bluuebunny/crossref_metadata_2025 huggingface dataset:
Some experimental artifacts in low energy electron diffraction studies of phase transitions
Authors: Unertl W. N. , Clark D. E. , Shern C. S.
Published: July 2002

Low energy electron diffraction (LEED) is an important experimental technique for the study of continuous order–disorder phase transitions. Extraction of the critical exponents and their associated amplitudes requires an accurate determination of the single-scattering intensity versus the parallel component of the scattering vector. Interpretation of measured intensities is complicated by multiple scattering, variation of the scattering factor, and thermal vibrations. These can cause the measured intensity profiles to be skewed and can add substantial intensity which is peaked at the Brillouin zone center. An example of a subsidiary structure induced by multiple scattering is given for Au(110). The effects on the measured critical exponents β, γ, and ν are shown to be small in most cases. However, the amplitudes associated with these exponents, such as the correlation length ξ, can be seriously affected. Some of these effects also occur in other diffraction methods.
An experimental/theoretical comparison of spin-polarized low energy electron diffraction from the Cu(100) surface
Authors: Lind D. M. , Jamison K. D. , Dunning F. B. , Walters G. K. , Davis H. L.
Published: July 2002

A detailed theoretical/experimental spin-polarized low energy electron diffraction (SPLEED) investigation of Cu(100) is under way to explore the utility of SPLEED measurements in structure determinations for surfaces of low atomic number. Preliminary SPLEED calculations show that, in certain energy ranges, the results are very sensitive to the assumed structural model. Good agreement between theory and experiment is obtained using the surface model, which incorporates multilayer relaxation, that was derived from analysis of earlier LEED intensity data. Work is continuing to refine this model by use of SPLEED data.
A solution to boron contamination at the substrate/epilayer interface of silicon grown by molecular beam epitaxy
Authors: Kubiak R. A. A. , Leong W. Y. , Dowsett M. G. , McPhail D. S. , Houghton R. , Parker E. H. C.
Published: July 2002

The presence of a localized p+ spike at the substrate/epilayer interface of Si grown by molecular beam epitaxy (MBE) has been routinely found in material originating in various laboratories. The p-type contaminant has been identified as boron with typical areal densities of ∼1012 cm−2, only part of which are electrically active after growth. The contamination arises from the use of borosilicate glassware in the MBE system (e.g., viewports), and the problem can be eliminated by replacing such components by quartz counterparts.
Electron ray tracing with high accuracy
Authors: Saito Kenichi , Okubo Tsuneo , Takamoto Kiichi , Uno Yasumichi , Kondo Mamoru
Published: July 2002

An electron ray tracing program is developed to investigate the overall geometrical and chromatic aberrations in electron optical systems. The program also computes aberrations due to manufacturing errors in lenses and deflectors. Computation accuracy is improved by (1) calculating electrostatic and magnetic scalar potentials using the finite element method with third-order isoparametric elements, and (2) solving the modified ray equation which the aberrations satisfy. Computation accuracy of 4 nm is achieved for calculating optical properties of the system with an electrostatic lens.
Bakeout controller for the use of helium closed-cycle refrigerators in ultrahigh vacuum applications
Authors: Celii Francis G. , Whitmore Paul M. , Janda Kenneth C.
Published: July 2002

Simple control electronics are described which provide automated bakeout of an ultrahigh vacuum (UHV) chamber equipped with a helium closed-cycle refrigerator. By preventing the refrigerator from reaching elevated temperatures (T>50 °C) during bakeout, these devices can be utilized in the ultrahigh vacuum environment.
A fast entry air-lock-compatible hot stage for the collection of Auger electron spectra at elevated temperatures
Authors: Underhill P. R. , Ellison K. A. , Smeltzer W. W.
Published: July 2002

A heating stage which allows Auger electron spectra to be obtained at elevated temperatures (at least 1000 °C) and which is compatible with a fork-type rapid introduction air lock is described. The design provides for temperature measurement with an accuracy of ±5 °C.
The atomic structure of the NiSi2–Si(111) interface
Authors: van Loenen E. J.
Published: July 2002

Several techniques, presently available to study the atomic structure of interfaces are compared. The ion focusing technique, which is based on the principles of ion channeling and blocking is described in detail, and results for the NiSi2–Si(111) system are presented. The interface structure is shown to consist of sevenfold coordinated Ni atoms and the bonding distance across the interface has been measured with an accuracy of 0.008 nm. These results are compared with results obtained from high-resolution TEM lattice imaging and the x-ray standing wave method.
Metal–anion bond strength and room temperature diffusion at metal/GaAs interfaces: Transition versus rare-earth versus Au metal overlayers
Authors: Grioni M. , Joyce J. J. , Weaver J. H.
Published: July 2002

We discuss synchrotron radiation photoemission results for several room temperature transition metal and rare–earth metal GaAs(110) interfaces (Ce, Sm, V, Cr) and Au. Analysis of normalized core intensity attenuation curves shows anion trapping that varies with, but is not entirely controlled by, the ionicity of interface bonds. In particular, very narrow reacted regions were observed for Ce and Sm [3–5 monolayers (ML)]. The reacted region is much wider for the transition metals (9 ML for V, 19 ML for Cr), reflecting a less effective barrier for intermixing. For Au, the amount of As and Ga in the near surface region greatly exceeds that for the transition metals.
Schottky barrier heights of epitaxial Ni–silicides on Si(111)
Authors: Liehr M. , Schmid P. E. , LeGoues F. K. , Ho P. S.
Published: July 2002

The correlation of Schottky barrier height and microstructure has been investigated for three different epitaxial Ni–silicides, type-A, type-B NiSi2 and NiSi, on n-Si(111). All these interfaces can be formed to yield a barrier height of 0.78 eV. This high barrier is obtained only for interfaces with almost perfect structures; otherwise less perfect interfaces formed with improper annealing or impurity incorporation yielded low barrier heights of 0.66 eV. The barrier seems to be primarily controlled by the degree of structural perfection, instead of the stoichiometry and the specific type of epitaxy at the interface. A low interface state density can explain the sensitivity of the barrier height of near-perfect interfaces on minor amounts of impurities, defects, and structural imperfections.
Internal stress in ion beam sputtered molybdenum films
Authors: Sun Sey-Shing
Published: July 2002

Stress in molybdenum films deposited by ion beam sputtering has been studied as a function of deposition parameters, such as accelerating voltage, incident angle, and chamber pressure. It has been found that the physical properties of deposited molybdenum films controlled primarily by the ion beam accelerating voltage and substrate orientation with respect to the ion beam. For films deposited at near normal incidence, measured stresses are highly compressive (2–5 GPa) and increase almost linearly with the accelerating voltage (600–1500 V). Under these conditions, deposited molybdenum films exhibit low resistivity and high optical reflectance. As the substrates are rotated to near grazing incidence, measured stress is either negligible or slightly tensile and are almost independent of accelerating voltage. The extremely high resistivity and low reflectance measured indicates the poor quality of the deposited film at grazing incidence. No significant effect was observed when the chamber pressure was varied between 7×10−5 and 5×10−4 Torr. The observations are interpreted by ‘‘structure zone model’’ and ‘‘atomic peening mechanism’’ (forward sputtering and recoil damage to the depositing films) previously proposed for films prepared by conventional sputtering and evaporation.
The use of nitrogen flow as a deposition rate control in reactive sputtering
Authors: Berg S. , Larsson T. , Blom H-O.
Published: July 2002

It is well known in reactive sputtering that the deposition rate generally drops drastically at a high enough partial pressure level of the active gas to form a compound on the target surface. At the point where the deposition rate drops, there exists a simple relationship between the consumed nitrogen and the deposition rate of stoichiometric films. This abrupt decrease in deposition rate can be measured indirectly by monitoring the processing gas by mass spectroscopy (MS) and studying the discharge by optical emission spectroscopy (OES). We have shown that it is possible to select a desired deposition rate by simply choosing a correct mass flow value of the active gas (nitrogen) while maintaining correct stoichiometry of the sputtered film. This can be achieved by presetting the mass flow of the nitrogen. Thereafter, the rf power is increased to the transition level, where the surface of the target changes from compound to elemental. The combination of mass flow control and diagnostic tools (MS) and (OES) enables precise control of the process.
Ion beam sputter deposited zinc telluride films
Authors: Gulino Daniel A.
Published: July 2002

Zinc telluride is of interest as a potential electronic device material, particularly as one component in an amorphous superlattice, which is a new class of interesting and potentially useful materials. This paper describes some structural and electronic properties of ZnTe films deposited by argon ion beam sputter deposition. Films (up to 3000 Å thick) were deposited from a ZnTe target. A beam energy of 1000 eV and a current density of 4 mA/cm2 resulted in deposition rates of approximately 70 Å/min. X-ray data were featureless for thinner films (1300 Å), giving no evidence of crystallinity. Such data on thicker films (3000 Å) showed some evidence of ordered structure. The optical band gap was found to be approximately 1.1 eV for thinner films (1000 Å) and 1.3 eV for thicker films (3000 Å). Intrinsic stress measurements showed a thickness dependence, varying from tensile for thicknesses below 850 Å to compressive for larger thicknesses. Room temperature conductivity measurements also showed a thickness dependence, with values ranging from 1.86×10−6 Ω−1 cm−1 for a 300 Å film to 2.56×10−7 Ω−1 cm−1 for a 2600 Å film. Measurement of the temperature dependence of the conductivity for these films showed complicated behavior which was thickness dependent. Thinner films showed at least two distinct temperature dependent conductivity mechanisms, as described by a Mott-type model. Thicker films showed only one principal conductivity mechanism.
Room temperature deposition of superconducting NbN for superconductor–insulator–superconductor junctions
Authors: Thakoor S. , LeDuc H. G. , Thakoor A. P. , Lambe J. , Khanna S. K.
Published: July 2002

Reactive dc magnetron sputtering is used to deposit hard, refractory, superconducting thin films of niobium nitride on amorphous (glass) as well as crystalline (sapphire) substrates held at room temperature. Stoichiometric NbN films so obtained possess the desired B1 crystal structure with a distinct (111) texture, and exhibit high (∼16 K) superconducting transition temperature. Room temperature deposition of the high Tc films is achieved primarily by optimizing the reactant fluxes of niobium and nitrogen reaching the substrate, through a systematic study of the nitrogen consumption versus injection characteristics which are found to be an absolute indicator of the quality of NbN formed. Superconductor–insulator–superconductor (SIS) junctions are fabricated by using high Tc NbN as the base electrode, a thin layer of native oxide grown in oxygen plasma or in room air as the insulator, and vacuum deposited Pb as the counterelectrode. The current versus voltage (I–V) characteristics of the junctions exhibit high (∼110) nonlinearity parameter and the superconducting gap parameter for NbN, Δ∼2.8 meV. The transition temperature, superconducting gap parameter, and nonlinearity parameter of the junctions are identical for the films deposited at room temperature with predominant (111) texture as well as the films deposited at elevated temperatures possessing (200) texture.
Induction heated plasma assisted chemical vapor deposition of SiN
Authors: Mito H. , Sekiguchi A.
Published: July 2002

We have demonstrated induction-heated (IH), plasma-assisted, chemical vapor deposition (CVD) of silicon nitride (SiN) films on silicon substrates. The IH plasma is generated in an inductively coupled quartz tube (12.5 mmφ) by supplying high rf power (3–4 kW) at 1 Torr pressure. Intense VUV emissions (120 nm) are radiated from the IH plasma, so it is expected that SiH4 is dissociated by the VUV emissions without ionic collisions. Gas in the IH plasma is thermally excited, so that radicals with long lifetimes are produced. Two deposition modes are now described: deposition mode I is photo (VUV emission) and radical assisted CVD where no plasma comes into contact with the substrates; deposition mode II is glowlike plasma generated around IH plasma assisted CVD. N2 and SiH4 are used as reactant gases. The following results were obtained: deposition mode I: deposition rate, 60 Å/min; refractive index, 1.95–2.05; etching rate (BHF), 270 Å/min; step coverage, excellent; infrared absorption, no observed N–H absorptions; deposition mode II: deposition rate, 500 Å/min; other characteristics are almost the same as deposition mode I films.
Ion-beam sputtered indium tin oxide for InP solar cells
Authors: Aharoni H. , Coutts T. J. , Gessert T. , Dhere R. , Schilling L.
Published: July 2002

The efficiency of indium tin oxide/indium phosphide (ITO/InP) solar cells depends on the rate of deposition of the ITO and the substrate temperature. In the case of rf sputter deposition, both of these parameters should be maintained as low as possible. However, it is still necessary to produce ITO window layers with as low a sheet resistance and high a transmittance as possible. This paper is concerned with the properties of such films fabricated by ion-beam sputtering under the above restrictive conditions. In particular, we have investigated the effects of varying the background partial pressure of oxygen, the film thickness, and the rate of deposition on the electro-optical properties of the films. (i) For very slow deposition rates (∼0.3 Å s−1) and low substrate temperatures (<40 °C), resistivities of <7×10−4 Ω cm have been obtained for films of thickness 250–1200 Å. This was for a partial pressure of oxygen, <10−6 Torr; for a partial pressure of 4×10−5 Torr, the resistivity of the films increased to 2×10−3 Ω cm. (ii) The refractive index increased from 1.95 to 2.00 over the same range of oxygen partial pressure. (iii) For very thin films, <200 Å in thickness, the refractive index decreased to ∼1.75. (iv) Carrier mobility shows a transition from lattice scattering ( μ∼25 cm2 V−1 s−1) to impurity scattering (25< μ<15 cm2 V−1 s−1) for a carrier density n≳3×1020 cm−3. (v) The optical constants vary significantly across the solar spectrum with oxygen partial pressure and film thickness. This should be taken into account in calculations of internal quantum efficiency of solar cells.
Laser spectroscopy of sputtered atoms
Authors: Gruen D. M. , Pellin M. J. , Young C. E. , Calaway W. F.
Published: July 2002

The use of laser radiation to study the sputtering process is of relatively recent origin. Much has been learned from this work about the basic physics of the sputtering process itself through measurements of velocity and excited state distributions of sputtered atoms and the effects of adsorbates on substrate sputtering yields. Furthermore, the identification, characterization, and sensitive detection of sputtered atoms by laser spectroscopy has led to the development of in situ diagnostics for impurity fluxes in the plasma edge regions of tokamaks and of ultrasensitive methods (ppb Fe in Si) for surface analysis with ultralow (picocoulomb) ion fluences. The techniques involved in this work, laser fluorescence and multiphoton resonance ionization spectroscopy, will be described and illustrations given of results achieved up to now.
High pressure studies of Hg0.8Cd0.2Te
Authors: Qadri S. B. , Skelton E. F. , Webb A. W. , Dinan J.
Published: July 2002

Hydrostatic compression measurements have been performed on Hg1−xCdxTe (x=0.2). The pressures of the B3-to-B9 and B9-to-B1 structural transitions are determined to be 2.2 and 6.8 GPa, respectively. Comparison between these values and those for HgTe supports the expectation that Cd reduces the stability range for the B9 phase. It is estimated that this phase should cease to exist at about x=0.73 and that the B3-to-B1 transition should occur at about 4.3 GPa.
Characterization of molecular beam epitaxially grown HgCdTe on CdTe and InSb buffer layers
Authors: Noreika A. J. , Farrow R. F. C. , Shirland F. A. , Takei W. J. , Greggi J. , Wood S. , Choyke W. J.
Published: July 2002

Molecular beam epitaxially (MBE) grown layers of (001)CdTe and (001)HgCdTe were examined by RHEED, DCRC, XTEM, and EDS to assess the effect of growth parameters on crystal perfection. The CdTe layers were further investigated via low temperature photoluminescence (PL) and SIMS analysis to determine potential impurity incorporation from InSb substrates. In both sets of analysis substrate temperatures and substrate preparation were the parameters which most influenced film growth. Double crystal x-ray rocking curve (DCRC) data showed weak substrate dependence in lattice matched (001)CdTe. PL data showed a stronger influence of substrate temperature on radiative defect incorporation. The HgCdTe alloy also showed structural dependence on substrate temperature in XTEM micrographs of precipitate formation which were confirmed by in situ EDS. Lateral compositional uniformity of alloy layers was determined by step-and-repeat infrared transmission measurements across a 3 in. GaAs wafer. The data have indicated an average 300 K cutoff wavelength of 7.05±0.5 μm across a full diameter.
Present status of molecular beam epitaxial growth and properties of HgTe–CdTe superlattices
Authors: Faurie J. P. , Sivananthan S. , Reno J.
Published: July 2002

We report here on recent characterizations of HgTe–CdTe superlattices and on the growth of related novel superlattice systems. X-ray diffraction investigations carried out during the annealing of HgTe–CdTe superlattices have shown that an appreciable interdiffusion occurs at the HgTe–CdTe interface for a temperature of 185 °C, which is the growth temperature. Hg1−xCdxTe–CdTe superlattices have been grown for the first time. Their Hall characterization, along with magnetotransport experiments seem to indicate that high hole mobilities observed in p-type HgTe–CdTe superlattices are due to some type of relationship between the 2D heavy hole gas and the interface state existing in type III superlattices. We report also on the successful growth of a novel strained superlattice system, i.e., HgTe–ZnTe, which appears to be an interesting infrared material.
Boron and indium ion-implanted junctions in HgCdTe grown on CdTe and CdTe/Al2O3
Authors: Bubulac L. O. , Lo D. S. , Tennant W. E. , Edwall D. D. , Robinson J. C.
Published: July 2002

This paper discusses the results of junction formation in p-type HgCdTe material which has been converted into n type by ion implantation processes. In was chosen as the candidate donor impurity because it has been observed to diffuse from the implanted source and to activate electrically in a Hg-vacancy doped material under certain anneal conditions. Our results indicate that In diffuses and activates in both Hg-vacancy doped and As-doped HgCdTe layers in both capped and uncapped with saturated Hg overpressure regardless of the background defect structure of the layer. Several apparently different diffusion mechanisms appear in In profiles giving fast, anomalous high concentration components and slow components with low concentration levels. However, under high temperature (400 °C) capped anneals, a single limited source diffusion mechanism appears to dominate (Deff=8×10−13 cm2/s). This mechanism is attributed to vacancies present in the background. Characteristics of indium implantation into arsenic-doped layers were observed in which n-type electrical activity is indium related and controllable by implant/anneal conditions. p-type electrical activity is due to arsenic and it could be controlled by adjusting the arsenic doping level during epitaxy.
Sputter deposition of Co–Cr thin-film media on high-speed rotating disk substrate
Authors: Niimura Yoshiro , Naoe Masahiko
Published: July 2002

A sputtering system which is capable of depositing films onto the disk substrate, rotating at very high speed in the vacuum chamber, has been developed. The maximum rotational speed of about 10 000 rpm has been attained in the Facing Targets Sputtering apparatus for preparing Co–Cr perpendicular recording disks. Properties of the film deposited on the rotating disk substrates have been investigated with regard to (1) the absolute linear velocity (m/s) of the substrates, and (2) the relation between the rotational speed (rpm) of the substrates and the deposition rate of the film. The experimental results show that the linear velocity realized in this study was not high enough to give the significant effects on intrinsic properties of the films. This means that even such a dynamic motion of the substrate does not bring any negative effects on the microstructure of the film. Meanwhile, it has been found that the effect of the substrate rotation appeared very clearly on the growth mechanism of the film. That is, the dispersion of the c-axis orientation in the Co–Cr film becomes better with the increase of the rotational speed (rpm) of the substrates probably due to the quasiepitaxial growth of the film.
Performance comparison of electrostatic lenses for field emission ion and electron sources
Authors: Burghard Ronald A. , Swanson Lynwood , Orloff Jon
Published: July 2002

Four electrostatic lenses are analyzed with respect to field emission ion and electron sources for beam energies of 5 to 50 keV. The ion sources considered are the hydrogen field ionization and gallium liquid metal ion sources, while the electron source considered is the thermal field emission source. The lenses analyzed are (1) the three-element asymmetric lens of Orloff and Swanson, (2) the previous lens only reversed, (3) a symmetric version of the previous three-element lenses, and (4) the four-element condenser lens of Kurihara. For the extraction voltage (7.5 keV) and working distance (50 mm) used in this study, the asymmetric lens of Orloff–Swanson operating in the acceleration mode typically results in a smaller spot at low beam energies (5 keV), while the four-element lens of Kurihara operating in the acceleration mode results in a smaller spot at higher beam energies (>15 keV).
Epitaxial growth, characterization, and phase diagram of HgZnTe
Authors: Smith E. J. , Tung T. , Sen S. , Konkel W. H. , James J. B. , Harper V. B. , Zuck B. F. , Cole R. A.
Published: July 2002

Epitaxial layers of Hg1−xZnxTe (0.11≤x≤0.22) were grown by the horizontal liquid-phase epitaxy technique on Cd1−yZnyTe substrates with 0≤y≤0.20. The structural and electrical properties of the Hg1−xZnxTe layers were characterized and compared with those of epitaxial Hg1−xCdxTe. It was found that the structural and electrical properties of long-wavelength infrared (LWIR) HgZnTe, when grown on closely lattice-matched CdZnTe substrates, are comparable to those of high-quality epitaxial LWIR HgCdTe. However, the annealing behavior of the Hg1−xZnxTe layers shows a decreased Hg diffusion rate relative to that in Hg1−xCdxTe. Liquidus temperatures of Te-rich ternary (Hg1−zZnz)1−yTey solutions were measured. The preliminary liquidus data indicate that, in the Te corner, the Hg–Zn–Te and Hg–Cd–Te phase diagrams are very similar.
Transmission electron microscope study of Hg-based multilayer structures
Authors: Otsuka N. , Ihm Y. E. , Harris K. A. , Cook J. W. , Schetzina J. F.
Published: July 2002

Mercury-based multilayer structures including the first superlattice containing layers of a narrow-gap diluted magnetic semiconductor Hg1−xMnxTe have been studied by transmission electron microscopy. A quantitative characterization of the interface sharpness of HgTe–CdTe superlattices has been carried out by intensity analysis of satellite spots in electron diffraction patterns. It is shown that interfaces in these structures are highly abrupt with a width of one or two monolayers. No appreciable difference in the interface width is observed between areas near the CdTe buffer and those near free surfaces. These observations suggest that no significant intermixing of layers occurs during the growth of these multilayer structures by molecular-beam epitaxy.
Correlation between resistance behavior and mass transport in Al–Si/Ti multilayer interconnects
Authors: Finetti M. , Suni I. , Armigliato A. , Garulli A. , Scorzoni A.
Published: July 2002

In this work we investigate the correlation between the resistance behavior and the mass transport in narrow line interconnects with a laminated structure incorporating single or multiple layers of Ti in Al–Si. For comparison, homogeneous Al–Si films are also studied. A temperature-ramp resistance analysis is applied at direct wafer level. In multilayer interconnects the resistance change is only detected above the typical failure temperatures of the homogeneous stripes. Different degradation mechanisms are also observed, although the activation energies suggest similar electromigration processes. The improved stability against electromigration in the laminated structures is related to the formation of a continuous barrier of the intermetallic compound TiAl3, preventing voids from propagating across the film.
Impact of step edges on W(001) surface reconstruction
Authors: Zuo J.-K. , Lu T.-M. , Wang G.-C. , Wendelken J. F.
Published: July 2002

Step edges on the W(001) surface can inhibit the reconstruction of the surface at low temperatures. However, the range of this inhibition, an important parameter for theoretical consideration, has been a matter of controversy. In this paper, we report our study on the impact of step edges on both the clean surface and H-induced reconstructions on the monotonically stepped W(001) surfaces using low-energy electron diffraction. First, the spread of the terrace widths which manifests itself as the broadening of the individual splitting beams from two high-density stepped W(001) surfaces (29- and 36-Å average terrace widths) was obtained by quantitative analysis of the angular intensity distribution of the splitting beams. The spread was found to be ∼13 Å for both stepped surfaces assuming a Gaussian terrace width distribution. Second, based on the spread of the terrace width and an assumed inhibition range the reconstruction domain size distributions were obtained by comparing the calculated and measured angular profiles of the superlattice beams (which do not split due to the random antiphase relationship among the domains) from both surfaces. The deduced inhibition range was 8±2 Å for both clean and H-induced reconstruction surfaces. These results contradict the findings of King and of Bauer and co-worker who suggested a long-range (≥20 Å) inhibition. Possible explanations of the discrepancy will be presented.
Preparation and characterization of plasma enhanced chemical vapor deposited silicon nitride and oxynitride films
Authors: Vuillod J.
Published: July 2002

A brief description of the plasma enhanced chemical vapor deposited unit is first presented as well as typical processing conditions used in the elaboration of silicon nitride and silicon oxynitride layers with refractive indices of 1.96 and 1.78, respectively, and with thicknesses superior to 30 nm. The compositional characterization of as-deposited films (prepared at 380 °C) has been carried out with infrared and Auger spectroscopies indicating a composition near the stoichiometry for nitride films (Si/N=0.8), a concentration of 16% of oxygen for oxynitride films, and a small amount of hydrogen. Extensive electrical measurements were made using I–V and C–V techniques as well as deep-level transient spectroscopy on metal-insulator semiconductor structures. Films with resistivities of 5×1016 Ω cm at a field of 2 MV/cm were obtained. The static dielectric constant is around 7 and 5.5 for nitride and oxynitride films, respectively. Finally C–V data indicate an interface state density lower than 3×1011 cm−2 eV−1 at the midgap and a positive fixed charge lower than 1012 cm−2.
Study of the structure and properties of the Ti/GaAs interface
Authors: Kniffin Margaret , Helms C. R.
Published: July 2002

Reactions between Ti thin films and (100) n-type GaAs substrates in the temperature range 250–600 °C were studied by Auger sputter profiling and correlated with electrical measurements. Annealing above 400 °C, caused significant intermixing of the Ti and GaAs, resulting in a layered structure of the type Ti/Ti:Ga/Ti:As/GaAs similar to the results of Wada et al. [Appl. Phys. Lett. 29 (1976)]. Both Ti–As and Ti–Ga compounds were identified by electron diffraction (Kim and Sinclair, unpublished). The effects of annealing on the Schottky barrier behavior were studied by a combination of I–V, C–V, and photoresponse measurements. Upon reaction of the Ti with the substrate, the barrier height saturated at a value of roughly 0.80 eV, a 100-meV increase over the as-deposited value. The effect interfacial impurities left by chemical cleaning procedures on the properties of the Ti/GaAs system was also investigated. Surface preparations, characterized by x-ray photoelectron spectroscopy and Auger electron spectroscopy were found to have a small (barrier heights ranged from 0.69 to 0.73 eV) effect on the as-deposited barrier height.
Optical emission properties of metal/InP and GaAs interface states
Authors: Viturro R. E. , Slade M. L. , Brillson L. J.
Published: July 2002

We have measured optical emission from interface states formed by metal deposition on UHV-cleaved InP(110) and GaAs(110) surfaces by means of cathodoluminescence spectroscopy. Our study reveals discrete levels distributed over a wide range of energies and localized at the microscopic interface. Our results demonstrate the influence of the metal, the semiconductor, and its surface morphology on the energy distributions. The detailed evolution of optical emission energies and intensities with multilayer metal deposition exhibits a strong correlation between the deep gap levels, the Fermi level movements, and Schottky barrier heights. The results demonstrate that in general electronic states deep within the band gap continue to evolve beyond monolayer coverage into the metallic regime.
Low-energy ion induced Auger electron spectra and energy thresholds for some pure elements, compounds, and alloys
Authors: Fan Chuizhen , Yu Zhenjiang , Chen Xuekang
Published: July 2002

By improvements of experimental method, ion induced Auger electron spectra (IAES) of pure elements, compounds, and alloys for 23 samples have been obtained successfully using a combined scanning Auger microscopy/secondary ion mass spectrometry instrument. Ar+ with energy up to 5 keV was the incident ion. The spectra measured are different from that obtained by electron-stimulated Auger, and correspondent Auger electron energies are not more than 500 eV. With increasing atomic number, the intensity of IAES peaks decreases. Some spectra of those samples and energy thresholds of all samples are given here. Many of them are not found yet in publications. The results showed that energy threshold values of elements go up with increasing atomic number and level off in the region of the fourth- and fifth-period elements. Among others, the thresholds of Mg, Al, and Si are 200, 350, and 600 eV, respectively, and much lower than the values reported before.
Change of surface composition of B4C single crystal due to heat treatment
Authors: Inoue S. , Fukuda S. , Hino T. , Yamashina T.
Published: July 2002

For a single crystal of B4C, change of the surface composition due to a heat treatment with temperature range from 600 to 1300 °C was studied by Auger electron spectroscopy analysis. The boron concentration of the surface was continuously measured after the heating temperature became constant. The boron concentration decreased with the heating time and became a steady-state value. The decreasing rate increased as the heating temperature. As the increase of the heating temperature, the boron concentration in the steady state became larger. At 1200 °C, the boron concentration became close to the bulk concentration. Evaporated particles from the surface of B4C were measured by a collector probe to examine the process of the change in boron concentration. It was found that only boron atoms evaporated from the surface. A simple model was applied to explain the change in composition. Estimated activation energies of boron for the diffusion and the evaporation were 4.8 and 2.5 eV, respectively. The present model agreed with the experimental result.
Angle resolved ultraviolet photoelectron spectroscopy study of ultrathin iron films on Si(111) surfaces
Authors: Urano T. , Ogawa T. , Kanaji T. , Fujimoto F.
Published: July 2002

Ultrathin iron films deposited on Si(111) 7×7 surfaces were investigated by low-energy electron diffraction–Auger electron spectroscopy (LEED–AES) and angle resolved ultraviolet photoelectron spectroscopy (ARUPS). On Si(111)7×7 surfaces, iron film grew layer by layer and formed an Fe(111) epitaxial film. At about the stage of monoatomic layer, the LEED pattern changed from 1×1 to 2×2 superstructure owing to annealing above 400 °C. At the same time a shift of Fe d-band peak to the higher binding energy side by 1.2 eV was observed by means of ARUPS measurements. It was also found that the peak intensity peculiar to 2×2 structure was sensitive to the angle of incident light as well as to the direction of emission.
Substrate temperature dependence of hillock, grain, and crystal orientation in sputtered Al–alloy films
Authors: Kobayashi Tsukasa , Kitahara Hiroaki , Hosokawa Naokichi
Published: July 2002

The effects of substrate temperature during deposition on hillock, grain and crystal orientation were investigated for Al, Al–Ti, Al–Si, Al–Si–Ti, and Al–Cu films. The films were deposited by magnetron sputtering in the substrate temperature range from room temperature to 350 °C and followed by vacuum annealing at 400 °C for 5 min. Hillock density was varied as a function of the substrate temperature in a different manner for each investigated material. The substrate temperature during deposition is a very important factor for suppressing the hillock formation. A close relationship between hillock density and grain size was observed. This was modified when the substrate temperature was changed. This is probably related to the change of grain texture morphology determined by the x-ray diffraction measurements.
Dynamics of polyimide curing and degradation: An i
n s
i
t
u x-ray photoemission study
Authors: Anderson Steven G. , Meyer H. M. , Atanasoska Lj. , Weaver J. H.
Published: July 2002

Dynamic time- and temperature-dependent x-ray photoemission studies of polyimide (PI) show the evolving valence bands and core level spectra, starting from partially polymerized PI and continuing through PI degradation at 500 °C. For temperatures below∼200 °C, we see little change, but curing above 300 °C is accompanied by changes in core level and valence-band positions relative to the Fermi level. These changes are associated with the removal of defect induced states in the band gap of the polymer. Comparison of the valence-band spectrum of the fully cured PI to recent electronic structure calculations shows good agreement. PI degradation occurs at temperatures between 450 and 500 °C, where there is a decrease in carbonyl and pyromellitic dianhydride benzene ring carbon 1s emission due to loss of CO or CO2, and an increase in carbon atom density. Nitrogen 1s spectra exhibit the growth of new low binding energy components which indicate that the feature previously assigned to an isoimide structure is a metastable reaction intermediate of the degradation process. The oxygen 1s features are primarily affected in the carbonyl oxygen peak, indicating ether oxygen bonds are more stable with respect to high temperatures.
A high ionization efficiency source for partially ionized beam deposition
Authors: Mei S.-N. , Lu T.-M.
Published: July 2002

The design and testing of a high ionization efficiency source for a partially ionized beam deposition (PIBD) system are described. The vaporized material from a crucible is partially ionized at the crucible exit, where the vapor has its highest density. The system can provide ionization efficiencies of up to 5% (ion/atom ratio) at ion energies ranging from 0.2 to 6 keV. Measurements of the ion current versus substrate bias potential along with the deposition rate are reported using Al as source material. A uniform ion beam intensity has been obtained over a 6-cm-diam substrate at a distance of 30 cm above the source. If the ionization source is placed a few centimeters away from the crucible, as it is in the conventional PIBD design, the ionization efficiency would reduce to <0.2% (ion/atom ratio). The reduction can be easily explained by geometry consideration.
Thermocouple mounting on semiconductor samples
Authors: Blair D. S. , Fowler G. L.
Published: July 2002

We have designed an alternate method of attaching a thermocouple to a semiconductor which is both simple and reliable. It consists of a tungsten base alloy thermocouple threaded through a hole in the sample and held in place by a tantalum strap. (AIP)
Titanium surface chemistry: Chlorine adsorption
Authors: Watson P. R. , Mokler S. M. , Mischenko J.
Published: July 2002

We have studied the adsorption of chlorine on the (0001) and (101̄0) surfaces of a titanium single crystal using Auger electron spectroscopy, low-energy electron diffraction (LEED), and thermal desorption spectroscopy. Chlorine adsorbs dissociatively on both surfaces and does not desorb below 750 °C, a temperature limit imposed by the phase change in bulk Ti. Chlorine overlayers are somewhat sensitive to electron-beam stimulated desorption. On the (0001) surface no ordered LEED patterns were observed unless a high-coverage surface was annealed to a temperature of 620 °C. The resulting (16×16) LEED pattern can be interpreted as due to a coincidence lattice on the Ti substrate, with the Cl unit mesh vectors aligned with that of Ti(0001). In contrast to earlier reports, the (101̄0) surface does not appear to reconstruct. On this surface, an annealed Cl overlayer produces simpler LEED patterns, which are probably due to Cl atoms residing in troughs in the (101̄0) surface.
Ferromagnetic order and critical behavior at surfaces of ultrathin V(100)p(1×1) films on Ag(100)
Authors: Rau C. , Xing G. , Robert M.
Published: July 2002

The magnetic order and critical behavior of well-defined (100)p(1×1) surfaces of ultrathin (1–7 monolayers) vanadium films deposited on atomically clean and flat Ag(100) substrates is studied by electron capture spectroscopy, a novel method which probes electron spin polarization (ESP) at the topmost surface. For all investigated films, the long-ranged ESP is nonzero, demonstrating the existence of long-ranged ferromagnetic order at the film surface. For a 5-monolayer-thick film, ferromagnetic order sets in at a critical surface temperature TCs=475.1 K. In the temperature range from 200 to 475.1 K, the ESP of the topmost surface layer follows the power law (TCs−T)β, with β=0.128±0.01. This result is in good agreement with the exact value β= (1)/(8) of the two-dimensional Ising model.
Nature of bonding between alkali metals and silicon surface
Authors: Batra Inder P. , Bagus Paul S.
Published: July 2002

In recent literature, diverse views have been expressed regarding the nature (ionic versus covalent) of bonding between alkali metals and the Si(001)-(2×1) surface. Also unsettled is the issue as to whether the metallicity upon K adsorption is due to the partial occupancy of the dangling bonds or due to the metallic K chain. The resolution of these outstanding problems is sought by performing electronic structure total energy calculations using cluster as well as slab models. The cluster model calculations have used an ab initio self-consistent field Hartree–Fock technique, whereas the slab model has employed pseudopotentials within the density functional formalism. Using a variety of criteria, we conclude that the bond is strong and ionic with negligible covalent effects. At the monolayer coverage, the charge from the adsorbed potassium atoms is transferred into the empty, antibonding dangling bond surface states resulting in the metallization of the Si(001) substrate surface. The presence of the dangling bond states prevents the alkali monolayer from metallization.
Overlayer interactions with (HgCd)Te
Authors: Davis G. D.
Published: July 2002

The interactions between both cleaved and ion-sputtered (HgCd)Te and deposited overlayers are reviewed. The overlayers are classified into four groups—ultrareactive, reactive, intermediate reactive, and unreactive—based on the relative heats of formation of the overlayer telluride and HgTe and CdTe. Ultrareactive overlayers react with both HgTe and CdTe to form an interfacial metallic telluride and elemental Hg and Cd (which are lost from the interface), while reactive overlayers react only with the HgTe component. Once the HgTe is depleted from the surface region, further deposition results in growth of a metallic film. Unreactive metals, on the other hand, do not react with the surface, but form a stoichiometric interface. Finally, the extent of interactions between intermediate overlayers and(HgCd)Te depend on other factors, including the stability or reactivity of the surface and substrate material, the heats of cation alloying, and the propensity of the overlayer element to diffuse into (HgCd)Te.
Beta energy driven uniform deuterium–tritium ice layer in reactor-size cryogenic inertial fusion targets
Authors: Martin A. J. , Simms R. J. , Jacobs R. B.
Published: July 2002

We have studied the effectiveness of beta heating on driving a deuterium–tritium (DT) ice layer toward uniformity within spherical inertial fusion targets. Beta heating results from the deposition of energy from the beta particles from the tritium decay in these targets. These targets are enclosed in a constant temperature environment. This study first considered a one-dimensional heat transfer model of an idealized target, geometry, and environment. We concluded that beta energy deposition can drive a nonuniform DT ice layer towards uniformity. The maximum rate at which this redistribution can occur is given by dδ/dt=δ̇=−δ/θTC, where δ=DT ice thickness in excess of that for a uniform layer and θTC=a time constant ≊1500 s. This translates to a factor of 10 reduction in nonuniformity every hour. We also evaluated, and continue to do so, the consequences of deviations from the idealized case assumptions and the selection of certain experimental parameters, on the actual behavior of DT ice in such cryogenic targets. The status of this work is such that we have confidence in the use of beta heating to drive the DT ice toward uniformity for reactor-size targets (∼1 mm and larger in diameter).
Deep level formation and band bending at metal/CdTe interfaces
Authors: Shaw J. L. , Viturro R. E. , Brillson L. J. , Kilday D. , Kelly M. , Margaritondo G.
Published: July 2002

We present depth resolved photoluminescence and soft x-ray photoemission spectra of cleaved (110) CdTe interfaces with Au and In measured as a function of thermal and laser annealing. These techniques reveal Fermi-level positions at the processed interfaces which are clustered around discrete energies, which in turn coincide with the energies of deep levels produced by interdiffusion and reaction at metal/CdTe interfaces.
Deposition and properties of zinc cadmium telluride films
Authors: Peters Michael G. , Fahrenbruch Alan L. , Bube Richard H.
Published: July 2002

Zinc cadmium telluride solid solution films with zinc/cadmium ratios as high as 40% have been deposited onto graphite substrates by the close-spaced vapor transport method, using sources consisting of polycrystalline zinc cadmium telluride or mixtures of cadmium telluride and zinc telluride powders. High zinc concentrations in the films have been obtained by using small temperature differences for atmospheric pressure depositions, and by depositions under low pressures (0.3 Torr) for larger temperature differences. Hole densities of 5×1015 cm−3 were obtained with no intentional doping and with no dependence on the zinc concentration. Heterojunctions with cadmium sulfide were prepared to explore the junction properties of these films.
The effect of heavy-ion bombardment on the properties of hard a-C:H (i-C) films
Authors: Zou J. W. , Schmidt K. , Reichelt K. , Stritzker B.
Published: July 2002

a-C:H films with high hardness (>3500 kp/mm2 ) and high internal stress have been bombarded with 4-MeV Ni+ ions at several doses. Hardness, internal stress, and hydrogen content were measured as a function of Ni+ dose. It was found that at doses between 3×1012 and 3×1013 ions/cm2 the hardness decreases. At doses below 1013 ions/cm2 the internal stress increases above its original value. Hydrogen concentration and internal stress decrease in the ion range between 3×1013 and 1015 ions/cm2. For large doses the three properties reach a constant value.
Distribution of intermediate oxidation states at the silicon/silicon dioxide interface obtained by low-energy ion implantation
Authors: Benkherourou O. , Deville J. P.
Published: July 2002

This work has been undertaken to understand the morphology of Si/SiO2 interfaces obtained by low-energy ion implantation. The crystallinity of the interface is determined by the observation of tetrahedral configurations [Si–(Si4−x–Ox) with x=0, 1,...,4] of silicon atoms bound to oxygen and/or silicon. The distribution over the whole interface also has been considered and the amorphous dioxide has been characterized by its interfacial depth and compared with the theoretical models such as the random bonding model or the random mixture model.
Neutralization and bonding mechanisms of shallow acceptors at grain boundaries in polycrystalline silicon
Authors: Kazmerski L. L. , Nelson A. J. , Dhere R. G. , Yahia A. , Abou-Elfotouh F.
Published: July 2002

Interactions between shallow acceptors (B, Al, Ga, and In) and hydrogen in polycrystalline Si are investigated. The bonding mechanisms involved in the acceptor neutralization process at grain boundaries are examined using microanalytical techniques. Differences in the incorporation of molecular and atomic hydrogen, and corresponding variations in electrical passivation at grain boundaries, are observed. Low-temperature Auger difference spectroscopy confirms Si–H bonding to dominate B, Ga, and In-doped cases, with no direct acceptor–hydrogen bonding. Al-rich grain boundaries show H-complex and hydroxyl bonding. The data confirm chemical bond strength trends with B<Ga<In. Volume-indexed Auger electron spectroscopy is utilized to compare bonding and H distributions in B- and Al-rich grain boundary regions.