Characteristics of sputtered amorphous carbon films prepared by a closed-field unbalanced magnetron sputtering method

We discuss the tribological performance of sputtered amorphous carbon (a-C) films deposited by closed-field unbalanced magnetron (CFUBM) sputtering with a graphite target using a mixture of helium (He) and argon (Ar) as sputtering gases. We investigated the effects of the graphite target power density on the micro-structural and physical properties. In the Raman spectra, the G-peak position moved to the higher wavenumbers. The I_D/I_G ratio increased with the increase of target power density in the fixed DC bias voltage. This was the result of the structural change in the a-C film that resulted with the increase in sp² bonding fraction. Also, the maximum hardness of the a-C film was 23 GPa, the friction coefficient was 0.1, and the critical load was 25.9 N on the Si wafer. In addition, the compressive residual stress of the film increased a little with increasing target power density. Consequently, the various properties of a-C films, with an increase of the target power density, were associated with the increase of cross-linked sp² bonding fraction and the cluster size. The tribological properties of a-C film showed clear dependence on the energy of ion bombardment with the increase of plasma density during film growth.     

Dependence of RF power on the phase transformation for boron nitride films deposited on graphite at room temperature

Cubic boron nitride (cBN) thick films deposited on mainly c-axis-oriented graphite substrate at room temperature and zero bias by radio frequency (RF) magnetron sputtering were studied. In the growth process, RF power plays a key role in determining the content of cubic phase in films, while the conventional substrate heating and biasing have been neglected. With increase in RF power, the dominated content of films converts from explosion boron nitride (eBN) to cBN. The transformation mechanism has been discussed. The unique structural properties of the “soft” graphite are favorable to propose simple conditions for growing “hard” cBN films. Furthermore, the optical band gap of BN films having ∼90% cubic phase is of ∼5.8 eV obtained from ultraviolet–visible optical transmission measurement. The electron field emission examination shows that cBN film on graphite has a high emission current density of 2.8×10⁻⁵ A/cm² at an applied field of ∼30 V/μm.     

Physical Properties of Zinc Oxide Films Prepared by dc Reactive Magnetron Sputtering at Different Sputtering Pressures

Thin films of zinc oxide were deposited by dc reactive magnetron sputtering onto glass substrates held at a temperature of 663 K and oxygen partial pressure of 1x10^‐3 mbar, and at different sputtering pressures in the range 3x10^‐2 ‐ 10x10^‐2 mbar. The effect of sputtering pressure on the structural, electrical and optical properties of the films were systematically studied. The films were polycrystalline in nature with preferred (002) orientation. The temperature dependence of Hall mobility indicated that the grain boundary scattering of the charge carriers are predominant in these films. The films formed at a sputtering pressure of 6x10^‐2 mbar showed a low electrical resistivity of 6.9x10^‐2 Ohm cm, optical transmittance of 83% with an optical band gap of 3.28 eV.     

Influence of annealing condition on the properties of sputtered hafnium oxide

Hafnium oxide thin films were deposited on p-type (1 0 0) silicon wafers by reactive dc magnetron sputtering. Prior to the deposition of HfO₂ films, a thin Hf film was deposited. Sputtered HfO₂ thin films deposited at room temperature remain amorphous at T<650°C and orthorhombic phases were observed above 650 °C. The monoclinic phase which is a stable HfO₂ polymorphic form appeared after annealing above 800 °C. Capacitance equivalent thickness values decreased and leakage characteristics are improved by the Hf interlayer and O₂ settlement process. The decrease of accumulation capacitance values upon annealing is due to the growth of an interfacial layer upon post-annealing. The flat band voltage (V_FB) shifts negatively due to positive charge generated during post-annealing.     

Evolution from (110) Fe to (111) Fe3O4 thin films grown by magnetron sputtering using Fe2O3 target

Fe and Fe₃O₄ thin films were grown by radio frequency magnetron sputtering. Fe₂O₃ was used as the target and hydrogen was introduced together with Argon gas to provide a certain reducing atmosphere. By varying H₂/Ar flow ratio, the changes in composition and structure of the thin films from (110) Fe to (111) Fe₃O₄ were observed by X-ray diffraction. The valence states of Fe in the thin films were analyzed by X-ray photoelectron spectroscopy. Magnetization measurements indicate that the Fe thin films grown with low H₂/Ar flow ratios possess large coercive force. It was ascribed to the increasing boundary density and the increasing amount of Fe oxides such as FeO distributed at the boundary.     

Amorphous tungsten-doped In2O3 transparent conductive films deposited at room temperature from metallic target

Amorphous tungsten-doped In₂O₃ (IWO) films were deposited from a metallic target by dc magnetron sputtering at room temperature. Both oxygen partial pressure and sputtering power have significant effects on the electrical and optical properties of the films. The as-deposited IWO films with the optimum resistivity of 5.8 × 10^?4 Ω·cm and the average optical transmittance of 92.3% from 400 to 700 nm were obtained at a W content of 1 wt%. The average transmittance in the near infrared region (700–2500 nm) is 84.6–92.8% for amorphous IWO prepared under varied oxygen partial pressure. The mobility of the IWO films reaches its highest value of 30.3 cm² V^?1 s^?1 with the carrier concentration of 1.6 × 10²⁰ cm^?3, confirming their potential application as transparent conductive oxide films in various flexible devices.     

Characterizations of a-Se based photodetectors using X-ray photoelectron spectroscopy and Raman spectroscopy

The ‘PLUMBICON’ was one of the first successful imaging tubes using amorphous selenium (a-Se) and many followed. Significant properties of a-Se based imaging tubes have been rediscovered through the invention of the ‘HARP (high-gain avalanche rushing amorphous photoconductor)’, but its operational mechanism and the physics, however are yet poorly described. Previously, we have fabricated photodetectors using nitrogen (N)-doped diamond as a cold cathode and a-Se as a photoconducting target, which successfully responded to light illumination, The device performance,in this case, deteriorates after continuous use largely due to the degradation of a-Se. In this paper, a-Se and amorphous arsenic selenide (a-As₂Se₃) films have been deposited Stoichiometry has been determined by XPS (X-ray photoelectron spectroscopy) followed by Raman spectroscopy characterization. We have found that even an extremely weak incident laser power causes sample degradation during signal accumulation. We speculate that either the incident laser itself and/or the temperature rise due to illumination causes the phase transition in a-Se films. In addition, when As is added into the film, the phase transition leading the degradation is hardly observed, implying that As affects the formation of crystalline Se making chemical bonds in the crystallographic network stronger.     

Thermoelectric Power of Polycrystalline Sb2Te3 Films

Polycrystalline stochiometric films of Sb₂Te₃ with different thickness were prepared on glass substrates by a flash evaporation technique at constant substrate temperature of 423 K. The thermoelectric power of these films was determined by measuring integrally the developed thermo — e.m.f. at different temperature differences between the hot and cold ends. The thermoelectric power of Sb₂Te₃ films was determined as a function of the temperature and thickness of the films. It was found that the Fermi level becomes pinned at higher temperatures. The values of γ, E₀, and A parameters were determined as functions of the thickness of the films. The dependence of the thermoelectric power on the reciprocal thickness of the films was explained on the basis of the grain size effect.     

Structure and Optical Properties of dc Reactive Magnetron Sputtered Zinc Oxide Films

Zinc oxide films were deposited on glass substrates in argon and oxygen atmosphere by dc reactive magnetron sputtering using a metallic zinc target. The influence of oxygen pressure and substrate temperature on the structure and optical properties of the films were systematically investigated and optimised the deposition parameters to prepare single phase zinc oxide films with preferred (002) orientation. At an optimum oxygen pressure of 1x10^-3 mbar and substrate temperature of 663 K, the films exhibited an optical transmittance of 83% with a band gap of 3.28 eV.     

Optical properties of Al‐doped ZnO thin films deposited by two different sputtering methods

Aluminum‐doped zinc oxide (AZO) thin films were deposited on sapphire (002) and glass substrates by two different sputtering techniques radio frequency magnetron cosputtering of AZO and ZnO targets and sputtering of an AZO target. The dependence of the photoluminescence (PL) and transmittance properties of the AZO films deposited by cosputtering and sputtering on the AZO/ZnO target power ratio, R and the O₂/Ar flow ratio, r were investigated, respectively. Only a deep level emission peak appears in the PL spectra of cosputtered AZO films whereas both UV emission and deep level emission peaks are observed in the PL spectra of sputtered AZO films. The absorption edges in the transmittance spectra of the AZO films shift to the lower wavelength region as R and r increase. Also effects of crystallinity, surface roughness, PL on the transmittance of the AZO films were explained using the X‐ray diffraction (XRD), atomic force microscopy (AFM), and PL analysis results. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structural study of undoped and (Mn, In)-doped SnO2 thin films grown by RF sputtering

Undoped and 5%(Mn, In)-doped SnO₂ thin films were deposited on Si(1 0 0) and Al₂O₃ (R-cut) by RF magnetron sputtering at different deposition power, sputtering gas mixture and substrate temperature. X-ray reflectivity was used to determine the films thickness (10–130 nm) and roughness (～1 nm). The combination of X-ray diffraction and Mössbauer techniques evidenced the presence of Sn⁴⁺ in an amorphous environment, for as-grown films obtained at low power and temperature, and the formation of crystalline SnO₂ for annealed films. As the deposition power, substrate temperature or O₂ proportion are increased, SnO₂ nanocrystals are formed. Epitaxial SnO₂ films are obtained on Al₂O₃ at 550 °C. The amorphous films are quite uniform but a more columnar growth is detected for increasing deposition power. No secondary phases or segregation of dopants were detected.     

Measuring the Electrical Conductivity of Carbon Nanotubes Grown on Sodalime Glass Substrates using Cu as Catalyst

We have studied the electrical resistance of carbon nanotubes (CNTs) grown on sodalime glass using Cu as catalyst at 580°C temperature. The conductivity was measured at room temperature using four point probe technique. The Cu catalyst was coated on glass substrate by using dc magnetron sputtering system and etched by hydrogen (H₂) gas in order to form nanometer sized catalytic particles. Mixture of C₂H₂/H₂/Ar (20:80:100 standard centimeter cubic per minutes) gases were heated at 580°C for growth of CNTs on a glass substrate by using Thermal Chemical Vapor Deposition (TCVD). The temperature dependence of sheet resistance and current-voltage characteristics of the film were measured by a four point probes method. The morphology of the catalyst surface was probed by Atomic Force Microscopy (AFM), and the growth behavior of CNTs was investigated by scanning electron microscopy (SEM).     

Optical band gap of zinc nitride films prepared by reactive rf magnetron sputtering

Polycrystalline Zn₃N₂ films are prepared on Si and quartz glass substrates by RF magnetron sputtering at room temperature. The structural and optical properties are studied by X‐ray diffraction and double beam spectrophotometer, respectively. X‐ray diffraction indicates that the Zn₃N₂ films deposited on Si and quartz glass substrates both have a preferred orientation in (321) and (442), also are cubic in structure with the lattice constant a=0.9847 and 0.9783 nm, respectively. The absorption coefficients as well as the film thickness are calculated from the transmission spectra, and their dependence on photon energy is examined to determine the optical band gap. Zn₃N₂ is determined to be an indirect‐gap semiconductor with the band gap of 2.11(2) eV. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electrical investigation of polythiophene–poly(vinyl acetate) composite films via VTF and impedance spectroscopy

Polythiophene (PTP) and poly (vinyl acetate) (PVAc) composite films were prepared by chemical oxidative polymerization method with FeCl₃ as an oxidant, in methanol at room temperature. Their dc conductivities as a function of temperature (313–358 K) were measured. An attempt has been made to investigate the effect of temperature and concentration of ferric chloride oxidant on the conductivity of polythiophene–poly(vinyl acetate) composite films. For fixed wt% of PVAc, the dc electrical conductivity of the film initially increases with the molar concentration of FeCl₃ and then decreases with the further increase in the concentration of FeCl₃. The temperature dependence of conductivity showed Arrhenius behavior. The conductivity isotherms show VTF behavior which is typical for ion conducting polymers. The Nyquist plot of Z′ vs. Z″ were plotted for frequency range 100 Hz–200 kHz and temperature range of 313–358 K. These plots consist of semicircles for higher temperatures. This suggests Debye type relaxation mechanism. The equivalent circuit consists of parallel combination of bulk resistance R_B and bulk capacitance C_B. The bulk resistance R_B of the samples decreased with increase in temperature.     

Confocal spectromicroscopy of amorphous and nanocrystalline tungsten oxide films

A Raman confocal spectromicroscopic system was used to study in situ phase composition and surface morphology in amorphous and nanocrystalline tungsten oxide and tungstate thin films, prepared on silicon and glass substrates by dc magnetron co-sputtering technique. The possible use of these films for the phase-change optical recording was demonstrated using 442 nm He–Cd laser with a variable power of up to 50 mW. The formation of nanocrystalline tungsten trioxide or tungstate phases was observed under the laser irradiation. These nanocrystalline phases show relatively strong Raman activity, which can be used for information reading purposes. A multilayer structure composed of several tungstate films with different chemical composition is proposed as potential write-once optical recording media.     

Structural analysis of Cd-Te-O films prepared by RF reactive sputtering

Crystalline and microcrystalline Cd-Te-O samples have been obtained by RF reactive sputtering from a CdTe target using N₂O as oxidant. The growth conditions were substrate temperatures of 323 K, 573 K and 773 K and cathode voltage of −400 V, corresponding to 30 W of forward power. The samples were studied by micro-Raman spectroscopy, X-ray diffraction and optical transmittance. The films are remarkably transparent in the visible range, with transmittances about 88% at 400 nm and band gap energies above the absorption edge of the glass substrates. Although only the samples prepared at 773 K present defined diffraction peaks, the analysis of the Raman spectra indicate that samples prepared at 323 K and 573 K have a defined microstructure indeed. The spectra fitting performed by comparison with pattern compounds demonstrate that Cd-Te-O films are formed of Te-O units similar to those present in metal oxide-doped tellurite glasses, such as TeO₃ and TeO_3 + 1 linked through Cd-O bonds. As the substrate temperature increases the microstructure evolves from a γ-TeO₂ richer state to Cd_xTe_yO_z. In the crystalline sample the main phase identified was CdTeO₃ even though evidence of other phases was observed.     

Effect of Electric Field on Dielectric Properties of SnO2 Sb2O3 and their Mixed Thin Films

Thin films of various thicknesses in the MIM structure have been prepared from the the powders of SnO₂, Sb₂O₃ and (SnO₂ + Sb₂O₃) of high purity by the thermal evaporation technique in a vacuum of 10⁻⁵ Torr. Dielectric properties of SnO₂, Sb₂O₃, and their mixed thin films have been studied with ac and dc electric fields and frequency. Capacitance and loss tangent are almost independent on dc voltage upto 1.0 V for SnO₂, 10.0 V for Sb₂O₃ and 2.5 V for mixed films. These capacitors become unstable at 1.0 V for SnO₂ films and 2.5 V for mixed films. For higher film thicknesses the decay in these films starts at higher voltages. Capacitance and loss tangent increases with applied ac voltage in SnO₂, Sb₂O₃, and their mixed films. A comparison of the capacitance values of SnO₂, Sb₂O₃, and their mixed films showed that the capacitance values are less in Sb₂O₃ as compared to SnO₂ films. In mixed films the capacitance is greater than the constituent films. These studies have shown that Sb₂O₃ films are found to be more stable compared to SnO₂ and their mixed films for ac and dc voltages. The results thus obtained on SnO₂, Sb₂O₃, and their films are presented and discussed.     

SiOx films prepared using RF magnetron sputtering with a SiO target

In this study, SiO_x thin films were prepared using reactive radio frequency magnetron sputtering at room temperature with a SiO sintered target. The obtained SiO_x films were identified using X-ray diffraction, transmission electron microscopy, infrared absorption spectroscopy, X-ray photoelectron spectroscopy and ultraviolet-visible transmittance measurement. The x in SiO_x film was controlled from 0.98 to 1.70 by changing the oxygen flow ratio at deposition. Increasing the oxygen flow ratio increased the optical gap of the SiO_x films from 3.7 to greater than 6 eV.     

Structure and growth morphology of Gd2O3-doped CeO2 thin films

Gd₂O₃-doped CeO₂ (Gd_0.1Ce_0.9O_1.95, GDC) thin films were synthesized on (1 0 0) Si single crystal substrates by a reactive radio frequency magnetron sputtering technique. Structures and surface morphologies were characterized by X-ray diffraction (XRD), Atomic Force Microscopy (AFM) and one-dimensional power spectral density (1DPSD) analysis. The XRD patterns indicated that, in the temperature range of 200–700 °C, f.c.c. structured GDC thin films were formed with growth orientations varying with temperature—random growth at 200 °C, (2 2 0) textures at 300–600 °C and (1 1 1) texture at 700 °C. GDC film synthesized at 200 °C had the smoothest surface with roughness of R_rms=0.973 nm. Its 1DPSD plot was characterized with a constant part at the low frequencies and a part at the high frequencies that could be fitted by the f^−2.4 power law decay. Such surface feature and scaling behavior were probably caused by the high deposition rate and random growth in the GDC film at this temperature. At higher temperatures (300–700 °C), however, an intermediate frequency slope (−γ₂≈−2) appeared in the 1DPSD plots between the low frequency constant part and the high frequency part fitted by f⁻⁴ power law decay, which indicated a roughing mechanism dominated by crystallographic orientation growth that caused much rougher surfaces in GDC films (R_rms>4 nm).