bluuebunny/crossref_metadata_2025 huggingface dataset:
Atomic force microscopy using single-wall C nanotube probes
Authors: Snow E. S. , Campbell P. M. , Novak J. P.
Published: July 2002

We examine the factors that govern the stability and resolution of atomic force microscopy (AFM) using single-wall C nanotubes as imaging probes. Nonvertical alignment of the nanotubes with respect to the sample surface causes such probes to bend in response to the surface–nanotube interaction forces during imaging. For long nanotubes this bending response causes the nanotube tip to jump into contact with the surface and renders it unsuitable for imaging. For short nanotubes, stable noncontact-mode imaging can be achieved using a small cantilever vibration amplitude. In such cases it is possible to achieve lateral resolution that is comparable to the diameter of the nanotube.
Secondary electron emission for layered structures
Authors: Yu SeGi , Yi Whikun , Jeong Taewon , Lee Jeonghee , Heo Jungna , Lee Chang Soo , Jeon D. , Kim J. M.
Published: July 2002

Semiempirical theory for secondary electron emission is extended to cover the layered structure. Secondary electron emission for the two-layered structure, i.e., a thin film on a substrate, is calculated and compared with the experiment. Good agreement between the two indicates the usefulness of this theory for the layered structure.
Direct simulation of rarefied gas flows in rotating spiral channels
Authors: Heo Joong-Sik , Hwang Young-Kyu
Published: July 2002

The pumping characteristics of a two-stage disk-type drag pump from the free molecular flow region to the slip flow region are calculated by the direct simulation Monte Carlo method. Spiral channels are cut on both upper and lower sides of rotating disks. For the molecular collision kinetics, the variable hard-sphere molecular model with the no time counter technique is employed. The Borgnakke–Larsen phenomenological model is adopted for calculation of the rotational energy exchange between the colliding molecules. Experiments are performed under the outlet pressure range of 0.4–526 Pa. Numerical results show good quantitative agreement with the experimental data.
Interface between poly (9,9-dioctylfluorene) and alkali metals: cesium, potassium, sodium, and lithium
Authors: Fung M. K. , Lai S. L. , Bao S. N. , Lee C. S. , Lee S. T. , Wu W. W. , Inbasekaran M. , O’Brien J. J.
Published: July 2002

In this article we study the interface between poly (9,9-dioctylfluorene) (PFO) and different alkali metals (Cs, K, Na, and Li) by photoelectron spectroscopy. The low work-function alkali metals led to low or no electron injection barrier at the PFO interface. From the ultraviolet photoelectron spectroscopy, alteration of electronic structures upon Cs, K, Na, or Li doping into PFO represented a charge transfer process among them. Two new gap states known as bipolaron states were found above the highest-occupied molecular orbital of PFO. Variations in the intensity and feature of these gap states with increasing coverage of the alkali metals were correlated with changes of C 1s shakeup peaks acquired from x-ray photoelectron spectroscopy. From the deduced energy level diagram, it is suggested that the new gap states may reduce the radiative recombination of holes and electrons in the polymer light-emitting devices. Films exposed either to residual gases at a pressure of 2.0×10−9 mbar for 3 h or to small amounts of oxygen or water vapor practically eliminated the gap states and restored the affected valence band structures. Deposition of a monolayer of Ag immediately onto the alkali metal/PFO interface protected the films from the influence of residual gases and hence retained the bipolaron states.
Microstructural analysis of Ti/Al/Ti/Au ohmic contacts to n-AlGaN/GaN
Authors: Chen J. , Ivey D. G. , Bardwell J. , Liu Y. , Tang H. , Webb J. B.
Published: July 2002

To develop high quality AlGaN/GaN heterostructure field effect transistors for use in high power, high frequency, and high temperature applications, low resistance, thermal stable ohmic contacts with good surface morphology are essential. Low specific contact resistances have been achieved using an Au/Ti/Al/Ti contact: a minimum value of 6.33×10−6 Ω cm2 was attained after annealing at 700 °C for 30 s. Microstructural analysis using transmission electron microscopy indicated that there is significant interaction between the metallization components and the semiconductor during annealing. The optimum electrical properties correspond to a microstructure that consists of Au2Ti and TiAl layers as well as of a thin Ti-rich layer (∼10 nm thick) at the metallization/AlGaN interface. Degradation of the contact occurred for annealing temperatures in excess of 750 °C, and was accompanied by decomposition of the AlGaN layer and formation of a Au–Ti–Al–Ga quaternary phase.
Determination of atomic potential energy for Pd adatom diffusion across W (111) islands and surfaces
Authors: Fu Tsu-Yi , Cheng Lung-Chieh , Tsong Tien T.
Published: July 2002

Using field ion microscopy, we probe the diffusion behavior of Pd adatoms on the W (111) surface and also in the vicinity of the surface step. An adatom approaching the step from the upper terrace is reflected by the step boundary with an extra reflective barrier of 0.61±0.01 eV. The behavior of an adatom approaching the step from the lower terrace is also studied. The activation energy for the step-up motion of a Pd atom at the W (111) step edge is 1.84±0.07 eV. The potential energy difference toward and away from the W (111) pole due to a free energy anisotropy is 0.013 eV/4.47 Å. Our energetic data for surface atomic processes are useful for understanding the impurity induced pyramidal facet formation.
Highly cross-linked polysilane as antireflective coating for deep ultraviolet lithography to improve durability during SiO2 etching
Authors: Sato Yasuhiko , Shiobara Eishi , Onishi Yasunobu , Yoshikawa Sawako , Nakano Yoshihiko , Hayase Shuzi , Hamada Yoshitaka
Published: July 2002

Highly cross-linked polysilanes were recently investigated in an attempt to improve drawbacks of bottom antireflective coatings (BARCs) composed of loosely cross-linked polysilanes that are used for deep ultraviolet (UV) lithography. A highly cross-linked structure was prepared by thermally crosslinking poly(phenylmethylsilane-co-methylhydrosilane-co-methysilyne) with m-diethynylbenzene during baking after coating. Resist profiles are achieved on it without producing a foot or leaving residue at the bottom of the resist. The refractive indices at the KrF excimer laser wavelength (248 nm) are n=1.93 and k=0.32. The reflection is reduced 0.9% regardless of variation in the thickness of the substrate. Highly cross-linked polysilanes improve the melting of loosely cross-linked polysilanes during BARC etching. They also improve the surface roughness of loosely cross-linked polysilanes after substrate (-SiO2) etching. The etch selectivity of the highly cross-linked polysilane BARC/resist during BARC etching is 2.1, which is higher than that of organic BARC/resist (∼1). The etch resistance of the highly cross-linked polysilane during substrate etching is 1.1 times greater than that of the resist. Highly cross-linked polysilanes can not only be etched with high selectivity against resist but can also be superior etch mask for substrate etching.
Nucleation and Growth of Thin Films as Observed in the Electron Microscope
Authors: Pashley D. W. , Stowell M. J.
Published: July 2002

The technique of direct observation of the growth of thin films involving the deposition of films inside the electron microscope, is described. Its merits, disadvantages, and limitations are discussed. The application of the technique to the study of the growth and intergrowth of the initial nuclei of a deposit, and also of larger compound islands, is described. It is shown that this can lead to appreciable “liquidlike” coalescence. The technique also provides detailed information on the manner in which the imperfection structure in the deposit changes as growth proceeds. The mechanisms of imperfection formation are discussed. If two islands of very different orientation coalesce, a recrystallization process can occur so that the fined compound island is in one single orientation. The general significance of this effect is discussed. The above phenomena are illustrated throughout by means of results obtained for the growth of gold on molybdenite (MoS2).
Sorption of Activated Hydrogen on Vycor Glass
Authors: Low M. J. D. , Argano E. S.
Published: July 2002

A flow system incorporating Pirani gauges was used to measure the sorption of hydrogen activated by an rf discharge by Vycor glass. The sorption was dependent on the pressure and the discharge intensity. A rapid, initial adsorption was followed by a slow sorption which obeyed a t1/2 law but then decelerated. The kinetics of the thermal release of hydrogen from the Vycor also followed a t1/2 law. The data suggest that a steady-state condition, dependent on the hydrogen-atom population in the gas phase, was established on the surface. Hydrogen diffused into the bulk, the rate being a function of the heating of the Vycor surface by hydrogen-atom recombination. Molecular hydrogen diffused to the surface when a sample was heated.
Monte Carlo simulation of spatially distributed beams in electron-beam lithography
Authors: Kyser D. F. , Viswanathan N. S.
Published: July 2002

The spatial distribution of energy deposited in a thin polymer film of polymethyl methacrylate (PMMA) by a laterally distributed electron beam is simulated with Monte Carlo calculations. The Monte Carlo simulation includes the significant contribution from electrons that are backscattered from the substrate (Si) into the film. Equienergy density contours (eV/cm3) are calculated for specific cases of beam voltage, film thickness, beam width, and beam-edge slope. A time-dependent solubility model is also incorporated to simulate the time evolution of the developed contours. A size effect is observed; i.e., the development time for a line depends on the line width. This intraproximity effect is ascribed to electrons backscattered from the substrate.
Impurity effects on the corrosion of aluminium
Authors: Towler C. , Collins R. A. , Dearnaley G.
Published: July 2002

The effects of impurity atoms on the oxidation of aluminum have been studied. Selected impurities were introduced by ion−implantation to a depth of 400 Å prior to the anodic growth of oxide in both oxalic acid and ammonium pentaborate solutions. Oxygen uptake and impurity movement during oxidation were studied using Rutherford backscattering of He+ ions. Correlation was observed between movement of the implanted species and oxygen uptake. Certain impurities (e.g., Bi and Pb) were found to enhance oxidation whilst others (e.g., Au and Cu) reduced the oxidation rate. The results are consistent with the oxide behaving as an n−type semiconductor with electron transport being rate determining. The effect of radiation damage during ion−implantation was shown to be of secondary importance.
Dynamic cathode contacts and transferred electron semiconductors
Authors: Grubin H. L.
Published: July 2002

We present calculations with a generalized time-dependent cathode contact model that accounts for the broad spectrum contact dependence of GaAs and InP oscillators.
Auger electron spectroscopic depth profiling techniques applied to ultrathin electrochemically deposited metal layers
Authors: Knotek M. L. , Quinn Rod K. , Armstrong N. R. , Vanderborgh N. E.
Published: July 2002

The Auger electron spectroscopic depth profiling technique is applied to the study of the initial equivalent monolayer of electrodeposited Ag on thin-film Pt electrodes. The ultimate depth resolution of this technique is determined by examining ultrathin layers of Ag which have been ion deposited from a zeolite source in ultrahigh vacuum. The exponential decay apparent in the examination of such layers is explained from elementary considerations of the sputtering process. These are seen to be the resolution-limiting factor for these layers. The depth resolution is shown to be on the order of 5 Å. Examination of monolayer and submonolayer films of Ag electrodeposited from an AgClO4/sulfolane solution shows that there is an adsorbed overlayer of S (of solvent origin) followed by the electrodeposited Ag film, which is rich in Cl (of solute origin), followed by the Pt substrate, which also contains high levels of Cl. The absence of underpotential deposition is clearly demonstrated. There appears to be two chemical states of Cl present which are distinguished by their relative thermal stabilities.
Model of the evaporation kinetics from a temperature-programmed large-area source. I. Pure selenium
Authors: Abowitz Gerald
Published: July 2002

A model of the evaporation kinetics of pure selenium from a large-area boat of complex geometry is presented. The model includes conductive and evaporative heat-transfer components in the liquid, accounts for the constantly decreasing liquid-pool height, and demonstrates that natural convection effects are unimportant. A good fit to the experimental data is obtained over most of the range except at the tail end of the evaporation, where small inclinations of the boat from the horizontal have large effects. The utility of the model lies in its ability to predict the evaporation kinetics when changes are made in such operating parameters as the heating rate or boat loading.
Structural studies of thin nickel films on silicon surfaces
Authors: Schaffer W. J. , Bené R. W. , Walser R. M.
Published: July 2002

Thin nickel films rf sputtered onto both (100) and (111) oriented silicon produce amorphous surface regions, as indicated by transmission electron diffraction (TED), in the equivalent thickness range 10?t?28 Å. AES measurements indicate to contaminants in these thin layers. Annealing 10-Å films at 400°C for one hour does not alter the pattern. At 15 Å, however, the anneal produces polycrystalline rings of δ-Ni2Si. In unannealed samples, Ni2Si polycrystalline rings are seen at a minimum deposited metal thickness of 30 Å and AES measurements show a splitting in the 92-eV silicon line previously reported for Ni2Si. Both NiSi and Ni2Si polycrystals are seen via TED at a deposition thickness of 120 Å upon anneal at 300°C for 30 minutes. These measurements indicate that Ni2Si is nucleated from an amorphous region whose structure (as indicated by TED) is independent of the amount of the Ni sputtered onto the substrate. This result is consistent with our published model of silicide nucleation.
Simple method for estimating energy levels of solids
Authors: Frese Karl W.
Published: July 2002

A simple method based on the linear relationship between experimental metal work functions and Pauling electronegativities has been used to obtain effective solid state Fermi energies for atoms, both metallic and nonmetallic. A simple arithmetic mean combination rule was used to give the intrinsic Fermi level of a solid, and this level was then combined with band gap data to give electron affinities. The method was applied to materials covering a wide range of band gaps and ionicity. The results were in good agreement with literature values of electron affinities.
Oxygen chemisorption on tin oxide: Correlation between electrical conductivity and EPR measurements
Authors: Chang Shih–Chia
Published: July 2002

Chemisorption of oxygen on tin oxide is studied. Correlations between electric conductivity and electron paramagnetic resonance (EPR) measurements are reported.
Changes in the structural properties of a Si(111) surface during ion bombardment, as revealed by Auger electron spectroscopy
Authors: Morgen P. , Ryborg F.
Published: July 2002

The Si L2,3VV Auger electron spectrum, produced by electron bombardment, was recorded after progressive Ar+ ion bombardments of an initially perfect Si(111) surface. Ion currents of about 1–10 μA at 3 keV were employed. Changes in the shape of the spectrum are observed which can be related to structural changes of the surface, as detected by low energy electron diffraction (LEED). At low ion doses (∠1015–1016 cm−2) the main effect is removal of intensity in spectral ranges with origin in the ordered Si(111) 7×7 surface structure. Larger doses (∠1017 cm−2) produce a markedly altered Auger spectrum.
Step coverage of rf-diode-sputtered SiO2 films
Authors: Serikawa T.
Published: July 2002

Step coverage profile dependences of rf-diode-sputtered SiO2 films on deposition parameters have been examined by SEM observations. The obtained results are summarized as follows: (1) With decreased spacing between substrate and target, slope of step coverage changes from negative to positive through vertical. (2) Decreasing argon pressure improves step coverage, resulting in a positive slope. (3) Negative dc voltage application to substrate holder makes step coverage negative. On the other hand, step coverage is improved at positive dc voltage. (4) Putting shield ring on substrates, smooth and positive slopes are obtained. The obtained results are successfully explained by shadowing effect of incidence SiO2 materials by substrate step.
Ion interaction with solids: Surface texturing, some bulk effects, and their possible applications
Authors: Auciello O.
Published: July 2002

Texturing of surfaces and some bulk effects produced during ion-solid interactions already are or have the potential to be useful and/or important in several different technologies, and/or experimental techniques, namely: (a) controlled thermonuclear fusion and vacuum technologies, (b) microelectronics, (c) surface acoustical and optical technologies, (d) solar energy conversion technology, (e) thin film technology, (f) biomedicine (implantology), (g) ion beam surface analysis, (h) field ion emission and electron microscopy, (i) surface enhanced Raman scattering spectroscopy, and (j) other technologies. In some cases texturing is desirable while the opposite is true for other situations. A review is presented on the possible technological applications of textured surfaces and some bulk effects produced when ion and electromagnetic radiations interact with solids in an attempt to bring together information which is dispersed among journals involving fields of research which are sometimes unrelated. Additionally, a critical analysis of the underlying physics of some phenomena is presented.
Self-consistent surface electronic band structure calculations: Changes upon chemisorption
Authors: Richter Roy , Wilkins John W.
Published: July 2002

This paper reviews the progress that has been made in understanding chemisorption from self-consistent electronic band structure calculations of adsorbate overlayers on transition metal thin films. Emphasis is placed on the information to be gleaned from the charge density difference associated with chemisorption. Simple interpretations are discussed in the following cases: saturation overlayers of hydrogen or cesium on tungsten{100}, of hydrogen or sulfur on nickel{100}, and of silver on palladium{100}. The basic features of LAPW method, used in many of these calculations, are reviewed.
Ion milling planarization for magnetic bubble devices
Authors: Hou T. W. , Mogab C. J. , Wagner R. S.
Published: July 2002

An ion beam milling technique is used to planarize the SiO2 steps in 8 μm period field-access magnetic bubble devices. A photoresist coating is first applied over the SiO2 steps to produce a smooth surface. The resist layer is then ion milled using conditions that give equal milling rates for the resist and SiO2 films. The planar resist surface is thus preserved in SiO2 after the resist layer is completely milled away. Magnetic bubble devices fabricated by this process are shown to operate at much lower in-plane drive field than similar devices fabricated by conventional nonplanar processes.
A compact isolation valve for use in roll coaters
Authors: Dobrowolski J. A. , Ranger M.
Published: July 2002

An isolation valve is described that is suitable for placement between the web and the array of sources of an optical thin film roll coater. The isolation valve is very thin and has a very short stroke. It is water cooled and its O-rings are protected from dirt and evaporant both in the closed and the open positions.
Temporary support for a UHV sample manipulator during bakeout
Authors: Hess B. V. , Felter T. E.
Published: July 2002

It is suggested that during bakeouts, XYZ translational stages be retrofitted with hardware that supports the bellows.
Initial stages of oxide formation on HgCdTe exposed to activated oxygen
Authors: Silberman J. A. , Laser D. , Lindau I. , Spicer W. E. , Wilson J. A.
Published: July 2002

The changes in chemistry and electronic structure of the (110) cleavage surface of Hg0.65Cd0.35Te and properties of the film produced are determined by monitoring with photoemission spectroscopy the growth of thin (10 Å) oxide layers on initially clean surfaces. Oxygen uptake, normally quite slow, is stimulated in this case by operating an ionization gauge in line of sight of the sample during the exposures so as to provide a stream of excited oxygen striking the surface. A complex Te oxide is formed which retains Cd but not Hg. The Cd content appears enhanced at the oxide surface. An explanation for the behavior observed is sought in terms of the species produced by the activating gauge and the chemistry of the alloy surface.
Quantitative analysis of a submonolayer adsorption system by angle resolved XPS: c(2×2)S on Ni(001)
Authors: Connelly R. E. , Fadley C. S. , Orders P. J.
Published: July 2002

The polar and azimuthal angular dependences of core-level x-ray photoelectron peak intensities from c(2×2)S on Ni(001) are studied in detail in order to determine the accuracy of such measurements for quantitative analyses of such adsorbate/substrate systems. Comparison of Ni 2p3/2, Ni 3p, and S 2p intensities and various intensity ratios with a simple quantitative model for polar angle variations shows very good agreement in general, and suggests accuracies of ≲±20% in determining the fractional monolayer coverages of the adsorbate. Properly averaging over strong x-ray photoelectron diffraction effects in the single-crystal substrate is essential. Also, a correct allowance for Ni satellite intensities is found to be important. Finally, it is found to be adequate to assume that the overlayer is nonattenuating for emission angles ≳20° above the surface.
A vibrational overtone study of C–O bond weakening on potassium-precovered ruthenium
Authors: DePaola R. A. , Hrbek J. , Hoffmann F. M.
Published: July 2002

Electron energy loss overtone spectroscopy is used to examine the C–O potential wells of carbon monoxide adsorbed on clean and potassium precovered Ru(001). While the C–O bond of CO adsorbed on the clean surface is found to be quite harmonic (ωeXe=18 cm−1), C–O bonds of CO coadsorbed with two different coverages of potassium exhibit highly anharmonic potential wells (ωeXe=70 cm−1, 95 cm−1).  Estimates of CO dissociation energies based on overtone frequencies indicate severely weakened CO bonds in agreement with 13C18O, 12C16O isotope scrambling thermal desorption results.
Structural analysis of Si(111)-7×7 by UHV-transmission electron diffraction and microscopy
Authors: Takayanagi K. , Tanishiro Y. , Takahashi M. , Takahashi S.
Published: July 2002

Structural analysis of the surface reconstructions investigated by ultrahigh vacuum (UHV) transmission electron microscopy (TEM) and diffraction (TED) is shown. By TED intensity analysis a new structural model of Si(111)-7×7 is derived. The model basically consists of 12 adatoms arranged locally in the 2×2 structure, nine dimers on the sides of the triangular subunits of the 7×7 unit cell and a stacking fault layer. UHV–HREM of Si (111)-7×7 surface is commented.
Chemically assisted sputter etching of permalloy using CO or CL2
Authors: Vasile M. J. , Mogab C. J.
Published: July 2002

Redeposition-free patterns have been etched in 3000 Å thick permalloy films using the technique of chemically assisted sputter etching. This technique involves the simultaneous adsorption of a reactant gas from a molecular beam source and normally incident argon ion bombardment. Experimental conditions with Cl2 adsorption can be maintained to etch the permalloy at 80 Å/min and to etch positive photoresist at 110 Å/min. These etch rates are not significantly different from rates obtained with argon ion milling, even though the permalloy surface is known to incorporate Cl2. Redeposited material observed with Cl2 chemically assisted sputtering has been shown to be water soluble, and can be completely removed from feature sidewalls prior to stripping the resist. Linewidth measurements show that no feature broadening occurs on 2 μ line and space patterns, within the precision of the measurement (±0.2 μ). Chemically assisted sputter etching with the adsorption of CO resulted in reduced etch rates and increased redeposition. Both of these effects are attributed to the formation of carbides on the alloy surface during the process.
Strain effects in Cd1−xMnxTe–CdTe superlattices
Authors: Blanks D. K. , Bicknell R. N. , Giles-Taylor N. C. , Schetzina J. F. , Petrou A. , Warnock J.
Published: July 2002

Quantum-size effects and strain effects have been calculated for the CdMnTe–CdTe superlattice. Unlike previous theories dealing with materials grown in the [100] direction, this work applies to CdMnTe–CdTe superlattices oriented in the [111] direction. A Kronig–Penney analysis is used to obtain the quantized conduction-band energies. Pikus–Bir deformation theory is employed to calculate the strain-induced splitting of the heavy and light-hole valence bands. Excitation luminescence spectra obtained for several CdMnTe–CdTe superlattices exhibit sharp peaks which correspond to heavy and light-hole excitonic transitions from the quantized conduction-band states. Observed transition energies from the n=1 conduction band state are used with the theory to obtain the heavy and light-hold exciton binding energies for the supperlattices. An increase in binding energies over the values for bulk CdTe is obtained and is attributed to the 2D nature of the quantum wells and possibly strain-induced distortion of the valence bands. The calculated transition energies from higher level (n=2,3,...) conduction-band states agree closely with the experimental data.
Investigation on the low pressure limit of the Bayard–Alpert gauge
Authors: Chou T. S. , Tang Z. Q.
Published: July 2002

To extend the pressure measurement capability of a Bayard–Alpert (BA) gauge, several commercial BA gauges are modified. To study the position dependence of filament on gauge sensitivity, hair-pin filaments instead of commercial helical filaments were used. The characteristics of the modified gauge, which included the variation of the gauge sensitivity on the applied voltage and the position of the filament, are reported. To monitor the normal and the reverse x-ray photocurrents, the gauge was inserted into a fixed size tube of 304 LN stainless steel. The validity of the self-modulation was confirmed. A sensitivity of 60 Torr−1 and an x-ray limit of 2.7×10−13 Torr (N2 equivalent) was obtained.
Properties of thin antimultipactor TiN and Cr2O3 coatings for klystron windows
Authors: Nyaiesh A. R. , Garwin E. L. , King F. K. , Kirby R. E.
Published: July 2002

Low secondary electron emission yield (1–1.3), low radio-frequency (rf) loss films are of interest as coatings for alumina ceramic high power klystron windows. Very thin (15–50 Å) Ti and TiN layers have been previously used with success in klystron tubes operating at lower power levels (<35 MW peak power) and short (2.5 μs) pulses but are subject to property changes during air exposure, tube bakeout (550 °C for up to 10 days) and in situ electron bombardment. Higher power tubes (≥50 MW) with longer (5 μs) pulse lengths require coatings that remain stable under these more rigorous conditions in order to avoid multipactoring and window failure due to overheating. Air-oxidized Cr films offer an alternative to TiN. This work shows that they have the required resistivity for low rf loss, combined with stability in the secondary electron emission (SEE) yield under bakeout and electron bombardment. SEE, AES, XPS, ELS, oxidation, bakeout, and electron bombardment results are presented for Cr and TiN layers deposited by sputtering onto high density alumina substrates. The surface of TiN oxidized to a 9 Å thick TiO2 layer which, under bakeout to 550 °C in vacuum, thinned to 6 Å. This extreme layer thinness resulted in a significant drop in the SEE yield which, unfortunately, was reversible upon reoxidation. The oxidized layer on Cr was 17 Å of Cr2O3 which thinned to 13 Å upon bakeout. This thicker oxide layer produced a stable SEE yield which, although not as low as oxidized TiN, is sufficient to prevent electron multipactor. Windows covered by air-oxidized Cr films are at least as good, under tube processing conditions, as the best TiN-coated windows.
Friction and wear behavior of ion-plated lead–tin coatings
Authors: Gupta B. K. , Kulshrestha S. , Agarwal A. K.
Published: July 2002

A systematic study of lead–tin alloys deposited by ion plating, vacuum deposition, and electrodeposition is carried out and reported in this paper. The effects of sliding distance and load on friction coefficient and wear are studied for lead–tin coatings having from 10 to 40 wt. %Sn. The lead–tin alloys were deposited on polished steel disk substrates. The coefficients of friction and wear were measured under lubricated conditions using ball-on-disk geometry. The tests were carried out under different loads from 15 to 145 N and for sliding distances from 250 to 1500–1800 m. The wear loss is evaluated by wear volume and maximum wear depth, and weight loss.
Adhesion of titanium thin film to oxide substrates
Authors: Kim Y.-H. , Chaug Y. S. , Chou N. J. , Kim J.
Published: July 2002

The adhesion behavior of Ti thin films to several oxide substrates has been studied. Ti was electron beam deposited onto single-crystal sapphire, magnesia, quartz, and fused silica substrates. Adhesion was measured by the peel test. Ti adhesion to sapphire was the highest, followed by magnesia, quartz, and fused silica, respectively. In situ x-ray photoelectron spectroscopy (XPS) studies demonstrate that the chemical effect is not a major factor in the adhesion strength in the systems investigated. The poor adhesion of Ti to fused silica and Ti reaction with fused silica detected by XPS suggest that the chemical reaction in the interface is not a sufficient condition for strong adhesion. It has been found that the mechanical effect of the substrate is more important in determining the peel strength.
On the use of nonresonant multiphoton ionization of desorbed species for surface analysis
Authors: Becker C. H.
Published: July 2002

Ionization subsequent to sputtering or desorption, for the purpose of mass spectrometry, is discussed along with a rationale for the choice of nonresonant multiphoton ionization. The surface analysis by laser ionization method employing intense untuned UV laser radiation, reflecting time-of-flight mass spectrometry, and flexible desorption mode is briefly reviewed. The main factors limiting the absolute quantitation of the method without use of standards are identified, namely, the velocity distributions and effective laser ionization volumes for different neutral particles. Three applications are then presented: depth profiling by Ar+ beam sputtering of a nonuniform Al–Ti thin film and a Ti implant, and measurement of the mass spectrum of a complex mixture of hydrocarbons evaporating from a cleaved olivine crystal.
Photoemission study of Cd loss and its effect on the electronic structure of etched Hg1−xCdxTe surfaces
Authors: Carey G. P. , Wahi A. K. , Silberman J. A. , Stahle C. M. , Spicer W. E. , Wilson J. A.
Published: July 2002

Quantitative measurements using x-ray photoemission spectroscopy and ultraviolet photoemission spectroscopy have been made of the Cd loss and surface Fermi-level position (Ef,s) on Hg1−xCdxTe substrates that have undergone chemical surface preparation. The surface cleaning techniques employed were representative of those used in Hg1−xCdxTe device fabrication: a bromine in dimethyl formamide polish, a bromine in ethylene glycol spray, and/or an ozone ash etch. For over 20 samples studied of bulk x=0.30, an average 30% of the original Cd was found to be removed from within the sampling depth of the surface (25 Å). In addition, Ef,s was found to be located 0.15±0.05 eV above the valence-band maximum (VBM) at room temperature for a predominate number of samples, independent of the bulk doping. Some of these samples were also studied at ∼150 K, and Ef,s was seen to rise an additional ∼0.05 eV to a location of 0.20±0.05 eV above the VBM at the lower temperature, again independent of bulk doping. Implications of these findings for device modeling are discussed and first-order surface band diagrams introduced.
Gettering in cryogenic applications
Authors: Boffito C. , Ferrario B. , Rosai L. , Doni F.
Published: July 2002

Metallic cryogenic Dewars and pipes, used for storage and transportation of cold fluids such as liquid N2 or He, usually have a vacuum jacket as a thermal insulator. In this case, vacuum has to be maintained in a range of 10−1 Pa or lower. Nonevaporable getters are often used for this purpose. They are particularly useful for sorbing H2 which is released by the warmer walls or by the multilayer insulation; H2 is neither cryocondensed by the cold surfaces nor sorbed by the molecular sieves which may be used to physisorb other gaseous species. The working temperature of the getters may range from room temperature down to the cryogenic fluid temperature. The getter material here considered, and which appears to be adequate for these applications, is the Zr–V–Fe nonevaporable getter alloy. Its sorption characteristics (particularly for H2) are studied both at room temperature and in a cryogenic fluid environment. The behavior of a gettered Dewar jacket is finally studied and discussed.
Properties of Sn-doped In2O3 by reactive magnetron sputtering and subsequent annealing
Authors: Yamamoto S. , Yamanaka T. , Ueda Z.
Published: July 2002

Sn-doped indium oxide (ITO) films have been prepared on the polyester substrate by reactive magnetron sputtering at different oxygen pressures and subsequent annealing in air at 170 °C. Highly transparent ITO films with a low resistivity of 1.8×10−4 Ω cm have been obtained by annealing suboxide films deposited in a limited range of oxygen flow rate. X-ray photoemission spectroscopy studies show that the Sn 3d5/2 peak can be resolved into two peaks and the relative intensity of the peak at the higher binding energy increases with an increase of the carrier density in ITO films. This fact suggests that the peak at the higher binding energy corresponds to the Sn donor while that at the lower corresponds to electrically inactive Sn.
Ion sputtering yield measurements for submicrometer thin films
Authors: Veisfeld Nina , Geller Joseph D.
Published: July 2002

Most of the published ion sputtering yield values are based on experimental techniques which do not correlate well with the ion sputtering process commonly used with surface analysis instrumentation. A need exists for ion sputtering yield measurements collected under the same conditions which will be used in practice. We have measured ion sputtering yields on several sputter-deposited metal films using the Auger electron spectroscopy ‘‘breakthrough’’ depth profile method, whereby characteristic Auger electron transitions for the thin film and the substrate are monitored while the thin film is being sputtered away. Rutherford backscattering spectrometry is used to measure the density of the films and a scanning stylus profilometer is used to measure the depth of the resulting sputter craters. The thin metal films exhibit a sputtering rate depth dependency, i.e., the sputtering decreases with the amount of material removed. It was shown that this phenomenon is related to surface roughening due to the directionality of the ion sputtering process. Reduction of the topographic effects with a significant improvement in depth resolution is demonstrated by continuously rotating the sample during ion bombardment.
The interface formation and thermal stability of Ag overlayers grown on cubic SiC(100)
Authors: Niles David W. , Höchst Hartmut , Zajac G. W. , Fleisch T. H. , Johnson B. C. , Meese J. M.
Published: July 2002

We have used photoemission spectroscopy with synchrotron radiation in the energy range hν=40–140 eV to study the interface formation of Ag overlayers on cubic SiC(100). Our data are consistent with a three-dimensional island growth mode of Ag at room temperature. The substrate attenuation curve supports a model of reduced lateral growth rates for the Ag islands. Annealing of a 340-Å-thick Ag overlayer in the temperature range 400–600 °C causes the film to coalesce, forming clusters which leave large parts of the SiC surface uncovered. Thermal treatment above 600 °C most likely leads to evaporation of Ag from the surface. At ∼1000 °C the surface is essentially free of Ag. The Ag/SiC(100) interface is nonreactive for Ag films deposited at 25 °C. It is equally stable at temperatures up to 1000 °C.
The effects of O2 plasma treatments on the surface composition and wettability of cold-rolled aluminum foil
Authors: Strohmeier Brian R.
Published: July 2002

The effects of oxygen plasma treatments on the surface composition and wettability of cold-rolled aluminum foil have been examined using x-ray photoelectron spectroscopy (XPS or ESCA) and contact angle measurements. Results have shown that oxygen plasma treatments have two main effects on the surface composition of cold-rolled aluminum: (i) Residual carbon contamination is removed efficiently, and (ii) the thickness of the aluminum oxide surface layer is increased. The removal of residual carbon species via plasma treatments results in a significant improvement in the foil wettability. The wettability of plasma treated cold-rolled foil has been shown to be as good as, or better than, that of the best annealed foils. However, it was found that the wettability of plasma treated foils can degrade with time following treatment, which is apparently due to the adsorption of airborne carbon species and other contaminants. Oxygen plasma treatments also cause additional aluminum oxide to grow on the metal surface. The composition of this additional oxide is similar to that of the native passivation oxide. The thickness of the aluminum oxide layer has been shown to increase with both the plasma rf power and/or the plasma exposure time.
Surface composition and structure changes in GaAs compounds due to low-energy Ar+ ion bombardment
Authors: Kang H. J. , Moon Y. M. , Kang T. W. , Leem J. Y. , Lee J. J. , Ma D. S.
Published: July 2002

We have carried out an experimental study of the surface composition and structural changes of GaAs under Ar+ ion sputtering using Auger electron spectroscopy (AES) and reflection high-energy electron diffraction (RHEED). The Auger results show that preferential sputtering of As atoms takes place in the GaAs compound and that such a composition change with depth occurs in a simple exponential form with Ga enrichment on the top surface layer. The grown surface undergoes a C(4×4) reconstruction, and after Ar+ ion sputtering this GaAs(001)–C(4×4) structure disappears resulting in an amorphous halo. But the characteristic surface which has a superlattice of (011) on GaAs (001) was found after sputtering and postannealing.
Scanning tunneling microscopy for studying the biomaterial–biological tissue interface
Authors: Emch R. , Clivaz X. , Taylor-Denes C. , Vaudaux P. , Descouts P.
Published: July 2002

A scanning tunneling microscope (STM) coupled with a high resolution reflective optical microscope has been developed to investigate some aspects of the interface between metallic biomedical implants and living tissue. Initial biological measurements show that fibronectin (Fn), a glycoprotein which plays an important role in the promotion of cell and bacterial attachment, is well adsorbed on Ti and V substrates, but is not biologically active on V. STM images of the Ti oxide layer and of single and multiple Fn molecules deposited on mica and shadowed with a conductive layer are presented. These images demonstrate the capability of the STM for studying clinical implant surfaces with roughness larger than 1 μm as well as interface biochemical processes at the molecular level.
Principal component analysis with integral Auger electron spectroscopy spectra
Authors: Turner N. H. , Wandass J. H. , Hutson F. L.
Published: July 2002

In this study, N(E) Auger electron spectroscopy (AES) depth profiles were obtained in the same determination for both the M2,3VV and LMM regions of Cu ion implanted in a 50–50 Co/Ni alloy. Principal component analysis (PCA) calculations on the M2,3 VV depth profile spectra suggested the presence of an additional component. The amount of Cu was estimated at about the detection limit in the M2,3VV depth profile when an averaged Co-Ni standard was used from the end of profile. This depth profile was similar to that obtained in an earlier study with derivative AES spectra. Simulated M2,3VV spectra (with added noise) for the ion implanted alloy indicated that Cu should be detected at a relative amount of 2 at. %. The number of components indicated by PCA in the integral LMM depth profile was the same as the number of standards employed. Again, the depth profile from the integral LMM spectra was similar to that obtained from the derivative spectra; in both cases the relative atomic amount of Cu was about three times that determined in the M2,3VV spectral region. Thus, preferential sputtering of Cu seems to be present and PCA could detect this effect. In addition, Co appeared to be preferentially sputtered compared to Ni. PCA analysis was not successful when loss features were removed (which cannot be done easily with derivative AES spectra) from both the M2,3VV and LMM spectra.
Morphology and crystal orientation of chromium thin films deposited by ion plating
Authors: Wang D. D. , Oki Takeo
Published: July 2002

Chromium thin films were deposited by ion plating. The influence of argon gas pressure and substrate bias voltage on the morphology and crystal orientation of the films was investigated by using scanning electron micrography (SEM) and x-ray diffraction. The preferred orientation of the films changed from (110) to (200) with the increase of argon gas pressure. Most of chromium films exhibited columnar structure and the width of the column became smaller at higher argon gas pressure. The chromium film which was deposited at higher argon pressure exhibited a finer granular structure. The microhardness of the films increased with the increase of bias voltage and argon gas pressure.
Surface reactions in Si chemical vapor deposition from silane
Authors: Gates S. M. , Greenlief C. M. , Kulkarni S. K. , Sawin H. H.
Published: July 2002

The kinetics and mechanisms of silane adsorption and decomposition on clean single crystal Si surfaces have been investigated under ultrahigh vacuum conditions. Individual reaction steps are studied experimentally in the surface temperature range −163–500 °C, and modeling results are extrapolated to Si film growth temperatures (400–1000 °C) for comparison with the literature. Static secondary ion mass spectrometry (SSIMS) has been used to identify the silicon hydride species formed by silane adsorption on both the Si(100)-(2×1) and Si(111)-(7×7) surfaces. Temperature programmed desorption of H2 has been used to measure the SiH4 reactive sticking probability (S) as a function of hydrogen coverage (ΘH). Kinetics of SiH3, SiH2, and SiH decomposition are compared here, and direct evidence for SiH decomposition as the rate-determining surface step leading to Si film growth is presented. The experimental data provide a firm basis for kinetic modeling of the growth of Si films from SiH4 by chemical vapor deposition (CVD). Preliminary modeling results are outlined here, including predictions of Si growth rate versus surface temperature (compared with data from the literature).
Polyimide/Cr/Cu in the presence of chloride ions
Authors: Katnani A. D. , Spalik J. , Rands B. , Baldwin J.
Published: July 2002

Chloride residues, elevated temperature, and humidity affect circuit line adhesion to dielectric material in electronic packaging. Effects of the above parameters on the polyimide (PI)/metal interface are discussed. Scrupulously cleaned, and HCl doped circuitized parts were exposed to elevated temperature and humidity for 250 h. The interface was investigated with scanning electron microscopy (SEM) and Auger electron spectroscopy (AES). SEM results showed that peeled circuit lines exhibit three types of interfacial separation. Areas near the edges exhibited Cr–Cu separation, regions in the center of the line exhibited cohesive separation in the PI, and randomly distributed islands exhibited Cu–Cu separation. Chloride ions promoted interfacial degradation, which propagated perpendicular to the edge of the circuit line. Furthermore, AES results revealed that the depth of the cohesive failure within the PI decreased as the chloride ion concentration increased. This result is attributed either to mechanical forces exerted during peeling the circuit line or to actual degradation of PI by copper diffusion. Actually, AES indicated the presence of an intermixed Cu-PI region.
Alloy source synthesis for vapor deposition by electrodischarge compaction and analysis of Ni–Co alloy films deposited on silicon
Authors: Sethuraman A. R. , Reucroft P. J. , De Angelis R. J. , Kim D. K. , Okazaki K.
Published: July 2002

Electrodischarge compaction (EDC) is a very effective method of producing alloys that cannot be produced by conventional alloying methods. The feasibility of this method for producing alloy sources for vapor deposition was evaluated by using a Ni–Co model system. Three compositions of Ni–Co alloy powders, 75%Ni–25%Co, 50%Ni–50%Co, and 25%Ni–75%Co by weight, were compacted by application of a high-voltage, high-density current through a powder column for about 200 μs. The compacted alloys were then evaporated on silicon substrates from an integrated alumina-tungsten crucible. The thin alloy films were studied by Auger electron spectroscopy (AES) depth profiling using Ar+ sputtering to etch the surface. Results of the depth profiling analysis of the deposited alloy films showed that they were of the desired compositions and the film compositions were very uniform indicating that the method of alloy source synthesis is successful. Transmission electron microscopy and x-ray diffraction studies confirmed the presence of an alloy phase. This new method of synthesis of alloy sources is not limited to alloy systems composed of metals of a similar character but can also be extended to alloy systems with greater dissimilarity between the individual components.
Adsorption of tin on the (111) and (100) silicon and germanium surfaces: A theoretical study
Authors: Toscano M. , Russo N.
Published: July 2002

The adsorption of tin atom on different clusters simulating the high symmetry chemisorption sites of Si and Ge (111) and (100) surfaces has been studied by the semiempirical modified neglect of differential overlap (MNDO) method. Results show that the preferred chemisorption site for both silicon and germanium (111) substrates is the three-coordinated one. For the Si and Ge (100) surfaces the computations indicate that the bicoordinated site is strongly preferred with the respect to the tetra and monocoordinated ones. The effect of relaxation and the reconstruction has been explored with a Si9H15 cluster and the results confirm that the main chemisorption parameters are not affected by these phenomena.