bluuebunny/crossref_metadata_2025 huggingface dataset:
Angular dependence of the redeposition rates during SiO2 etching in a CF4 plasma
Authors: Cho Byeong-Ok , Hwang Sung-Wook , Lee Gyeo-Re , Moon Sang Heup
Published: July 2002

The angular dependence of the redeposition rates during SiO2 etching in a CF4 plasma was studied using three types of Faraday cages located in a transformer coupled plasma etcher. The SiO2 substrates were fixed on sample holder slopes that have different angles to the cathode. The substrate was subjected to one of three processes depending on the design of the Faraday cage, i.e., redeposition of sputtered particles from the SiO2 bottom surface (case I), substrate etching by incident ions (case II), or simultaneous etching and redeposition (case III). Both the redeposition and the etch rates were measured by changing the substrate–surface angle and the self-bias voltage in the range of −100 to −800 V. The redeposition-only rates (case I) at −450 and −800 V closely followed the quadratic curve of the angle whereas the rates at −100 V followed the cubic curve, indicating different mechanisms of the bottom SiO2 etching depending on the energy regimes. The steep increase of the redeposition rate with the angle was attributed to three factors: the substrate–bottom distance, the angular distribution of emitted particles from the bottom surface, and the particle incident angle on the substrate surface. The etch-only rate curves (case II) closely followed the cosine of the surface angle. The etch-rate curve changed into a reverse-S shape when the substrate was subjected to simultaneous etching and redeposition (case III). The net etch rate for case III decreased drastically above 60°, showing a negative value, i.e., a net redeposition, beyond 75°. The drastic decrease in the net etch rate coincided with the steep increase in the redeposition rate, implying the significant effect of redeposition.
Influence of substrate bias on the structure and properties of (Ti, Al)N films deposited by filtered cathodic vacuum arc
Authors: Cheng Y. H. , Tay B. K. , Lau S. P. , Shi X.
Published: July 2002

(Ti, Al)N films were deposited by an off-plane, double-bend, filtered cathodic vacuum arc technique in N2 atmosphere at room temperature. The (Ti, Al)N films deposited are atomically smooth. The influence of substrate negative bias at the wide range (0–1000 V) on the deposition rate, surface morphology, crystal structure, internal stress, and mechanical properties of (Ti, Al)N films were systematically studied. Increasing substrate bias results in the decrease of deposition rate and the increase of surface roughness monotonically. At the bias of 0 V, (Ti, Al)N films are amorphous, and the internal stress, hardness, and Young’s modulus for the deposited films are fairly low. With increasing substrate bias to 200 V, single-phase face-centered cubic-type nanocrystalline (Ti, Al)N films can be obtained, and the internal stress, hardness, and Young’s modulus increase to the maximum of 7 GPa, 28 GPa, and 240 GPa, respectively. Further increase of substrate bias results in the decrease of intensity and the broadening of x-ray diffraction lines, and the gradual decrease of internal stress, hardness, and Young’s modulus in (Ti, Al)N films.
Integration of piezoelectric (Pb, La)TiO3 on (100)InP by using a CeO2 buffer layer
Authors: Vasco E. , Vázquez L. , Zaldo C. , Coya C. , Kling A. , Soares J. C.
Published: July 2002

(Pb, La)TiO 3 /CeO 2 /(100)InP multilayers have been prepared by pulsed laser deposition (PLD) using a KrF laser. CeO2 films deposited in a low oxygen pressure (PO2=10−5 mbar) exhibit the coexistence of stoichiometric CeO2 and oxygen deficient CeO2−x phases. The latter can be best avoided by a postdeposition annealing in a higher oxygen pressure (PO2=0.1 mbar). The PLD conditions leading to largest grain size and [111] textured CeO2 are a substrate temperature Ts=575 °C and a laser fluence of 4 J/cm2. (Pb, La)TiO3 films are deposited at Ts=650 °C and PO2=0.1 mbar. The CeO2 buffer stimulates [001] (Pb, La)TiO3 texture. The films have sharp layer interfaces and uniform composition inside their respective layers.
Electron emission from ion bombarded stainless-steel surfaces coated and noncoated with TiN and its relevance to the design of high intensity storage rings
Authors: Hanson A. L. , Thieberger P. , Steske D. B. , Zajic V. , Zhang S. Y. , Ludewig H.
Published: July 2002

High intensity proton synchrotrons and proton storage rings are being designed with TiN coated vacuum components to reduce electron cloud buildup, which can lead to multipacting and instabilities. It has been established that when the surfaces are irradiated with energetic electrons, the TiN coatings reduce the electron cloud buildup because the TiN has a higher work function when compared to metallic surfaces. The present work investigates the electron emission from these coatings when the surface is bombarded with 28 MeV protons, 126 MeV oxygen ions, and 182 MeV gold ions. Understanding the electron emission from ion bombardment is important for the machine collimator regions, where the beam halo is removed.
Method for navigating two scanning probes to a common point without additional microscopes
Authors: Okamoto Hiroshi , Chen Dongmin
Published: July 2002

We have developed an efficient method for navigating two scanning tunneling microscope tips into proximity. Using a combined five degrees of freedom coarse positioning system, the two tunneling microscopes are brought to a special reference sample consisting of three mutually nonparallel planes. Successive tunneling on each of these surfaces leads the tips to a common point. This method is simple, inexpensive, and advantageous in restricted conditions such as in ultrahigh vacuum and very low temperature, where the incorporation of an additional guiding system such as an optical telescope or electron microscope is cumbersome.
Etch characteristics of iridium in chlorine-containing and fluorine-containing gas plasmas
Authors: Chung Chee Won , Chung Ilsub
Published: July 2002

The etch characteristics of iridium thin films with a photoresist mask were studied by varying the etch chemistries in an inductively coupled plasma. The etch rates and etch profiles of iridium films were investigated with respect to etch gases, which included Cl2/Ar, SiCl4/Ar, C2F6/Ar, HBr/Ar, and C2F6/Cl2/Ar mixtures. Fluorine-containing gases were the most effective in achieving clean etch profiles without any redeposition or residue. However, the etch rate of iridium was found to be faster in chlorine-containing gases than in any of the others tested. Field emission auger electron spectroscopy was employed for the analysis of the redeposited materials and transient etch profiles by time progression were observed by scanning electron microscopy. It can be concluded that iridium films are etched mainly by physical sputtering in chlorine-containing gases and by a chemically assisted sputtering etching component in fluorine-containing gases. A residue-free iridium etching with a sidewall angle of approximately 45°–50° was obtained by using a gas mix of C2F6, Cl2, and Ar.
Influence of anisotropic in-plane strain on critical point resonances in reflectance difference data
Authors: Hingerl K. , Balderas-Navarro R. E. , Bonanni A. , Stifter D.
Published: July 2002

The sharp resonances in reflectance difference spectroscopy (RDS) data at the critical points of the dielectric function of bulk semiconductors have been assigned to surface-bulk transitions, photon localization, or optical transitions from bound dimer states to excited dimer states. For the case of ZnTe, CdTe, and ZnSe, we present experimental data indicating that a uniaxial in-plane stress component induces sharp resonances at these critical points by lifting the degeneracy of the optical transitions at the Λ and Γ points due to the resulting anisotropic strain. Even small stresses of about 1–5 MPa, or strains on the order of 1×10−5 can be detected with RDS.
Reaction of gas-phase atomic hydrogen with NO on Ru(001)
Authors: Kim Tae Won , Weiss Michael J. , Hagedorn Chrisopher J. , Weinberg W. Henry
Published: July 2002

The reactions of gas-phase atomic hydrogen [H(g)] and deuterium [D(g)] with preadsorbed nitric oxide [NO(a)] on the hexagonally close-packed Ru(001) surface have been studied by means of temperature-programmed desorption and high-resolution electron energy loss spectroscopy (HREELS). Exposure of gas-phase atomic deuterium to the saturated NO overlayer at a surface temperature of 100 K results in the observation of N2O, D2O, D2, NO, N2, and O2 in subsequent thermal desorption spectra. Since D2O is formed at low surface temperatures, an Eley–Rideal-like mechanism in which deuterium atoms from the gas phase react with the oxygen end of the preadsorbed NO is suggested. Spectroscopic evidence for this reaction on the Ru(001) surface is provided by HREEL spectra which show vibrations at 983 cm−1 [after H(g) exposure] and 977 cm−1 [after D(g)]. Since the loss at 983 cm−1 has not shifted significantly upon deuterium substitution, these losses are assigned to weakened N–O stretches of NOH (NOD) species. These species are stable after annealing to 200 K on Ru(001).
Fabrication of parallel-plate nanomirror arrays for extreme ultraviolet maskless lithography
Authors: Shroff Yashesh , Chen Yijian , Oldham William
Published: July 2002

A micromirror array for extreme ultraviolet (EUV) maskless lithography was designed and fabricated. The arrays are composed of devices with less than a 350 nm actuation gap and a surface area ranging from 1 μm2 to 20 μm2. The mirror layer is composed of silicon in lieu of the Mo/Si stack used for EUV mirrors in order to debug the process and to simplify the initial fabrication. Germanium was used as a sacrificial material while α-Si acts as a hinge for this parallel-plate design. Silicon migration into germanium was observed, so the thermal budget was restrained to 450 °C for the entire process. Scanning electron microscope images of working devices are provided.
Optical diagnostics of radio-frequency plasmas containing CHF3 and CHF3/O2: Laser-induced fluorescence of CF2, CF, and O atoms, and optical emission from H, F, and O
Authors: Hancock G. , Sucksmith J. P.
Published: July 2002

Laser-induced fluorescence (LIF) has been used to measure absolute concentrations of CF2, CF, and O atoms in a parallel-plate capacitatively coupled radio-frequency-driven plasma containing CHF3 and its mixtures with Ar and O2 at pressures between 50 and 500 mTorr. In CHF3 the spatial distribution of CF2 peaks at the driven electrode, and shows the importance of surface processes for its production. Time-resolved studies show evidence for its homogeneous chemical removal. CF concentrations are an order of magnitude lower than those of CF2, and removal by reaction with H atoms is consistent with time-resolved data taken on plasma extinction. For both radicals the absolute concentrations are higher than those found for similar plasmas in CF4. In the presence of O2 the fluorinated radical concentrations drop to below the detection limit, and the influence of surface removal processes is again invoked to explain the increase in O atom concentration observed when a small amount of CHF3 is added to a dominantly O2 gas flow. Optical emission from excited F, H, and O atoms is observed, and even when corrected by actinometry, is shown to be an unreliable indicator of the relative concentration of the ground-state species because of contributions from dissociative excitation of stable species in the discharge. Excited H atoms are found to be translationally hot from measurements of their linewidths, and are clearly not all formed from excitation of H atoms. Time-resolved actinometry (TRA) can be used in some cases to remove the contribution to the emission from dissociative excitation, but in the case of O atoms where both LIF and TRA were compared, the influence of a time-dependent dissociative excitation step complicates the analysis and is attributed to the presence of other species such as O2(a1Δg) in the discharge.
Chemical vapor deposition of HfO2 films on Si(100)
Authors: Sayan S. , Aravamudhan S. , Busch B. W. , Schulte W. H. , Cosandey F. , Wilk G. D. , Gustafsson T. , Garfunkel E.
Published: July 2002

HfO 2 films were grown on Si(100) by chemical vapor deposition as an attempt to develop an industrially straightforward gate dielectric deposition process. During deposition at ∼400 °C the decomposition of the hafnium-tetra-tert-butoxide Hf(C4H9O)4 precursor provides sufficient oxygen to produce a stoichiometric HfO2 film. Medium energy ion scattering, high resolution transmission electron microscopy, atomic force microscopy, and ellipsometry were used to identify the structure and composition of the film and its interface to the Si substrate. Local crystallinity in the films increased significantly with annealing. Capacitance–voltage and current–voltage methods were used to characterize the electrical properties of simple capacitor structures. When grown on high quality ultrathin oxides or oxynitrides, the deposited films displayed very good physical and electrical properties.
Growth kinetics and initial stage growth during plasma-enhanced Ti atomic layer deposition
Authors: Kim H. , Rossnagel S. M.
Published: July 2002

We have investigated the growth kinetics of plasma-enhanced Ti atomic layer deposition (ALD) using a quartz crystal microbalance. Ti ALD films were grown at temperatures from 20 to 200 °C using TiCl4 as a source gas and rf plasma-produced atomic H as the reducing agent. Postdeposition ex situ chemical analyses of thin films showed that the main impurity is oxygen, mostly incorporated during the air exposure prior to analysis. The thickness per cycle, corresponding to the growth rate, was measured by quartz crystal microbalance as a function of various key growth parameters, including TiCl4 and H exposure time, rf plasma power, and sample temperature. The growth rates were independent of TiCl4 exposure above 1×103 L, indicating typical ALD mode growth. The key kinetic parameters for Cl extraction reaction and TiCl4 adsorption kinetics were obtained and the growth kinetics were modeled to predict the growth rates based upon these results. Also, the dependency of growth kinetics on different substrate materials was investigated during the early stages of deposition with various thin films predeposited on the crystal rate monitor surface by sputtering or evaporation. The initial growth rates on Pt, Al, Au, and Cu are higher due to the higher Cl extraction rates, while those on Si and amorphous C are smaller due to etching of substrate materials by atomic H.
Patterning of wave guides in LiNbO3 using ion beam etching and reactive ion beam etching
Authors: Hines D. S. , Williams K. E.
Published: July 2002

A number of current and future optoelectronic components require the creation of waveguides in LiNbO3. In order to accomplish this, trenches between one and ten microns deep must be patterned into the LiNbO3 substrate. We have demonstrated the formation of near-vertical, smooth-walled trenches up to ten microns deep using Ar ion beam etching (IBE) and Ar/CHF3 reactive ion beam etching (RIBE) processes. Both Ar IBE and Ar/CHF3 RIBE processes can achieve etching rates of up to 100 nm/minute. Our patented RIBE process [K. E. Williams, et al. U.S. Patent No. 6,238,582 (29 May 2001)] has the additional advantage of providing up to a 5:1 selectivity for etching the LiNbO3 over a photoresist mask. The collimated beam available with IBE and RIBE allows control over feature profiles and redeposition removal. Using a combination of RIBE and a multiangle process, the sidewall angle and smoothness of the mask have been transferred into LiNbO3 substrates to depths between one and ten microns. This depth range can be expanded in either direction if an appropriate mask can be fabricated.
Scanning Electron Diffraction of Film Growth
Authors: Grigson C. W. B. , Dove D. B.
Published: July 2002

A discussion is given of the scanning-electron-diffraction technique. The importance of energy analysis of the diffracted beams in both reflection and transmission diffraction is emphasized. Details are given of the results of experiments in which intensity patterns are recorded while metal films are being deposited onto room-temperature carbon substrates inside the electron-diffraction system. Intensity profiles across the Debye-Scherrer rings have been obtained at 10- to 20-sec intervals, corresponding typically to 10-Å increments in film thickness; thus, diffraction patterns corresponding to the earliest stages of growth could be recorded. Representative specimens were examined by electron microscopy. Growth sequences have been recorded for Al, Ag, An, Ni, 80/20 Ni/Fe, Fe, and Ge. The growth characteristics are discussed and correlated with observations by electron microscopy. Attention is given to the interpretation of electron-diffraction patterns from very thin films and from (so-called) amorphous films.
Double scattering of rare gas ions from polycrystalline gold and copper
Authors: Sharma S. P. , Buck T. M.
Published: July 2002

Energy spectra of Ne, Ar, and Kr backscattered from polycrystalline gold and copper have been measured at various scattering angles for primary energies (E0) in the range 4−30 keV. In these experiments, the heavier noble gas ions exhibit wider double−scattering shoulders than do the lighter noble gas ions as expected from kinematic considerations in case of Au. However, in case of Cu, the kinematic calculations give wider double−scattering shoulders for Ne+ than for Ar+ for ϑ?120°. The soulders depend upon ϑ and the ratio of the scattering yield at the shoulder to scattering yield at the main peak (I2/I1) decreases with increasing scattering angle ϑ in all systems studied in this paper, as expected from scattering cross−section considerations. However, for a given primary ion the ratio (I2/I1) is lower for gold than for copper at a given E0 and ϑ in these experiments contrary to what might be expected from scattering cross−section considerations.
Abstract: SIMS—a useful complement to other depth profiling techniques
Authors: Baun W. L. , McDevitt N. T.
Published: July 2002

Secondary ion mass spectroscopy (SIMS) used alone has been shown to be a powerful tool for elemental surface characterization.1,2 Used in conjunction with another technique such as ion scattering spectroscopy (ISS) or Auger electron spectroscopy (AES), SIMS becomes even more powerful. SIMS has been combined in our laboratory with both of the above techniques using quadrupole mass analyzers from two different manufacturers.

The complementary nature of SIMS−ISS and SIMS−AES make them especially useful when they are used together. The weakness of one is generally the strength of the other. Specific examples of this strength−weakness relationship are shown. Interesting SIMS results at ion beam accelerating energies of as low as 100 V are discussed for materials studied in research on adhesive bonding.
A thin film temperature sensor
Authors: McLennan W. D. , Ooten R. T. , Bynum D. S. , Palmer J. L. , Pendley K. N. , Baxter C. R.
Published: July 2002

Using vacuum−deposition techniques, a thin film thermistor has been developed. The device consists of a tin selenide sensing material, platinum leads, and quartz encapsulation deposited on a 1/4 mil kapton substrate. The resistance of a typical sensor shows increases of 2 1/2 orders of magnitude for a corresponding temperature decrease from 30 to −130°C. The room temperature resistance and resistance vs temperature dependence of the sensor can be controlled by a proper choice of the deposition parameters and the device configuration.
The atomic arrangement in the 1×1 structure of a silicon−ordered monolayer on Mo{001}
Authors: Ignatiev A. , Jona F. , Jepsen D. W. , Marcus P. M.
Published: July 2002

The reaction of a clean Mo{001} surface with Si vapor was studied with low−energy electron diffraction (LEED) and Auger electron spectroscopy (AES). For an apparent coverage of one monolayer of Si atoms, the symmetry and the periodicity of the surface structure are the same as for the clean surface; this structure is therefore conventionally designated Mo{001} 1×1−Si. An analysis of the intensities of the diffracted beams reveals that the Si atoms are adsorbed in the fourfold coordinated pyramidal hollows formed by four adjacent Mo atoms on the {001} surface. The distance between the plane of adsorbed Si atoms and that of the top layer of Mo atoms is 1.16±0.1 Å.
Abstract: Influence of substrate temperature and small oblique incidence on the anisotropy field, H
k, of Ni−Co−Fe films—a new−found oscillatory behavior
Authors: Dey S. K.
Published: July 2002

Ternary Ni−Co−Fe films of nominal composition 64:13:23, thickness 1000 Å and diameter 5−10 mm were deposited by electron beam gun on 7059 substrates at temperatures from ambient to 200°C. The anisotropy fields, Hk, were measured by a special low−signal, third−harmonic susceptibility technique previously reported. Film composition differed slightly from that of the melt. However, Hk showed an oscillatory fluctuation decreasing from 22 Oe at ambient to about 12.5 Oe at 88°C before passing through a maximum of 25.2 Oe at 120°C. Samples prepared at normal and small oblique incidence showed some variations in Hk values but retained the over−all temperature dependence. The results are interpreted in terms of texture constraint, grain size, and possible fluctuations in the cobalt−iron or nickel−iron pairing.
Use of flexible reflective surfaces for solar energy concentration
Authors: Jacobi William I.
Published: July 2002

Historically, many techniques for utilizing solar energy have suggested reflective optics, although usually with glass mirrors. The requirements of spacecraft and their associated thermal control problems provided the impetus to develop lightweight, flexible reflectors. Thin metallic vapor deposits such as aluminum and silver on a clear flexible film such as Teflon have been used to act in reflectances as high as 94%, with long−term stability even in a space environment. The high reflectance, coupled with present processing techniques, makes these materials candidates for solar energy concentrators. A flexible metalized film, stretched drum−head fashion, can form a mirror that can be oriented to direct sunlight to a central receiver. The use of taut membrane is being explored as part of a NSF/RANN grant studying feasibility of a large−scale solar thermal power plant. The evaluation of any reflector requires measurement of the spectral response, specularity, and over−all flatness. Integrating the spectral response to the energy distribution of sunlight gives the total reflected energy. Of equal importance is the specularity or divergence of the reflected beam. The combination of these factors will determine a candidate reflector’s suitability. A device for measuring the bi−directional reflectance−distribution function is described and data are presented. A discussion of membrane−reflector development and data from life tests are presented.
Deposition of CdS by evaporation through a gas discharge
Authors: Berg R. S. , Nasby R. D.
Published: July 2002

Cadmium sulfide is an important material used in thin−film photovoltaic devices. The deposition of cadmium sulfide films by single indirect source evaporation through a gas discharge is investigated and the effects of the discharge on film properties and deposition rates are discussed. The discharge has a direct and advantageous effect on both the electrical and optical properties of the CdS thin films. These properties may be altered by suitable choices of evaporation and gas discharge parameters. Control of these properties is important in device applications and it is proposed that this technique is a practical method for controlling properties of CdS thin films.
From chemisorption to surface reactions to catalysis in catalytic oxidation reactions
Authors: Schmidt L. D.
Published: July 2002

Some of the factors which must be considered in order to describe catalytic reactions on an atomistic scale are discussed and illustrated using recent results in the author’s laboratory on oxidation reactions of NH3 and CO on Pt, Rh, and Pd. From observations of reactions kinetics, surface morphology, and surface chemical composition, it is possible to obtain a fairly complete picture of the processes occurring in NH3 oxidation. The reactivity and selectivity observed in industrial HNO3 production are predicted quite well by incorporating heat and mass transfer effects with measured kinetics. Differences between Pt, Rh, and Pd catalysts are shown to be caused by different reaction rates and by changes in surface morphology. Oxidation of Co on Pt at high pressures produces several surface complexes of variable reactivity. These complexes cause unusual transient reaction rates which can be altered by controlling temperature and reactant composition.
Abstract: Near−surface light atom detection in metals by a proton backscattering technique
Authors: Blewer Robert S.
Published: July 2002

Recent interest in the behavior of helium and hydrogen isotopes in first wall CTR candidates has stimulated efforts to develop a technique capable of profiling light atom species in the near−surface region of metals. The ion elastic backscattering technique is essentially nondestructive and would be ideal for such determinations, except that the distribution of low Z elements in metals is difficult to observe by this technique because the elemental Rutherford scattering cross section at a given energy decreases as the square of the decreasing atomic number. For this reason, detection of helium and hydrogen isotopes in heavier host materials is especially difficult and, in fact, has been considered beyond the capabilities of the Rutherford backscattering technique. 1 However, it has recently been shown that a specialized form of proton backscattering is capable of detecting not only the above mentioned elements, but also all light element impurities (except 1H), which may be present in thin film or foil substrates up to 10 μ in thickness. 2,3 The data obtained are straightforward to interpret and exhibit simultaneously the depth distribution of all impurities lower in Z than flourine in volume elements as small as 10−9 cm3. Depth resolution and detection are 400 Å and 0.5 at.% for 4He in copper and 690 Å and 7 at.% for deuterium in titanium. It has more recently been demonstrated that the enhancement in elastic scattering cross sections of D and 4He for 2.5 MeV protons is sufficient to use proton backscattering to measure the depth distribution of these elements in thick targets as well as in foils. 4 Alternatively, the presence of helium which has been implanted in metals can be observed as a notch in the backscattering peak of the host material and the depth distribution deduced therefrom. 5 Details of these developments as well as a review of the basic technique will be presented and examples of its application in fields such as range energy measurements and fusion reactor materials research will be discussed.
Abstract: SIMS studies of adsorption on aluminium
Authors: Dawson Peter H.
Published: July 2002

Secondary-ion mass spectrometry (SIMS) of polycrystalline aluminum surfaces has been studied at low-primary-ion energies (150–500 eV) and low bombardment currents (<10−8 A/cm2). Yields of Al+, Al+2, and O− were monitored as a function of the oxygen exposure of a cleaned surface. Comparison with previous measurements of oxygen uptake and work function changes shows that the saturation uptake of 1.5 O atoms per Al surface atom occurs in two stages. The first, between ϑ=0 and ϑ=1, which causes a small decrease in work function, is associated with increases in Al+ and O− yields and a linear decrease in the Al+2/Al+ ratio. This is postulated to involve incorporation of the oxygen atoms below the surface aluminum atoms. Between ϑ=1.0 and 1.5, where the work function begins to increase, the Al+ yield declines, the O− yield rapidly increases, and the Al2+/Al+ ratio remains constant. This indicates oxygen adsorption on the surface. Removal of the surface species by sputtering supports the two-stage model.
Abstract: Basic concepts for calculating the characteristics of active carbon
Authors: Jäntti O.
Published: July 2002

The present paper describes a system by which it is possible to determine the most favorable pore dimensions for a given adsorbate. In addition, chemical parameters may be applied to indicate which chemical properties are favorable for the adsorption of a given adsorbate. We have only used acidity quantities for grouping the carbon brands. According to the same principle, other chemical quantities may equally be employed. It is possible, by the aid of data programs, to demonstrate rapidly the significance which these values possess.
Pioneer Venus large probe neutral mass spectrometer
Authors: Hoffman J. H. , Hodges R. R. , Duerksen K. D.
Published: July 2002

A neutral particle mass spectrometer has been constructed to measure the composition and abundance of the atmospheric gases of the planet Venus. This instrument is being flown on the Pioneer Venus Multiprobe and will sample the planet’s atmosphere from an attitude of 67 km to its surface. The mass spectrometer is a single focusing magnetic sector field instrument capable of scanning the mass range from 1–208 amu with a sensitivity of better than 1 ppm relative to the dominant gas, CO2. It possesses a unique inlet system which is capable of sampling gases from an environment of 770 K and 100 atm. Operation of the instrument is under the control of a microprocessor. Through this powerful device, a highly efficient peak stepping and data compression program is effected permitting transmission to earth of the entire mass spectral output in only 64 seconds at a data rate of 40 bits/s resulting in an excellent altitude resolution of variations of atmospheric composition. An isotope ratio measurement cell purges an atmospheric sample of active gases yielding an enriched rare gas sample for isotopic ratio analysis. To maintain an ultraclean vacuum in the mass analyzer tube, a combination of ion pumping and chemical gettering is employed. Instrument weight is 11 kg, volume is 10 650 cm3, and power is 14 W.
Theory of polar semiconductor surfaces
Authors: Harrison Walter A.
Published: July 2002

Effective atomic charges of atoms at the surface and in the bulk of a polar semiconductor are systematically calculated by modifying the nuclear charges of a homopolar semiconductor and estimating the electronic charge redistribution. Poisson’s equation is then integrated through the surface to determine possible charge accumulation or possible dipole layers, both of which are assumed energetically unfavorable. Finally, the simplest surface geometry is sought which contains neither. A planar (through reconstructed) surface is favorable on a (110) face, but we obtain a (111) As face with an overlayer, corresponding to one quarter of an atomic plane of Ga. A similar overlayer was suggested by Nosker, Mark, and Levine, but it is proposed here that the Ga atoms are in bridging positions saturating three quarters of the dangling As hybrids. A corresponding geometry with Ga and As interchanged is anticipated for the (111) Ga surface. These are consistent with the observed 1×1 on (110) and 2×2 on (111) Ga, but the observed 1×1 on (111) As must be attributed to randomization of the pattern since a true 1×1 gives charge localization. On the (100) surface the simplest favored geometry is a 1×4 pattern two atom layers deep and analogous to the Webb model of the 2×1 reconstruction on silicon (100) surfaces. The observed centered 2×8 is not consistent with a favored pattern less than four atom layers deep.
Electron Beam Proximity Printing: Mask life investigations
Authors: Bohlen H. , Greschner J. , Nehmiz P.
Published: July 2002

Electron-beam Step and Repeat Proximity Printing is a lithographic method for replicating repetitive mask patterns directly onto wafers. Shadow projection of the mask pattern using intense EB illumination gives very short exposure times. The self-supporting masks have chip size, i.e., the masks have to sustain a great number of exposures to make the EB Proximity Printer an economic exposure tool.
Improvement of voltage contrast in the scanning electron probe by floating the ground level of a device
Authors: Furukawa Y. , Goto Y. , Inagaki T.
Published: July 2002

A simple way to improve the voltage contrast in an SEM and its application are described. The electron beam probe is an effective medium for function testing and fault analysis of semiconductor devices. The voltage contrast is caused by the retarding fields above the specimen surfaces. It often happens, however, that good contrast cannot be obtained in the area of negative surface voltage of a semiconductor device, because of its narrow dynamic range. It is proposed that the voltage contrast for the negative voltage range of a device is improved by floating the ground level of the device above the ground level of the measurement system. The secondary electron signal in our SEM was entirely saturated. Adopting the floating method, the secondary electron signal becomes linear against the surface voltage down to −8 V. This effect is applied to the logic function test of a semiconductor device operating in both the positive and negative voltage ranges. Changes in voltage contrast image corresponding to the change of the logic function status are effectively extracted by a subtraction method.
Magnet design for high-current implanters or small isotope separators
Authors: Keller J. H. , Hicks W. W.
Published: July 2002

During the development of a high-current ion implanter, we designed an optical system that can function as a small, high-current isotope separator. The key element of this system is a sector magnet with a gap of 5.0 cm and a magnetic path length of 60 cm. This magnet serves as the only focusing element in the system. The system has a measured mass resolution of 650 and is capable of passing high-beam currents at high-beam efficiency for energies from 10 to 60 keV. In the system design, a uniform-field magnet was arbitrarily chosen. Rather than using the normal conditions of double focusing (point-to-point), we used a slit-to-point focus with an image distance twice the object distance. This focus condition and asymmetric arrangement allowed us to shorten the entrance distance and thus increase the acceptance angle to slightly more than ±100 ms. Using computer-aided ray tracing and least-squares fitting techniques, we corrected the magnet aberrations in the radial and transverse directions to give a minimum, final focal-spot size. The final computeraided design gave a mass dispersion of 600 mm, A focal-spot size of 0.6×4.0 mm, and a theoretical mass resolution of greater than 1000 for an assumed line source of 0×40 mm and a divergence of ±100×0.6 ms. Experimentally we observed beam widths of 1 mm (full width at 1/10 maximum) at beam focus for analyzed currents of greater than 6 mA As+ and a beam energy of 40 keV.
Blazing speed monolithic integrated circuits
Authors: Yoder Max N.
Published: July 2002

The need for extremely high speed/frequency monolithic functional devices is illustrated in terms of the revolutionary approaches to electromagnetic system design thereby engendered. A comparison of various approaches (e.g., silicon, III–V, Josephson) is made for current laboratory state-of-the-art and future projections for each are rendered. Research opportunities in the various technologies are offered.
Structuring of bubble overlays by reactive sputter etching in an Ar–H2O atmosphere
Authors: de Werdt R. , Meeuwissen W. A. M.
Published: July 2002

The structuring of magnetic bubble propagation overlay patterns by sputter etching, using photoresist as a mask, becomes imperfect for high definition structures. In the past, reactive sputter etching in an O2 containing atmosphere has been introduced as an alternative, the mask material being a metal such as V, Ti, or Cu. The present paper describes how the etch rate ratio between NiFe and Ti can be considerably increased to at least 10 by replacing oxygen with water vapor. The masking Ti layer can than be extremely thin, which has a beneficial effect on the patterning accuracy.
Novel ’’heat-pipe’’ rotating anode for x-ray lithography
Authors: Wittry D. B. , Messenger R. S. , Rao-Sahib T. S. , Jones A. B. , Reekstin J. P.
Published: July 2002

A unique rotating anode has been developed in which heat is removed from the bombarded target area by conversion of water to vapor. A ’’heat-pipe’’ principle is also incorporated, whereby the vapor is condensed on a cooled plate which is a part of the rotating anode. The condensate is rapidly returned to the reservoir by centrifugal action. The great potential of the heat-pipe rotating anode lies in the fact that, since it is to a large extent hollow, it can be made much lighter than a directly cooled anode of comparable size. Also, the hydrostatic pressures encountered in the heat-pipe anode are very much lower. This makes possible increased diameters and rotation rates for rotating anodes, and consequently x-ray sources with higher power output and brightness.
Compressive stress and inert gas in Mo films sputtered from a cylindrical-post magnetron with Ne, Ar, Kr, and Xe
Authors: Hoffman D. W. , Thornton John A.
Published: July 2002

Previous work by the present authors on metal films sputtered from cylindrical-post magnetron sources has established the existence of an abrupt transition in internal stress and other properties that occurs as the working pressure is lowered. High compressive stress, maximum reflectance, minimum resistivity, entrapped inert gas, and dense, Zone-T microstructure were found in a wide variety of pure metals and alloys when sputtered in argon at sufficiently low pressures. The present study reports this same phenomenon for a single metal (Mo) sputtered in a variety of gases (Ne, Ar, Kr, Xe). In this case the transition pressure varies inversely with the mass of the sputtering gas, from less than 0.3 Pa for xenon to over 0.9 Pa for neon. The concentration of inert gas in the films also varies inversely with the mass, increasing by two orders of magnitude from krypton to neon. Deposition through a narrow slit-aperature established that the entrapped gas comes from the sputtering cathode (backscattered, neutralized ions) by line-of-sight trajectories. Moreover, right-angle scattering of gas from the sides of the cylindrical-post magnetron, as viewed by a given substrate, becomes increasingly prominent for the heavier gasses, and is shown to be a principal factor in causing compressive stresses. The evidence indicates that compressive stress and the presence of entrapped inert gas in the films are both by-products of inert gas bombardment of the condensing material during deposition. A significant correlation is found between the variation in transition pressure and the decreased scattering cross sections reported in the literature for energetic inert gas particles, such as those scattered from sputtering targets of greater mass.
Positronium emission from metal surfaces
Authors: Rosenberg I. J. , Weiss A. H. , Canter K. F.
Published: July 2002

Positronium (Ps, a positron–electron bound pair) emission as a result of slow positron (30–1000 eV) bombardment of Cu, Al, Ni, and Ag surfaces has been investigated as a function of incident positron energy, sample temperature, and surface contamination. The fraction of 30 eV positrons that were reemited as Ps at 380 K with <5% surface contamination ranged from 0.43 to 0.47. The emission fraction is found to increase with both increasing surface contamination and incident positron energy. Both thermally activated and nonthermally activated Ps emission is suggested by the data. A one-step thermal activation model applied to the data yields activation energies of 0.44±0.04, 0.46±0.04 and 0.75±0.05 eV for Al(100), Ag(polycrystalline), and Ni(100), respectively.
Plasma uniformity of microwave ion sources
Authors: Tokiguichi K. , Sakudo N. , Suzuki K. , Kanomata I.
Published: July 2002

The ion saturation current uniformities of two different type plasma sources, a coaxial and a Lisitano coil type, are investigated using a moveable Langmuir probe. They both operate under off-resonance microwave discharge. H2 or Ar is used as the discharge gas. The coaxial source provides better uniformities for ion saturation current, electron temperature, and electon density than the Lisitano coil, independent of the discharge gas species. The ion saturation current with the coaxial source is uniform within ∠15% inside a 40-mm-diam circle for a 0.17 Pa H2 discharge. However, with the Lisitano coil, uniformity is limited to a 20-mm-diam circle. Furthermore, the Lisitano coil easily suffers from heat distortion because of difficulties in realizing a cooled system. It is also experimentally confirmed that the coaxial-type source is more appropriate for obtaining high density plasma under continuous operation.
Growth, synergism, and advocacy—The American Vacuum Society in 1980
Authors: Vossen J. L.
Published: July 2002

This paper is the text of an address given by the outgoing President of the Society at the 27th National Symposium in Detroit. The Society has continued to grow at an accelerated rate during 1980. Following a discussion of a few examples of important areas of growth, a thesis is developed which explains the reasons for the growth and for the strength of the Society as it enters a new decade. These reasons include the development of new and important technical areas of interest to the membership providing a place for these new developments within the Society, and encouraging synergistic interactions among the Society’s Divisions which have apparently disparate objectives. Finally, a report on the events surrounding and following the intervention of several branches of the U.S. Government in the First International Conference on Bubble Memory Materials and Process Technology sponsored by the Society is given. These events unwillingly thrust the Society into the role of lead advocate for the entire technical community in resolving the issues raised by that intervention.
AC conductivity of unoxydized tetrathiafulvalene (TTF) polymer thin films
Authors: Thompson W. A. , Schroeder A. H. , Kaufman F. B.
Published: July 2002

This new class of pendant group polymeric coatings has been of interest in obtaining stable electroactive surfaces. To understand the electronic conduction mechanism within the polymer, wide frequency (10−3–106 Hz) and temperature (2.6–316 K) range admittance measurements were carried out in a sealed cryogenic vacuum chamber. Submicron thick samples were spun onto e-beam evaporated platinum, with a gold or other metal counterelectrode. Low field results indicate a power law frequency dependence of both the conductance and capacitance parts of the admittance, giving a frequency independent phase angle similar to some other systems. The power law exponent is temperature dependent, approaching 1 as the temperature decreases to 0. The data support a model by Pike based on classical hopping over barriers with a height distribution caused by random spatial site distribution. The dc conductivity has an activation energy of 0.53 eV and exhibits a Poole–Frenkel dependence at high fields.
Argon ion impact desorption cross sections of chlorine and carbon from nickel
Authors: Peña J. L. , Dieball J. W. , Lichtman David
Published: July 2002

Total desorption cross sections have been measured for Cl (σCl) and C (σC) on Ni(111) by Argon ion bombardment for an incidence angle of 60 ° from the surface normal. For the bombardment an ion gun with low current density (i0∠1×10−7 A cm−2) at low system pressure (∠10−9 Torr) was used. The detection was performed by AES and the data was sensitivity factor corrected. The AES analysis of the surface after adsorption showed that Ni, C, and Cl contributed to more than 95% of the atomic composition. With known i0, it is possible to obtain σ from the adsorbate signal vs ion bombardment time curve. For ion energies between 0.2 to 1.0 keV the measured values for σCl and σC are 0.35–3.5×10−15 cm2 and 0.9–75×10−17 cm2, respectively.
Transient capacitance spectroscopy of semiconductor/insulator interface states: Thermally activated capture cross section of Si/SiO2 interface states
Authors: Kamieniecki E. , Gomma N. , Kloc A. , Nitecki R.
Published: July 2002

A modified transient capacitance technique is introduced which is capable of characterizing continuously distributed semiconductor/insulator interface states. Using this technique, Si/SiO2 interface states located in the upper half of the Si bandgap have been studied in n-type MOS structures. In agreement with previous reports, it was found that the interface state density continuously increase towards the conduction band edge. The interface state density close to mid-gap was about 1010 eV−1 cm−2. For the first time, it was experimentally shown that the electron capture cross section, σn, of the interface states located in the upper half of the bandgap is thermally activated, i.e., described by the formula σn = σo exp(−ΔE/kT), where σo?3×10−17 cm2 is independent of temperature and the energy location of the interface states. The observed decrease of the activation energy ΔE(10–40 meV in the energy range 0.3–0.1 eV below the conduction band). The observed interface states are shown to be indentical with the ’’ion-electron (configurational) interface states’’ whose existence was suggested previously from conductance and photocapacitance measurements of Si–MOS structures.
Critique of tight binding (orbital removal) method: Ideal vacancy and surface states
Authors: Krieger J. B. , Laufer P. M.
Published: July 2002

We have investigated the basis dependence of calculated energy eigenvalues of gap states, introduced by ideal vacancies and surfaces, in the tight binding (orbital removal) method by employing a Green’s function analysis. We find that (a) if Wannier functions are employed there are no ideal vacancy or surface gap states; (b) if atomic orbitals are used, no ideal vacancy gap states exist in the limit as the number of orbitals on the atom to be removed approaches infinity, although (c) spurious solutions for finite band models can exist. We find the reason for these results is that the orbital removal method is not equivalent to removing the potential of the removed atom. We show that if the size of the basis set is allowed to increase without limit, the orbital removal method yields the same energy eigenvalues as the Hamiltonian of the unperturbed system. This result is independent of the method used to solve the eigenvalue equation. Finally, employing a Green’s function technique, we show how these states may be calculated within the framework of the orbital removal method by incorporating the change in potential into the matrix elements. However, we note with Pena and Mattis that if the true vacancy state is not orthogonal to the orbitals on the removed atom, then the application of the orbital removal method is not justified.