bluuebunny/crossref_metadata_2025 huggingface dataset:
Radio frequency hollow cathode discharge for large-area double-sided foil processing
Authors: Korzec D. , Schott M. , Engemann J.
Published: July 2002

A radio frequency (13.56 MHz) cold hollow cathode discharge (HCD) plasma source has been developed for double side surface treatment of foils, membranes, and textile products. A membrane with up to 30 cm width can be moved between two symmetrical, capacitively coupled active radio frequency (rf) electrodes (cathodes). The hollow cathodes consist of a number of parallel troughs separated with ribs oriented perpendicular to the direction of membrane motion. The troughs are open at both ends to establish an electrical contact between the plasma in hollow cathode troughs and the rf grounded electrodes (anodes). Two modes of plasma source operation are observed: diode discharge—comparable to the typical capacitively coupled two electrode rf discharge, and the much more intensive HCD. The HCD mode of operation can be sustained for a pressure range from 0.01 to 4 mbar for argon and from 0.01 to 0.2 mbar for oxygen. The influence of the geometry (trough width), of the cathode surface material (aluminum and alumina), and gas (argon and oxygen) on the source performance was investigated. The ignition pressure of the HCD decreases with increasing trough width and is higher for oxygen than for argon. Ion concentration and electron temperature distributions along the trough were measured by use of a double Langmuir probe. Maximum ion concentrations 1.4×1011 cm−3 for argon and 0.8×1011 cm−3 for oxygen at rf powers as low as 100 W were achieved. The ion concentration increases for a diode discharge and decreases for a HCD, when the hollow cathode surfaces are covered with thin plates of alumina. Electron temperatures twice as high for the HCD operation mode (8 eV) than for diode discharge operation mode (4 eV) are typical.
Reactive direct current magnetron sputtering of aluminum oxide coatings
Authors: Sproul W. D. , Graham M. E. , Wong M. S. , Lopez S. , Li D. , Scholl R. A.
Published: July 2002

Aluminum oxide coatings were reactively direct current magnetron sputtered using an arc suppression unit to stop arcing on the cathode. The process was very controllable when the arc suppression unit was used, and it did not produce any debilitating arcing as is commonly found with conventional reactive direct current magnetron sputtering. Arc suppression is a major advancement in reactive dc magnetron sputtering technology. With the automatic feedback partial pressure control of the reactive gas, all compositions of AlOx, where 0≤x≤1.5, are possible. There are no forbidden compositions as there are with flow control of the reactive gas. All coatings were deposited with a floating substrate bias, and the color of the AlOx films ranged from metallic when there was no or a small partial pressure of oxygen during deposition to a very clear film when the oxygen partial pressure was 0.08 mTorr. The clear film was amorphous, and its average index of refraction, n, was 1.6. The Vickers hardness of the clear film was only 830 kgf mm−2 due to its amorphous structure, and the scratch test critical load for a 1.9 μm thick film on an M2 steel substrate, was only 0.4 kgf. It is believed that substrate bias will improve the mechanical and optical properties of the films.
Monte Carlo simulation of the thermalization of sputtered atoms and reflected atoms in the magnetron sputtering discharge
Authors: Yamamura Y. , Ishida M.
Published: July 2002

The Monte Carlo simulation code acat−gas has been developed in order to simulate the whole system of a planar magnetron sputtering discharge. The atomic collisions in the cathode, which lead to sputtering and reflection, are simulated by the acat routine of the acat−gas code; the thermalization of emitted atoms in the background gas within the a planar sputtering discharge is simulated by the Monte Carlo technique, where the Thomas–Fermi–Morse potential is used to describe collisions between ejected atoms and background gas atoms. The simulated average energy of sputtered atoms at the midpoint between the cathode and the substrate is in good agreement with experimental results. It is found that various physical quantities such as the velocity distributions of sputtered atoms and reflected atoms, the transmission rate of sputtered atoms and reflected atoms, the average energies in the background gas, and the normalized energy of arriving reflected atoms at the substrate depends strongly on the discharge voltage at the low pressure (<2 Pa).
A model catalyst for methanol synthesis: Zn-deposited and Zn-free Cu surfaces
Authors: Nakamura I. , Fujitani T. , Uchijima T. , Nakamura J.
Published: July 2002

The synthesis of methanol by the hydrogenation of CO2 over Zn-deposited and Zn-free single-crystal copper surfaces has been studied using an x-ray photoelectron spectroscopy apparatus combined with a high-pressure flow reactor (18 atm). The order of plane for the catalytic activity was (110)≳(311)≳(100)≳(111) for Zn-free copper surfaces. The Zn-deposited Cu(111) (ΘZn=0.19) was 13 fold more active than the Zn-free Cu(111). The activation energy for the methanol synthesis (73–84 kJ/mol) was close to each other regardless of the surface structure or the presence of Zn. It was shown that the Zn deposited on Cu(111) acted as a promoter for the methanol synthesis, while the Zn on Cu(110) and Cu(100) had no such a promotional effect. On the postreaction surfaces of Zn-deposited and Zn-free copper samples, a small amount of formate species was always detected which was more stable than that on clean Cu surfaces. This formate species’s coverage was proportional to the activity for methanol formation.
Fluorocarbon radicals and surface reactions in fluorocarbon high density etching plasma. II. H2 addition to electron cyclotron resonance plasma employing CHF3
Authors: Takahashi Kunimasa , Hori Masaru , Goto Toshio
Published: July 2002

Gas phase reactions of CFx (x=1–3) radicals and F atoms in an electron cyclotron resonance (ECR) downstream plasma have been investigated at 300 W and a CHF3 pressure of 0.4 Pa by adding H2 to CHF3. The behaviors of CFx radical densities were measured using infrared diode laser absorption spectroscopy, while F atom density was estimated with actinometry. Furthermore, the composition of fluorocarbon films deposited on the chamber walls in the CHF3/H2 ECR plasma has been investigated with x-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. On the basis of measurement results, the correlation between the characteristics of fluorocarbon films and the behaviors of radicals in the plasma has been investigated. The CF radical density was found to be changed by the variation of the composition, in particular F/C ratio, of the films deposited on the chamber walls. Under the same conditions as the measurements of radical densities, the deposition rates of fluorocarbon films formed on the substrate set in the downstream plasma region were measured. The behavior of CF radical density followed the deposition rates, which suggested that the CF radical played an important role for the formation of carbon-rich fluorocarbon films in the CHF3/H2 ECR plasma.
Reactive ion beam assisted deposition of zirconium oxyfluoride thin films
Authors: Gibson U. J. , Cornett K. D.
Published: July 2002

Zirconium oxyfluoride thin films of varying composition and refractive index were made by ion beam assisted deposition and concurrent O+2 ion bombardment of thermally deposited ZrF4. The oxygen ion bombardment parameters control the index of refraction over the range 1.52–1.8. The composition of the ZrOxFy films, as determined by Rutherford backscattering and x-ray photoelectron spectroscopy, varied from ZrO0.4F3.6 to ZrO2F1. Below 300 eV there is little change in oxygen content or refractive index, but at 600 eV the bombardment flux controls the material properties. Low loss (1 dB/cm) optical wave guides were fabricated using this technique.
Pulse–time-modulated electron cyclotron resonance plasma discharge for highly selective, highly anisotropic, and charge-free etching
Authors: Samukawa Seiji , Ohtake Hiroto , Mieno Tetsu
Published: July 2002

Highly selective, highly anisotropic, notch-free, and charge-buildup damage-free silicon etching is performed using electron cyclotron resonance (ECR) Cl2 plasma modulated at a pulse timing of a few tens of microseconds. A large quantity of negative ions are produced in the afterglow of the pulse-time-modulated plasma. The decay times of electron density, electron temperature, and sheath potential are considerably reduced. This is attributable to negative-ion generation. Furthermore, the pulse-time-modulated plasma reduces the time averaged sheath potential. As a result of these effects, charged particles in the sheath are drastically modified from the continuous discharge, and they should improve the selective etching in the pulsed ECR plasma and eliminate charge accumulation on the substrate. Additionally, negative-ion generation dramatically improves the plasma potential distributions in the nonuniform ECR plasma. This technique is also suitable for large scaled etching processes.
Geometrical capacitance of the tip–semiconductor junction
Authors: Sakai A. , Kurokawa S. , Hasegawa Y.
Published: July 2002

Capacitance–distance (C–s) and capacitance–voltage (C–V) characteristics have been measured for the tip–sample capacitance on Si(001)2×1 and Si(111)7×7 surfaces. On both surfaces, the C–s characteristics are found to be little affected by the types of sample doping and also show no appreciable bias dependence. These observations suggest that the space-charge region of the semiconductor gives no contribution to the tip–sample capacitance because of the high density of surface states on clean Si surfaces.
Adsorption and ionization of HCl on an ice surface
Authors: Banham Sally F. , Sodeau John R. , Horn Andrew B. , McCoustra Martin R. S. , Chesters Michael A.
Published: July 2002

In this article, we describe a series of experiments investigating the interaction of the important stratospheric reservoir species HCl with the surface of a thin ice film. Reflection absorption infrared spectroscopy and thermal desorption spectroscopy have been used to identify the nature of the ionic hydrates formed under a variety of pressure, temperature, and exposure regimes.
Predictions of scanning tunneling microscope images of furan and pyrrole on Pd(111)
Authors: Futaba D. N. , Chiang S.
Published: July 2002

We use a computational method, based on extended Hückel molecular orbital theory, for predicting the scanning tunneling microscope images of furan and pyrrole adsorbed onto Pd(111). We calculated images for both isolated molecules and for molecules chemisorbed onto a metal cluster. From binding energy calculations, the low energy geometries for three binding sites were determined. We found many similarities between furan and pyrrole in the preferred binding site geometries and images.
Characterization of metal clusters (Pd and Au) supported on various metal oxide surfaces (MgO and TiO2)
Authors: Xu C. , Oh W. S. , Liu G. , Kim D. Y. , Goodman D. W.
Published: July 2002

Au clusters supported on the TiO2(001)/Mo(100) surface and Pd clusters supported on the MgO(100)/Mo(100) surface have been studied using temperature programmed desorption, ion scattering spectroscopy, scanning tunneling microscopy, and scanning tunneling spectroscopy. Three dimensional growth has been observed at 300 K for both cases. The adsorption energy of Au on the TiO2(001) surface has been measured to be 50 kcal/mol using temperature programmed desorption, compared to the adhesive energy of 90 kcal/mol for the bulk Au metal. At an equivalent Au coverage of 1.8 ML, very homogenous, hemispherical Au particles with an average diameter of 25 Å and a height of 10 Å are present on a TiO2(001)/Mo(100) surface. Increasing the Au coverage to 3 equivalent monolayers produces ∼60 Å diameter clusters. The scanning tunneling spectroscopy measurements show a gradual development of the metallic character of the Au clusters with increasing cluster size. Very similar results have been obtained for the Pd clusters supported on the MgO(100)/Mo(100) surface.
Auger electron spectroscopy and electron energy loss spectroscopy study of the adsorption of nitrogen on a polycrystalline zirconium surface
Authors: Kurahashi M. , Yamamoto M. , Mabuchi M. , Naito S.
Published: July 2002

Auger electron spectroscopy (AES) and electron energy loss spectroscopy (EELS) were used to investigate the adsorption of nitrogen gas on a polycrystalline zirconium surface at room temperature. It was found that the adsorption of nitrogen is saturated at an exposure of ∼10 L, the thickness of the nitride formed on the specimen surface is 0.4–0.5 nm at a nitrogen exposure of 100 L, and the surface has the same large electronic density of states 4–5 eV below the Fermi energy as ZrN. The measured AES and EELS spectra are consistent with the electronic structure calculated for the Zr(0001)-(1×1)-N structure.
Chemical sputtering measurements in Tore Supra by aftershot mass spectrometry outgassing studies
Authors: de la Cal E. , Gauthier E.
Published: July 2002

One of the main issues of the high-density, high-radiation plasma-edge scenario for long-pulse operation in future fusion devices is to reduce physical sputtering by lowering the edge electron temperature. If carbon-based materials are used as plasma-facing components in next generation machines such as ignition device to test engineering concepts, the role of chemical with respect to physical sputtering increases as the net erosion mechanism limiting the component’s lifetime. This is due to the fact that the physical sputtering yield decreases stronger when decreasing the ion energy in the 30–150 eV energy range, although very recent laboratory experiments have concluded an important chemical sputtering yield decrease at low deuterium impact energies (down to 10 eV). Because laboratory experiments cannot reproduce the real plasma-wall interaction conditions, principally the high bombarding flux conditions, it is important to determine experimentally and in situ the chemical sputtering yields. The global chemical sputtering yield for a tokamak with carbon walls has been estimated in Tore Supra by analyzing the aftershot molecular outgassing with a differentially pumped mass spectrometer. Quantitative measurements of molecular outfluxes during plasma operation are difficult due to the strong cracking probability of the neutral species. The aftershot outgassing method takes advantage of the fact that just after the termination of the plasma, the molecular desorption responsible for chemical sputtering continues, although in a decreasing way. This avoids the plasma perturbation effect due to molecule cracking. Even though the analysis of the spectrum is difficult due to the complex decomposition pattern of organic compounds containing hydrogen and deuterium, the characteristic time evolution of the different outgassing species can help to deconvolute the mass spectrum. The main product is CD4 and the measured chemical sputtering yield (YCD4=methane outflux from the wall/deuterium flux to the wall) is 3×10−3<YCD4<9×10−3 for D2 discharges. The contribution of second order hydrocarbons and of CO to the total chemical erosion yield is also studied. The dependence of the yields on plasma flux and surface conditions is discussed, as well as the pros and cons of the method used.
High energy aluminum ion implantation using a variable energy radio frequency quadrupole implanter
Authors: Amemiya Kensuke , Ito Junya , Tokiguchi Katsumi
Published: July 2002

A high energy aluminum ion implantation using a variable energy radio frequency quadrupole (RFQ) implanter has been studied for the fabrication of high power semiconductor devices. The implanter consists of a microwave ion source with a crucible for AlCl3 sublimation, a sector type mass separator, a magnetic quadrupole triplet, a variable energy four-rod RFQ linac as an additional accelerator, an energy analyzer, and an implantation chamber. Al2+ ions, with energies of 1.0 MeV and 0.9 MeV, are implanted into a 6-inch diameter wafer, and the depth profile and dose uniformity are measured by secondary ion mass spectroscopy and sheet resistivity, respectively. Results show that the depth profile has the desired features for the projected range, and the dose non-uniformity is 0.7%.
Microstructure and electronic properties of the refractory semiconductor ScN grown on MgO(001) by ultra-high-vacuum reactive magnetron sputter deposition
Authors: Gall D. , Petrov I. , Madsen L. D. , Sundgren J.-E. , Greene J. E.
Published: July 2002

ScN layers, 180 nm thick, were grown on MgO(001) substrates at 750 °C by ultra-high-vacuum reactive magnetron sputter deposition in pure N2 discharges. N/Sc ratios, determined by Rutherford backscattering spectroscopy, were 0.98±0.02. X-ray diffraction θ–2θ scans and pole figures combined with plan-view and cross-sectional transmission electron microscopy showed that the films are strongly textured, both in plane and along the growth direction, and have a columnar microstructure with an average column width near the film surface of 30±5 nm. During nucleation and the early stages of film growth, the layers consist of approximately equal volume fractions of 002- and 111-oriented grains. However, preferred orientation evolves toward a purely 111 texture within ≃40 nm as the 002 grains grow out of existence in a kinetically limited competitive growth mode. 002 grains exhibit local cube-on-cube epitaxy with an orientation relationship (001)ScN∥(001)MgO and [010]ScN∥[010]MgO while 111 grains have a complex fourfold 90°-rotated in-plane preferred orientation in which strained ScN triangular {111} surface unit cells exhibit local epitaxy with square MgO unit cells yielding the orientation relationship (111)ScN∥(001)MgO, [11̄0]ScN∥[11̄0]MgO, and [112̄]ScN∥[110]MgO. Room-temperature electrical resistivity ρ is 1.2×104 μΩ cm while dρ/dT was found to be negative, indicating semiconducting behavior, with ρ varying from 1.6×104μΩ cm at 80 K to 1.1×104 μΩ cm at 400 K. Optical absorption coefficients ranged from 1×104 cm−1 at 1.5 eV to 2.6×105 cm−1 at 3.5 eV with a well-defined edge corresponding to a direct transition at 2.37±0.05 eV.
Quantitative measurement of nodule formation in W–Ti sputtering
Authors: Lo Chi-Fung , Draper Darryl
Published: July 2002

Titanium–tungsten alloys have been used as a diffusion barrier between Si substrates and Al-based interconnect metallization for more than two decades. Due to the increasing complexity of integrated circuits, the primary concern has been focused on the reduction of particles during sputtering. Flaking of the redeposited nodules on the target surface was suspected to be one of the particulate sources. To control the nodule formation, a fundamental knowledge of the nodule formation mechanism is required. In this study, the influence of target properties and sputtering parameters on nodule formation in sputtering targets of tungsten with 10 and 15 wt % titanium was investigated. The amount and life of the nodules as a function of target life was determined. A parabolic relation showed a saturated nodule size with increased sputtering life. The existence of fractured nodules confirms the nodules to be the particulate source.
Achievement of extremely high vacuum in an electrolytically polished stainless steel vacuum chamber
Authors: Watanabe Shu , Kurokouchi Satoshi , Kato Shigeki , Aono Masakazu
Published: July 2002

In order to lower the ultimate pressure of a vacuum chamber, it is necessary to reduce the outgassing rate from the chamber and to improve the pumping ability. To reduce the outgassing rate, the chamber surface was treated by electrolytic polishing. The pumping speed was improved by a reduction of gases dissolved in a filament of a titanium sublimation pump. We succeeded in achieving extremely high vacuum (XHV) of the order of 10−11 Pa from atmospheric pressure within one day. XHV without baking was also achieved.
Decay length of the pressure dependent deposition rate for magnetron sputtering
Authors: Drüsedau Tilo P. , Löhmann Mirko , Garke Bernd
Published: July 2002

The pressure dependence of the deposition rate for magnetron sputter deposition of various elemental semiconductors and metals was investigated by x-ray measurements on sputtered films and quartz monitor measurements. It was found that for all elements investigated the dependence of the rate Φ on pressure-distance (pd) is well described by Φ=Φ0(1−e−cpd)/cpd. The value of c equals the inverse characteristic pressure-distance product (pd)0, which is the characteristics of the exponential decay of rate with pressure for low pressures. The experimental data of (pd)0 vary from 4.6 Pa cm for aluminum to 120 Pa cm for tungsten. It is shown that (pd)0 depend on both material specific properties and process parameters. The material specific properties are mainly the atomic mass and diameter, and the surface binding energy. The process parameters target voltage and power density act via the increase of the mean free path and the reduction of gas density, respectively, on (pd)0. As a first approximation, the characteristic pressure-distance product for argon as sputtering gas is proportional to the product of target atomic mass, average atomic energy and thermal mean free path.
Development of a novel structure zone model relating to the closed-field unbalanced magnetron sputtering system
Authors: Kelly P. J. , Arnell R. D.
Published: July 2002

It is well established that the microstructure of a thin film strongly influences its physical and chemical properties. Microstructure, in turn, is determined by a number of deposition and process parameters which control the energy delivered to the growing film. The closed-field unbalanced magnetron sputtering (CFUBMS) process has now been developed to the stage where it can be routinely used to deposit very high quality, well adhered coatings of a wide range of metals and ceramics. A key factor in the success of this process is the ability to transport large ion currents to the substrate. This can enhance the formation of fully dense coating structures at relatively low homologous temperatures, compared to other sputtering systems. The importance of microstructure on the performance of a coating has led to the development of models designed to describe coating structure in terms of specific deposition parameters. Several such structure zone models (SZMs) relating to various physical vapor deposition (PVD) processes have been published. However, because of the advantages of operating in the CFUBMS mode, the structure of coatings deposited in this mode do not conform to those predicted by existing SZMs relating to other PVD processes. Also, in most existing SZMs, the final coating structure is described in terms of the homologous temperature of the coating and one other parameter which attempts to describe the additional influence on the structure of the simultaneous ion bombardment of the growing film. Several parameters have been used to fill this role including coating pressure, substrate bias voltage, and an energy parameter defined as the average energy carried by the arriving ions per condensing atom. However, other studies have shown that ion energy and ion flux are fundamental parameters in ion-assisted PVD processes and their effects must be considered separately when describing coating structures. A detailed investigation has now been carried out into the CFUBMS process. As a result of this, a SZM relating to the CFUBMS system has been developed, in which coating structures are described in terms of homologous temperature, bias voltage and the ion-to-atom ratio incident at the substrate. This is a novel model which allows the influence of ion flux and ion energy to be considered separately. This study has also highlighted a number of other characteristics of the CFUBMS system. For example, both ion current density and deposition rate are directly proportional to the target current, although their coefficients of proportionality differ. Deposition rate decreases more rapidly with increasing substrate-to-target separation than ion current. Consequently the ion-to-atom ratio incident at the substrate increases with separation. Indeed, with magnetrons of fixed magnetic configuration, in order to increase the ion-to-atom ratio for any set of deposition parameters, it is necessary to increase the substrate-to-target separation.
Surfactant and ordering effects of arsenic interlayers at the Pb/InP(110) interface
Authors: Schömann S. , Chassé T.
Published: July 2002

(Soft) x-ray photoelectron spectroscopy and x-ray photoelectron diffraction (XPD) were used to investigate interface reaction, film morphology and surface order at both the Pb/InP(110) interface and the corresponding interface including an arsenic interlayer. The core level spectra did only reveal very weak interface reaction, which could be suppressed by arsenic. Growth of three dimensional islands of metallic lead was observed on the Pb/InP(110) interface. Lead deposition onto an ordered arsenic monolayer on InP(110) was accompanied by segregation of approximately half the arsenic. The growth mode of the lead film changed dramatically from three-dimensional island growth to a layer-by-layer-like mode due to the surfactant arsenic. XPD patterns provided evidence of ordered lead growth on the original system while the arsenic induced smooth Pb films show strong disorder.
Thermal and electron-driven chemistry of CCl4 on clean and hydrogen precovered Si(100)
Authors: Junker K. H. , Hess G. , Ekerdt J. G. , White J. M.
Published: July 2002

The thermal and electron activated properties of CCl4 on Si(100), with and without adsorbed hydrogen, have been investigated in the temperature range 100–1100 K using temperature programmed desorption (TPD), electron stimulated desorption, and x-ray photoelectron spectroscopy. Dosed at 100 K but not exposed to electrons, molecular CCl4 desorbs from both surfaces between 120 and 170 K with coverage-dependent monolayer and multilayer peaks. An etching product, SiCl2 desorbs from Si(100), but not H–Si(100). Electron irradiation of CCl4 on both surfaces at 100 K drives reactions with ejection and retention of products. Compared to thermal activation, SiCl2 TPD is enhanced on Si(100), while on H–Si(100), the SiCl2 TPD channel opens and HCl peaks appear at 610 and 820 K in TPD. Ejection of neutral CClx (x⩽4) and Cl is observed on both Si(100) and H–Si(100), and the CCl+ ion signal decays with a cross section of (1.3±0.1)×10−16 on Si(100) and (2.8±0.5)×10−17 cm2 on H–Si(100). On both surfaces, the electron activated cross section describing the decay of the CCl4 TPD peak area is 9×10−17 cm2. C2Clx (x=2, 4, and 6) appear in post-irradiation TPD.
Atmospheric permeation of austenitic stainless steel
Authors: Moore Boude C.
Published: July 2002

The wall thickness of austenitic stainless steel, now in common use on vacuum chambers, is based on an overestimate of the permeation of atmospheric hydrogen through the walls. This error is based on (1) the use of data from an experiment with pure hydrogen, not atmospheric; (2) neglect of the evidence for the strong influence of oxygen and oxide layers on the reduction of permeation; (3) a simplified extrapolation procedure; (4) neglect of the change in vacuum outgassing rates due to recombination of atomic hydrogen. There has been no experimental demonstration of the existence of such permeation. The actual room temperature permeation is estimated to be less than the accepted estimate by several orders of magnitude. Thus, vacuum systems may be designed with substantially thinner walls, as thin as they can be made to withstand atmospheric pressure. These in turn, will permit much simpler outgassing procedures, and the achievement of lower outgassing rates in practice.
Diamond synthesis in capacitively coupled 13.56 MHz radio frequency plasma using parallel plate electrodes with the addition of direct current power
Authors: Asakura Y. , Chattopadhyay K. K. , Matsumoto S. , Hirakuri K.
Published: July 2002

Capacitively coupled radio frequency plasmas offer some advantages over other techniques such as microwave induced plasmas with regard to the large area homogeneous deposition of thin films. Diamond films were synthesized from methane and hydrogen gas mixtures in a capacitively coupled radio frequency plasma using a standard 13.56 MHz source in a popular parallel plate electrode geometry with the addition of dc power. The rf+dc plasma is stable and homogeneous and suitable for prolonged operation. The diamond films deposited by this method were characterized by x-ray diffraction, scanning electron microscopy and Raman spectra measurements. Preliminary experiments with electrodes having a diameter of 60 mm were done to investigate the possibility of scaling up of this technology for large-area diamond deposition.
Molecularly engineered low temperature atomic layer growth of aluminum nitride on Si(100)
Authors: Liu Herng , Rogers J. W.
Published: July 2002

Trimethylamine alane (TMAA) and deuterated ammonia (ND3) were used to grow aluminum nitride (AlN) thin films on Si(100) based upon a molecularly engineered atomic layer growth process. Atomic layer growth requires, in part, self-limiting adsorption of both precursors. Self-limiting behavior of TMAA only occurred at temperatures below 400 K as confirmed by x-ray photoelectron spectroscopy (XPS). Although the adsorption of ND3 on the surface is self-limiting between 300 and 675 K, alternating exposures of TMAA and ND3 at 380 K did not fully dehydrogenate ND3 into nitride. However, by sequentially exposing the substrate to ND3 at 675 K and TMAA at 380 K, we achieved atomic layer growth of AlN. The growth scheme consists of the adsorption of ND3 on Si(100) at 675 K which generates ND2 species on the surface. Then TMAA is exposed to the ND3-derivatized surface at 380 K. As the surface temperature is raised back to 675 K for the next ND3 exposure, AlN was formed by the bridge bonding of Al between two nitrogen centers and desorption of HD. Minor surface species include AlHxNDy (x=1–2, y=1–2). Further adsorption of ND3 at 675 K resulted in (i) direct nitride formation by decomposition of AlHxNDy to AlN and (ii) the formation of ND2 species bonded to surface Al. Similar to the first TMAA dose, the second exposure produced AlN and AlHxNDy. The mechanisms are consistent with the expected D2 and HD desorption during temperature programmed desorption after each exposure cycle. The carbon contamination after each ND3 exposure is below the detection limit of XPS. The layer-by-layer growth mode is confirmed by the close match between predicted and measured attenuation of XPS substrate features and Al/N atomic ratios.
Patterning of NiFe and NiFeCo in CO/NH3 high density plasmas
Authors: Jung K. B. , Hong J. , Cho H. , Onishi S. , Johnson D. , Park Y. D. , Childress J. R. , Pearton S. J.
Published: July 2002

The CO/NH3 plasma chemistry operated under conventional reactive ion etching conditions does not etch NiFe or NiFeCo. However, under high density plasma conditions, etch rates up to ∼500 Å min−1 are obtained for both materials provided optimized ratios of CO:NH3 and values of ion flux and ion energy are employed. The etch mechanism still has a strong physical component and appears to depend on having sufficient CO to form carbonyl etch products, and to avoid formation of a carbide-like surface layer. Under nonoptimized conditions, the latter can lead to net deposition rather than etching.
Breaking the Ga–CH3 bond at cryogenic temperatures using atomic hydrogen. Adsorbed trimethylgallium reactivity
Authors: Mawhinney Douglas B. , Glass John A. , Yates John T.
Published: July 2002

The chemical interaction of adsorbed trimethylgallium and atomic hydrogen was investigated on a powdered silicon dioxide substrate containing various coverages of hydroxyl groups. The adsorption of trimethylgallium occurs nondissociatively at 128 K. Desorption of trimethylgallium occurs near 160 K by a nondissociative route. Atomic hydrogen, produced on a hot tungsten filament, reacts with adsorbed trimethylgallium at 128 K. This reaction produces infrared absorbances characteristic of dimethylgalliumhydride dimers or higher polymers, with Ga–H–Ga bridge bonds with a broad absorbance centered at 1690 cm−1. These hydrogenated species are much more resistant to subsequent reaction with atomic hydrogen than trimethylgallium. Variations of the surface hydroxyl coverage on the silicon dioxide had no effect on the reaction of trimethylgallium with atomic hydrogen. Surface hydroxyl groups do not react with trimethylgallium below 173 K. The highly dehydroxylated silicon dioxide surface also does not react with trimethylgallium below 173 K.
Ultraviolet/high resolution electron energy loss spectroscopy of CO on Pt(110) and benzene on Pt(110)
Authors: Thomas F. , Chen N. , Lee I. , Ford L. , Blowers P. , Masel R. I.
Published: July 2002

Recently there has been some controversy about how CO and benzene adsorb on platinum. With CO, there is disagreement over whether there is back donation of electrons from the metal to the CO 2π* orbital. With benzene, there is disagreement, over whether benzene adsorbs in a distorted state. In this article we use a standard high resolution electron energy loss (HREELS) spectrometer with modified electronics to measure the equivalent of a ultraviolet (UV) spectrum for two different systems: CO on Pt(110) and benzene on Pt(110) and benzene on Pt(110). In the case of CO, the UV spectrum shows peaks at 5.6 and 8.2 eV that may shift slightly with coverage. By comparison, gas-phase CO shows peaks at 6.2 and 8.3 eV. The difference between the gas-phase peak positions and those on the surface are indicative of the antibonding orbitals being stabilized, as one would expect from the Blyholder model. With benzene we observe two different spectra: a first monolayer spectrum with a broad peak centered at 4.9 eV, and a multilayer spectrum with peaks at 0.75, 3.82, 4.71, 6.20, and 6.84 eV. The multilayer spectrum matches the spectrum of condensed benzene, while the first monolayer spectrum is quite different and resembles that of a diene. Together, these results show that UV/HREELS spectroscopy provides useful information about adsorbates on surfaces.
Atom probe analysis of the dissociation of CO and N2 gases on a W(110)-oriented tip
Authors: Shimizu Tetsuo , Ohi Akihiko , Tokumoto Hiroshi
Published: July 2002

We studied the dissociation of CO and N2 gases on a W(110)-oriented tip by an atom probe (AP) technique. We paid attention to the effect of electric field induced dissociation as well as the temperature dependence of dissociation probabilities. We first show that the AP can discriminate between physisorbed and trapped states based on the difference in desorption field strength. Then we show that field-induced dissociation can be properly measured. Finally, we conclude the activation energy required for the conversion from the trapped state to the dissociated state to be 30 meV for CO gas and 22 meV for N2 gas.
Self-assembled CaF2 nanostructures on silicon
Authors: Petrovykh D. Y. , Viernow J. , Lin J.-L. , Leibsle F. M. , Men F. K. , Kirakosian A. , Himpsel F. J.
Published: July 2002

A method for chemical imaging of CaF2, CaF1, and Si by scanning tunneling spectroscopy is presented. This method is utilized for identifying the growth regimes of CaF2 and CaF1 on stepped Si(111)7×7. For CaF2 on Si(111), we find random islands, stripes, and ordered islands, depending on the supersaturation. For CaF2 on a CaF1 monolayer on Si(111), we find regular stripes that are continuous and separated from each other. CaF2 structures are attached to the bottom edge of a step when growing directly on Si, but they prefer the top of a step edge when growing on a CaF1 buffer layer. These highly regular, linear arrays of CaF2 stripes and dots can serve as masks for assembling more sophisticated nanostructures.
High-rate deposition of biaxially textured yttria-stabilized zirconia by dual magnetron oblique sputtering
Authors: Kaufman D. Y. , DeLuca P. M. , Tsai T. , Barnett S. A.
Published: July 2002

Biaxially textured yttria-stabilized zirconia thin films were deposited at high rates (≈3 μm/h) using a two-target reactive magnetron sputtering geometry. The two small-area magnetron targets were mounted at 45° or 56° with respect to, and on opposite sides of, the substrate normal. The films showed strong (001) out-of-plane texture. Azimuthal x-ray diffraction scans confirmed strong in-plane texture with a best (111)-peak full width at half maximum of 23°. The alignment was presumably due to directed impingement of sputtered atoms and/or energetic Ar neutrals reflected from the Zr–Y target surfaces. The film texture was not as strong when only one sputter source was used. Sputtering geometries useful for large-scale deposition of textured films are described.
Silicon nitride film growth for advanced gate dielectric at low temperature employing high-density and low-energy ion bombardment
Authors: Sekine Katsuyuki , Saito Yuji , Hirayama Masaki , Ohmi Tadahiro
Published: July 2002

Direct nitridation of silicon surface can be realized at a temperature as low as 430 °C by using high-density plasma above 1012 cm−3 featuring low ion bombardment energy below 7 eV. This study shows that stoichiometric silicon nitride can be obtained for the first time at a temperature of 400 °C by precise control of the nitrogen partial pressure to generate N2+ in the plasma. Moreover, hysteresis in the capacitance–voltage data that has been attributed to charge traps in silicon nitride film can be reduced dramatically by adding hydrogen to Ar/N2 plasma for terminating dangling bonds with hydrogen. The dielectric strength of silicon nitride films is nearly equivalent to those of thermally grown silicon nitride and silicon oxide. The leakage current of silicon nitride film is dramatically reduced compared to that of thermally grown silicon oxide even if their equivalent thicknesses are equal. The silicon nitride films have almost no stress-induced leakage current and very little trap generation even in high-field stress.
Effects of growth temperature on Mg-doped GaN epitaxial films grown by plasma-assisted molecular beam epitaxy
Authors: Myoung J. M. , Kim K.
Published: July 2002

A series of Mg-doped GaN films were grown by plasma-assisted molecular beam epitaxy at different temperatures and the resulting surface morphology, crystallinity, and electrical properties were examined. Although the films were grown under N-rich conditions which usually do not give rise to high quality films, very smooth surfaces were obtained at high temperatures (Ts⩾650 °C) when doped with Mg. From the information on grain size measured with an atomic force microscope, the activation energy for Ga diffusion was determined to be ∼1.0 eV. This low value is considered to be responsible for promoting the diffusion of Ga atoms on the growing surface and facilitating two-dimensional growth at high temperatures. It was found, with no surprise, that the concentration of Mg incorporated into the film depends on the growth temperature and that the type of electrical conduction in the films is determined by the competition between the background electron concentration and Mg-doping. Mg-doped GaN films grown at temperatures between 650 °C and 700 °C exhibited the p-type electrical properties with smooth surfaces (root-mean-square roughness ∼2 nm) and good crystallinity (full width at half maximum ⩽20 arcmin).
Photoinduced dichroism and its low-temperature characteristics in obliquely deposited amorphous As–Ge–Se–S thin films
Authors: Lee Hyun-Yong , Chun Jin-Young , Yeo Cheol-Ho , Chung Hong-Bay
Published: July 2002

The photoinduced dichroism and its low-temperature characteristics in obliquely deposited amorphous As–Ge–Se–S thin films have been studied using a linearly polarized 632.8 nm He–Ne laser light and a control system capable of increasing the film temperature from 77 K. Our experimental results have been discussed on the basis of native valence-alternation pairs depended on the film fabrication. Although the absorption slopes in the extended region (hν>Eop) decrease with increasing deposition angle, the optical energy gap Eop remains the same as for 0° films, i.e., Eop=2.04 eV. A columnar structure with an inclination angle of approximately 70° is formed in 80° deposited films. While the value of saturated dichroism Dsat itself remains constant, independent of the intensity, it depends strongly on the deposition angle θ and the film temperature T, i.e., Dsat(θ,T). For example, Dsat(80°,77 K) is more than four times Dsat(80°,300 K), and the values of Dsat(0°,300 K) and Dsat(80°,300 K) are about 4.2% and 6.0%, respectively. We believe that an enhanced D in a columnar film is attributed to the increase of disorder (boids and dangling bonds). The photoinduced dichroism relaxes during a dark relaxation after its saturation and eventually sustains any value of nonzero, which depends on the inducing light energy and especially the value obtained after a prolonged exposure (∼3.3 h) is evaluated to be about 4.5 for 80° deposited film. However, it is eliminated completely by the exposure of nonpolarized light only for about 3 min.
Study of the effect of layer thickness, beam energy, and metal density on the resistless silicide direct-write electron-beam lithography process for the fabrication of nanostructures
Authors: Lavallée Eric , Beauvais Jacques , Drouin Dominique , Corbin Jacques
Published: July 2002

To overcome the limitation of resists in electron beam lithography, a resistless electron beam lithography technique was recently developed. In the silicide direct-write electron-beam lithography process (SiDWEL), a thin metallic film is deposited on a silicon surface. A low-energy (<3 keV) electron beam is then used to enable the intermixing of the metal and the silicon layers through thermal effects. A chemical etch is then used to remove the unexposed metal regions. Thermal calculations are performed using a Monte Carlo simulation of electron trajectories and are correlated with experiments using Ni as the thin metallic film. A comparison of the doses required for the formation of several metals is also done. Results show that the SiDWEL process is possible when the electrons lose all their energy in a layer thickness comparable to the phonon mean free path. Finally, experiments are performed using multilayer samples to form silicide structures.
Identification of surface chemical functional groups correlated to failure of reverse osmosis polymeric membranes
Authors: Beverly Sharon , Seal Sudipta , Hong Seungkwan
Published: July 2002

The goal of this study is to identify the causes of membrane failure observed during a 15-month operation of a low pressure reverse osmosis (RO) membrane pilot plant to treat a highly organic surface water from the Hillsborough River in Tampa, Florida, using various surface analytical techniques. Three different commercial RO membranes, made of cellulose acetate or polyamide, were used in this pilot study, and all of these membranes showed performance deterioration presumably due to membrane fouling and degradation at given experimental conditions. In order to elucidate the mechanisms of membrane failure, scanning electron microscopy with energy dispersive spectrometry (SEM/EDS), x-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR) were performed on the surface of the polymeric RO membranes used. More specifically, molecular composition including surface functional groups were identified from XPS analysis, confirmed by FTIR, and correlated to membrane failure. In addition, surface morphology and fouling layer composition were determined by SEM/EDS. The results indicated that the cellulose acetate membrane was biologically damaged, while the polyamide membrane was compromised by chlorine oxidation. The biodegradation of cellulose acetate was evidenced by the presence of nitrogen on XPS and FTIR scans. Chlorine uptake shown in XPS and FTIR scans of used polyamide membranes was a good indicator of chemical degradation. This study demonstrated that XPS, combined with FTIR and SEM/EDS, is a valuable diagnostic tool for failure analysis of polymeric RO membranes and provides valuable information to aid the manufacturers in designing better membranes for reverse osmosis.
Fabrication of submicron crossed square wave gratings by dry etching and thermoplastic replication techniques
Authors: Lehmann H. W. , Widmer R. , Ebnoether M. , Wokaun A. , Meier M. , Miller S. K.
Published: July 2002

Crossed square wave grating structures with periodicities below 0.4 μm have been fabricated in SiO2 and replicated into PVC. The structure in SiO2 is made by optically contact printing a Cr mask onto a trilevel structure consisting of an amorphous quartz plate, an a-Si film and positive photoresist and subsequent reactive sputter etching in CCl2F2 and CHF3 to pattern the a-Si and SiO2, respectively. Up to 1 μm deep structures have been made in SiO2 and replicated into PVC by embossing with a Ni master. These PVC replicas can be used as efficient substrates for SERS (surface enhanced Raman scattering) after angle evaporation of a very thin Cu film. SERS spectra for Nile Blue are shown.
Mass spectrometric studies of plasma etching of silicon nitride
Authors: Clarke P. E. , Field D. , Hydes A. J. , Klemperer D. F. , Seakins M. J.
Published: July 2002

Basic chemical processes in a CF4/O2 plasma during etching of silicon nitride have been investigated using mass spectrometry. Samples of the discharge are extracted through a quartz capillary and the resulting variations in species abundance at a nitride/oxide interface yield information on etch reaction pathways. Mechanisms of F and CF2 attack and SiF4, N2, NO, and CN product formation are proposed. The experimental data are suitable for application in mass spectrometric endpoint detection.
Surface studies by optical second harmonic generation: An overview
Authors: Shen Y. R.
Published: July 2002

Optical second harmonic generation for surface and interface studies is briefly reviewed, with numerous examples illustrating how powerful and versatile this new surface analytical technique can be.
Laser investigation of the dynamics of molecule–surface interaction: Rotational and translational energy of scattered molecules
Authors: Häger J. , Walther H.
Published: July 2002

Combining molecule surface scattering with state-selective laser-induced fluorescence and laser resonance ionization the internal energy distributions and state- and angular-resolved velocity distributions of surface-scattered NO molecules have been measured. In the experiments a supersonic NO beam was scattered from graphite and platinum surfaces. The parameters being varied were surface temperature and average velocity of the incoming molecular beam. The NO/Pt system shows a trapping/desorption behavior for all surface temperatures and a full rotational accommodation at low and only incomplete rotational accommodation at high temperatures. In the case of the weakly inelastic scattering of NO/graphite a similar behavior of the rotational energy of the scattered molecules was observed. The angle- and state-resolved velocity distributions show at low surface temperatures the coexistence of a quasispecular and an isotropic part. The diffusively scattered NO molecules gain rotational energy, but transfer much more translational energy to the surface, so that the energy balance is considerably negative. For the specularly scattered molecules energy loss and gain are balanced at low surface temperatures. With increasing temperatures the scattered molecules may gain translational energy, but the rotational energy stays constant, resulting under certain conditions in an energy transfer from the surface to the scattered molecules.