bluuebunny/crossref_metadata_2025 huggingface dataset:
Properties of TiCN coatings prepared by magnetron sputtering
Authors: Deng Jianguo , Braun Manuel , Gudowska Irena
Published: July 2002

TiCN coatings were deposited onto AISI 420 substrates by a magnetron sputtering technique using a reactive gaseous mixture of methane and nitrogen. The structure and composition of the coatings have been analyzed by x-ray diffraction and Rutherford backscattering spectrometry. In addition, the microhardness, friction coefficient, and wear behavior of the coatings were also measured. The influence of deposition parameters on the characteristics of the coatings has been investigated. The experimental results show that the TiCN coatings exhibit a strong (111) or (200) preferred orientation. The maximum hardness of the coating is about 3648 kg mm−2. Adhesion of the coating is excellent. The maximum scratch test critical load is about 8.2 kg. The characteristics of wear resistance for the TiCN coatings are also excellent in comparison with either pure TiN or TiC coatings.
Causes of nonstability and nonreproducibility in widely used Bayard–Alpert ionization gauges
Authors: Bills D. G.
Published: July 2002

This is the second in a set of related reports on (1) nonstable behavior of widely used ionization gauges, (2) causes of nonstability and nonreproducibility in widely used Bayard–Alpert (BA) gauges, and (3) a stable and reproducible BA gauge design with approximately a tenfold improvement in both stability of gauge calibration and reproducibility gauge-to-gauge compared to older ionization gauge designs. Computer simulations of electron and ion trajectories are utilized to illustrate a variety of causes of changes in BA gauge sensitivity with time of operation and in reproducibility gauge-to-gauge. Both computer simulation and experiment confirm that the ion production and collection rates in a BA gauge are far more sensitive to small changes in electrode geometry and potentials than has been commonly realized. Any change in geometry or potential of any electrode or insulator in the vicinity of electron or ion trajectories will affect gauge sensitivity as will any change in electron or ion space charge. Changes in the distribution of emission along the cathode will affect sensitivity if large axial field components are present in the anode volume. If these physical changes occur from gauge to gauge, the sensitivity of the gauges will differ, and this will cause them to give different pressure indications when exposed to the same actual gas density. If the changes occur with time of operation in a given gauge, the gauge sensitivity will change with use and the pressure indication will be in error even if the gauge has been carefully calibrated. This new understanding has been used to develop a significantly more stable and reproducible BA gauge.
Correlation between the surface configurations and hydrogenolysis: Aniline on the Pt(111) surface
Authors: Huang Sean X. , Fischer Daniel A. , Gland John L.
Published: July 2002

A correlation has been developed between the structure of adsorbed reaction intermediates and their hydrogenolysis reactivity for aniline in hydrogen pressures up to 0.001 Torr on the Pt(111) surface. The composition and orientation of the species involved in aniline hydrogenolysis were characterized using temperature programmed reaction (TPR) and near edge x-ray absorption fine structure (NEXAFS) measurements. The benzene and ammonia formed by aniline hydrogenolysis during TPR on the Pt(111) surface increase substantially in the presence of hydrogen atmospheres. At reaction temperatures, the aromatic ring in aniline remains parallel to the surface in the presence of coadsorbed hydrogen, while in the absence of hydrogen the aromatic ring is tilted relative to the surface. This correlation between orientation and reactivity suggests that a parallel configuration may facilitate hydrogenolysis of the C–N bond in aniline. These in situ studies provide new insight into the structure of surface intermediates which may play a critical role in the mechanisms of aniline hydrogenolysis on the Pt(111) surface in 0.001 Torr of hydrogen.
Diamond-like carbon films grown using a saddle field source
Authors: Panwar O. S. , Sarangi D. , Kumar Sushil , Dixit P. N. , Bhattacharyya R.
Published: July 2002

This article reports the measurement of deposition rate, dark conductivity versus temperature, optical band gap, refractive index, extinction coefficient, hardness, adhesion, and internal stress of diamond-like carbon (DLC) films grown by aspirating hydrocarbon gases (CH4 and C2H2) and C6H6 vapors into a saddle field source. The source operates at 0.7–1.0 kV in the pressure range of 1.0×10−4–7.0×10−4 Torr and is of a modular design to cover increasingly larger areas. DLC films have been grown for the first time using CH4 by this technique. The effect of source to substrate distance on the deposition rate and uniformity of the films has been studied at varying power to the source using C2H2 gas. The films are found to be hard and they adhere well to 7059 glass, quartz, silicon, Mo, and Mylar substrates. Though the deposition rate increases with increasing power and with increasing carbon to hydrogen ratio of the hydrocarbon feedstock, the material properties are relatively independent of the type of hydrocarbon used.
Importance of the surface oxide layer in the reduction of outgassing from stainless steels
Authors: Ishikawa Yuichi , Yoshimura Toshihiko
Published: July 2002

Temperature dependence of outgassing was measured for differently surface treated type 316L stainless steel chambers in the temperature range of 25–330 °C. Based on the temperature dependence and outgassing characteristics of major outgassing species, the mechanism of outgassing from the stainless steel surface is discussed and the technique to produce an extremely low outgassing surface is indicated. The following are the important findings. (1) At temperatures below 250 °C, the outgassing species is predominantly hydrogen, which is released by diffusive outgassing from the bulk of the stainless steel. (2) At temperatures above 250 °C, the contribution from water and carbon monoxide outgassing becomes significant because of the enhanced surface reaction to generate these gas species. (3) The surface oxide layer formed by the oxidation in air is predominantly iron oxide and appears to serve as a more effective diffusion barrier for hydrogen outgassing compared with the mixed iron and chromium oxide layer formed on the fully degassed surface. (4) The oxidation reduces carbon contaminants on the surface which are a possible source of carbon containing outgassing species.
Characterization of substrate temperature and damage in diamond growth plasmas by multichannel spectroellipsometry
Authors: Wakagi M. , Hong Byungyou , Nguyen Hien V. , Collins R. W. , Drawl W. , Messier R.
Published: July 2002

The growth of diamond thin films in enhanced chemical vapor deposition (CVD) processes requires high substrate temperatures (400–1000 °C) and gas pressures (1 Torr to 1 atm), as well as high-power excitation of the gas source (e.g., 1 kW microwave plasma). Thus determining the substrate temperature in this severe environment is a challenge. The issue is a critical one since substrate temperature is a key parameter for understanding and optimizing diamond film growth. We have developed and utilized methods for precise (∼±5 °C) Si substrate temperature calibration based on rapid-scanning spectroscopic ellipsometry. In this approach the E1 critical point energy in Si is used to deduce the temperature of the top ∼200 Å of the substrate. In addition, the broadening parameter associated with the critical point transitions can provide information on near-surface plasma damage. As an application of the temperature calibration, we have measured the kinetics of diamond film growth by the microwave plasma-enhanced CVD process.
Probing reactive deposition and surface dynamics using in situ, real-time emission microscopy
Authors: Kordesch Martin E.
Published: July 2002

Emission microscopy images of surface processes during chemical vapor deposition and catalytic reactions show a number of dynamic reaction phenomena that illustrate problems suitable for observation with the emission microscope: nucleation and growth of adsorbed layers, adsorbate controlled diffusion from the bulk, pattern formation, melting and evaporation. A qualitative examination of deposit morphology is made and is compared to the formation of Liesegang rings.
Thermal stability of silver in ion-exchanged soda lime glasses
Authors: Wang Paul W.
Published: July 2002

X-ray photoelectron spectroscopy was used to study the thermal stability of silver in ion-exchanged sodium calcium silicate glasses during heat treatment in ultrahigh vacuum. The changes in concentration, in line shape, and in binding energy as functions of sample temperature show that silver diffuses toward the surface and the chemical structure of the sample surface changes. Judging from a comparison of the line shapes and the binding energies of the samples to those of pure silver and silica, the concentration variations in bridging and nonbridging oxygens, and the binding energy shifts of nonbridging oxygens, it is concluded that the SiO2 glass network starts breaking up during Ag+ diffusion at sample temperatures below 200 °C, metallic silver clusters form, and nonbridging oxygens originally surrounded by silver atoms reconnect to silicon atoms at sample temperatures above 200 °C. The relaxation of surface stress introduced by the exchange process and the net reduction of Gibbs free energy cause the surface diffusion and segregation of silver and the reconnection between oxygen and silicon. The estimated activation energy of the silver surface diffusion is 0.16 eV.
Wave propagation and damping in plasma crystals
Authors: Zuzic Milenko , Thomas Hubertus M. , Morfill Gregor E.
Published: July 2002

Wave propagation through plasma crystals provides an interesting experimental approach towards understanding strongly coupled plasmas as well as certain solid state properties of crystals. In order to build up our basic understanding of conditions and processes, oscillation modes of one- and two-particle systems are investigated first, and the damping process is identified by studying the amplitude variations of the oscillations as a function of the excitation frequency. Next, single layer plasma crystals are investigated using the same techniques. An induced spontaneous transition from the solid to the gas phase is observed, and its possible origin is discussed.
Solid/liquid/gaseous phase transitions in plasma crystals
Authors: Thomas Hubertus M. , Morfill Gregor E.
Published: July 2002

We present further observations of the solid/liquid and liquid/gaseous phase transition in plasma crystals. Plasma crystal is the term used to describe the recently discovered ‘‘state’’ that a colloidal plasma may assume under certain conditions—a state which has properties resembling those of metals. During the melting transition from solid to liquid the system passes through an intermediate ‘‘flow and floe’’ stage that has not been observed in other model crystals before. It may well be that this intermediate stage is a general feature of the solid/liquid phase transition in crystals. In this case it is clearly important. The fact that this stage could be detected for the first time is a consequence of the unique properties of plasma crystals: global charge neutrality, very fast response and little damping, easy experimental control, detailed imaging, and fine time resolution of the dynamics of individual particles (‘‘atoms’’).
Correlation between gas phase composition of rf plasma of argon diluted tetraethylgermanium and chemical structure of therewith deposited Ge/C films
Authors: Gazicki M. , Szymanowski H. , Tyczkowski J. , Schalko J. , Olcaytug F.
Published: July 2002

Quadrupole mass spectrometry (QMS) and optical emission spectroscopy (OES) have been applied to the characterization of rf plasma of tetraethylgermanium-argon mixture. QMS analysis shows that under low power input conditions, when organogermanium plasma polymer films are deposited, the gas phase consists primarily of monomer molecules and their largest fragments. In contrast, at high power input, under conditions of hydrogenated germanium/carbon alloy film formation, tetraethylgermanium undergoes nearly complete fragmentation forming atomic germanium, atomic and molecular hydrogen, and a number of hydrocarbon species. A dramatic increase of molecular hydrogen concentration with the increasing rf power is confirmed by OES actinometric measurements. Strong dependence of atomic hydrogen concentration in the gas phase on rf power supports the concept of the formation of Ge–H bonding in the films via saturation of germanium dangling bond with hydrogen and, therefore, provides an argument to the hypothesis of a competition between Ge–H and Ge–O bond formation.
Preparation of transparent and conductive In2O3–ZnO films by radio frequency magnetron sputtering
Authors: Minami Tadatsugu , Kakumu Toshikazu , Takata Shinzo
Published: July 2002

Highly transparent and conductive In2O3–ZnO films have been prepared by rf magnetron sputtering using targets composed of In2O3 and ZnO. Polycrystalline Zn2In2O5 films were deposited at a substrate temperature of 350 °C using targets with a Zn content [Zn/(Zn+In)] of about 10–60 at. %. A uniform spatial resistivity distribution on the substrate surface was obtained even in Zn2In2O5 films deposited at room temperature. A resistivity of 3.4×10−4 Ω cm was obtained in Sn-doped Zn2In2O5 films deposited at 350 °C. A sheet resistance of 400 Ω/sq and an average transmittance above 90% in the visible range were obtained for an undoped Zn2In2O5 film with a thickness of about 20 nm. The etching rate of In2O3–ZnO films when using HCl as the etchant could be controlled by the Zn content in the films.
Formation of electrically conductive nitrogen-doped amorphous hydrogenated carbon (diamond-like carbon) films by the supermagnetron plasma chemical vapor deposition method
Authors: Kinoshita Haruhisa , Yamauchi Atsushi
Published: July 2002

Using a supermagnetron plasma apparatus, electrically conductive amorphous hydrogenated carbon (a-C:H) films were formed at wafer temperatures below 60 °C. CH4/N2 mixed gas was introduced into the discharge chamber and nitrogen-doped a-C:H films were formed on thermally oxidized Si wafers. A high electrical conductivity of 1.02×10−4 Ω cm−1 was obtained at a N2 concentration of 25%, a gas pressure of 50 mTorr, and a radio-frequency power of 600 W. Measured film growth rate and microhardness were 160 nm/min and 1650 kg/mm2, respectively. Nitrogen inclusion in a film was confirmed by secondary-ion-mass spectroscopy, and its atomic concentration was measured to be about 4×1022 atoms/cm3.
Characterization of carbon nitride produced by high-current vacuum arc deposition
Authors: Hartmann J. , Siemroth P. , Schultrich B. , Rauschenbach B.
Published: July 2002

Carbon nitride thin films were deposited using the high-current arc (HCA) evaporation technique varying the pressure in the chamber and the position of the samples with respect to the evaporation source. At direct deposition the nitrogen content in the films measured by elastic recoil detection analysis saturates at an atomic ratio of 0.18 due to chemical sputtering. At positions where the substrates are shaded from the carbon plasma by the sample holder the nitrogen content increases up to 48 at. %. This observation can be explained by a decreased energy of the carbon ions, a higher arrival ratio of nitrogen to carbon ions and the high degree of ionization using the HCA technique. Varying the sample position the binding character of nitrogen to carbon atoms in the films changes from sp3 to sp2. When the energy of the deposited particles is reduced graphitic clusters are formed in an amorphous matrix.
Photoluminescence and photoreflectance studies of defects in GaAs epitaxial layers grown by liquid phase epitaxy at different supercooling temperatures
Authors: Torres-Delgado G. , Mendoza-Alvarez J. G. , Vazquez-Lopez C. , Alejo-Armenta C.
Published: July 2002

The defect formation during the growth of intrinsic GaAs epitaxial layers grown by the liquid phase epitaxy technique using supercooled melts has been studied through the optical characterization of the layers using the low temperature photoluminescence (PL) and the photoreflectance (PR) spectroscopies. Different degrees of supercooling in the range ΔT: 0–15 °C were used to grow several GaAs layers. It was found that for growth temperatures (Tg) around the equilibrium temperature (Teq∼804 °C), the PL spectra showed a strong exciton peak and emission bands related to the presence of C and Si impurities; and no low-energy defect-related bands were detected. As soon as Tg falls a few degrees below Teq(ΔT⩾2 °C), an emission band centered around 855 nm appears in the PL spectra whose intensity increases as ΔT does. The corresponding PR spectra for the different samples present Franz–Keldysh oscillations which were analyzed under the intermediate-electric-field regime and showed that, as ΔT increases, there is a monotonic increase in the density of ionized impurities, in agreement with the results from the PL spectra. We have identified this defect as the cation antisite double acceptor GaAs which is produced as a result of the increase in the density of As vacancies when the supercooling parameter increases. Results on the dependence of the ratio of the peak intensities between the exciton and the other impurity-related bands are presented and discussed.
Structural transition of Fe and Co sublayers in Fe/Zr and Co/Zr multilayered films investigated by magneto-optical spectroscopy
Authors: Kudryavtsev Y. V. , Kucherenko A. Y. , Dubowik J. , Smardz L. , Lee Y. P.
Published: July 2002

The experimental and computer-simulation study of the magneto-optical properties (equatorial Kerr effect) of Fe/Zr and Co/Zr multilayered films was carried out. Drastic changes in the magneto-optical properties of the Fe/Zr and Co/Zr multilayered films were observed with the ferromagnetic sublayers that had less than the critical thickness. Such a behavior is connected with a polycrystalline–amorphous transformation in these sublayers. An annealing of the multilayered film led to a significant increase in the equatorial Kerr effect value which is caused by a partial crystallization of the amorphous Fe or Co sublayers. The real interface structures of the Fe/Zr and Co/Zr multilayered films were estimated by a fitting procedure between the experimental and the computer-simulated equatorial Kerr effect spectra of the multilayered films.
Atomistic simulations of organic thin film deposition through hyperthermal cluster impacts
Authors: Qi Lifeng , Sinnott Susan B.
Published: July 2002

Atomistic simulations have been used to study thin film growth through the impact of energetic acetylene molecular clusters with three nonrigid, diamond (111) surfaces in vacuum. The surfaces considered include clean, bare-carbon diamond (111), clean hydrogen-terminated diamond (111), and hydrogen-terminated diamond (111) partially covered by a hydrocarbon film. The velocities considered are in the hyperthermal region (corresponding to external kinetic energies of about 20 eV/molecule) and are comparable to those that can trigger shock-induced chemistry in energetic materials. The collision caused the molecules in the cluster to undergo addition chemistry with other cluster molecules and/or with the surface resulting in thin film growth. We discuss the effect of surface reactivity on the products of the collision, including the resulting thin film morphology.
Synthesis of diamond using a low pressure, radio frequency, inductively coupled plasma
Authors: Noda Hideyuki , Nagai Hisao , Shimakura Masao , Hiramatsu Mineo , Nawata Masahito
Published: July 2002

Diamond was successfully synthesized using a low pressure, radio frequency (rf), inductively coupled plasma. A source mixture of methanol (CH3OH), hydrogen (H2), and water vapor (H2O) was introduced into a reaction chamber through a quartz tube of 12 mm inner diameter. A seven-turn rf coil was mounted on the quartz tube to produce high-density plasma. The Si substrate was located in a downstream region. Diamond formation was carried out with varying mixture ratio of source gases at total pressures of 70–140 mTorr. Diamond crystals exhibiting a well-defined 1332 cm−1 diamond Raman peak can be formed using CH3OH/H2/H2O mixtures at total pressures below 140 mTorr.
III–V surface plasma nitridation: A challenge for III–V nitride epigrowth
Authors: Losurdo M. , Capezzuto P. , Bruno G. , Leo G. , Irene E. A.
Published: July 2002

GaAs (001), GaP (001), and InP (001) surfaces were exposed to N2 and N2–H2 plasmas in order to investigate the substrate nitridation process. In situ real time ellipsometry was used to assess the nitridation self-limiting kinetics. Ex situ x-ray photoelectron spectroscopy and atomic force microscopy fingerprint the surface composition and morphology, respectively. For GaAs, N2 plasma nitridation forms a GaN layer whose thickness is limited by the As segregation at the GaAs/GaN interface. For GaP and InP substrates, a phosphorous nitride capping layer was formed which inhibits further nitridation. For all substrates, the H2 addition to N2 plasmas results in an increase of the nitridation depth since hydrogen favors the desorption of AsHx and PHx species thereby reducing the inhibition effect of both the As segregation and phosphorus nitride formation.
Enantiospecific adsorption of chiral hydrocarbons on naturally chiral Pt and Cu surfaces
Authors: Power Timothy D. , Sholl David S.
Published: July 2002

Stepped surfaces of face-centered-cubic crystals are naturally chiral if the step edges include asymmetric steps. These surfaces can, in principle, exhibit enantiospecific adsorption properties if chiral molecules adsorb on them. To provide theoretical characterizations of these enantiospecific properties, we have used Monte Carlo simulations to examine adsorption of two chiral hydrocarbons, trans-1,2-dimethyl-cyclopropane and trans-1,2-dimethyl-cyclobutane, on Pt(643) and Cu(921), two naturally chiral surfaces. These simulations are the first to include the effects of intramolecular relaxations. We also present a simple procedure for predicting the low pressure enantioselectivity of adsorption from a racemic gas phase mixture based on simulations of individual enantiomers.
Dry etching of platinum films with TiN masks in an Ar/O2 helicon wave plasma
Authors: Chiang Ming-Chung , Pan Fu-Ming , Cheng Han-Chung , Liu Jeng-Shu , Chan Shih-Hsiung , Wei Ta-Chin
Published: July 2002

Platinum thin films have been successfully patterned without fence residues using an Ar/O2 helicon wave plasma. Photoresist and silicon oxide masks were also studied for comparison. The etch rate of the TiN mask decreases, but the etch slope increases with an increase of the oxygen concentration in the Ar/O2 gas mixture. An etch rate of about 670 Å/min was obtained by operating at 4 mTorr with an Ar/O2 flow rate of 32/8 sccm. The etch selectivity is enhanced with the addition of oxygen to Ar, and a high Pt-to-TiN selectivity of above 14 could be obtained. X-ray photoelectron spectroscopy and Auger electron spectroscopy indicated that a thick TiO2 layer could be formed on the TiN mask in the Ar/O2 plasma. The high etch selectivity of platinum to TiN may be attributed to the presence of a TiO2 layer of ∼60 Å thickness on the TiN surface. A high etch selectivity and fence-free Pt etching with sidewall angles of ∼70° could be achieved using a thin TiN hard mask without a postwet cleaning.
Plasma abatement of perfluorocompounds in inductively coupled plasma reactors
Authors: Xu Xudong “Peter” , Rauf Shahid , Kushner Mark J.
Published: July 2002

Perfluorinated compounds (PFCs), gases which have large global warming potentials, are widely used in plasma processing for etching and chamber cleaning. Due to underutilization of the feedstock gases or by-product generation, the effluents from plasma tools using these gases typically have large mole fractions of PFCs. The use of plasma burn-boxes located downstream of the plasma chamber has been proposed as a method for abating PFC emissions with the goals of reducing the cost of PFC abatement and avoiding the NOx formation usually found with thermal treatment methods. Results from the two-dimensional Hybrid Plasma Equipment Model have been used to investigate the scaling of plasma abatement of PFCs using plasma burn-boxes. An inductively coupled plasma (ICP) etching chamber is modeled to determine the utilization of the feedstock gases and the generation of by-products. The effluent from the etching chamber is then passed through a plasma burn-box excited by a second ICP source. O2, H2, and H2O are examined as additive gases in the burn-box. We find that C2F6 (or CF4) consumption in the etching reactor increases with increasing ICP power deposition at constant C2F6 (or CF4) mole fraction, and decreasing C2F6 (or CF4) mole fraction or total gas flow rate at constant power. The efficiency of removal of C2F6 (eV/molecule), however, is strongly dependent only on the C2F6 mole fraction and total gas flow rate. All PFCs in the effluent can generally be abated in the burn-box at high power deposition with a sufficiently large flow of additive gases. In general CF4 generation occurs during abatement of C2F6 using O2 as an additive. CF4 is not, however, substantially produced when using H2 or H2O as additives. The efficiency of PFC abatement decreases with increasing power and decreasing additive mole fraction.
Phase development of radio-frequency magnetron sputter-deposited Pb(Mg1/3Nb2/3)O3–PbTiO3 (90/10) thin films
Authors: Lee Jeon-Kook , Park Dongkyun , Cheong Deok-Soo , Park Jong-Wan , Park Chul Soon
Published: July 2002

Pb(Mg 1/3 Nb 2/3 )O 3 –PbTiO 3 (PMN–PT) films were deposited by the radio-frequency magnetron sputtering technique with Pb- and Mg-enriched ceramic targets. The perovskite structural growth was carried out over a wide range of processing parameters. PMN–PT targets were synthesized by the columbite technique. Surface cracking was due to the residual stress induced by low-temperature deposition. To reduce the surface-layer delamination, the substrate temperature during deposition was increased to 500 °C. Even though the amount of the perovskite phase decreased, the surface morphology was free of macrodelaminations and better than the case of room-temperature deposition. By stress releasing, high-temperature deposition reduces the delaminations of the PMN–PT thin films on the Pt/Ti/SiO2/Si substrate. By controlling the sputtered-particle kinetic energy and the film composition, the surface morphologies were changed to be smooth and delamination-free.
Atom-probe study of silicide formation at Ni/Si interfaces
Authors: Nishikawa Osamu , Shibata Mezame , Yoshimura Toshihiko , Nomura Eiichi
Published: July 2002

Nickel was deposited on Si substrates and the feasibility of studying the formation process of Ni silicides with the atom-probe mass spectrometer was examined by atomic layer-by-layer mass analysis of the specimen from the deposited layer to the substrate through the interface. The epitaxially grown silicide with a well ordered cubic structure was observed when the specimen was heated above 800 K. The main part of the Ni–Si mixed layer formed at room temperature was Ni-rich Ni2Si regardless of substrate materials, Ni or Si. At high temperatures the Ni concentration in the mixed layer depends on the substrate materials. The result indicates that the silicide composition is regulated by the diffusivity of Ni into Si at low temperatures and by the relative quantities of Ni and Si at high temperatures. A clear interface between the silicide and the Si substrate was formed at around 800 K.
Selective laser-stimulated desorption of molecules by internal vibration excitation
Authors: Jedrzejek C.
Published: July 2002

The photodesorption model of Gortel, Kreuzer, and collaborators in which a laser is resonantly coupled to an internal vibration mode of an absorbed molecule is considered. The importance of including anharmonicity of the internal vibration and a broadening of energy levels of a zero-order Hamiltonian is demonstrated. A numerical calculation of the photodesorption as a function of a laser intensity is presented for a multilevel system of CH3F on NaCl and compared with experimental data. In comparison to previous assumption of only harmonic motion for the internal vibration where the values of the laser fluences for laser-stimulated desorption are calculated to be too low, our results (saturation intensities ∼105–106 W/cm2) are in closer agreement with experiment.
Low temperature oxidation of silicon using a microwave plasma disk source
Authors: Roppel T. , Reinhard D. K. , Asmussen J.
Published: July 2002

A new reactor concept, referred to as a microwave plasma disk source, is implemented and is used as a source of negative oxygen ions for low temperature oxidation of silicon. Oxide growth rates of 1000 Å per hour, with only 100 W of absorbed power in the plasma, have been achieved on unheated silicon wafers in two configurations. In the first case, positively biased wafers are in actual contact with the plasma and in the second, the positively biased wafers are 15 cm downstream from the plasma ion source. In both cases the bias current density due to electrons and negative ions is on the order of 100 mA/cm2 and the plasma source electron density is on the order of 2×1012 cm−3. Oxide growth rates are correlated with plasma absorbed power, bias current, pressure, and plasma density. The reactor utilizes a single-mode, internally tuned resonant cavity that can be continuously operated over a wide range of gas flow and pressure (>10 to <10−3 Torr). The plasma disk source is scalable with frequency. In the present configuration, the excitation frequency is 2.45 GHz, the plasma disk diameter is 10 cm, and the disk thickness is 1.5 cm.
Modulated molecular-beam studies of the surface chemistry of silicon reaction with reactive gases
Authors: Olander D. R. , Balooch M. , Abrefah J. , Siekhaus W. J.
Published: July 2002

The method of studying the kinetics of gas–solid surface reactions using modulated molecular beams and mass-spectrometric detection is described. Results obtained for Si(111) etching by H(g) and deposition from SiH4 are presented.
Negative differential conductivity in lateral surface superlattices
Authors: Bernstein G. , Ferry D. K.
Published: July 2002

We have used electron-beam lithography in single level poly(methylmethacrylate) (PMMA) to fabricate a novel quantum device in which a lateral surface superlattice is used for the gate of a high-electron-mobility transistor. We have observed strong negative differential conductivity which we believe is due to the onset of Bloch oscillations.
Electrostatic probe analysis of microwave plasmas used for polymer etching
Authors: Heidenreich J. E , Paraszczak J. R. , Moisan M. , Sauve G.
Published: July 2002

Microwave plasma etching [S. Dzioba, G. Esten and H. M. Nagub, J. Electrochem Soc. 129, 2537 (1982); K. Suzuki, S. Okudaira, S. Nishimatsu, K. Usami, and I. Kanomata, J. Electrochem. Soc. 129, 2764 (1982)] is a novel technique which promises to have wide application in the semiconductor industry for the removal of silicon and polymeric materials. Its advantages include relatively high concentrations of both ions and chemically excited species and the ability to etch isotropically. This allows high etch rates to be achieved with a minimum of ion bombardment. Langmuir probe studies have been performed on microwave (915 MHz) plasmas in O2 to determine the spatial variation of the plasma parameters (ion density, electron temperature, and space potential), as well as their dependence on gas pressure, microwave power, and the addition of CF4. Probes have also been used in microwave plasmas with an rf bias applied to an internal electrode (combination plasmas). Ion densities on the order of 2×1010 cm−3 were typical in the spatial afterglow of microwave plasmas with an O2 pressure of 100 mTorr, and values as high as 7×1010 cm−3 were observed at lower pressures. Average electron temperatures between 1 and 2 eV were prevalent in the microwave plasmas while rf biasing the substrate electrode leads to a value of 7 eV near the etching surface.
Two-dimensional energy bands at the CaF2/Si(111) interface
Authors: Himpsel F. J. , Heinz T. F. , McLean A. B. , Palange E. , Burstein E.
Published: July 2002

We have chosen CaF2/Si(111) as a prototype to study the two-dimensional band structure of an ordered interface using angle-resolved photoemission and optical second harmonic generation. A pair of interface state bands is found, one occupied, the other empty. The former disperses from EF−0.8 eV at Γ to EF−1.4 eV (−1.6 eV) at M (K). An interface band gap of 2.4 eV is determined via resonant second harmonic generation using a truly buried interface with 500 Å of CaF2 on top of Si. Therefore, the interfacial gap is twice as large as the gap in Si and five times smaller than the gap in CaF2. The pair of interface bands can be understood as bonding/antibonding combinations of the Si dangling bond orbital and the Ca 4s orbital, with Ca in the 1+oxidation state.
Gold–silicon interface modification studies
Authors: Hallen H. D. , Fernandez A. , Huang T. , Buhrman R. A. , Silcox J.
Published: July 2002

We have performed ballistic electron emission microscopy measurements on the Au–Si system with and without controlled monolayer impurities at the interface. At moderate sample to scanning tunneling microscopy tip biases (<2.5 V) we have observed, and at high biases (>3 V) modified the local ballistic transmittance (BT), i.e. the scaling factor of the collector current versus voltage spectra, of the interface. Spatially, the modification typically consists of a region of decreased BT a few hundred Å in diameter surrounded by a ring of increased BT. No change in Schottky barrier height is found. A model is presented which describes the decrease in terms of Au–Si interdiffusion, and the enhancement in terms of a thinning of an impurity layer between the Au and Si; connections are made to observations of the unstressed system.
The art and science and other aspects of making sharp tips
Authors: Melmed Allan J.
Published: July 2002

A partial review of the development of schemes for making sharp points for use in various microscopies is presented. The major and some minor techniques are discussed with emphasis on electropolishing methods.
Effects of surface features upon the Au(111) surface state local density of states studied with scanning tunneling spectroscopy
Authors: Everson M. P. , Davis L. C. , Jaklevic R. C. , Shen Weidian
Published: July 2002

The local density of states of the Au(111) surface state on flat planes, monatomic steps, narrow terraces, and in monatomic pits were measured with a scanning tunneling microscope. The experiments were performed on a single-crystal Au(111) sample in ultrahigh vacuum. We measure a decrease in the surface-state intensity by a factor of 2–10 on monatomic steps. The surface-state local density of states for narrow terraces has been found to be relatively unchanged from the value on flat (111) planes. Preliminary results for monatomic-deep sputter pits with diameters of order 25 Å show surface-state density of states peak shifts on the order of +100 meV with respect to the value on flat (111) planes. Our results are consistent with the treatment of steps as a region of weakly repulsive potential with respect to the two-dimensional nearly free-electron-like surface state. A model of surface-state tunneling incorporating this result has been developed and produces reasonable quantitative agreement with the data.
The growth of Ag films on Ni(100)
Authors: Brodde A. , Wilhelmi G. , Badt D. , Wengelnik H. , Neddermeyer H.
Published: July 2002

Using scanning tunneling microscopy, low-energy electron diffraction (LEED), and Auger electron spectroscopy we have studied the growth of Ag films with coverages between 1/6 and 1.45 monolayers on room temperature Ni(100) substrates. In the submonolayer coverage range we observe a condensation of the Ag deposit in form of a network of connected islands of monoatomic height preferentially at step edges of the substrate. Two domains are identified on the Ag islands by the presence of orthogonal line structures. They are interpreted in terms of the c(2×8) LEED pattern. The Ag islands coalesce for a coverage of less than one monolayer. The second atomic Ag layer shows a different growth structure indicating a more perfect arrangement of Ag atoms in a face-centered-cubic (fcc) (111) layer.
Parametric evaluation of electron cyclotron resonance deposited SiO2 using a multicusp plasma applicator
Authors: Buckle K. A. , Pastor K. , Constantine C. , Johnson D.
Published: July 2002

Plasma deposition of SiO2 on silicon substrates in a microwave (2.45 GHz) electron cyclotron resonance N2O/SiH4/He discharge has been investigated as a function of radio frequency (13.56 MHz) self-biasing of the sample, pressure, microwave power, substrate temperature, and gas mixture. Deposition rates between 30 and 90 nm/min have been observed with quality films over a range of parameter combinations. The films have been analyzed for thickness and index of refraction by ellipsometry and for chemical structure by Fourier transform infrared spectroscopy. The deposition process yielded films with virtually no Si–H, N–H, or Si–N bonding groups and only traces of OH bonds. Analysis of the Si–O–Si stretching peak reveals a film quality which compares favorably with good quality thermal oxides grown at much higher substrate bulk temperatures. Also, the relative insensitivity to the He content of the gas mixture indicates the surface chemistry of this process is fundamentally different from previously reported plasma enhanced chemical vapor deposition processes.
Low-temperature formation of device-quality SiO2/Si interfaces by a two-step remote plasma-assisted oxidation/deposition process
Authors: Yasuda T. , Ma Y. , Habermehl S. , Lucovsky G.
Published: July 2002

This article describes a new approach to the low-temperature (200–300 °C) formation of electronic-quality SiO2/Si heterostructures in which the steps of interface formation and bulk oxide deposition are separately controlled to optimize the electronic properties of the resulting device structure. This approach combines an in vacuo cleaning/passivation step for removal of residual C-atom surface contamination with a passivation of the Si surface by an ultrathin oxide layer, ∼0.5 nm, and then completes the SiO2/Si heterostructure with a plasma-assisted deposition of the SiO2 thin film. The new process differs both qualitatively and quantitatively from conventional high-temperature, ∼850–1000 °C, thermal, or rapid thermal oxidation in which interface formation and oxide film growth are accomplished at the same time through a continuous consumption of the Si substrate.
Rapid thermal annealing for reducing stress in tungsten x-ray mask absorber
Authors: Diawara Y. , Lafontaine H. , Chaker M. , Kieffer J. C. , Pépin H. , Cochrane R. W. , Currie J. F. , Haghiri-Gosnet A. M. , Ravet M. F. , Rousseaux F.
Published: July 2002

X-ray masks are one of the key issues of x-ray lithography. In order to eliminate distortions, a good mask necessitates a low stress x-ray absorber layer. Tungsten is one of the most promising materials for use as an x-ray absorber, but the stress strongly depends on deposition conditions. Therefore, it is very difficult to control precisely the stress during the deposition process. A new approach is proposed, which consists of ‘‘fine tuning’’ the stress in the deposited layer with an annealing treatment. In this article, a process is presented which controls the stress in tungsten deposited thin films using rapid annealing. Stresses of less than 2×108 dyn/cm2 can be routinely obtained in annealed films for which initial compressive stresses after deposition were up to 3×109 dyn/cm2. This allows better film deposition process latitude for the sputtering gas pressure and substrate temperature. The evolution of stress with annealing temperature and time is studied and x-ray diffraction and scanning electron microscopy measurements are discussed.
Strain-relaxed InGaAs buffer layers grown by molecular-beam epitaxy for 1.3 μm Fabry–Pérot optical modulators
Authors: Hammons B. E. , Fritz I. J. , Brennan T. M. , Howard A. J. , Olsen J. A.
Published: July 2002

The effects of various growth temperatures on molecular-beam epitaxially grown, compositionally graded, In0.33Ga0.67As buffers and 1.33 μm optoelectronic device structures were investigated. Buffer structures grown at 400 °C on GaAs substrates showed ≳99.5% lattice relaxation with minimal threading dislocation content. Multiple quantum well superlattices grown at 400 °C upon this buffer exhibited strong excitonic absorption at 1.33 μm and good surface morphology with slight crosshatching. A Fabry–Pérot-cavity reflectance modulator grown at 400 °C on this buffer exhibited strong excitonic absorption and good reflectance contrast at 1.33 μm.
Dual beam atomic absorption spectroscopy for controlling thin film deposition rates
Authors: Benerofe S. J , Ahn C. H. , Wang M. M. , Kihlstrom K. E. , Do K. B. , Arnason S. B. , Fejer M. M. , Geballe T. H. , Beasley M. R. , Hammond R. H.
Published: July 2002

We have developed a stable (<1% drift/h at 1 Å/s), fast (∼200 ms), sensitive (S/N∼10–200 at 1 Å/s) evaporation rate monitor for controlling electron beam sources. Based on dual beam atomic absorption spectroscopy (AAS), in which a reference arm compensates for drift in the light source and signal detection apparatus, this technique is very wavelength and hence element specific, allowing many elements to be simultaneously and independently monitored. Furthermore, the system can operate at very high background gas pressures, as well as under ultrahigh vacuum conditions. Also, because only the light must enter the vacuum chamber and pass through the evaporant, minimal periodic maintenance inside the chamber is necessary. The versatility and sensitivity of this AA system make it a viable candidate for in situ monitoring of various other thin film processes, including sputtering, ion milling, and reactive ion etching.
Operation of a molecular-beam epitaxy machine employing a valved solid phosphorus source
Authors: Wicks G. W. , Koch M. W. , Johnson F. G. , Varriano J. A. , Kohnke G. E. , Colombo P.
Published: July 2002

The use of an elemental source molecular-beam epitaxy (MBE) machine for the growth of phosphides requires hardware and operating procedures different from those normally encountered in the growth of arsenides. The main hardware alterations are the use of valved group V cracker sources and different pumping schemes. Operating procedures must be developed to cope with higher operating pressures and flammable deposits. High-quality phosphides and abrupt arsenide/phosphide interfaces are now possible using elemental source MBE.
Scanning force microscope using a piezoelectric microcantilever
Authors: Itoh T. , Suga T.
Published: July 2002

This paper presents a simple force microscope that makes a use of a piezoelectric microcantilever for sensing its vibration amplitude. The microcantilever is a composite beam, which consists of a piezoelectric ZnO thin film and a thermal SiO2 film, and has a ZnO whisker tip at its end. The cantilever used has the first natural resonance frequency of 140 kHz and the calculated spring constant of 14 N/m. Vibration amplitude of the lever driven near its resonance frequency by external oscillator was sensed by detecting the induced piezoelectric charge. The output charge with the lever amplitude of 1.0 nm was 0.028 fC. The microscope was operated in cyclic contact mode. Recordings of the output versus the sample position and imaging of deposited Au film surface were successfully performed in air. We present two kinds of cyclic contact forces which were calculated from parameters of the lever used.
Time dependent, self-consistent simulations of field emission from silicon using the Wigner distribution function
Authors: Jensen K. L. , Ganguly A. K.
Published: July 2002

Field emission current calculations from semiconductors typically rely on the assumptions that the emitted current is negligible and that the band bending at the surface may be calculated via Poisson’s equation with a Fermi–Dirac momentum distribution of electrons [the zero emitted current approximation (ZECA)]. This approach cannot take into account complications due to quantum confinement near the surface, and problems associated with scattering for large applied field. We have developed and applied a time-dependent, self-consistently calculated Wigner distribution function (WDF) approach for dealing with the semiconductor field emission problem, and have applied it to the case of silicon for the cases of 300 and 900 K. In particular, effects of self-consistency and scattering on the density and potential profiles were examined, comparing the results to the ZECA approach to show when quantum and scattering effects become significant. At low fields, the WDF approach may be coupled with the transmission coefficient approach to yield reasonable current estimates. At high fields, it is shown that current saturation effects set in, in which the current no longer exponentially rises with applied field. Finally, the time dependence of the current and particle densities after a sudden shift in the applied field are examined.
Reliable tip preparation for high-resolution scanning tunneling microscopy
Authors: Albrektsen O. , Salemink H. W. M. , Mo/rch K. A. , Thölen A. R.
Published: July 2002

We describe a method to prepare electron emitters (tips) designed to achieve routine atomic resolution in a scanning tunneling microscope. Highly reliable results were obtained with repeated sputter-anneal processes in ultrahigh vacuum using polycrystalline tungsten wires as the base material. A tip apex radius of less than 5 nm and an atomic resolution of III–V (110) semiconductor surfaces are routinely obtained. The analysis involves scanning electron microscopy, transmission electron microscopy, scanning tunneling microscopy, and current–voltage characteristics in the field emission regime.
Cross-section X-scanning force microscopy analysis of different hard coatings and thin films
Authors: Pischow K. A. , Adamik M. , Barna P. B. , Korhonen A. S.
Published: July 2002

In the study of thin films and hard coatings the cross-sectional structural information is of vital importance in order to understand and control the desired properties of the coating substrate systems. This information has been so far obtained using scanning electron microscopy or cross-section transmission electron microscopy (X-TEM). We have developed a sample preparation technique allowing us to use cross-section scanning force microscopy for cross-section studies. Results from thin hard coatings and from thin films on silicon wafers are presented, results obtained are compared with X-TEM analysis, and the prospects and limitations of the method are discussed.
New compound quantum dot materials produced by electron-beam induced deposition
Authors: Weber M. , Koops H. W. P. , Rudolph M. , Kretz J. , Schmidt G.
Published: July 2002

Electron-beam induced deposition represents a new technology for production of three-dimensional nanoscale structures. The properties of the deposited material are determined by the precursor material as well as the deposition parameters. The deposits of very different organometallic precursor molecules show similar morphologies. The metal content of those deposits is strongly dependent on the beam current and the energy of the primary electrons. Using high beam currents for deposition a polycrystalline material is built up, consisting of single crystallites with diameters of 1–4 nm embedded in an amorphous carbon containing matrix. The distance between the metallic crystallites is in the angstrom range. Thus electrical conductivity of the material is accomplished by tunneling between the nanocrystallites. Wires built up from these materials are able to carry current densities up to 2 MA cm−2. Several materials have been characterized by transmission electron microscopy, energy-dispersive x-ray spectroscopy, and electrical measurements.