bluuebunny/crossref_metadata_2025 huggingface dataset:
Compositional variations in doped iron oxide magnetic thin films
Authors: Hermsmeier B. , Brundle C. R. , Baglin J. E. E.
Published: July 2002

Iron oxide films are candidates for high-density thin-film disk storage media. The films are usually prepared by postdeposition oxidation to produce γ-Fe2O3. Films are usually doped to control grain size and coercivity. Recent work by polarized neutron reflection and Kerr rotation has shown that a magnetic dead layer sometimes exists at the γ-Fe2O3 surface. We have investigated such films by x-ray photoelectron spectroscopy (XPS), Auger spectroscopy, and Rutherford backscattering spectroscopy (RBS). The samples fall into two sets: Fe3O4 bulk composition and the γ-Fe2O3 films formed by postoxidation. 500–2600 Å films were used. The γ-Fe2O3 films, which show the magnetic dead-layer behavior, are shown by Auger and XPS in conjunction with Ar+ profiling to have a depleted Os or Co dopant level over the dead-layer depth. The Fe3O4 films have uniform dopant concentration profiles. For the Os doped films RBS at grazing angle provides quantitative nondestructive elemental composition analysis with a ∼30-Å depth resolution. The depletion of the Os at the surface for the γ-Fe2O3 films is confirmed and owing to the high Os cross section and good separation from the Fe signal excellent quantification is obtained. In addition RBS shows that though x-ray diffraction indicates nearly pure Fe3O4 and pure γ-Fe2O3 phases, the overall stoichiometries can deviate significantly. Finally some information on the chemical state of the dopant is provided from XPS data.
A chemical and structural investigation of Schottky and ohmic Au/GaAs contacts
Authors: Coulman D. , Newman N. , Reid G. A. , Liliental-Weber Z. , Weber E. R. , Spicer W. E.
Published: July 2002

Recently we have shown that the gold contacts deposited on ultrahigh vacuum cleaved (110) n-GaAs exhibit strongly rectifying Schottky barrier-type behavior which becomes ‘‘ohmic’’ upon annealing due to a nonrectifying low-resistance current pathway at the periphery of the contact. These Au/n-GaAs contacts are of particular interest because of this rectifying to ohmic transition. Using scanning Auger electron spectroscopy (AES), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques combined with electrical device measurements, we are able to correlate the change in ohmic behavior for diodes annealed in a nitrogen environment above 360 °C with the formation of very thin, long, predominantly Au crystallites on the surface of the GaAs at the periphery of the contact. These crystallites are typically 5–10 μ long, 500–2000 Å wide, and are crystallographically oriented along the GaAs 〈110〉 direction. TEM and AES sputter profiles have shown that these structures are ∼100–150 Å thick. Glancing incidence sputtering using 1-keV Ar ions with sample rotation, as well as a wet chemical mesa etch (H2SO4:H2O2:H2O), were used to selectively remove the crystallites from around the periphery. AES, SEM, and TEM confirm the removal of the crystallites. After this removal, the rectifying behavior of the diode was restored. This demonstrates that the presence of the thin Au crystallites can be correlated with the ohmic behavior in this system.
Combining transmission probabilities of different diameter tubes
Authors: Santeler D. J. , Boeckmann M. D.
Published: July 2002

Numerical simulations were used to study the molecular flow transmission probability through two tubes of different diameters connected in series. It is well known that Oatley’s simple area ratio correction to the exit loss is inexact due to beaming of the gas from one tube to the next. Many months of computer time on a PC-AT with 80287 numerical processing unit and a VAX-780 were required to obtain sufficiently accurate data on numerous different diameter ratios in order to allow for high-accuracy curve fitting to various potential correction equations for interpolation. The method of analysis used was similar to one by Santeler for two tubes of the same diameter in series. It was found that Oatley’s area correction has a maximum error of 5%. A curve-fit equation is provided that reduces this error to 0.6%.
Stabilization of tetragonal ZrO2 with Al2O3 in reactive magnetron sputtered thin films
Authors: Gilmore C. M. , Quinn C. , Qadri S. B. , Gossett C. R. , Skelton E. F.
Published: July 2002

Thin-film mixtures of zirconia and alumina 1–2 μm in thickness were produced by sputtering composite targets of zirconium and aluminum metals and reacting the metal vapor with oxygen. X-ray and selected area electron diffraction indicated that the films deposited at room temperature were amorphous. Rutherford backscattering measurements indicated that the films were stoichiometric. Annealing at 1000 °C for 48 h produced ordering of the zirconia phase, and the zirconia crystal structure was strongly dependent upon the relative amounts of zirconium and aluminum. Pure zirconia was monoclinic as was a mixture with a zirconium-to-aluminum atom ratio of 0.76:0.24. For the mixture with a zirconium-to-aluminum atom ratio of 0.52:0.48 the tetragonal phase of zirconia was observed with only a trace of the monoclinic phase. The alumina phase apparently orders much more slowly than zirconia, and no alumina diffraction peaks were observed in any of these mixtures with zirconium-to-aluminum atom ratios down to 0.52:0.48.
Al, Al–N alloy, and AlN-coated steel corrosion behavior in O2-free KCl solutions
Authors: Tait W. S. , Huber C. O. , Begnoche B. C. , Siettmann J. R. , Aita C. R.
Published: July 2002

Al, Al–N alloy cermet, and AlN films were grown on 1008 steel substrates using reactive sputter deposition. Corrosion rates of the steel+coating composite in an O2-free 0.2M KCl electrolyte were measured under conditions of cathodic polarization. The results show that an AlN coating lowered the corrosion rate of steel by over an order of magnitude. However, the corrosion rate was enhanced and under certain conditions exceeded that of steel when Al–N alloy cermet and Al coatings were used. This phenomenon was explained in terms of a reactive porous electrode model.
Residual hydrogen concentration levels in graphite
Authors: Bastasz R.
Published: July 2002

Hydrogen concentration versus depth profiles obtained with secondary ion mass spectrometry of a high-purity graphite (POCO) indicate that unannealed POCO has a residual subsurface H level on the order of 0.4% H/C. Vacuum annealing to 910 °C for several hours reduces this level by over an order of magnitude. However, reabsorption of hydrogen containing gases during air exposure occurs in the near surface region. Prolonged air exposure brings the residual hydrogen level within 5 μm of the surface back to the levels seen in unannealed POCO samples.
Direct-current magnetron fabrication of indium tin oxide/InP solar cells
Authors: Coutts T. J. , Wu X. , Gessert T. A. , Li X.
Published: July 2002

Interest in InP-based solar cells has recently been renewed due to the demonstration of excellent radiation resistance and the achievement of device efficiencies in excess of 20% (AM 1.5). Previous analysis of the indium tin oxide (ITO)/InP cell show it to be an extremely shallow homojunction which could, in principle, offer an even greater resistance to radiation than the deliberately grown organometallic chemical vapor deposition homojunctions. In this work, we have fabricated efficient solar cells of ITO/InP using dc magnetron deposition of the ITO into single-crystal InP substrates. The aim was to optimize the efficiency by varying the proximity of the substrate to the target and the input power to the plasma. Slight variations in efficiency have been observed but correlation with the fabrication parameters has been weak. Nevertheless, efficiencies over 16.5% have been achieved and verified at the Solar Energy Research Institute. This is the highest ever achieved for devices of this construction. Detailed studies of the annealing behavior of the cells have been made and interfacial changes observed using Raman spectroscopy and secondary ion mass spectroscopy. These observations, together with measurements of light and dark current/voltage, and quantum efficiency characteristics, have been used to model the behavior of the cells and explain their lack of sensitivity to the fabrication conditions.
Area selective chemical vapor deposition of boron carbide achieved by molecular masking
Authors: Jansson Ulf , Carlsson Jan-Otto
Published: July 2002

The difference in adsorption behavior of hydrocarbons on molybdenum and titanium was used to attain area selective deposition of boron carbide to titanium substrate areas. Hydrocarbons, added to the reaction gas mixture, caused a considerable decrease in the nucleation rate on molybdenum but not on titanium. Hence conditions for selective deposition to titanium areas were obtained. The selectivity was improved by increasing the hydrocarbon concentration in the vapor or by substituting ethylene for methane. This demonstrates that molecular masking of substrate areas can be used to induce or improve the selectivity in a chemical vapor deposition process even at high temperatures (1400 K).
Friction and wear properties of thin films of carbon with diamond structure prepared by ionized deposition
Authors: Okada Katsuzo , Namba Yoshikatsu
Published: July 2002

The friction and wear properties for thin films of carbon with diamond structure, prepared by ionized deposition, slid with copper have been examined in a pressure range of 5×10−4 to 105 Pa. The friction coefficient shows a tendency to decrease with the increase of pressure and it is <0.2 because the surfaces of thin films of carbon with diamond structure are very smooth. The specific wear rate of copper sliders decreases as the pressure becomes lower. However, no wear is detected on thin films of carbon with diamond structure.
Surface recombination velocity of anodic sulfide and ZnS coated p-HgCdTe
Authors: Finkman E. , Schacham S. E.
Published: July 2002

The surface recombination velocity s has been determined for Hg1−xCdxTe (x∼0.2) for two different surface passivations: (i) anodic sulfide with an overcoating of ZnS and (ii) ZnS coating on freshly etched samples. The method used was photoelectromagnetic effect, in which a magnetic field is applied perpendicular to the diffusion current of optically generated injected carriers. Analysis of the magnetic field dependence of the resulting current can yield s, as well as carrier mobility, lifetime, etc. The temperature dependence of s is very similar for the two passivations at temperatures higher than 50 K, and is increasing with decreasing temperature. At low temperatures s continues to rise for ZnS passivation and stays flat for the native anodic sulfide. Two activation energies are determined: 12.5±1.5 meV at temperatures higher than 60 K, and 2.3±0.2 meV at temperatures lower than 30 K. The high-temperature activation energy is identical for both passivations. It is concluded that the same surface traps control the surface recombination rate for the two passivations, and their concentration is equal in both cases. The traps are apparently ‘‘intrinsic,’’ and can be related to lattice defects, most probably vacancies. Their concentration at the surface is similar to that in the bulk.
Band gap and optical constants of microcrystalline CdTe thin films
Authors: Meléndez-Lira M. , Jiménez-Sandoval S. , Hernández-Calderón I.
Published: July 2002

We report the results obtained from optical characterization studies of CdTe thin films grown by the standard rf sputtering technique. Films were grown at different substrate temperatures (Ts) in the 70–200 °C range. From the analysis of absorption spectra we determined the index of refraction and absorption coefficient. Employing a model of direct transitions, the fundamental absorption edge E0 was calculated. The same experiments and analyses were performed for annealed films at 400 °C in N2 atmosphere. The optical constants do not show a clear correlation with substrate temperature for Ts<200 °C. Higher substrate temperatures and/or thermal annealing does bring the optical parameters closer to the single-crystal values. An important and consistent reduction of E0 was observed for all films after thermal annealing. Defect induced absorption, transformation of the metastable hexagonal to the cubic phase of CdTe, and quantum size effects caused by the microcrystalline structure of the films are discussed as possible sources for the observed shifts of the fundamental absorption edge E0.
An anomalous diffusion barrier case: The Hg1−xCdxTe/Yb/Ag junction
Authors: Raisanen A. , Haugstad G. , Yu X. , Ceccone G. , Franciosi A.
Published: July 2002

Synchrotron radiation photoemission measurements of Hg1−xCdxTe/Ag junctions both with and without thin Yb interlayers show that the Yb layer acts to reduce Ag indiffusion at all interlayer thicknesses investigated, although three different types of behavior are observed depending on the layer thickness and morphology. We characterized the Yb layer morphology by means of the photoemission of adsorbed xenon technique. Thin (3–6 Å) Yb interlayers are only partially effective, with substantial Ag indiffusion still evident. We associate this behavior with a two-dimensional island morphology of the interlayer. Thick (10–15 Å) Yb interlayers are highly effective in reducing Ag indiffusion, due to the presence of a continuous reacted Yb layer and of a Yb-rich metallic phase with high alloying enthalpy for Ag. Intermediate thickness (8 Å) Yb interlayers, effectively reduce Ag indiffusion at low Ag coverages (<20 Å), only to fail catastrophically upon further Ag deposition.
Nucleation and growth of a monolayer oxide on Cu(110)
Authors: Chua F. M. , Kuk Y. , Silverman P. J.
Published: July 2002

The process of oxygen chemisorption on a Cu(110) surface has been observed dynamically using scanning tunneling microscopy. The chemisorbed oxygen was found to nucleate on terraces, and not at step edges. Isolated chains grow along the 〈001〉 by homogeneous nucleation. The driving force for the growth is a repulsive interaction along the 〈11̄0〉 and an attractive interaction along the 〈001〉 between 0 atoms.
Fourier transform infrared studies of polyimide and poly(methyl-methacrylate) surfaces during downstream microwave plasma etching
Authors: Leu Jihperng , Jensen Klavs F.
Published: July 2002

The change in chemical structure of the top surface layer of thin poly(methylmethacrylate) (PMMA) and polyimide (PI) films (200–1500 Å) during downstream microwave NF3/CF4/O2 plasma etching are investigated by in situ Fourier transform infrared (FTIR) reflection–absorption spectroscopy. Plasma fluorination of PI by either NF3 or CF4 leads to significant surface fluorination characterized by the formation of aliphatic fluorine compounds (CFx), acyl fluoride, benzoyl fluoride, acyl hypofluorite, and polyfluorinated benzene. The surface fluorination process is found to be controlled by diffusion in the product layer and the depth of fluorination is estimated from infrared absorbance to be approximately 500 Å. Addition of oxygen leads to a reduction in the fluoride species and the development of broad absorption bands representing oxygenated surface species. The FTIR data are supplemented by ex situ x-ray photoelectron spectroscopy observations and mechanisms for the observed modifications of the polymer surfaces are proposed. The effect of humidity on the plasma-modified polymers is studied by comparing infrared spectra collected in situ after controlled exposure to moisture. PI fluorinated in NF3 show no significant changes, whereas a slow but noticeable change in the carbonyl bands is detected for NF3/Ar plasma-fluorinated PMMA. Addition of oxygen to the microwave plasma increases the sensitivity of the modified polymer to moisture. These observations are interpreted in terms of the wettability of the polymer surface.
Use of light scattering in characterizing reactively ion etched profiles
Authors: Giapis Konstantinos P. , Gottscho Richard A. , Clark Linda A. , Kruskal Joseph B. , Lambert Diane , Kornblit Avi , Sinatore Dino
Published: July 2002

Currently, profile control in plasma etching of submicron structures requires inspection of cleaved samples by scanning electron microscopy. This is time consuming, destructive, and limited to a small subset of processed wafers. We show that light scattering can be used to rapidly characterize submicron differences in reactively ion etched, periodic Si structures. A similar approach has been used previously to monitor etching rates and undercutting using specular and first order diffraction peaks. Here, we measure all orders scattered over 180° as a function of incident angle and polarization and focus on the use of this technique coupled with statistical methodology to distinguish subtle changes in line profile. Although scatter from grating test patterns is examined here, this method should also be applicable to complex, submicron device structures.
Redeposition behavior of seeds in oblique cone evolution
Authors: Morishita S. , Okuyama F.
Published: July 2002

Cones developed on Cu surfaces bombarded with an obliquely incident Ar+ –ion beam, while simultaneously supplying Mo ‘‘seeds’’ by sputtering, were observed by scanning and transmission electron microscopy. Seed atoms were found to preferentially deposit on the cone slopes which received high fluxes of these species, forming crystalline thin layers there. The seed overlayers thus grown were ribbon-like in configuration and composed of Mo crystallites arranged in a preferred orientation. An explicit relationship was found between the crystallographic orientations of overlayer and substrate, but it was inconsistent with the existing model of epitaxy. Also, the cone population decreased with decreasing local seed flux and vice versa for the average cone dimension. This may indicate that the key role of seeds is to promote the nucleation of cones, not to enhance the development of nucleated cones.
Surface chemistry of GaAs treated with buffered HF and NH4F solutions: Slow reactions of process residuals
Authors: Yota J. , Burrows V. A.
Published: July 2002

The surface chemistry of GaAs after treatment with NH4F and with HF buffered with NH4F (BHF) was studied using surface infrared spectroscopy in the multiple internal reflection mode. These two treatments not only dissolved the GaAs native chemical oxide, but also deposited a thin inorganic film comprised of ammonium salts (NH4F and NH4F HF) that further react through a series of complex reactions with the semiconductor substrate to form ammonium hexafluorogallate [(NH4)3GaF6]. These reactions are apparently driven by favorable thermodynamics, but occur very slowly. The reactions on BHF-treated GaAs proceed over approximately one day, while reactions on the NH4F-treated GaAs can extend for more than three days. Although the fluoride and bifluoride salts are quite soluble in alcohols as well as in aqueous solutions, the hexafluorogallate is completely insoluble in alcohols, and can only be removed by a thorough water rinse.
Angularly resolved x-ray photoelectron spectroscopy investigation of PTFE after prolonged space exposure
Authors: Dalins I. , Karimi M.
Published: July 2002

Monochromatized angularly resolved x-ray photoelectron spectroscopy (ARXPS) was used to study PTFE (Teflon) that had been exposed to an Earth orbital environment for approximately six years. The primary interest of the research is on a very reactive component of this environment (atomic oxygen) which, because of the typical orbital velocities of a spacecraft, impinge on exposed surfaces with 5 eV energy. Generation of such particles in a laboratory is not practical, thus, the atomic oxygen aspect must eventually be resolved in a space flight environment. This presentation deals with the method of analysis, the findings as they pertain to a rather complex carbon, oxygen, and fluorine XPS peak analysis, and the character of the valence bands. An improved bias referencing method, based on ARXPS, will also be demonstrated for evaluating specimen charging effects. It was found that the polymer molecule tends to resist the atomic oxygen attack by reorienting itself, so that the most electronegative CF3 groups are facing the incoming hyperthermal oxygen atoms. The implications of these findings to ground-based laboratory studies will also be discussed.
Particle contamination during sputter deposition of W–Ti films
Authors: Wickersham C. E. , Poole J. E. , Mueller J. J.
Published: July 2002

Particle contamination during sputter deposition of W–Ti films depends upon the target density, the amount of Ti rich β(Ti,W) in the target, the target impurity content, and the film compressive stress. Particle contamination densities decrease from ∼1.5 cm−2 to less than 0.1 cm−2 as the sputtering target microstructure is changed from a 76% dense multiphase mixture of Ti rich β(Ti,W) and β-W to a 99% dense two phase combination of β-W and α-Ti. A process map is provided to guide the selection of optimum powder compaction process for W–Ti targets. We propose that particle emission from the Ti rich β(W–Ti) phase in W–Ti sputtering targets occurs by argon bombardment induced compressive stress fracture of the Ti rich β(Ti,W) phase. Particle contamination density increases at a rate of 1.5×10−4 particles/cm2 for each (parts per million by weight) of target impurity. An inverse relationship between the total deposited film thickness and the film compressive strain was found. Increasing the W–Ti film compressive strain reduces the film thickness at which stress fracture (flaking) of the film deposited on the system shields occurs. A reduced stress fracture thickness means that particle emission from the system shielding will occur at an early stage as film accumulates on the exposed shielding.
High-rate aluminum oxide deposition by MetaModeTM reactive sputtering
Authors: Lehan J. P. , Sargent R. B. , Klinger R. E.
Published: July 2002

MetaModeTM reactive sputtering was employed to produce optical quality aluminum oxide films at rates an order of magnitude higher than those possible with conventional reactive magnetron sputtering. System pressure, reactive-to-nonreactive gas flow ratio, and ion-source current density were varied to investigate their effects on rate, process stability, and film properties. It was found that the coatings deposited at a reduced pressure (0.27 Pa) produced dense, water-free coatings without compromising optical quality or deposition rate.
Formation of high adhesive and pure Pt layers on TiO2
Authors: Kondo Ichiharu , Yoneyama Takao , Takenaka Osamu , Kinbara Akira
Published: July 2002

The formation of a high adhesive noble metal layer on an oxide layer has been investigated in the Pt/(Ti)/TiO2/SiO2/Si system, prepared in a vacuum evaporation apparatus. The thermosonic ball bonding test and the conventional pull test were successively applied to the evaluation of adhesion. The Ti inserted layer between the Pt and the TiO2 layer was found to improve the adhesion. A Ti layer of approximately 10 nm was found to be necessary for stronger adhesion. Auger electron spectroscopy (AES) depth profile results showed that a part of the Ti atoms in the inserted layer were segregated to the Pt surface from the interface by annealing at 1373 K for 30 min, while the rest of Ti atoms in the inserted layer remained and acted as a ‘‘glue’’ at the interface between the Pt and the TiO2 layer. It should be noted that Ti could not be detected in the Pt layer within the AES detection limits. Scanning electron microscope and energy dispersive x-ray spectroscopy observations showed that Ti diffusion occurred through the grain boundaries of the Pt layer and Ti atoms appeared at surface grain boundaries on top of the Pt layer.
Effects of different pretreatments on the surface structure of silicon and the adhesion of metal films
Authors: Kondo I. , Yoneyama T. , Kondo K. , Takenaka O. , Kinbara A.
Published: July 2002

Interface structures and adhesion to silicon after different surface pretreatments have been investigated for Ni(500–1000 nm)/Ti(250 nm) films prepared in a dc planar magnetron sputtering apparatus. In order to obtain high adhesion, a chemical pretreatment (with buffered HF) has been found to be favorable in comparison with a conventional Ar ion bombardment pretreatment (with cathodic voltage: 400 V). High resolution transmission electron microscopy (HRTEM) showed that there were two layers between Ti and Si in the case of Ar ion bombardment pretreatment. Energy dispersive x-ray spectroscopy (EDS) and electron diffraction (ED) showed that they were amorphous Ti–Si alloy and amorphous Si containing Ar. Moreover, a peeling pattern, after the test with adhesive tape, could be found at the boundary between the amorphous Ti–Si alloy layer and the amorphous Si layer containing Ar by using x-ray photoelectron spectroscopy (XPS). In the case of chemical pretreatment, only an amorphous Ti–Si alloy layer was observed between Ti and Si, and peeling was not observed. The differences in interface structure and adhesion are considered to be influenced by the Ar implanted during the Ar ion bombardment pretreatment.
Study of palladium mono- and multilayers on Ta(110) between 300 and 1500 K
Authors: Ruckman M. W. , Jiang L. Q. , Strongin Myron
Published: July 2002

Core level photoemission was used to study the growth and thermal modification of Pd films deposited on Ta(110) between 300 and 1500 K. The Ta(110) substrate had Ta 4f core level spectral components which could be identified with the Ta(110) terrace and edge sites. The deposition of Pd causes a 175±100 meV shift of these surface-related core level components. Little or no additional core level shift is seen when the interface is modified by heating. A decrease in the intensity of the bulk Ta 4f component is observed and is consistent with the growth of a Pd–Ta surface alloy. However, changes in the ratio of the components derived from the edge and terrace sites argue for changes in the size of the Ta(110) terraces due to the preferential growth of the alloy phase at the edges or the development of additional surface facets. These changes in surface morphology appear to be reversed when the Ta substrate becomes hot enough to remove the Pd.
Visualization of circular DNA molecules labeled with colloidal gold spheres using atomic force microscopy
Authors: Shaiu Wen-Ling , Vesenka James , Jondle Daniel , Henderson Eric , Larson Drena D.
Published: July 2002

We have imaged gold-labeled DNA molecules with the atomic force microscope (AFM). Circular plasmid DNA was labeled at internal positions by nick-translation using biotinylated dUTP. For visualization, the biotinylated DNA was linked to streptavidin-coated colloidal gold spheres (nominally 5 nm diam) prior to AFM imaging. Reproducible images of the labeled DNA were obtained both in dry air and under propanol. Height measurements of the DNA and colloidal gold made under both conditions are presented. The stability of the DNA-streptavidin colloidal gold complexes observed even under propanol suggests that this labeling procedure could be exploited to map regions of interest in chromosomal DNA.
Angle-resolved x-ray photoelectron spectroscopy method for the thickness measurement of metal oxide/metal ultrathin films
Authors: Chen Liangyu , Hoffman Richard W.
Published: July 2002

An angle-resolved x-ray photoelectron spectroscopy (XPS) method based on a flat, uniform, isotropic, and layered model is first introduced for the thickness measurement of ultrathin (<100 Å) double-layer films, such as metal oxide/metal. Since only the relative intensities, at two electron exit angles, of characteristic XPS peaks of metallic species, the material densities and mean free paths of photoelectrons with certain kinetic energy are involved, no dependence of either instrumentation constants or the elemental sensitivities for different species exists in this method and the influence from surface contamination is eliminated intrinsically. The results with error analysis for Al2O3/Al films are reported.
Langmuir probe diagnostics of a radio frequency magnetron discharge for deposition of high T
c YBCO films
Authors: Mishra S. K. , Sarkar A. , Ray S. K. , Bhattacharya D. , Chopra K. L. , Das S. R.
Published: July 2002

Determination of the key internal discharge parameters such as charge particle concentration, plasma potential, and electron temperature has been made for sputter deposition of superconducting YBCO films in Ar and Ar+O2 plasma using a tuned Langmuir probe technique. The plasma parameters measured from probe characteristics have been used to qualitatively explain the effect of deposition conditions on film property. The behavior of dc self-bias at the target is discussed in the light of the combined effect of O−2 ion emission and Ba+ ion interaction with the target.
Erratum: ‘‘Optical emission investigation of the plasma enhanced chemical vapor deposition of silicon oxide films’’ [J. Vac. Sci. Technol. A 10, 3395 (1992)]
Authors: Banerjee A. , DebRoy T.
Published: July 2002

An error in the reference list was detected. The correct version is as follows.
Cleaning of metal parts in oxygen radio frequency plasma: Process study*
Authors: Korzec D. , Rapp J. , Theirich D. , Engemann J.
Published: July 2002

The removal of different lubricants (oils and greases) from metal surfaces by use of a capacitively coupled 13.56 MHz low-pressure oxygen discharge has been examined. Stainless steel, tool steel, brass, aluminum, and copper were used as a substrate materials. The ion bombardment and chemical reactions occurring at the metal surfaces in such a discharge allow for high cleaning speed. A hollow-cathode discharge has been used to increase the plasma density in contrast to a plane cathode discharge configuration. The cleaning process was characterized by use of emission spectroscopy and mass spectroscopy. Influence of rf power (up to 1 kW), pressure (from 0.01 to 1 mbar), and magnetic field (up to 20 mT) on the process duration and surface cleanliness has been investigated. The criteria for detection of the process end point are formulated and checked. The spectral information is useful for end point detection only in restricted regions of the process conditions. Results indicate a strong influence of the lubricant temperature on the process duration. The removal rate of N62 oil at 140 °C is twice as high as that at 50 °C. For temperatures higher than 140 °C the creation of a hardly removable solid residue occurs. The influence of the initial lubricant area and lubricant thickness on the process duration has been investigated. The increase of the lubricant area results in an increase of the process time (loading effect for cleaning process). The increase of the lubricant film thickness results in a proportional increase of the process time.
Dynamic rate and thickness metrology during poly-Si rapid thermal chemical vapor deposition from SiH4 using real time in situ mass spectrometry
Authors: Tedder L. L. , Rubloff G. W. , Cohaghan B. F. , Parsons G. N.
Published: July 2002

Real-time in situ mass spectrometry has been applied to poly-Si rapid thermal chemical vapor deposition (RTCVD) (from SiH4) on thermally grown SiO2 as a way to determine film thickness at the end of the process and to infer dynamic deposition rate during the process for run-to-run and real-time control applications. Monitoring process ambient at 5 Torr is achieved using two-stage differential pumping of a sampling aperture in the exhaust stream, and a rapid response time (∼1 s for a ∼30 s process cycle) allows for real time sensing of reactant input, product generation, and reactant depletion. Active mass spectrometric sampling of the reaction by-product (H2 generated by SiH4 decomposition) provides a monitor of the total reaction/deposition rate during poly-Si RTCVD in the range 550–850°C. Product generation as a function of temperature is readily distinguished from reactant cracking fragments by spectral analysis. A well-defined monotonic correlation between the time-integrated H+2 product signal and the poly-Si film thickness, determined ex situ by single-point interferometry (Nanometrics), demonstrates that the integrated mass spectrometric signal can provide real-time thickness metrology. In addition, the time-dependence of product and reactant signals provides a real-time indication of detailed equipment behavior during the process.
Electronic and vibrational spectra of InP quantum dots formed by sequential ion implantation
Authors: Mu R. , Henderson D. O. , Tung Y. S. , Ueda A. , Hall C. , Collins W. E. , White C. W. , Zuhr R. A. , Zhu Jane G.
Published: July 2002

Sequential ion implantation of indium and phosphorus into silica combined with controlled thermal annealing has proven to be a novel and effective technique to fabricate InP quantum dots in dielectric hosts. This technique has been applied to synthesize other III–V and II–VI quantum dots. Due to the unique bimodal distribution of the indium in a silica host and a stoichiometric mismatch between the indium and phosphorus concentration profiles, it is believed that two different-sized InP quantum dots were fabricated. More importantly, we have shown that the infrared reflectance technique is a very effective method to identify the species in the dielectric host and is also a powerful tool to investigate surface phonon modes.
Effects of readsorption on outgassing rate measurements
Authors: Redhead P. A.
Published: July 2002

Outgassing rates from the walls of a vacuum chamber are usually measured by one of two methods, (1) the throughput method, where the outgassing rate is derived from the pressure drop across a known conductance during evacuation, or (2) the pressure rise method (aka the gas accumulation method) where the chamber is sealed off at a low pressure and the rise in pressure with time measured. A model of the throughput method is analyzed to show that readsorption of desorbed gas results in the measured outgassing rate Qm being considerably less than the intrinsic rate Qi (the outgassing rate in the absence of readsorption). The ratio of outgassing rates Qm/Qi varies with the pumping parameter S/A (S is the pumping speed and A the adsorbing area) and the sticking probability s. Qm is found to vary with the pumping parameter and the sticking probability at zero coverage s0, except when a/As0≪kt−1, where a is the effective area of the orifice, A the adsorbing area, k is a constant involving the heats of adsorption, and t the pumping time. Measurements by the pressure-rise method on stainless steel systems show that the gas evolved is hydrogen, and that the pressure rise is linear for as long as 103 h with the pressure increasing by a factor as large as 106, indicating a constant outgassing rate. It is shown that if readsorption occurs then the p(t) curve will be nonlinear. A model is proposed to explain the observed constancy of outgassing rate and the apparent absence of readsorption which assumes that (a) the outgassing rate is desorption limited and (b) the rate of diffusion of H atoms to the surface is much greater than the rate of desorption of H2 or the rate of arrival of molecules from the gas phase at empty sites.
Estimation and verification of the optical properties of indium tin oxide based on the energy band diagram
Authors: Knickerbocker S. A. , Kulkarni A. K.
Published: July 2002

Indium tin oxide (ITO) is a transparent conducting material used in optoelectronic applications. In order to optimize the optical properties of ITO, it is necessary to determine these properties as a function of the free carrier concentration (i.e., doping In2O3 with Sn). Based on an ab initio Hartree–Fock calculation of the energy band diagram of indium oxide and indium oxide doped with tin, an empirical relationship of the electron effective mass as a function of the ideal free carrier concentration is established. The importance of the varying electron effective mass in the prediction of the complex dielectric function, the refractive index, extinction coefficient, and finally the optical transmission based on Drude’s theory is shown here by comparing the estimated results with measured and published results. The agreement between estimated values and measured or published experimental results is very good.
Supersonic-jet-assisted growth of GaN and GaAs films
Authors: Ferguson B. A. , Sellidj A. , Doris B. B. , Mullins C. B.
Published: July 2002

We present the results of investigations of the growth of two semiconductor materials using supersonic jets. Homoepitaxial growth of GaAs films was accomplished by directing a supersonic jet of the single source precursor (t-Bu)2(Ga–As)(t-Bu)2 seeded in helium at a heated GaAs(100) substrate. Epitaxial GaAs films were produced with substrate temperatures of 400–500 °C, while a wafer temperature of 300 °C yielded degraded crystallinity in the deposited film. Atomic force microscopy revealed that the GaAs films were relatively smooth, with a root mean square roughness of 8.1 Å. We have also successfully grown GaN films on sapphire (0001) using supersonic jets of nitrogen atoms and a gallium effusion source. The nitrogen atoms were generated from a mixture of 1% N2 in He by a radio frequency discharge. A growth rate of 0.65 μm/h was obtained, independent of substrate temperature over the range 600–750 °C. The films were single crystalline wurtzite GaN as determined by x-ray diffraction and in situ reflection high energy electron diffraction (RHEED). The peak width of the (0002) GaN reflection, as measured by high resolution x-ray diffraction, was as low as 38 arcmin, indicating a crystalline quality that is comparable to GaN films deposited by other plasma-assisted molecular beam epitaxy techniques, but inferior compared to films currently grown by metalorganic chemical vapor deposition. In addition, the peak width decreases with increasing growth temperature, indicating that the crystalline quality of the film improves. The RHEED images also indicate that the GaN films have a rough surface morphology.
Determination of the components of stress in a polycrystalline diamond film using polarized Raman spectroscopy
Authors: Mossbrucker J. , Grotjohn T. A.
Published: July 2002

Polarized Raman spectroscopy is used to measure the hydrostatic and axial stress components along the [111] and [100] direction of a 2-in.-diam polycrystalline diamond film showing mainly [111] and [110] facets. The theoretical background and the instrumentation necessary to measure stress and crystal orientation are presented. Experimental examples of a [111] oriented single crystal having uniaxial stress along the [111] direction, as well as a [100] oriented single crystal having uniaxial stress along the [100] direction, are presented. The diamond Raman peak height and shift indicating hydrostatic stress are measured at 1776 different locations across the entire film. The hydrostatic stress, the axial stress along the [100] direction, and the axial stress along the [111] direction of 441 neighboring crystals of a center portion of the film are also determined. The results show a very clustered distribution of the hydrostatic and axial stress with a variation of up to 0.8 GPa.
Wavelength tunable fiber Bragg grating devices based on sputter deposited resistive and piezoelectric coatings*
Authors: Fox G. R. , Muller C. A. P. , Setter N. , Costantini D. M. , Ky N. H. , Limberger H. G.
Published: July 2002

Two all-fiber wavelength tunable devices, one utilizing thermal tuning and a second based on strain tuning, have been produced by combining resistive Ti/Pt and piezoelectric ZnO fiber coatings with fiber Bragg gratings (FBGs). The Ti and Pt coatings with thicknesses of 40 and 300 nm, respectively, were deposited by sequential magnetron sputter deposition. ZnO fiber coatings with a thickness of 18 μm were deposited by dual magnetron reactive sputtering. Joule heating of the Ti/Pt fiber coating was employed for the thermally tunable FBG device, which exhibited a tuning efficiency of 4.1 nm/W. The piezoelectric fiber Bragg grating device allowed for modulated tuning of the FBG wavelength through a strain modulation induced by the piezoelectric ZnO coating. A wavelength modulation amplitude of 0.044 nm was achieved at a driving potential amplitude of 1.26 V and frequency of 15.26 MHz.
Field emission characteristics of SiC capped Si tip array by ion beam synthesis
Authors: Chen Dihu , Cheung W. Y. , Wong S. P. , Fung Y. M. , Xu J. B. , Wilson I. H. , Kwok R. W. M.
Published: July 2002

High dose carbon implantation into Si tip array was performed to synthesize SiC/Si heterostructure tip array. This was done using a high beam current density metal vapor vacuum arc ion source. Silicon tip arrays were prepared by anisotropic chemical etching. An implantation energy of 35 keV using a dose of 1.0×1018 ions/cm2 was performed. The array was subsequently annealed in argon ambient at 1200 °C, for various times to form the SiC surface layer. Scanning electron microscopy shows that the Si tips were sharp and uniformly arranged. X-ray photoelectron spectroscopy confirmed that a thin SiC surface layer had been formed. Results show that electron emission properties measured in ultrahigh vacuum depended on the sample treatment. A typical turn-on field was 15 V/μm when the emission current density reaches 1 μA/cm2. This compares with a turn-on field of about 35 V/μm for an unimplanted Si tip array.
Use of a one atmosphere uniform glow discharge plasma to kill a broad spectrum of microorganisms
Authors: Kelly-Wintenberg K. , Hodge Amanda , Montie T. C. , Deleanu Liliana , Sherman Daniel , Reece Roth J. , Tsai Peter , Wadsworth Larry
Published: July 2002

The medical, industrial, and food processing industries are constantly in search of new technologies to provide improved methods of sterilization and pasteurization. Proposed techniques must deal with such problems as thermal sensitivity and destruction by heat, formation of toxic by-products, cost, and inefficiency in performance. We report results from a newly invented plasma source, a one atmosphere uniform glow discharge plasma (OAUGDP), which is capable of operating at atmospheric pressure in air and providing antimicrobial active species at room temperature. OAUGDP exposures have reduced log numbers of bacteria (Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa), bacterial endospores (Bacillus subtilis and Bacillus pumilus), and various yeast and bacterial viruses on a variety of surfaces. These surfaces included polypropylene, filter paper, paper strips, solid culture media, and glass. Experimental results showed at least a ⩾5 log10 colony forming units (CFU) reduction in bacteria within a range of 15–90 s of exposure, whether the samples were exposed in conventional sterilization bags or exposed directly to the plasma. An exception to these very short exposure times were experiments with solid culture media in which 5 min of plasma exposure was necessary to produce ⩾5 log10 CFU reduction in bacterial counts. The effects of plasma treatment on bacterial cell structures were investigated by exposing cells to plasma for various durations and examining them by transmission electron microscopy. The results showed that cell breakage (lysis) occurred with the release of cellular contents. These data were consistent with spectrophotometric results in which the release of cellular constituents was measured as a change in ultraviolet absorption at 260 nm. With all microorganisms tested, a biphasic survival curve (logarithmic number of survivors versus time) was observed in plots of dose-response data. Differences in susceptibilities of microorganisms observed on various surfaces suggested that the degree of lethality was dependent upon the time of diffusion of active species through the medium to the organism and the makeup of the microbial cellular surface.
Temperature programmed desorption from graphite
Authors: Schleussner D. , Rösler D. , Becker J. , Knapp W. , Edelmann Ch. , Garcı́a-Rosales C. , Franzen P. , Behrisch R.
Published: July 2002

An experimental setup that allows quantitative measurements of the temperature programmed desorption of different gases from any sample is described. The samples to be analyzed are uniformly heated to temperatures up to 2100 K by electron bombardment from the rear side at a rate of about 10 K/s. The temperature is controlled and can be measured on the front side by a pyrometer. The gases released from a sample are measured with a quadrupole mass spectrometer according to the partial pressure change in the residual gas. In order to get quantitative results the equipment is calibrated for different gases. The facility was tested with measurements of the hydrogen inventory and desorption temperatures for graphite samples from the vessel walls of the fusion experiment ASDEX Upgrade.
Effect of thermal annealing on hole trap levels in Mg-doped GaN grown by metalorganic vapor phase epitaxy
Authors: Zhu Qin-Sheng , Nagai H. , Kawaguchi Y. , Hiramatsu K. , Sawaki N.
Published: July 2002

Deep trap levels in a Mg-doped GaN grown by metalorganic vapor phase epitaxy are studied with deep level transient spectroscopy (DLTS). The Mg concentration of the sample was 4.8×1019 cm−3, but the hole concentration was as low as 1.3×1017 cm−3 at room temperature. The DLTS spectrum has a dominant peak D1 with an activation energy of 0.41±0.05 eV, accompanied by two additional peaks with activation energies of 0.49±0.09 eV (D2) and 0.59±0.05 eV (D3). It was found that the dominant peak D1 consists of five peaks, each of which has different activation energy and capture cross section. In order to investigate these deep levels further, we performed heat treatment on the same samples to observe the variations of activation energy, capture cross section, and amplitude of DLTS signals. It was found that the longer the heat treatment duration is, the lower the amplitude of DLTS peaks become. This suggests that the decrease of the DLTS signal originates from hydrogen atom outgoing from the film during the annealing process. The possible originality of multiple trap levels was discussed in terms of the Mg–N–H complex.
Magnetic stability of novel exchange coupled systems
Authors: Inomata A. , Jiang J. S. , You C.-Y. , Pearson J. E. , Bader S. D.
Published: July 2002

The magnetic stability of two different interfacial exchange coupled systems is investigated using the magneto-optic Kerr effect during repeated reversal of the soft layer magnetization by field cycling up to 107 times. For uniaxial Fe/Cr(211) exchange biased “double-superlattice” systems, small but rapid initial decay of exchange bias field HE and the remanent magnetization is observed. Also the Sm–Co/Fe bilayers grown epitaxially with uniaxial in-plane anisotropy show similar decay. However, the HE of biaxial and random in-plane bilayers shows gradual decay without large reduction of the magnetization. These different decay behaviors are explained by their different microstructure and interfacial spin configurations.