Combination Of Pulsed Laser Deposition Research Articles

Epitaxial growth of high-quality yttria-stabilized zirconia films with uniform thickness on silicon by the combination of PLD and RF sputtering

High-quality (100)-oriented yttria-stabilized zirconia (YSZ) films with uniform thickness were epitaxially grown on silicon substrates by a two-step process of pulsed laser deposition (PLD) and radio-frequency magnetron sputtering (RFS). First, we fabricated a YSZ-seed layer on (001)-oriented silicon substrates using a PLD apparatus, and then transferred the YSZ-seed substrate to an RFS equipment to complete the growth of a thicker YSZ film. The dependence of YSZ crystal quality on RFS-growth temperature was investigated in the range of 200 to 850 °C. All the resulting YSZ films exhibited pure (100) orientation, and the full width at half maximum of the YSZ (200) X-ray rocking curve was as low as 0.64° for the YSZ film grown at 850 °C, and increased to 1.02° with the RFS-growth temperature declining to 200 °C. The results evidenced that the YSZ film can be epitaxially grown at 200 °C in the presence of a YSZ-seed layer. However, the splitting of the YSZ (200) X-ray diffraction peak appeared at 500 °C and 200 °C, which may be attributed to a transformation of the intrinsic stress in the YSZ films from compressive to tensile stress with decreasing temperature. In addition, the YSZ film had a uniform thickness distribution with an inhomogeneity of less than 5 % and a very flat and dense surface with root-mean-square surface roughness below 1 nm.

LOW-TEMPERATURE CATALYZED GROWTH AND PLASMONIC PROPERTIES OF COLUMNAR Au-SiOx NANOCOMPOSITE THIN FILMS

The optical properties of noble metal nanoparticles (NPs) can be efficiently controlled by their incorporation into host matrix films. Here, we report on the fabrication of composite films of gold NPs in a silicon suboxide matrix by a novel approach using a combination of pulsed laser deposition for NP production and gas-jet, electron-beam plasma chemical vapor deposition for low-temperature (300°C) synthesis of a SiO<sub>x</sub> (x = 0.38-1.55) thin film as a matrix for the NPs. The produced nanocomposite exhibits unexpected plasmonic properties, non-monotonically dependent on the matrix thickness, due to a porous columnar matrix structure grown from the NPs with variable oxygen content along the columns. This implies that low-temperature, gold-catalyzed oxidation of silicon occurs during the structure growth. Calculations based on Mie theory show that the refractive index of the obtained SiO<sub>x</sub> matrix can be as low as 1.2 at certain film thicknesses. Mechanisms of the columnar structure formation at different deposition stages are discussed. The synthesis approach can be used for the fabrication of optical thin-film materials with controllable low refractive index.

Plasma Emission Spectroscopy to Study the Resputtering Produced by Pulsed Laser Deposition of Au and in Combination With Magnetron Sputtering of ZnO

Optical emission spectroscopy (OES) has been used as an in-situ method to monitor the film deposition carried out using a combination of two plasma-assisted techniques; pulsed laser deposition (PLD) and magnetron sputtering (MS). In this work, the plasmas produced during the PLD ablation of a gold target in an argon atmosphere and its simultaneous use with MS of ZnO were characterized by OES. Neutral atoms of Au, Ar, and Zn and ions of Au were identified, and the temporal and spatial evolution of their emission lines was studied along the axis of the PLD plasma expansion. During the PLD of Au an increment in the emission intensity of neutral Au near the substrates, as a function of the laser pulse fluence, demonstrated resputtering of the Au deposit by the high energy species produced by PLD. When the combination of PLD of Au and MS of ZnO was performed, a similar increment was observed in the emission intensity, but in this case of neutral Zn that was caused by the preferential resputtering of Zn from the ZnO-Au deposit. The MS plasma neither significantly affect the PLD plasma expansion nor did it affect the resputtering of the films.

Enhancement of Ic of BaHfO3 -Doped REBCO Thick Coated Conductor Using Vapor-Liquid-Solid Growth Technique

The vapor-liquid-solid (VLS) growth technique is a combination of pulsed laser deposition (PLD) method and liquid phase epitaxy (LPE) and is expected to fabricate structures with high crystallinity at a high deposition rate. To utilize superconducting coated conductors (CCs) for applications such as superconducting magnets, it is indispensable to decrease the fabrication cost of CCs. Therefore, we have devised a method to achieve a deposition rate of 26.0 nm/s by changing the partial pressure of O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> during deposition. Furthermore, an enhanced crystallinity was maintained by using the VLS growth technique, with a thickness of up to 10 μm, and we achieved a critical current I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> of 625 A/cm-w.

Growth of Pr2Ir2O7 thin films using solid phase epitaxy

(111)-oriented pyrochlore Pr2Ir2O7 epitaxial thin films were successfully fabricated on yttria-stabilized zirconia (111) substrates by means of solid phase epitaxy, namely, the combination of pulsed laser deposition (PLD) of an amorphous precursor film at room temperature, followed by epitaxial crystallization in an ex situ post-annealing process in air. The Pr2Ir2O7 phase cannot be obtained in a conventional in situ PLD process because of severe Ir loss. The Pr2Ir2O7 thin films showed metallic electronic conductivity and the spontaneous Hall effect. These transport properties are similar to the ones reported for bulk single crystal samples, indicating that the thin films had high crystalline quality.

High-quality nonpolar a-plane GaN epitaxial films grown on r-plane sapphire substrates by the combination of pulsed laser deposition and metal–organic chemical vapor deposition

High-quality a-plane GaN epitaxial films have been grown on r-plane sapphire substrates by the combination of pulsed laser deposition (PLD) and metal–organic chemical vapor deposition (MOCVD). PLD is employed to epitaxial growth of a-plane GaN templates on r-plane sapphire substrates, and then MOCVD is used. The nonpolar a-plane GaN epitaxial films with relatively small thickness (2.9 µm) show high quality, with the full-width at half-maximum values of GaN() along [] direction and GaN() of 0.11 and 0.30°, and a root-mean-square surface roughness of 1.7 nm. This result is equivalent to the quality of the films grown by MOCVD with a thickness of 10 µm. This work provides a new and effective approach for achieving high-quality nonpolar a-plane GaN epitaxial films on r-plane sapphire substrates.

Raman and EPR spectroscopic studies of chromium-doped diamond-like carbon films

The diamond-like carbon (Cr-free DLC) and chromium-doped DLC (Cr doped-DLC) films prepared by a hybrid technology using a combination of pulsed laser deposition and magnetron sputtering were studied by Raman and electron paramagnetic resonance (EPR) spectroscopy. Raman spectra are dominated by the well-known carbon (D/G) band. The intensity ratio of the D/G bands was found to increase with the increase of the Cr content. Careful elimination of the substrate-related (SiO2) peaks enabled us to identify new weak features attributable to the presence of the CCr bonds. Two EPR signals were observed in Cr-free and Cr-doped DLC films. The EPR signal at g = 2.0025(3) was attributed to the sp2 coordinated carbon-related defect (CRD) and the second EPR signal at g = 2.0064 was assigned to the Pb0 interface defect which may appear due to the formation of the oxidized Si on the interface of the DLC film and SiO2 substrate. The observed temperature behavior of the CRD EPR signal g-factor in Cr free DLC films was described by the model of exchange coupled two spin systems (localized defects and conduction electrons) in the bottleneck regime. From the temperature dependence of the linewidth and integral intensity of the CRD EPR signal it was concluded that ferromagnetic ordering occurs in the spin system with exchange constant of J = 0.069 meV. The spin density of the CRD was found to be significantly decreased in Cr-doped DLC films, possibly due to the formation of the CCr bonds. The observed change of the CRD lineshape from Lorentzian in Cr free DLC films to Gaussian in Cr-doped DLC films indicates that there is a superhyperfine coupling between unpaired spins of the CRD and surrounding Cr nuclei.

High-Performance GaN-Based LEDs on Si Substrates: The Utility of &lt;italic&gt;Ex Situ&lt;/italic&gt; Low-Temperature AlN Template With Optimal Thickness

Ex situ low-temperature (LT)-AlN templates are employed to realize GaN-based light-emitting diodes (LEDs) on Si substrates by the combination of pulsed laser deposition and metal organic chemical vapor deposition. The influence of ex situ LT-AlN template thickness on the properties and performance of as-grown LEDs has been carefully studied. The LED wafer grown on 70-nm-thick ex situ LT-AlN template exhibits a crack-free surface, good crystalline quality, and excellent multiple quantum wells (MQWs) structural property. The $500\times 500~\mu \text{m}^{\mathbf {2}}$ LED chips fabricated with lateral structure show the highest light output power of 70.2 mW at an injection current of 300 mA. Through optimizing the thickness of ex situ LT-AlN template, the light output power is greatly improved by 39%. Theoretical analysis has been taken to study the enhancement mechanism of luminous intensity in this LED. It reveals that the residual stress in as-grown wafers is significant to enhance the luminescence of LEDs. The largest residual tensile stress in the LED presents great potential to enhance the carrier injection and transportation, increase the carrier concentrations, and improve the radiative recombination intensity in MQWs, which is crucial to improve the luminous intensity of LEDs.

Adhesion and differentiation of Saos-2 osteoblast-like cells on chromium-doped diamond-like carbon coatings.

Diamond-like carbon (DLC) thin films are promising for use in coating orthopaedic, dental and cardiovascular implants. The problem of DLC layers lies in their weak layer adhesion to metal implants. Chromium is used as a dopant for improving the adhesion of DLC films. Cr-DLC layers were prepared by a hybrid technology, using a combination of pulsed laser deposition (PLD) from a graphite target and magnetron sputtering. Depending on the deposition conditions, the concentration of Cr in the DLC layers moved from zero to 10.0 at.%. The effect of DLC layers with 0.0, 0.9, 1.8, 7.3, 7.7 and 10.0 at.% Cr content on the adhesion and osteogenic differentiation of human osteoblast-like Saos-2 cells was assessed in vitro. The DLC samples that contained 7.7 and 10.0 at.% of Cr supported cell spreading on day 1 after seeding. On day three after seeding, the most apparent vinculin-containing focal adhesion plaques were also found on samples with higher concentrations of chromium. On the other hand, the expression of type I collagen and alkaline phosphatase at the mRNA and protein level was the highest on Cr-DLC samples with a lower concentration of Cr (0-1.8 at.%). We can conclude that higher concentrations of chromium supported cell adhesion; however DLC and DLC doped with a lower concentration of chromium supported osteogenic cell differentiation.

Synthesis of TiC coating on Ti substrate using pulsed laser deposition and mechanical milling techniques along with statistical modeling of the process by response surface methodology

In this work, two methods including mechanical milling (MM) and pulsed laser deposition (PLD) followed by MM were employed for coating of Ti samples by TiC powder. The objective of the present study is finding the relationships between the input variables and the process responses as well as making the predictive model used in the design of TiC coating on Ti substrate. Central composite design (CCD) was applied to optimize some important factors involved in the mechanical coating procedure. Three factors including milling time, rotation per minute and employed technique (PLD+MM and MM) were examined as numerical, numerical, and categorical factors, respectively. Coating thickness, microhardness, and scratch hardness number were defined as process responses. The study revealed that the effect of all factors on the responses was significant. Optimum levels obtained using the response surface method (optimization levels: 27h, 350rpm and PLD+MM method) met the corresponding experimental results. The obtained results proved that CCD can be efficiently used in predicting behavior of the given system. Regarding the optimized condition, it was observed that combination of PLD and MM methods presents better outcomes. Moreover, the results proposed that the model provides desirable TiC coating properties.

A new approach to epitaxially grow high-quality GaN films on Si substrates: the combination of MBE and PLD.

High-quality GaN epitaxial films have been grown on Si substrates with Al buffer layer by the combination of molecular beam epitaxy (MBE) and pulsed laser deposition (PLD) technologies. MBE is used to grow Al buffer layer at first, and then PLD is deployed to grow GaN epitaxial films on the Al buffer layer. The surface morphology, crystalline quality, and interfacial property of as-grown GaN epitaxial films on Si substrates are studied systematically. The as-grown ~300 nm-thick GaN epitaxial films grown at 850 °C with ~30 nm-thick Al buffer layer on Si substrates show high crystalline quality with the full-width at half-maximum (FWHM) for GaN(0002) and GaN(102) X-ray rocking curves of 0.45° and 0.61°, respectively; very flat GaN surface with the root-mean-square surface roughness of 2.5 nm; as well as the sharp and abrupt GaN/AlGaN/Al/Si hetero-interfaces. Furthermore, the corresponding growth mechanism of GaN epitaxial films grown on Si substrates with Al buffer layer by the combination of MBE and PLD is hence studied in depth. This work provides a novel and simple approach for the epitaxial growth of high-quality GaN epitaxial films on Si substrates.

Erratum to: The properties of samarium-doped zinc oxide/phthalocyanine structure for optoelectronics prepared by pulsed laser deposition and organic molecular evaporation

Samarium-doped zinc oxide (ZnO:Sm)/zinc phthalocyanine (ZnPc) thin film multilayer structure was prepared by combination of pulsed laser deposition (PLD) and organic molecular evaporation (OME). ZnO:Sm thin film was grown by PLD (Nd:YAG, λ = 266 nm, τ = 6 ns) from Sm2O3:ZnO (1 % Sm) target in oxygen ambient at pressure of 10 and 20 Pa at room temperature on fused silica and Si(100) substrates. ZnPc thin film was deposited on ZnO:Sm layer by OME. ZnO:Sm films of c-axis-oriented hexagonal wurtzite structure and α-form ZnPc were obtained. Emission of intra-4f transition in Sm3+ ions and photoluminescence enhancement of near-band-edge emission of ZnO in ZnO:Sm/ZnPc were observed. Electrical properties were not affected by Sm3+ dopant as ZnO:Sm film exhibited high electrical resistivity ~5 × 104 Ω cm.

Adjusting island density and morphology of the SrTiO3(110)-(4 × 1) surface: Pulsed laser deposition combined with scanning tunneling microscopy

The first stages of homoepitaxial growth of the (4×1) reconstructed surface of SrTiO3(110) are probed by a combination of pulsed laser deposition (PLD) with in-situ reflection high energy electron diffraction (RHEED) and scanning tunneling microscopy (STM). Considerations of interfacing high-pressure PLD growth with ultra-high-vacuum surface characterization methods are discussed, and the experimental setup and procedures are described in detail. The relation between RHEED intensity oscillations and ideal layer-by-layer growth is confirmed by analysis of STM images acquired after deposition of sub-monolayer amounts of SrTiO3. For a quantitative agreement between RHEED and STM results one has to take into account two interfaces: the steps at the circumference of islands, as well as the borders between two different reconstruction phases on the islands themselves. Analysis of STM images acquired after one single laser shot reveals an exponential decrease of the island density with increasing substrate temperature. This behavior is also directly visible from the temperature dependence of the relaxation times of the RHEED intensity. Moreover, the aspect ratio of islands changes considerably with temperature. The growth mode depends on the laser pulse repetition rate, and can be tuned from predominantly layer-by-layer to the step-flow growth regime.

A novel method for enhancing interface strength of TiC coated layer/Ti substrate

In this work, a novel surface coating technique, namely pulsed laser deposition (PLD), along with a high-energy mechanical milling (MM) methods were used to deposit well-bonded TiC coatings on a titanium grade (II) substrate. For this reason, TiC particles were coated on titanium plates, with and without PLD layer, using ball milling process at different conditions. The effects of mechanical milling parameters, such as milling time and rotation speed, as well as the effect of PLD have been investigated. The microstructure of coated samples was studied by scanning electron microscopy (SEM). Chemical composition was analyzed by energy dispersive X-ray spectroscopy (EDS). Microhardness and scratch tests were carried out to examine the mechanical and adhesion properties of the coatings, respectively. The coated surface SEM images showed that the dense TiC coating with strong bonding to the substrate could be achieved by using a combination of mechanical milling (MM) and pulsed laser deposition (PLD) techniques. In addition, a possible mechanism was proposed for the formation of TiC coatings during mechanical milling on the PLD-TiC coated substrate. Finally, it was observed that combination of PLD and MM methods (PLD+MM) can produce well-bonded coatings with extraordinary properties, compared to just mechanical milling method.

Very Smooth FeSb2Te and Ce0.1Fe0.7Co3.3Sb12 Layers Prepared by Modified PLD

We report on the preparation of thermoelectric layers of FeSb2Te and Ce0.1Fe0.7Co3.3Sb12 on silicon (100) and fused silica substrates via a combination of pulsed laser deposition (PLD) and rapid thermal annealing methods. A wide range of deposition conditions were tested including on- and off-axis approaches and variation of the annealing temperature profile. Wavelength dispersive x-ray spectroscopy was used to determine stoichiometry. An optical microscope, mechanical profilometer, and atomic force microscopy served to map layer topology. For the FeSb2Te layers, Sa was between 1.4 nm and 6 nm, with Sq ranging from 2.1 nm to 7.8 nm. For Ce0.1Fe0.7Co3.3Sb12 layers, Sa was from 1.3 nm to 4.2 nm and Sq between 1.7 nm and 6.2 nm. Crystalline structure was determined by x-ray diffraction. The best layers (in terms of smooth surface and crystalline structure) prepared using a modified off-axis PLD arrangement were then characterized for thermoelectric properties. The smooth, stoichiometric and crystalline layers of both types were prepared at an annealing temperature of 423 K for 10 min. All experiments were conducted with the aim of finding the deposition condition providing smooth and crystalline layers. These conditions should be used for the deposition of multilayered systems composed of the FeSb2Te and Ce0.1Fe0.7Co3.3Sb12 layers with a period of about 1 nm, where there could be layer roughness comparable to the period.

Hybrid Laser Technology for Creation of Doped Biomedical Layers

Hybrid laser technologies for deposition of thin films and basic schemes of combination of pulsed laser deposition (PLD) with magnetron sputtering and RF discharges or two lasers or three laser deposition systems are presented. Experiences with deposition of chromium doped diamond-like carbon (DLC) films for coating of prostheses are described. Layers of different chromium concentrations were prepared using hybrid systems (PLD + magnetron sputtering or by double PLD). Results of physical and mechanical characterization of film properties and biomedical tests of trivalent and toxic hexavalent chromium are given. Experiences with double laser deposition of DLC layers doped with silver are also mentioned.

Bonding and bio-properties of hybrid laser/magnetron Cr-enriched DLC layers.

Chromium-enriched diamond-like carbon (DLC) layers were prepared by a hybrid technology using a combination of pulsed laser deposition (PLD) and magnetron sputtering. XRD revealed no chromium peaks, indicating that the layers are mostly amorphous. Carbon (sp(2) and sp(3) bonds) and chromium bonds were determined by XPS from C 1s, O 1s, and Cr 2p photoelectron peaks. Depending on the deposition conditions, the concentration of Cr in DLC layers moved from zero to 10 at.% for as-received sample surfaces, and to about 31 at.% after mild sputter-cleaning by argon ion cluster beam. It should be noted that the most stable Cr(3+) bonding state is in Cr2O3 and Cr(OH)3, and that there is the toxic Cr(6+) state in CrO3. The surface content of hexavalent chromium in the Cr 2p3/2 spectra is rather low, but discernible. The population density of Saos-2 cells was the highest in samples containing higher concentrations of chromium 7.7 and 10 at.%. This means that higher concentrations of chromium supported the cell adhesion and proliferation. In addition, as revealed by a LIVE/DEAD viability/cytotoxicity kit, the cells on all Cr-containing samples maintained high viability (96 to 99%) on days 1 and 3 after seeding. However, this seemingly positive cell behavior could be associated with the risk of dedifferentiation and oncogenic transformation of cells.

Current rectifying and resistive switching in high density BiFeO3 nanocapacitor arrays on Nb-SrTiO3 substrates.

Ultrahigh density well-registered oxide nanocapacitors are very essential for large scale integrated microelectronic devices. We report the fabrication of well-ordered multiferroic BiFeO3 nanocapacitor arrays by a combination of pulsed laser deposition (PLD) method and anodic aluminum oxide (AAO) template method. The capacitor cells consist of BiFeO3/SrRuO3 (BFO/SRO) heterostructural nanodots on conductive Nb-doped SrTiO3 (Nb-STO) substrates with a lateral size of ~60 nm. These capacitors also show reversible polarization domain structures, and well-established piezoresponse hysteresis loops. Moreover, apparent current-rectification and resistive switching behaviors were identified in these nanocapacitor cells using conductive-AFM technique, which are attributed to the polarization modulated p-n junctions. These make it possible to utilize these nanocapacitors in high-density (>100 Gbit/inch2) nonvolatile memories and other oxide nanoelectronic devices.

Investigation on the Properties of Nonpolar m-Plane GaN-Based Light-Emitting Diode Wafers Grown on LiGaO2(100) Substrates

High-quality nonpolar m-plane GaN-based light-emitting diode (LED) wafers on LiGaO2(100) substrates have been grown in this work by the combination of pulsed laser deposition and molecular beam epitaxy technologies. This work systemically studies the crystalline quality, surface morphology, as well as optoelectronic properties of as-grown nonpolar m-plane GaN-based LED wafers. The as-grown nonpolar m-plane GaN-based LED wafers on LiGaO2(100) substrates show good structural properties with estimated dislocation density ∼108 cm−2 and abrupt InGaN/GaN interfaces. A photoluminescence peak at approximately 446 nm with full-width at half-maximum (FWHM) of 21.2 nm is identified at room temperature. A strong electroluminescence (EL) peak observed at 446 nm with FWHM of 20.7 nm is obtained at an injection current of 20 mA. Furthermore, there is a slight blue shift in the EL emission wavelength with increase in the injection current, while the EL FWHM can be kept stable thanks to the absence of the quantum confined Stark effect. This study of high-quality nonpolar m-plane GaN-based LEDs is of paramount importance for future application of high-efficiency GaN-based devices.

Chromium-doped DLC for implants prepared by laser-magnetron deposition.

Diamond-like carbon (DLC) thin films are frequently used for coating of implants. The problem of DLC layers lies in bad layer adhesion to metal implants. Chromium is used as a dopant for improvement of adhesion of DLC films. DLC and Cr-DLC layers were deposited on silicon, Ti6Al4V and CoCrMo substrates by a hybrid technology using combination of pulsed laser deposition (PLD) and magnetron sputtering. The topology of layers was studied using SEM, AFM and mechanical profilometer. Carbon and chromium content and concentration of trivalent and toxic hexavalent chromium bonds were determined by XPS and WDS. It follows from the scratch tests that Cr doping improved adhesion of DLC layers. Ethylene glycol, diiodomethane and deionized water were used to measure the contact angles. The surface free energy (SFE) was calculated. The antibacterial properties were studied using Pseudomonas aeruginosa and Staphylococcus aureus bacteria. The influence of SFE, hydrophobicity and surface roughness on antibacterial ability of doped layers is discussed.