Preferred growth of epitaxial TiN thin film on silicon substrate by pulsed laser deposition

Epitaxial TiN thin films on silicon substrates were prepared by pulsed excimer laser (KrF, 34 ns) ablation of a hot-pressed TiN target in nitrogen gas atmosphere. X-ray diffraction (XRD) showed that the preferred orientations of TiN thin films did not change with substrate temperatures, nitrogen gas pressure and film thickness; however, they did change with the orientations of substrates. The epitaxial orientation relationships between high-quality epitaxial TiN thin films and silicon substrates [2 4 2] TiN [2 4 2] Si, (1 1 1) TiN(1 1 1) Si and [3 1 1] TiN [3 1 1] Si, (1 0 0) TiN(1 0 0) Si. The full-width at half-maximum (FWHM) of the rocking curve of XRD and the minimum channelling yield of Rutherford backscattered spectroscopy (RBS) of the epitaxial TiN thin film were estimated to be 0.3 ° and 7.3%, respectively, indicating excellent crystalline quality of the grown film. X-ray photoelectron spectroscopy confirmed that the binding energies of Ti 2p 3/2 and N 1s core levels in epitaxial thin film were 455.2 and 397.1 eV, respectively, corresponding to those of TiN bulk. By calibrating the RBS spectra, the chemical composition of TiN thin films was found to be titanium-rich. The typical surface roughness of TiN thin film observed by scanning probe microscopy was about 1.5 nm. © 1998 Chapman & Hall     

Preparation of ferroelectric NaNbO(3) thin films on MgO substrate by pulsed laser deposition

We successfully fabricated good quality NaNbO(3) (NN) films on MgO substrate by pulsed laser deposition using a K-Ta-O (KTO) buffer layer. An SrRuO(3) (SRO) lower electrode layer was deposited on a KTO buffer layer/(100)MgO substrate and then the NN film was deposited on top. X-ray diffraction showed that the SRO and NN films were epitaxially grown on (100)MgO substrate. Transmission electron microscopy showed a crystallographic relationship of [001](NN)//[001](MgO) between NN and MgO. The relative dielectric constant, epsilon(r), and dielectric loss, tan delta, of the film were 350 and 0.05 at 1 kHz, respectively. The polarization vs. electric field (P-E) hysteresis loop of the NN film was characteristic of ferroelectric behavior.     

Epitaxial aluminum nitride films on sapphire formed by pulsed laser deposition

Highly oriented aluminum nitride thin films were grown on sapphire (0001)-substrate by pulsed laser deposition technique. Characterization was done by X-ray-diffraction, elastic recoil detection analysis and Rutherford backscattering/channeling measurements. The epitaxial properties were studied as function of the substrate temperature and the deposition rate. An epitaxial relation to the sapphire substrate is found to be AlN [0001] || Al₂O₃ [0001] and AlN [11 0] || Al₂O₃ [10 0]. XRD-texture-analysis on films deposited at 850°C shows a full width half maximum Δω of 0.13° (rocking curve) and Δ of 1.1° (in-plane).     

Growth of pseudocubic perovskite-type SrRuO3 thin films on quartz substrate using pulsed laser deposition method

Strontium ruthenium oxide (SrRuO₃) thin films have been grown using pulsed laser deposition technique on silicon, Pt coated silicon and quartz substrates. The effect of substrate temperatures on the structural, microstructure, and electrical properties of the SrRuO₃ films on quartz substrate has been investigated using XRD, SEM, AFM and four-probe method, respectively. The lowest resistivity at room temperature for the SrRuO₃ thin film on quartz substrate has been achieved at substrate temperature of 700 °C. Furthermore, the comparisons of SrRuO₃ thin films deposited on various substrates have been done with respect to structural, microstructural and electrical properties. XRD patterns exhibit that all thin films are a single phase, pseudo-cubic perovskite structure. Study of surface morphology shows that grain size and roughness varies with respect to substrate. It is observed that SrRuO₃ thin films yield larger grain size and root mean square roughness on Pt/Si substrate. Investigation of electrical properties shows that SrRuO₃ thin films can serve the purpose of the bottom electrode in dielectric and ferroelectric devices.     

Synthesis of amorphous silicon carbonitride films by pulsed laser deposition

Silicon carbonitride (SiC_xN_y) films were grown on silicon substrates using the pulsed laser deposition (PLD) technique. A silicon carbide (SiC) target was ablated by the beam of a KrF excimer laser in a nitrogen (N₂) background gas. The morphology, structure, composition, as well as the optical and mechanical properties of the coatings were investigated as functions of the N₂ pressure (1–30 mtorr) and substrate temperature (250–650 °C). Smooth, amorphous films were obtained for all the processing parameters. The concentration of nitrogen in the deposits was found to increase when increasing the N₂ pressure, while the silicon and carbon concentrations decreased concurrently. At a N₂ gas pressure of 30 mtorr, a nitrogen content in the range of 28–34 at.% was obtained. Two growth regimes were identified as a function of the N₂ pressure. For a pressure up to 10 mtorr, highly dense and homogeneous films were observed, while textured deposits were obtained at higher pressures. The latter regime was characterized by an oxygen contamination of the coatings, whose severity increased when increasing the N₂ pressure or when reducing the deposition temperature. The hardness of the films was found to be a function of the growth regime; the highest values of the hardness were obtained in the low-pressure regime, in the range of 27–42 GPa.     

Amorphous Terfenol-D films using nanosecond pulsed laser deposition

Thin films of Terfenol-D were produced by nanosecond pulsed laser deposition (PLD) at two fluences. Electron dispersive spectroscopy conducted using scanning electron and transmission electron microscopes showed that the film compositions were similar to that of the PLD target. Contrary to previous assertions that suggested that nanosecond PLD results in crystalline films, X-ray diffraction and transmission electron microscopy analysis showed that the films produced at both fluences were amorphous. Splatters present on the film had similar compositions to the overall film and were also amorphous. Magnetic measurements showed that the films had high saturation magnetization and magnetostriction, similar to high quality films produced using other physical vapor deposition methods.     

Structural and discharging properties of MgO thin films prepared by pulsed laser deposition

In this work, pulsed laser-deposited thin films of MgO were studied for application in plasma display panels. The firing voltage (FV) of discharge cells with MgO films was measured and the film structure was investigated as a function of film deposition conditions. MgO thin films were deposited at oxygen pressure and substrate temperature between 0.02-5 Pa and 260-600 °C, respectively. The structure of thin films was investigated by using X-ray diffraction, X-ray reflection and atomic force microscopy methods. It was found that the FV is strongly correlated with the film deposition conditions and structural properties. In general, the FV values were smaller for the films with higher crystallinity and density. The crystallinity and the density of the films increased when the deposition temperature was raised and the O₂ pressure was reduced. The lowest FV values (~ 120 V) were obtained at the growth temperature of 550 °C and at O₂ pressures below 1 Pa.     

PLD方法生长ZnO/Si异质外延薄膜的研究

用脉冲激光沉积法在Si(111)衬底上制备了ZnO薄膜。RHEED和XRD测试表明,直接沉积在Si衬底上的ZnO薄膜为多晶薄膜,且薄膜的结晶质量随衬底温度的升高而下降。相比之下,生长在一低温同质缓冲层上的ZnO薄膜则展现出规则的斑点状RHEED图像,说明它们都是外延生长的高质量ZnO薄膜。XRD与室温PL谱分析表明,外延ZnO薄膜的质量随衬底温度的升高得到明显的改善。在650℃生长的样品具有最好的结构和发光特性,其(002)衍射峰的半高宽为0.185°,UV峰的半高宽仅为86meV。     

Brush-shaped ZnO heteronanorods synthesized using thermal-assisted pulsed laser deposition

Brush-shaped ZnO heteronanostructures were synthesized using a newly designed thermal-assisted pulsed laser deposition (T-PLD) system that combines the advantages of pulsed laser deposition (PLD) and a hot furnace system. Branched ZnO nanostructures were successfully grown onto CVD-grown backbone nanowires by T-PLD. Although ZnO growth at 300 °C resulted in core-shell structures, brush-shaped hierarchical nanostructures were formed at 500-600 °C. Materials properties were studied via photoluminescence (PL), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) characterizations. The enhanced photocurrent of a SnO(2)-ZnO heterostructures device by irradiation with 365 nm wavelength ultraviolet (UV) light was also investigated by the current-voltage characteristics.     

Luminescence characterization of ultrathin MgO films of high crystallinity prepared by pulsed laser deposition

Thin MgO films with thicknesses ranging from 127 to 35 nm were prepared by pulsed laser deposition on Si substrates. The crystalline films were smooth (rms roughness 0.6–1.2 nm) with an average density of 3.5 g/cm³. Cathodoluminescence study revealed emissions peaked at 7.65 eV and ascribed to the edge emission of large radius exciton states as well as luminescence due to the F and F⁺ colour centres in the range of 2–4 eV. This luminescence is efficiently excited in the absorption band peaked at 6.2 eV and in the intrinsic absorption with the onset at 7.4 eV via energy transfer processes.     

Investigation into the dielectric behavior of ferroelectric superlattices formed by pulsed laser deposition

In an attempt to reproduce the functional properties associated with relaxor electroceramics, pulsed laser deposition has been used to fabricate thin-film capacitor structures in which the dielectric layer is composed of a superlattice of Ba_0.8Sr_0.2TiO₃ and Ba_0.2Sr_0.8TiO₃. The properties of the capacitors were investigated as a function of superlattice periodicity. The dielectric constant was enhanced at stacking periodicities of a few unit cells, consistent with relaxor behavior. However, enhancement of the dielectric constant was found to be associated with high dielectric loss. Analysis of the imaginary permittivity as a function of frequency shows that fine-scale superlattices conform to Maxwell–Wagner behavior. This suggests that the observed enhancement of the real part of the dielectric constant is an artefact produced by carrier migration. A comparison of this data with that already published on dielectric superlattices suggests that previous claims of an enhancement in dielectric constant may also be due to the Maxwell–Wagner effect. The onset of Maxwell–Wagner behavior was attributed to increasing density of defect zones associated with discontinuities in the superlattice structures. In an attempt to exaggerate the influence of such zones, deliberate delays between deposition of successive dielectric layers were introduced. This resulted in reproduction of several features normally associated with relaxors: enhancement of dielectric constants by over an order of magnitude; strong frequency dispersion around and below T_m; migration of T_m with frequency. However, these features were again associated with relatively high loss.     

Large-sized-mismatched group-V element doped ZnO films fabricated on silicon substrates by pulsed laser deposition

Pulsed laser deposition has been utilized to synthesize impurity-doped ZnO thin films on silicon substrate. Large-sized-mismatched group-V elements (A^V) including P, As, Sb and Bi were used as dopants. Hall effect measurements show that hole concentration in the order of 10¹⁶-10¹⁸ cm⁻³, resistivity in the range of 10-100 Ω cm, Hall mobility in the range of 10-100 cm²/Vs were obtained only for ZnO:As and ZnO:Bi thin films. X-ray diffraction measurements reveal that the films possess polycrystallinity or nanocrystallinity with ZnO (002) preferred orientation. Guided by X-ray photoemission spectroscopy analyses and theoretical calculations for large-sized-mismatched group-V dopant in ZnO, the A_Zn^V-2V_Zn complexes are believed to be the most possible acceptors in the p-type A^V-doped ZnO thin films.     

Nd:YAG pulsed laser deposition of AlVO4 thin films on alumina and monocrystalline MgO

AlVO₄ thin films were prepared by infrared Nd:YAG pulsed laser deposition on two different substrates (polycrystalline Al₂O₃ and monocrystalline MgO). The distance between the target-substrate (30 mm) and the partial oxygen pressure (0.14 mbar) during the deposition process were chosen taking into account the previous experiences with other oxides. The substrate temperature was varied between 300 and 600 °C finding an optimum at about 400 °C. At higher temperatures, the vanadium seems to evaporate from substrate surface with a strong change of stoichiometry. Preferential growth of AlVO₄ films in the direction (022), were grown on MgO substrates. A very high sensitivity of these films to a flux of NO₂ gas is also shown.     

Nanocrystalline silicon films formed under the impact of pulsed excimer laser radiation on polyimide substrates

Polycrystalline silicon films on polyimide substrates were obtained by a method based on the crystallization of amorphous films under the impact of nanosecond pulses of excimer laser radiation. Characteristics of the film structure were studied by methods of Raman scattering and high-resolution electron microscopy. For the laser crystallization regimes employed, nanocrystalline silicon films with an average grain size of 5 nm were obtained. The results are of interest for the development of large-scale microelectronic devices (active thin-film transistor matrices) on cheap flexible substrates.     

Design and performance of a ZnSe tetra-prism for homogeneous substrate heating using a CO2 laser for pulsed laser deposition experiments

We report on the design and performance of a ZnSe tetra-prism for homogeneous substrate heating using a continuous wave CO(2) laser beam in pulsed laser deposition experiments. We discuss here three potential designs for homogenizing prisms and use ray-tracing modeling to compare their operation to an alternative square-tapered beam-pipe design. A square-pyramidal tetra-prism design was found to be optimal and was subjected to modeling and experimental testing to determine the influence of interference and diffraction effects on the homogeneity of the resultant intensity profile produced at the substrate surface. A heat diffusion model has been used to compare the temperature distributions produced when using various different source intensity profiles. The modeling work has revealed the importance of substrate thickness as a thermal diffuser in producing a resultant homogeneous substrate temperature distribution.     

基板预热温度对激光金属沉积成形零件微观组织的影响

基板预热可以显著降低激光金属沉积成形（laser metal deposition shaping, LMDS）过程的热应力,从而抑制成形过程裂缝的产生,但基板预热温度的高低对成形零件的微观组织有着重要的影响,因此研究不同基板预热温度下激光金属沉积成形零件的微观组织变化规律对基板预热温度的选择具有非常重要的意义.利用中国科学院沈阳自动化研究所自行研制的激光金属沉积成形系统和基板预热系统,采用Ni60A金属粉末在基板未预热和预热到200,300,400,500和600 ℃时分别进行成形试验.然后利用扫描电子显微镜和能量散射谱仪对成形试件的微观组织进行深入的研究,得到不同基板预热温度对激光金属沉积成形零件微观组织的影响规律,为基板预热温度的优化选择提供了重要参考.     

Synthesis of nanostructured SiC using the pulsed laser deposition technique

We report the new results on the direct synthesis of nanostructured silicon carbide (SiC) materials using the pulsed laser deposition technique. Scanning electron microscopy images revealed that SiC nanoholes, nanosprouts, nanowires, and nanoneedles were obtained. The crystallographic structure, chemical composition, and bond structure of the nanoscale SiC materials were investigated using X-ray diffraction, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and Raman scattering spectroscopy. The transverse optical mode and longitudinal optical mode in Raman spectra were found to become sharper as the substrate temperature was increased, while the material structure evolved from amorphous to crystalline.     

Nd-doped fluoride film grown on LiYF4 substrate by pulsed laser deposition

The realization of a monocrystalline nanofilm of Nd³⁺-doped fluoride on LiYF₄ substrates by pulsed laser deposition is reported. The film was obtained by laser ablation with 355 nm photons of a bulk LiYF₄ crystal doped with Nd³⁺ ions at 1.5% atomic concentration. The measurements of the sample thickness obtained by an in situ interferometric technique, and the film optical characteristics analyzed via laser induced fluorescence spectroscopy upon UV and IR excitation, are presented. Lifetime measurements of the fundamental Nd³⁺ ion transition in the film were also performed. All the results were compared with those obtained in a Nd³⁺:LiYF₄ bulk crystal. The emission spectra of the deposited film following IR excitation seem to indicate the obtained deposit is Nd³⁺:YF₃.     

Preparation and analysis of chemically gradient functional bioceramic coating formed by pulsed laser deposition

Bioactive ceramic coatings based on calcium phosphates yield better functionality in the human body for a variety of metallic implant devices including orthopaedic and dental prostheses. In the present study chemically and hence functionally gradient bioceramic coating was obtained by pulsed laser deposition method. Calcium phosphate bioactive ceramic coatings based on hydroxyapatite (HA) and tricalcium phosphate (TCP) were deposited over titanium substrate to produce gradation in physico-chemical characteristics and in vitro dissolution behaviour. Sintered targets of HA and α-TCP were deposited in a multi target laser deposition system. The obtained deposits were characterized by X-ray diffraction, fourier transform infrared spectroscopy, scanning electron microscopy and energy dispersive X-ray analysis. Inductively coupled plasma spectroscopy was used to estimate the in vitro dissolution behaviour of coatings. The variation in mechanical property of the gradient layer was evaluated through scratch test and micro-indentation hardness. The bioactivity was examined in vitro with respect to the ability of HA layer to form on the surface as a result of contact with simulated body fluid. It could be inferred that chemically gradient functional bioceramic coating can be produced by laser deposition of multiple sintered targets with variable chemical composition.     

XTEM study of Al doped TiO2 anatase epitaxial films deposited on MgO by pulsed laser deposition

Al doped TiO₂ anatase films epitaxially grown by Pulsed Laser Deposition (PLD) on MgO single crystal substrates have been studied by cross-section transmission electron microscopy. The main structural features of such films are the columnar morphology of the anatase grains and the formation of a spinel buffer layer at the TiO₂/MgO interface. The spinel layer is Al rich and displays a steep gradient in Mg composition. Correlation between the microstructure and the optical properties of the films is presented also.