Laser-induced voltage effects in Ca3Co4O9 thin films on tilted LaAlO3（001） substrates grown by chemical solution deposition

Laser-induced voltage effects in c-axis oriented Ca3Co4O9 thin films have been studied with samples fabricated on 10 tilted LaAlO3(001) substrates by a simple chemical solution deposition method. An open-circuit voltage with a rise time of about 10 ns and full width at half maximum of about 28 ns is detected when the film surface is irradiated by a 308-nm laser pulse with a duration of 25 ns. Besides, open-circuit voltage signals are also observed when the film surface is irradiated separately by the laser pulses of 532 nm and 1064 nm. The results indicate that Ca3Co4O9 thin films have a great potential application in the wide range photodetctor from the ultraviolet to near infrared regions.     

Reversal transient laser-induced voltages in La2/3Ca1/3MnO3 films

This paper reports that the transient laser-induced voltages have been observed in La2/3Ca1/3MnO3 thin films on MgO （001） in the absence of an applied current. A peak voltage of - 0.15 V was detected in response to 0.015J pulse of 308 nm laser. It is demonstrated that the signal polarity is reversed when the films are irradiated through the substrate rather than at the air/film interface. Off-diagonal thermoelectricity may support the inversion of the signal when the irradiation direction is reversed.     

Surface characteristics of SiO_2-TiO_2 strip fabricated by laser direct writing

SiO_2-TiO_2 sol-gel films are deposited on SiO_2/Si by dip-coating technique.The SiO_2-TiO_2 strips are fabricated by laser direct writing using an ytterbium fiber laser and followed by chemical etching.Surface structures,morphologies and roughness of the films and strips are characterized.The experimental results demonstrate that the SiO_2-TiO_2 sol-gel film is loose in structure and a shrinkage concave groove forms if the film is irradiated by laser beam.The surface roughness of both non-irradiated and laser irradiated areas increases with the chemical etching time.But the roughness of laser irradiated area increases more than that of non-irradiated area under the same etching time.After being etched for 28 s,the surface roughness value of the laser irradiated area increases from 0.3 nm to 3.1 nm.     

The Influence of Au-Doping on Morphology and Visible-Light Reflectivity of TiN Thin Films Deposited by Direct-Current Reactive Magnetron Sputtering

Ti, TiN and Au-TiN （Au content： from 0.5%to 7.7%） thin films were deposited on stainless steel substrates by dc reactive magnetron sputtering with a metal Ti target. The crystal structure, surface morphology and visiblelight reflectivity of the films for different film compositions are studied in detail. Distinctly different surface morphologies appear for the Ti, TiN and Au-TiN thin films. It can be observed that the surface morphology of the TiN film is affected by the Au-doping, when the Au content increases from 0% to 7.7%, surface roughness enlarges from 62.4 to 82.8 nm. Moreover, visible-light reflectivity varies significantly with increasing A u contents in the TiN films. However, the rettectivity of the TiN thin film at 550-800 nm is higher than that of the Au-TiN thin film. The present work illustrates the dependence of metal elements on the surface morphology and on the reflectivity of Au-TiN thin films. It is speculated that the addition of Au can suppress the formation and growth of TiN grains so that it changes the surface morphology and the Au-TiN thin film has potential applications in spectral selective coating.     

Working Pressure Dependence of Properties of Al2O3 Thin Films Prepared by Electron Beam Evaporation

The effects of working pressure on properties of Al2O3 thin films are investigated. Transmittance of the Al2O3 thin film is measured by a Lambda 900 spectrometer. Laser-induced damage threshold （LIDT） is measured by a Nd：YAG laser at 355 nm with a pulse width of 7ns. Microdefects were observed under a Nomarski microscope. The samples are characterized by optical properties and defect, as well as LIDT under the 355 nm Nd：YAG laser radiation. It is found that the working pressure has fundamental effect on the LIDT. It is the absorption rather than the microdefect that plays an important role on the LIDT of Al2O3 thin film.     

Effect of microstructure on the thermoelectric properties of CSD-grown Bi2Sr2Co2Oy thin films

Three Bi2Sr2Co2Oy thin films with different microstructures have been prepared by chemical solution deposition on LaAlO 3(001) through varying the annealing temperature.With the decrease in the annealing temperature,both the size and c-axis alignment degree of grains in the film decrease as well,leading to an increase in the film resistivity.In addition,the decrease in the annealing temperature also results in a slight increase in the Seebeck coefficient due to the enhanced energy filtering effect of the small-grain film.The nanostructured Bi2Sr2Co2Oy film with an average grain size of about 100 nm shows a power factor comparable to that of films with larger grains.Since the thermal conductivity of the nanostructured films can be depressed due to the enhanced phonon scattering by grain boundary,a higher figure of merit is expected in Bi2Sr2Co2Oy thin film with grains in nanometer size.     

SbOx Thin Films Used for Write-Once Blue Laser Recording

SbOx thin films are deposited by reactive dc-magnetron sputtering from an antimony metal target in Ar＋O2 with the relative O2 content 7%. It is found that the as-deposited films can represent a two-component system comprising amorphous Sb and amorphous Sb2 O3. The crystallization of Sb is responsible for the changes of optical properties of the films. The results of the static test show that the SbOx thin films have good writing sensitivity for blue laser beams and the recording marks are very clear and circular. High reflectivity contrast of about 41% is obtained at a writing power 6mW and writing pulse width 300ns. In addition, the films show a good stability after reading 10000 times.     

Characteristics of Sb_6Te_4/VO_2 Multilayer Thin Films for Good Stability and Ultrafast Speed Applied in Phase Change Memory

The Sb_6Te_4/VO_2 multilayer thin films are prepared by magnetron sputtering and the potential application in phase change memory is investigated in detail. Compared with Sb_6Te_4, Sb_6Te_4/VO_2 multilayer composite thin films have higher phase change temperature and crystallization resistance, indicating better thermal stability and less power consumption. Also, Sb_6Te_4/VO_2 has a broader energy band of 1.58 eV and better data retention(125℃ for 10 y). The crystallization is suppressed by the multilayer interfaces in Sb_6Te_4/VO_2 thin film with a smaller rms surface roughness for Sb_6Te_4/VO_2 than monolayer Sb_4Te_6. The picosecond laser technology is applied to study the phase change speed. A short crystallization time of 5.21 ns is realized for the Sb_6Te_4(2 nm)/VO_2(8 nm)thin film. The Sb_6Te_4/VO_2 multilayer thin film is a potential and competitive phase change material for its good thermal stability and fast phase change speed.     

Lateral photovoltaic effects in Bi2Sr2Co2Oy thin films

Lateral photovoltaic （LPV） effects are observed in Bi2Sr2Co2Oy （BSCO） thin fihns. Upon illumination of a 532-111n constant laser, the lateral photovoltage is observed to vary linearly with tile laser position between two electrodes on tile film surface, and the position sensitivity can be enhmlced by coating a layer of graphite on the surface of the BSCO film as a light absorber. Results suggest that the LPV effect ill the thin fihn is independent of the photo-generated carriers but originates from thermoelectric effects. The present work demonstrates a potential application of BSCO films in position-sensitive photo （thermal） detectors.     

Ultrafast Photoelectric Effects in Heterojunctions of La0.7Sr0.3MnO3 and Si

Ultrafast photoelectric effects have been observed in p-n heterojunctions of La0.7Sr0.3MnO3(LSMO)/Si and LSMO/SrTiO3_/Si for the first time. The rise time was about 1 ns and the full width at half maximum was about 2ns for the photovoltaic pulse when the heterojunction was irradiated by a laser of -25 ps pulse duration and 1064 nm wavelength. The photovoltaic sensitivity was as large as 435 mV//mJ for a 1064 nm laser pulse. No such pulse was observed with irradiation from a pulsed 10.6 μm CO2 laser.     

RESPONSE TIME OF PHOTOEMISSION OF ULTRAFINE PARTICLE THIN FILM

The response time of photoemissive materials is required for detecting ultrashort duration laser pulses. In this paper, the response time of photoemission in ultrafine particle thin film is studied, and the transit time spread (TTS) and response time of peak value (t_M) are discussed. The photoelectron's response time will increase with increasing energy of photons. If the surface potential barrier of thin film declines, the photoemissive sensitivity or quantum yield will rise, however the response time will also increase, which means that response-time characteristic gets worse. As an example, the response time for Ag-O-Cs thin film is calculated for different cases when photoelectrons, excited in Ag ultrafine particles, travel through Cs₂O semiconductor layer to the surface and escape into vacuum. The calculated response time is about 50 fs if this thin film is irradiated by infrared rays of wavelength 1.06μm.     

Magneto-optical and Microwave Properties of LuBiIG Thin Films Prepared by Liquid Phase Epitaxy Method from Lead-Free Flux

Lu2.1Bi0.9Fe5O12 （LuBiIG） garnet films are prepared by liquid phase epitaxy （LPE） method on gadolinium gallium garnet （GGG） substrates from lead-free flux. Three-inch single crystal garnet films with （444） orientation and good surface are successfully fabricated. The lattice mismatch to the GGG（111） substrate is as small as 0.08%. The ferromagnetic resonance （FMR） linewidth of the film is 2AH = 2.8-5.10e, the Faraday rotation is 1.64 deg/μm at 633nm at room temperature and the optical absorption coefficient of the film is 600cm-1 in visible range and about 100-170 cm-1 when the wavelength is larger than 800 nm. The epitaxy film possesses dominating in-plane magnetization with a saturation magnetization of about 1562G. These superior optical, magnetic-optical （MO） and microwave properties of our garnet films have potential applications in both MO and microwave devices.     

Photoinduced Resistance Change in an Oxygen-Deficient La 0.9 Sr 0.1 MnO 3-δ Thin Film

Photoinduced resistance change （ △ R/R） in an oxygen-deficient La0.9Sr0.1MnO3-δ thin film is studied. At room temperature, the resistance change of about 30% and response time of about 75 ns are observed under the illumination with a 532nm laser pulse of 7ns and light power of 750mW. It is also found that △ R/R changes with the light power. The phenomena are explained in terms of the photoinduced hole carriers and localized insulator-to-metal transition, which may have potential applications in optoelectronic devices.     

Yield strengths and stress induced crackles in copper films：effects of substrate and passivated layer

Yield strengths in unpassivated and 530 nm TiN passivated Cu films deposited on Ti, high-speed steel and Ni substrates have been measured by x-ray diffraction (XRD) in combination with the four-point bending method. The results show that, although the texture and average grain size, investigated by XRD and transmission electron microscopy respectively, do not vary with different substrate, the yield strength of the Cu film increases obviously when a thin passivated layer is present and varies slightly with substrates. Many crackles appear in the passivated Cu film on Ti substrate but do not appear in other samples. The experimental results have been explained satisfactorily with an expression for the yield strength of thin films given previously.     

Helium—Charged Titanium Films Deposited by Pulsed Laser Deposition in an Electron—Cyclotron—Resonance helium Plasma Environment

Titanium thin films incorporated with helium are produced by pulsed laser deposition in an electron cyclotron resonance helium plasma environment.Helium is distributed evenly in the film and a relatively high He/Ti atomic ration(-20%) is obtained from the proton backscattering spectroscopy.This high concentration of helium leads to a surface blistering which is observed by scanning electron microsocopy.Laser repetition rate little influence on film characters.Substrate bias voltage is also changed for the helium incorporating mechanism study,and this is a helium ion implantation process during the film growth.Choosing suitable substrate bias voltage,one can avoid the damage produced by ion implantation,which is always present in general implantation case.     

Influence of Surface Transition Layers on Phase Transformation and Pyroelectric Properties of Ferroelectric Thin Film

Taking into account surface transition layers （STLs）, we study the phase transformation and pyroelectric properties of ferroelectric thin films by employing the transverse Ising model （TIM） in the framework of the mean field approximation. The distribution functions representing the intra-layer and inter-layer couplings between the two nearest neighbour pseudo-spins are introduced to characterize STLs. Compared with the results obtained by the traditional treatments for the thin films using only the single surface transition layer （SSL）, it is shown that the STL model reflects a more realistic and comprehensive situation of films. The effects of various parameters on the phase transformation properties have shown that STL can make the Curie temperature of the film higher or lower than that of the corresponding Sulk material, and the thickness of STL is a key factor influencing the film properties. For a film with definite thickness, there exists a critical STL thickness at which ferroelectricity will disappear when the intra-layer and inter-layer interactions are weak.     

Magnetostatic Coupling in Ba0.8Sr0.2TiO3/CoFe2O4 Magnetoelectric Composite Thin Films of 2-2-Type Structure

Ba0.8Sr0.2 TiO3/CoFe2O4 （BST/CFO） magnetoelectric composite thin films of 2-2-type structures are prepared onto Pt/Ti/SiO2/Si substrates by a sol-gel process and spin coating technique. The structure of the prepared thin film is substrate/BST/CFO/. . ./CFO/BST. Three CFO ferromagnetic layers are separated from each other by a thin BST layer. The upper CFO layer is magnetostatically coupled with the lower CFO layer. Subsequent scanning electron microscopy investigations show that the prepared thin films exhibit good morphologies and have a compact structure, and the cross-sectional mierographs clearly display a multilayered nanostructure of multilayered thin films. The composite thin films exhibit good magnetic and ferroelectric properties. The spacing between ferromagnetic layers can be varied by adjusting the thickness of intermediate BST layer. It is found that the strength of magnetostatic coupling has a great impact on magnetoelectric properties of composite thin film; that is, the magnetoelectric voltage coefficient of the composite thin film tends to increase with the decrease of pacing between two neighboring CFO ferromagnetic layers as a result of magnetostatic coupling effect.     

Room-temperature epitaxial growth of V2O3 films

Herein we report the room-temperature epitaxial growth of V2O3 films by laser molecule beam epitaxy. X-ray diffraction profiles show the room-temperature epitaxial V2O3 films orient in the [110] direction on α-Al2O3(0001) substrates. Atomic force microscopy measurements reveal that the ultra-smooth surfaces with root-mean-square surface roughness of 0.11 nm and 0.28 nm for 10-nm-thick and 35-nm-thick V+2O3 film, respectively. X-ray photoelectron spectroscopy results indicate the V3 oxidation state in the films. Typical metal-insulator transition is observed in films at about 135 K. The resistivities at 300 K are approximately 0.8 mΩ cm and 0.5 mΩ cm for 10-nm-thick and 35-nm-thick V2O3 film, respectively.     

Transparent conductive reduced graphene oxide thin films produced by spray coating

Reduced graphene oxide thin films were fabricated on quartz by spray coating method using a stable dispersion of reduced graphene oxide in N,N-Dimethylformamide.The dispersion was produced by chemical reduction of graphene oxide,and the film thickness was controlled with the amount of spray volume.AFM measurements revealed that the thin films have near-atomically flat surface.The chemical and structural parameters of the samples were analyzed by Raman and XPS studies.It was found that the thin films show electrical conductivity with good optical transparency in the visible to near infrared region.The sheet resistance of the films can be significantly reduced by annealing in vacuum and reach 58 k?with a light transmittance of 68.69%at 550 nm.The conductive transparent properties of the reduced graphene oxide thin films would be useful to develop flexible electronics.     

Comparative studies on Zn0.95Co0.05O thin films on C- and R-sapphire substrates

Zn0.95Co0.05 O precipitate-free single crystal thin films were synthesized by a dual beam pulsed laser deposition method.The films form a wurtzite structure whose hexagonal axis is perpendicular or parallel to the plane of the surface depending on the C-plane (0001) or R-plane (11 ˉ 20) sapphire substrate.Based on the results of high-resolution transmission electron microscopy and x-ray diffraction,C-plane films show larger lattice mismatch.The films exhibit magnetic and semiconductor properties at room temperature.The coercivity of the film is about 8000 A/m at room temperature.They are soft magnetic materials with small remanent squareness S for both crystal orientations.There is no evidence to show that the anisotropy is fixed to the hexagonal axis (C-axis) for the wurtzite structure.