bluuebunny/crossref_metadata_2025 huggingface dataset:
Source of radiation damage to MOS devices during S-GunR metallization
Authors: Vossen J. L. , O’Neill J. J. , Hughes G. W. , Taft F. A. , Snedeker R.
Published: July 2002

A study of radiation damage to MOS capacitors metallized using an S-Gun magnetron sputtering source has shown that hole traps are created that cannot be annealed out at metal–sinter temperatures up to 500°C. These hole traps can be thermally emptied by 500°C annealing but subsequent high–energy irradiation results in larger flatband–voltage shifts for S-Gun metallized capacitors than for evaporated Al capacitors. Precoating the oxides with 100 Å of evaporated Al resulted in a reduction in this damage. Precoating with 300 Å of evaporated Al eliminated the damage entirely. To determine whether magnetron sputtering damage was due to electron bombardment or vacuum ultraviolet (VUV) irradiation, oxides were precoated with 100 and 300 Å of evaporated aluminum and then irradiated with 600 eV electrons to a dose of 500 μC/cm2. This was the estimated maximum dosage that could occur during magnetron–sputtering metallization. The electron induced flatband shift could be annealed completely at 450°C for 40 min in forming gas. After subsequent 1 MeV electron irradiation to a dose of 106 rad the threshold-voltage shifts for 600 eV electron bombarded samples were the same as for those not bombarded. Since 600 eV electron bombardment damage can be annealed completely while magnetron-sputtering damage cannot we conclude that S-Gun damage is caused by VUV photons. In actual MOS integrated circuits a polysilicon gate of any reasonable thickness should be adequate for absorbing the photons of energy ?8 eV that create radiation damage in SiO2, and no damage should occur.
Physical adsorption studies with the vacuum microbalance
Authors: Robens E.
Published: July 2002

The survey deals with the application of gravimetric measuring techniques to the investigation of physical adsorption processes. The principal topics covered in this paper are the definition of the term ’’adsorption’’; the types of surfaces under investigation; the most important measuring procedures, i.e. measuring isotherms, measuring isobars, and evaluating the results; the advantages, limitations, and typical errors involved in gravimetry compared with competing methods; and limitations and development perspectives of gravimetric investigations of physisorption.
Furnace profile effects on glass shell formation
Authors: O’Holleran T. P. , Downs R. L. , Homyk B. D.
Published: July 2002

In the course of blowing glass shells in a furnace drop tower it has been observed that furnace temperature profile affects shell aspect ratio. Wall uniformity appears less sensitive to temperature profile as long as some minimum-time/temperature history is achieved for a given glass composition. Quantitative results will be reported from experiments wherein the furnace temperature profile is systematically varied and the resultant shells are statistically analyzed for aspect ratio and wall uniformity.
Photoemission studies of heterojunction interface formation: Ge–GaAs(110) and Ge–Si(111)
Authors: Margaritondo G. , Stoffel N. G. , Katnani A. D. , Edelman H. S. , Bertoni C. M.
Published: July 2002

A comparison between the formation mechanisms of Ge–GaAs(110) and Ge–Si(111) interfaces is presented. The localized valence band states and core-level states were detected by photoemission spectroscopy with synchrotron radiation. Evidence was found that both kinds of interfaces are sharp and that Ge forms smooth overlayers at room temperature. The shifts in energy of the localized electronic states saturates at a much earlier stage of the interface formation for Ge–GaAs than for Ge–Si. The measured band discontinuities sharply disagree with the predictions of ’’linear’’ interface models. More sophisticated interface models give band discontinuities in excellent agreement with our experimental results for Ge–GaAs—while no satisfactory theoretical explanation is currently available for our Ge–Si results.
Atomic structure of GaP (110) and (111) faces
Authors: Lee B. W. , Ni R. K. , Masud N. , Wang X. R. , Wang D. C. , Rowe M.
Published: July 2002

Low energy electron diffraction (LEED) intensities have been measured for the (110) and (111) faces of GaP. The LEED intensities of the (110) face have been analyzed using a dynamical multiple-scattering model of the diffraction process. The intralayer multiple scattering is treated exactly, while for the interlayer multiple scattering, the renormalized-forward-scattering method is used. Comparison of the calculated and observed LEED intensities suggests that both the Ga and the P atoms on the (110) face may exhibit a contracted outermost layer spacing with a rippled geometry. The surface layer is compressed by about 5% such that the top layer spacing is reduced by 0.1 Å. The P atoms protrude from the surface, whereas the Ga atoms are displaced inward such that no nearest-neighbor bond lengths are altered. LEED intensity analysis of the first order beams indicates that the bond-rotational angle ω is approxiimately 27 °. The quality and stability of the LEED patterns of the Gap (110) and (111) faces have been compared with the LEED patterns of the GaAs (110) and (111) faces. It is concluded that the Gap (110) face is less stable than the GaAs (110) face, but the Gap (111) face is far more stable than the GaAs (111) face. Phosphorus atoms start vaporizing from the GaP (111) face at an annealing temperature of 650 °C. Continued heating at 650 °C for 10 min resulted in a complete vaporization of phosphorus atoms and left a pure gallium surface layer on the GaP (111) face. A clear 1×1 threefold symmetry LEED pattern was observed on this Ga and Gap (111) surface. This indicates that the gallium atoms crystallize on the Gap (111) face and it appears reasonable to conclude that a good Schottky contact would be relatively easy to obtain on the GaP (111) face.
Molecular beam epitaxy of Ge–GaAs superlattices
Authors: Chang C.-A. , Chu W. -K. , Mendez E. E. , Chang L. L. , Esaki L.
Published: July 2002

We have fabricated Ge–GaAs superlattices on (100) GaAs over a wide range of individual layer thickness by molecular beam epitaxy. The superlattices have excellent surface finish, and high epitaxial quality in terms of low defect density and well-resolved periodicity. The effect of interdiffusion significantly affects the periodic structure only for ultrathin layers of the order of a few tens of angstroms.
Ultraviolet grating polarizers
Authors: Sonek G. J. , Wagner D. K. , Ballantyne J. M.
Published: July 2002

Wet and dry processing technologies are applied to the development of high-aspect-ratio gratings in SiO2. Planar gratings having nearly vertical sidewalls and periods of 3000 Å are used as the basic structure for generating ultraviolet polarizers which perform at wavelengths well below 3000 Å. Extinction ratios of 0.5 at wavelengths of 2400 Å have been obtained. With new techniques available for generating fine-period surface gratings, it should be possible to fabricate planar polarizers with high polarization efficiencies at even shorter wavelengths.
Masked ion-beam lithography: A feasibility demonstration for submicrometer device fabrication
Authors: Bartelt J. L. , Slayman C. W. , Wood J. E. , Chen J. Y. , McKenna C. M. , Minning C. P. , Coakley J. F. , Holman R. E. , Perrygo C. M.
Published: July 2002

Masked ion-beam lithography (MIBL) is a high-resolution pattern-replication process that offers high throughput capability with submicrometer resolution. In MIBL, a collimated beam of protons is directed through a mask to expose a resist-covered wafer in proximity to the mask. We report here on four key MIBL technology issues: (1) mask technology, (2) radiation-damage effects, (3) resist materials, and (4) fabrication of NMOS devices using MIBL. We have established a process for fabricating thin (0.7 μm) silicon-membrane masks with submicrometer e-beam-generated gold absorber patterns. We have evaluated mask-induced beam scattering (<0.4° for channeled 175-keV-protons) and mask in-plane thermal distortions (<0.1 μm over 1 cm2 for 0.1 W/cm2 beam power) which are the principle factors affecting resolution and throughput. Radiation-damage effects were studied by simulating MIBL fabrication of MOS test chips. No statistically significant radiation effects were found after annealing at 450°C. We have demonstrated submicrometer resist patterning in both positive (PMMA) and negative (PS) resists, and have used these resists in the fabrication of submicrometer-gate NMOS test devices using MIBL exposures on all levels.
Ion beam exposure profiles in PMMA–computer simulation
Authors: Karapiperis L. , Adesida I. , Lee C. A. , Wolf E. D.
Published: July 2002

A comprehensive Monte Carlo program (piber) has been developed for the simulation of ion beam exposure of resists. piber has been used to study ion ranges, backscattering coefficients, and energy-loss distribution data for various combinations of incident ions and multilayered targets. For lithographic applications, the spatial ion energy-loss distribution in polymethyl methacrylate (PMMA) generated with piber for a δ-function exposure is convoluted with realistic incident ion beam shape (Gaussian, square, etc.) to produce latent images. A string development model is then used to generate developed ion beam exposure profiles in PMMA. The developed profiles for isolated lines have been studied as a function of parameters such as ion energy, resist thickness, and exposure dosage. Closely spaced lines have also been simulated in order to study proximity effects. It is demonstrated that proximity problems are greatly reduced in comparison with electron beam exposed patterns.
Photoelectric properties of CdS–MgPc heterojunction solar cells
Authors: Wagner H. J. , Loutfy R. O.
Published: July 2002

Heterojunction organic solar cells made by sequential deposition of very thin films of cadmium sulfide (CdS) and magnesium phthalocyanine (MgPc) onto a conductive glass substrate have been studied. The short circuit photocurrent Isc under AMO illumination approached 160 μA/cm2 and an open circuit voltage of 0.69 V was obtained. The fill factor ff ranged from 20% to 40%. The action spectra and capacitance-voltage measurements indicated that the active region is located within the MgPc film at the CdS–MgPc interface. The optimum thickness of the CdS and MgPc layers have been found to be 100 and 60 nm, respectively. A band model of the heterojunction is proposed, which accounts for the observed results.
Silicon MBE apparatus for uniform high-rate deposition on standard format wafers
Authors: Bean J.C. , Sadowski E.A.
Published: July 2002

The design and operation of a second generation silicon MBE apparatus are described. A large sample loading interlock permits rapid introduction of standard format 3–4-in.-diam silicon and sapphire substrates. Silicon and metallic species are deposited from dual e-beam evaporation sources at rates of up to 1/3 μm/min. Dopants are introduced by evaporation from conventional Knudsen cells or by simultaneous, low energy ion implantation. Silicon, metal and ionized dopant fluxes are directly sensed and regulated to within ∠1% of preprogrammed values. Rotation of the substrate yields deposition uniformity of ?1% across a 3-in. wafer. The system includes instrumentation for low and high energy electron diffraction, Auger electron spectroscopy and residual gas analysis.
The composition of oxides grown on PbInAu films by rf oxidation
Authors: Baker J. M. , Magerlein J. H. , Johnson R. W.
Published: July 2002

Oxides grown on PbInAu alloys using a combined thermal and rf oxidation process have been examined with x-ray photoemission spectroscopy (XPS or ESCA) and ellipsometry. The oxides were prepared on alloy films deposited at 300 K containing 13 and 26 at. % In in the PbIn phase and on fine-grain alloy films deposited at 95 K containing 13 at. % In. Following an in situ thermal oxidation at 75 °C, the films were rf-plasma oxidized while mounted on an electrode coated with either In or photoresist. The XPS spectra showed that both lead oxide and indium oxide were present, in agreement with previous findings that the bulk of such oxides consists of a layer of In2O3 overlying a layer of PbO. The binding energy of the Pb 4f peak from the oxide was shifted by 0.9–1 eV from the metal peak, a shift characteristic of PbO. Analysis of the XPS intensities based on a layered structure indicated that oxides on the films deposited at 300 K consisted of about 2.7 nm of In2O3 on top of 1.6 nm of PbO. Oxides on the fine-grained alloy were composed of about 4.3 nm of In2O3 and only about 0.4 nm of PbO. The ellipsometric determination of the total thickness agreed with the XPS thickness. The increased amount of In2O3 on the fine-grained film is attributed to the increased availability of In during oxidation as a result of enhanced diffusion through the grain boundaries of the metal film.
Surface donors and acceptors on GaAs and InP exposed to oxygen
Authors: Nedoluha A.
Published: July 2002

A quantitative analysis of existing experimental data on the surface Fermi energies of vacuum- cleaved n- and p-type GaAs and InP as a function of oxygen exposure has been performed. A systematic approach has been developed for a two-level model with surface acceptor and donor energies Ea, Ed and densities Na,Nd to determine the admissible regions in the Ea,Ed plane. Two admissible energy regions are found for GaAs, but just one very restricted region for InP. With some reservations, the conventional assignments for Ea,Ed in GaAs and InP may be considered as compatible with these admissible regions. The derived dependence of Na,Nd on oxygen exposure, both for GaAs and InP, suggests the existence of two oxidation mechanisms, the first active at low surface exposures and saturating at 104–105 Langmuir, the second becoming dominant at 0.02–  0.05 monolayers of surface oxygen coverage and saturating at high-exposure levels.
Growth and photoluminescence characterization of a GaAsxP1−x/GaP strained-layer superlattice
Authors: Gourley P. L. , Biefeld R. M.
Published: July 2002

We have succeeded in growing a GaAsxP1−x/GaP strained-layer superlattice (SLS). The structure was grown by alternate metal–organic chemical vapor deposition of thin (60 Å) layers (20 each) of GaAs0.4P0.6 and GaP. These layers were deposited onto a GaAsxP1−x layer which was graded in composition from x = 0 (composition of underlying GaP substrate) to x = 0.2 (average composition of SLS). Photoluminescence studies of the SLS were carried out to determine the optical band gap. At T = 78 K, the emission from the SLS exhibits a dominant peak at 2.03 eV, as well as weaker peaks at higher energies. We attribute these peaks to direct transitions between SLS conduction and valence band states. The measured energies for the fundamental gap and higher energy transitions are in good agreement with recent theoretical results.
Comparative LEED studies of AlxGa1−xAs(110) and GaAs(110)–Al(ϑ)
Authors: Kahn A. , Carelli J. , Miller D. L. , Kowalczyk S. P.
Published: July 2002

LEED intensity profiles recorded from AlxGa1−xAs(110) MBE surfaces are compared with data obtained from GaAs(110)-Al(ϑ) annealed interfaces. This comparison confirms the hypothesis of a heat induced Al–Ga replacement reaction and the formation of AlGaAs when Al is annealed on GaAs(110). AlAs(110) produces I–V profiles very different from those of GaAs(110) and preliminary modeling computations indicate small surface atomic reconstructions. The effect of the elemental As layer used to protect AlxGa1−xAs(110) surfaces during ambient transfer is also investigated.
Chemisorbed hydrogen on a-carbon films
Authors: Nyaiesh A. R. , Nowak W. B.
Published: July 2002

Hard, relatively transparent, amorphous carbon films have potential applications as wear-resistant coatings, including those in the optical industry. We have investigated some of the effects of elevated temperature on these films, deposited by glow discharge from methane. Differential scanning calorimetry (DSC) has shown a broad, asymmetric, exothermic peak at about 550 °C and a larger energy release at about 750 °C. The latter corresponds to a structural transformation (graphitization) and the sample becomes soft and black. The former appears to correspond to the release of hydrogen, similar to Si:H films. An analysis shows that the energy released, as measured in the DSC, is consistent with literature values for the energy of chemisorbed H on carbon and for the amount of ‘‘unbonded’’ H observed from a-carbon films. Models are presented for the film structures needed to account for this chemisorbed H and for the film densities and transmission electron microscope images.
Interaction of thin layers of Al and Ge with cleaved (Hg,Cd)Te surfaces
Authors: Davis G. D. , Byer N. E. , Daniels R. R. , Margaritondo G.
Published: July 2002

The interaction of Hg0.72Cd0.28Te substrates with submonolayer-deposited films of Al and Ge has been investigated by ultraviolet photoelectron spectroscopy (UPS) using a sychrotron radiation source. The surfaces of the p-type samples were formed by cleaving in ultrahigh vacuum—a process which resulted in n-type surfaces. Very thin layers of Al(0.2–1 Å) were found to interact very strongly with the surface, causing a dramatic loss in the amount of Hg at the surface and a much smaller loss of Cd. As a result, the measured Cd/Hg concentration ratio increased by more than a factor of 2 for 1 Å of Al. At the same time, the valence-band features shifted downward in energy, reflecting an apparent change in the local band gap. In contrast, Ge was relatively inert with regard to the cleaved surface and caused little change in the substrate composition. The behavior of both deposited films can be predicted from the decreasing thermodynamic stability of Al2Te3, CdTe, HgTe, and GeTe and may be important to the formation of good Ohmic contacts.
The Si–SiO2 interface: Correlation of atomic structure and electrical properties
Authors: Hahn P. O. , Henzler M.
Published: July 2002

The roughness at the Si–SiO2 interface has been determined quantitatively on an atomic scale by SPA-LEED (spot profile analysis of low energy electron diffraction) in ultrahigh vacuum after removal of the oxide. At the Si–SiO2 interface the steps are randomly distributed. With the help of model calculations the measured spot broadening provides the step atom density and therefore the roughness on an atomic scale. The roughness will be decreased by low oxidation rates (thick oxides, dry atmosphere) and appropriate annealing in N2 and will be increased by high oxidation rates (thin oxides and wet atmosphere). Furthermore metal oxide semiconductor (MOS) structures were built on chips which were also suited for LEED measurements. Hall mobilities for Si(111) p-channel inversion layers MOS-FETs with varying roughness at the Si–SiO2 interface have been measured at temperatures between 4.2 K and room temperature. It was found that there exists a strong correlation between Hall mobility and atomic roughness at high inversion, nearly a proportionality. Even at room temperature the transistors with the lower interface roughness exhibit the higher mobility. Further quasistatic capacitance–voltage (C–V) measurements have been performed on Si(111) MOS structures with different but well-known atomic roughness. The results demonstrate a strong correlation between atomic roughness and interface state density too, even after an additional postmetallization-annealing (PMA) treatment. A simple model which is associated with each kind of step atom, i.e., edge or kink atoms, suggests the creation of a dangling bond and therefore, a surface state can explain the result. Assuming that ionized atoms which are responsible for Qfix are located preferentially at those steps or kinks which are also correlated to the dangling bonds at the interface, we confirm the general opinion that Qfix and surface states have at least one common physical origin: the atomic roughness.
The nuclear microprobe and its applications to controlled fusion research
Authors: Doyle B. L.
Published: July 2002

A nuclear microprobe analysis system attached to Sandia’s EN tandem Van de Graaff accelerator is described. A magnetic quadrupole doublet lens is used for the final focus to obtain beams of 2 μm diameter. Several illustrative applications of the microprobe involving its use in the 1D, 2D, and 3D profiling analysis of fusion reactor components are given.
Surface morphology of platinum modified aluminide coatings
Authors: Boone D. H. , Deb P. , Purvis L. I. , Rigney D. V.
Published: July 2002

The processing variables which lead to the rough, convoluted surface topologies of platinum modified aluminide coatings were studied. Platinum deposition techniques such as electroplating, ion plating, and sputtering were examined as were postplating diffusion treatments and aluminizing processes. It was found that while the initial Pt surface could be varied by the deposition process and procedures selected, the principal factor influencing surface topology was Pt substrate (IN-738) interdiffusion. Subsequent aluminizing processing had a much smaller additional effect. The effects of the surface roughness and phases and porosity found in the Pt layer on subsequently aluminized coatings performance are not known.
Contact resistance behavior of titanium nitride
Authors: Ernsberger C. , Nickerson J. , Miller A. , Banks D.
Published: July 2002

This paper describes a highly automated contact resistance probe developed as part of our study of the contact properties of materials based on stoichiometric titanium nitride. Comparative results are shown for selected TiN samples, noble metal, and non-noble metal contacts under conditions of accelerated environmental aging and wear. Contact resistance and its temperature dependence as a function of H2O+O2 levels present during reactive sputtering are also presented.
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u calibration of the sensitivity factor S of a quadrupole mass spectrometer for hydrogen and argon during rf sputtering for the growth of thin a-Si:H layers
Authors: Swart P. L. , Aharoni H.
Published: July 2002

Calibration curves for the sensitivity factor S in a quadrupole mass spectrometer for Ar and H2 are presented. The data are gathered in a sputtering system for which the partial pressures of Ar and H2 (10−2–10−3 Torr and 10−3–10−4 Torr, respectively) are appropriate for sputtering of hydrogenated amorphous silicon (a-Si:H). A continuous sampling system added to the sputtering system enables in situ mass spectrometry before and during sputtering. The method can be used for different vacuum systems, mass spectrometers, and residual gases. It enables identification of contaminants which may have a considerable effect on the semiconductor properties. This can serve to obtain both a better quality material and to bring about more reproducible results. The relationship between the mass spectrometer ion current and the partial pressure of Ar is found to be nonlinear. However, it is possible to approximate the curve by two straight line segments, with a break point at 1.6×10−5 Torr. The pressure reduction ratios of the sampling aperture is not constant for Ar, but is a slightly decreasing function of pressure at a rate of 8.6×105 Torr−1 for an aperture with a diameter of 1.5 mm. These effects were not observed for hydrogen over the range of pressures investigated. With more than one gas present, it was observed that the introduction of argon into the vacuum system influences the ion current reading of the mass spectrometer for the other gases. This phenomenon is thought to occur as a result of a charge exchange interaction.
Quantitative interdiffusion studies of noble metal/Si(111)-7×7 interfaces by angle-resolved Auger electron emission
Authors: Chambers S. A. , Greenlee T. R. , Howell G. A. , Weaver J. H.
Published: July 2002

Polar-angle resolved Auger electron emission and related modeling have been used to determine quantitative details of composition and diffusion phenomena in the Cu/Si(111) and Au/Si(111) interface systems. The extent of Si outdiffusion increases with coverage in a gradual fashion for Au, with characteristic diffusion lengths (CDL) ranging from 18% of the overlayer thickness at a 2 Å coverage to 39% at 20 Å. In contrast, Si CDL values in Cu increase abruptly from 20% of the overlayer thickness at 2 Å to ∼35% at coverages from 5 to 20 Å. Au diffuses deeply into the Si substrate, whereas Cu indiffuses only slightly (CDL=1–2 Å). These model predictions are consistent with the more substantial lattice disruption brought about by Au, leading to no long-range order in the overlayer, and the persistent diffusion of Si to the surface of 150-Å-thick Au overlayers.
Photoplasticity and fracture in HgCdTe
Authors: Pellegrino Joseph , Galligan J. M.
Published: July 2002

We have observed a time delay in HgCdTe in the photoplastic response of these crystals. The magnitude of the time delay and the total change in stress Δσ are dependent on the wavelength of the irradiation. The observation of a time delay provides a basis for establishing that the photoplastic process is a dynamic one, in contrast to prior treatments of the problem as a static process. We also present data on the influence of light on the fracture toughness of the crystals.
Raman characterization of Hg1−xCdxTe and related materials
Authors: Amirtharaj P. M. , Tiong K. K. , Parayanthal P. , Pollak Fred H. , Furdyna J. K.
Published: July 2002

We report Raman scattering (RS) measurements from Hg1−xCdxTe (x≊0.2) and related materials HgTe, Hg1−xMnxTe (x≊0.1 and band gap ∼100 meV at 77 ° K) at 77 °K and Br/methanol polished 〈100〉 CdTe at 300 °K. Polarization dependent RS from the three principal faces, i.e., 〈100〉, 〈11̄0〉, and 〈111〉 of Hg1−xCdxTe and HgTe was studied and the symmetries of the various spectral features were identified. All measurements were made in the back-scattering geometry using the 5145 Å line of the Ar+ laser. In addition to the q=0 transverse and longitudinal optical (TO and LO) phonon features in HgTe, Hg1−xCdxTe and Hg1−xMnxTe (mixed-mode behavior in alloys) we observed several features that indicate surface quality (S– mode) and deviations from ideal crystallinity (‘‘defect mode’’, ‘‘clustering mode’’, and symmetry forbidden TO mode). The extremely surface sensitive S– feature observed at 132 cm−1 in p-Hg0.8Cd0.2Te is assigned to a coupled LO phonon-intersubband excitation. A 108 cm−1 feature present in HgTe and some samples of Hg0.8Cd0.2Te was confirmed to possess TO symmetry and may originate in antisite defects. The strong peak observed at 135 cm−1, displaying Γ1 symmetry, from all Hg1−xCdxTe samples may arise from clustering of the cations or vacancies; a weak feature observed at 132 cm−1 from Hg1−xMnxTe may also originate from clustering effects. The presence of a symmetry forbidden TO feature in 〈100〉 HgTe as well as 〈100〉 Hg0.8Cd0.2Te may be due to surface morphology or built in strains in the crystals. The HgTe RS contained a broad feature with an atomic displacement LO symmetry at 133 cm−1, slightly below the LO peak (139 cm−1), probably as a result of a screened LO mode. The Br/methanol treated 〈100〉 CdTe was found to have a thin (∼10 Å) surface layer of Te that could be removed by a rinse in 1 N KOH/methanol.
Interface chemistry of Hg1−xCdxTe
Authors: Philip P. , Franciosi A. , Peterman D. J.
Published: July 2002

We present preliminary studies of room temperature formation of the Hg1−xCdxTe(110)–Cr interface. For Cr coverages below 2 Å, Cr atoms replace Hg atoms in a 10–13 Å thick semiconductor layer while elemental Te is released at the surface. The typical high coverage interface morphology consists of an elemental Te surface, a metallic Cr film, a Hg-depleted subsurface layer where Cr is bonded to Te, and finally the ternary semiconductor bulk. This complex interface chemistry is compared with recent results for Hg1−xCdxTe interfaces with simple and noble metals.
Structural study of the diamond phase carbon films produced by ionized deposition
Authors: Namba Yoshikatsu , Mōri Toshio
Published: July 2002

Diamond phase carbon films have been prepared with the aid of an ionized deposition technique. The structures of these films were examined by transmis- sion electron microscopy and transmission electron diffraction. It was found that the crystal structure of these films depends strongly on the deposition conditions, especially on the substrate potential. For a negatively biased substrate potential, a film having a halo or diamond pattern was obtained, while the graphite patterns were observed for a positively biased potential. These structures were confirmed by directly comparing them with those of diamond or graphite powder. The observed average grain size of the diamond film was several hundred angstroms and was much smaller than that of graphite. Finally, we discuss the formation process of diamond phase carbon films.
Novel material properties of strained-layer superlattices
Authors: Osbourn G. C.
Published: July 2002

Strained-layer superlattices (SLS’s) are high quality structures grown from lattice-mismatched semiconductor materials. Recent Sandia studies have demonstrated that a variety of SLS material properties can be tailored through the flexible choice of layer materials and thicknesses and through the use of quantum size effects, zone folding effects, and strain effects. The use of strained layers in SLS’s allows these structures to exhibit a number of novel features. Examples of these features include: independently variable band gap and lattice constant using mismatched ternaries; strain-induced band gap shifts; and strain-modified effective masses. These features provide the opportunity for a variety of fundamental and applied materials studies using SLS systems.
Reactive radio frequency sputter deposition of higher nitrides of titanium, zirconium, and hafnium
Authors: Yee D. S. , Cuomo J. J. , Frisch M. A. , Smith D. P. E.
Published: July 2002

Higher nitrides of Ti, Zr, and Hf have been prepared by reactive rf sputtering of Ti, Zr, and Hf metals in a pure nitrogen atmosphere. The electrical and optical properties of these films are highly dependent on two deposition parameters, namely, the substrate temperature and the target voltage. We find that at each particular target voltage, there exists a critical temperature below which the higher nitride phase can be deposited and above which the phase cannot form. This suggests that the higher nitride phase (which is speculated to be an ordered defect structure) is metastable and is not energetically favored at high processing temperature or at high input power. At 2000 V target voltage, this critical temperature is determined to be approximately 200 °C for Hf–N, 25 °C for Zr–N, and is unknown for Ti–N system. The optical band gap of the ZrNx films decreases from 5.31 to 1.66 eV as the substrate temperature varies from −196 to 750 °C. Thermal analyses, using modulated beam mass spectrometry for monitoring the desorption rate of N2 gas, show that the principal decomposition reaction for TiNx, ZrNx, and HfNx films peak at 753, 773, and 788 °C, respectively.
Diagnostics of microwave plasma by laser induced fluorescence
Authors: Ninomiya Ken , Suzuki Keizo , Nishimatsu Shigeru , Okada Osami
Published: July 2002

CF radicals in a C3F8 microwave plasma were detected by laser induced fluorescence (LIF). CF2 radicals in C3F8 and CF4 plasma were also observed by using the same technique. At discharge pressures of 0.13 and 4.0 Pa, the relative densities of both radicals were measured as a function of microwave input power over a range of 40–240 W. The dependencies of these radical densities on discharge pressure were also measured over a pressure range of 6.7×10−2 to 13 Pa. The reaction mechanism in the plasma is discussed in terms of experimental results.
Combined electrochemical/surface science investigations of Pt/Cr alloy electrodes
Authors: Daube K. A. , Paffett M. T. , Gottesfeld S. , Campbell C. T.
Published: July 2002

Chromium addition improves the performance of carbon-supported Pt electrodes for oxygen reduction in phosphoric acid fuel cells. To clarify the role of chromium and its chemical nature at the electrode surface, we have performed a combined electrochemical/surface science investigation of a series of bulk PtxCr1−x alloys (0≤x≤1). In this paper we report the surface characterization of the starting electrodes by XPS, electrochemical results from cyclic voltammetry in 85% phosphoric acid, and postelectrochemical surface characterization. For Cr contents less than 40%, the electrodes were quite stable up to +1.6 V versus dynamic hydrogen electrode (DHE). The surface Cr was largely oxidized to Cr+3 for surfaces at open circuit and those exposed at potentials <+1.4 V. For intermediate Cr levels, Cr was leached from the surface region by +1.5 V, leaving a porous Pt electrode with increased electrochemical hydrogen adsorption capacity. For Pt0.2 Cr0.8, treatments at +1.4 V and above led to the appearance of Pt+4 and Cr+6 species, apparently stabilized in a porous phosphate overlayer up to 50 Å thick. The Pt electrochemical hydrogen adsorption capacity was simultaneously increased by a factor of 15.
Growth of HgCdTe and other Hg-based films and multilayers by molecular beam epitaxy
Authors: Harris K. A. , Hwang S. , Blanks D. K. , Cook J. W. , Schetzina J. F. , Otsuka N.
Published: July 2002

A molecular beam epitaxy (MBE) system specifically designed for growing Hg-based films and multilayer structures is described. It consists of a preparation and analysis chamber, a main MBE chamber equipped with a refillable Hg source, and a load lock for introducing and retrieving samples from either chamber. The system has been used to grow CdTe, HgCdTe, and HgTe films as well as HgTe–CdTe superlattices. The optical, electrical, and structural properties of the films and multilayers are discussed.
(100) and (111) oriented superlattices of (Cd,Mn)Te on (100)GaAs
Authors: Gunshor R. L. , Kolodziejski L. A. , Otsuka N. , Chang S. K. , Nurmikko A. V.
Published: July 2002

Previously reported (111) oriented superlattices of the (Cd,Mn)Te system on (100)GaAs have exhibited unusual exciton properties speculated to be related to characteristics of the (111) heterointerface. The epitaxial growth of both (111) oriented and (100) oriented CdTe on (100)GaAs provides an opportunity to investigate effects of orientation on the optical properties of these (Cd,Mn)Te superlattices. Techniques for the growth of (100) oriented superlattices on (100)GaAs by three different growth methods for the selection of the (100) orientation of CdTe are described. Significant differences in the optical properties of superlattices grown with the two orientations are shown, with emphasis on photoluminescence and excitation spectra.
Hydrogen isotope retention and release from copper
Authors: Wilson K. L. , Causey R. A. , Baskes M. I. , Kamperschroer J.
Published: July 2002

The Tokamak Fusion Test Reactor (TFTR) at the Princeton Plasma Physics Laboratory is considering the use of tritium neutral beams during the deuterium–tritium phase of operation in 1990. A concern is the tritium inventory that will develop in neutral beam components such as the copper calorimeter. In this paper we report on measurements and calculations of hydrogen isotope retention and release for copper under ion bombardment. Retention of deuterium trapped in the near-surface region is measured as a function of temperature using the D(3He, p) α nuclear reaction technique with an 800-keV 3He+ analysis beam. The rate of molecular recombination (Kr) at the copper–vacuum interface is determined from plasma driven permeation studies in our Tritium Plasma Experiment facility. The measurements indicate that Kr=6.7±0.1×10−18 cm4/s over the temperature range 575–825 K, in agreement with theory. These data are used as inputs to the diffuse computer code to provide a model for tritium–copper interactions. The model is tested against measured pressure rises during discharges in the TFTR neutral beam line, and is then used to predict tritium inventory in the copper ion beam dumps during future TFTR tritium operation.
Electrical and optical properties of thin Ta and W oxide films produced by reactive direct current magnetron sputtering
Authors: Hichwa B. P. , Caskey G. , Betz D. F. , Harlow J. D.
Published: July 2002

Reactively sputtered thin metal oxide films are used in the production of some electro-optic devices. To design and engineer such devices, knowledge of the physical characteristics of these films is essential. Investigations of the resistivity, reflection, and transmission properties of WOx and TaxOy thin films were done under a wide range of sputtering conditions. Reactive sputtering rates were determined for base argon pressures from 2.5 to 20 mTorr, O2 partial pressures from 0.5% to 50%, and power level from 2 to 8 kW. The maximum power density achieved was 34 W/cm2. Film thicknesses varied from 30 to 250 nm and were measured by a mechanical surface profile technique. Reflection and transmission characteristics and the corresponding optical constants were obtained from UV, visible, and near-infrared spectrophotometric scans of the films. The resistivities of the films were also measured, and they ranged from 101 to 108 Ω cm. The measured physical properties of these thin films were then related to the sputtering process parameters. Comparisons to corresponding evaporated metal oxide thin films indicate the differences in optical properties and resistivities.
Low-temperature oxidation of nonstoichiometric sputter deposited vanadium pentoxide
Authors: Aita Carolyn Rubin , Kao Mei Lee
Published: July 2002

V2O5 is a layered compound in which alternating sheets of V2O5 atoms and O atoms alone are oriented parallel to the 〈010〉 lattice direction. Recent interest in O-deficient V2O5 centers around its use as an oxidation catalyst. In the present paper, nonstoichiometric V2O5 films were sputter deposited onto glass substrates and annealed in air at 280 °C. Changes in crystallography and optical absorption in the 390 to 700 nm wavelength region were determined as a function of time at temperature. Low-temperature oxidation is used here as a probe for understanding the structure of the as-deposited film and to study the evolution of film structure as annealing progresses.
A study of nitrogen-rich titanium and zirconium nitride films
Authors: Ristolainen E. O. , Molarius J. M. , Korhonen A. S. , Lindroos V. K.
Published: July 2002

Thin titanium nitride (TiN) and zirconium nitride (ZrN) films containing excess nitrogen up to 59 and 63 at. % N, respectively, were deposited on austenitic stainless-steel substrates by reactive triode ion plating at about 823 K. The film structure and surface chemistry were studied using x-ray diffraction, scanning Auger spectroscopy, and electron energy-loss spectroscopy (EELS). In TiN films only the face-centered-cubic mononitride phase was detected. The lattice parameter of the stoichiometric TiN film was larger than the corresponding bulk value and it increased with increasing nitrogen content. The lattice parameter of overstoichiometric ZrN films showed abnormal behavior when calculated from different diffracting planes. This behavior together with the EELS and other measurements indicate that a dielectric Zr3N4 phase was formed at overstoichiometric compositions.
Deposition and redeposition in magnetrons
Authors: Rossnagel S. M.
Published: July 2002

The deposition probability and spatial distribution of atoms sputtered from a magnetron cathode have been semiquantitatively measured for a variety of chamber pressures for Cu and Al cathodes in Ne, Ar, and Kr gases. In this experiment, a large substrate plane was mounted parallel to a planar cathode. The cathode-to-sample distance was varied from 5 to 14.5 cm. Deposited films were measured on the sample plane, the area to the side of the cathode, and areas on the cathode itself. Deposition probabilities were calculated by comparison to the starting number of atoms. The deposition probability increased with decreasing pressure, throw distance, gas mass, and increasing cathode atom mass or discharge power. The redistribution back onto the cathode correlated inversely roughly with the deposition onto the sample plane. In the worst cases, sputtered atoms were more likely to redeposit onto the cathode surface than deposit on the sample plane. A clear trend was observed correlating gas scattering effects with local changes in the gas density due to thermalization effects in the background gas.
Epitaxial orientation and morphology of thin CoSi2 films grown on Si(100): Effects of growth parameters
Authors: Yalisove S. M. , Tung R. T. , Loretto D.
Published: July 2002

CoSi2 can be grown epitaxially on Si(100) with two dominant epitaxial orientations: CoSi2(100) on Si(100) where [100]CoSi2∥ [100]Si with [011]CoSi2∥ [011]Si , and CoSi2(110) on Si(100) where [011̄]CoSi2 ∥[100]Si with [011]CoSi2 ∥[011]Si . A rotated variant of the CoSi2(110) orientation is also observed where [011]CoSi2 ∥[100]Si with [011̄]CoSi2 ∥[011̄]Si. These films require a template technique in UHV conditions to grow high-quality material. By varying the growth conditions, films which are >95% of either orientations have been obtained. The relationships between these growth parameters and the epitaxial orientation of the resulting thin film are discussed and a possible model is suggested for some particular growth conditions.
Ultraviolet spectra of II–VI organometallic compounds and their application to i
n s
i
t
u measurements of the photolysis in a metalorganic chemical vapor deposition reactor
Authors: Fujita Y. , Fujii S. , Iuchi T.
Published: July 2002

The photoabsorption cross sections of Cd, Te, Zn, S, and Se alkyls have been measured at wavelengths between 190 and 400 nm, based on measurements of UV absorption spectra. These spectra have intense absorption bands from 190 to 250 nm. The peak values of these cross sections are 1–6×10−17 cm2 molecule−1. The in situ measurements of photolysis of these alkyls have been achieved by monitoring UV absorption spectra in a metalorganic chemical vapor deposition (MOCVD) reactor. The results show that the photolysis of these alkyls can be quantitatively controlled by varying the laser power. As applications of above studies, photoassisted MOCVD of CdTe, HgTe, and ZnS has been demonstrated using ArF and KrF excimer lasers. Specular surfaces were obtained at growth temperatures of 100 to 150 °C.
Electrical properties of tungsten trioxide films
Authors: Xu Z. , Vetelino J. F. , Lec R. , Parker D. C.
Published: July 2002

Selectively doped semiconducting metal oxide (SMO) films have been shown to have applications as the sensing element in gas microsensors. Critical to the design and operation of these sensors is the SMO film. In the present work, the electrical properties of both intrinsic and extrinsic (doped with gold) tungsten trioxide (WO3) films, which selectively sorb hydrogen sulfide (H2S), are investigated. Hall effect measurements are performed as a function of film thickness, temperature, gold-doping concentration, and H2S gas concentration. The conductivity was found to be n type and strongly dependent on temperature, gold doping concentration, and H2S gas concentration and less dependent on film thickness. The mobility was relatively high while the intrinsic carrier concentration was low when compared to typical semiconductor materials. The conductivity was shown to exhibit anomalous behavior at certain temperatures and H2S gas concentrations.
Probing bimetallic surfaces with photoelectron diffraction: Au/Cu(001) and Fe/Cu(001)
Authors: Tobin J. G. , Hansen J. C. , Wagner M. K.
Published: July 2002

Photoelectron diffraction has been used to investigate Au/Cu(001) and Fe/Cu(001). In the case of Au/Cu(001), a structural determination of the 1/2 ML, c(2×2) surface has been performed, indicating that it is a surface alloy with Au and Cu atoms together in the topmost plane and pure Cu(001) underneath. Moreover, the Au/Cu(001) system has been studied as a function of temperature and concentration, allowing a detailed picture of surface alloying and dealloying.
Cluster formation of Li on the Si(111)7×7 surface
Authors: Hasegawa Yukio , Kamiya I. , Hashizume T. , Sakurai T. , Tochihara H. , Kubota M. , Murata Y.
Published: July 2002

Using a field ion-scanning tunneling microscope (FI-STM), the adsorption process of Li on the Si(111)7×7 surface has been studied. At the initial stage, trimers are formed preferentially in the faulted half of the 7×7 unit cell. At higher coverages, these trimers coalesce to form six-atom and nine-atom clusters across the interface between the faulted and unfaulted halves. It is suggested, based on the careful study of the adsorption sites, that the Si adatoms of the dimer–adatom-stacking fault (DAS) model may be removed upon the Li adsorption.
Friction studies in ultrahigh vacuum of Fe surfaces with thin films from exposure to perfluorodiethylether
Authors: DeKoven Benjamin M. , Meyers Gregory F.
Published: July 2002

The coefficient of friction for both clean and oxidized contacting polycrystalline Fe surfaces following exposure to a perfluorodiethylether (PFDE), (CF3CF2)2O, was measured in ultrahigh vacuum (UHV) using a pin-on-flat device (0.05–0.30 N loads). This system was chosen to examine the influence of thin films on friction using a molecule having functionalities that are present in perfluoropolyether lubricants. The friction coefficient measured for the clean (∼0.2–1.0 Å oxide) surfaces in UHV was ∼3.0. The friction was measured for both oxidized and clean Fe surfaces in PFDE atmospheres (3–150 Pa). During this exposure the friction for the oxidized Fe surfaces dropped to 0.7–0.9 compared to 1.2–1.5 obtained in O2 environments. The friction for clean Fe surfaces measured in UHV following similar PFDE exposures showed two distinct friction ranges, 0.1–0.8 and 1.2–1.8. The Fe surfaces were examined in situ in the same UHV chamber using x-ray photoelectron spectroscopy and showed the formation of a Fe fluoride film (8–16 Å). High resolution profiles of these surface scars using scanning tunneling microscopy in air revealed a contact morphology dependent upon the coefficient of friction. The lower-range friction scars had multiple point contacts while the higher-range scars exhibited single point contacts with deep surface ploughing.
Hollow cathode discharge sputtering device for uniform large area thin film deposition
Authors: Koch H. , Friedrich L. J. , Hinkel V. , Ludwig F. , Politt B. , Schurig T.
Published: July 2002

Hollow cathode discharges produce higher densities of sputtered particles than conventional discharges and can be utilized for thin film deposition. A prototype hollow cathode sputter source has therefore been built and tested. The deposition of copper and the superconductor YBa2Cu3O7−x produced thin films of good quality. The method can be upscaled for a uniform deposition of tapes, wires, large-area substrates, and for the parallel deposition of multiple substrates.
Cerium silicide formation in thin Ce–Si multilayer films
Authors: Hsu C. C. , Ho J. , Qian J. J. , Wang Y. T.
Published: July 2002

Alternating layers of Si(200 Å thick) and Ce(200 Å thick) up to 26 layers altogether were deposited by electron evaporation under ultrahigh vacuum conditions on Si(100) substrate held at 150 °C. Isothermal, rapid thermal annealing has been used to react these Ce–Si multilayer films. A variety of analytical techniques has been used to study these multilayer films after annealing, and among these are Auger electron spectroscopy, Rutherford backscattering, X-ray diffraction, and high resolution transmission electron microscopy. Intermixing of these thin Ce–Si multilayer films has occurred at temperatures as low as 150 °C for 2 h, when annealed. Increasing the annealing temperature from 150 to 400 °C for 1 h, CeSi2 forms gradually and the completion of reaction occurs at ∼300–400 °C. During the formation of CeSi2 from 150–400 °C, there is some evidence for small grains in the selected area diffraction patterns, indicating that CeSi2 crystallites were present in some regions. However, we have no conclusive evidence for the formation of epitaxial CeSi2 layers, only polycrystals were formed when reacted in the solid phase even after rapid thermal anneal at 900 °C for 10 s. The formation mechanism has also been discussed in combining the results of the La–Si system.