bluuebunny/crossref_metadata_2025 huggingface dataset:
Calibrated scanning capacitance microscopy investigations on p-doped Si multilayers
Authors: Basnar B. , Golka S. , Gornik E. , Harasek S. , Bertagnolli E. , Schatzmayr M. , Smoliner J.
Published: July 2002

Using Si samples with 400-nm-wide alternately high and low doped p-type layers on p-type substrate, we investigate the dependence of the scanning capacitance microscope (SCM) signal amplitude as a function of oxide thickness and dopant concentration. The oxide layers were created by a standard industrial high temperature oxidation process. Together with the implementation of the newly developed conductive diamond tips, good and quantitatively reproducible contrast for differently doped domains is obtained on all samples. A comparison with conventional metal-oxide-semiconductor theory shows good correlation for the decrease of the capacitance signal with increasing insulator thickness and increasing dopant concentration. Furthermore, geometry effects, such as the influence of the domain width on the SCM signal, are discussed.
Nanofabrication of two-dimensional photonic crystal mirrors for 1.5 μm short cavity lasers
Authors: Happ T. D. , Markard A. , Kamp M. , Forchel A. , Anand S. , Gentner J.-L. , Bouadma N.
Published: July 2002

We have developed a fabrication scheme for two-dimensional (2D) triangular photonic crystals (PCs) on InP-based material systems involving high resolution electron beam lithography, pattern transfer to a SiO2 etch mask, and a Cl2/Ar electron cyclotron resonance reactive ion etch step yielding PCs with periods of a=300–450 nm and air fill factors of f=18%–63%. These PCs are employed as high reflectivity mirrors for 1.5 μm short cavity lasers, which are key components in future highly integrated PC based photonic circuits. We have fabricated lasers with 2 PC mirrors and cavity lengths down to 100 μm. Threshold currents as low as 7.6 mA were achieved for the shortest lasers with 2 PC mirrors. The short laser cavity results in a large Fabry–Pérot mode spacing and mode competition leads to single mode lasing over a reasonably large current range up to 4.5× threshold. Lasers with one PC back mirror and a cleaved output facet show a higher threshold current of 13 mA and a maximum output power of more than 4 mW. The variation of laser performance with different cavity lengths is presented and discussed.
Scaling considerations for high performance 25 nm metal–oxide–semiconductor field effect transistors
Authors: Saha Samar
Published: July 2002

This article presents a systematic simulation-based study on scaling gate oxide thickness and the source–drain extension junction depth to achieve high performance 25 nm metal–oxide–semiconductor field effect transistor devices for low power operation. In order to obtain the target 25 nm devices, complementary metal–oxide–semiconductor (CMOS) technologies were designed by scaling source–drain extension junction depths to 14, 20, and 26 nm and the corresponding gate lengths to 40, 50, and 60 nm, respectively. Each technology was separately optimized for each value of the equivalent gate oxide thickness 1, 1.5, and 2 nm to achieve the target value of off-state leakage current of about 10 nA/μm for 25 nm devices. The simulation results show that for a low voltage operation of 25 nm devices with a fixed off-state leakage current, the magnitude of threshold voltage, subthreshold slope, and the drain-induced barrier lowering is too high while the magnitude of drive current is too low for gate oxide thickness ⩾1.5 nm. However, the variation in the magnitude of threshold voltage, subthreshold slope, drain-induced barrier lowering, and the drive current for the similar devices is insignificant within the range of source–drain extension junction depth between 14 and 26 nm. It is also found that the increase in the gate delay is ⩾12% for 25 nm devices with the source–drain extension junction depth ⩾20 nm compared to the similar devices with a source–drain extension junction depth of about 14 nm. This article demonstrates that the continuous scaling of gate oxide thickness below 1.5 nm and the source–drain extension junction depth below 20 nm is essential for achieving high performance CMOS technologies with 25 nm nominal devices for low power application.
Nanostructure patterns written in polycarbonate by a bent optical fiber probe
Authors: Chen Sy-Hann , Chen Yung-Fu
Published: July 2002

An atomic force microscope operated in tapping mode using a homemade bent optical fiber probe was used to pattern nanometer-scale features. Trenches of different dimensions were written on polycarbonate that was pre-exposed to an excimer laser. Lines with widths varying from 260 to 600 nm and depths ranging from 30 to 120 nm have been made. The present technique as a complementary tool to other lithographic processes has been demonstrated to be potentially suitable for low-cost and high-precision applications.
Effects of bias voltage on the corrosion resistance of titanium nitride thin films fabricated by dynamic plasma immersion ion implantation-deposition
Authors: Tian Xiubo , Fu Ricky K. Y. , Chu Paul K.
Published: July 2002

Dynamic plasma-based thin-film deposition incorporating ion mixing and plasma immersion is an effective technique to synthesize nitride-based hard films. We have fabricated TiN films using a filtered titanium vacuum arc in a nitrogen plasma environment. A pulsed high voltage is applied to the target for a short time when the metallic arc is fired to attain simultaneous plasma deposition and ion mixing. We investigate the dependence of the corrosion resistance and interfacial structure of the treated samples on the applied voltage. Our Auger results reveal an oxygen-rich surface film due to the non-ultra-high-vacuum conditions and high affinity of oxygen to titanium. The corrosion current is reduced by two orders of magnitude comparing the sample processed at 8 kV to the untreated sample, but the 23 kV sample unexpectedly shows worse results. The pitting potential diminishes substantially although the corrosion current is similar to that observed in the 8 kV sample. The polarization test data are consistent with our scanning electron microscopy observation, corroborating the difference in the pitting distribution and appearance. This anomalous behavior is believed to be due to the change in the chemical composition as a result of high-energy ion bombardment.
Effect of O2 gas partial pressure on mechanical properties of SiO2 films deposited by radio frequency magnetron sputtering
Authors: Fujiyama H. , Sumomogi T. , Endo T.
Published: July 2002

The effect of O2 partial pressure on the mechanical properties of SiO2 films deposited by rf magnetron sputtering is studied. The sputtering rate of SiO2 in argon gas with added O2 gas is lower than that in pure argon gas, whereas the rate is independent of O2 partial pressure. The internal stresses in films are compressive, and the magnitude decreases from 0.8 GPa for films sputtered in pure argon gas to 0.4 GPa for films sputtered in argon gas with O2 gas partial pressure above 9×10−3 Pa. Although the internal stress decreases with increasing O2 partial pressure, the magnitudes of hardness and adhesion increase conversely. X-ray diffraction measurements indicate that the crystal structure of sputtered SiO2 films is amorphous at all O2 partial pressures investigated. The argon content in the film obtained from an electron probe microanalyzer decreases with increasing O2 partial pressure. An atomic force microscopy observation reveals that the surface topography of sputtered SiO2 films show a turnover from needle structure to a spherical structure, and the fracture section varies from columnar to no discernible features as O2 partial pressure is increased.
Fast closed loop control of piezoelectric transducers
Authors: Schitter Georg , Stemmer Andreas
Published: July 2002

Closed loop control of piezoelectric transducers is very important for nanopositioning applications. Up to now usually proportional integral (PI) controlled systems were used which are not fast enough for high performance applications such as fast scanning probe microscopy. Utilizing modern control methods, the performance of the closed loop operated system can be improved which is demonstrated on a standard piezotransducer system. For the design of the model based controller a system identification of the piezodynamics was made. The designed controller was subsequently implemented on a digital signal processor system. A system with a step response of the closed loop operated transducer settling 18-times faster than the standard PI-controlled piezo was realized.
Active pixel sensor architectures in a-SiH for medical imaging
Authors: Karim Karim S. , Nathan Arokia , Rowlands John A.
Published: July 2002

The most widely used architecture in large area amorphous silicon (a-Si) flat panel imagers is the passive pixel sensor (PPS), which consists of a detector and a readout switch. While the PPS has the advantage of being compact and amenable towards high-resolution imaging, reading the low PPS output signal requires external circuitry such as column charge amplifiers that produce additional noise and reduce the minimum readable sensor input signal. This work presents a voltage mediated active pixel sensor (APS) on-pixel readout circuit for diagnostic medical imaging to minimize external component count and hence external readout noise sources. Preliminary results indicate excellent APS linearity along with a pixel readout time suitable for mammography or radiography.
Atomistics of III–V semiconductor surfaces: Role of group V pressure
Authors: Grosse Frank , Barvosa-Carter William , Zinck Jenna J. , Gyure Mark F.
Published: July 2002

Combining theoretical and experimental methods, we investigate the influence of group V fluxes of As2 and Sb2 on the InAs(001) surface. We find that equilibrated surfaces under As2 flux change their surface stoichiometry continuously for InAs in the technologically relevant α2(2×4)-β2(2×4) reconstruction region and that the As-dimer density increases with increasing As2 flux. The change of the surface morphology under Sb2 exposure is also studied and discussed specifically in the context of interface formation. The existence of a common α2(2×4) reconstruction allows for the possibility of keeping the In sublattice unchanged when switching from As2 to Sb2 flux.
Scanning capacitance microscopy measurements using diamond-coated probes
Authors: Yabuhara Hidehiko , Ciappa Mauro , Fichtner Wolfgang
Published: July 2002

Diamond-coated cantilevers have been used for scanning capacitance microscopy (SCM) as an alternative for metal-coated cantilevers in order to improve the stability of probes. It is shown that the diamond-coated probes produce adequate intensity of dC signal and high contrast for both p-type and n-type silicon samples and also provide superior endurance characteristics to metal-coated probes. Due to the robustness of the diamond-coated probes, we are able to evaluate the reproducibility of measurements and the homogeneity of the ultrathin oxide for both dry oxidation (heated up to 300 °C in air under ultraviolet illumination) and wet oxidation (immersed into a hydrogen peroxide solution at 70 °C). The dry oxidation shows better reproducibility, while the wet oxidation shows better homogeneity. Finally, comparison of SCM with secondary ion mass spectrometry measurement shows that diamond-coated probes can be used at least for one-dimensional quantitative SCM measurements without any significant effect of depletion in the diamond-coated tip itself.
Growth and characterization of Ga0.8In0.2(N)As quantum wells with GaNxAs1−x(x⩽0.05) barriers by plasma-assisted molecular beam epitaxy
Authors: Govindaraju Sridhar , Holmes Archie L.
Published: July 2002

GaInNAs has received significant attention due to the ability to achieve 1300 nm wavelengths on GaAs substrates. In most cases, nitrogen is added directly into the GaInAs quantum wells, which degrades their optical properties. In this work, we investigate how the placement of nitrogen in Ga0.8In0.2As/GaAs heterostructures affects their optical characteristics. The location of nitrogen was studied in three different structures: nitrogen in barriers alone, nitrogen in wells alone, and nitrogen in the wells and barriers. Our results show that placing nitrogen in the barriers instead of wells provides better luminescence properties. We also observed that the addition of a GaAs spacer at the barrier-well interfaces further improves the luminescence properties of the structure.
Photoluminescence characteristics of GaInNAs quantum wells annealed at high temperature
Authors: Ng T. K. , Yoon S. F. , Wang S. Z. , Loke W. K. , Fan W. J.
Published: July 2002

The photoluminescence (PL) characteristics of GaInNAs quantum wells (QWs) after high-temperature postgrowth annealing were studied. The QWs were grown using a radio-frequency nitrogen plasma source in conjunction with a solid-source molecular-beam epitaxy system. It was found that annealing at high temperature (840 °C) and long duration (10 min) results in significant improvements to the PL characteristics of the GaInNAs QWs. The shift of the GaInNAs and GaInAs PL peak wavelength resulting from high-temperature annealing is dependent on the In composition. It is suggested that the dominant mechanisms that give rise to the blueshift of the PL peak wavelength in GaInNAs QWs with high-In composition are residual-strain-induced GaAs/GaInNAs/GaAs interface interdiffusion, and defect-assisted diffusion-related effects, both of which originate from the growth process.
1.3 μm InAsP multiquantum well laser diodes with the n-type modulation-doped InAsP/InP/InGaP active region
Authors: Lei Po-Hsun , Wu Ming-Yuan , Wu Meng-Chyi , Lee Chong-Yi , Ho Wen-Jeng , Lin Chia-Chien
Published: July 2002

In this article, we report the fabrication and analysis of 1.3 μm InAsP multiquantum well laser diodes (MQW LDs) with the n-type modulation-doped (MD) InAsP/InP/InGaP active region grown by metalorganic chemical vapor deposition. We theoretically analyze the threshold current density, differential quantum efficiency, internal quantum efficiency, and internal optical loss as a function of thickness and doping concentration of n-type Si-doped InGaP barrier and InP intermediate layer for the 1.3 μm MD-MQW LDs. The optimum thickness is 2 nm for the n-type doped barrier and 6.2 nm for the doped intermediate layer while remaining 4.4-nm-thick undoped in the InP intermediate layer to prevent from lateral diffusion of Si-doped atoms into the InAsP well. Besides, the optimum doping concentration of doped InGaP barrier and doped InP intermediate layer is 1×1018 cm−3. With these optimum conditions, the LDs will reduce the threshold current density and threshold gain to 0.8 kA/cm2 and 43.08 cm−1 as compared to those of 1.6 kA/cm2 and 44.1 cm−1 for the undoped active region, respectively.
Electron trapping in noncrystalline remote plasma deposited Hf-aluminate alloys for gate dielectric applications
Authors: Johnson R. S. , Hong J. G. , Hinkle C. , Lucovsky G.
Published: July 2002

The physical and electrical properties of noncrystalline Hf-alumiunate alloys, (HfO2)x(Al2O3)1−x, were investigated. Characterization by Auger electron spectroscopy and Fourier transformation infrared spectroscopy confirm these alloys are homogeneous and pseudobinary in character, displaying increased thermal stability against crystallization with respect to the respective end-member oxides. Capacitance–voltage and current density-voltage data as a function of temperature demonstrate that the Hf d states of these alloys act as localized electron traps, and are at an energy approximately equal to the conduction band offset energy of HfO2 with respect to Si. This work also provides additional insight into a previously reported study of Ta-aluminate alloys with localized electron traps associated with d states of the Ta atoms.
Adsorption–Desorption of Residual Gases in High Vacuum
Authors: Lichtman David
Published: July 2002

Measurements have been made on the adsorption and desorption of residual gases in an ultra-high-vacuum ion-pumped system using mass spectrometer analysis. The predominant residual gases in our system are hydrogen, carbon monoxide, and water vapor at a total pressure of about 5×10−10 Torr. Mass analysis indicates two hydrogen peaks, one carbon monoxide peak, and no water vapor peak on thermally heating a molybdenum ribbon from room temperature to 1000 °C. Desorption and readsorption are observed continuously by monitoring ion desorption induced by an extremely low density (∼10−7A/cm2) electron beam. Data obtained by this technique correlated very well with that obtained by thermal flashing and aids in understanding the reactions that are occurring. The use of electron-induced ion desorption coupled with mass analysis is seen to be a very useful tool in studying adsorption–desorption phenomena in high vacuum by allowing continuous observation as substrate conditions are changed.
Thermal Reemission of Inert Gas Atoms in Tungsten and Gold
Authors: Erents K. , Layson R. P. W. , Carter G.
Published: July 2002

Inert gas ions of energies between 100 eV and 2 KeV have been injected into polycrystalline tungsten and gold. The subsequent thermal desorption of entrapped ions from these targets has distinct peak structures, and an attempt has been made to correlate the energies associated with these peaks in the desorption spectrum with normal defect-migration processes in the target materials.
A Magnetron-Type Ion Source for Low-Pressure Residual Gas Analysis
Authors: Davis W. D.
Published: July 2002

A conventional electron bombardment ion source operating at 10–100 μA emission is difficult to outgas sufficiently to allow accurate analysis of the residual gas at pressures below 10−12 Torr. In addition, the ions formed by electron bombardment of the surface may contribute specific mass peaks or a broad background of scattered ions to the mass spectrum. By using a magnetron-type ion source to increase the electron path, both these effects can be substantially reduced. The results obtained using this type ion source on a 5-cm radius magnetic sector instrument are described. Using an electron emission of 4×10−8 A, an ion current of 2×10−4 A/Torr is obtained for N2. The two major peaks at low pressure are H2 (1.5×10−13 Torr) and mass 28 (3×10−14 Torr). No electronically desorbed ions have yet been observed and the background ion current is less than 10−17 Torr.
RF Sputtering of Multilayer Thin Films
Authors: Herte L. , Lang A. , Myers D. O.
Published: July 2002

Thin-film deposition rates and uniformity are presented for a large area rf diode of conventional style, with optimized parameters producing 1500 Å/min copper and 500 Å/min SiO2 without external magnetic field. Measurements of rate and corresponding uniformity were also made for Si3N4, Al2O3, nickel, molybdenum, and gold, where the thickness uniformity inside a 5-in.-diam. circle was ±2.5% for nickel and ±2% for SiO2. The sputtering apparatus consists of two 8-in.-diam water-cooled targets fed with 2.5 kW rf power, spaced 1-in. away from the substrate table. Influence of forward-coupled rf power on rate is also discussed.
Problems Encountered During Deposition of Optical Thin Films with Reproducible Characteristics in an Automatic Coater
Authors: Pulker H. K. , Girardet E.
Published: July 2002

Investigations have shown that it is possible to control optical layers with high precision by means of a quartz crystal monitor (measurement of the deposited mass). This was possible by using a very precise quartz crystal monitor and by a thorough investigation of the phenomena of condensation on the substrate and also of the effect caused by interaction of residual gas on the film during the deposition process. On the basis of this experience a fully automatic control unit has been developed which may be used for the production of optical layers as well as for electronic applications.
Optical Surface Degradation from Combined Ultraviolet Radiation and Outgassed Materials
Authors: Scannapieco J. F. , Griffin R. N.
Published: July 2002

Among problems, which have been encountered in testing and flight of spacecraft, have been those related to the outgassing of materials in vacuum. Two of the major problems caused by outgassing are electrical corona discharge, and condensation onto critical surfaces. The surfaces of a spacecraft most susceptible to damage by condensation of a foreign material are those used for thermal control and those used in optical systems. This paper describes the techniques used to determine the effects of outgassed materials condensed on MgF2 over-coated aluminum mirrors while the mirrors were irradiated with ultraviolet light in vacuum. Mirror temperatures as low as −60 °C were used to determine the point at which condensation was incipient. The measurements performed on these mirrors included reflectance at Lyman α (1216 Å) and infrared analysis of the deposit. The initial results obtained with this system demonstrate that Lyman α reflectance is essentially unaffected by heavy condensates of some materials but almost completely destroyed by very thin deposits of other materials.
Preparation of Oxide Films by Pyrolysis and Investigation of their Structure Sensitive Properties
Authors: Ryabova L. A. , Savitskaya Ya. S.
Published: July 2002

Some experimental data are given on the preparation of insulating oxide films (ZnO, In2O3, Al2O3) by the pyrolysis of approximate metal-organic compounds. It is shown that these oxide films may be prepared by the pyrolysis method with a large range of structures varying from amorphous to single crystal and with different electrophysical properties. Temperature ranges for growth of amorphous and crystalline phases were established. Using the amorphous In2O3 and Al2O3 films metal–In2O3–metal and metal–Al2O3–metal samples were prepared. These devices have two stable electrical states, namely, they may be either in a conductive or a nonconductive state. The influence of heat treatment upon the structure and resistivity of the films was studied. The In2O3 films am most sensitive to heat treatment, i.e., the amorphous films became crystalline, and in the process their resistivities decreased five orders.
Abstract: Beam energy transfer and propagation in a fully ionized magnetized plasma
Authors: Ekdahl C. , Greenspan M. , Sethian J. , Wharton C. B.
Published: July 2002

The interaction of a relativistic electron beam (300–500 kV, 5–40 kA, ν/2<2) with a fully ionized magnetic mirror-confined plasma column (1012 cm−3<ne<5×1013 cm−3; 0.01<nb/ne<0.3) has been experimentally investigated. Beam density profiles have been obtained using a small Faraday cup with a thin foil-covered aperture, and by measuring the intensity of x rays generated in small targets. Spatially resolved current profiles have been measured with small magnetic flux loops. Beam energy has been determined by varying the foil thickness covering the Faraday-cup aperature and by graded-foil-absorber energy analysis of the target x-ray emission. The energy transfer to the plasma column has been measured with diamagnetic loops, and the ion energy distribution has been determined with a multichannel analyzer.

Results indicate up to 8% transfer of the diode energy to heating of the plasma column with the energy per electron–ion pair increasing linearly with the beam to plasma density ratio nb/ne. Ion energy distribution with high energy tails is observed. Following beam injection, oscillations are observed on the plasma column which propagate with the Alven velocity. 80%–98% current neutralization is observed. From the decay of currents which persist after the passage of the beam, a plasma resistivity can be inferred for the plasma column which is three to four orders of magnitude greater than the Spitzer resistivity calculated for the plasma column.
Abstract: New x-ray mask of Al–Al2O3 structure
Authors: Funayama T. , Takayama Y. , Inagaki T. , Nakamura M.
Published: July 2002

This paper describes the fabrication and performance of a newly developed x-ray lithography mask consisting of an aluminum substrate and an Al2O3 film which was grown on the aluminum substrate by anodization. Transparent membranes of Al2O3 film were made by chemically etching parts of the aluminum substrate beneath the film on which gold absorber patterns were fabricated. Gold micropatterns were replicated successfully by Al Kα (8.34 Å) x rays. Properties of this mask include ease of fabrication, transparency, feasibility of realignment by optical means, and high mechanical strength allowing the capability of larger window size.
Fabrication of high-strength unsupported metal membranes
Authors: Pickhardt Vincent Y. , Smith Donald L.
Published: July 2002

Metal membranes ?1 μm thick would be useful as diaphragms for capacitance manometers and acoustic transducers, as x-ray windows, and as deformable mirrors in optical systems. The high strength-to-density to Ti makes that metal particularly suitable for fast-response deformable membranes. Ti films 1/4–2 μm thick and 2–12 cm in diameter were vacuum-deposited at 20–100 Å/s from an electron-beam source at 2×10−7 Torr onto Corning 0317 glass substrates which were held at 500°C by contacting with Ga to a Ti heating block. These substrates are very smooth and match the thermal expansion of Ti to a few percent. Pre-evaporation of a 300 Å thick CaF2 parting layer allowed membrane removal by water-assisted peeling. Pressure testing showed membranes to have bulk tensile strength of 4.6–6.2×109 dyn/cm2 (68–92 Kpsi) and to behave elastically. They could be mounted under high tension by heating while clamped to a high thermal expansion coefficient Nylon flange.
Investigation of the Au–Ge–Ni and Au–Ge–Pt system used for alloyed contacts to GaAs
Authors: Wittmer M. , Finstad T. , Nicolet M-A.
Published: July 2002

Widely used metallization schemes for alloyed contacts to n-type GaAs consist of a Au–Ge alloy with a cover layer of Ni or Pt. We have studied the interaction of these elements (Au–Ge and Ni, Au–Ge and Pt) upon heat treatment on an inert substrate. Our results show that Ni and Pt play an active role in contact formation. During heat treatment the Ge diffuses out of the Au into the Ni or Pt layer, respectively, where it forms stable compounds. Due to the fact that Ni and Pt act as a sink for Ge the composition and, as it is shown, the uniformity of the heat-treated layers depend on the ratio of the amount of evaporated Ge to Ni or to Pt.
Differentially pumped six-inch metal sealed gate valve
Authors: Harra D. J.
Published: July 2002

Vacuum valves rely on an ability to make and remake intimate contact between their seal and seat materials over their entire main seal perimeters. In many applications, valves must be operable in the presence of small amounts of particulate matter. In such applications, a common failure mode for both metal and elastomer sealed valves results from the inadvertent incorporation of foreign particles into the main seal area during their operation. The use of a back-up seal with differential pumping of the intermediate space is a well-known technique for reducing the effect of small leaks. A modification to allow differential pumping of the main seal of a six-inch metal sealed valve described previously is discussed. Experimental results obtained with a modified valve are presented.
Structure and morphology of chemical-sprayed CdS films
Authors: Berg R. S. , Nasby R. D. , Lampkin C.
Published: July 2002

Chemical spray pyrolysis is a technique for film growth which is of interest because of its potential for very large-scale, inexpensive production of semiconductor materials such as CdS for photoconductor and photovoltaic applications. In this study, CdS films were prepared by spraying ∠0.1-M aqueous solutions of CdCl3 and NH2CSNH2 (thiourea) onto SnO2-coated glass substrates heated to 380°C. The films developed very intricate surface morphologies consisting of a variety of nodular and serpentine structures about 5–10 μm in size. Grain sizes were about 200 nm, with their c-axis generally normal to the local surface. The grain structure and morphology produce very large optical scattering and high effective absorption for wavelengths larger than the CdS band-gap wavelength of 500 nm. Films 3–4 μm thick typically have effective absorption constants of about 500 cm−1 at 1000-nm wavelength. The films were relatively impure, with total impurity contents of about 2 wt. % consisting of reaction products (principally chlorine), impurities picked up from the spray process (oxygen, iron, and others), and mobile glass species (such as sodium and potassium). These impurities may be an important factor in limiting grain size. Electrically, the carrier concentrations are on the order of 1016 cm−3, with mobilities of the order of 10 cm3/V s. Some of the effects of these properties on fabricated CdS/Cu2S photovoltaic devices are discussed.
Structural analysis of rf and dc sputtered Nb3Ge thin films containing oxygen
Authors: Alessandrini E. I. , Laibowitz R. B. , Tsuei C. C.
Published: July 2002

Using electron microscopy, diffraction, microprobe, scanning microscopy, and nuclear back-scattering techniques to analyze rf and dc sputtered N3Ge thin films, it was found that the film structure was strongly dependent on film preparation methods. Amorphous Nb3Ge films were prepared by both sputtering techniques, on substrates held at liquid nitrogen temperature. Identical crystallization heat treatments were then carried out in a He furnace at 750°C for 65 h. Analyses by nuclear back-scattering indicated that crystallized rf-prepared films contained about three times as much oxygen as crystallized dc films. Structure studies showed that although both types of crystallized films exhibited the A-15 structure, the data on the rf films indicate the presence of the crystalline oxide, Nb2O5. In addition, the lattice parameter for the rf film was slightly smaller * dc-prepared films while the grain size of the former is about 10 times larger. These data appear to be correlated to differences in the superconducting transition temperature of both types of films. A high Tc (∠16 K) was observed for rf-prepared samples. The annealed dc-sputtered films did not become superconducting for temperatures above 1.5 K. In summary, the results of this work indicate that large grain size is conducive to high Tc superconductivity in Nb–Ge system and provide some evidence for oxygen stabilization of the high TcA-15 phase.
Electrostatic einzel lenses with reduced spherical aberration for use in field-emission guns
Authors: Riddle G. H. N.
Published: July 2002

Focusing properties and aberration coefficients are calculated for electrostatic einzel lenses suitable for use as preaccelerator lenses in field-emission electron guns. Various lens shapes are analyzed, and asymmetric designs with conical central electrodes are found to have reduced spherical aberration. A lens shape with optimized geometry is found to have a spherical aberration coefficient of less than six times the working distance from the lens to the focal point. This lens has a bored conical central electrode located close to a thin first electrode. Calculations indicate that a field-emission gun using such a lens should be able to provide a 0.24 μA beam from a 1100 Å effective source size into an emission half-angle of 2.4×10−2 rad. At lower emission angles the source size would be limited by chromatic rather than spherical aberration.
Study of radiation damage in metals by positron annihilation
Authors: Gauster W. B.
Published: July 2002

Positron annihilation is a sensitive technique for probing defects in metals and it has recently been shown to be a valuable tool for the study of radiation damage. After an introduction to the three basic experimental methods (angular correlation, Doppler broadening, and lifetime measurements), the interaction of positrons with lattice defects is reviewed. Results for the annealing of damage after low-temperature irradiation are used to show that positron annihilation has provided new information on annealing kinetics. The role of positron techniques in characterizing complex defect structures resulting from high-temperature neutron irradiation is reviewed and the possible utility of positron annihilation as a nondestructive monitor of property changes is pointed out.
Surface composition of polycrystalline Au–Cu alloys as a function of temperature
Authors: Losch Wolfgang , Kirschner Jürgen
Published: July 2002

The surface composition of polycrystalline Au–Cu alloys is studied by means of Auger electron spectroscopy (AES) in the composition range from 7.5 to 56.3 at. % Au. Well equilibrated surfaces show predominant Au segregation in the temperature range from 200° to 550°C as observed by the low-energy Cu (58/60 eV) and Au (66/69 eV) Auger transitions. The Au segregation decreases linearly with increasing temperature. Quantitative evaluation, based on internal and external calibration shows Au enrichment up to 100%. The deeper layers, studied by means of the high-energy Cu (920 eV) and Au (2024 eV) Auger transitions, generally do not show Au but Cu enrichment. This result is consistent with depth profiling by Ar+ sputtering. Segregation of S or O impurities at T?600°C leads to strong, chemically induced Cu enrichment on the surface as identified by the appearance of fine structure in the sulfur Auger transition. Current theories of segregation for pure alloys are discussed. Lowering of surface and lattice distortion energy are found to be important, whereas the heat of sublimation has no influence on segregation in Au–Cu alloys.
Energy transfer effects in surface diffusion
Authors: Masel R. I.
Published: July 2002

Energy transfer effects should play an important role in diffusion on surfaces, just as they do in diffusion in gas, liquid, and solid systems. Here a model is proposed which considers the energy transfer processes explicity. The idea is to treat the diffusing specie as a particle freely translating in a periodic potential, with energy transfer processes contributing to excitation and decay. Decay processes are treated via an inelastic lifetime; lifetimes are estimated from gas/surface scattering data. The results show that hopping-model-like behavior would be expected for diffusion of a high-molecular-weight chemisorbed atom on high-molecular-weight substrate. For light atoms, multi-unit cell hops should be prevalent. Weakly interacting moble precursor states should have a diffusivity which decreases with increasing temperature.
Order–disorder transition of oxygen on (111) nickel
Authors: Kortan A. R. , Cohen P. I. , Park Robert L.
Published: July 2002

We have studied the order–disorder transition of the double-spaced oxygen structure on (111) Ni by LEED, AES, and work function measurements, with particular emphasis on the profiles of the half-order diffraction spots. This appears to be the same transition reported somewhat earlier for this face [C. Davisson and L. H. Germer, Phys. Rev. 30, 705 (1927)]. At room temperature, ordering occurs at a critical coverage about half that corresponding to uniform coverage by the double-spaced structure. The transition temperature increases with coverage to a limiting value of about 415 K. At lower coverages, the sticking coefficient decreases below Tc, but additional oxygen can be incorporated, which gradually extinguishes the half-order spots. Work function measurements show the bonding of the ’’excess’’ oxygen to be different from the ordered. It is shown that the order–disorder transition can be identified with an abrupt onset of broadening of the half-order spots.
Focused ion beam designs for sputter deposition
Authors: Kaufman H. R. , Harper J. M. E. , Cuomo J. J.
Published: July 2002

For efficient deposition of thin films using ion beam sputtering, a high ion current density is desired. We have redesigned the ion extraction optics of a broad beam multiaperture ion source to focus the beam to a 2.5-cm-diam target area. Two focusing methods are described. One uses spherically dished grids, current densities of Ar+ up to 26 mA cm−2 at 1000 eV are acheived at a focal distance of 13 cm, etching a Si target up to 300 Å s−1. The average current density over the target area is 7.7 mA cm−2, more than six times the current density delivered by a parallel beam system with the same aperture dimensions.
Production of molecular noble gas ions in a hot cathode ion source
Authors: Wittmaack K.
Published: July 2002

The feasibilty of a hot cathode ion source for the production of molecular noble gas ion has been investigated. The experiments were performed in the primary ion column of a sanning ion microprobe in which the beam is fed through a small aperture after a drift length of approximately one meter. It was found that noble gas ion beams can be produced with a relative dimer-to-monomer content of about 1%. The influence of the source pressure and the discharge voltage on the molecular ion current has been studied in detail. The molecular ion current increases with with decreasing discharge voltage and becomes largest at the minimum accessible (stable) discharge voltage. With increasing source pressure the dimer (and trimer) ion current at the target increases up to a maximum which results from the counteraction of molecular ion production in the source and ion beam attenuation due to interaction with neutrals effusing from the source. The results are discussed with the aim of providing optimization criteria for instrument design and operation.
Radiation effects in MOS devices caused by x-ray and e-beam lithography
Authors: Peckerar M. , Fulton R. , Blaise P. , Brown D. , Whitlock R.
Published: July 2002

In this study we have found that electron–beam and x-ray irradiations of metal (or polysilicon) -oxide-semiconductor devices performed at typical PBS or PMMA exposure levels create temperature-bias-stress (TBS) instability. Experimental results can be most reasonably explained by assuming that exposure to both of these types of ionizing radiation causes mobilization of positive charge in the insulator. The positive charge is forced closer to the semiconductor–gate-oxide interface during the positive bias phase of the TBS test. This damage mechanism was found in HCl, H2/O2, and dry grown oxides. HCl oxides exhibited the effect the least of the three oxide types studied. N2 anneals performed at 500° and 900°C, and H2 anneals performed at 500°C (all for 30 min) did not substantially reduce TBS instability. A 900°C anneal in H2 for 30 min did create a marked reduction in the TBS-induced instability.
Comparison of the early stages of condensation of Cu and Ag on Mo(100) with Cu and Ag on W(100)
Authors: Soria F. , Poppa H.
Published: July 2002

The adsorption and condensation of Cu and Ag, up to several monolayers in thickness, onto Mo(100) has been observed at pressures below 2 ×10−10 Torr in a study that used combined LEED, Auger, TDS, and work function measurements in a single experimental setup. The results show that Cu behaves similarly on Mo(100) and W(100) substrates, while some differences are found for Ag adsorption.
Desorption properties of Sb on a GaAs (100) surface
Authors: Naganuma Mitsuru , Miyazawa Shintaro , Iwasaki Hiroshi
Published: July 2002

Desorption properties of Sb on a GaAs(100) surface are investigated by Auger electron spectroscopy (AES). On surfaces covered with an Sb monolayer, two kinds of desorption process were observed with desorption energies of 2.4 and 2.6 eV. The difference in desorption energies is discussed from the viewpoint of elastic strain energy caused by a pseudomorphic structure of Sb.
Approach to the measurement of short wavelength absorption properties of photoresists
Authors: Bohn Paul W. , Taylor James W. , Guckel Henry
Published: July 2002

A technique for measuring the absorption coefficients of photoresist materials at short wavelengths is described. The approach consists of supporting the photoresist on 1000 Å thick SiO2 windows which have been preferentially etched into single crystal silicon wafers. Results with thin films of polymethylmethacrylate (PMMA), polybutene-1-sulfone (PBS) and Kodak 747 microresist are presented between 60–400 Å to illustrate feasibility.
Hillock growth on lead films upon cycling to cryogenic temperatures
Authors: Fu C. Y. , Van Duzer T.
Published: July 2002

Measurements are reported in which lead films were continuously monitored with a scanning electron microscope as the temperature was reduced from room temperature to -130°C and then raised again. It was observed that hillocks grew on the surface only when the temperature rose beyond approximately -10°C. This temperature is about one-half of the melting temperature, a value at which several stress-relief mechanisms are active.
Development of high-quality titanium–tritide targets for the rotating-target neutron source
Authors: Jones L. M. , Makowiecki D. M. , Steward S. A.
Published: July 2002

The Rotating-Target Neutron Source II (RTNS II) at Lawrence Livermore Laboratory (LLL) is the most intense continuous source of 14-MeV D-T neutrons currently available and is a national center for the study of the effects of these neutrons on materials of interest to the fusion community. The 14-MeV neutrons are produced when a 400-keV deuteron beam strikes an approximately 10-μm-thick titanium–tritide layer that adheres to a dish-shaped water-cooled copper-alloy substrate, rotating at 5000 rpm. The lifetimes and average neutron source strengths of the targets used during routine operation on the older and less powerful RTNS I and during early operation on RTNS II have varied widely, and several targets have performed below minimum standards. A study at LLL for improving the reliability of each target and increasing the average neutron source strength and lifetime has been successfully completed. Four 20-cm-diam. targets were produced. The first was used on RTNS I for over 200 h, more than twice the previous average, and the neutron source strength was increased 6%. The three other targets were tested on RTNS II and were compared with three standard production targets. The greater average neutron source strength of the LLL targets was statistically significant. We attribute this success to the production of high-quality titanium–tritide layers. Materials characterization and the titanium evaporation and tritium reaction systems are described, as well as special production techniques.
Grain boundary diffusion in thin film couples
Authors: Chen C. Y. , Huang H. L.
Published: July 2002

The effect of a partial sink on the grain boundary diffusion in binary polycrystalline thin films has been examined. A general solution to the diffusion equation subjected to the boundary conditions of a constant source and an out diffusion flux, F = kC where k is a constant satisfying 0<k<∞ and C the concentration of the diffusing species, has been analytically obtained. Based on surface concentration and accumulation measurements we are able to determine the out diffusion flux, hence k, and unambiguously the grain boundary diffusivity and its related activation energy. Our results for the surface concentration can be reduced to that of Gilmer and Farrel if k is allowed to go to infinity, and becomes Cs∠(4/π)e−atas k→0. The latter bears good resemblance to that of Hwang and Balluffi despite the fact that their boundary conditions are dissimilar to ours. Comparison is made with experimental data.
Influence of oxygen and water vapor on the ion induced desorption from stainless steel
Authors: Erlandsson R.
Published: July 2002

Ion induced neutral gas desorption, residual gas composition, and pumpdown times were measured after 1 h exposures of a baked stainless steel tube (SS 304 L) to the following atmospheres (atmospheric pressure): (a) pure N2, (b) normal air, (c) pure 80% N2, 20% O2 mixture, (d) pure N2 with the system open during the exposure. It is shown that exposure to oxygen-containing atmospheres increases the subsequent ion induced desorption of CO, CH4, and CO2 while the H2 desorption is reduced. Exposure to water-containing atmospheres, on the other hand, stimulates the ion induced desorption of all the four commonly desorbing species (CO, H2, CH4, and CO2). The effects of exposure to ordinary air on the ion induced desorption and residual gas composition is attributed mainly to its water vapor content. It is shown that if filaments (ion gauges, etc.) are on during low pressure oxygen exposures, the ratio between the ion induced desorption of CO and CO2 will be affected, probably due to the formation of excited oxygen molecules at the filaments. Backfilling the vacuum system with pure N2 before opening to air is shown to give a considerable decrease in surface contamination, which is seen from the ion induced desorption response as well as the reduced evacuation time.
Plasma analysis based on newly found similarities in the relative populations of excited states produced by sputtering and by electron impact
Authors: Kelly Roger , Shivashankar S. A. , Cuomo J. J.
Published: July 2002

It is shown, by considering relevant theory, that the inelastic energy ΔEe transferred to sputtered atoms should have a similar distribution dN/d(ΔEe) to that transferred in medium-energy (≳100 eV) electron–atom collisions: dN/d(ΔEe)∝1/(ΔEe)2. The correctness of this proposition is demonstrated by comparing the relative populations of excited atoms and ions (Al i, Al ii, Al iii) formed by bombarding solid Al with 30 keV Ar+ with those formed by bombarding gaseous Al with energetic electrons, and at the same time comparing both populations with a statistical theory based on the 1/(ΔEe)2 distribution. From the point of view of plasma analysis, this means that the recently developed theory of excited-state formation in sputtering can be extended without alteration to that component of plasmas due to medium-energy, electron–atom collisions.
Characterization of the initial growth of Si on cubic stabilized zirconia
Authors: Loebs V. A. , Haas T. W. , Solomon J. S.
Published: July 2002

The interface of Si grown epitaxially on the (100) plane of yttria-stabilized cubic zirconia (ZrO2,Y2O3) (CZS) has been investigated using XPS, LEED, and Auger depth profile analysis. Submicron thick Si films were deposited by vacuum sublimation onto heated CSZ substrates. Results show that the CSZ crystal was chemically reduced when heated in UHV, yellowing and then darkening the crystal presumably through loss of oxygen from the bulk. This reduction could be reversed by heating the crystal in O2. Initial Si depositions resulted in the formation of SiOx and further reduction of the ZrO2. After further depositions, when only elemental Si was detected, the Zr was completely reduced from its oxide state within the sampling depth of the XPS. Yttria remained unchanged throughout heating and Si depositions. Auger depth profiles showed that the SiOx layer remained at the interface even for film thicknesses greater than 200 nm. CSZ crystals with hydrocarbon contamination on their surfaces underwent chemical reaction upon heating in UHV to form zirconium carbides. Epitaxy on this surface is difficult or impossible. Removal of the carbide can be accomplished by heating in an oxygen ambient.
First spectroscopic investigation of the Yb/Si interface at room temperature
Authors: Rossi G. , Nogami J. , Lindau I. , Braicovich L. , Abbati I. , del Pennino U. , Nannarone S.
Published: July 2002

We report the results of a preliminary synchrotron radiation photoemission and Auger experiment on the Yb/Si interface, prepared in situ by depositing monolayers of Yb onto vacuum-cleaved Si(111) surfaces at room temperature. Spectra were taken for the Si 2p and Yb 5p core levels at several different values of escape depth. The evolution of the valence band and the Si L2,3 VV Auger line shape with coverage also were depth examined. The first monolayer of Yb is adsorbed onto the Si surface without apparent mixing or reaction. For 1.5–2 monolayers, there is evidence of chemical interaction from core level shifts and changes in the Si LVV line shape. At higher coverages, the surface becomes essentially Yb metal; the region of intermixing appears to be limited to 2–3 atomic layers at room temperature.