bluuebunny/crossref_metadata_2025 huggingface dataset:
Modification of niobium film stress by low-energy ion bombardment during deposition
Authors: Cuomo J. J. , Harper J. M. E. , Guarnieri C. R. , Yee D. S. , Attanasio L. J. , Angilello J. , Wu C. T. , Hammond R. H.
Published: July 2002

The effect of ion bombardment on film stress was studied by evaporating Nb thin films in the presence of a controlled ion beam from a Kaufman ion source. Films were deposited at 4 Å/s by electron-beam evaporation with ion bombardment over the energy range 100–800 eV, at ion current densities of 0.001 to 1.1 mA/cm2. Film stress was measured by an x-ray bending-beam technique on Si substrates. Stress values were found to depend strongly on both ion flux and sample temperature. For films deposited at 400 °C, film stress is tensile in the absence of ion bombardment. Increasing argon ion flux causes a change toward compressive stress, in some cases passing through zero. For films deposited at room temperature, film stress is compressive in the absence of ion bombardment, due to incorporation of oxygen. Argon ion bombardment causes a change toward tensile stress, correlating with an improvement in film purity by preferential resputtering of oxygen. With 100 eV argon ions, an ion-to-atom ratio of only 3–10 % is sufficient to cause reversal of the sign of film stress in most cases. Results are interpreted as a combination of cleaning by resputtering and annealing or compacting the film microstructure. In addition, nitrogen ion bombardment is shown to produce superconducting NbN films with a superconducting transition temperature up to 14.5 K.
Model of bias sputtering in a dc-triode configuration applied to the production of Pd films
Authors: Ziemann P. , Kay E.
Published: July 2002

A simple model is presented, which describes film deposition by bias sputtering in a dc-triode system. The model is applied to sputtering of Pd films in a Kr discharge and allows analysis of the experimental results in terms of normalized energy (energy delivered to the growing film by impinging Kr ions per arriving Pd atom) and normalized currents (number of arriving species/number of deposited Pd atoms) in a way similar to dual beam experiments. A linear relation has been found between this normalized energy and the percentage of Pd atoms resputtered from the growing film. This reaffirms that basic results of static sputtering theory can readily be applied to the dynamic situation as encountered in a glow discharge sputter deposition experiment. The asymmetry of the triode configuration due to the injection of the electron beam, which results in spatially nonuniform deposition rates, is taken into account.
Photoelectric work function measurement of a cesiated metal surface and its correlation with the surface-produced H− ion flux
Authors: Wada M. , Berkner K. H. , Pyle R. V. , Stearns J. W.
Published: July 2002

For application in plasma heating, fueling, and current drive of magnetic fusion devices, high current negative deuterium ion sources for intense neutral beam injectors are being developed using efficient production of negative hydrogen isotope ions on low work function metal substrates imbedded in hydrogen plasmas. In order to investigate the correlation between work function and negative hydrogen ion production, photoelectron emission from a cesiated metal surface, which is immersed in a hydrogen plasma with an electron density less than 5×1010/cm3, was measured in the photon energy range of 1.3 to 4.1 eV. The work function determination was based on Fowler’s analysis, and at the optimum coverage a work function of less than 1.5 eV was observed for a Cs–Cu surface. Measured values of work functions for different Cs coverages were compared to the negative hydrogen currents produced at the metal surface in the discharge; the surface production of negative hydrogen ion current is monotonically increasing with decreasing work function.
Electronic properties of deep levels in p-type CdTe
Authors: Collins R. T. , McGill T. C.
Published: July 2002

DLTS and associated electrical measurements were made on unintentionally doped CdTe crystals obtained from several vendors, on Cu-doped CdTe, and on Te-annealed CdTe. All of the crystals were p-type. Four majority carrier deep levels were observed in the temperature range from 100–300 K with activation energies relative to the valence band of 0.2, 0.41, 0.45, and 0.65 eV. Two of these levels were specific to certain crystals while the other two were seen in every sample and are attributed to common impurities or native defects. Fluctuations in the concentrations of levels across samples and as a result of modest sample heating (400 K) were also observed.
Dry etching for submicron structures
Authors: Wolf E. D. , Adesida I. , Chinn J. D.
Published: July 2002

Various drying etching techniques are briefly reviewed and application of some of these techniques for the fabrication of small structures in electronic and metallic materials are discussed. Experimental results from reactive ion etching, reactive ion beam etching, and chemically assisted ion beam etching will be shown for a number of substrate/etch mask systems at dimensions well below 1 μm linewidths.
Electron escape depth variation in thin SiO2 films measured with variable photon energy
Authors: Hecht M. H. , Grunthaner F. J. , Pianetta P. , Johansson L. I. , Lindau I.
Published: July 2002

We have used a double crystal monochromator at the Stanford Synchrotron Radiation Laboratory to study the Si/SiO2 interface using photon energies of hν=1950–3700 eV. This photon energy range allows interfaces to be observed through oxide layers 50 Å thick or more. Variations in electron escape depth and/or oxide density as a function of distance from the interface are observed over the entire kinetic energy range (100–3600 eV). We attribute these differences to a strained oxide layer near the interface.
Characteristics of dc magnetron, reactively sputtered TiNx films for diffusion barriers in III–V semiconductor metallization
Authors: Noël J.-P. , Houghton D. C. , Este G. , Shepherd F. R. , Plattner H.
Published: July 2002

TiNx films have been deposited on C, Si, InP, and glass substrates by reactive sputtering of Ti in a dc magnetron system. The value of x and the crystal structure varied with the deposition parameters around the pressure hysteresis loop typical of reactive sputtering. With a fixed argon flow of 5 standard cm3min−1 (sccm) and a dc current of 2 A, the total pressure P remained constant at 0.23 Pa up to nitrogen flows f(N2) of 5.2 sccm. For 0≤f(N2)<4.1 sccm, only the hcp α-Ti phase was observed by x-ray and electron diffraction, but the films tended to be amorphous for f(N2)∼4.1 sccm. At f(N2)=5.1 sccm, the fcc TiN0.8 phase was observed with a lattice constant a0 of 0.422 nm; the value of x was obtained by Rutherford backscattering spectrometry (RBS) and nuclear reaction analysis (NRA). At f(N2)=5.2 sccm, the pressure increased rapidly to 0.35 Pa; thereafter, P varied linearly with f(N2) until f(N2) was reduced to 3.0 sccm. This behavior is due to the formation of a nitride layer on the Ti target. In this condition, fcc TiN1.2 films with a0=0.428 nm were obtained for all f(N2). The diffusion barrier characteristics of these films were determined by annealing Au/TiN1.2/InP samples at different temperatures. Comparisons were made with samples where 50 nm thick TiN1.2 films were replaced by 50 nm Cr or Pt. Whereas 1 wt.% In was detected in the Au after annealing for 60 s at 500 °C for Pt and 300 s for Cr, no In was detected for the TiN1.2 barrier after 24 h.
Preparation–physical structure relations in SiC sputtered films
Authors: Roy R. A. , Messier R.
Published: July 2002

Both amorphous and crystalline SiC and hydrogenated SiC films were prepared by rf sputtering in which the deposition parameters of gas pressure (Ar) and composition (Ar+H2) and the substrate temperature were controlled. The resulting physical structure of the films were consistent with the various structure zone models. Five evolutionary structural levels were observed for 5 μm thick films prepared under low mobility conditions. By increasing film bombardment and by additions of hydrogen to the sputtering gas, adatom mobility is increased leading to denser, higher zone structures. The physical structure development appears to be independent of the crystallinity of the film.
Chemisorbed oxygen on Ni(110) studied by spin polarized inverse photoemission
Authors: Feigerle C. S. , Seiler A. , Peña J. L. , Celotta R. J. , Pierce D. T.
Published: July 2002

Dissociative chemisorption of O2 on the surface on Ni(110) has been investigated by the techniques of AES, LEED, and spin polarized inverse photoemission spectroscopy (SPIPES). SPIPES provides a unique method for studying the empty electronic states of the majority and minority spin bands separately and at the same time serves as a surface magnetometer. For increasing oxygen surface concentration [clean, O(2×1), O(3×1), saturated oxidation] it is found that the density of empty minority d states at EF decreases, whereas the features of the majority band are conserved up to the point of beginning bulk oxidation. This is taken as evidence for interactions of the adsorbate with the d levels of the substrate.
Synthesis and characterization of zinc thin films formed in a glow discharge
Authors: James W. J. , Tseng Pei-Li
Published: July 2002

The synthesis of continuous pinhole-free, mirrorlike, thin (<2000 Å) crystalline zinc films is affected by introducing diethyl zinc vapor into an inductively coupled, rf glow discharge reactor. The deposition rate profile of films formed on the back sides of the glass substrates is strongly correlated with the shape of the plasma waves, which in turn is dependent upon the reactor operating parameters, in particular the ratio of power to the initial system pressure, W/P0. Those Zn films which are highly reflective and exhibit sharp x-ray diffraction spectra appear to be virtually free of carbon when examined by Auger–ESCA spectroscopy. Sheet electrical conductivities of these films exhibit values approaching those of bulk metal zinc, namely, 104Ω−1 cm−1.
Plasma spray deposition efficiencies
Authors: Wuest G. , Keller S. , Nicoll A. R. , Donnelly A.
Published: July 2002

The plasma spraying of coatings on aeroengine components in an economic and consistent manner requires proper equipment selection, precise control of the plasma torch and component movement together with efficient deposition rates. The latter are achieved using careful control of the plasma parameters with respect to the design of the torch. Deposition experiments were carried out using thermal spray powders for the production of abradable, wear, and zirconia coatings. Attention was paid to component-torch working distance, optimization of the plasma parameters, and powder–plasma interactions.
Plasma spray synthesis of TiB2–Fe coatings
Authors: Champagne B. , Dallaire S.
Published: July 2002

Titanium boride possesses so high a hardness that it could be considered a good candidate for the production of wear-resistant coatings. However, conventional coating processes failed to achieve thick TiB2 coatings with appropriate mechanical strength for industrial application. To overcome their brittleness and take advantage of their hardness, titanium boride should be adequately dispersed in an appropriate metal matrix. To meet these requirements, TiB2–Fe coatings were produced via a synthesis process. In this work, TiB2–Fe coatings have been synthesized through the endothermic reaction of ferrotitanium with ferroboron. The fabrication technique consists in plasma spraying micropellets comprising the reagents and in depositing the as-reacted products onto a substrate. Spraying parameters were studied and optimized to ensure the synthesis of TiB2. By this one-step process, thick abrasion resistant TiB2–Fe coatings have been obtained.
Effect of ion assisted deposition on optical scatter and surface microstructure of thin films
Authors: Al-Jumaily G. A. , McNally J. J. , McNeil J. R. , Herrmann W. C.
Published: July 2002

Ion bombardment of a film during deposition has pronounced effects on the electrical, mechanical, and optical properties of the film. One important optical property is the optical scatter characteristic of the film. This is determined by the film surface and volume microstructure, and thus can be used as a convenient diagnostic technique to examine film morphology. We have examined these effects for metal (Cu and Mo) and dielectric (SiO2 and TiO2) films. We observe, for example, a significant reduction in optical scatter due to surface structure of period <3 μm in the case of films deposited with simultaneous ion bombardment. Other experimental data and a simple model to explain this possible smoothing effect are presented.
Multichamber plasma processing system for research laboratory use
Authors: Supple R. W. , Stoneham E. B.
Published: July 2002

A system for reactive ion etching and plasma chemical vapor deposition permits individual processes to be developed using a wide variety of reactants without concern for interference by carryover of tenacious reactants or products such as carbon and halogen compounds. To avoid interference, each investigator has exclusive use of one or more chambers which can be attached easily to a computer controlled console in a matter of minutes. The functions of the console include multiple gas supply and monitoring and control of deposition and etch conditions by means of a dedicated computer. The gas flow within each chamber is conventional but the mechanical design has been simplified so that additional chambers are simple and inexpensive to build and design changes are easily executed. Parameters controlled include pressure, flow rate, temperature, power, and frequency. A unique feature of the chambers is the ability to monitor etch or deposition progress visually. Pressure and power limits for stable plasma operation are presented as are pressure vs flow relationships.
Interaction of a plasma impinging on a cold gas
Authors: Neuman W. A. , McCullen J. D. , Morse R. L.
Published: July 2002

A numerical simulation of a plasma interacting with a cold gas is done. The calculation utilizes a one-dimensional, steady-state kinetic approximation, in which momentum transferring collisions are neglected, to produce self-consistent electrostatic potential and density profiles. This technique can be applied to a range of physical situations by modifying the imposed boundary conditions. A specific application is made to a charge-exchange system in which a helium plasma is impinging on a slowly drifting neutral cesium gas. Quasiresonant charge exchange will selectively populate the 1P1 state of He0 leading to a possible population inversion. In addition to charge exchange, electron impact ionization processes will affect the development of the potential and are included in the calculation. The results of the calculation yield a region of physical solutions which produce population inversions.
Surface preparation and characterization by spectroellipsometry: Application to (100)GaAs
Authors: Aspnes D. E.
Published: July 2002

The stability in various aqueous solutions of abrupt (100)GaAs surfaces prepared by Br-methanol treatment is investigated as an example of preparation and characterization of surfaces by spectroellipsometry (SE). The abrupt (100)GaAs surface is stable in strongly basic (1 M KOH) solutions but the interface width broadens at lower pH values, quite rapidly in acidic solutions. An analysis of SE data for an acid-treated surface reveals the microstructural origin of the broadening. The behavior is consistent with chemically treated (100)GaAs surfaces being terminated by Ga atomic planes passivated by OH. The generality of the microscopic roughening process suggests that it is due to the atomic structure of the crystal.
The fabrication of 100 to 200-nm-diameter orifices in free-standing 100 and 200-nm-thick foils
Authors: Beecken B. P. , Zimmermann W.
Published: July 2002

Orifices having somewhat irregular cross sections 100 to 200 nm in diameter have been prepared in free-standing nickel foils 100 and 200 nm thick. These orifices were produced by means of electron-beam lithography, using both PMMA and Honeywell EP-25H resists, followed by argon ion-beam milling and oxygen plasma etching. Blockage of these orifices during preparation by a tough unknown material posed a significant problem. We believe that this blockage was caused by the redeposition of resist during ion-beam milling and plasma etching. These orifices were made for use in the study of the flow of superfluid 4He.
Ferromagnetic resonance in ultrahigh vacuum: Effect of epitaxial overlayers on Fe
Authors: Heinrich B. , Arrott A. S. , Cochran J. F. , Liu C. , Myrtle K.
Published: July 2002

The analysis chamber of a Physical Electronics Model 400 Molecular Beam Epitaxy system is used to house a ferromagnetic resonance (FMR) probe. The sensitivity of FMR on Fe to surface structure and overlays of other materials is investigated. Surface sulfides, for example, increase the FMR linewidth. The elements Cr, Mn, and Ni grow epitaxially in the bcc phase on the (100) surface of Fe. MnO grows epitaxially from the Mn overlayers at room temperature. Only Ni has a significant effect on the position of the Fe  FMR lines. It seems reasonable to conclude from FMR line shifts that bcc Ni is ferromagnetic with a Curie temperature well above 80 K.
Reconstruction of aluminum and indium overlayers on Si(111): A systematic study with high-resolution electron energy loss spectroscopy and low-energy electron diffraction
Authors: Kelly M. K. , Margaritondo G. , Anderson J. , Frankel D. J. , Lapeyre G. J.
Published: July 2002

We describe a detailed study of the different reconstructions obtained by depositing Al or In overlayers on Si(111)2×1 and Si(111)7×7 substrates, and of the reconstructions obtained by thermal annealing of these overlayers. We correlate the information obtained by low-energy electron diffraction (LEED) with high-resolution electron energy loss spectra (HREELS).
Effect of the sintering process on the formation and passivation of PtSi
Authors: Chang Chin-An , Segmüller A. , Huang H.-C. W. , Turene F. E. , Cunningham B. , Totta P. A.
Published: July 2002

PtSi films have been formed using different annealing sequences and ambients. Using sputtered Pt, the passivating oxide layer formed on the PtSi films shows a clear dependence on the annealing sequence and ambient used. Using a one-temperature sequence at 550 °C in forming gas (N2–H2 9 : 1), nitrogen or oxygen, the passivating oxide layers all show very poor resistance against etching in aqua regia, an undesirable condition for device fabrication. This is attributed to the incomplete reaction between Pt and Si using such a process. Using a three-temperature sequence at 200–300–550 °C in forming gas, a much improved oxide is obtained with excellent resistance against etching in aqua regia. The process is shown to allow a complete reaction between Pt and Si, a necessary step for the subsequent formation of high quality surface oxide. The three-temperature process using nitrogen or oxygen, however, shows incomplete reaction between Pt and Si, and surface oxide of poor quality, similar to those obtained by the single-temperature process in various gases.
Characterization of the interface between Al–1% Si and rapidly annealed Mo–polycide
Authors: Ho V. Q. , Beerkens R. P. , Calder I. D.
Published: July 2002

In this paper, the results of an investigation of the Mo–polycide/Al–1% Si interface characteristics are reported. Mo–polycide was produced by sputtering a 0.3 μm MoSi2.2 film on 0.3 μm of phosphorus doped poly-Si. The composite layer was rapidly annealed at 1100 °C for 10 s with a tungsten halogen lamp. A 0.25 μm Al–1% Si film was sputtered onto the Mo–polycide and then sintered in forming gas (10% H2, 90% N2) for 45 min at temperatures ranging from 400 to 550 °C. RBS and AES analysis indicated that the Al–1% Si/MoSi2 interface was stable up to 500 °C. Al and Si interdiffusion across the silicide layer was only observed at 550 °C. After a sinter at 450 °C, an abrupt interface between MoSi2 and Al–Si was observed by cross-sectional TEM and a contact resistance of 0.5 Ω was measured for 5×5 μm2 contact windows. This was approximately seven times lower than the Al/n+ poly-Si contact resistance.
Excimer laser induced deposition of InP
Authors: Donnelly V. M. , Brasen D. , Appelbaum A. , Geva M.
Published: July 2002

InP thin films have been deposited on several types of substrates, via 193 nm excimer laser induced photochemical decomposition of In(CH3)3 and P(CH3)3 gas-phase precursors. Deposition results from gas-phase photochemistry, while surface irradiation stimulates removal of carbon and crystallization. InP films deposited on (100)InP substrates have been studied by scanning electron microscopy, transmission electron microscopy, and Rutherford backscattering spectroscopy (RBS). Films range from amorphous to epitaxial, depending upon conditions (most notably fluence incident on the substrate). The best film deposited at ∼0.1 J/cm2 and at a steady-state temperature of only ∼320 ° C, had an RBS spectrum indistinguishable from that of the single crystal substrate. To our knowledge, this is the first report of a 100% photochemically induced deposition of an epitaxial, III–V compound semiconductor thin film (i.e., no growth in the absence of light), and also the first report of an epitaxial InP film deposited from organometallic precursors at a steady-state temperature below the incongruent decomposition temperature of InP (∼350 °C). A more detailed account of this invited paper has been published elsewhere.1,2
Superlattices: Progress and prospects
Authors: McGill T. C. , Wu G. Y. , Hetzler S. R.
Published: July 2002

The current status of HgTe–CdTe superlattices is reviewed. The properties predicted for the superlattices have been studied qualitatively in the cases where both theory and experiment exist. In particular, it has been found by both infrared absorption and photoluminescence that band gaps of the superlattices are substantially less than those of the alloy with the same average composition. Theoretical studies have concentrated on the factors (strain, band offsets, interdiffusion) that could result in substantial deviation of the properties of the superlattices from those predicted by the original simple theories. Some of the areas requiring further development are reviewed and discussed.
A new photon counter for inverse photoemission
Authors: Allen P. M. G. , Dobson P. J. , Webber P. R.
Published: July 2002

Data are presented obtained from a new design of high-resolution (70 meV) and high-sensitivity, fixed isochromat detector for use in inverse photoemission whose peak quantum efficiency is 20% at an energy of 10.08 eV. The detector design is of the Geiger type with a novel combination of a CaF2 window and CS2 vapor fill. The performance of this detector is compared with others currently being used. It is suggested that this design could provide an inexpensive viable alternative for high-resolution spectroscopy systems. Inverse photoemission spectra obtained from a CuNi(111) surface in ultrahigh vacuum are presented.
Chemical vapor deposition of zinc phosphide thin films
Authors: Papazoglou E. , Russell T. W. F.
Published: July 2002

The design and analysis of a laboratory scale system for the chemical vapor deposition of thin zinc phosphide films is reported. The deposited films, on mica or glass substrates, were uniform, continuous, and of low electrical resistivity (400–1000 Ω cm). The reactor was made of nonporous graphite (H-490) and was operated at 1 atm using elemental zinc and phosphine. Model equations describing the evaporation of zinc, the cracking of phosphine, and the deposition reaction have been developed. The evaporation rate of zinc is a function of its temperature and the helium flow rate above its surface. The film growth is controlled by the surface reaction between adsorbed zinc and phosphorus. A Langmuir–Hinschelwood expression for the reaction rate agrees well with the experimental data over a range of substrate temperatures and reactant concentrations.
Movable needle type of liquid-metal-ion sources for boron and phosphorus ions
Authors: Ishitani T. , Umemura K. , Aida T.
Published: July 2002

A movable needle type of liquid-metal-ion source (LMIS) has been developed for boron (B) and phosphorus (P) ions. The needle movement is very effective for accomplishing good wetting between the needle and the molten metal as well as for balancing the ion emission and inflow of the source metal at the needle apex. These features lead to stable ion emission under a wide range of experimental conditions. The B-LMIS using a combination of carbon or carbide needle and Ni–B–Si alloy emits stable B+ ions with an atomic fraction of 25% to 35%. The P-LMIS using Pt–P–Sb alloy provides a large amount of P+ and P++ atomic fractions (15%–30%) with a P++/P+ ratio of 0.5 to 2. The experimental results on energy spread per unit charge, ΔE(Mn+)/n, agree with the general relationship [ΔE(M++)/2≤ΔE(M+)<ΔE(M++)]. The source lifetime is more than 250 and 150 h for the B- and P-LMIS’s, respectively. These LMIS’s have the capability of providing stable B and P focused-ion-beams (FIB’s) by mounting them on an FIB apparatus.
Dry etching of n- and p-type polysilicon: Parameters affecting the etch rate
Authors: Berg S. , Nender C. , Buchta R. , Norström H.
Published: July 2002

The etch rate of doped polycrystalline silicon films (polysilicon) was studied as a function of dopant concentration, degree of dopant activation, and dopant type, in a parallel-plate reactor, using a CFCl3 plasma. The significant difference in etch rate between n-doped and p- or undoped polysilicon observed indicates that the electrical activity of the bulk (and surface) plays an important role when etching at a plasma frequency of 13.56 MHz. However, at lower frequencies this difference in etch rate for n- and p-doped polysilicon is less pronounced.
Systematics of electronic structure and local bonding for metal/GaAs(110) interfaces
Authors: Joyce J. J. , Grioni M. , del Giudice M. , Ruckman M. W. , Boscherini F. , Weaver J. H.
Published: July 2002

We present high-resolution synchrotron radiation core level photoemission results which reveal the evolving electronic structures and morphologies of metal/GaAs interfaces for the metals Ce, Sm, Ti, V, Cr, Fe, Co, Cu, and Au. By studying a wide range of overlayer metals we sought to identify common interface characteristics and discriminate between chemical and morphological effects. Quantitative fitting of the Ga and As 3d core level emission provided insight into the stages of interface development. Our results indicate that Ga is found in solution at these interfaces with chemical shifts from −0.40 eV for Au to −1.78 eV for Ce (relative to Ga in GaAs). In contrast, the results for As indicate well-defined local chemical environments and, in some cases, the possibility of surface segregation. A direct correlation between overlayer electronegativity and core level shifts is observed.
Angle resolved ultraviolet photoemission spectroscopy study of the electronic structure of InSb(111) surfaces along the [110] azimuth
Authors: Hernández-Calderón I. , Höchst H. , Mazur A. , Pollmann J.
Published: July 2002

The analysis of non-normal photoemission spectra of the polar A(111) and B (1̄1̄1̄) surfaces of InSb along the [110] azimuth indicates strong contribution from bulk features. Transitions common to both surfaces around 1.4, 2.6, 3.3, and 6.2 eV are associated with critical points in the bulk band structure. Umklapp scattering of photoelectrons with reciprocal vectors of the InSb(1̄1̄1̄)(3×3) surface is identified for transitions around 3.3 eV. Modifications in the spectra of this surface after Sn coverage suggest contribution from a surface resonance band around 1.4 eV; bands around 4.3 and 4.9 eV dispersing within a gap of the projected bulk band structure calculated by a realistic empirical tight-binding method are tentatively assigned to backbond states.
Thermochemical modeling of interfacial reactions and selective deposition at growth from the vapor
Authors: Carlsson J. O.
Published: July 2002

Advances in various computational techniques for chemical equilibria now enable complex multicomponent chemical vapor deposition systems to be analyzed. The results obtained from the thermodynamical calculations can be used to construct ‘‘road maps’’ indicating how changes in the experimental parameters can affect deposition conditions. In this paper, thermochemical modeling and its use are discussed for two major areas: (i) Interfacial reactions at the initial stages of growth. These reactions influence adhesion, autodoping, grain size, and topography of the interface. (ii) Selective deposition processes based on differences in chemical reactivity between different substrate areas. Parameters for prediction of selectivity and for identification of selectivity modifiers are introduced.
Hydrogen dissociation and incorporation into amorphous silicon produced by electron beam evaporation
Authors: Franghiadakis Y. , Tzanetakis P.
Published: July 2002

A simple and efficient source of atomic hydrogen to be used for reactive evaporation or ionized cluster beam deposition of amorphous silicon films was developed. The intensity of the H beam over a large area of substrates is known and can easily reach 1016 atoms cm−2 s−1. Using this source, a series of films was grown by electron gun evaporation of Si and variable H beam flux. The main objective was to study the fundamental and practical aspects of hydrogen incorporation in a-Si and not to produce device quality films. It is found that the growing films retain atomic H with a probability close to 1 for H/Si atomic ratios lower than 1%. The role of the excess H flux and the reaction products of atomic hydrogen and silicon on the walls, in determining film quality, is discussed.
Dependence of the electrical properties of KNO3 memory devices on fabrication and processing parameters
Authors: Kulkarni A. K. , Rohrer G. A. , McMillan L. D. , Adams S. E.
Published: July 2002

Several fabrication and processing parameters such as deposition rate, thickness of the sample, annealing time and temperature, and electrode materials were varied in Au–KNO3 –Au thin-film ferroelectric memory devices to optimize the electrical properties of these devices. The deposition rate was varied from 2.5 to 10 nm/min in steps of 2.5 nm/min. The samples deposited at a rate of 5 nm/min yielded better electrical results compared to samples deposited at other rates. The electrical testing involved pulse testing and capacitance–voltage measurements. The switching time of these devices decreased with a decrease in the thickness of KNO3 as expected. However, the switching thresholds were sharper in the 200-nm-thick KNO3, as compared to 160- and 120-nm-thick KNO3 samples. The samples were annealed in forming gas at 6, 10, 17, 21, 24, and 44 h and no significant changes were observed in the switching time and polarization. Instead of gold electrodes, indium–tin electrodes gave better performance but they were not easily repeatable.
The II–VI compounds: 30 years of history and the potential for the next 30 years
Authors: Reynolds R. A.
Published: July 2002

The past 30 years of progress in II–VI compounds is briefly summarized. Existing problems with both the materials and methods for their production are noted. The probable future use of the II–VI compounds is in infrared sensors and photonics. Possible applications are discussed.
Delta doping of III–V compound semiconductors: Fundamentals and device applications
Authors: Schubert E. F.
Published: July 2002

Delta-function-like doping profiles can be obtained in semiconductors by growth-interrupted impurity deposition during molecular-beam epitaxy. The spatial localization of dopants is assessed by the capacitance–voltage profiling technique and secondary ion mass spectroscopy which yield profile widths of 20 and 37 Å for Be δ-doped GaAs grown at 500 °C, respectively. The diffusion coefficients of Si, Be, and C in GaAs and of Si in AlxGa1−xAs are determined and diffusion is shown to be negligible at low growth temperatures. At elevated growth temperatures, dopant redistribution occurs during epitaxial growth. The redistribution is shown to be due to (i) diffusion of dopants and (ii) Fermi-level pinning induced segregation of dopants along the growth axis. Fermi-level pinning induced segregation of dopants is a novel mechanism which results in a redistribution of dopants predominantly toward the growing surface due to electrostatic attraction of dopants and carriers localized in surface states. This mechamism is shown to be relavant at elevated growth temperatures of ≥600 °C. Electronic devices such as homostructure and heterostructure field-effect transistors which employ the δ-doping technique have a number of advantages including (i) high carrier density, (ii) proximity between electron channel and gate electrode, (iii) large breakdown voltage of the gate, and (iv) reduced short-channel effects. In addition, high transconductances are obtained in such δ-doped field-effect transistors. The optical properties of doping superlattices are significantly improved using the δ-doping technique. Quantum-confined interband transitions in doping superlattices are observed for the first time in such improved doping superlattices. Furthermore, a tunable doping superlattice laser is demonstrated, which has a tuning range of 35 Å. The tunable doping superlattice laser has a potential tuning range of 220 Å and is a candidate for a tunable source in future optical communication systems.
Investigation of buried homojunctions in p-InP formed during sputter deposition of both indium tin oxide and indium oxide
Authors: Gessert T. A. , Li X. , Wanlass M. W. , Nelson A. J. , Coutts T. J.
Published: July 2002

Although it is apparent that direct current (dc) magnetron sputter deposition of indium tin oxide (ITO) leads to the formation of a buried homojunction in single crystal p-type InP, the actual mechanism of type conversion of the InP surface is not clear, nor is it immediately obvious how further improvements may be achieved. Previously, we have suggested that type conversion is caused by indiffusion of Sn during the ITO deposition process and additionally demonstrated that this effect is strengthened by the presence of hydrogen in the sputtering gas. Recently, however, efficiencies of almost 17% (Global) have been achieved for cells fabricated by sputter depositing In2O3(IO) alone, strongly suggesting that the Sn may not be an essential part of type conversion. In this work, a variety of electrical and optical techniques has been used to assess the changes at the ITO/InP and IO/InP interfaces. From these, it is concluded that several mechanisms, including passivation of acceptors by hydrogen and ‘‘sputter damage,’’ occur simultaneously. This analysis suggests several directions for further improvement of these devices.
Titanium oxide formation by dynamic ion beam mixing
Authors: Miyake S. , Kobayashi T. , Satou M. , Fujimoto F.
Published: July 2002

Titanium–oxide films were deposited on Si wafers and/or quartz plates by a dynamic ion beam mixing method. High energy O+2 and/or O+ beams (30–40 keV) were injected during the deposition of Ti vapor onto the samples. Analysis of the film structure revealed the formation of TiO rather than TiO2, and the film growth varied from (111) to (200) plane of TiO with a decrease in the Ti:O arrival rate of Ti atoms and O+ ions onto the sample. Annealing of prepared films at 600 °C in the open air changed the film structure to include TiO2.
Electronic and vibrational properties of semiconducting crystalline FeSi2 layers grown on Si(111)
Authors: Rizzi Angela , Moritz Heiko , Lüth Hans
Published: July 2002

Semiconducting FeSi2 thin layers have been grown on Si(111) by solid state reaction under ultrahigh vacuum (UHV) conditions. The different reaction steps in the temperature range 380–750 °C were followed in situ by Auger electron spectroscopy (AES) and electron energy-loss spectroscopy (EELS). FeSi2 is formed between 550 and 680 °C. At higher temperatures the silicide thin film disrupts forming islands as shown by EELS and ex situ medium-energy ion scattering (MEIS). The low energy excitation spectra of the thin FeSi2 layers were measured by high-resolution electron energy-loss spectroscopy (HREELS). Surface phonon excitations at 50 meV energy are observed and explained in the framework of dielectric theory of surface scattering. This is the first time that Fuchs–Kliewer surface phonons, typical for heteropolar crystals such as GaAs, ZnO, etc. are so clearly observed on a silicide surface by HREELS. Their presence gives evidence of the semiconducting character of the FeSi2 overlayer. A broad loss structure occurs in the higher energy range corresponding to the excitation of electronic interband transitions. The onset of this structure at ∼0.8 eV gives an indication of the band gap energy of the silicide. Its intensity together with the small experimental q∥ transfer is an evidence of a direct band gap for the FeSi2 layer.
Time-resolved measurements of electron and ion densities in low-frequency discharges by high-frequency impedance analysis
Authors: Thompson B. E. , Utagikar A. , Avona P.
Published: July 2002

The densities of ions and electrons as a function of time within low-frequency (100 kHz) glow discharges have been measured using a new technique of impedance measurement and analysis. The technique was used to examine both an electropositive discharge (Ar) at 3 Torr and an electronegative discharge (SF6) at 0.35 Torr. The impedances of the Ar plasmas are influenced by the sheath capacitance and an electron concentration of ∼1016 m−3 in the bulk of the plasma. The impedance of the SF6 discharges is affected by both the electron concentrations and the much higher ion concentrations of 5×1017 m−3 in the bulk. The electron concentration varies from less than 1012 to about 8×1014 m−3 over the cycle due to fast rate constants for electron attachment that may or may not be balanced by electron generation from ionization.
Effect of microstructure and hydrogen content on the characteristics of amorphous hydrogenated carbon protective coatings
Authors: Kokaku Y. , Kohno M. , Fujimaki S. , Kitoh M.
Published: July 2002

Amorphous hydrogenated carbon films have splendid wear characteristics as protective coatings. In the present work we have studied the relation between wear durability and microstructure of the amorphous hydrogenated carbon films prepared with radio-frequency plasma-enhanced chemical vapor deposition. Wear rates of pin-on-disk sliding tests for the films deposited at various conditions have been compared with the results of spectroscopic analysis. Wear durability of the films has been found to be described with a combination of two factors, one is the shoulder-to-main peak ratio of Raman spectra and the other is content of chemically bonded hydrogen atom. The former factor stands for the amount of ‘‘graphitelike’’ regions and the latter stands for the amount of ‘‘organic’’ regions in the carbon films.
Time-of-flight static secondary ion mass spectrometry of additives on polymer surfaces
Authors: Mawn M. P. , Linton R. W. , Bryan S. R. , Hagenhoff B. , Jürgens U. , Benninghoven A.
Published: July 2002

A comparison of a polyethylene additive extract sample, deposited from solution as a submonolayer on Ag, was made to an in situ surface analysis of a bulk polyethylene sample using time-of-flight static secondary ion mass spectrometry (TOF-SIMS). The in situ analysis was able to confirm most of the additives detected in the extract. The additive mass range of 200–1200 Daltons was relatively free of spectral interferences due to the polyethylene matrix. High mass resolution studies were used to assist in the assignment of molecular identities to the additives. Molecular ions for the additives were predominantly Ag cationized adducts for the extract sample, and [M+H]+ or [M+Na]+ species for the bulk polyethylene. Deposition of standard additive solutions on Ag demonstrated the detection sensitivity of TOF-SIMS, illustrating the potential for molecular imaging of polymer domains as small as a few μm2 . The relative extent of oxidation of Naugard 524, an antioxidant additive, also was compared for a standard, polyethylene extract, and an in situ analysis using the [M+O]+ and [M+H]+ secondary ion signals. The additive was more extensively oxidized after aging in the polymer matrix based upon measurements of [M+H]+ /[M+O]+ ratios.
Commensurate–incommensurate phase transition between 6×6 and √3×√3 + satellite structures of the Au/Si(111) surface
Authors: Yuhara J. , Inoue M. , Morita K.
Published: July 2002

Alternate annealing in the low- (≤250 °C) and high- (≥400 °C) temperature regimes of the Au/Si(111) surface at different Au coverages prepared by room-temperature deposition and isothermal annealing in the high-temperature regime at over-(ML) coverages have been studied by means of low energy electron diffraction (LEED), Auger electron spectroscopy (AES), and Rutherford backscattering spectroscopy (RBS). It is found that the 6×6 pattern and the √3×√3+satellite pattern are formed at 0.9–2.2 ML coverages by annealing for several minutes at 250 and 500 °C, respectively, when there exist an Au surface peak and a diffusion tail extended towards the lower energy behind the Au peak and that the phase transition between both patterns is reversible by alternate annealing in two temperature regimes as long as the diffusion tail is not diminished. From this result, the 6×6 structure is ascribed to excess embedded Au atoms situated at the ordered sites and Au atoms constituting the √3×√3 structure at the top surface. Moreover, it is found that the phase transition between the √3×√3 structure and the mixed structure of √3×√3+5×1 are also reversible by alternate annealing in the two temperature regimes at the actual coverages of 0.72–0.84 ML. Furthermore, from analysis of the isochronal annealing data at 1.7 ML, the activation energy of the diffusion of Au in Si is found to be 1.3 eV.
Influence of metal substrates on photochemistry: SO2/Ag(111)
Authors: Sun Z.-J. , White J. M.
Published: July 2002

To explore the quenching of molecular excited states on metals, the dynamical properties of SO2/Ag(111) photochemistry have been studied by time-of-flight mass spectroscopy using pulsed laser excitations of 193, 248, and 351 nm. Parent molecule desorption occurs at all coverages, but photoreactions destroying SO2 occur only in multilayers. The two demonstrated reactions of adsorbed SO2, one unimolecular and the other bimolecular, behave differently as a spacer layer, hexane, is added. When the SO2–metal spacing is less than about 20 Å, a nonclassical or modified classical theory is needed to describe the quenching process.
Interferometric measurements of the energy of sputtered copper atoms in a magnetron discharge
Authors: Turner G. M. , Falconer I. S. , James B. W. , McKenzie D. R.
Published: July 2002

Emission line profiles of sputtered Cu atoms in a cylindrical postcathode magnetron have been measured using a high-resolution scanning Fabry–Pérot interferometer. The filling gas used was Ne. A deconvolution procedure was used to unfold the velocity distributions from the emission line profiles, measured in a direction parallel and close to the cathode surface. The velocity distributions were found to be a combination of two components—a broad component associated with high velocity atoms entering the measuring volume directly from the cathode, and a narrow near-Maxwellian distribution attributed to partly thermalized atoms re-entering the measuring volume. At high pressures (greater than 10 Pa) the near-Maxwellian distribution dominates, corresponding to a temperature of 650–750 K. At lower pressures the energy associated with the motion parallel to the cathode surface is about 2 eV, and is slightly larger than the energy calculated using a Monte Carlo simulation.
High quality Y1Ba2Cu3O7−δ ultrathin films produced in situ by high growth rate chemical vapor deposition
Authors: Chen Ling , Schmidt Berthold E. , Kaloyeros Alain E. , Luo Li
Published: July 2002

A simple and technologically useful conventional cold-wall chemical vapor deposition (CVD) process was developed for the growth of superconducting YBa2Cu3O7−δ ultrathin layers at high growth rates (12 Å/s). The process was successfully employed for the growth of ultrathin YBCO layers with thicknesses between 60 and 1800 Å on lanthanum aluminate (LaAlO3) using a two-cycle substrate processing scheme which involved a critical substrate conditioning cycle in pure oxygen prior to actual deposition. All samples were superconducting, regardless of thickness, although their superconducting transition temperature and critical current density decreased with film thickness from, respectively, 91.5 K and 2×106 A/cm2 (B=0, 77 K) for the 1800 Å sample down to 64 K and 30 A/cm2 (B=0, 62 K) for the 60 Å sample. The improved quality of the ultrathin YBCO films thus produced by conventional cold-wall CVD was attributed to the role of pure oxygen in substrate surface cleaning prior to deposition as well as in preventing surface oxygen depletion.
Development of ultrahigh vacuum technology for particle accelerators and magnetic fusion devices
Authors: Dylla H. F.
Published: July 2002

The development of ultrahigh vacuum technology for high-energy particle accelerators and magnetic fusion devices provided essential contributions to the progress in these two scientific endeavors over the last four decades. Storage rings were first proposed as an efficient means of producing intense high-energy particle beams by G. K. O’Neill in 1956. The milestone demonstrations of the importance of this invention came with the operation of the ISR device at CERN in 1971, a 2 km long vacuum vessel which operated at 10−12 Torr and the SPEAR electron-positron collider at Stanford in 1972. These achievements required development of new materials, materials processing techniques, vacuum components, and vacuum instrumentation. UHV development continues through the present design efforts for the 27 km LHC ring at CERN, and numerous high intensity synchrotron light sources worldwide. A similar progression in UHV development preceded the operation of the present generation of large tokamaks built to demonstrate the scientific feasibility of magnetic fusion energy: The JET device in Europe (U.K.), the JT-60 in Japan, and TFTR at Princeton. Development efforts in UHV compatible first-wall materials, efficient vessel conditioning procedures, and high capacity pumps are essential for the operation of these devices and continue to be active areas of research for the next generation of fusion demonstration devices.
New high-power fast atom beam source
Authors: Shimokawa Fusao , Kuwano Hiroki
Published: July 2002

This article describes a new high-power fast atom beam (FAB) source incorporating an electromagnet. The electromagnet increases the total path length of electrons entering the source, enabling this source to produce higher plasma densities. Beam current densities up to 1 mA/cm2, which is about ten times that of a conventional FAB source, are obtained by using an electromagnet and a multiaperture grid. The beam current density can also be controlled by adjusting the flux density of the electromagnet and the gas pressure in the source. The beam neutralization coefficient is more than 90% almost independent of the flux density, discharge current, and source configuration. This coefficient does, however, strongly depend on the gas pressure of the FAB source, rapidly increasing as gas pressure increases. Most of the fast atoms have a kinetic energy about equal to the discharge voltage. Ions generated in the glow discharge are accelerated, and collisions with gas molecules near the cathode convert these ions into fast atoms without loss of kinetic energy.