Pulsed Laser Deposition System Research Articles

Novel multilayer nano-composite protective coatings for metallic medical tools

Abstract Requirements for tribological protective coatings for medical tools, which would increase their wear and corrosion resistance, are very high. The presented paper deals with novel nano-composite, multilayer protective coatings for tissue interaction elaboration and their diagnosis on metallic substrates. A hybrid pulsed laser deposition system was used for coating deposition. In the presented work, nano-composite Cr/CrN + [Cr/a-C : H implanted by metallic nanocrystals] multilayer coatings were developed for surface protection. The mechanical properties of the coatings were investigated by means of micro-hardness and elasticity modulus measurements. Bio-medical tests were conducted using eukaryotic cells. Microstructural analysis by means of transmission electron microscopy indicated that chromium which was implanted into a-C : H layers reacted with carbon forming chromium carbides.

Anomalous redox properties and ultrafast chemical sensing behavior of double perovskite CaBaCo2O5+δ thin films

Perovskite oxide CaBaCo2O5+δ (CBCO) thin films with two divalent alkaline earth metal ions and the transition metal Co ion were prepared by pulsed laser deposition (PLD) system. X-ray diffraction reveals that the as-grown CBCO thin films have good crystallinity of the perovskite structure. Redox electrical properties and chemical sensing behavior on the as-grown CBCO thin films were systematically studied under various chemical environments. The electrical transport property studies indicate that the electrical resistivity increases with increase of temperature under reducing atmosphere and the temperature dependence of resistivity of the CBCO thin film in the oxidation processing above room temperature can be well fitted by small polaron hopping model. The chemical sensing property measurements reveal that the CBCO thin film is very sensitive to oxidizing/reducing environments in the temperature ranges from 620 K to 970 K. Especially, the reduced CBCO thin films with Co2+ and high oxygen vacancy concentration have a superfast oxygen sensing response from 620 to 970 K.

Surface-step-terrace tuned magnetic properties of epitaxial LaBaCo2O5.5+δthin films on vicinal (La,Sr)(Al,Ta)O3substrates

Interface-engineered double-perovskite structural LaBaCo2O5.5+δ thin films were highly epitaxially fabricated on (001) (La,Sr)(Al,Ta)O3 substrates with various miscut angles of 0°, 1°, 3° and 5° using a pulsed laser deposition system. All the LaBaCo2O5.5+δ thin films have a c-axis orientation with a highly epitaxial crystalline quality. Moreover, the effect of the interface tuning mechanism on the magnetic properties has been systematically investigated using physical properties measurement systems. Larger strain can be obtained by increasing the substrates’ surface miscut angles and can further enhance the magnetic properties of the LaBaCo2O5.5+δ thin films. All these results reveal that interface engineering using surface-step-terraces is an effective way of tuning/controlling the magnetic properties of LaBaCo2O5.5+δ films.

Enhanced photoluminescence of Co2+ ions in ZnCoO/ZnMgO multiple quantum wells and the fluorescence energy transfer mechanism

Using a pulsed laser deposition system, ZnCoO/ZnMgO multiple quantum well (MQW) samples were grown on c-plane sapphire substrate with a ~20nm thick ZnO buffer layer. Compared with monolayer ZnCoO film, the MQW samples exhibited obviously enhanced Co2+ photoluminescence (PL) at ~1.80eV and multiple-phonon resonant Raman scattering (RRS). The enhancement in multiple-phonon RRS was due to the introduction of ZnMgO barrier layer. The enhanced Co2+ PL was assigned to the quantum confinement effect (QCE) of MQW samples. However, QCE was found not helpful to prevent the band-gap PL quenching. Co2+ 3d electronic states were proved to be highly localized and a mechanism of fluorescence resonance energy transfer (FRET) between ZnO excitons and the localized Co2+ 3d states was proposed.

Structural and optical properties of Cd and Mg doped zinc oxide thin films deposited by pulsed laser deposition

The 7 wt % Cd doped and 15 wt % Mg doped ZnO thin films were deposited on quartz substrate by pulse laser deposition system. The structural and optical properties of the prepared ZnO, Cd:ZnO and Mg:ZnO films were investigated by X-Ray diffraction (XRD), photoluminescence and UV-Vis spectroscopy techniques. XRD results indicate that the doped ZnO films maintain wurtzite crystal symmetry without any defects and are oriented along c- axis. Photoluminescence studies show a sharp band edge emission peak at 384 nm for pure ZnO film. This peak is blue shifted to 381 nm with Cd doping and red shifted to 395 nm with Mg doping. UV visible absorption studies reveals a decrease in band gap with Cd doping and an increase in band gap with Mg doping.

Scanning tunneling microscopy/spectroscopy on perovskite oxide thin films deposited in situ.

Complex oxide surfaces and interfaces, consisting of two or more cations and oxygen anions, have attracted a great deal of attention because their properties are crucial factors in the performance of catalysts, fuel cells, and Li-ion batteries. However, atomic-scale investigations of these oxide surfaces have been hindered because of the difficulties in surface preparation. Here, we demonstrate atomic-scale surface studies of complex perovskite oxides and the initial growth processes in oxide epitaxial films deposited on (✓13 × ✓13)-R33.7° reconstructed SrTiO3 (001) substrates using a scanning tunneling microscope integrated with a pulsed laser deposition system. The atomically ordered, reconstructed SrTiO3 (001) surface is stable under the typical conditions necessary for the growth of oxide thin films, and hence is considered suitable for the study of the initial growth processes in oxide films. The atomic-scale microscopic/spectroscopic characterizations performed here shed light on the microscopic origin of electronic properties observed in complex oxides and their heterostructures.

One-chip multicolor electroluminescence from an isotype heterojunction light-emitting diode

Both direct current (DC) and alternating current (AC) driving electroluminescence were obtained from isotype heterojunction (n-i-n: n-ZnO/i-HfO2/n-GaN) light-emitting diodes (LEDs) fabricated by a pulsed laser deposition system. The n-ZnO film maintained the same growth orientation as the n-GaN film and was of high crystalline quality even on a polycrystalline high-k HfO2 thin film. The as-produced n-i-n LEDs can emit strong visible light or dominant ultraviolet light at ∼392 nm, depending on the polarity of the applied DC voltages. The individual spectrum under either forward or reverse bias can be integrated to one spectrum by applying 50 Hz AC driving voltages (sinusoidal signals). More importantly, near white-light can be obtained by tuning the symmetric driving AC sinusoidal signals to the asymmetric ones. This simple and facile method only by applying AC asymmetric signals to achieve white light emission on one single chip may provide an easy route for the white-light solid-state lighting industry.

Magnetocapacitance Properties of Multilayered CoFe2O4/BaTiO3/CoFe2O4Thin Film by Pulsed Laser Deposition

CoFe₂O₄(CFO)/BaTiO₃(BTO)/CoFe₂O₄(CFO) multilayered thin films were deposited on Pt/TiO₂/SiO₂/Si substrates by the pulsed laser deposition (PLD) system with KrF excimer laser (λ = 248 nm). BTO, CFO, BTO/CFO and CFO/BTO/CFO structured thin films were prepared and their crystal structures and microstructures, as well as their magnetic and magneto-electrical properties, were studied. The C-V characteristics of these multilayered thin films with different capacitor structures were obtained to confirm the change in their capacitances under a magnetic field. Finally, the capacitance of the CFO/BTO/CFO thin film as a function of bias voltage under an in-plane magnetic field of 1,000 Oe increased to 951.04 pF at 1 MHz, from 831.90 pF measured under no magnetic field, indicating 14.3% increase in magnetocapacitance.

Effect of growth conditions on microstructure of BiFeO3-0.33BaTiO3 films and performance of bulk acoustic wave resonators

The effect of growth conditions on the microstructure of BiFeO3-0.33BaTiO3 (BF-BT) films and the performance of bulk acoustic wave (BAW) resonators is analyzed using test structures with the BF-BT films grown at different positions relative to the plume axis in the pulsed laser deposition system. The BF-BT film grain size and surface roughness reveal a strong asymmetric surface distribution and decrease significantly in the film region facing the laser beam-plume interaction area. The (100) BF-BT texturing is enhanced in this film region. The variations in the BF-BT film microstructure result in corresponding variations of the BAW resonator performance. Their correlations are established using the model of the roughness induced attenuation of the reflected acoustic waves and theory of the dc field induced piezoelectric effect. The BAW resonators with the highest parameters are obtained in the BF-BT film region facing the laser beam-plume interaction area. The BAW resonators located in this film region reveal a mechanical Q-factor of 200 at 4.2 GHz, an effective electromechanical coupling coefficient of 10% and a tunability of the series resonance frequency of 4.5%.

Growth and in situ high-pressure reflection high energy electron diffraction monitoring of oxide thin films

Interface and surface physics is an important sub-discipline within condensed matter physics in recent decades. Novel concepts like oxide-electronic device are prompted, and their performance and lifetime are highly dependent on the flatness and abruptness of the layer surfaces and interfaces. Reflection high-energy electron diffraction (RHEED), which is extremely sensitive to surface morphology, has proven to be a versatile technique for the growth study of oxide thin films. A differential pumping unit enables an implementation of RHEED to pulsed laser deposition (PLD) systems, ensuring an in situ monitoring of the film growth process in a conventional PLD working oxygen pressure up to 30 Pa. By optimizing the deposition conditions and analyzing the RHEED intensity oscillations, layer-by-layer growth mode can be attained. Thus atomic control of the film surface and unit-cell control of the film thickness become reality. This may lead to an advanced miniaturization in the oxide electronics, and more importantly the discovery of a range of emergent physical properties at the interfaces. Herein we will briefly introduce the principle of high-pressure RHEED and summarize our main results relevant to the effort toward this objective, including the growth and characterization of twinned La2/3Ca1/3MnO3 thin films and ReTiO3+δ/2 (Re = La, Nd; δ = 0 ∼ 1) A n B n O3n+2 structures, on YSZ-buffered ‘Silicon on Insulator’ and LaAlO3 substrates, respectively, as well as the study of the initial structure and growth dynamics of YBa2Cu3O7−δ thin films on SrTiO3 substrate. Presently we have realized in situ monitoring and growth mode control during oxide thin film deposition process.

In situ laser annealing during growth of Pb(Zr0.52Ti0.48)O3 thin films

A pulsed laser deposition system with in situ laser annealing was utilized to grow Pb(Zr0.52Ti0.48)O3 thin films on a laser crystallized Pb(Zr0.20Ti0.80)O3 seed layer, at a temperature of ∼370 °C. Polycrystalline 1.1 μm thick films exhibited columnar grains with small grain sizes (∼30 nm). The films showed well-saturated hysteresis loops (with ∼25 μC/cm2 remanent polarization, ∼50 kV/cm coercive field) and exhibited loss tangents <2.5% with a permittivity of ∼730. Film orientation could be controlled via the substrate choice; {111} Pb(Zr0.52Ti0.48)O3 films were grown on oriented (111) Pb(Zr0.30Ti0.70)O3 sol-gel seed layers, while {001} films were prepared on (100) SrTiO3 single crystals.

PLD Grown Polycrystalline Tungsten Disulphide (WS2) Films

Polycrystalline WS2 films were grown by pulsed laser deposition (PLD) system at relatively low temperature. The main objective of this study is to optimize the growth conditions for polycrystalline WS2 films at relatively low temperature to use them for photovoltaics (PVs). Different growth conditions and substrates are used and examined systematically. It is found out that films grown on strontium titanate SrTiO3 (STO) substrate have the best structural properties when compared to other substrates examined in this work. X-ray diffraction and optical characterizations of these films reveal crystallographic growth and very promising optical properties for PVs. Furthermore, it was observed that higher growth temperature (>300°C) has an unfavorable effect on the layers by creating some tungsten metallic droplets.

Epitaxial growth and electrical properties of ultrathin La2Hf2O7 high-k gate dielectric films

Ultrathin La2Hf2O7 (LHO) high-k gate dielectric films (∼3.4nm) have been epitaxially grown on Si (001) substrates through a pulsed laser deposition system. The epitaxial growth characteristics, composition, interface with Si, optical band gap, and electrical properties of the ultrathin LHO films have been investigated by in situ reflection high-energy electron diffraction (RHEED), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), ultraviolet–visible diffuse reflectance spectroscopy (UV–vis DRS) and transmittance spectroscopy, as well as semiconductor characterization analysis. Results show that ultrathin LHO film grown at 800°C shows a good crystallinity and no obvious interfacial layer forms. La is deficient and oxygen is slightly excessive in LHO film. The epitaxial LHO film has a band gap of ∼5.7eV. The gate leakage current density Jg of the ultrathin epitaxial LHO film follows the space-charge limited conduction mechanism and Jg is ∼0.3A/cm2 at a gate voltage of 1V. Additionally, a suitable permittivity∼16.7, a small hysteresis∼30mV and a low capacitance equivalent thickness∼0.79nm have been obtained.

Pulsed laser deposition with simultaneous in situ real-time monitoring of optical spectroscopic ellipsometry and reflection high-energy electron diffraction

We present a pulsed laser deposition system that can monitor growth by simultaneously using in situ optical spectroscopic ellipsometry (SE) and reflection high-energy electron diffraction (RHEED). The RHEED precisely monitors the number of thin-film layers and surface structure during the deposition, and the SE measures the optical spectra of the samples simultaneously. The thin-film thickness information obtained from RHEED facilitates the SE modeling process, which allows extracting the in situ optical spectra, i.e., the dielectric functions of thin-films during growth. The in situ dielectric functions contain indispensable information about the electronic structure of thin-films. We demonstrate the performance of this system by growing LaMnO3+δ (LMO) thin-films on SrTiO3 (001) substrates. By using in situ SE and RHEED simultaneously, we show that real-time thickness and dielectric functions of the LMO thin-films can be effectively extracted. The simultaneous monitoring of both optical SE and RHEED offers important clues to understand the growth mechanism of atomic-scale thin-films.

Properties in vanadium dioxide thin film synthesized from V2O5 annealed in H2/Ar ambience

Owning to its sharp metal-insulator transition at ～340 K, VO2 is becoming an attractive candidate for the electrical and optical material. Here we report on the fabrication and characterization of VO2 thin film obtained from the V2O5 thin film annealed in Ar/H2 ambience. V2O5 thin film is fabricated by using the pulsed laser deposition system on the R-sapphire substrate under several different conditions by varying the substrate temperature and the pressure of the growth atmosphere to optimize the growth condition. Then we carry out the annealing treatment on the V2O5 thin film in different annealing conditions. The VO2 thin films are characterized using X-ray diffraction, X-ray photoelectron spectroscopy and R-T measurement. When annealed in a temperature range of 500–525 ℃ for 3 h in H2(5%)/Ar ambience, the V2O5 thin film can be converted into the mixed-structures of metastable monoclinic structure (B) and the monoclinic rutile structure (M) which is responsible for the phase-change property. And under the same conditions, when the annealing time reaches 4.5 h, the pure VO2(B) is obtained. Further we anneal the VO2(B) in pure Ar ambience and tentatively realize the resistivity reduced by nearly four orders with the temperature increasing from 25 ℃ to 105 ℃. The transition temperature is nearly 350 K. And the transition between VO2 (B) and VO2 (M) is realized.

Effects of laser energy fluence on the onset and growth of the Rayleigh–Taylor instabilities and its influence on the topography of the Fe thin film grown in pulsed laser deposition facility

The effect of laser energy fluence on the onset and growth of Rayleigh–Taylor (RT) instabilities in laser induced Fe plasma is investigated using time-resolved fast gated imaging. The snow plow and shock wave models are fitted to the experimental results and used to estimate the ablation parameters and the density of gas atoms that interact with the ablated species. It is observed that RT instability develops during the interface deceleration stage and grows for a considerable time for higher laser energy fluence. The effects of RT instabilities formation on the surface topography of the Fe thin films grown in pulsed laser deposition system are investigated (i) using different laser energy fluences for the same wavelength of laser radiation and (ii) using different laser wavelengths keeping the energy fluence fixed. It is concluded that the deposition achieved under turbulent condition leads to less smooth deposition surfaces with bigger sized particle agglomerates or network.

Effects of Oxygen Working Pressure on Structural and Optical Properties of TiO2 Films Grown on Glass Substrate

TiO2 thin films were grown on glasses using a pulsed laser deposition (PLD) system. In order to fully clarify the correlation between their properties and the working pressure of oxygen at which they are grown, a wide range of pressures from 10 to 75 mTorr was investigated. The optical gap of TiO2 films gradually increased from 3.3 to 3.41 eV with increasing working pressure up to 25 mTorr but became notably large at 50 mTorr and continued to increase significantly with further pressure increase. X-ray diffraction (XRD) results showed that the films grew preferentially along the (101) orientation. (101) peak intensity increased as working pressure increased up to 25 mTorr. However, the peak intensity began to decrease and eventually disappeared with further increase in working pressure, indicating structural changes from crystalline to disorderlike phases. The TiO2 films showed high crytallinity with large grains at 25 mTorr but showed a columnar structure with small grains at 75 mTorr. The growth mode of TiO2 thin films was observed to change from lateral to islandlike growth in response to the increase in working pressure. The correlation between oxygen pressure and film properties is discussed in terms of structural and compositional changes.

Effect of SiC‐Impurity Layer and Growth Temperature on MgB2 Superconducting Tapes Fabricated by HPCVD

AbstractThe influence of SiC‐impurity layer and growth temperature on microstructure and superconducting properties are studied for MgB2 superconducting tapes. A pulsed laser deposition (PLD) system is used for the deposition of amorphous SiC‐impurity layers on flexible metallic Cu(001) tapes. The MgB2 superconducting tapes are fabricated by growing MgB2 films on the top of SiC/Cu tapes, over a wide temperature range of 460–600 °C, by using hybrid physical (HP) CVD system. Among all tapes, the MgB2/SiC/Cu tape deposited at a temperature of 540 °C has the highest Tc of ∼37.7 K. Scanning electron microscopy (SEM) images reveal hexagonal‐shaped MgB2 grains with good connectivity, and their sizes are found to vary with growth temperature. When compared to MgB2/Cu tapes, the MgB2/SiC/Cu tapes exhibit an opposite trend in the dependence of critical current density (Jc) with deposition temperatures. The improved Jc(H) behavior can be explained on the basis of the enhanced flux pinning force density (Fp) for MgB2/SiC/Cu tapes upon increasing the growth temperature

Solid-state source of atomic oxygen for low-temperature oxidation processes: Application to pulsed laser deposition of TiO2:N films

An atomic oxygen (AO) source has been redesigned to coordinate with a pulsed laser deposition system and used to grow nitrogen-doped TiO(2) films by deposition of TiN and simultaneous irradiation of the substrate with AO. The AO source uses an incandescently heated thin tube of zirconia as an oxygen permeation media to generate pure AO of low kinetic energy. The emission flux is calibrated using a silver-coated quartz crystal microbalance. The thin shape of the probe and transverse emission geometry of this emission device allow the emission area to be positioned close to the substrate surface, enhancing the irradiation flux at the substrate. AO irradiation is crucial for formation of TiO(2) phases via oxidation of the deposited TiN laser plume, and is effective for decrease of the substrate temperature for crystallization of anatase phase to as low as around 200 °C.

Gasochromic performance of WO3-nanorod thin films fabricated with an ArF excimer laser

Thin films with tungsten trioxide (WO3) nanorods were fabricated by using an ArF pulsed laser deposition system. Because the ArF excimer laser operates at a very short wavelength of 193 nm, short enough to expect strong absorption of the photons in the semiconductor oxide targets, and because the clusters incoming to the substrates have high momentum, we could build thin films with good surface morphology. Highly homogeneous arrays of nanorods with sizes mostly in the range of 30–40 nm were observed. The absorbance response towards hydrogen (H2) gas was investigated for a WO3 film coated with 25-A-thick palladium (Pd). The Pd/WO3-nanorod thin films exhibited excellent gasochromic response when measured in the visible-NIR range (400–1000 nm). As low as 0.06% H2 concentration was clearly sensed. A significant reversible absorbance change and fast recovery (<2 min) were observed when the films were exposed to H2 at different concentrations.