bluuebunny/crossref_metadata_2025 huggingface dataset:
Force and Power Estimation in Fish-Like Locomotion Using a Vortex-Lattice Method
Authors: Kagemoto H. , Wolfgang M. J. , Yue D. K. P. , Triantafyllou M. S.
Published: July 2002

The forces and power needed for propelling at constant speed an actively swimming flexible fish-like body are calculated. A vortex-lattice method based on a linearized theory is employed and the results are compared against slender body theory predictions, as well as experimental data from an eight-link robotic instrument, the RoboTuna. Qualitative agreement is found between our method and slender body theory; with quantitative agreement over certain parametric ranges and disagreement for other ranges of practical interest. The present linearized vortex lattice calculations predict the power needed for propelling the RoboTuna with less than 20 percent error in most experiments conducted. [S0098-2202(00)01202-5]
Finite Element Analysis of the Initial Yielding Behavior of a Hard Coating/Substrate System With Functionally Graded Interface Under Indentation and Friction
Authors: Stephens L. S. , Liu Yan , Meletis E. I.
Published: July 2002

The initial yielding behavior due to the indentation and friction process between an elastic cylindrical surface and hard coating/functionally graded substrate system is analyzed by finite element modeling. A thin hard DLC film deposited on a soft Ti–6Al–4V alloy substrate is considered as a model system. Two functional gradient substrate conditions are considered: (i) a gradient in yield strength and (ii) a gradient in elastic modulus. In both cases, appropriate gradients result in significant benefits to the reliability of the coated system compared to the case of an ungraded substrate. The results indicate that systems with an appropriate gradient in yield strength: (i) can withstand significantly higher applied contact stresses (3–12 times higher for the present model system), (ii) shift the location of the initial yield point deeper into the substrate (at least by a factor of 2 for the present model system), and (iii) can use coatings of greater thickness. Finally, the results indicate that an appropriate gradient in elastic modulus results in a dramatic reduction in equivalent stress on the contact surface and at the interface as compared to the ungraded case. The present results suggest distinct benefits to the durability of coated systems when using a substrate with functionally graded properties. [S0742-4787(00)02002-6]
Some Studies on Life Prediction of Thermal Sprayed Coatings Under Rolling Contact Conditions
Authors: Sarma B. Y. , Mayuram M. M.
Published: July 2002

Design of engineering components is concerned with their strength and durability characteristics. While design for strength is influenced by the bulk material characteristics, the design for durability is dependant on the surface characteristics. Majority of the component failures are surface originated. Surface engineering could play a vital role in minimizing such failures. Thermal sprayed coatings, one of the versatile surface coating techniques, can be applied to components of machinery surfaces to avoid such failures. The present paper presents a methodology for contact stress evaluation of surface coated elements, adopting a layered structure approach, and thereby analytically predict their spalling life. Further data on cycles to single pit formation, and spalling of spray fused coatings obtained from experimental testing are presented for assessing the applicability of life prediction models to layered structures such as sprayed coatings. Experimental investigations were conducted on spray fused coatings using a twin disk RCF test setup. The surface and subsurface contact stress distribution have been obtained analytically by Smith–Liu equations along with first order model perturbation method (FOMP), to account for the variation of elastic modulus constants of the layered structure. Applying Lundberg-Palmgren and Tallian life prediction models, the spalling life of these coatings has been predicted analytically and compared with experimental life values. [S0742-4787(00)02502-9]
THD Analysis of High Speed Heavily Loaded Journal Bearings Including Thermal Deformation, Mass Conserving Cavitation, and Turbulent Effects
Authors: Zhang Chao , Yi Zixia , Zhang Zhiming
Published: July 2002

Theoretical and experimental THD analyses of high speed heavily loaded journal bearings are presented. Numerical solutions include thermal deformation, mass conserving cavitation and turbulent effects. The pressure and temperature distributions, the eccentricity ratio, and the flow rate are measured. Agreement between theoretical results and experimental data is satisfactory. [S0742-4787(00)00803-1]
A Three-Dimensional Coupled Internal/External Simulation of a Film-Cooled Turbine Vane
Authors: Heidmann James D. , Rigby David L. , Ameri Ali A.
Published: July 2002

A three-dimensional Navier–Stokes simulation has been performed for a realistic film-cooled turbine vane using the LeRC-HT code. The simulation includes the flow regions inside the coolant plena and film cooling holes in addition to the external flow. The vane is the subject of an upcoming NASA Lewis Research Center experiment and has both circular cross-sectional and shaped film cooling holes. This complex geometry is modeled using a multiblock grid, which accurately discretizes the actual vane geometry including shaped holes. The simulation matches operating conditions for the planned experiment and assumes periodicity in the spanwise direction on the scale of one pitch of the film cooling hole pattern. Two computations were performed for different isothermal wall temperatures, allowing independent determination of heat transfer coefficients and film effectiveness values. The results indicate separate localized regions of high heat flux in the showerhead region due to low film effectiveness and high heat transfer coefficient values, while the shaped holes provide a reduction in heat flux through both parameters. Hole exit data indicate rather simple skewed profiles for the round holes, but complex profiles for the shaped holes with mass fluxes skewed strongly toward their leading edges. [S0889-504X(00)02802-6]
Mechanism-Based Evaluation of Thermal Ratcheting due to Traveling Temperature Distribution
Authors: Igari Toshihide , Wada Hiroshi , Ueta Masahiro
Published: July 2002

Recently, structural design against a new type of thermal ratcheting under a null-primary-stress condition has been required. The representative case is the thermal ratcheting of a hollow cylinder caused by a traveling temperature distribution. In this paper, the mechanism of this ratcheting is proposed, and the evaluation method of ratcheting strain is shown based on this mechanism. The proposed evaluation method is basically based on the hoop-membrane stress due to the axial temperature distribution, and considers the influence of axial bending stress and traveling distance of temperature distribution. Predicted results by this method correspond to numerical results by FEM and can conservatively estimate the experimental results with several kinds of traveling distance, stress levels, and two types of temperature hold for types 316 and 316FR stainless steels. [S0094-9930(00)01102-1]
Analysis of Poly(tetrafluoroethylene) (PTFE) by XPS
Authors: Girardeaux Christophe , Pireaux Jean-Jacques
Published: July 2002

We report x-ray photoemission spectra of poly(tetrafluoroethylene) (PTFE). XPS spectra were measured with the SSI, SSX-100 model, using monochromated Al Kα x-rays. We present the survey spectrum (binding energy range of 0–1000 eV) and narrow scans of C 1s and F 1s. The polymer is used as a reference to study the influence of PTFE surface modification by an excimer ultraviolet laser (λ = 193 nm).
Diagnosis of positive ions from the near-cathode region in a high-voltage pulsed corona discharge N2 plasma
Authors: Tang Shukai , Wang Wenchun , Liu Jiahong , Yang Xuefeng , Wu Yan
Published: July 2002

Positive ions from the near-cathode region in a wire-plate high-voltage pulsed corona discharge nitrogen plasma were characterized using a molecular beam mass spectrometer under severe electromagnetic interference. The N+ current is 2–8 times greater than that of N2+ at N2 pressure of 5–25 Torr, peak voltage of 4–10 kV, and repetition rate of 10–70 Hz. The nitrogen ion signals rise with increasing peak voltage and repetition rate of pulsed discharge, but exhibit a clear peak over the N2 pressure range studied. The kinetics of the physicochemical processes involved in the earlier N2 plasma has been studied. Nitrogen ion generation near the corona wire area and migration path to the cathode plate are the key areas in the understanding the phenomenon and mechanisms that are involved.
Electron-Stimulated Desorption as a Tool for Studies of Chemisorption: A Review
Authors: Madey Theodore E. , Yates John T.
Published: July 2002

Bombardment of solids by low-energy electrons (<500 eV) can cause various changes in the surface region, particularly if the surface contains an adsorbed layer. Electron bombardment can promote the desorption of energetic neutral and ionic fragments from the surface, can alter the bonding of surface species, and in some cases can cause decomposition of the surface region. These processes are termed electron-stimulated desorption (ESD) phenomena, and this review is primarily concerned with the use of ESD in studies of species adsorbed on surfaces. Topics covered include experimental methods, a theoretical discussion of physical mechanisms, and a detailed discussion of certain specific and well-studied adsorbate–substrate systems.
Plasma enhanced direct current planar magnetron sputtering technique employing a twinned microwave electron cyclotron resonance plasma source
Authors: Jun Xu , Xinlu Deng , Shiji Yu , Wenqi Lu , Tengcai Ma
Published: July 2002

The dc discharge of a planar magnetron was enhanced by a twinned microwave electron cyclotron resonance plasma source. The magnetic cusp geometry formed in the processing chamber was used for plasma confinement. The sputtering discharge characteristics were investigated and a combined mode of voltage and current was observed at a pressure as low as 0.007 Pa. Carbon–nitride thin films were synthesized using this method. Characterization of the films show that deposition rate was high, the films were composed of a single amorphous carbon nitride phase with N/C ratio close to that of C3N4, and the bonding was mainly of C–N type.
Multilayered (Ti, Al) ceramic coating for high-speed machining applications
Authors: Zeng X. T. , Zhang Sam , Tan L. S.
Published: July 2002

A multilayered (Ti, Al) ceramic hard coating was deposited on tunsten-carbide ball-nose end mills for high-speed machining using an unbalanced magnetron-sputtering system. The process parameter dependence of the coating properties was studied. X-ray diffractometry, x-ray photoelectron spectroscopy, nanoindentation, and scratch tests were used to characterize the structural, compositional, and mechanical properties of the coatings. High hardness, up to 40 GPa; good adhesion strength, up to 100 N in scratch critical load; and high-oxidation resistance were achieved, leading to excellent performance in high-speed milling on hardened tool steel at a speed of 260 m min−1. The results show that the tool life with this coating is improved by a factor of 4 or better under the testing conditions used compared to the uncoated tools. The surface finish of the machined steel achieved with this coating is also significantly better.
Stability of cerium oxide on silicon studied by x-ray photoelectron spectroscopy
Authors: Preisler E. J. , Marsh O. J. , Beach R. A. , McGill T. C.
Published: July 2002

The silicon–cerium oxide interface is studied using x-ray photoelectron spectroscopy. The oxidation and reduction of species at the interface are examined as a function of annealing temperature both in vacuum and oxygen ambient, in order to determine their relative stabilities. By depositing a very thin CeO2 film (∼30 Å), the cerium and silicon core level peaks can be monitored simultaneously. The presence of characteristic chemical shifts of the Si 2p peak gives information about any SiOx layer that may form at the interface. The oxidation state of the cerium can be probed from three different areas of the spectrum. From this information we can infer the oxidation state of both the silicon and the cerium. For the first time a complete picture of the interface is obtained. The implications of these findings on the utility of CeO2 in device applications are discussed.
Parametrization of optical properties of indium–tin–oxide thin films by spectroscopic ellipsometry: Substrate interfacial reactivity
Authors: Losurdo M. , Giangregorio M. , Capezzuto P. , Bruno G. , De Rosa R. , Roca F. , Summonte C. , Plá J. , Rizzoli R.
Published: July 2002

Indium–tin–oxide (ITO) films deposited by sputtering and e-gun evaporation on both transparent (Corning glass) and opaque (c-Si, c-Si/SiO2) substrates and in c-Si/a-Si:H/ITO heterostructures have been analyzed by spectroscopic ellipsometry (SE) in the range 1.5–5.0 eV. Taking the SE advantage of being applicable to absorbent substrate, ellipsometry is used to determine the spectra of the refractive index and extinction coefficient of the ITO films. The effect of the substrate surface on the ITO optical properties is focused and discussed. To this aim, a parametrized equation combining the Drude model, which considers the free-carrier response at the infrared end, and a double Lorentzian oscillator, which takes into account the interband transition contribution at the UV end, is used to model the ITO optical properties in the useful UV–visible range, whatever the substrate and deposition technique. Ellipsometric analysis is corroborated by sheet resistance measurements.
Photoresist Materials and Applications
Authors: Lussow R. O.
Published: July 2002

Photoresists can be classified as either positive resists or negative resists depending on their mode of interaction with light. With the exception of photomasking, the process handling considerations for these two classes are similar. Photoresist performance is highly dependent on processing techniques. Typical processing procedures are discussed along with process problems and performance limitations of currently available materials. General materials chemistry of typical photoresists is discussed, and possible photomechanisms, development mechanisms, and adhesion mechanisms are considered. Substrates to which a resist is applied introduce another variable for consideration when evaluating resist performance.
Composition of rf-sputtered refractory compounds determined by x-ray photoelectron spectroscopy
Authors: Wheeler Donald R. , Brainard William A.
Published: July 2002

rf-sputtered coatings of CrB2, MoSi2, Mo2C, TiC, and MoS2 were examined by x-ray photoelectron spectroscopy (XPS). Data on stoichiometry, impurity content, and chemical bonding were obtained. The influences of sputtering target history, deposition time, rf power level, and substrate bias were studied. Significant deviations from stoichiometry and high oxide levels were related to target outgassing. The effect of substrate bias depended on the particular coating material studied.
Effects of vacuum processing erbium dideuteride/ditritide films deposited on chromium underlays on copper substrates
Authors: Provo J. L.
Published: July 2002

Thin films of erbium dideuteride/ditritide have been experimentally produced on chromium underlays deposited on copper substrates. The chromium underlay is required to prevent erbium occluder/copper substrate alloying which inhibits hydriding. Data taken has shown that vacuum processing affects the erbium/chromium/copper interaction. With an in situ process in which underlay/occluder films are vacuum deposited onto copper substrates and hydrided with no air exposure between these steps, data indicates a minimum of 1500 Å of chromium is required for optimum hydriding. If films are vacuum deposited as above and air-exposed before hydriding, a minimum of 3000 Å of chromium was shown to be required for equivalent hydriding. Data suggests that the activation step (600°C for 1 h) required for hydriding the film of the second type is responsible for the difference observed. Such underlay thickness parameters are important, with regard to heat transfer consideration in thin film hydride targets used for neutron generation.
Surface point defects and Schottky barrier formation on ZnO(101̄0)
Authors: Göpel W. , Brillson L. J. , Brucker C. F.
Published: July 2002

We have created well-defined concentrations of surface point defects (oxygen vacancies, Vos) on ZnO(101̄0) surfaces under controlled UHV conditions and have tested their influence on Schottky barrier formation. ZnO(101̄0) with and without surface defects exhibit almost identical Schottky barrier features, independent of the evaporated metal. Surface work function and band bending variations with metal coverage are qualitatively different for Au vs Al interfaces, regardless of defect concentration. Barrier formation occurs relatively slowly for Au on ZnO, while Al on ZnO induces a pronounced dipole with the first half monolayer.
An approach to correct the proximity effect in electron beam proximity printing
Authors: Nehmiz P. , Bohlen H. , Greschner J. , Bretscher E. , Vettiger P.
Published: July 2002

Electron beam proximity printing employs shadow projection for submicron lithography. The pattern mask has physical holes for the transmitted electrons. The mask stencil problem (ring shaped apertures would fall out of these masks) is overcome by distributing the pattern to be printed on two complementary masks. The use of two complementary masks provides means to correct the proximity effect, known to impede micron resolution in electron beam lithography. To that end, for a shape in the first complementary mask a smaller correction shape in the second is introduced. The double dose deposited in the central position of the shape modifies the development process so that the proximity effect can be corrected. Experiments are reported which demonstrate the feasibility of this proximity correction method.
MOCVD growth of CdTe and HgCdTe
Authors: Schmit J. L.
Published: July 2002

This paper summarizes the status of MOCVD (metal–organic chemical vapor deposition) growth of CdTe and HgCdTe at several laboratories. The data are from publications and from the results of a questionnaire sent to approximately 34 laboratories. The growth of single-crystal HgTe, CdTe, and HgCdTe has been reported. CdTe is grown between 306 and 500 °C having hole concentrations approaching 1015 cm−3. HgCdTe is grown between 400 and 430 °C having electron concentrations as low as 4×1015 cm−3. RSRE (Royal Signals and Radar Establishment), Honeywell , Raytheon, and Rensselaer Polytechnic are using MOCVD for growth of CdTe and HgCdTe; two other organizations report that their work in this area is proprietary, and four organizations report plans to begin MOCVD growth soon. This paper has three sections covering (1) results of a worldwide survey, (2) published results (Cal Tech, RSRE, Raytheon, and Rensselaer), and (3) results of the Honeywell effort.
Metal polyimide interface: A titanium reaction mechanism
Authors: Ohuchi F. S. , Freilich S. C.
Published: July 2002

Chemical bonding and reaction of in situ deposited Ti on a series of polyimide surfaces have been investigated. X-ray photoelectron spectroscopy has been used to probe site specific information for bonding of various functional groups of polyimide molecules, while ultraviolet photoelectron spectroscopy has been applied to monitor the change of the Ti d bands and the polyimide molecular orbitals near the Fermi energy as a function of overlayer coverage. At low coverages, the polyimide surfaces react strongly with Ti and strong charge transfer via the carbonyl group occurs. As the coverage increases, a Ti–C bond formation has been identified. A detailed mechanism for the reaction of Ti with polyimides is described, and this mechanism is confirmed by model pyromellitimide reaction with Ti0 suspension in solution.
Charged particle fluxes from planar magnetron sputtering sources
Authors: Window B. , Savvides N.
Published: July 2002

We have investigated the charged particle fluxes from circular planar magnetrons with different magnetic field configurations and report measurements of the currents to earthed substrates, the substrate self-biasing voltages, the ion currents to substrates at −100 V, and deposition rates as functions of axial and radial positions with respect to the target. The magnetrons fall into two classes, whose characteristics are explained in terms of electron motion in inhomogeneous magnetic fields. Both low and high electron/ion bombardment of the growing film can be achieved by small alterations to the magnetic field configuration.
Modeling of reactive sputtering of compound materials
Authors: Berg S. , Blom H-O. , Larsson T. , Nender C.
Published: July 2002

An experimentally verified useful new model for reactive sputtering is presented. By considering the total system (target erosion, gas injection, chamber wall deposition, reactive gas gettering at all surfaces, etc.) during deposition it is possible to evaluate quite simple relationships between processing parameters. We have expanded earlier treatments to include these phenomena. The model involves that gettering of the reactive gas takes place at the target and at the walls opposite to the target. Arguments are also presented for how the sputtered materials (elemental target atoms and the formed compound) contribute to the formation of the surface composition of the walls opposite to the sputtering electrode. The mass flow of the reactive gas has been chosen as the independent parameter in this presentation. Results for partial pressure and sputter rate are presented. The theoretical values are compared with experimental results from reactive sputtering of TiN. It is also pointed out that the calculated values agree extremely well with results presented in the literature by several other authors.
A new technique for characterization of thin-film ferroelectric memory devices
Authors: Rohrer G. , Narayan S. , McMillan L. , Kulkarni A.
Published: July 2002

Pulse switching and hysteresis measurements are commonly employed to characterize thin-film ferroelectric materials. Capacitance–voltage (C–V) techniques have found wide applications in semiconductor technology to determine interface trap charge in silicon metal–oxide–semiconductor devices. C–V measurements made on potassium nitrate (KNO3 ) thin-film memory devices at high frequency (1 MHz) with slow ramp rates (200–2000 mV/s) are reported here for the first time. The C–V plots are integrated to determine the quantity of displaced charge during switching. These data are compared with the corresponding results from pulse and hysteresis measurements. The effect of ramp rate on the C–V measurements suggests mobile charge (ion) migration under bias. The fatigue problem in the device structures is explained by means of buildup of charge at KNO3 /contact interfaces during continuous switching.
Photo-metalorganic molecular-beam epitaxy: A new epitaxial growth technique
Authors: Tokumitsu Eisuke , Yamada Takumi , Konagai Makoto , Takahashi Kiyoshi
Published: July 2002

Metalorganic molecular-beam epitaxy (MOMBE) combines many important advantages of molecular-beam epitaxy and metalorganic chemical vapor deposition. One of the most important features of MOMBE is that photochemical reaction can be used and we can call this new technique ‘‘photo-MOMBE.’’ Triisobutylaluminum (TIBA) has been used in photo-MOMBE instead of triethylaluminum (TEA) as a new aluminum source in order to enhance the photodecomposition. The optical absorption coefficient of TIBA for 193 nm was found to be three times greater than that of TEA. Selective deposition of Al, AlAs, and GaAlAs was carried out by using an ArF excimer laser. The Al mole fraction of GaAlAs ternary alloy grown with the excimer laser irradiation was greater than that of the film grown without the laser irradiation.
Influence of conductor steps in passivation stress in magnetic bubble memory devices
Authors: Umezaki H. , Sato T. , Toyooka T. , Suzuki R.
Published: July 2002

Stress from the overlay passivation (sputtered SiO2) significantly degrades bubble propagation margins in ion-implanted bubble devices. The present work investigated the stress field from the passivation by computer simulations (boundary element method). In order to reduce the passivation stress, a buffer layer between the passivation and the conductors was investigated. The effects of two factors in the buffer layer have been discussed: (i) Young’s modulus of the buffer layer and (ii) a planarizing characteristic of the buffer layer. The simulation shows that changing Young’s modulus is not effective in reducing the passivation stress. On the other hand, a degree of planarization has a great relation with the passivation stress, i.e., the passivation stress decreases with increasing the planarization by the buffer layer. Therefore, we introduced the thermal-reflow-type polyimide which exhibits excellent planarization. The devices with this structure were fabricated and showed no influence from SiO2 passivation.
Copper oxide thin-film growth using an oxygen plasma source
Authors: Luzeau P. , Xu X. Z. , Laguës M. , Hess N. , Contour J. P. , Nanot M. , Queyroux F. , Touzeau M. , Pagnon D.
Published: July 2002

We present measurements of the oxidation level (Cu+ and Cu2+ concentration) of copper thin films deposited using a new type of oxygen plasma source. This oxygen plasma source is operated under ultrahigh vacuum, and allows one to oxidize copper up to nearly pure Cu2+ oxide at rather low temperature (<500 °C) and low molecular oxygen background pressure (2×10−6 Torr). High growth rate and high substrate temperature promote the formation of Cu+ oxide, whereas Cu2+ oxide is mainly obtained at low growth rate (0.5 Å s−1) and low substrate temperature (450 °C). The active species for oxidation is mostly atomic oxygen produced in the plasma. When the plasma is off, while the oxygen flux remains unchanged, no copper oxide is detected in the films.
Aluminum surface mobility on silicon nitride and on several silicon oxides
Authors: Levenson L. L. , Swartzlander A. B. , Yahashi A. , Usui H. , Yamada I.
Published: July 2002

This report concerns the measurement of Al atom surface mobility on various substrates during physical vapor and neutral cluster deposition. One objective is to determine Al surface mobility dependence on substrate type and temperature. Another objective is to compare Al diffusion distances produced by an effusive source and a cluster beam source. The experiment is done with a simple wire mask held on the substrates during Al deposition. During deposition, the substrates were held at constant temperatures between 80 and 400 °C. After the wire is removed, the shadowed areas are examined by optical and electron microscopy, mechanical profilometer, and Auger electron line scans. Measurements show that Al diffusion distances in the shadow zones are between 8 and 16 μm on oxidized Si films on Si substrates. The diffusion distance of Al on silicon nitride ranges from 20 to 25 μm. The diffusion distances of Al on all substrates can be understood in terms of the mean diffusion distance X=(2Dsτs)1/2, where Ds is the surface diffusion coefficient and τs is the mean time to desorption after Al atoms are deposited. These results show that on the micrometer scale the diffusion distance of Al atoms, while temperature and substrate dependent, is independent of the deposition method.
First-principles theory of the scanning tunneling microscopy simulation
Authors: Tsukada Masaru , Kobayashi Katsuyoshi , Ohnishi Shuhei
Published: July 2002

Method of theoretical simulations for the scanning tunneling microscopy/spectroscopy (STM/STS) are presented based on the nonempirical electronic state calculations of the tip and the sample surface. For the tunnel active protrusion on the tip, cluster models are used. Some examples of the STM image and the STS spectrum are reported for graphite and benzene molecule by the use of tip clusters W4, W5, W8, W10. Theoretical STS curve explains well the experimental results, if the width of the cluster levels is assumed larger than 1 eV. Abnormal STM images of graphite is found to be caused by interference effect of the tunnel current contributed by different atoms.
Effect of the radio-frequency voltage phase in a balanced triode plasma etching reactor
Authors: Thomas J. H. , Singh B.
Published: July 2002

The effect of the relative electrical phase applied to the two driven electrodes of a rf excited (13.56 MHz) triode plasma reactor has been investigated. Langmuir probe measurements, visible light emission, external voltage measurements, and CF4 and SF6/O2 etching of silicon were used to characterize the plasma formed by exciting the electrodes in phase and 180° out of phase. In-phase excitation does not result in the formation of a plasma between the plates. For 180° out-of-phase excitation, a plasma is formed and the intense glow regions observed next to their respective electrodes appear to originate from a region between the sheath and the plasma. The plasma potential, ion energy, and electron energy are strongly affected by phase. These initial results indicate the critical importance of the phase angle in determining the fundamental plasma parameters in triode plasma etchers and deposition reactors.
Detailed x-ray photoelectron spectroscopy valence band and core level studies of select metals oxidations
Authors: Barr Tery L. , Yin Mengping , Varma Shikha
Published: July 2002

The present study reports the use of monochromatic, high resolution x-ray photoelectron spectroscopy to investigate the evolution of the s and p bands of select metals, and the resulting O(2p) bands of their oxides as the process of oxidation (or reduction) sequentially occurs. Those metals in the groups I B, II B, III A, and IV A, with their relatively deep d bands, are of principal concern. Such questions as the uniformity (or lack thereof) of the movement of electron density between bands, and subband regions, have been explored. Correlations are also drawn between the changes experienced by the core and valence states. The progressive difference found for oxide formation throughout this region of the Periodic Table is considered. The unique property of Sidgwick inert s pairs is also investigated.
Electronic structure of K/Si(111) interfaces
Authors: Weitering H. H. , Chen J. , DiNardo N. J. , Plummer E. W.
Published: July 2002

Photoemission studies of the K/Si(111)7×7 and K/Si(111)(√3×√3)R30°-B interfaces show that both interfaces are semiconducting at room temperature saturation coverage. At both types of interfaces, a dispersionless K-induced surface state is observed below the Fermi level. We argue that these interfaces are correlated systems. We provide conclusive evidence that the onset of metallization and long-range conductivity occurs during the development of the second and third layers at cryogenic temperatures.
Surface cleaning with the carbon dioxide snow jet
Authors: Sherman Robert , Hirt Drew , Vane Ronald
Published: July 2002

Surface cleaning using a carbon dioxide snow jet incorporates a high-velocity stream of small dry ice particles and gas which is directed towards a contaminated surface. The resulting interactions between the snow particles and surface contamination lead to particulate and hydrocarbon removal. Past work has demonstrated removal of micron and submicron particles and also hydrocarbon and silicone-based stains from many different samples including Si, GaAs, InP wafers, metals, ceramics, UHV components, glass, optical components, and electronic devices. Several typical applications and examples are discussed along with the experimental parameters for effective carbon dioxide snow cleaning. The above results supports previous findings that carbon dioxide snow cleaning is nondestructive, nonabrasive, and residue-free, thus making this cleaning procedure acceptable for many critical cleaning applications.
Hyperthermal neutral beam etching
Authors: Giapis Konstantinos P. , Moore Teresa A. , Minton Timothy K.
Published: July 2002

A pulsed beam of hyperthermal fluorine atoms with an average translational energy of 4.8 eV has been used to demonstrate anisotropic etching of Si. For 1.4 Hz operation, a room-temperature etch rate of 300 Å/min for Si(100) has been measured at a distance of 30 cm from the source. A 14% undercutting for room-temperature etching of Novolac-masked Si features was achieved under single-collision conditions, with no detectable mask erosion. Translational energy and angular distributions of scattered fluorine atoms during steady-state etching of Si by a normal-incidence, collimated beam demonstrate that unreacted F atoms can scatter inelastically, retaining a significant fraction of their initial kinetic energies. The observed undercutting can be explained by secondary impingement of these high-energy F atoms, which are more reactive upon interaction with the sidewalls than would be expected if they desorbed from the surface at thermal energies after full accommodation. Time-of-flight distributions of volatile reaction products were also collected, and they show evidence for a dominant nonthermal reaction mechanism of the incident atoms with the surface in addition to a thermal reaction channel.
The design, performance, and application of an atomic force microscope-based profilometer
Authors: McEachern R. L. , Moore C. E. , Wallace R. J.
Published: July 2002

Rayleigh–Taylor instabilities during implosions of inertially confined fusion capsules affect capsule performance. During acceleration, surface imperfections grow and can, if large enough, lead to an asymmetric implosion or even shell breakup. For this reason, characterizing the topography of target capsules is extremely important. We have developed a profilometer based on an atomic force microscope combined with a precision rotary air bearing. Averaged one-dimensional (1D) surface height power spectra obtained with this instrument are converted to two-dimensional mode spectra that are used as input to hydrodynamic simulations. We describe the design of the system and its performance in terms of runout and repeatability. We also discuss the simulation of these measurements and the statistics involved in averaging 1D power spectra. Finally, we show the application of this measurement technique to capsules whose surfaces have been modified by laser ablation, resulting in a well-defined surface topography. This special case provides an excellent test for the system since the expected results are exactly calculable.
Surface functionalization of polymeric substrates from radio frequency-plasma-generated silylium ions
Authors: Hua Z. Q. , Denes F. , Young R. A.
Published: July 2002

The mechanism of rf-discharge-induced fragmentation of SiCl4 was studied by separating the components of the molecular mixture (GC-MS, HR-MS) resulting from the ex situ recombination of plasma-generated active species and by simulating the plasma-induced chemistry under low-energy electron mass spectroscopy conditions. It was found that SiCl+3 (silylium) ions and corresponding radicals were the predominant molecular fragments in the discharge; accompanied by small quantities of SiCl2- and SiCl-based species. Plasma origin SiClx active species were effectively implanted onto polypropylene, polyester, cellulose, and polytetrafluoroethylene surfaces and the modified relative surface atomic compositions were evaluated by photoelectron spectroscopy. Analytical data indicate that SiClx fragments can effectively replace H, OH, and even fluorine atoms on the polymeric structures. Surface characteristics like wettability and morphology of the plasma modified polymeric substrates were estimated by dynamic contact angle evaluation and atomic force microscopy. It was demonstrated that the surface modifications are reproducible and stable with time. Potential applications of SiCl4 plasma modified polymeric surfaces are suggested.
Very high frequency capacitively coupled discharges for large area processing
Authors: Meyyappan M. , Colgan M. J.
Published: July 2002

A two-dimensional fluid model is used to study the characteristics of a capacitively coupled discharge system at drive frequencies of 13.56–100 MHz. Results are presented for a large reactor that can accommodate 300 mm wafers. The plasma density and ion flux scale approximately as the square of the frequency at constant applied voltage which agrees well with measurements. The rf current, ionization rate, and sheath thickness also scale favorably with frequency. The simulations reveal that the plasma and ion characteristics are uniform across the electrode except near the edge.
Ion beam induced chemical vapor deposition procedure for the preparation of oxide thin films. II. Preparation and characterization of AlxTiyOz thin films
Authors: Leinen D. , Lassaletta G. , Fernández A. , Caballero A. , González-Elipe A. R. , Martín J. M. , Vacher B.
Published: July 2002

Aluminum titanate thin films were prepared by ion beam induced chemical vapor deposition (IBICVD). By this method it is possible to control the Al/Ti ratio in the film. Films with Al/Ti≂2 (i.e., a ratio similar to Al2TiO5) were characterized by scanning electron microscopy and transmission electron microscopy, x-ray photoelectron spectroscopy, electron energy loss spectroscopy at the electron microscope, and x-ray absorption spectroscopies. These techniques showed that after calcination the films are amorphous, although at T=823 K the local environment around the Ti and Al ions is very similar to that of these ions in a crystalline Al2TiO5 phase. At T≥1023 K the formation of a TiO2 phase shows that the aluminum titanate dissociates at this temperature into TiO2 and Al2O3. Reaction of the latter with the SiO2 substrate at T≥1523 gives a mullite phase. The optical quality of the aluminum titanate films was checked by ultraviolet-vis spectroscopy. After calcination, the aluminum titanate films prepared by IBICVD were very transparent. Those with a ratio Al/Ti=2.18 have a diffraction index n=1.9 and a band gap Eg=4.1 eV. These values and the absence of the characteristic absorption gap of TiO2 support the formation of a mixed AlxTiyOz phase.
Growth of SiC and SiCxNy films by pulsed laser ablation of SiC in Ar and N2 environments
Authors: Soto G. , Samano E. C. , Machorro R. , Cota L.
Published: July 2002

Amorphous SiC and SiCxNy films have been deposited by pulsed laser deposition on single crystal silicon substrates by KrF (248 nm) excimer laser ablation of a SiC sintered target in a vacuum system at room temperature using nonreactive, Ar, and reactive, N2, background gases at different pressures. The pressure range in the growth chamber was from 4×10−8 Torr to 80 mTorr. The optical properties and stoichiometry of films were varied by the introduction of a background gas. The resulting films are inspected by spectroellipsometry in the photon-energy range of 1.5<hv<5.0 eV. In situ high resolution x-ray photoemission spectroscopy characterization was performed on every film to obtain the atomic concentration and bonding constitution of the elements as a function of background gas pressure. The ideal stoichiometry for SiC films was obtained at Ar pressures higher than 30 mT. The existence of a new phase, given by SiCN2, was suggested from surface techniques and ellipsometric data in the deposition of SiCxNy films at N2 pressures higher than 30 mTorr.
Molecular beam epitaxy and interface reactions of layered GaSe growth on sapphire (0001)
Authors: Chegwidden Scott , Dai Zurong , Olmstead Marjorie A. , Ohuchi Fumio S.
Published: July 2002

We have investigated the growth of GaSe, a layered semiconductor, on single crystal Al2O3(0001)(sapphire), an ionic crystal. We have used reflection high energy electron diffraction, x-ray photoelectron spectroscopy, and transmission electron microscopy and diffraction to study the growth, interface reaction, and resultant film structure. When a clean, heated (T=620 °C) sapphire substrate is exposed to Ga and Se from a compound GaSe source (Ga2Se and Se2) and a separate uncracked Se source (Sex, x∼6), a polycrystalline film is formed with stoichiometry close to that of cubic Ga2Se3. After annealing to 1100 °C, the film evaporates, leaving a reacted interface layer containing both Ga and Se. Subsequent deposition on this reacted surface under the same conditions leads to growth of 500–1000 Å grains of layered GaSe, which have their c axis normal to the substrate surface but random orientation parallel to the substrate. A mechanism is proposed that describes the formation of the interface layer and its effect on the subsequent growth of GaSe.
Ge(001):B gas-source molecular beam epitaxy: B surface segregation, hydrogen desorption, and film growth kinetics
Authors: Kim H. , Greene J. E.
Published: July 2002

Ultrahigh B-doped Ge(001) layers, with concentrations CB up to 8×1021 cm−3, were grown by gas-source molecular beam epitaxy from Ge2H6 and B2H6 at temperatures Ts=325 °C (in the surface-reaction-limited regime) and 600 °C (in the flux-limited regime). The samples were quenched, D site exchanged for H, and D2 temperature-programed desorption (TPD) used to determine B coverages θB as a function of CB and Ts by comparison with B-adsorbed Ge(001) reference samples with known θB values. During Ge(001):B film growth, strong surface B segregation to the second layer was observed with surface-to-bulk B concentration ratios ranging up to 6000. The TPD spectra exhibited α2 and α1 peaks associated with dideuteride and monodeuteride desorption as well as lower-temperature B-induced α2* and α1* peaks associated with deuterium desorption from Ge* surface atoms with B backbonds. Increasing θB expanded the area under α2* and α1* at the expense of α2 and α1 and decreased the total D coverage θD. The TPD results were used to determine the B segregation enthalpy, −0.64 eV, and to explain and model the effects of high B coverages on Ge(001) growth kinetics. At Ts=325 °C, where B segregation is kinetically hindered, film deposition rates RGe are not a strong function of CB, exhibiting only a small decrease at CB≳5×1018 cm−3. However, at Ts=600 °C, RGe decreases by up to 40% with increasing CB≳1×1018 cm−3. This is due primarily to the combination of B-induced Ge dimer vacancies and the deactivation of surface dangling bonds caused by charge transfer to Ge–B backbonds. Calculated RGe(CB,Ts) curves, based upon equilibrium segregation, exhibit very good agreement with deposition rate data at Ts=600 °C and overestimate the effect of B on RGe at 325 °C.
Characteristics of silicon removal by fine focused gallium ion beam
Authors: Yamaguchi H. , Shimase A. , Haraichi S. , Miyauchi T.
Published: July 2002

A 30 kV fine focused ion beam machining system was constructed in which a Ga ion beam extracted from a needle-type liquid metal source is focused into a submicron spot by a three-electrode electrostatic lens and deflected by an octapole deflector. Vacuum rate at the work stage is 10−7–10−8 Torr. With blanking electrodes, the machined area can be confined to any rectangular area determined by the cursol lines on the scanning ion microscopic display. Probe current is higher than 0.3 nA for a 0.3 μm diam spot and current density is over 0.71 A/cm2. At a scanning speed of 100 μm/s, grooves 0.2 μm wide are made in a gold film 0.1 μm thick. By scanning repeatedly, a groove is produced in a (100)Si wafer yielding a cross section having a very sharp V shape with an aspect ratio of 8:1. Two-dimensional scanning removal is performed under various conditions at the same dose of 1.9×1018 ion/cm2, resulting in very different hole shapes. Removal at a scanning speed of 1 mm/s with 200 repetitions produces a uniform shallow hole shape, while removal at 5 μm/s with one repetition results in an inclined deep hole shape. Observation of the cross section shows that this inclined area protrudes from the side wall of the hole, formed through the redeposition of sputtered silicon. These results show the importance of the redeposition process in removal utilizing fine focused ion beams. Also, the differing results of two scanning methods appear to demonstrate the nonlinear sputter effect in fine focused ion beam machining.
High-resolution electron-beam induced deposition
Authors: Koops H. W. P. , Weiel R. , Kern D. P. , Baum T. H.
Published: July 2002

A finely focused electron beam is used as a source of energy to decompose molecules, e.g., organometallics or hydrocarbons, adsorbed on the surface of a substrate. Films deposited by these means can be used as etch mask for reactive ion etching, as an absorber for various types of radiation, or directly as part of a device structure. A vector scan electron beam system with a LaB6 cathode has been equipped with a temperature controlled reservoir to supply vapors into a differentially pumped sample chamber. The substrate is mounted on a stage which can be cooled or heated in the range of −40 to +110 °C. The ability to utilize backscattered electron micro- scopy is maintained. Area, line, and spot deposition rates have been measured for tungsten hexacarbonyl [W(CO)6] and dimethyl–gold–trifluoro–acetylacetonate [Me2Au(tfac)] at various fluxes, sample temperatures, and current densities. Three-dimensional buildup of tips and free standing lines across holes in membranes and resolution better than 0.25 μm have been achieved. The composition of the deposited films has been analyzed and each deposit is rich in metal and carbon. Tungsten rich deposits can be used as a highly selective etch mask for oxygen plasmas. Effects limiting the ultimate resolution, such as backscattering from the substrate, and scattering from the deposited material are discussed.
Manganese oxide microswitch for electronic memory based on neural networks
Authors: Ramesham R. , Daud T. , Moopenn A. , Thakoor A. P. , Khanna S. K.
Published: July 2002

High-density, nonvolatile, associative electronic memories based on neural network models require large arrays of highly uniform, small area, resistive connections (synapses). Such passive, two terminal resistors (very weak connections, 105 to 106 Ω for a 1000×1000 matrix) are uncommon in the current very large scale integration (VLSI) technology. We report on a solid-state, resistance tailorable, programmable-once, binary, nonvolatile memory switch based on manganese oxide (MnOx) thin films. MnOx exhibits irreversible memory switching from a conducting (on) to an insulating (off) state, with the off to on resistance ratio of greater than 104. The switching mechanism is current triggered chemical transformation of a conductive MnO2−Δ to an insulating Mn2O3 state. The energy required for the ‘‘switching’’ is of the order of 4 to 20 nJ/μm2. Apart from the high density information storage in such MnOx microswitch arrays as programmable read only memory (PROM), the ‘‘tailorable MnOx fusible links’’ may also be suited for post-fabrication, ‘‘function-specific programming’’ of microcircuit architectures.
A novel method for the growth of good quality GaAs at extremely low substrate temperatures (as low as 120 °C)
Authors: Tadayon Bijan , Tadayon Saied , Zhu J. G. , Spencer M. G. , Harris G. L. , Griffin J. , Eastman L. F.
Published: July 2002

In this work, a novel method for the growth of good quality GaAs at extremely low substrate temperatures (as low as 120 °C) is introduced. This novel method is based on three different methods: The migration-enhanced epitaxy method, the indium doping method, and the low growth rate method. The good quality of the GaAs layers are confirmed by Raman spectroscopy, 4 K photoluminescence, and transmission electron microscopy. This novel growth method results in the best GaAs material ever grown at 120 °C by any growth method using a molecular beam epitaxy machine.