bluuebunny/crossref_metadata_2025 huggingface dataset:
X-ray photoelectron spectroscopy and scanning electron microscopy characterization of novel poly(monosubstituted) acetylenes containing doping species
Authors: Russo M. V. , Polzonetti G. , Furlani A. , Bearzotti A. , Fratoddi I. , Altamura P.
Published: July 2002

The chemical structure of two homogeneously doped polyenes, namely poly(propargylalcohol) (PPOH) and poly(N,N-dimethylpropargylamine) (Pd-PDMPA), has been investigated by means of x-ray photoelectron spectroscopy (XPS). The study of FeCl3 and I2 doped PPOH films gave evidence of different chemical states for the dopants into the polymeric chain. This result confirms that a charge transfer reaction between the polymer and dopant occurs, as found for analogous systems. An interaction between PPOH and the FeCl3  species, involving the metal and the pendant groups of the polymer, is observed. The analysis of HCl doped Pd-PDMPA films shows that the dopant interacts with the polymer by an acid-base reaction leading to the protonation of the N atoms. Scanning electronic microscopy images of the PPOH and Pd-PDMPA pristine films show that the final result of the polymerization process is the formation of a flat, enamel-like surface. The chain growth of Pd-PDMPA occurs by a dendrite growth. The enamel-like surface of the PPOH films is maintained upon homogeneous doping reaction, whereas a “craquelet ” effect is observed when the pristine films are exposed to iodine vapors. Homogeneous doping of Pd-PDMPA with HCl exhibits a dramatic modification of the surface with the appearance of a crystalline structure, due to the acid-base reaction also revealed by the XPS study.
Effects of initial annealing treatments on the electrical characteristics and stability of unpassivated CdSe thin film transistors
Authors: Belkouch S. , Landheer D. , Masson D. P. , Das S. R. , Quance T. , LeBrun L. , Rolfe S. J.
Published: July 2002

Secondary ion mass spectrometry shows that when CdSe is annealed in air at 350 °C oxygen diffuses inside the grains and the diffusion is enhanced at the grain boundaries. Subsequent vacuum annealing removes oxygen from inside the grains and from the grain boundaries, but leaves a film with residual tightly bound oxygen and a reduced donor concentration. Annealing in vacuum at 390 °C results in a highly conductive layer with a positive threshold voltage drift resulting from the chemisorption of oxygen. Annealing in dry or wet air at 350 °C produces a highly resistive material with lower donor concentrations at the surface and in the bulk, and a lower concentration of acceptor traps at the grain boundaries. The effects of dry- and wet-air annealing on the threshold voltage drift for unpassivated CdSe thin film transistors exposed to ambient air have been monitored. A negative threshold voltage drift, which may be enhanced by the presence of a water-related species, was observed.
Complementary metal–oxide–semiconductor-compatible micromachined two-dimensional vertical Hall magnetic-field sensor: A modified design
Authors: Kahrizi M. , Paranjape M. , Landsberger L. M.
Published: July 2002

This article presents the design and characterization of a complementary metal–oxide–semiconductor-compatible magnetic-field sensor. The present design is a variation of the original concept for a vertical Hall magnetic-field sensor. Our sensor measures two magnetic-field components parallel to the device surface. The carriers flow in a plane perpendicular to the device surface. The induced Hall potential is due to the Lorentz force and measures the intensity of the magnetic field. In order to reduce the cross-sensitivity and increase the sensitivity of the sensor, the carrier regions in the sensor are confined by reverse-biased p+ walls. To avoid any premature pinch-off, the p+ regions are fabricated skewed at an angle to each other, in such a way that, as the potential difference varies across the carrier regions, the boundaries between the depletion regions remain parallel along the carrier’s path from the central to the outer current contacts. In this way, the potential impact of carrier confinement is increased, thereby increasing sensor response by >3×. In addition, the overall sensitivity is increased by 2× while the cross sensitivity is further reduced, in comparison with the previous sensor.
Characterization of annealed high-resistivity InP grown by He-plasma-assisted epitaxy
Authors: Pinkney H. , Thompson D. A. , Robinson B. J. , Mascher P. , Simpson P. J. , Myler U. , Kang J. U. , Frankel M. Y.
Published: July 2002

In this work we report on the effect of annealing high-resistivity InP grown by gas source molecular beam epitaxy in the presence of an electron cyclotron resonance generated He plasma. Previous work has shown that InP grown using this technique exhibits resistivity greater than 105 Ω cm and Be-doped InGaAsP (lattice matched to InP, band-gap wavelength 1.5 μm) exhibits subpicosecond carrier lifetime. This behavior is due to the presence of defects caused by the plasma particles during growth. To gain a better understanding of the nature of these defects, samples were annealed over the temperature range 500–700 °C and evaluated by variable energy positron annihilation measurements, transient ellipsometric surface photoreflectance, sheet resistance, and n–i–n device resistivity studies. For all samples, the resistivity increased with annealing, as did the carrier lifetime from the optical measurements which suggests the presence of more than one defect type in the material. Positron annihilation studies suggest that the open volume defects, present in the as-grown material as single vacancies and vacancy clusters, become larger upon annealing although this effect may be obscured in the Be-doped samples at higher annealing temperatures. The Be-doped samples were found to be more resistive and optically faster than the undoped material. Also, the sheet resistance measurements may indicate that the Be in the doped samples is activated at annealing temperatures above 600 °C, since the material changes from weakly n-type to p-type.
Temperature-programmed desorption and high-resolution electron energy loss spectroscopy studies of the interaction of water with the GaAs (001)-(4×2) surface
Authors: Chung Chan-Hwa , Yi Sang I. , Weinberg W. Henry
Published: July 2002

The adsorption, desorption, and dissociation of water on the GaAs(001)-(4×2) surface have been studied using Auger electron spectroscopy (AES), temperature-programmed desorption, and high-resolution electron energy loss spectroscopy. We have found that water first adsorbs molecularly at 100 K and dissociates readily upon annealing by virtue of overlapping desorption and dissociation temperatures between 150 and 200 K. The dissociation probability of water on the GaAs(001)-(4×2) surface is approximately 0.8 at low coverages (exposures below 0.5 L). However, the decomposition products of water exhibit a high recombination probability, making the oxidation of GaAs difficult. A large fraction of surface hydroxyls are rehydrogenated to produce desorbing water at temperatures between 300 and 700 K. Hence, we have applied a cycling treatment (repeated adsorption of water at 100 K followed by annealing to 750 K) in order to effectively oxidize the GaAs surface. During cycling, we have monitored GaAs–oxide growth using AES. In addition, thermal desorption spectra recorded after exposure of the cycling-treated GaAs surface to water at 100 K point to molecular adsorption and intact desorption of water with little evidence of dissociation, which suggests that the surface has been significantly oxidized by the cycling treatment of water.
First principles calculations of the different structures of a monolayer of Sb on Si (111)
Authors: Takeuchi Noboru
Published: July 2002

We have performed first-principles calculations to determine the surface atomic structure of a monolayer of Sb on the Si (111) surface. Scanning tunneling microscopy and low energy electron diffraction experiments have found (1×1), (2×1), and (∛×∛) reconstructions. Our calculations show that several structures have similar total energies, suggesting that different Sb geometries can coexist on Si (111). Besides the structures previously observed experimentally, we found a new structure (with similar total energy) formed by a sequence of two kind of trimers: one centered on a T4 site and the following on a H3 site.
Giant magnetoresistance behavior of granular Fe and Co implanted Ag thin films
Authors: Soares J. C. , Redondo L. M. , de Jesus C. M. , Marques J. G. , da Silva M. F. , Pereira de Azevedo M. M. , Mendes J. A. , Rogalski M. S. , Sousa J. B.
Published: July 2002

The magnetoresistive behavior of granular thin films prepared by Fe and Co implantation in Ag thin films is reported. Ag thin films (∼2000 Å) were deposited by evaporation or laser ablation onto Si and SiO2 substrates and implanted with Fe or Co at fluences up to 1017 at. %/cm2. The magnetoresistive response obtained after implantation was found to increase with the implanted fluence. An increase of the magnetoresistive response by a factor of 3–4 can be achieved after annealing the films in a conventional furnace at 620 K under vacuum. The best value of magnetoresistance obtained so far is 9% at 10 K and 1.5% at room temperature for a film implanted with Co at a fluence of 8×1016 at. %/cm2 and annealed at 620 K.
Silane consumption and conversion analysis in amorphous silicon and silicon nitride plasma deposition using in situ mass spectroscopy
Authors: Chowdhury Ashfaqul I. , Klein Tonya M. , Anderson Timothy M. , Parsons Gregory N.
Published: July 2002

In situ mass spectroscopy is used to sense plasma deposition of silicon and silicon nitride, to analyze gas phase reactant depletion, and the efficiency of silane conversion into the thin film. A double-differentially pumped quadrupole mass spectrometer was used to monitor the SiH4, Si2H6, and H2 effluent from 100% SiH4 and 2% SiH4/He silicon deposition, and SiH4/He/N2 silicon nitride deposition processes. No significant changes in gas phase nitrogen related species were observed during nitride deposition. However, the Si species show significant process dependence allowing reaction analysis. Disilane species were produced at low powers in the SiH4/He/N2 process, but no amino–silane species were observed. The silane consumption and silicon incorporation efficiency are shown to depend on gas dilution, residence time, and reactor geometry.
Gate leakage current: A sensitive characterization parameter for plasma-induced damage detection in ultrathin oxide submicron transistors
Authors: Jiang J. , Awadelkarim O. O. , Werking J.
Published: July 2002

We report the results of experiments performed to study plasma-induced damage in ultrathin gate oxide of metal-oxide-semiconductor field-effect transistors (MOSFETs). The transistors used were 0.35 μm n-channel MOSFETs with ⩽65-Å-thick gate oxides fabricated on 200 mm p/p+ boron-doped silicon substrates using a full complementary metal-oxide-semiconductor flow up to and including metal 2 processes. Our results show that threshold voltage, maximum transconductance, and subthreshold swing as well as charge pumping current became ineffective in discerning charging damage in these thin oxide MOSFETs. In contrast, gate leakage current Ig, measured at a gate-to-substrate voltage of 2 V, is shown to emerge as the more sensitive damage indicator in this case. The sensitivity of Ig is attributed to trap-assisted direct tunneling which is enhanced by decreasing oxide thickness. The sensitivity of Ig in probing charging damage is demonstrated using special MOSFET structures that utilize charge antennas at the polycrystalline silicon gate definition etch, contact etch, and metal etch steps.
Structural and magnetic properties of Fe/Rh(001) sputter deposited multilayers
Authors: Tomaz M. A. , Harp G. R. , Mayo E. , Lederman D. , Wu R. , O’Brien W. L.
Published: July 2002

We present details of the crystal structure and magnetic behavior of Fe/Rh (001) sputter deposited multilayer thin films. We find that the films undergo a structural phase transformation from a body-centered-tetragonal (bct) to a face-centered-tetragonal (fct) lattice which is concomitant with a magnetic transformation from a ferromagnetic to a nonferromagnetic state. We identify the Rh spacer thickness where both bct and fct phases first coexist as the critical thickness (tcrit). In the region prior to the critical thickness, both Fe and Rh are ferromagnetic with Rh moments of at least 1μB and Fe moments enhanced as much as 30% relative to their bulk value. In the postcritical region, we find the films to be nonferromagnetic. The experimental results are compared with theoretical calculations on similar structures.
Co on stepped Cu(100) surfaces: A comparison of experimental data with Monte Carlo growth simulations
Authors: Coyle S. T. , Scheinfein M. R. , Blue James L.
Published: July 2002

Monte Carlo simulations of the growth of Co/Cu(100) in the presence of steps, terraces, and kinks were performed. The beginning stages of Co growth enhance the roughening of step edges. Interdiffusion increases with increasing temperature and decreasing growth rate. Varying the step orientation from 〈100〉 to 〈110〉 produced a steady decrease in interdiffusion. The lateral width of the interdiffused region in steps (10%–90% concentration) is ∼0.7–1.5 nm. Decreasing the Co–Cu binding energy produced an increase in the frequency of double-height islands and step edge decoration. A value of ∼0.21 eV/nearest neighbor bond produced step edge decoration indicative of a Schwoebel barrier with very few double-height islands. Simulation results were compared to growth results obtained via nanometer resolution ultrahigh vacuum scanning electron microscopy. Island statistics compare favorably with growth results. Experimentally observed large etching features at steps were not well reproduced by the model, suggesting an exchange mechanism may be important.
Characterization and photoemission dichroism of epitaxially grown Gd(0001)/Y(0001)
Authors: Mishra S. R. , Cummins T. R. , Waddill G. D. , Goodman K. W. , Tobin J. G. , Gammon W. J. , Sherwood T. , Pappas D. P.
Published: July 2002

Gadolinium thin films approximately 100 Å thick have been grown epitaxially on a Y(0001) substrate. A threefold characterization has been performed. The surface structural analyses of the yttrium substrate and the gadolinium films were performed using x-ray photoelectron diffraction (XPD) and low-energy electron diffraction (LEED). The results of the XPD and LEED studies strongly suggest that gadolinium films have an effective C6v surface symmetry, consistent with earlier studies of other hcp (0001) surfaces. The elemental analysis of the substrate and the film was done with x-ray photoemission using Mg, Al Kα x rays and synchrotron radiation. The magnetic analysis is based upon magnetic x-ray dichroisms observed in angle-resolved photoelectron spectroscopy, using both linearly polarized and circularly polarized synchrotron x-ray radiation as the excitation. Photoemission from the Gd 4f and 5p core-level states were used in this magnetic characterization and will be presented. This includes novel magnetic linear dichroism angular distribution results for the Gd 5p, which exhibit up to 40% asymmetry, on a par with the previously reported circular dichroism results.
Observation of channel shortening in n-metal–oxide–semiconductor field-effect transistors arising from interconnect plasma processing
Authors: El Hassan Motasim G. , Awadelkarim O. O. , Werking J.
Published: July 2002

Very recently we have demonstrated the possible role of an interconnect layout in the degradation of n-metal–oxide–semiconductor field-effect transistors (MOSFETs) during interconnect plasma processing. It was suggested that this role is that of shaping the potential differences between the n-MOSFET’s terminals in such a way as to electrically stress the device. In this study, we further investigate this degradation and examine its effect on hot carrier reliability. Shifts in gm and Vth after a brief hot carrier stress have shown the weak stress resistance of the n-MOSFETs. After additional charge pumping and transconductance measurements, it is suggested that this weak resistance is due to a channel shortening effect in as-processed devices induced by a positive oxide-trapped charge overlapping the drain edge of the channel. Therefore, even a slight change in the magnitude of the charge by either electron or hole injection at that edge ultimately leads to changing the effective channel length and, hence, most of the dc parameters of the n-MOSFETs.
Hydrogen and disilane adsorption on low energy ion-roughened Si (100)
Authors: Gong B. , Jo S. , Hess G. , Parkinson P. , Ekerdt J. G.
Published: July 2002

The adsorption and desorption of H2 and Si2H6 on ion roughened Si (100) have been studied by temperature programmed desorption. In addition to reacting with surface dangling bonds, hydrogen can readily diffuse into the bulk and occupy defect sites after ion bombardment with an activation energy of 0.09±0.02 eV. The extent of surface roughness and bulk defects created by ion sputtering can be discriminated by adjusting the ion energy. At low ion energies (<100 eV), only surface roughness and near-surface bulk defects are present. Both monohydride and dihydride coverages increase after 50 eV ion sputtering compared with H2 desorption from a smooth surface, implying an increased surface area due to ion roughening. However, only dihydride coverage increases with increased sputtering time. Because of the dramatically increased density of surface defects, adsorption probability of Si2H6 on the surface is greatly quenched after inert gas ion roughening.
Contact etch scaling with contact dimension
Authors: McNevin S. C. , Cerullo M.
Published: July 2002

It is known that the contact etch rate decreases with decreasing diameter. Etch depth measurements for deep submicron contacts will be shown to depend linearly on (1/contact diameter). This experimental dependence will then be compared to that predicted for various theoretical etching models. One way in which these models differ is the assumed rate limiting species: ions or neutrals. Another difference is the interaction of neutrals with the sidewalls of the contact. The nature of this interaction differs for the various models. The models also differ in the effect of the contact sidewalls on the ion trajectory. All of the models predict a decreasing etch depth as a function of contact diameter. However, some of the models more accurately predict the observed (1/contact diameter) dependence of the measured etch depth. It will be suggested that elements of the various theoretical models be combined. In particular, contact etching probably depends on both the ions and neutrals. Accurate models would therefore take into account the different aspect ratio dependences of these charged and uncharged species. It is also urged that modeling should address not only the etch depth at a given etch time, but also as a function of the etch time. The models and experiments should also look at a range of contact diameters (0.1–1.0 μm). Both models and experiments should also determine the side wall angle and the curvature of the etching front in the oxide.
Surface chemistry and damage in the high density plasma etching of gallium arsenide
Authors: Leonhardt D. , Eddy C. R. , Shamamian V. A. , Holm R. T. , Glembocki O. J. , Butler J. E.
Published: July 2002

Anisotropic pattern transfer with low damage in compound semiconductor dry etching requires an in depth understanding of the chemical processes that occur at the plasma/semiconductor interface that promote the removal of volatile product species. In situ mass spectrometry has been used to study product evolution during high density plasma etching of GaAs in a Cl2/Ar chemistry. Through definitive surface temperature control and configuration of the mass spectrometer to sample through the substrate platen, a comprehensive picture of the etch process was obtained. Evolution of etch products of GaAs (AsClx and GaClx) was monitored as neutral flux (pressure), ion flux (microwave power) and ion energy (substrate bias) are varied to identify conditions where ion-driven surface chemistry is dominant. Observations show that fluxes of atomic chlorine neutrals and ions are required at the substrate to maximize etch product formation. These conditions are optimally met at low microwave powers (⩽300 W) and pressures (⩽1.0 mTorr) in our system. The ion energy dependence of product formation shows regions of thermal/chemical etching for energies less than 50 eV, ion-assisted chemical etching for energies between 50 and 200 eV, and sputtering for energies greater than 200 eV. Ideal processing conditions are ascertained from the trade off between maximum ion-assisted etch rate and minimal electronic damage, as measured by photoreflectance spectrometry. The effectiveness of post-etch chlorine treatments on returning of the surface Fermi level to its pre-etched value was also investigated.
Real-time substrate misalignment monitor and automatic recalibration
Authors: Hosokawa Akihiro , Demaray Ernest , Mullapudi Ravi , Inagawa Makoto
Published: July 2002

Real-time substrate misalignment monitoring and automatic position recalibration were demonstrated in the Applied Komatsu Technology physical vapor deposition cluster tool. To accomplish this, two techniques were used to detect substrate misalignment and determine the source of the error. The cluster tool consists of an atmospheric cassette load station, a load lock station, a transfer chamber, a preheat chamber and four process chambers. Accelerometers were installed at each module of the cluster tool to detect any unexpected vibration of the substrate as it is lowered into processing position. The substrate misalignment is monitored at the atmospheric cassette load station with a ±0.5 mm threshold value using an optical sensor. If excessive substrate misalignment is detected at the atmospheric cassette load station, the accelerometer data is used to determine which specific module of the cluster tool was operating improperly. Using the monitored misalignment value at the atmospheric cassette load station, the specific module can be automatically recalibrated and proper operation of the cluster tool can be maintained without substrate breakage. Real-time substrate misalignment calibration avoids substrate breakage in the cluster tool, which results in an increase in the mean time between failure for the cluster tool. This technique has many practical applications for manufacturing operations in a vacuum environment.
Improved accuracy in monitoring Si monolayer incorporation in GaAs during molecular beam epitaxy
Authors: Däweritz L. , Schützendübe P. , Reiche M. , Ploog K. H.
Published: July 2002

Simultaneous reflection high-energy electron diffraction and reflectance difference spectroscopy measurements are used to monitor characteristic changes in the short- and long-range order that accompany Si incorporation on GaAs(001) and Si segregation during GaAs overgrowth. A new difference-function approach between reflectance difference spectra taken from Si-covered and from bare GaAs(001) surfaces allow us to detect not only As and Ga dimers but also Si dimers and As dimers on Si. Transients measured at characteristic photon energies provide a detailed picture of the surface kinetics and its dependence on the misorientation. For Si deposition on singular surfaces with (2×4)β reconstruction the nucleation occurs at randomly distributed sites, due to Si incorporation on unoccupied Ga sites in the trenches of this structure, and the phase transitions occur at higher coverages than for pulsed Si supply on a well prepared vicinal surface with (2×4)α reconstructed terraces. In the latter case well-ordered structures are developed at well defined coverages. These differences in the incorporation kinetics explain the diverging findings of carrier concentration saturation in delta-doped samples reported in the literature.
Field emission characteristics of patterned free-standing diamond films
Authors: Kim S. H. , Han I. T.
Published: July 2002

By depositing diamond films on Mo substrates (thickness=3 mm) with approximately 0.2 mm wide and 1.0 mm deep hole-type grooves, we easily obtained tubular-volcano-type patterned free-standing diamond films. The hole diameter at the film surface decreased with the film growth, eventually forming circular cones. Protrusions as high as ∼50 μm occurred at the substrate side of the films. For the tubular-volcano-type patterned free-standing diamond films, field emission characteristics were greatly enhanced, including lower turn-on voltages and higher current density. The surface morphologies of the films were correlated with the field emission characteristics. Reasons for the enhancement of the field emission characteristics for the tubular-volcano-type patterned free-standing diamond emitters were discussed.
Comparison of the initial oxidation of polycrystalline indium and ultrathin deposits of indium on the Au (111) surface
Authors: Robinson M. C. , Slavin A. J.
Published: July 2002

Previous studies have shown that alloying occurs when indium deposits equivalent to a few monolayers are evaporated onto Au (111). This article compares the initial oxidation of the ultrathin alloy to that of polycrystalline bulk indium. Auger electron spectroscopy, electron energy loss spectroscopy, low energy electron diffraction, and work-function change measurements were conducted under ultrahigh vacuum conditions at room temperature. Oxidation of the polycrystalline sample follows first-order Langmuir kinetics, and saturates by 1×103 L (1 L=10−6 Torr s), to form a 4.5 Å thick oxide layer. The stoichiometry of the compound is In2O3. The oxygen uptake of the alloy saturates with less than two layers of In–Au alloy present, and an oxide layer of different stoichiometry is generated, 4.2 Å thick. It is suggested that gold may be participating in the alloy stoichiometry. The results are compared to another study of oxidation of bulk indium.
State resolved dynamics of methyl desorption from GaAs
Authors: Wang H. , Zhu X.-Y. , Xin Q.-S.
Published: July 2002

The thermal desorption dynamics of methyl radical from GaAs (100) has been characterized by time-of-flight distribution measurement and resonance-enhanced multiphoton ionization spectroscopy. While the translational energy is nearly thermal neutral, the vibrational distribution in the umbrella mode is superthermal. These results suggest that the methyl radical must desorb promptly from the surface with an “early” transition state. The present study provides a quantitative basis for further theoretical investigations.
Electronic structure calculations of small molecule adsorbates on (110) and (100) TiO2
Authors: Ferris Kim F. , Wang Li-Qiong
Published: July 2002

Electronic structure calculations were performed for water and methanol adsorbed onto model structures for ideal (110) and (100) rutile TiO2 surfaces. Both molecular and dissociated forms of water and methanol were examined for each surface, and the reaction coordinate for interconversion of the two forms. Our results indicate a strong thermodynamic favor for the dissociative form in each case; however, there is a potential energetic barrier to proton transfer to generate the dissociative form for the (110) surface. Based upon the structural differences between these surfaces, it is proposed that multiple hydrogen bonding interactions with the adsorbed species facilitate proton transfer.
Voltage-dependent scanning tunneling microscopy images of the Ge(111)-c(2×8) surface
Authors: Lee Geunseop , Mai H. , Chizhov Ilya , Willis R. F.
Published: July 2002

We present scanning tunneling microscopy images of the Ge(111)-c(2×8) surface where both clean and impurity-containing portions exhibit significant voltage-dependent variations. While only adatoms are observed in empty state images, both adatoms and rest atoms simultaneously appear in filled state images but changing contrast with varying bias voltage. The filled state image taken with a voltage as low as 0.5 V confirms that a surface state exists between rest-atom bands and the Fermi level and it is not dangling-bond-like, i.e., its associated charge is found to be distributed over both adatoms and rest atoms. The voltage-dependent images of the impurity-containing surface show delocalized features around the impurity. These delocalized features are observed for the first time on the surface other than III–V semiconductor surfaces. It is attributed to the charged impurity relative to the clean part, causing the band bending near the impurity.
Carbon monoxide oxidation on Ir (110)
Authors: Burghaus U. , Ding Junqi , Weinberg W. H.
Published: July 2002

We report measurements of CO oxidation by CO molecular beam titration of an Ir (110) surface precovered with atomically bonded oxygen. The CO2 formation rate increases with increasing CO fluence and depends strongly on both oxygen precoverage and surface temperature. The self-accelerating CO2 formation kinetics may be qualitatively discussed in the framework of coverage-dependent kinetics of the Langmuir–Hinshelwood type.
Nonstoichiometry on TiO2(110) and Cu–TiO2 interfaces
Authors: Wagner M. , Kienzle O. , Bonnell D. A. , Rühle M.
Published: July 2002

A number of reconstructions have been observed on the (110) surface of TiO2 in the rutile modification that accommodates oxygen deficiency. We present atomically resolved scanning tunneling microscope images that describe a new reconstruction with (3×2) symmetry. A model for the observed reconstruction is discussed where this symmetry is achieved by removing 1/3 or 2/3 of the oxygen in the bridging oxygen rows such that a shift in position of missing oxygen by one lattice space vector along the [001] direction occurs in every second row. This structure contrasts those reported previously in which entire rows are modified or removed. Furthermore, nanometer-sized Cu islands on TiO2(110) surfaces fabricated by vapor deposition onto TiO2 at 200 °C were studied by conventional and high-resolution transmission electron microscopy (TEM). Our TEM studies show that Cu forms faceted islands (40 nm in width) on the surface with the orientation relationship given by Cu{110}∥TiO2(110) and Cu〈001〉∥TiO2[11̄0]. The orientation relationship differs from that resulting from room temperature deposition onto stoichiometric surfaces.
Photoelectron microspectroscopy observations of a cleaved surface of semiconductor double heterostructure
Authors: Kiyokura Takanori , Maeda Fumihiko , Watanabe Yoshio , Kadota Yoshiaki , Iketaki Yoshinori , Horikawa Yoshiaki , Oshima Masaharu , Shigemasa Eiji , Yagishita Akira
Published: July 2002

We have developed a submicron-area high energy resolution photoelectron spectroscopy system equipped with a multilayer-coated Schwarzschild objective for forming a soft x-ray microbeam. We show the photoelectron microspectroscopy results of the cross section of a semiconductor double heterostructure sample, namely an epitaxial film [InP (50 nm thick)/ In0.53Ga0.47As (2.3 μm thick)/InP (100) substrate] grown by metalorganic chemical vapor deposition. The core-level photoelectron spectra were obtained from the cross section of the cleaved sample. The As 3d, Ga 3d, and In 4d peaks were observed in the In0.53Ga0.47As region. In the InP region, the As 3d and Ga 3d peaks were not observed, and only the In 4d peak was. This result corresponds to the structure observed by cross-sectional scanning electron microscopy. Moreover, we observed an irradiation effect that was caused by the microbeam. These results suggest that this photoelectron microspectroscopy system is a powerful tool for studying chemical and electronic states of submicron-area surfaces.
Auger electron spectroscopy depth profiling of Ge/Si multilayers using He+ and Ar+ ions
Authors: Menyhard M. , Sulyok A.
Published: July 2002

Various Ge/Si layer structures (multilayers with 2 and 3 nm layer thicknesses, step function transition, and 1 nm Si imbedded between thick Ge layers) were depth profiled by using 1 keV He+ and Ar+ sputtering with angle of incidence of 83°. The specimen was rotated during sputtering. The depth resolution determined on the step function transition weakly depended on the type of projectile used. Similarly there was not a strong deviation of depth profiles recorded on the imbedded Si layer (thickness 1 nm) if Ar+ or He+ projectile was used. In contrast a serious difference between the depth profiles measured by Ar+ and He+ sputtering was observed in the case of the multilayer systems. Based on these observations we concluded that the depth resolution (determined according to the standard) is not a sufficient characterization of a depth profiling device. It is proposed that depth profiling of some standardized multilayer structure, with layer thicknesses of 1–2 nm should also be added to the characterization of the sputtering device.
Two-dimensional imaging of surface morphology by energy-analyzed secondary electrons and Auger electron spectroscopy for stepped Si(111) surfaces
Authors: Suzuki M. , Mogi K. , Homma Y.
Published: July 2002

We have experimentally investigated two-dimensional imaging of stepped Si surfaces by energy-analyzed electrons and Auger electron spectra from atomically flat surfaces. A stepped Si(111) surface was prepared by direct-current heating to around 1250 °C in ultrahigh vacuum. The stepped surface consisted of atomically flat terraces and step bands where atomic steps bunched in the height of about 5 nm. We found that the stepped structure could be imaged by using only the energy-analyzed secondary electrons (SEs) when the intensity was defined as the difference between the peak height and the background intensity. The image from the energy-analyzed SEs was in good agreement with the conventional SEM image obtained with non-energy-analyzed SEs. The electron-emission spectrum obtained in the direct mode included only characteristic Auger peaks of silicon SE peak. It is found that the electron-emission spectrum obtained from the atomically flat Si(111) terrace has relatively higher background than that from a sputter-cleaned Si surface. Also, it is revealed that the fine structure exists at 2.2 eV in the SE peak.
Design of a low cost, low magnetic susceptibility, ultrahigh vacuum compatible, flanged electrical break
Authors: Mapes M. , Hseuh H. C. , Cameron P.
Published: July 2002

At Brookhaven National Laboratory, the g-2 experiment, a muon storage ring, requires a totally nonmagnetic vacuum system. All the vacuum components must have a low magnetic susceptibility. The design of the beam vacuum system requires flanged electrical breaks on pumping manifolds in order to prevent ground loops. The electrical breaks developed at Brookhaven consist of a ceramic disk clamped between two Conflat flanges. A nonconductive retaining ring is used to support and center the ceramic disk and seals with respect to the flanges. Two Helicoflex Delta seals are used to seal the flanges to the ceramic disk which has metallized surfaces in the seal area. Threaded rods which are electrically insulated from the flanges with bushings are used to provide the clamping force necessary to compress the vacuum seals. The assembly remains leak tight after repeated bakeouts up to 200 °C. This design offers several advantages over commercially available Conflat flanged ceramic breaks. These breaks do not use Kovar and are totally nonmagnetic. In addition to the cost being lower the overall length of the break is much shorter than commercial breaks. The same design concepts can be used for different sized Conflat flanges and for other types of flanges. The detailed design and the performance of this break are presented in this article.
Generation of vapor stream using a porous rod in an electron beam evaporation process
Authors: Ohba Hironori , Shibata Takemasa
Published: July 2002

An evaporation technique with high thermal efficiency in an electron beam evaporation process is presented for the generation of copper vapor. A molybdenum hearth liner and a porous rod made of sintered tungsten with evaporation material were set into a bare water-cooled copper crucible. While the top surface of the porous rod was heated by an electron beam, the molten copper surrounding the rod is transferred to the top surface of the rod through pores in the rod by capillarity and then copper vapor stream was generated from there. The evaporation characteristics were measured with a quartz crystal sensor, a charge coupled device camera, deposited weights, and a quadrupole mass spectrometer. An extremely high vapor flux with high stability was obtained for a long period of time even at low input power without contamination by tungsten atoms which are porous materials and also without the formation of the dimers.
Atomic force microscopy study of microcrystalline SiC fabricated by ion beam synthesis
Authors: Wu W. , Chen D. H. , Xu J. B. , Cheung W. Y. , Wong S. P. , Wilson I. H. , Kwok R. W. M.
Published: July 2002

Ion beam synthesis of silicon carbide (SiC) layers was performed by metal vapor vacuum arc implantation. Subsequent furnace annealing was carried out in nitrogen at various temperatures to form stoichiometric SiC layers. The implanted layers were characterized by various techniques. Rutherford backscattering spectrometry analysis revealed the carbon distribution and formation of the SiC layers. Fourier transform infrared spectroscopy spectra showed absorption peaks produced by the amorphous and β-phase crystalline SiC layers. The crystallinity was increased by high temperature annealing. The dependence of the surface morphology and dynamics of the crystallization on annealing temperature and time was studied by atomic force microscopy (AFM) for the first time. At about 900 °C, nanocrystalline SiC was formed on the sample surface and contained columnar grains with a full width of half maximum of tens of nanometers and a height of 10 nm. A conducting AFM was used to study the electrical properties of the formed SiC layer on the nanometer scale.
Desorption of metastable particles induced by electronic excitation at the surface of rare-gas solid with physisorbed hydrogen
Authors: Hayama A. , Kuninobu T. , Hirayama T. , Arakawa I.
Published: July 2002

The effect of physisorbed hydrogen on the desorption of metastable particles induced by electronic excitation from the surface of rare-gas solids (Ar, Kr, and Xe) was investigated systematically. When the surface of a rare-gas solid was exposed to a very small quantity of hydrogen at a temperature of about 30 K, in all cases, the desorption of hydrogen metastables was observed, and new desorption species of Kr* via cavity ejection process appeared in time-of-flight spectra for Kr. For Ar, although no significant increase of desorption yield was found, the kinetic energy of Ar* desorbed through cavity ejection process was increased by hydrogen adsorption. These results will be discussed in terms of the change of electron affinity of the matrix and the interaction between hydrogen and rare-gas molecules in excited states.
Effects of surface phosphorus on the kinetics of hydrogen desorption from silane-adsorbed Si (100) surface at room temperatures
Authors: Suemitsu M. , Tsukidate Y. , Nakazawa H. , Enta Y.
Published: July 2002

Effects of presence of phosphorus on the hydrogen desorption kinetics from SiH4/Si (100) surface has been investigated by H2-temperature-programmed-desorption (TPD) measurements. The β1-TPD peak shifted toward higher temperatures by about 10 °C when phosphorus was predeposited to θP=0.25 ML, and the shift increased with decreasing SiH4 exposure. Two analyses, the Arrhenius plot and the order plot, have been applied to the TPD spectra, clarifying that the 0.25 ML phosphorus on clean Si (100) surface suppresses the hydrogen desorption by increasing both the activation energy from 2.0±0.2 to 2.5±0.1 eV and the reaction order from 1.0±0.2 to 2.0±0.2.
Inductively coupled plasma etch processes for NiMnSb
Authors: Hong J. , Caballero J. A. , Lambers E. S. , Childress J. R. , Pearton S. J.
Published: July 2002

Plasma chemistries based on SF6, NF3, or CH4/H2 were investigated for inductively coupled plasma (ICP) etching of NiMnSb Heusler alloy thin films. The resulting etch rates were a strong function of ion energy, ion flux, and plasma composition. In SF6/Ar discharges, the etch rates increased from 100 to 300 Å min−1 under conventional reactive ion etch conditions to >10 000 Å min−1 with the addition of even relatively small amounts (200 W) of ICP source power. The etched surface becomes enriched in Mn under these conditions. In NF3/Ar discharges the etch rates actually decrease as ICP source power is increased, leading to net deposition at either high NF3 percentages or high ICP powers. The etched surface is also enriched in Mn under these conditions, with a Sb-deficient region underneath. In CH4/H2/Ar discharges, the etch rates are slower than with pure Ar and show no evidence of a chemical component in the etch mechanism. Since the etch rates are so high in ICP SF6/Ar discharges, it is necessary to pay careful attention to removal of the native oxide on NiMnSb, which prevents etching while it is present, and thus may cause extremely rough surfaces if it not uniformly removed.
Studying low-pressure chemical vapor deposition a-Si:B alloys by optical spectroscopy
Authors: Yang G.-R. , Zhao Y.-P. , Tong B. Y.
Published: July 2002

As-deposited and wet oxidized a-Si:B alloys deposited by low-pressure chemical vapor deposition with various boron content were studied by visible optical spectroscopy and Fourier transform infrared spectroscopy. It is found that the optical band gap of a-Si:B varies with respect to the boron content. This effect is associated with the structure change induced by B content. After oxidation, the Si–O stretching peak at 1108 cm−1 shifted to 1079 cm−1. The oxidation behaviors of films with boron content 3%–25% are different from those with boron content exceeding 30%. For B content between 3% and 25%, besides the remarkable change around 1100 cm−1, there are also notable changes around 1600–1300 cm−1, and 1000–500 cm−1, which indicate the increase of B–O bonds and decrease of B–B bonds. However, when the B content exceeded 30%, the change of Si–O bonds was enhanced while the change of B–O bonds and B–B bonds was suppressed. A possible structure and oxidation mechanism for different boron content a-Si:B films is proposed.
Surface characterization of thin films of tetrathiofulvalene 7,7,8,8-tetracyano-p-quinodimethane evaporated on NaCl(001)
Authors: Fraxedas J. , Caro J. , Figueras A. , Gorostiza P. , Sanz F.
Published: July 2002

Thin films of tetrathiofulvalene 7,7,8,8-tetracyano-p-quinodimethane, a quasi-one-dimensional charge transfer organic metal, have been grown on cleaved NaCl substrates by evaporation in high vacuum. The films are polycrystalline and textured, and are comprised of rectangular c*-oriented microcrystals with their a and b axis parallel to both the [110] and [−110] substrate directions. The growth is basically determined by an oriented nucleation and the one dimensionality of the compound induced by the π bonding along the stack. An x-ray photoelectron spectroscopy analysis of the films reveals that the films are stoichiometric and suggests that the charge transfer is not homogeneously distributed and that it should be negligible at the surface.
Plasma deposition chemistry of amorphous silicon–carbon alloys from fluorinated gas
Authors: Cicala G. , Bruno G. , Capezzuto P.
Published: July 2002

Hydrofluorinated amorphous silicon–carbon alloys (a-Si1−xCx:H,F) are obtained by plasma decomposition of SiF4–CH4–H2 mixtures. The analysis of the plasma phase, by mass spectrometry and optical emission spectroscopy, and of the resultant material, by Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy, allows us to gain information about the film growth chemistry. The growth kinetics and the material composition of the a-Si1−xCx:H,F films are studied as a function of the added CH4 amount to the SiF4. The peculiarity of SiF4–CH4 system is that small CH4 addition (10%) to SiF4 produces silicon carbon alloys with high C incorporation (60 at. %). This has been explained on the basis of a growth model in which the chemisorption of CHn on the surface prevails on that of SiFn.
Structure, mechanical and tribological properties of Ti–B–N and Ti–Al–B–N multiphase thin films produced by electron-beam evaporation
Authors: Rebholz C. , Ziegele H. , Leyland A. , Matthews A.
Published: July 2002

Titanium-based multiphase ceramic coatings were deposited by electron-beam plasma-assisted physical vapor deposition, evaporating mixtures of Ti, TiB2, and (Ti0.6Al0.4)B2.19N1.47 material in Ar or Ar/N2 plasmas. All exhibited dense microstructures, however varying amounts of droplets or spits incorporated in the coatings produced could be observed for the different evaporation materials depending on their fabrication route. Results on the chemical composition of the coatings, obtained from glow discharge optical emission spectroscopy and Auger electron spectroscopy, showed no preferential evaporation of any element from the different evaporation source materials used, resulting in very similar compositions between evaporant and coating. Hardness values of up to 40 GPa were found for Ti–B–N based coatings containing both TiB2 and c-BN phases. Lower hardness values of around 30 GPa were observed for coatings deposited within the quaternary Ti–Al–B–N system, due to the presence of h-BN. Two micron thick Ti–Al–B–N coatings showed only minimal wear in pin-on-disk sliding wear tests against cemented tungsten carbide balls and, with increasing h-BN content, a slight decrease in “stick–slip” oscillation and friction coefficient. In contrast to Ti–Al–B–N coatings (whose impact adhesion was relatively poor) Ti–B–N coatings approximately 1.5 μm thick showed no coating spallation in impact tests against cemented tungsten carbide balls and consequently superior impact wear resistance.
Growth kinetics and relationship between structure and mechanical properties of a-C(N):H films deposited in acetylene–nitrogen atmospheres
Authors: Jacobsohn L. G. , Freire F. L. , Franceschini D. F. , Lacerda M. M. , Mariotto G.
Published: July 2002

Amorphous hydrogenated carbon–nitrogen films, a-C(N):H, were deposited by plasma enhanced chemical vapor deposition using acetylene–nitrogen mixtures. Film composition and density were determined by means of ion beam techniques being the film microstructure studied by infrared and Raman spectroscopies. Films were obtained with nitrogen content up to 22 at. %. As for films obtained using other gas mixtures, the deposition rate showed a strong decrease upon nitrogen incorporation, although with a smaller rate. The film growth kinetic is discussed and some specific features of acetylene–nitrogen precursor gas mixtures are pointed out. A remarkable decrease on the C atom sp3 fraction was inferred for nitrogen contents higher than 10 at. %, and was correlated to the film density behavior. The mechanical hardness and internal stress were relatively insensitive to low nitrogen incorporation, with a systematic decreasing behavior for nitrogen contents above 10 at. %.