Rf-Magnetron Sputtering Research Papers - Academia.edu (original) (raw)

Metal-doped TiO 2 RF-magnetron sputtering Sol-gel method Visible light irradiation a b s t r a c t Cr-or Fe-ion-doped TiO 2 thin films have been synthesized by radio-frequency magnetron sputtering and a sol-gel method to study hydrogen generation by photocatalytic watersplitting under visible light irradiation. The doping method, dopant concentration, charge transfer from metal dopants to TiO 2 , and type of dopants used for modification of TiO 2 were investigated for their ability to enhance photocatalytic activity. UV-Visible spectra show that the metal-doped-TiO 2 obtained by sputtering is much more efficient than that obtained by the sol-gel technique at inducing a red shift of the absorption edge in the visible light range. Low concentration metal ion doping must be done near the conducting indium tin oxide (ITO) -TiO 2 interface to avoid the formation of recombination centers for photo-generated electron-hole pairs. H 2 production rate (mmol/h) is higher for Fe-doped TiO 2 (15.5 mmol/h) than for Cr-doped TiO 2 (5.3 mmol/h) due to the ability of Fe ions to trap both electrons and holes, thus avoiding recombination, while Cr can only trap one type of charge carrier. A constant H 2 generation rate is obtained for long periods of time by all the investigated TiO 2 films because of the separate evolution of H 2 and O 2 gases, thus eliminating the back-reaction effect. ª (R. Dholam). A v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / h e

2013

We report on fabrication of novel field-effect transistors (FETs) based on transition metal dichalcogenides. The unique structure of single crystals of these layered inorganic semiconductors enables fabrication of FETs with intrinsically low field-effect threshold and high charge carrier mobility, comparable to that in the best single-crystal Si FETs (up to 500 cm 2 /Vs for the p-type conductivity in the WSe 2 -based FETs at room temperature). These novel FETs demonstrate ambipolar operation. Owing to mechanical flexibility, they hold potential for applications in "flexible" electronics.

2005, Thin Solid Films

Zinc oxide is a well-known wide band gap semiconductor material (3.4 eV at room temperature, in the crystalline form), which has many applications, such as for transparent conductors, varistors, surface acoustic waves, gas sensors, piezoelectric transducers and UV detectors. More recently, it is attracting considerable attention for its possible application to thin film transistors. In this paper, we present some of the recent results already obtained as well as the ones that are being developed in our laboratory. The main advantage presented by these new thin film transistors is the combination of high channel mobility and transparency produced at room temperature which makes these thin film transistors a very promising low cost device for the next generation of invisible and flexible electronics. Moreover, the processing technology used to fabricate this device is relatively simple and it is compatible with inexpensive plastic/flexible substrate technology. D

1997, Thin Solid Films

Al-doped zinc oxide (AZO) films are prepared by RF magnetron sputtering on glass and Si substrates with specifically designed ZnO targets containing different amounts of A1203 powder as a doping source. The physical properties of the AZO films are investigated in terms of the preparation conditions, such as A120 3 content in the target, RF power (PRF), substrate temperature (T~) and working pressure (Pw). The crystal structure of the AZO film is hexagonal wurtzite, and all the films show the typical crystallographic orientation, with the c-axis perpendicular to the substrate. The growth rate increases with increasing Pro,, but decreases with increasing T~ and Pw. Films 1500 ,~ thick with the lowest resistivity (p) of 4.7 × 10 .4 ~ cm and the transmittance over 90% at the visible region are prepared by using norminal 3 wt.% A1203 target at T s = 150°C, Pw = 2 mTorr an d Pay = 150 W. Optical transmittance measurements show that AZO films are degenerate semiconductors with direct bandgap. The optical energy bandgap for undoped ZnO film is ~ 3.3 eV and those for AZO films increase as the carrier concentration (n e) in the film increases. The blue shift in the AZO films is proportional to one third power of he. © 1997 Elsevier Science S.A.

1992

The polycrystalline mercuric iodide thick-film array was deposited by hot wall physical vapor deposition (HWPVD) method using an aluminum alloy mask. The pixel size of the 4×4 array is 5×5 mm 2 , and pixel spacing is about 0.2mm.

2008, IEEE Electron Device Letters

In this letter, we report for the first time the use of a sheet of cellulose-fiber-based paper as the dielectric layer used in oxide-based semiconductor thin-film field-effect transistors (FETs). In this new approach, we are using the cellulosefiber-based paper in an "interstrate" structure since the device is built on both sides of the cellulose sheet. Such hybrid FETs present excellent operating characteristics such as high channel saturation mobility (> 30 cm 2 /Vs), drain-source current on/off modulation ratio of approximately 10 4 , near-zero threshold voltage, enhancement n-type operation, and subthreshold gate voltage swing of 0.8 V/decade. The cellulose-fiber-based paper FETs' characteristics have been measured in air ambient conditions and present good stability, after two months of being processed. The obtained results outpace those of amorphous Si thin-film transistors (TFTs) and rival with the same oxide-based TFTs produced on either glass or crystalline silicon substrates. The compatibility of these devices with large-scale/large-area deposition techniques and lowcost substrates as well as their very low operating bias delineates this as a promising approach to attain high-performance disposable electronics like paper displays, smart labels, smart packaging, RFID, and point-of-care systems for self-analysis in bioapplications, among others.

2010, Applied Physics Letters

P-type thin-film transistors ͑TFTs͒ using room temperature sputtered SnO x ͑x Ͻ 2͒ as a transparent oxide semiconductor have been produced. The SnO x films show p-type conduction presenting a polycrystalline structure composed with a mixture of tetragonal ␤-Sn and ␣-SnO x phases, after annealing at 200°C. These films exhibit a hole carrier concentration in the range of Ϸ10 16 -10 18 cm −3 ; electrical resistivity between 10 1 -10 2 ⍀ cm; Hall mobility around 4.8 cm 2 / V s; optical band gap of 2.8 eV; and average transmittance Ϸ85% ͑400 to 2000 nm͒. The bottom gate p-type SnO x TFTs present a field-effect mobility above 1 cm 2 / V s and an ON/OFF modulation ratio of 10 3 .

2006, Applied surface science

Transparent conductive ZnO/Ag/ZnO multilayer electrodes having much lower electrical resistance than the widely used transparent electrodes were prepared by simultaneous RF magnetron sputtering of ZnO and DC magnetron sputtering of Ag. An Ag film with different thickness was used as intermediate metallic layers. The optimum thickness of Ag thin films was determined to be 6 nm for high optical transmittance and good electrical conductivity. With about 20-25 nm thick ZnO films, the multilayer showed high optical transmittance in the visible range of the spectrum and had color neutrality. The electrical and optical properties of the multilayers were changed mainly by Ag film properties. A high quality transparent electrode, having sheet resistance as low as 3 ohm/sq and high transmittance of 90% at 580 nm, was obtained and could be reproduced by controlling the preparation parameter properly. The above property is suitable as transparent electrode for dye sensitized solar cells (DSSC).

2000, Thin Solid Films

. Highly conductive and transparent in the visible range Al-doped ZnO ZnO:Al and undoped ZnO films have been deposited by RF magnetron sputtering. Reflection high-energy electron diffraction observations characterized them as textured. The habitus of the microcrystallites forming the texture depends on the Al doping. The layer texture of undoped ZnO films has texture axis parallel to the substrate. The ZnO:Al films, instead, show a columnar texture with texture axis perpendicular to the substrate. The Raman spectra of the films obtained by non-resonant excitation are completely different from those of the target material which is polycrystalline ZnO. For the interpretation of the different bands in the Raman spectra the existence of a depletion region near the grain boundaries has been assumed. The most intensive band in the Raman spectra at approximately 570 cm y1 has been assigned to electric field-induced Raman scattering on longitudinal optical phonons. The built-in electric field in the depletion region induces the Raman activity of the B modes and a band at 276 cm y1 appears in the spectra. Phonon 2 modes highly localized near the grain boundaries have been detected at 516 cm y1 and 468 cm y1 which are well pronounced in the Raman spectra for the doped samples. Localized modes were observed also in the infrared reflection spectra of the doped films. Surface enhanced Raman scattering has been applied and the band in the range 830᎐920 cm y1 has been interpreted as due to adsorbates from the ambient air. It has been shown that the non-resonant Raman scattering can be used for qualitative study of some details of the microstructure of the zinc oxide films like the built-in electric field and the adsorbates in the films. ᮊ M. Tzolov . 0040-6090r00r$ -see front matter ᮊ 2000 Elsevier Science B.V. All rights reserved. Ž . PII: S 0 0 4 0 -6 0 9 0 0 0 0 1 4 1 3 -9 ( ) M. Tzolo¨et al. r Thin Solid Films 379 2000 28᎐36 29

2011

ZnO thin films were fabricated on glass substrate by sol-gel method. A stable and homogeneous solution was prepared by dissolving zinc acetate dehydrate as a starting material in a solution of 2-methoxyethanol and monoethanolamine (MEA). The precursor concentration was selected as the parameter to optimize the thin films quality. The molar ratio of zinc acetate dehydrate was kept at 1. The thin films were preheated at 300° C for 10 minutes after each coating. After depositing all layers, the thin films are annealed for 1 hour in order to obtain transparent ZnO thin films. It was found that the precursor concentration affect the IV characteristic, transmittance, and the thickness of the resultant ZnO thin films.

2000, Journal of Applied Physics

ZnO thin films were epitaxially grown on α-Al2O3 (0001) substrate by radio-frequency (rf) magnetron sputtering. Among the ZnO films deposited at 550 °C, the film deposited at 80 W has the narrowest full width half maximum (FWHM) of x-ray diffraction (XRD) θ-rocking curve, 0.16°, indicating a highly c-axis oriented columnar structure. The FWHM of XRD θ-rocking curve of the ZnO film deposited at 120 W and 600 °C was 0.13° with a minimum channeling yield, 4%-5%. In photoluminescence (PL) measurement, only the sharp near band edge emission was observed at room temperature (RT). The FWHM of PL peak was decreased from 133 to 89 meV as rf power increased from 80 to 120 W at 550 °C, and that of film deposited at 120 W and 600 °C showed 76 meV which is lower value than any other ever reported. These PL results were somewhat opposite to that of XRD. From transmission electron microscopy analysis, grain size and defects were found to affect the PL properties. In this study, the PL property of undoped ZnO thin films is discussed in terms of the crystalline structure and the size of grain.

2006, Journal of Non-crystalline Solids

Multicomponent amorphous oxides are starting to emerge as a class of appealing semiconductor materials for application in transparent electronics. In this work, a high performance bottom-gate n-type transparent thin-film transistors are reported, being the discussion primarily focused on the influence of the indium zinc oxide active layer thickness on the properties of the devices. For this purpose, transparent transistors with active layer thicknesses ranging from 15 nm to 60 nm were produced at room temperature using rf magnetron sputtering. Optical transmittance data in the visible range reveals average transmittance higher than 80%, including the glass substrate. The devices work in the enhancement mode and exhibit excellent saturation drain currents. On-off ratios above 10 7 are achieved, but this value tends to be lower for devices with thicker semiconductor films, as a result of the decrease in the resistance of the channel region with increasing thickness. Channel mobilities are also quite respectable, with some devices presenting values around 40 cm 2 /V s, even without any annealing or other post-deposition improvement processes. Concerning the evolution of threshold voltage with the thickness, this work shows that it increases from about 3 V in thicker films up to about 10 V in the thinnest ones. The interesting electrical properties obtained and the versatility arising from the fact that it is possible to modify them changing only the thickness of the semiconductor makes this new transparent transistors quite promising for future transparent ICs.

2004, Journal of Applied Physics

This work presents a study of intrinsic zinc oxide thin film as ozone sensor based on the ultraviolet ͑UV͒ photoreduction and subsequent ozone re oxidation of zinc oxide as a fully reversible process performed at room temperature. The films analyzed were produced by spray pyrolysis, dc and rf magnetron sputtering. The dc resistivity of the films produced by rf magnetron sputtering and constituted by nanocrystallites changes more than eight orders of magnitude when exposed to an UV dose of 4 mW/ cm 2 . On the other hand, porous and textured zinc oxide films produced by spray pyrolysis at low substrate temperature exhibit an excellent ac impedance response where the reactance changes by more than seven orders of magnitude when exposed to the same UV dose, with a response frequency above 15 kHz, thus showing improved ozone ac sensing discrimination.

2008, MRS Proceedings

Titanium dioxide thin films have been prepared from tetrabutyl-orthotitanate solution and methanol as a solvent by sol-gel dip coating technique. TiO 2 thin films prepared using a sol-gel process have been analyzed for different annealing temperatures. Structural properties in terms of crystal structure were investigated by Raman spectroscopy. The surface morphology and composition of the films were investigated by atomic force microscopy (AFM). The optical transmittance and reflectance spectra of TiO 2 thin films deposited on silicon substrate were also determined. Spectroscopic ellipsometry study was used to determine the annealing temperature effect on the optical properties and the optical gap of the TiO 2 thin films. The results show that the TiO 2 thin films crystallize in anatase phase between 400 and 800 • C, and into the anatase-rutile phase at 1000 • C, and further into the rutile phase at 1200 • C. We have found that the films consist of titanium dioxide nano-crystals. The AFM surface morphology results indicate that the particle size increases from 5 to 41 nm by increasing the annealing temperature. The TiO 2 thin films have high transparency in the visible range. For annealing temperatures between 1000 and 1400 • C, the transmittance of the films was reduced significantly in the wavelength range of 300-800 nm due to the change of crystallite phase and composition in the films. We have demonstrated as well the decrease of the optical band gap with the increase of the annealing temperature.

2007, Journal of Physics and Chemistry of Solids

Cu2ZnSnSe4 (CZTSe) thin films were grown in a single step procedure by RF magnetron sputtering from a compacted powder consisting of blended chalcogenides. Targets with various chalcogenide mole ratios were designed for the purpose of preparing stoichiometric as-grown films. The material concentrations of the films grown at room temperature were found to depend on the mole ratio of the chalcogenides in the targets. It was found that a significant deviation of material concentration of the films from ideal stoichiometry led to the formation of CuSe, ZnSe and SnSe secondary phases. CZTSe films with a stannite phase could be grown even at room temperature from the sputtering target containing Cu2Se with corresponding growth orientations of (101), (112), (220/204), (312/116) and (332/316). The p-type CZTSe film grown at a substrate temperature of 150C showed a high absorption coefficient of 10cm with an optical band gap of 1.56 eV, resistivity as low as 1.482Ωcm and carrier concentration of 1×10cm. These results suggested that the control of the target compositions was crucial to grow single phase and stoichiometric quaternary CZTSe films.

2002, Microelectronic Engineering

2005, Science and Technology of Advanced Materials

This review article summarizes briefly some important achievements of our recent reserach on anatase and/or rutile TiO 2 thin films, fabricated by helicon RF magnetron sputtering, with good crystal quality and high density, and gives the-state-of-the-art of the knowledge on systematic interrelationship for fabrication conditions, crystal structure, composition, optical properties, and bactericidal abilities, and on the effective surface treatment to improve the optical reactivity of the obtained films. q

1995, Journal of Biomedical Materials Research

2003, Superconductor Science & Technology

We have grown epitaxial CeO 2 buffer layers on biaxially textured Ni-W substrates for YBCO coated conductors using a newly developed metal organic decomposition (MOD) approach. Precursor solution of 0.25 M concentration was spin coated on short samples of Ni-3 at%W (Ni-W) substrates and heat-treated at 1100 • C in a gas mixture of Ar-4%H 2 for 15 min. Detailed x-ray studies indicate that CeO 2 films have good out-of-plane and in-plane textures with full-width-half-maximum values of 5.8 • and 7.5 • , respectively. High temperature in situ XRD studies show that the nucleation of CeO 2 films starts at 600 • C and the growth completes within 5 min when heated at 1100 • C. SEM and AFM investigations of CeO 2 films reveal a fairly dense microstructure without cracks and porosity. Highly textured YSZ barrier layers and CeO 2 cap layers were deposited on MOD CeO 2 -buffered Ni-W substrates using rf-magnetron sputtering. Pulsed laser deposition (PLD) was used to grow YBCO films on these substrates. A critical current, J c , of about 1.5 MA cm −2 at 77 K and self-field was obtained on YBCO (PLD)/CeO 2 (sputtered)/YSZ (sputtered)/CeO 2 (spin-coated)/Ni-W.

1996, Physica Status Solidi (a)

Copper oxide thin films were prepared by reactive rf magnetron sputtering of a pure copper target in an oxygen-argon atmosphere. The phases of the deposited films strongly depend on the oxygen content in the sputtering gas. X-ray diffraction studies show that by controlling the oxygen partial pressure single phase CuzO and CuO can be obtained. The resistivity of the CuzO film in the present study is 43 SZ cm. The optical constants were evaluated from transmission and reflection measurements.

2005, Applied Surface Science

Indium tin oxide (ITO) thin films were deposited onto glass substrates by rf magnetron sputtering of ITO target and the influence of substrate temperature on the properties of the films were investigated. The structural characteristics showed a dependence on the oxygen partial pressure during sputtering. Oxygen deficient films showed (4 0 0) plane texturing while oxygen-incorporated films were preferentially oriented in the [1 1 1] direction. ITO films with low resistivity of 2.05 Â 10 À3 V cm were deposited at relatively low substrate temperature (150 8C) which shows highest figure of merit of 2.84 Â 10 À3 square/V # 2005 Published by Elsevier B.V.

2011, Current Applied Physics

Novel grapheneeTiO 2 (GReTiO 2 ) composite photocatalysts were synthesized by hydrothermal method. During the hydrothermal process, both the reduction of graphene oxide and loading of TiO 2 nanoparticles on graphene were achieved. The structure, surface morphology, chemical composition and optical properties of composites were studied using XRD, TEM, XPS, DRS and PL spectroscopy. The absorption edge of TiO 2 shifted to visible-light region with increasing amount of graphene in the composite samples. The photocatalytic degradation of methyl orange (MO) was carried out using grapheneeTiO 2 composite catalysts in order to study the photocatalytic efficiency. The results showed that GReTiO 2 composites can efficiently photodegrade MO, showing an enhanced photocatalytic activity over pure TiO 2 under visible-light irradiation. The enhanced photocatalytic activity of the composite catalysts might be attributed to great adsorptivity of dyes, extended light absorption range and efficient charge separation due to giant p-conjugation system and two-dimensional planar structure of graphene.

2008, International Journal of …

TiO 2 RF magnetron sputtering Sol-gel method Visible light irradiation a b s t r a c t TiO 2 thin films have been synthesized by radio-frequency magnetron sputtering and solgel method to study the hydrogen generation by photocatalytic water splitting under visible light irradiation. Photoelectrochemical cell with chemical bias, involving photoanode in form of TiO 2 film deposited on conducting indium tin oxide (ITO) film and Pt as cathode, is developed. The effect of conducting ITO layer on photo-voltage is studied by varying the thickness of ITO films. Constant H 2 generation rate is obtained for long period of time by both the TiO 2 films because of the separated evolution of H 2 and O 2 gas, thus eliminating the back-reaction effect. Sputter-deposited film as compared to sol-gelsynthesized film showed better H 2 generation rate, mainly explained in terms of the higher visible light absorption achieved by oxygen vacancies created in the TiO 2 film by the energetic target ions during deposition in pure Ar gas pressure. ª (R. Dholam). A v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / h e

2003, Thin Solid Films

To fabricate lateral-field excitation (LFE)-mode solid mounted resonator (SMR)-type film bulk acoustic resonators (FBARs), piezoelectric ZnO layers were deposited in an RF magnetron sputtering system. Control of the crystallinity, microstructure and electric properties of the piezoelectric layers was essential for fabricating high-quality LFE-mode SMR-type FBARs. In the appropriate deposition condition for FBAR devices, ZnO thin films with highly c-axis-preferred orientation (XRD rocking curve, ss2.178), high resistivity of 10 V cm and surface roughness of 10.6 A were deposited. Optimal substrate rotation was especially 6i mportant for improvement of the c-axis-preferred orientation of ZnO films. Plasma properties such as the electron temperature, plasma density and saturated ion current were also analyzed for optimal ZnO deposition conditions using a Langmuir doubleprobe system. The resonator, for which the active piezoelectric area was 200=200 mm , consisted of 1.25-mm-thick ZnO film 2 and a 110-nm Au electrode. Its series and parallel resonance frequencies appeared at 1.68 and 1.71 GHz, respectively, and the quality factor was 201.4"7.4. ᮊ

1997, Journal of Biomedical Materials Research

2004, Thin Solid Films

Transparent and highly conducting gallium-doped zinc oxide films were successfully deposited by rf sputtering at room temperature. The lowest resistivity achieved was 2.6=10 V cm for a thickness of 1100 nm (sheet resistance f1.6 Vysq), y4 with a Hall mobility of 18 cm yVs and a carrier concentration of 1.3=10 cm . The films are polycrystalline with a hexagonal 2 2 1 y3 structure and a strongly preferred orientation along the c-axis. A linear dependence between the mobility and the crystallite size was obtained. The films present a transmittance in the visible spectra between 80 and 90% and a refractive index of approximately 2, which is very close to the value reported for bulk material. ᮊ

2014

LiFePO 4 /C composite fibers were synthesized by using a combination of electrospinning and sol-gel techniques. Polyacrylonitrile (PAN) was used as an electrospinning media and a carbon source. LiFePO 4 precursor materials and PAN were dissolved in N,N-dimethylformamide separately and they were mixed before electrospinning. LiFePO 4 precursor/PAN fibers were heat treated, during which LiFePO 4 precursor transformed to energy-storage LiFePO 4 material and PAN was converted to carbon. The surface morphology and microstructure of the obtained LiFePO 4 /C composite fibers were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and elemental dispersive spectroscopy (EDS). XRD measurements were also carried out in order to determine the structure of LiFePO 4 /C composite fibers. Electrochemical performance of LiFePO 4 /carbon composite fibers was evaluated in coin-type cells. Carbon content and heat treatment conditions (such as stabilization temperature, calcination/carbonization temperature, calcination/carbonization time, etc.) were optimized in terms of electrochemical performance.

1993, Journal of Non-crystalline Solids

Copper nitride thin films were deposited on silicon wafers by reactive RF magnetron sputtering at various N 2 -gas partial pressures and substrate temperatures. X-ray diffraction measurements show that the films are composed of Cu 3 N crystallites with anti-ReO 3 structure and exhibit preferential orientation to either the [1 1 1] or [1 0 0] direction at particular N 2 pressures and substrate temperatures. The film growth prefers the [1 1 1] direction at the N 2 pressures and substrate temperatures below 2.50 mTorr and 1508C, respectively, and the [1 0 0] preference is achieved at 3.75 mTorr and 2508C, respectively. Such preferential film growth is interpreted as being due to the variation of Cu nitrification rate with N 2 pressure and substrate temperature. The pseudodielectric function of a Cu 3 N/Si film was measured by spectroscopic ellipsometry in the 0.8-5.0 eV range. It shows strong Fabry-Perot interference oscillations at low energies due to optical transparency of Cu 3 N. The fundamental optical band-gap energy of the compound is determined to be 1.5 eV. #

1999, Thin Solid Films

Aluminium-doped ZnO thin films, with a doping level in the range 2–2.8 at.%, were deposited by RF magnetron sputtering. Sputtering processes with pure Ar and Ar/H2 gas mixtures have been explored. Electrical conductivity and Hall mobility of ZnO:Al films were measured in a wide temperature range. It has been found that the addition of hydrogen to the sputtering gas is an effective method to modify the morphological, structural and electrical properties of the ZnO:Al films. A low hydrogen dilution is able to produce a noticeable improvement of the conductivity by means of a better effectiveness of the Al doping. ZnO:Al films deposited at low hydrogen dilution showed a columnar structure whereas at high hydrogen dilution spherical shaped domains were present, formed by many stacked crystallites. Carrier mobility for the former structure was limited by bulk mechanisms, particularly by acoustical phonon and ionized impurity scattering. Carrier mobility for the latter structure was limited by grain boundary mechanisms, particularly by tunnelling effect between neighbouring spherical macroaggregates.

2004, Solar Energy

Polycrystalline II-VI semiconductor materials show great promise for efficient, low-cost photovoltaics. Large-area deposition of the II-VI semiconductors such as CdTe is possible by a variety of methods but the use of a plasma-based method such as magnetron sputtering can have significant advantages. Here we present recent results in the fabrication of CdS/CdTe cells using rf magnetron sputtering and discuss some of the advantages that accrue from the use of sputtering methods in this class of materials. Some of these advantages are particularly relevant as the polycrystalline thinfilm PV community addresses issues related to the fabrication of tandem cells with efficiencies over 25%. Our best results have been obtained with sputtered ZnO:Al to achieve a CdTe solar cell having 14.0% efficiency at one sun with an air mass 1.5 global spectrum. We have also studied reactive sputtering of ZnTe:N which shows promise for use as a transparent back contact or as a recombination junction with ZnO:Al for II-VI based alloy top cells in a tandem solar-cell configuration. Finally, some advances have been made in substrate-configuration CdTe cells on Mo using sputter deposition that hold promise for flexible CdTe-based PV.

2002, Bulletin of Materials Science

Highly conducting and transparent ZnO : Al thin films were grown by off-axis rf magnetron sputtering on amorphous silica substrates without any post-deposition annealing. The electrical and optical properties of the films deposited at various substrate temperatures and target to substrate distances were investigated in detail. Optimized ZnO : Al films have conductivity of 2200 S cm -1 and average transmission in the visible range is higher than 85%. The conductivity and mobility show very little temperature dependence.

2008, Surface & Coatings Technology

Thin calcium phosphate coatings with a thickness of 0.09 to 2.7 µm were prepared by radio-frequency magnetron sputtering deposition on NiTi and Ti substrates at a substrate temperature of 500°C in argon atmosphere. Scanning electron microscopy (SEM) showed that the surface structure is uniform and dense without visible defects (pores and microcracks). Rutherford backscattering spectroscopy (RBS) and energy-dispersive X-ray spectroscopy (EDX) confirmed that the coating contains calcium, phosphorus, and oxygen with a uniform composition. Crystallographically, the coating consists of crystalline hydroxyapatite which is also supported by infrared spectroscopy. The mechanical characteristics of the coating were measured by nanoindentation (Vickers indenter), giving a nanohardness of 10 GPa and a Young's modulus of 110 GPa. The strength of adhesion of the calcium phosphate coating to the metallic substrates depended on the coating's thickness and decreased for a thickness larger than 1.6 µm. No difference was observed between NiTi and Ti substrates.

1995, Japanese Journal of Applied Physics

2011, Thin Solid Films

Typically, Cu(In,Ga)Se 2 (CIGS) thin films for photovoltaic devices are deposited by co-evaporation or, alternately, by deposition of the metals with or followed by treatment in a selenium environment. In this article, we describe CIGS films that are instead deposited by RF magnetron sputtering from a single quaternary target without any additional selenization. Devices built with these films exhibit efficiencies as high as 8.9%. We demonstrate that deposition power can be varied in order to change the film morphology and improve device performance.

2008, Solar Energy Materials and Solar Cells

Spectrally selective TiAlN/AlON tandem absorbers were deposited on copper and stainless steel substrates using a reactive DC/RF magnetron sputtering system. The compositions and thicknesses of the individual component layers were optimized to achieve high absorptance (a ¼ 0.931-0.942) and low emittance (e ¼ 0.05-0.06) on copper substrate. The experimental spectroscopic ellipsometric data have been fitted with the theoretical models to derive the dispersion of the optical constants (n and k). In order to study the thermal stability of the tandem absorbers, they were subjected to heat treatment (in air and vacuum) for different durations and temperatures. The tandem absorber deposited on Cu substrates exhibited high solar selectivity (a/e) of 0.946/0.07 even after heat treatment in air up to 600 1C for 2 h. At 625 1C, the solar selectivity decreased significantly on Cu substrates (e.g., a/e ¼ 0.924/ 0.30). The tandem absorber on Cu substrates was also stable in air up to 100 h at 400 1C with a solar selectivity of 0.919/0.06. Studies on the accelerated aging tests indicated that the activation energy for the degradation of the tandem absorber is of the order of 100 kJ/mol.

2004, Journal of Magnetism and Magnetic Materials

A series of ferrites was prepared using microwave sintering, starting with both hematite and magnetite precursors in the Ni 1Àx Zn x Fe 2 O 4 (x=0À1) system. X-ray diffraction measurements were performed to yield the lattice constant as function of the amount x of Zn substitution. For both hematite and magnetite series, the lattice parameter was found to increase with increasing x. M. ossbauer spectroscopy was performed at room temperature and spectra were analyzed using the binomial distribution. The hyperfine magnetic field of the octahedral sublattice was found to decrease with increasing the number of Zn nearest neighbors for all values of the substitution level. The area of the tetrahedral sublattice decreases with increasing x and the sublattice area of the octahedral sites increases correspondingly for both series of samples, as a result of substitution of iron by zinc in the tetrahedral sites. The hyperfine magnetic field of the tetrahedral sublattice was found to decrease as function of Zn amount x, for both hematite and magnetite series. However, in most cases, the hyperfine magnetic fields for the magnetite series are slightly less than those corresponding to the hematite series. r

2001, Thin Solid Films

Ž . X-Ray diffraction and X-ray texture analysis have been carried out on RF magnetron sputtered ITO indium tin oxide thin films on glass substrates in order to understand their crystal growth behaviour. Films deposited at various deposition rates and gas compositions were subjected to investigation. X-Ray diffraction analysis revealed the polycrystalline structure of the films Ž . with a difference in crystallographic orientation without any change in the BCC Body Centred Cubic structure. Both the increase in deposition rate and gas composition reflects the change in crystallographic orientation. X-Ray texture analysis on the grown films revealed also a difference in film texturization following the change in crystallographic orientation. Strong orientation Ž . of crystallites perpendicular to the substrate were observed for films grown with 400 preferential plane. ᮊ C. Minarini . 0040-6090r01r$ -see front matter ᮊ 2001 Elsevier Science B.V. All rights reserved. Ž . PII: S 0 0 4 0 -6 0 9 0 0 1 0 0 8 2 0 -3 ( )

2006, Journal of Micromechanics and Microengineering

TiO 2 thin films were prepared under various conditions by using a reactive RF sputtering technique. The structural, optical and electrical characteristics of the films have been investigated. All as-deposited films were amorphous. After annealing at T > 673 K, the crystallinity of the observed tetragonal anatase phase appeared improved. The optical band gap, determined by using Tauc plot, has been found to amount to 3.38 AE 0.03 and 3.21 AE 0.03 eV for the direct and indirect transition, respectively. Also the complex optical constants for the wavelength range 300-2500 nm are reported. Using the two-point probe technique, the dark resistivity has been measured as a function of the film thickness, d. The resistivity, r, of the samples has been found to decrease markedly with increasing thickness, but only for d < 100 nm. The behaviour of rd versus d was found to fit properly with the Fuchs and Sondheimer relation with parameters r o = 4.95 Â 10 6 V cm and mean free path, l = 310 AE 2 nm. The log r versus 1/T curves show three distinct regions with values for the activation energy of 0.03 AE 0.01, 0.17 AE 0.01 and 0.50 AE 0.02 eV, respectively.

2009, Applied Surface Science

This study experimentally investigates the capabilities of iron-gallium nanowire arrays as artificial cilia transducers. The experiments are conducted with a custom manipulator device incorporated into the stage of a scanning electron microscope (SEM) for observation. Individual nanowires of varying size and composition are mechanically tested statically and dynamically to determine the elastic properties and failure modes. Magnetic force microscopy (MFM) is used to observe the effect of stress on the magnetic domain structure of these nanowires. Entire arrays of close packed wires are mounted onto giant magnetoresistance (GMR) sensors to measure the coupled magnetic induction response resulting from bending the array. This data is compared with expected results from theory.

2008, Journal of Physics D-applied Physics

Ferroelectric SrBi2Ta2O9 (SBT) thin films have been deposited by the radio-frequency magnetron sputtering technique on bare p-Si as well as on HfO2 insulating buffer p-Si. XRD patterns revealed the formation of a well-crystallized SBT perovskite thin film on the HfO2 buffer layer. The electrical properties of the metal-ferroelectric-insulator-semiconductor (MFIS) structure were characterized by varying thicknesses of the HfO2 layer. The MFIS structure exhibits a maximum clockwise C-V memory window of 1.60 V when the thickness of the HfO2 layer was 12 nm with a lower leakage current density of 6.20 × 10-7 A cm-2 at a positive applied voltage of 7 V. However, the memory window reaches a maximum value of 0.7 V at a bias voltage of ±5 and then decreases due to charge injection in the case of the insulating buffer layer thickness of 3 nm. The density of oxide trapped charges at/near the buffer layer-ferroelectric interface is studied by the voltage stress method. Capacitance-voltage (C-V) and leakage current density (J-V) characteristics of the Al/SBT/HfO2/Si(1 0 0) capacitor indicate that the introduction of the HfO2 buffer layer prevents interfacial diffusion between the SBT thin film and the Si substrate effectively and improves the interface quality. Furthermore, the Al/SBT/HfO2/Si structures exhibit excellent retention characteristics, the high and low capacitance values clearly distinguishable for over 1 h and 30 min. This shows that the proposed Al/SrBi2Ta2O9/HfO2/Si structure is ideally suitable for high performance ferroelectric memories.

Amorphous tantalum oxide thin films were deposited by reactive rf magnetron sputtering onto ͓001͔ silicon substrates. Growth temperature, oxygen partial pressure, and total gas pressure have been varied to obtain thin films with different densities. The thin films were analyzed by glancing angle-of-incidence x-ray diffraction, atomic force microscopy, and variable angle-of-incidence spectroscopic ellipsometry in the near infrared to vacuum ultraviolet spectral region for photon energies from Eϭ1 to 8.5 eV, and in the infrared region from Eϭ0.03 to 1 eV. We present the dielectric function of amorphous tantalum oxide obtained by line shape analysis of the experimental ellipsometric data over the range from Eϭ0.03 to 8.5 eV ͑40 m-145 nm͒. In the infrared spectral region the ellipsometric data were analyzed using Lorentzian line shapes for each absorption mode observed in the spectra. Amorphous tantalum oxide optical properties in the near infrared to vacuum ultraviolet spectral region were extracted by using a Kim and Garland parameter algorithm ͓C. C. Kim et al., Phys. Rev. B 45, 11 749 ͑1992͔͒ in order to model the absorption due to the fundamental band gap of the material. We consider thin film porosity, and therefore analyzed the experimental ellipsometric data by an effective medium approach. We obtain information on the tantalum oxide optical properties, a percentage of void fraction, and film thickness. The ''optical'' percentage of void fractions corresponds to surface roughness measured by atomic force microscopy and depends on deposition parameters.

2006, Thin Solid Films

In this paper we present results of indium zinc oxide deposited at room temperature by rf magnetron sputtering, with an electron mobility as high as 60 cm 2 /Vs. The films present a resistivity as low as 5 Â 10 À 4 V cm with an optical transmittance of 85%. The structure of these films seems to be polymorphous (mix of different amorphous and nanocrystalline phases from different origins) as detected from XRD patterns with a smooth surface and from SEM micrographs, is highly important to ensure a long lifetime when used in display devices. D

2008, IEEE Transactions on Electron Devices

During the last years, oxide semiconductors have shown that they will have a key role in the future of electronics. In fact, several research groups have already presented working devices with remarkable electrical and optical properties based on these materials, mainly thin-film transistors (TFTs). Most of these TFTs use indium-tin oxide (ITO) as the material for source/drain electrodes. This paper focuses on the investigation of different materials to replace ITO in inverted-staggered TFTs based on gallium-indium-zinc oxide (GIZO) semiconductor. The analyzed electrode materials were indium-zinc oxide, Ti, Al, Mo, and Ti/Au, with each of these materials used in two different kinds of devices: one was annealed after GIZO channel deposition but prior to source/drain deposition, and the other was annealed at the end of device production. The results show an improvement on the electrical properties when the annealing is performed at the end (for instance, with Ti/Au electrodes, mobility rises from 19 to 25 cm 2 /V · s, and turn-on voltage drops from 4 to 2 V). Using time-of-flight secondary ion mass spectrometry (TOF-SIMS), we could confirm that some diffusion exists in the source/drain electrodes/semiconductor interface, which is in close agreement with the obtained electrical properties. In addition to TOF-SIMS results for relevant elements, electrical characterization is presented for each kind of device, including the extraction of source/ drain series resistances and TFT intrinsic parameters, such as µ i (intrinsic mobility) and V Ti (intrinsic threshold voltage).

2006, Vacuum

Synthesis of various functional nanoassemblies, by using a combination of low-pressure reactive plasma-enhanced chemical deposition and plasma-assisted rf magnetron sputtering deposition is reported. This paper details how selective generation and manipulation of the required building blocks and management of unwanted nanoparticle contaminants, can be used for plasma-aided nanofabrication of carbon nanotip microemitter structures, ultra-high aspect ratio semiconductor nanowires, ordered quantum dot arrays, and microporous hydroxyapatite bioceramics. Emerging challenges of the plasma-aided synthesis of functional nanofilms and nanoassemblies are also discussed. r

2002, Materials Science and Engineering: C

Experimental investigation of functionally graded calcium phosphate-based bio-active films on Ti -6Al -4V orthopaedic alloy prepared in an RF magnetron sputtering plasma reactor is reported. The technique involves concurrent sputtering of Hydroxyapatite (HA) and Ti targets, which results in remarkably enhanced adhesion of the film to the substrate and stability of the interface. The films have been characterized using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The XPS data show that the films are composed of O, Ca, P and Ti, and reveal the formation of OjP groups and hybridization of O -Ca -P. The XRD pattern shows that the Ca -P thin films are of crystalline calcium oxide phosphate (4CaOÁP 2 O 5 ) with preferred orientation varying with processing parameters. High-resolution optical emission spectra show that the emission of CaO is dominant. The CaO, PO and CaPO species are strongly influenced by deposition conditions. The introduction of Ti element during deposition provides a stable interface between bio-inert substrates Ti -6Al -4V and bioactive HA coating. In-vitro cell culturing tests suggest excellent biocompatibility of the Ca -P -Ti films. D

2011, Chemistry - A European Journal

We present here a cruciform oligo(phenylenevinlyene) 2,5,2′,5′-tetrastyrylbiphenyl (TSB) exhibits excellent properties as host material for blue emitting guest molecule 1,4-di(4′-N,N-diphenylaminostyryl)benzene (DPA-DSB). TSB, which is constructed by linking two rigid distyrylbenzene (DSB) through the phenyl-phenyl bond, shows good optical and electronic properties e.g. high photoluminescent (PL) efficiency and wide band gap similar to DSB. Meanwhile, the central biphenyl core in TSB, which allows the relatively free rotation of two DSB segments along the biphenyl bond, makes it to be conformational multiformity and relatively flexible. As the result, TSB shows the good film forming property and larger loading ability to the guest molecules. The PL efficiencies of guest-host films of DPA-DSB and TSB arrive at the high level around 70% (68% for the 2 wt % DPA-DSB doped film and 72% for the 8 wt % DPA-DSB doped film), which is approaching the PL efficiency of the guest DPA-DSB in dilute solution (78%), indicating that the host TSB can sufficiently disperse the guest DPA-DSB with little aggregation. The organic light-emitting devices using DPA-DSB (2 wt %) doped TSB as blue emitting layer show the maximum efficiency of 12.2 cd/A (6.2%) and 6.39 lm/W, and the maximum brightness of 17350 cd/m 2 . Upon further analysis, it has been revealed that the Förster energy transfer and charge trapping are demonstrated to cooperatively work in this doping system.

2011

We have carried out the powder x-ray diffraction and dielectric studies on multiferroic particulate composite xNi 0.9 Zn 0.1 Fe 2 O 4 /(1-x)PbZr 0.52 Ti 0.48 O 3 with x=0.15, 0.30, 0.45, 0.60, 0.75 and 0.90 to explore the structural and ferroelectric properties. A conventional double sintering method was used to prepare the xNi 0.9 Zn 0.1 Fe 2 O 4 /(1-x)PbZr 0.52 Ti 0.48 O 3 composites. The structure of one of the component Ni 0.9 Zn 0.1 Fe 2 O 4 is spinel cubic with space group , while the other component PbZr 0.52 Ti 0.48 O 3 is selected around the morphotropic phase boundary region in which the tetragonal and monoclinic phases with space group P4mm and Cm coexist respectively. We have carried out Rietveld refinement of the structure to check the formation of ideal composites with separate ferroelectric and ferrite phases. Even though the structural characterization does not reveal the formation of any new phase due to reaction between the two components of the composite during sintering, the tetragonality of the PbZr 0.52 Ti 0.48 O 3 continuously decreases with increasing the ferrite fraction while the lattice parameter of ferrite phase increases with increasing fraction of the ferroelectric phase. Similarly, the dielectric study reveals clear shift in the ferroelectric to paraelectric phase transition temperature of PbZr 0.52 Ti 0.48 O 3 during composite formation suggesting that part of Ni 2+ , Zn 2+ / Fe 3+ ions are diffusing at the B-site of PbZr 0.52 Ti 0.48 O 3 replacing Ti 4+ , which in turn decreases its transition temperature. Scanning electron micrograph of sintered pellet surface confirms the presence of two types of particle morphology in the particulate composite, corresponding to ferrite and ferroelectric phases.