bluuebunny/crossref_metadata_2025 huggingface dataset:
Linearization and temperature compensation up to one atmosphere for the spinning rotor gauge
Authors: Lindenau B. E. , Fremerey J. K.
Published: July 2002

While the deceleration-versus-pressure characteristic of the spinning rotor gauge (SRG) shows excellent proportionality under molecular flow conditions, strong deviations built up at the viscous flow regime. By linearization of the SRG characteristic and on-line thermal correction of the gas parameters entering the SRG pressure evaluation procedure an accuracy of 5% has been achieved for a variety of common gases under viscous flow conditions. For the thermal correction the new system comprises an ohmic temperature sensor attached to the rotor chamber. The linear pressure range of the SRG now extends from 1 μPa up to 1 atm (11 decades). Furthermore, the system is well suited for determination of the gas viscosity and its thermal increment.
As-sputtered electrochromic films of nickel oxide
Authors: Wruck D. A. , Dixon M. A. , Rubin M. , Bogy S. N.
Published: July 2002

Electrochromic nickel oxide films were deposited by radio-frequency magnetron sputtering of a Ni target in gas mixtures of Ar and O2. When electrochemically cycled in 0.1 N KOH solution, large reversible changes in visible absorption were obtained within the first 10 bleach/color cycles. Films which showed the greatest changes in optical properties and charge capacity were produced within a narrow range of oxygen flow rates. The coloration efficiency was found to be insensitive to the sputtering conditions and stoichiometry, with a value of 34±4 cm2C−1 at 550 nm. This indicates that microstructure and charge capacity determine the absorption coefficient. The reaction rate was found to depend on the concentration of OH− in the electrolyte, indicating that OH− diffusion in the electrolyte limits the rate of reaction.
Surface chemistry of catalyst preparation studied by using flat alumina model supports
Authors: Borg H. J. , van den Oetelaar L. C. A. , van Ijzendoorn L. J. , Niemantsverdriet J. W.
Published: July 2002

Rhodium on alumina model catalysts have been made by using a flat, electrically conducting support consisting of a thin film of aluminum oxide on an aluminum foil. Rhodium was applied in the same way as is usual in the preparation of powder catalysts, by adsorption from an aqueous solution of rhodium (III) chloride. The catalysts were studied with monochromatic x-ray photoelectron spectroscopy (XPS), static secondary ion mass spectrometry (SIMS), and Rutherford backscattering spectrometry (RBS). Because the systems have electrical conductivity, XPS spectra of high resolution are obtained while informative molecular clusters of the type RhCl− and RhO−n appear in static SIMS. Angle-dependent XPS spectra of Rh and Al yield an effective layer thickness of Rh, as well as the extent to which the support is covered. RBS indicates that the Rh concentration is in the order of 1015 atoms/cm2.
Effect of sulfur on oxygen adsorption and oxidation of the Ni(111) surface
Authors: Liu Jun , Lu J. P. , Chu P. W. , Blakely J. M.
Published: July 2002

The effect of sulfur (S) on oxygen chemisorption and the initial stages of oxidation of the Ni(111) crystal surface have been studied with Auger electron spectroscopy, low-energy electron diffraction, and x-ray photoelectron spectroscopy at room temperature under ultrahigh vacuum conditions. It is found that sulfur strongly retards the oxygen adsorption kinetics, but does not change the oxidation mechanism. The initial chemisorption sticking coefficient (s) is found to follow the relationship s ∝ (1 − 3θs)2, where θs is the S coverage. Oxidation of S precovered surfaces can be described fairly well by an island growth model; the decrease in oxidation rate, relative to that of the S-free surface, can be attributed to the reduction in the density of oxide nuclei. Some experimental observations indicate that the oxide layer is partially removed by S at 440 K. Sulfur is believed to remain at the Ni/NiO interface during oxidation.
TiOx film formation process by reactive sputtering
Authors: Kinbara A. , Kusano E. , Baba S.
Published: July 2002

TiOx thin films were prepared by the sputtering of Ti atoms from a Ti target in a discharge gas including Ar and O2. O2 partial pressure during the sputtering was measured as a function of O2 gas flow rate introduced into the sputtering chamber. The pressure was found to increase linearly with the flow rate except for a region related with the sputtering mode change. In order to interpret the pressure change, a simple model for metal thin film formation was modified and applied. Fundamental relations expressing time change of the number density of Ti atoms and O2 molecules on a substrate surface were derived. Two-dimensional (2D) motion of Ti atoms on the substrate was taken into account and 2D mean free path of those atoms was calculated. The collision frequency of Ti atoms with O2 molecules was then estimated and the rate of consumption (gettering) of O2 molecules was evaluated. It was found that the number density of Ti atoms on the substrate is one of the main factors determining the gettering effect. The observed change of the O2 partial pressure with its flow rate can well be interpreted by our model. Deposition rate of TiOx thin films was also measured as a function of O2 flow rate and the results were consistent with our gettering model.
X-ray photoelectron spectroscopy study of surface layers on orthopaedic alloys. II. Co–Cr–Mo (ASTM F-75) alloy
Authors: Lewis Gladius
Published: July 2002

The differences and similarities between the compositional details of the layer formed on the surface of a Co–Cr–Mo alloy specimen when exposed for 1 h to laboratory air or wet steam are identified. An estimate of the thickness of each of these layers is also obtained.
Using Fourier transform infrared absorption spectrometry to probe the injected neutral gas in a plasma having a high ionization fraction
Authors: Goeckner M. J. , Breun R. A.
Published: July 2002

Knowledge of the neutral gas composition in a discharge is important for understanding the chemical processes involved in both etching and deposition environments. We have performed a test to see if Fourier-transform infrared (FTIR) absorption spectrometry can be used to measure the density of the injected neutral gas in a plasma having a high ionization fraction (≥1%). The results from the test are compared to results [R. L. McClain, Ph.D. thesis, Department of Chemistry and Engineering Research Center for Plasma-Aided Manufacturing, University of Wisconsin–Madison, 1991 (unpublished)] found with an IR diode laser. For this measurement, using a FTIR spectrometer represents a major improvement over using an IR diode laser, in terms of both cost and time. Finally, we discuss methods that one should employ to improve the signal-to-noise ratio when using FTIR spectrometry for similar measurements. If one employs these methods, then one should be able to use FTIR spectrometers to accurately monitor neutral gas densities in low-pressure high-plasma density discharges.
Nucleation and growth in metal-on-metal homoepitaxy: Rate equations, simulations and experiments
Authors: Evans J. W. , Bartelt M. C.
Published: July 2002

We illustrate the utility of the ‘‘mean-field’’ rate equation treatment of nucleation and growth with critical size i≥1 for both isotropic and strongly anisotropic diffusion. Some comparison is made of rate equation predictions for mean densities and size distributions of stable islands with predictions from ‘‘exact’’ simulations for the low coverage precoalescence regime. We also consider island separation distributions, depletion effects, and associated splitting of kinematic diffraction profiles. We necessarily treat other issues via simulations. These include analysis of (i) transitions in island shape from compact to dendritic, as observed for Pt/Pt(111), and extraction of associated edge diffusion barriers; and (ii) adlayer percolation, which sometimes mediates the population of higher layers. We also briefly comment on nucleation and growth behavior in the specific systems M/M(100) with M=Fe, Pd, Au, Cu, Ni, and Ag.
Performance of an ionization gauge with a large-angle ion deflector. II. Mass analysis of residual gas and electron stimulated desorption ions*
Authors: Satou T. , Oshima C.
Published: July 2002

Time of flight (TOF) mass analysis has been applied to residual gas in extreme high vacuum. By a combination of energy analysis with TOF measurement through the deflector, we have separated the molecular species of gas-phase ions from the electron stimulated desorption (ESD) ions generated at the ionization grid. Only H2 molecules are detected for the gas-phase ions at 10−10 Pa, while H+, H+2, O+, and other molecules are observed for the ESD ions. The outgassing from the instrument was negligible under the present experimental conditions.
Neuronal cells cultured on modified microelectronic device surfaces
Authors: Offenhäusser Andreas , Rühe Jürgen , Knoll Wolfgang
Published: July 2002

The recording of the electrical activity of a large number of neurons in tissue culture over a period of weeks or even months should be very helpful in the understanding of the development and function of biological neuronal networks. Ideally, a method for the detection of the changes in interacellular voltage in such a system should have both high spatial and temporal resolution. One approach could be to record with a fixed electrode array built into the floor of the tissue culture chamber. We have chosen to detect the electrical signal of the neuron by direct coupling with a field effect transistor. Such a coupling is the first step toward multisite recording in neuronal nets and the development of a neuronal network. On a microelectronic device surface it is necessary, to control adhesion and outgrowth of neurons on a microscopic scale. To achieve biocompatibility the chemical composition of the surfaces of such devices has to be modified. Our approach to control the chemical architecture at the interface is to attach ultrathin polymer films to the device surface by using a novel ‘‘grafting from’’ procedure. It can be shown that the chemical composition of the interface can be tuned in such a way that Purkinje neurons show good adhesion to such a surface and survive and grow on it for weeks.
The early stages of ruthenium oxidation
Authors: Hrbek J. , van Campen D. G. , Malik I. J.
Published: July 2002

The interaction of atomic oxygen with a Ru(001) surface was studied using x-ray photoelectron spectroscopy, thermal desorption, and electron diffraction. The onset of the reaction of dissolved oxygen with the Ru host starts only for equivalent oxygen coverages higher than 50 monolayers (ML). A new Ru 3d core level shifted by 0.7 eV toward higher binding energy grows with increasing atomic oxygen exposure. Further weak features 1.5 and 2.6 eV above the metallic Ru 3d binding energy appear for higher oxygen coverages. The O 1s peak shows additional components at higher binding energy than that of chemisorbed oxygen. At the highest coverage studied (880 ML), almost all the Ru metal within the probing depth is oxidized.
Low-temperature diamond growth in a pulsed microwave plasma
Authors: Ring Zoltan , Mantei Thomas D. , Tlali Spirit , Jackson Howard E.
Published: July 2002

Polycrystalline diamond films have been synthesized at backside substrate temperatures down to 300 °C in a low-pressure CH4–H2–O2 microwave plasma. Diamond growth at low substrate temperatures was greatly assisted by magnetic field discharge activation and by pulse modulation of the input microwave power. Diamond films grown at backside substrate temperatures of 300–500 °C exhibit characteristic 1333 cm−1 Raman phonon peaks with linewidths of 5.7–3.1 cm−1, while scanning electron micrographs show clearly defined crystallites. The nondiamond carbon content of the films remains low for temperatures down to 350 °C, as estimated from the broad peak of the Raman spectra around 1550 cm−1.
Large area radio frequency plasma for microelectronics processing
Authors: Yu Z. , Shaw D. , Gonzales P. , Collins G. J.
Published: July 2002

Radio-frequency (rf) inductively coupled planar plasma (ICP) provides a better way to generate spatially confined high density gas discharge plasmas for microelectronics processing. Commercial processing equipment using this technique is currently available, but is limited in size to 20 cm in diameter by problems with plasma uniformity and antenna dielectric window erosion. We have developed a new planar ICP antenna and dielectric window design that allows for larger dimensions (up to 50 cm in diameter) with good uniformity. The current art ICP antenna requires a thick quartz (or ceramic) plate vacuum window to separate the rf inductor and the plasma. The larger the antenna diameter the thicker the dielectric. The thick dielectric reduces inductive coupling efficiency. The large area coil and associated matching network can introduce plasma uniformity problems. Our device incorporates both the rf inductor and the dielectric window inside the vacuum chamber, allowing space for a thin layer of quartz or other dielectric material. Thus, the dielectric window design is only focused on materials for the given process chemistry to be placed between the coil and the excited plasma, rather than also including mechanical strength to hold a vacuum over a wide area. This thin dielectric layer with our newly designed planar coil coupler allows the plasma to be scaled to a 50 cm diameter while maintaining radial uniformity. In this article we report only plasma ashing results for a 20 cm planar ICP device that shows 2% nonuniformity across 15 cm wafers. The measured flux of atomic oxygen and atomic hydrogen generated by a larger planar ICP scale device is also presented.
Aging of photochemical vapor deposited silicon oxide thin films
Authors: Parada E. G. , González P. , Pou J. , Serra J. , Fernández D. , León B. , Pérez-Amor M.
Published: July 2002

Further development of the microelectronic technology requires the growing of stable and passivated dielectric thin films. Photochemical processes are very promising methods to obtain silicon dioxide films for microelectronic purposes. In this article, the aging of silicon oxide films obtained by ArF laser chemical vapor deposition at low temperature is studied. The evolution of the properties of films has been followed up using infrared spectroscopy and ellipsometry, and compared with aging of thermally oxidized silica films. The role of moisture in film aging is also clarified by comparing films exposed to humid and to dry atmospheres. Si–OH groups are incorporated into the film in a specific local bonding environment and relaxation in the film structure takes place while new Si–O groups can be created. Moreover, the dependence of the stability of film properties on the processing parameters is analyzed.
Power dissipation and impedance measurements in radio-frequency discharges
Authors: Spiliopoulos N. , Mataras D. , Rapakoulias D. E.
Published: July 2002

An improved method for the measurement of the power consumed in low pressure, radio frequency discharges is presented. The method involves the measurement of current and voltage waveforms outside the reactor, and the determination of the discharge impedance and the network of parasitics. The measured waveforms are transformed to the equivalent ones at the powered electrode, by using an electrical circuit model of the stray impedance of the cell, with experimentally determined components. A tunable shunt circuit is used for minimizing displacement currents. The equivalent circuit contains elements which account also for resistive power losses in the cell-shunt circuit. The obtained discharge power is compared with measurements of the total power output of the generator made by a power meter. Results concerning power consumption and impedance in argon and silane discharges are presented as a function of the excitation voltage and the pressure. In both cases there is a discharge impedance drop, for higher voltage or pressure, which leads to higher power consumption in the discharge. The measurements show that only a small, nonconstant part of the power is consumed in the discharge, whereas, the inclusion of resistive loses leads to more accurate results. The mechanisms of the discharge impedance drop are further discussed in terms of their relation to microscopic plasma phenomena and quantities.
Global model for high pressure electronegative radio-frequency discharges
Authors: Lee Y. T. , Lieberman M. A. , Lichtenberg A. J. , Bose F. , Baltes H. , Patrick R.
Published: July 2002

We develop a global model for high pressure (0.1–1 Torr) electronegative rf discharges and apply it to model a capacitively driven plasma etcher. The molecular gases considered consist of either pure chlorine species or a mixture of chlorine and helium species. The charged and neutral heavy particle densities together with the electron density and electron temperature are calculated by using the equations of particle balance and power balance for the input discharge parameters rf power or rf current, inlet pressure, gas flow rates, reactor diameter, and gap spacing. The power is deposited in the electrons via ohmic heating and in those ions accelerated across the dc sheath potential. The voltage across the sheath is calculated self-consistently with the densities and the electron temperature by using a collisional Child law sheath model. Analytic scaling laws for the dependence of charged and neutral particle densities, electron temperature, rf voltage and current, sheath width, and plasma impedance on pressure and absorbed rf power are presented and used to explain the numerical results obtained from the global model. The model results are compared to recent experimental measurements in a chlorine discharge over a range of absorbed power Pabs=20–180 W at an inlet pressure pin=0.4 Torr and a range of pressure 0.1–1.6 Torr with a fixed input power of 100 W. We obtain reasonable agreement for Pabs<200 W and for 0.2 Torr<pin<1 Torr.
Pd, Cu, and Au particles on Al2O3 thin films: An infrared reflection absorption spectroscopy study of monometallic and bimetallic planar model supported catalysts
Authors: Rainer D. R. , Xu C. , Holmblad P. M. , Goodman D. W.
Published: July 2002

The chemisorptive behavior of CO on several planar model monometallic and bimetallic Pd, Cu, and Au catalysts supported on thin film Al2O3 has been investigated using infrared reflection absorption spectroscopy (IRAS). For Pd and Cu monometallic catalysts, CO adsorption spectra indicate a high representation of low index planes, while the morphologies of smaller particles are characterized more by high densities of low coordinated step/edge defect sites. For Au particles, CO was observed to be present on the surface at conditions where low index Au single crystals have been observed to be inactive for CO adsorption, indicating the modified chemisorptive properties at step/edge sites. For the IRAS studies of supported Pd–Au and Pd–Cu catalysts, no conclusive indications of ligand effects were apparent in the CO stretching frequencies. The spectra for the bimetallics resemble combinations of both analogous monometallic catalysts, even though a significant degree of metal mixing is apparent from thermally induced changes in the IRAS, and from previous ion scattering spectroscopy studies. A peak possibly attributable to Pd diluted in the surface by the presence of a dissimilar metal is apparent for each of these bimetallic supported catalysts.
Effect of reactor size on plasma polymerization of perfluoropropene
Authors: Kim H. Y. , Yasuda H. K.
Published: July 2002

Effects of the reactor size on the deposition characteristics and the chemical structure of deposited polymers during the plasma polymerization of perfluoropropene were investigated. A 132 cm long glass tube with a diameter of 1.8, 3.3, or 4.7 cm was chosen for a small, medium, or large reactor, respectively. Plasma was formed by a capacitively coupled 13.56 MHz rf power generator. Deposition rate profiles along the reactor tube showed that the dependence of the deposition rate on the operating conditions depended on the reactor size. As the size (diameter) of a tubular reactor decreases, the dissipation of energy to the reactor wall increases since the surface to volume ratio of a tubular reactor increases. Therefore, the plasma polymerization domain changes from the monomer deficient to the energy deficient domain as the reactor size decreases under the same (externally controllable) operating conditions. Electron spectroscopy for chemical analysis was used to analyze the chemical composition and structures of deposited polymers. The chemical composition and structures were varied depending on the reactor size which were also due to the change of the plasma polymerization domain. The plasma polymers prepared in the monomer deficient domain showed a similar composition and structures regardless of the reactor size or the operating conditions. Generally, large amounts of CF3 and CF2 groups were present in the polymer prepared in the monomer deficient domain, and the F/C ratios were approximately 1.6. As the W/FM (energy input per unit mass of monomer) value decreased to the energy deficient domain, the composition and the structures were changed sensitively but following a complicated pattern according to the change of operating conditions.
Real-time ultraviolet ellipsometry monitoring of gate patterning in a high-density plasma
Authors: Vallon S. , Joubert O. , Vallier L. , Ferrieu F. , Drévillon B. , Blayo N.
Published: July 2002

The use of in situ diagnostic tools, allowing real-time control during plasma-processing steps, may become a key issue in designing robust processes and reducing costs for the next generations of integrated circuits. Real-time ellipsometry is capable of monitoring the growth and the etching of various materials, but its use has generally been restricted to unpatterned areas. In this study, we focus on the monitoring of polysilicon and poly SiGe gate patterning using real-time ellipsometry in the ultraviolet. It is shown that the same characteristic signature is obtained at the end of the polysilicon etching in unpatterned and low pattern-density areas. The analysis of this signature reveals the presence of a perturbed layer at the surface of polysilicon during etching. In addition, whatever the nature of the etched materials, the mask layout, and the underlying topography, ellipsometric real-time traces can be used for process end pointing and control.
Nanometer-scale structure of hectorite–aniline intercalates
Authors: Porter Timothy L. , Thompson D. , Bradley M. , Eastman Michael P. , Hagerman Michael E. , Attuso Jennifer L. , Votava Amy E. , Bain Edlin D.
Published: July 2002

The inclusion of the organic guest aniline into Cu(II)-exchanged hectorite thin films has been investigated. The subsequent polymerization of aniline on the clay surface and in the intergallery regions are studied using scanning force microscopy (SFM), electron paramagnetic resonance (EPR) spectroscopy, powder x-ray diffraction (XRD), and impedance spectroscopy. EPR and XRD data show that in addition to strong polymerization of aniline on the clay surface, polymerization also occurs in the intergallery regions of the clay. Using standard lift-off techniques or razor cleaving, the exposed intergallery polyaniline is successfully imaged for the first time using noncontract SFM in phase-contrast mode. The nearly two-dimensional polymer sheets formed in these regions exhibit none of the nanometer-scale grain or bundle structure commonly associated with polyaniline synthesized using techniques such as electrochemical or vacuum deposition. The electrical response of the resulting clay-conducting polymer composites is also investigated for thin films fabricated on 15 μm interdigitated arrays. Preliminary results indicate that these composite materials may be highly suitable as chemical sensors for a variety of important gases and vapors such as ethanol and hexane.
Adhesion improvement of plasma-deposited silica thin films on stainless steel substrate studied by x-ray photoemission spectroscopy and in situ infrared ellipsometry
Authors: Bertrand N. , Drévillon B. , Gheorghiu A. , Sénémaud C. , Martinu L. , Klemberg-Sapieha J. E.
Published: July 2002

Adhesion of plasma-deposited SiO2 on stainless steel is shown to be enhanced after Ar, N2, and NH3 plasma pretreatments of the substrate. Adhesion is related to the chemical bonding at the interface. Therefore, it is studied by x-ray photoemission spectroscopy (XPS) and in situ IR ellipsometry performed on very thin films (≈30 Å thick). IR ellipsometry reveals the removal of adsorbed hydrocarbons on the metallic surface by all plasma treatments. XPS measurements show the removal of NOx species, related to the sample electropolishing, using N2 and NH3 plasmas; in contrast, Ar has practically no effect in this case. Plasma-induced modifications are not limited to surface cleaning. Some nitrogen is incorporated in the substrate after N2 and NH3 plasmas. In particular, nitrogen is found bonded to Si and to Cr after NH3 and N2 treatments, respectively, we interpret the adhesion enhancement by hardening of the substrate surface region in the case of N2 plasma, while, in the case of NH3, it may be related to the formation of silicon nitride. Cr–N–Si linkages between the substrate and the film may also contribute to adhesion improvement. We also observed changes in the early stages of the film growth. A higher sticking coefficient of dissociated species on the surface is revealed after plasma pretreatment. Narrowing of the Si 2p peak in XPS spectra observed in pretreated samples is attributed to a better ordered SiO2 structure at Si sites in terms of bond angles and/or lengths. In contrast, both IR ellipsometry and XPS show no change at O sites.
Iridium thin films deposited by radio-frequency magnetron sputtering
Authors: El Khakani M. A. , Chaker M. , Le Drogoff B.
Published: July 2002

Deposition of metallic iridium thin films has been achieved by sputtering an Ir target with argon. The deposition of the Ir films was investigated at argon gas pressures in the (10–40) mTorr range with various rf power densities. The stress, resistivity, and structure of the Ir films were systematically determined as a function of both the Ar pressure and the rf power density. While all the deposited Ir films are polycrystalline with a preferred (111) orientation, not only their stress but also their resistivity were found to be particularly sensitive to the Ar gas pressure. As for many sputtered metal thin films, the stress of Ir films, deposited at a power density of 5 W/cm2, drastically changes from highly compressive (−2 GPa) to highly tensile (+1.2 GPa) in a relatively narrow range of Ar pressure (10.5–25.5 mTorr). Likewise, the room-temperature resistivity of Ir sputtered films changes by a factor of about 5 when the Ar pressure is increased from 22.8 to 36.0 mTorr. Deposition conditions yielding Ir films which combine the lowest resistivity (17 μΩ cm) and very low stress levels (few tens of MPa) are identified. Finally, it is established that the stress of Ir films scaled linearly with the lattice-parameter dilatation of the (111) preponderant phase.
New perspectives in vacuum high voltage insulation. I. The transition to field emission
Authors: Diamond William T.
Published: July 2002

Vacuum high-voltage insulation has been investigated for many years. Typically, electrical breakdown occurs between two broad-area electrodes at electric fields 100–1000 times lower than the breakdown field (about 5000 MV/m) between a well-prepared point cathode and a broad-area anode. Explanations of the large differences remain unsatisfactory, usually evoking field emission from small projections on the cathode that are subject to higher peak fields. The field emission then produces secondary effects that lead to breakdown. This article provides a significant resolution to this long standing problem. Field emission is not present at all fields, but typically starts after some process occurs at the cathode surface. Three effects have been identified that produce the transition to field emission: work function changes; mechanical changes produced by the strong electrical forces on the electrode surfaces; and gas desorption from the anode with sufficient density to support an avalanche discharge. Material adsorbed on the cathode surface increases the work function of the metal, leading to a much higher threshold for field emission and higher breakdown fields. Localized regions of lower work function can be produced on the cathode by the transfer of microparticles from the anode and by stripping small areas of the cathode. The regions of low work function then serve as the source of enhanced field emission, leading to secondary effects which produce breakdown. Gas desorption is produced at an unconditioned anode as the voltage is increased. None of these effects are significant for a point cathode opposite a broad-area anode, but account for much of the large difference between microscopic and macroscopic breakdown fields. Careful surface preparation of electrodes increases the work function and reduces the number of weakly bound microparticles. Experiments designed to optimize these two different effects have led to electric fields as high as 90 MV/m at a 1 mm gap and 50 MV/m at a 4 mm gap, with no measurable field emission with plane-parallel electrodes made from copper, aluminum, titanium, and niobium. These fields, with no field emission or sparks during the conditioning phase, are comparable to the highest fields ever reached between plane-parallel electrodes of the same gap by any traditional conditioning method. The experimental results have been applied to operation of the electrostatic deflector of the Chalk River superconducting cyclotron. It has been used reliably for thousands of hours at fields up to 15 MV/m at a 5 mm gap, usually with no field emission. Experiments have also demonstrated that there is little enhancement in field emission at gaps up to 4 mm and that the only total-voltage effect for these gaps is from reduced thermal stability of the anode as the power density from the electrons increases with increasing voltage.
Thickness distribution in pulsed laser deposited PZT films
Authors: Tyunina M. , Wittborn J. , Björmander C. , Rao K. V.
Published: July 2002

The two-dimensional spatial distribution of the thickness of pulsed laser deposited lead zirconate titanate films has been studied experimentally as a function of the laser characteristics and ambient oxygen pressure. The profiles obtained in vacuum are in agreement with a model of adiabatic expansion of the plume with an adiabatic index of the vapor γ=5/3 and initial height of the plume 10−2 mm. An increase in the growth rate and nonmonotonic “broadening” of the profiles of the films found with increasing oxygen pressure is shown to correlate well with the change in the sorption kinetics on the substrate surface.
Effects of ion pretreatments on the nucleation of silicon on silicon dioxide
Authors: Basa C. , Hu Y. Z. , Tinani M. , Irene E. A.
Published: July 2002

Low energy ion pretreatment of silicon dioxide (SiO2) surfaces results in a reduced incubation time (tinc) for polycrystalline silicon (poly-Si) deposition by rapid thermal chemical vapor deposition. By pretreating SiO2 surfaces with inert (He+, Ar+) and chemically active species (H+, N+), it was determined that ion pretreatments reduce tinc and increase the poly-Si nuclei density by creating nucleation sites via a physical damage mechanism, rather than a chemical process.
Color, structure, and properties of TiN coatings prepared by plasma enhanced chemical vapor deposition
Authors: Nah Jae-Woong , Kim Byoung-June , Lee Dong-Kak , Lee Jung-Joong
Published: July 2002

TiN coatings were deposited onto M2 high speed steels by the plasma enhanced chemical vapor deposition process using a gas mixture of TiCl4, NH3, H2 and Ar at various NH3/TiCl4 flow rate ratios [Q(NH3)/Q(TiCl4)]. Coatings of gold color with high hardness, high elastic modulus, and low resistivity could be formed at low flow rate ratios. At higher ratios, on the other hand, brown colored coatings with considerably decreased microhardness and elastic modulus were formed. By structural and compositional analyses, as well as by observing the surface morphology of the coatings, factors which are known to affect the color of TiN coatings have been examined. Brown coatings showed a porous microstructure and possessed a great amount of oxygen compared to gold ones. However, the main factor for the color change seems to be the surface roughness of the coatings rather than the presence of oxygen or the N/Ti ratio.
Growth of Hf and HfN on GaN by molecular beam epitaxy
Authors: Parkhomovsky A. , Ishaug B. E. , Dabiran A. M. , Cohen P. I.
Published: July 2002

Hf and HfN thin films were grown on n-type GaN(0001̄) by molecular beam epitaxy using a custom built Hf electron beam source and an ammonia leak. The films were characterized by reflection high-energy electron diffraction (RHEED) and atomic force microscopy. It was found that epitaxial growth of Hf is possible even at room temperature. GaN films varying in thickness from 0.6 to 1.8 μm were grown on c-plane sapphire, using ammonia as a precursor, to serve as substrates. Then the films were annealed in ammonia as the temperature was lowered in order to produce a N termination. Hf was then deposited on top of the GaN at temperatures between 20 and 730 °C, both with and without ammonia incident on the sample. Deposition of pure Hf at room temperature revealed an epitaxial two-dimensional (2D) (although with some three-dimensional character) RHEED pattern with sixfold symmetry. The surface is reconstructed with a (2×2) R30° structure. We propose that the pattern is rotated 30° with respect to that of the substrate GaN because of a HfN interlayer between the GaN and Hf layers. When the films were annealed in vacuum up to 730 °C, the 2D pattern became more transmission like. If Hf was deposited at substrate temperatures of 350 °C and higher, a diffraction pattern corresponding to that of a polycrystalline material was observed.
Comparison of morphology and interfacial composition of Pd ultrathin films on 6H–SiC and 4H–SiC at different annealing temperatures
Authors: Lu W. J. , Shi D. T. , Burger A. , Collins W. E.
Published: July 2002

Pd/SiC Schottky diode has been applied as a chemical sensor for hydrogen and hydrocarbon gases at high temperatures. The diffusion and interfacial reactions between the metal thin film and SiC substrate are known to alter the electrical properties of the device. In this work, the morphology and interfacial composition of Pd ultrathin films on 6H–SiC and 4H–SiC are investigated after thermal annealing using atomic force microscopy and x-ray photoelectron spectroscopy. The Pd ultrathin films of about 3 nm thickness are deposited by radio frequency sputtering. The SiC substrates are 3.5° tilted, Si-face, and n-type, 6H–SiC and 4H–SiC, and the Pd thin film deposition and annealing conditions are identical for both samples. The samples are annealed consecutively from 100 to 600 °C in air for 30 min. The Pd ultrathin film on 6H–SiC and 4H–SiC has a good uniformity as deposited, and there are no significant morphological changes for either sample at the low annealing temperatures. At 300 °C, a nanofeatured layer and Pd2Si were formed on both samples. The irregularly shaped cracks on the Pd nanofeatured layer are observed on 4H–SiC substrate, while the Pd on 6H–SiC exhibits a uniform nanofeatured layer. The interaction between Pd and 4H–SiC is more enhanced than between Pd and 6H–SiC. At 500 and 600 °C, Pd on both 4H–SiC and 6H–SiC substrates becomes nanosize clusters. Pd2Si reacted with SiC to form PdSi at 500 °C for Pd/4H–SiC, and at 600 °C for Pd/6H–SiC. The surface composition and morphology of Pd/6H–SiC and Pd/4H–SiC are almost identical after annealing at 600 °C. The Schottky barrier heights are 1.4 and 1.7 eV for Pd as deposited on 6H–SiC and 4H–SiC, respectively. No significant changes in Schottky barrier height are found on either Pd/6H–SiC or Pd/4H–SiC after annealing.
Heat transfer in ultrahigh vacuum scanning thermal microscopy
Authors: Müller-Hirsch W. , Kraft A. , Hirsch M. T. , Parisi J. , Kittel A.
Published: July 2002

We report investigations of the heat transfer in scanning tunneling microscopy and scanning thermal microscopy under ultrahigh vacuum conditions. The distance dependence of the heat transfer is found to increase significantly for tip-sample distances smaller than several 10 nm, indicating the existence of a proximity effect in heat transfer between tip and sample. Upon scanning the thermal probe over the sample, topographic features of the sample can be clearly seen in the thermal image with down to 10 nm size.
Quantum-dot cellular automata
Authors: Snider G. L. , Orlov A. O. , Amlani I. , Zuo X. , Bernstein G. H. , Lent C. S. , Merz J. L. , Porod W.
Published: July 2002

An introduction to the operation of quantum-dot cellular automata (QCA) is presented, along with recent experimental results. QCA is a transistorless computation paradigm that addresses the issues of device density and interconnection. The basic building blocks of the QCA architecture, such as AND, OR, and NOT are presented. The experimental device is a four-dot QCA cell with two electrometers. The dots are metal islands, which are coupled by capacitors and tunnel junctions. An improved design of the cell is presented in which all four dots of the cell are coupled by tunnel junctions. A noninvasive electrometer is presented which improves the sensitivity and linearity of dot potential measurements. The operation of this basic cell is confirmed by an externally controlled polarization change of the cell.
Current-induced nanochemistry: Local oxidation of thin metal films
Authors: Martel R. , Schmidt T. , Sandstrom R. L. , Avouris Ph.
Published: July 2002

A novel method is introduced for oxidizing thin metal films with nanometer-scale resolution. Simply by subjecting Ti and Nb films to local current densities of 107 A/cm2, metal-oxide tunneling barriers of 10–50 nm width can be fabricated in a self-limiting fashion. The high spatial resolution of the process results from its strongly nonlinear dependence on the current density. Our experiments suggest that the oxidation involves current-induced atomic rearrangements and local heating. At the final stages of the barrier formation, when only atomic-scale channels remain unoxidized, the oxidation rate decreases drastically while the conductance drops in steps of about 2e2/h. This behavior gives evidence of ballistic transport and of the superior stability of such metallic nanowires against current-induced forces compared with that of the bulk metal. Finally, we show that current-induced local oxidation is a valuable process for the fabrication of novel nanoelectronic devices. As an example, we prepared a single electron transistor that exhibits a Coulomb staircase at room temperature.
Work function modification of indium–tin–oxide used in organic light emitting devices
Authors: Tadayyon S. M. , Griffiths K. , Norton P. R. , Tripp C. , Popovic Z.
Published: July 2002

We report measurements on the modification of the work function (WF) of indium–tin–oxide (ITO) by deposition of Au and Pt overlayers, chosen because of their high WF and inertness. ITO films on glass substrates (resistance∼10 Ω/sq) were cleaned with an ultraviolet (UV)–ozone treatment before entry into an ultrahigh vacuum system. Auger electron spectroscopy was used to determine the surface composition. The change of WF of the surface (±10 mV) was determined by a Kelvin probe technique and correlated with the absolute coverage (in the range 0<θ<2×1016 Au(Pt) cm−2 calibrated by Rutherford backscattering). The topography of the films was determined by atomic force microscopy. The original ITO surface contains grains of about 50–60 nm in size. Initially, low coverages of gold atoms fill the “valleys” between the bumps formed by ITO grains. UV–ozone cleaned surfaces exhibited the highest WF. Surprisingly, in sequential Au deposition experiments, the WF decreased to a minimum at ∼1×1015 Au cm−2 before increasing again and becoming constant at θ>5×1015 Au cm−2. The final WF values were not very different from the non-UV–ozone treated samples. Studies on bulk Au and ITO covered by Au in a single deposition, showed that the low final WF value in the sequential experiments was attributable to adsorption of hydrocarbons from the 1×10−10 Torr vacuum, and that useful increases in WF are attainable on ITO electrodes with gold layers which are thin enough to cause no obvious change in ITO’s transparency (⩽10%). A similar trend was observed for the Pt layer but with less sensitivity to hydrocarbon adsorption.
Radio frequency reactive sputter etching—control of etch rates
Authors: Horwitz Chris M.
Published: July 2002

Etch rate variability in a reactive sputter-etching process can come from many factors, and here the etching of SiO2 in CHF3 is used in a study of the effects of various parameters on the etch rate, although other materials are also considered. It is found that this SiO2/CHF3 combination is remarkably insensitive to chamber pump-out time and the initial chamber condition, at least at high applied rf voltages (1.5 kV peak to peak). However, the gas pressure, flow rate, applied rf voltage, and the target electrode configuration do have a strong effect on rates. This latter result is shown to agree with presently available data on the capacitance of sputtering glow discharges. An etch rate reproducibility of ±2% over a period of four months has been demonstrated.
PMMA electron resists with narrow molecular weight distribution
Authors: Deckman H. W. , Dunsmuir J. H.
Published: July 2002

Narrow molecular weight distribution (M̄w/M̄n<1.1) poly (methyl methyacrylate) [PMMA] with low molecular weight (M̄w<200 000) has been evaluated as an electron resist. It is shown that sensitivity and contrast of these narrow distribution resists can be altered by prebaking either above or below the glass transition temperature. Sensitivity of narrow distribution PMMA resists prebaked below the glass transition temperature (Tg) can be a factor of 5 greater than the same resist prebaked above Tg . Sensitivity improvement is shown to be caused by solvent trapped in the network of narrow distribution resists prebaked below Tg . Trapped solvent preswells the polymer network so that small perturbations to the molecular weight distribution of the PMMA cause it to become soluble in developer. Low molecular weight broad distribution resists similarly prepared are readily soluble in the developer and do not exhibit improved sensitivity in usable lithographic images. When narrowly fractionated PMMA is baked above Tg, the sensitivity is found to be slightly different from broad distribution material, and the contrast is significantly improved. Electron beam exposure of these narrow distribution PMMA resists baked below and above Tg has produced 2000 and 800 Å period gratings, respectively.
Atomic-resolution studies of surface dynamics by electron microscopy
Authors: Smith David J.
Published: July 2002

High resolution electron microscopy (HREM) has been applied to the characterization of surfaces and surface rearrangements using the profile imaging method. This review paper outlines the basic principles of the technique and then surveys the recent atomic-level observations of metal, semiconductor, and oxide particle surfaces. Advantages and possible drawbacks of the technique are briefly discussed.
Ohmic contacts to n-type GaAs
Authors: Boudville W. J. , McGill T. C.
Published: July 2002

We present a model of the metal–semiconductor junction, for heavily doped GaAs, so that tunneling dominates the current. It is assumed that the imaginary part of the wave vector in the semiconductor is given by the two-band model. Modifications in the barrier potential due to image charge, negative charge near the interface, and the degenerate doping of the semiconductor are included. The role of the L-point minimum in the GaAs in determining the position of the Fermi level in the semiconductor is included. The energy distribution of the conductance as a function of doping and barrier height is given. The contact resistance as a function of doping and barrier height is also presented. The results suggest that previous calculations are substantially in error due to the simple models that were used for the dependence of the imaginary part of the wave vector on energy.
Theoretical investigation of the effect of strain on phase separation in epitaxial layers
Authors: Zur A. , McGill T. C.
Published: July 2002

We have theoretically investigated the phenomenon of alloy clustering in epitaxial films and, in particular, the case of AlxGa1−xAs grown epitaxially on GaAs. We show in the general case that the elastic strain in the film, caused by the finite mismatch between the lattice parameters of the film and the substrate, may change the miscibility properties of the film. A miscibility gap could be opened in the material composing the film, even if there is no such gap in the bulk material. Conversely, the strain could stabilize a solid solution in the film in cases where there is a miscibility gap in the bulk material of which the film is composed. We estimate that these effects are too small to account for phase separation in the case of AlxGa1−xAs on GaAs, but could be important in other systems, such as In(As, Sb).
Properties of Cd1−xMnxTe–CdTe superlattices grown by molecular beam epitaxy
Authors: Bicknell R. N. , Giles-Taylor N. C. , Blanks D. K. , Yanka R. W. , Buckland E. L. , Schetzina J. F.
Published: July 2002

Single-crystal multilayers of the dilute magnetic semiconductor Cd1−xMnxTe alternating with CdTe have been successfully grown for the first time by MBE. Experimental techniques used to prepare the various superlattice samples are described. Results of x-ray diffraction and photoluminescence film characterization experiments are also discussed.
Ruthenium-induced surface states on n-GaAs surfaces
Authors: Ludwig Matthias , Heymann Günter , Janietz Peter
Published: July 2002

Studies were conducted to investigate the properties of the Ru–GaAs interface. An analysis was made of two sets of experimental findings, namely the distribution of surface states of GaAs covered by submonolayers of ruthenium, as well as of electrical measurements on Ru–GaAs contacts. It was found for the present case that a deep state near Et≊0.3 eV above valence band maximum is induced at the surface. Thus the influence of the intrinsic defects is at least compensated. Using a simple model, it was investigated to which degree surface states and their energy would govern the barrier height. It was further studied how Fermi level pinning depends on the doping concentration of the semiconductor.
Magnetic field extraction of secondary electrons for accurate integrated circuit voltage measurement
Authors: Garth S. C. J. , Nixon W. C. , Spicer D. F.
Published: July 2002

A detector for electron beam waveform measurement on operating integrated circuits is presented. The detector has been designed to minimize the effects of local electric fields on voltage measurements. Waveforms have been measured to 2% accuracy on lines with 0.5-μ spacings. In addition, quantitative waveforms have been measured through insulating passivation layers.