Films In High Vacuum Research Articles

Volatile Products Formed during Electrical Breakdown of Polyethylene Terephthalate and Polypropylene Films in High Vacuum

Volatile Products Formed during Electrical Breakdown of Polyethylene Terephthalate and Polypropylene Films in High Vacuum

Volatile products formed during electrical breakdown of polyethylene terephthalate and polypropylene films in high vacuum

In this article we present the results of time-of-flight mass spectrometry of volatile products formed during the electrical breakdown of polyethylene terephthalate and polypropylene polymer films in high vacuum. During the breakdown of films, all the substance emitted from the breakdown channel is a gas of low-molecular products of destruction of macromolecules. The breakdown mass spectra do not contain lines of carbon molecules, the presence of which could indicate carbonation of the channel. To explain the formation of charge carriers, the ionization mechanism of destruction of macromolecules in an electric field is used without the involvement of impact ionization. The final stage of electrical breakdown (the flow of a high-density conduction current) occurs when the critical concentration of traps and electrons ~1024 m-3 is reached. Keywords: electrical breakdown, mass spectrometry, thermodestruction, ionization, macromolecule, trap.

Летучие продукты, образующиеся при электрическом пробое пленок полиэтилентерефталата и полипропилена в высоком вакууме

In this article we present the results of time-of-flight mass spectrometry of volatile products formed during the electrical breakdown of polyethylene terephthalate and polypropylene polymer films in high vacuum. During the breakdown of films, all the substance emitted from the breakdown channel is a gas of low-molecular products of destruction of macromolecules. The breakdown mass spectra do not contain lines of carbon molecules, the presence of which could indicate carbonation of the channel. To explain the formation of charge carriers, the ionization mechanism of destruction of macromolecules in an electric field is used without the involvement of impact ionization. The final stage of electrical breakdown (the flow of a high-density conduction current) occurs when the critical concentration of traps and electrons ≈ 10^24 1/m^3 is reached.

Simplified Determination of RHEED Patterns and Its Explanation Shown with the Use of 3D Computer Graphics.

The process of preparation of nanostructured thin films in high vacuum can be monitored with the help of reflection high energy diffraction (RHEED). However, RHEED patterns, both observed or recorded, need to be interpreted. The simplest approaches are based on carrying out the Ewald construction for a set of rods perpendicular to the crystal surface. This article describes how the utilization of computer graphics may be useful for realistic reproduction of experimental conditions, and then for carrying out the Ewald construction in a reciprocal 3D space. The computer software was prepared in the Java programing language. The software can be used to interpret real diffractions patterns for relatively flat surfaces, and thus it may be helpful in broad research practice.

Laser ablation of boron nitride in vacuum and in water

ABSTRACTThe laser ablation of boron-nitride (BN) ceramic was employed for the preparation of thin films in high vacuum and nanoparticles and nanocrystals generated in water. The obtained plasma was investigated using ion detectors to determine the ion velocity, the energy per charge state and the plasma temperature and describing the acceleration mechanism.The kinetics of laser ablation in water and the comparison of different ablation rates in the vacuum and in water, and the possible applications of the BN thin film and nanoparticles are presented and discussed.

Bias voltage dependence of superlubricity lifetime of hydrogenated amorphous carbon films in high vacuum

Abstract We deposit hydrogenated amorphous carbon (a-C:H) films by magnetron sputtering of graphite in an Ar + C 2 H 2 mixture at various bias voltages. The mechanical properties, Raman spectra, and high-vacuum frictional behaviors of the a-C:H films indicate that the films deposited at bias 0, –50, and −100 V are polymer-like carbon (PLC) films and the film deposited at −150 V is a diamond-like carbon (DLC) film. The lifetimes of superlubricity, with friction coefficient ∼0.002, of the PLC films in high-vacuum increase from 10000 to 28000 cycles with increasing bias, although the film thicknesses decrease. The DLC film's wear-life is ∼600 cycles. The enhanced wear-resistance in PLC films is attributed to improvement of the crosslinking degree of the PLC network and the film compactness.

Interface design for a-C:H film with super long wear life in high vacuum environment

In the present work, a special interface between substrate and carbon films is introduced to prolong wear life of a-C:H film in high vacuum, and the optimized film exhibits an ultra-long life of 2.6×105 cycles, corresponding to 9796.8m at the normal load of 5N. Experimental results show that gradient interlayer significantly decreases internal stress, increases adhesion strength as well as improves interface fracture toughness, and then anti-wear ability shows a corresponding improvement. This study discloses that interface design plays important roles in determining tribological behavior of a-C:H film in vacuum, which provides a novel method for developing new generation space lubrication film.

Phase stabilization of VO2 thin films in high vacuum

A new growth approach to stabilize VO2 on Al2O3 in high vacuum is reported by reducing vanadium oxytriisopropoxide (VTIP) with vanadium metal. Phase stabilization and surface wetting behavior were studied as a function of growth parameters. The flux balance of VTIP to V in combination with growth temperature was identified to be critical for the growth of high quality VO2 thin films. High V fluxes were required to suppress the island formation and to ensure a coalesced film, while too high V fluxes ultimately favored the formation of the undesired, epitaxially stabilized V2O3 phase. Careful optimization of growth temperature, VTIP to V ratio, and growth rate led to high quality single phase VO2 thin films with >3.5 orders of magnitude change in resistivity across the metal-to-insulator transition. This approach opens up another synthesis avenue to stabilize oxide thin films into desired phases.

Microcantilever Q control via capacitive coupling

We introduce a versatile method to control the quality factor Q of a conducting cantilever in an atomic force microscope (AFM) via capacitive coupling to the local environment. Using this method, Q may be reversibly tuned to within ∼10% of any desired value over several orders of magnitude. A point-mass oscillator model describes the measured effect. Our simple Q control module increases the AFM functionality by allowing greater control of parameters such as scan speed and force gradient sensitivity, which we demonstrate by topographic imaging of a VO2 thin film in high vacuum.

Real-time investigation on photocatalytic oxidation of gaseous methanol with nanocrystalline WO3–TiO2 composite films

Here we report on our investigation on photocatalytic oxidation (PCO) of gaseous methanol with WO3–TiO2 composite films. WO3 and WO3–TiO2 composite thin films were prepared by drop casting method. PCO of gaseous methanol and hydrogen generation process on platinum loaded WO3–TiO2 composite thin films in high vacuum were investigated using a home-made reactor with a six-channel quadrupole mass spectrometer at real-time scale under UVA (300–400nm) light illumination.In the case of Pt loaded WO3 thin films, PCO of gaseous methanol proceeds through intermediates viz. formaldehyde, CO and finally to CO2 and H2. PCO of gaseous methanol occurs via direct hole transfer over Pt loaded WO3 thin films. On the other hand, PCO of gaseous methanol over Pt loaded WO3–TiO2 composite thin films proceeds with competitive direct and indirect hole transfer reactions. Our real-time analysis of gas phase photocatalysis realized the identification of direct and indirect hole transfer processes and the reaction intermediates thereof.

Intricate photocatalytic decomposition behavior of gaseous methanol with nanocrystalline tungsten trioxide films in high vacuum

Gas phase photocatalytic decomposition of methanol with nanocrystalline tungsten trioxide (WO3) thin films in high vacuum was investigated. WO3 thin films were prepared from a novel precursor prepared using peroxo-tungstic acid and polyethylene glycol (PEG300) in water. Uniform thin films of WO3 with different morphologies such as micro-sheets, platelets, nanorods and nanoparticles were fabricated by varying the concentration of PEG300 in the precursor solution and by optimizing other preparative parameters. Nanocrystalline thin films were obtained with 20% of PEG300 in the precursor solution and at a calcination temperature of 350°C, followed by post annealing in air at 500°C. Photocatalytic decomposition of gaseous methanol in high vacuum was examined with nanocrystalline WO3 thin films using a quadrupole mass spectrometer at a real-time scale under visible (400–700nm) and UVA (300–400nm) illumination. Methanol was first decomposed to formaldehyde via direct hole transfer mechanism. Subsequently formaldehyde was decomposed to CO and finally to CO2. As a result, the partial pressures of CH2O, CO and CO2 showed a switching phenomenon according to the ON/OFF of light illumination. A rapid decrease in the photocatalytic activity was observed due to photo-induced desorption of methanol during the initial light pulse and gradual decrease at longer times was observed because of formation of tungsten bronze. Thus, the overall process of methanol decomposition over WO3 films is complex convolution of elementary steps that involve several intermediates.

Surface potentials of few-layer graphene films in high vacuum and ambient conditions

The surface potentials of few-layer graphene (FLG) films in high vacuum and ambient conditions have been investigated by employing electrostatic force microscopy. It is found that the surface potential of FLG films in ambient air has a constant large depression compared to that measured in a high vacuum. Our experimental results indicate that the shift is most likely caused by the presence of ambient adsorbates on the outmost graphene surfaces. The surface potentials increase with the number of graphene layers and approach the bulk value for five or more graphene layers in high vacuum as well as in ambient air. Since the contribution of the surface adsorbates is a constant value, we further show that the thickness dependence of the surface potential can be sufficiently explained by the nonlinear Thomas–Fermi Theory in both conditions.

Graphene: Patterned Growth of Graphene over Epitaxial Catalyst Small 11/2010

The cover picture illustrates the formation of a triangular graphene film inside a pit of epitaxial metal catalyst. Rectangular- and triangular-shaped microscale graphene films are grown on epitaxial Co films deposited on single-crystal MgO substrates with (001) and (111) planes, respectively. Thermal decomposition of polystyrene over the epitaxial metal film in high vacuum gives unique pits, whose orientation and shape are strongly dependent on the crystallographic orientation of the MgO substrate. Raman-mapping measurements reveal preferential formation of few-layer-graphene films inside these pits. These graphene films are transferred onto a SiO2/Si substrate while maintaining the original shape, and field-effect transistors are fabricated using the transferred films. These findings offer lithography-free patterned growth of graphene for future electronics. For more information, please read the Full Paper “Patterned Growth of Graphene over Epitaxial Catalyst” by H. Ago et al., beginning on page 1226.

Pd/native nitride/n-GaAs structures as hydrogen sensors

In this study, a novel Pd/native nitride/ n -GaAs structure was developed and investigated as hydrogen sensor. Thin layers of native nitride on n -GaAs (1 0 0) epitaxial crystals was grown by anodic nitridation, and Pd thin layer as gate electrode was evaporated on the native nitride film in high vacuum. Electrical and hydrogen sensing properties of the structures were obtained from the current–voltage ( I – V ), capacitance–voltage ( C – V ) and capacitance–time ( C – t ) characteristics measured in a computer controlled flow set-up at temperatures of 50, 90 and 130 °C, respectively. The samples show a behavior like a Schottky diode. The thicker sample has smaller leakage current and greater breakdown voltage. The sensor responses are totally reversible with response and recovery times, 35 and 40 s, respectively. The device with the thickest native nitride film showed better sensitivity, and the detection limit was lower than 20 ppm for H 2 .

Photocatalytic Hydrogen Production from Gas-phase Methanol and Water with Nanocrystalline TiO2 Thin Films in High Vacuum

ABSTRACTPhotocatalytic hydrogen production with gas-phase reactions in high vacuum was examined for nanocrystalline anatase-type titanium dioxide (TiO2) thin films. The hydrogen generation process on platinized TiO2 specimens was investigated using a quadrupole mass spectrometer at a real-time scale under various partial pressures of gaseous methanol and water. As a result, hydrogen generation was successfully detected under ultraviolet ray (UV) illumination even in high vacuum (∼ 10−7 Torr). And the amount of produced H2 largely depends on the temperature of TiO2 samples, probably due to different surface states of TiO2. This study suggests the possibility of new high-speed H2 production system with gas-phase photocatalytic reactions.

Frictional behavior of diamondlike carbon films in vacuum and under varying water vapor pressure

In this study, we investigated the frictional behavior of both hydrogenated and hydrogen-free diamondlike carbon (DLC) films in high vacuum (10−6 Pa) at room temperature. Water was also introduced into the vacuum chamber to elucidate its effects on DLC film tribology. The hydrogen-free DLC (also referred to as tetrahedral amorphous carbon, or ta-C) was produced by an arc-PVD process, and the highly hydrogenated DLC was produced by plasma-enhanced chemical-vapor deposition. Tribological measurements of these films were made with a pin-on-disc machine with coated steel balls and coated steel discs in matched pairs under a 1 N load. The ball/disk pairs were rotated at sliding speeds in the range of 0.025–0.075 m/s. In vacuum, the steady-state friction coefficient of ta-C was of the order of 0.6 and the wear was severe, whereas for the highly hydrogenated film, friction was below 0.01, and in an optical microscope no wear could be detected. Adding water vapor to the sliding ta-C system in a vacuum chamber caused friction to decrease monotonically from 0.6 to ≈0.07. In contrast, adding water vapor to the sliding DLC system caused the friction to increase linearly with pressure from 0.01 to 0.07. The results illustrate the importance of taking into account environmental conditions, especially the presence of water, when DLC films are being considered for a given application.

Characterization of low dielectric constant polyaniline thin film synthesized by ac plasma polymerization technique

Polyaniline thin films were prepared by ac plasma polymerization technique. Capacitance, dielectric loss, dielectric constant and ac conductivity of these films were investigated in the frequency range from 100 Hz to 1 MHz and in the temperature range from 300 to 373 K. Capacitance and dielectric loss decreased with frequency and increased with temperature. This type of behaviour was found to be in good agreement with an existing model. The ac conductivity σ(ω) was found to vary as ωs with the index s⩽1. Annealing of polyaniline thin films in high vacuum at 373 K for 1 h was found to reduce the dielectric loss. FTIR studies reveal that the aromatic ring is retained in the polyaniline thin films, which enhances the thermal stability of the polymer films.

Photoluminescence Study of C70 Film Manufactured by Physical Jet Deposition

We have fabricated C70 film by physical jet deposition (PJD) technique and measured the absorption and photoluminescence (PL) spectra of this kind C70 film. In comparison with the deposited C70 film in high vacuum, the absorption and integrated PL spectra are similar, but there is a big difference in the time-resolved PL. The C70 film made by PJD shows a very fast PL decay of less than 20 ps which should result from the fast relaxation process of C70 molecule in the excited state S1 of this new kind film.

Heating stage for in situ studies of thin-film reactions

We describe a method for measuring and controlling the temperature of thin ceramic plates which are used as substrates for the deposition of thin films in high vacuum. The ceramic plates have an embedded platinum resistor which acts as both heating element and thermometer. The temperature of the substrate is controlled by an electronic feedback circuit. This arrangement enables accurate measurements of the thin-film temperature. In addition, the system has a fast response time and excellent long-term temperature stability. We describe an application where the temperature control system is combined with ac resistance measurements to study the kinetics of a solid-state interdiffusion reaction in Ni-Zr multilayers.

The Effect of Anion Vacancies on the Tribological Properties of Rutile (TiO2-x), Part II: Experimental Evidence

Friction and wear tests were completed with the (001) and (110) planes of single crystal rutile (TiO 2-x ) specimens sliding against selected ceramic counterfaces, in well-defined crystallographic directions. The purpose of the experiments was to investigate the environmental influences on anion vacancy formation, as related to a recent hypothesis connecting oxygen substoichiometry with predictable variations in the tribological properties of rutile. The data were obtained with two, entirely different test machines operating at various loads, speeds, temperatures, sliding directions and durations, as well as test specimen atmospheres. The results independently confirmed the predicted, anion vacancy-controlled formation of certain low and high lattice (strain) energy crystallographic shear systems (i.e., Magnèli phases) and that their generation is overwhelmingly environment-dependent. The stoichiometry-controlled lattice energy of these rutile phases influences the surface and bulk shear strength (τS) of the oxide single crystal. τS values were calculated for the (001)[110] surface as a function of rutile stoichiometry. The τS of (001)[110] rutile at an estimated stoichiometry of TiO 1.93–1.98 was as low as 8 MPa, equivalent to the τS of run-in MoS2 films in high vacuum.