successfully deposited on a 4-in. Si(100) wafer, exhibiting a large amount of non-sp3 bonding. The effects of plasma properties on the diamond film are addressed.
Thin film confinement effects on the thermal properties of model photoresist polymers
Authors: Soles Christopher L. , Lin Eric K. , Lenhart Joseph L. , Jones Ronald L. , Wu Wen-li , Goldfarb Darı́o L. , Angelopoulos Marie
Published: July 2002

The demand to print increasingly smaller microelectronic device features means that the thickness of the polymer films used in the lithographic processes must decrease. The thickness of these films is rapidly approaching the unperturbed dimensions of the polymer, length scales at which confinement deviations and dewetting are a significant concern. We combine specular x-ray reflectivity (SXR) and incoherent neutron scattering (INS) to probe the thermal stability and dynamical effects of thin film confinement in poly(hydroxy styrene) (PHS), a polymer used in a majority of the 248 nm deep UV photoresists. PHS forms stable thin films (down to 5 nm) that do not dewet over a wide temperature range on Si surfaces ranging from hydrophilic to hydrophobic. The surface energy has a profound influence on the magnitude of the thin film expansion coefficient, especially above the glass transition, in films as thick as 100 nm. Confinement also appears to suppress the mean-square atomic displacements and the level of anharmonicity in the dynamics, primarily above the bulk glass transition.
Optical, electrical, and structural characteristics of yttrium oxide films deposited on plasma etched silicon substrates
Authors: Araiza J. J. , Aguilar-Frutis M. A. , Falcony C.
Published: July 2002

Yttrium oxide thin films were deposited on Si(100) substrates using the rf-sputtering technique at low power density and low temperatures (up to 300 °C). Previous to deposition, the substrates were plasma etched during different lengths of time. The characteristics of these films and the effect of surface etching on the substrate were studied by ellipsometry, x-ray diffraction at grazing angle, atomic force microscopy, and x-ray energy dispersive spectroscopy (EDS). The deposited films were polycrystalline, presenting cubic and/or monoclinic phases. The deposition rate, refractive index, surface roughness, and degree of crystallinity were strongly dependent on etching time of the substrate, especially for low deposition temperatures. The electrical characterization of the films incorporated in a metal–oxide–semiconductor structure showed a good dielectric constant value (up to 11), surface states densities as low as 6.7×1011 cm−2 eV−1 at midgap and breakdown strength in the range of 1.16–4.84 MV/cm. EDS measurements on these films showed a higher oxygen content than expected for Y2O3 stoichiometry.
Characterization of ultrashallow dopant profiles using spreading resistance profiling
Authors: Tan L. S. , Tan L. C. P. , Leong M. S. , Mazur R. G. , Ye C. W.
Published: July 2002

It has been noticed that for ultrashallow ion implanted dopant profiles, the metallurgical junction is not at the same location as the peak of the spreading resistance profile, i.e., the on-bevel junction. This can be attributed to the carrier redistribution effect. Furthermore, the pressure under the spreading resistance probes causes band-gap narrowing of the material under the probes. This pressure-induced band-gap narrowing effect increases the intrinsic carrier concentration of the semiconductor material. An inverse algorithm used to convert spreading resistance profiles into the electrically active dopant profiles, taking both carrier redistribution and band-gap narrowing into account, is presented in this article. Using this algorithm, the depth of the metallurgical junction of a shallow ion implanted p+n profile is determined to be 0.121 μm from the surface, whereas the on-bevel junction depth is 0.089 μm. The recovered dopant concentration profile agrees very well with that obtained from secondary ion mass sepctrometry. The algorithm is shown to work very well also for an n+p junction.
Two-dimensional modeling of long-term transients in inductively coupled plasmas using moderate computational parallelism. II. Ar/Cl2 pulsed plasmas
Authors: Subramonium Pramod , Kushner Mark J.
Published: July 2002

Quantifying transient phenomena such as pulsed operation is important to optimizing plasma materials processing. In particular, pulsed electronegative plasmas are promising candidates for reducing notching and charge buildup in features during microelectronics fabrication. In this article, a two-dimensional plasma equipment model is employed to investigate pulsed inductively coupled plasmas in Ar/Cl2 gas mixtures. The consequences of varying pulse repetition frequency (PRF), duty cycle, power, pressure, and Cl2 mole fractions on plasma properties are quantified. The nonmonotonic temporal dynamics in Cl− density observed in experiments are well captured by the model. We found that for constant peak power, a lower duty cycle resulted in higher peak electron temperatures at the leading edge of the power pulse due to a lower initial electron density at the end of the afterglow. Increasing the PRF produces an increase in the time averaged electron density due to a lower rate of attachment in the afterglow. The inertia of Cl− ions produces a sluggish response to rapid changes in plasma potential which results in “islands” of higher Cl− density in the periphery of the reactor. The results show that as the Cl2 fraction increases, the transition from electron–ion to ion–ion plasma is more pronounced.
Nondestructive analysis of ultrashallow junction implant damage by combined technology of thermal wave and spectroscopic methods
Authors: Hovinen Minna , Opsal Jon
Published: July 2002

Boron and arsenic low-energy (200–5000 eV) implants are studied after implantation, prior to annealing. We present results of optical measurements that provide new information on the damage depth profile. In addition, a method for simultaneous determination of implant dose and energy is proposed. Thermal wave and spectroscopic methods are observed to support each other in the analysis of arsenic ultrashallow junctions. New results are reported on the boron induced implant damage and the necessity for a combined technology is addressed. A combination of optical spectroscopy and thermal wave techniques are shown to provide a highly repeatable, nondestructive metrology to assist in ultrashallow junction fabrication.
Photoreflectance spectroscopy of AlGaAs/GaAs heterostructures with a two-dimensional electron gas system
Authors: Méndez-Garcı́a V. H. , Zamora L. , Lastras-Martinez A. , Saucedo N. , Peña R. , Guillén A. , Rivera Z. , Meléndez M. , López M. , Hernández F. , Huerta J.
Published: July 2002

We report a study of AlGaAs/GaAs semiconductor heterostructures with a two-dimensional electron gas system grown under different conditions by molecular beam epitaxy in three different laboratories. We performed photoreflectance (PR) measurements of this set of samples and analyzed the Franz–Keldysh oscillations associated with the E0 transition of GaAs. We found that the sample with the highest electron mobility, as observed in Hall measurements at 77 K exhibited the lowest electric field strength. In addition, the 12 K photoluminescence (PL) spectra of the samples revealed intense and narrow free exciton luminescence in the sample with the highest electron mobility, while samples with lower mobility values showed impurities related PL lines. It is suggested that the electron mobility is affected by unintentional C impurities, which act like dispersion centers in the 2-DEG and increase the internal electric fields in the GaAs region. On the other hand, the PR spectra close to the AlGaAs band-gap energy region presented broad PR signals, due to the Si-doping in the alloy. The sample with the highest quality presented the most intense AlGaAs PR signal. We believe that low AlGaAs PR signal intensities are caused by unintentional incorporation of impurities during the preparation of the samples, which degrade the optical properties of the alloy.
InAs-based bipolar transistors grown by molecular beam epitaxy
Authors: Averett K. L. , Maimon S. , Wu X. , Koch M. W. , Wicks G. W.
Published: July 2002

Large mobilities and electron saturation velocity make InAs a promising material for high speed devices. Investigations into materials characteristics of doped InAs show nonideal behavior with standard molecular beam epitaxy dopants, silicon, and beryllium. Critical thicknesses for cracking of AlxIn1−xAs on InAs were empirically determined as a function of x. Mesa pn junctions in InAs show no effects of surface Fermi level pinning and exhibit good rectification with low reverse leakage. Bipolar junction transistor and heterojunction bipolar transistor devices are presented, along with their dc electrical characteristics. Common emitter current gains of 100 have been achieved in these bipolar devices.
Quantum transport through one-dimensional aluminum wires
Authors: Batra Inder P. , Sen Prasenjit , Ciraci S.
Published: July 2002

Quantum conductance in narrow channels has been well understood by using the two-dimensional electron gas, a model system which has been realized in semiconductor heterojunctions. An essential property of this electron gas is its ability to support a constriction of width comparable to the Fermi wavelength, a property not shared by even thin metal films. The advent of scanning tunneling microscope has made possible the fabrication of metallic wires of atomic widths. We investigate one-dimensional wires consisting of aluminum atoms, to be specific. Using the first-principles density functional calculations, we obtain the optimal structures and report the bonding as deduced from the charge density analysis. With the calculated electronic structure in hand, we discussed the quantum ballistic transport using channel capacity arguments motivated by the Heisenberg’s uncertainty principle. By comparing our results with the detailed pioneering calculations by Lang, we inferred an average value for channel transmitivity and touched upon material specific contact resistance. Finally, the validity of the Wiedemann–Franz law in the quantum domain is established by studying thermal conductance in nanowires.
Role of Submicroscopic Projections in Electrical Breakdown
Authors: Tomaschke H. E. , Alpert D.
Published: July 2002

Observations with an electron microscope and with a modified field-emission microscope verify the formation of submicroscopic, whiskerlike projections on the cathode surface, thus lending additional supporting evidence for the association of electrical breakdown with field emission from such sites. Several mechanisms for the formation of whiskers are identified. The predischarge current, with which the initiation of breakdown is associated, is observed to exhibit large fluctuations in the presence of contamination on either or both electrodes, and a tentative explanation is set forth in terms of a special proliferation of small protuberances.
Solar-energy conversion at high solar intensities
Authors: Backus Charles E.
Published: July 2002

The concentration of sunlight offers distinct advantages for solar–electrical generation either by thermal conversion or by photovoltaics. A large variety of concentration techniques are available with concentration ratios of 1–1000. Concentration is required for thermal conversion systems to attain the high temperatures needed for efficiencies in the desired range of about 25%–35%. The projected costs for some of the solar thermal systems (especially the central receiver and the fixed mirror) indicate that they could be economically competitive in the southwestern states. The southwest may be required for these high-concentration systems to overcome the main disadvantage of concentration, which is the use of the direct component of sunlight only. Other concerns of high-intensity systems are in tracking requirements, reflective surface accuracy, and material lifetimes of both the reflecting and absorbing components. Selective surface absorbers will be required for systems with concentration ratios below a few hundred. The present high cost of solar-cell-generated electricity can be reduced considerably by using concentrators. Cells can be used with any of the concentrator designs, and the major concern is keeping them at acceptable operating temperatures. Planar silicon cells, vertical multijunction, and gallium–aluminum–arsenide cells all look attractive for concentrating systems.
Angular-dependent Ne+-ion scattering from a solid Au target
Authors: Brongersma H. H. , Hazewindus N. , van Nieuwland J. M. , Otten A. M. M. , Smets A. J.
Published: July 2002

Ion-scattering spectroscopy (ISS) is a technique used for composition analysis of solid surfaces. The angular dependence of low-energy ion scattering has been investigated in order to assess the possibility of using large scattering angles in ISS. The equipment used for these experiments is described. It allows for measurements of the angular dependence of the scattering process between 0° and 150°. A detailed discussion of the special ion optical design of the primary beam train and the analyzing system for the scattered ions, comprising a retarding system and a 127° cylindrical analyzer, is given. Results are presented for 2-keV-Ne+ scattering from Au. It is found that increasing the scattering angle beyond 60° has little effect on the intensity of the scattered ions. However, it does increase the mass resolution, thus favoring large angle scattering for surface analytical studies. From a comparison of the measured scattered ion current with computed charge-independent scattering cross sections, the ion fractions P+ of the scattered particles have been determined as a function of scattering angle. Scattering cross sections have been calculated using a Firsov, Molière, and two different Born–Mayer interaction potentials. It was found that the neutralization of the ions is mainly governed by a direct interaction with the target atom and to a smaller extent by interaction with the neighboring surface.
Effects of specific surface treatments on type 304 stainless steel
Authors: Bonham R. W. , Holloway D. M.
Published: July 2002

Proterctive coatings for stainless steel containers for deuterium/tritium gas mixtures (gas mass spectrometer calibration standards) have been evaluated by auger electron spectroscopy. An iron/oxygen rich coated surface minized isotopic exchange. (AIP).
X-ray photoelectron spectroscopy with x-ray photons of higher energy
Authors: Wagner C. D.
Published: July 2002

There have been few studies using ionizing photons higher in energy than Al Kα (1487 eV). However, characteristic x rays such as Au Mα (2123 eV) and Ag Lα (2984 eV) are nearly as narrow in energy, and can provide deeper core photoelectron lines and their companion core-type Auger lines in the spectra of 26 elements that otherwise cannot be recorded. Such data are of special value in identifying chemical states by the two-dimensional approach. This involves plotting Auger kinetic energy against photoelectron kinetic energy. The Auger Parameter is the difference between these two energies. Chemical shifts in the Auger parameter provide information on polarization effects in the medium. New data are shown for solid compounds of silicon, sulfur, bromine, and tungsten, obtained with Au Mα x rays. Other reported data obtained with x rays ≳1500 eV are included for comparison. The data for the eighteen compounds of tungsten show considerable variation in chemical shifts in the M5N7N7 Auger line as well as those of the 3d5/2 photoelectron line; neither of these lines is accessible by Al Kα radiation.
Radio frequency magnetron sputtering of thick film amorphous beryllium
Authors: Burt R. J. , Meyer S. F. , Hsieh E. J.
Published: July 2002

Thick film coatings of beryllium, needed for the low-Z ablator layer in proposed laser fusion targets, have been prepared using high rate magnetron rf sputtering. The requirements for these Be coatings include thicknesses from 5 to 50 μm, complete freedom from surface defects, and an average surface roughness of 100 nm or less. These specifications are difficult to achieve if crystalline growth occurs during sputtering, since the surface roughness of thick grainy films can be on the order of micrometers. We have sputtered very smooth, dense Be films up to 25 μm thick with surface roughness less than 100 nm. X-ray diffraction analysis of impurity doped films indicates an amorphous-like structure. Impurity stabilized amorphous Be with smooth surfaces is reported on both 15°C cooled copper and nominal 200°C glass substrates. The sputtering parameters (substrate temperature, deposition rate, argon pressure, and impurity gas levels) affecting surface roughness and film structure are discussed in terms of SEM, AES, and x-ray diffraction results.
Vibrational spectra of CO chemisorbed on Fe (110)
Authors: Erley W.
Published: July 2002

The chemisorption of CO on an Fe (110) surface has been investigated at 120 K using high resolution electron energy loss spectroscopy (EELS) and low energy electron diffraction (LEED). At CO exposures up to 0.7 L two vibrational losses around 456 cm−1 and 1890 cm−1 are observed both shifting to higher frequencies with coverage. These losses can be attributed to the symmetric vibrations of ’’on top’’ bonded CO molecules. The intensity of both losses increases continuously in this exposure range. Above 0.7 L the low frequency loss continues to grow whereas the intensity of the high frequency loss remains constant up to saturation coverage. The latter observation may be explained by depolarization of the dynamic dipole moments of the CO molecules. Simultaneously at 0.7 L a new loss appears around 360 cm−1 which may be attributed to the frustrated rotation of the adsorbed CO molecule when changing the adsorption site symmetry from C2v to Cs. Adsorption models are presented which are in agreement with both the LEED and EELS observations.
Quantitative Auger microanalysis of the silicon–oxygen–nitrogen system
Authors: van Oostrom A. , Augustus L. , Habraken F. H. P. M. , Kuiper A. E. T.
Published: July 2002

Auger depth profiling data are presented for thin films of silicon oxide grown by thermal oxidation and for thin films of silicon nitride and silicon oxynitride deposited by low pressure chemical vapor deposition. Samples are bombarded by 500 eV argon ions, and Auger data is collected in either the N(E) or the dN/dE mode of operation. By probing the N, O, and Si(KLL) peaks a quantitative analysis of these films has been made.
Thermal desorption measurements for estimating bakeout characteristics of vacuum devices
Authors: Beavis L.
Published: July 2002

The present paper deals with experiments which indicate that vacuum devices with proper bakeout will remain at vacuum for several year periods when isolated from pumps and pumping.(AIP)
Characterization of multilayer diffusion barriers by electron probe microanalysis and Auger electron spectroscopy
Authors: Bierlein John C. , Gaarenstroom Stephen W. , Waldo Richard A. , Ottolini Albert C.
Published: July 2002

Several electron probe microanalysis and Auger electron spectroscopy profiling techniques were used to characterize diffusion behavior and intermetallic compound formation at diffusion barriers in engine bearings. Four Auger techniques were employed: sputtering, taper sectioning, ball cratering, and cross sectioning with examination by a high resolution electron beam. Cross sections of the bearings were also studied using both scanning and focused-spot techniques of the electron probe microanalyzer. The advantages and shortcomings of the various preparation and analysis methods are discussed. No single method could adequately characterize the system, but the combination of techniques proved sufficient. The analyses showed current single-barrier bearings underwent undesired diffusion during engine operation. Results of the chemical composition profiles were mapped onto ternary and quaternary diagrams. These diagrams were used to optimize the relative layer thicknesses in a new trimetal barrier bearing with improved score resistance.
Metastable solid solutions in vapor deposited Cu–Cr, Cu–Mo, and Cu–W thin films
Authors: Dirks A. G. , van den Broek J. J.
Published: July 2002

The equilibrium phase diagrams of Cu–Cr, Cu–Mo, and Cu–W show no measurable solid solubility except for a small solubility of Cr in solid Cu at higher temperatures. Even in the liquid state, the mutual solubilities in these systems are very limited. Simultaneous vapor deposition of elements on unheated substrates was used to produce alloy films covering the complete composition range of those three binary alloy systems. The films were characterized with the help of x-ray diffraction, transmission electron microscopy, and electron diffraction. In fcc Cu films, at least 10 at.% Cr, Mo, or W may be dissolved, whereas the bcc Cr, Mo, or W alloy films may accommodate at least 40 at.% Cu; the fcc and bcc solid solutions are separated by narrow two-phase fields. We further measured the composition dependence of the internal stress and of the electrical resistivity. Discontinuities in the measured curves generally coincide with the presence of phase boundaries in the (metastable) alloy films.
Long-term stability of two types of hot cathode ionization gauges
Authors: Wood S. D. , Tilford C. R.
Published: July 2002

We have monitored the nitrogen sensitivity of four gauges each of two selected types of hot cathode ion gauges over a 500-day test period. Gauges of one type, a tungsten filament conventional triode, changed by about 12% during this time, with most of the decrease caused by ‘‘high’’ pressure operation. Gauges of the second type, a twin tungsten filament Bayard–Alpert gauge, changed by no more than 6% and with no obvious correlation between sensitivity changes and ‘‘high’’ pressure operation or exposure to air. There were no significant differences in the sensitivity changes for the two filaments in a given Bayard–Alpert gauge, although their operating times differed by a factor of 10.