Showing papers on "Evaporation (deposition) published in 1994"

The influence of thermal diffusion on laser ablation of metal films

Abstract: Single-shot ablation thresholds of nickel and gold films in the thickness range from 50 nm to 7 μm have been measured for 14 ns laser pulses at 248 nm, using photoacoustic shock wave detection in air. The metal films were deposited on fused silica substrates. The ablation threshold was found to increase linearly with film thickness up to the thermal diffusion length of the film. Beyond this point it remains independent of film thickness. The proportionality between threshold fluence and thickness allows the prediction of ablation thresholds of metal films from the knowledge of their optical properties, evaporation enthalpies and thermal diffusivities. Physically it proves that ablation is driven by the energy density determined by the thermal diffusion length. A simple thermodynamic model describes the data well. Thermal diffusivities, an essential input for this model, were measured using the technique of transient thermal gratings. In addition, the substrate dependence of the ablation threshold was investigated for 150 nm Ni films.

Dielectric properties of electron‐beam deposited Ga2O3 films

Abstract: We have fabricated high quality, dielectric Ga2O3 thin films. The films with thicknesses between 40 and 4000 A were deposited by electron‐beam evaporation using a single‐crystal high purity Gd3Ga5O12 source. Metal‐insulator‐semiconductor (MIS) and metal‐insulator‐metal structures (MIM) were fabricated in order to determine dielectric properties, which were found to depend strongly on deposition conditions such as substrate temperature and oxygen pressure. We obtained excellent dielectric properties for films deposited at substrate temperatures of 40 °C with no excess oxygen and at 125 °C with an oxygen partial pressure of 2×10−4 Torr. Specific resistivities ρ and dc breakdown fields Em of up to 6×1013 Ω cm and 2.1 MV/cm, respectively, were measured. Static dielectric constants between 9.93 and 10.2 were determined for these films. Like in other dielectrics, the current transport mechanisms are found to be bulk rather than electrode controlled.

Thermal conductivity of sputtered and evaporated SiO2 and TiO2 optical coatings

Abstract: The thermal conductivity of SiO2 and TiO2 optical coatings are measured in the temperature range 80–400 K. For SiO2, the thermal conductivity of sputtered and evaporated films are 77% and 55% of the bulk value, respectively, independent of temperature. Similarly, the thermal conductivity of evaporated TiO2 is 63% of the conductivity of sputtered TiO2.

Single-Wall Carbon Nanotubes Growing Radially from Ni Fine Particles Formed by Arc Evaporation

Abstract: DC arc evaporation of nickel-graphite composite in helium atmosphere produces single-wall (SW) nanotubes. Electron microscopy examination of carbonaceous soot synthesized by this method revealed that the SW tubes grew radially from ultrafine nickel particles, and that they were found exclusively in soot material formed on the surface of a sluglike deposit grown on the end of a cathode.

Effect of Gold Topography and Surface Pretreatment on the Self-Assembly of Alkanethiol Monolayers

Abstract: Thin films of vapor deposited and sputtered Au are prepared as substrates for comparative studies of alkanethiol self-assembly. Vapor deposition of Au is carried out on freshly cleaved heated mica substrates in ultrahigh vacuum at 25, 150, 300, 450, and 500 o C. The Au surface roughness is controlled by the mica substrate temperature during Au evaporation becoming atomically flat at 450-500 o C as shown by AFM. Surprisingly the formation of dense blocking self-assembled alkanethiol monolayers (CH 3 (CH 2 ) n SH, n=9, 11, 13, 15, 17) becomes greatly inhibited as the Au/mica becomes smoother. In comparison, the effect of surface pretreatment of microscopically rougher Au substrates, prepared by sputtering onto Si(100) substrates, was also investigated

Tin selenide (SnSe) thin films prepared by reactive evaporation

Abstract: Polycrystalline thin films of tin selenide have been prepared by reactive evaporation at substrate temperatures ranging from 473–600 K. Crystallites of the films prepared at substrate temperatures below 525 K are randomly oriented, while they have a strong preferred orientation on the substrate surface at higher substrate temperatures. Optical absorption studies indicate that the fundamental absorption starts at 1.21 eV and it is due to an allowed direct transition.

Thin silver films: influence of substrate and postdeposition treatment on morphology and optical properties

Abstract: In an effort to understand the experimental parameters that influence thin metal film morphology and optical characteristics, thin Ag films are examined with a combination of atomic force microscopy (AFM), optical absorption, and surface-enhanced Raman spectroscopy (SERS). The morphology of 5 nm of Ag vapor deposited onto glass, derivatized glass, Formvar-coated glass, and mica is explored. The substrate is found to have a large effect on both Ag film surface morphology and optical properties. In addition, micrographs of a Ag film before and after exposure to solvent suggest solvent-induced morphological changes. 32 refs., 8 figs., 5 tabs.

Structure and performance of Si/Mo multilayer mirrors for the extreme ultraviolet

Abstract: We report the results of structural, chemical, and extreme ultraviolet (EUV) characterization of Si/Mo multilayers grown by sputtering and by UHV evaporation. This study includes mirrors designed for normal incidence with peak reflectivities Rpeak between 22 and 24 nm, and 45° mirrors having Rpeak between 16 and 19 nm. The deposition conditions were varied to produce multilayers with a wide range of interface morphologies. A variety of techniques were used to determine the structure and composition of the multilayers, including x‐ray diffraction, transmission electron microscopy, Rutherford backscattering spectroscopy, and Auger depth profiling. All of the mirrors have amorphous Si layers and polycrystalline Mo layers with thin amorphous alloy interlayers. We obtain good fits to the low‐angle x‐ray diffraction data only when these interlayers are taken into account. The best sputter‐deposited mirrors were made at the lowest Ar pressure studied, 3 mTorr. The best evaporated mirrors were produced at a subst...

Characteristics of titanium oxide films deposited by an activated reactive evaporation method

Abstract: Titanium di- and sesquioxide films were epitaxially grown on the (001) surface of sapphire single-crystalline substrates by an activated reactive evaporation method. Formation range for each titanium oxide was determined as a function of oxygen pressure (Po2) by means of x-ray diffraction, transmission electron microscopy, and Raman spectroscopy. Films prepared at Po2 ≥ 2.0 × 10−4 Torr were stoichiometric (100)-oriented rutile of TiO2, and with decreasing Po2 they would accommodate more and more Ti3+ ions in the rutile structure. At Po2 = 0.6 × 10−4 Torr, on the other hand, (001)-oriented Ti2O3 was formed and an electrical transition was clearly detected at about 400 K. However, the large lattice mismatch between the substrate and these films leads to a periodic introduction of misfit dislocations in the case of the TiO2 films and a mixing of stacking sequences for the Ti2O3 films.

Formation of hydroxyapatite coating on pure titanium substrates by ion beam dynamic mixing

Abstract: A hydroxyapatite (HAp) coating was deposited onto pure Ti substrates using an ion beam dynamic mixing (IBDM) method. In this study, a high energy Ca + ion beam of 50 keV was irradiated concurrently during evaporation of HAp vapor onto Ti substrates to deposit the HAp film. The structure, solubility in Hanks' solution and adhesive strength of the coatings were evaluated. The as-coated film was amorphous and was almost dissolved within 1 day in the solution. A thin Ca-P-Ti hydroxide complex layer, however, was formed on the substrate surface, indicating that the IBDM film might possess a “self-repairing function.” The crystallinity of the HAp film was improved by heat treatment at 873 K in air, and the film obtained was slightly soluble in the solution. The adhesive strength of the as-coated film was more than 59 MPa. The strength decreased to 41 MPa after the heat treatment, but even this value exceeds that obtained using conventional methods.

Evaporation of small fragments during the scattering of argon clusters at thermal kinetic energies from a graphite surface

Abstract: We present a thermokinetic model together with new experimental results for the scattering of large argon clusters off a graphite surface. Both angular and time‐of‐flight distributions are shown for a large range of surface temperatures, incidence angles, and incident cluster sizes. A quantitative comparison between the proposed thermokinetic model and our measurements allows one to interpret most of the experimental results as due to thermal evaporation of very small fragments from their parent clusters gliding along the surface. The coefficient of tangential velocity conservation cF and the local temperature Tlocal of the evaporating fragments have been determined quantitatively. Although the investigated parameters were varied over a large range, Tlocal remains essentially constant around (140 ± 20) K. The coefficient cF turns out to be approximately (0.80 ± 0.05) independent of surface temperature and incident cluster size for all incidence angles larger than 40°. It increases, however, rapidly to 1.4...

Structure and conductance evolution of very thin indium oxide films

Abstract: The conductance of transparent conducting oxide films as a function of their coverage has been investigated in situ. The films have been prepared by means of reactive evaporation of In in the presence of oxygen on the glass substrate at different substrate temperatures. The analysis shows that island growth, percolation, coalescence, and ohmic stages can be identified. Critical parameters of the films can be determined during the growth, such as anisotropic and percolative growth modes, resistivity, a lower limit of the effective dopant concentration. The technique shows a potential for in‐depth characterization of very thin film growth.

Measuring the Mechanical Properties of Thin Metal Films by Means of Bulge Testing of Micromachined Windows

Abstract: Free-standing films of gold and aluminum have been fabricated using standard micro-machining techniques. LPCVD silicon nitride films are deposited onto (100) silicon wafers. Square and rectangular silicon nitride membranes are made by anisotropic etching of the silicon substrates. Then, metal films are deposited onto the silicon nitride membranes by means of evaporation. Finally, the sacrificial silicon nitride film is etched away by means of reactive plasma etching, resulting in well-defined, square and rectangular metal membranes. Bulge testing of square windows allows one to determine the biaxial modulus of the film as well as the residual stress in it. Testing rectangular windows yields the plane-strain elastic modulus and the residual stress. Since deformation in rectangular membranes approaches plane-strain deformation, this geometry is ideal for studying the plastic properties of the metal films. Stress-strain curves can be readily determined from the load-deflection curves of rectangular membranes. The gold films have a biaxial modulus of 161±3 GPa and a plane-strain modulus of 105±5 GPa, slightly lower than the literature values for a (111) textured film. The yield stress of these films is approximately 231±17 MPa at 10−4% plastic strain. The elastic moduli of the aluminum films are 105±3 GPa and 76.4±0.7 GPa, respectively; the yield stress of these films is 187±30MPa.

TixZryC12 and TixHfyC12 (x+y=8): Binary metal metallocarbohedrenes

Abstract: We report the production of binary metal metallocarbohedrenes. Direct laser vaporization of mixtures of zirconium or hafnium powders with titanium carbide yield the species TixZryC12 and TixHfyC12 (x+y=8). These results are discussed in the context of recent theoretical models addressing the stabilities and structures of the metallocarbohedrenes, their formation mechanism and possible implications for the synthesis of ‘‘doped’’ metallocarbohedrenes.

Young's modulus and stress of CrN deposited by cathodic vacuum arc evaporation

Abstract: It is generally recognized that a high degree of ionization which is a characteristic of the cathodic vacuum arc evaporation (CVAE) process is necessary to form the chromium mononitride in single-phase or near-single-phase condition. This study concerns the properties of CVAE chromium nitride coatings made at low temperature (200°C) and at a more usual industrial temperature (400°C). A phase analysis is made followed by a derivation of the residual stress. The Young's modulus of the coating was derived from a series of coatings on various substrates. The modulus value of 232–244 GPa is well below the 400 GPa which is often cited.

The Preparation of Carbon Nanotubes

Abstract: Carbon nanotubes were prepared by dc arc-discharge evaporation of graphite rods, by varying the pressure and the kind of atmospheric gas Nanotubes, included in the carbon deposit on the cathode, were observed by scanning electron microscopy (SEM)

Orientation of MgO Thin Films on Si(100) and GaAs(100) Prepared by Electron-Beam Evaporation

Abstract: MgO thin films were prepared on Si(100) and GaAs(100) by electron-beam evaporation. MgO thin films with (100) orientation were obtained at 610°C with the deposition rate of 0.5 A/s, and those with (111) orientation were obtained below 440°C with deposition rate higher than 8 A/s, on Si substrates. (100) oriented MgO thin films, however, grew on Si at 440°C upon decreasing the deposition rate to 0.3 A/s. MgO thin films with (100) orientation having cube-on-cube epitaxy were obtained on GaAs substrates at the temperature as low as 280°C even at the deposition rate of 1.4 A/s.

Deposition of metal nanostructures onto Si(111) surfaces by field evaporation in the scanning tunneling microscope

Abstract: Islands of gold or copper having dimensions as small as 200 A in diameter and 10 A in height were prepared by field evaporation from a tip of the appropriate metal in a scanning tunneling microscope (STM). The field emission of metal is induced by the application of tip‐negative bias pulses having amplitudes of 6–20 V, and durations of 2 μs to 2 ms. The metallic composition of the protrusions observed by STM are confirmed by ex situ elemental analysis using the field emission scanning Auger microprobe (FE‐SAM). Tip‐positive bias pulses also produce protrusions, however these are unstable either to STM imaging or to exposure to high‐energy electron beams, as in the FE‐SAM instrument. It is therefore probable that nonostructures formed via tip‐positive bias pulses are not metallic. These data provide the first direct experimental evidence for metal transfer between an STM tip and a surface.

SiO2 formation by thermal evaporation of SiO in oxygen atmosphere used to fabrication of high performance polycrystalline silicon thin film transistors

Abstract: A reactive evaporation of SiO in an oxygen atmosphere was investigated for forming a good interface of SiO2/Si. SiO2 films are formed at room temperature by evaporation of a SiO powder in an oxygen atmosphere with a flow rate of 2 sccm at a pressure of 1×10−4 Torr. The interface trapping density at SiO2/Si was lower than 5×1010 cm−2 eV−1. n‐ and p‐channel Al‐gate polycrystalline silicon thin film transistors (poly‐Si TFTs) were fabricated at 270 °C with the present SiO2 films as a gate oxide and laser crystallized poly‐Si films formed using a pulsed XeCl excimer laser. They showed good characteristics of a low threshold voltage of 1.1 V (n‐channel) and −1.2 V (p‐channel), and a high carrier mobility of 450 cm2/V s (n‐channel) and 270 cm2/V s (p‐channel).

Process for preparing high crystallinity oxide thin film

Abstract: A process for preparing an oxide thin film which has a crystalline, clean and smooth surface on a substrate. The process is conducted by using an apparatus comprising a vacuum chamber in which an oxidizing gas of O₂ including O₃ can be supplied near the substrate so that pressure around the substrate can be increased while maintaining high vacuum near an evaporation source and Knudsen cell evaporation sources arranged in the vacuum chamber wherein the substrate is heated, molecular beam of constituent atoms of the oxide excluding oxygen are supplied from the K cell evaporation sources and an oxidizing gas is locally supplied to the vicinity of the substrate.

Vacuum processing apparatus, and a film deposition apparatus and a film deposition method both using the vacuum processing apparatus

Abstract: A vacuum processing apparatus for performing various processes on a wafer in a vacuum chamber, and a film deposition method and a film deposition apparatus using this vacuum processing apparatus. The vacuum processing apparatus, the film deposition method and the film deposition apparatus using the vacuum processing apparatus according to this invention are characterized in that temperature control of the wafer is performed in a film deposition process, and particularly characterized in that after the emissivity calibration using a combination of a temperature calibration stage and a shutter is performed, the substrate is transferred to stages in a vacuum film deposition process chamber, and a film is deposited on the substrate by controlling the substrate temperature to a specified temperature.

Electron beam deposition of gallium oxide thin films using a single high purity crystal source

Abstract: Disclosed is a method of fabricating a stoichiometric gallium oxide (Ga2 O3) thin film with dielectric properties on at least a portion of a semiconducting, insulating or metallic substrate. The method comprises electron-beam evaporation of single crystal, high purity Gd3 Ga5 O12 complex compound combining relatively ionic oxide, such as Gd2 O3, with the more covalent oxide Ga2 O3 such as to deposit a uniform, homogeneous, dense Ga2 O3 thin film with dielectric properties on a variety of said substrates, the semiconducting substrates including III-V and II-VI compound semiconductors.

Magnetic anisotropy of epitaxial Fe/Pt(001) multilayers.

Abstract: The structure of epitaxial Fe/Pt(001) multilayers deposited by e-beam evaporation was characterized by a four-circle x-ray diffractometer and the magnetic anisotropy was investigated using a torque magnetometer. For epitaxial Fe/Pt(001) multilayers, a structural transition of the Fe layer is found to occur with increasing Fe layer thickness. The critical thickness is around 8 \AA{}. Magnetic anisotropy and coercive force change with the transition. The out-of-plane volume anisotropy decreases for the Fe layer thickness less than 8 \AA{}. The fourfold in-plane anisotropy is lost for the Fe layer thickness less than 8 \AA{}. For the Fe layer thickness beyond 8 \AA{}, it is found that the in-plane interface anisotropy is negative and that the in-plane volume anisotropy is identical to the magnetocrystalline anisotropy of bulk bcc Fe.