以Al2O3为过渡层脉冲激光法制备PZT铁电薄膜

为实现PZT铁电薄膜与半导体衬底的直接集成引入Al2O3为过渡层，首先用真空电子束蒸发法在Si(100)，多昌金刚石（111）衬底上生长约20nm厚的Al2O3过渡层，接着在上述衬底上采用脉冲激光淀积（PLD）法淀积PZT薄膜，衬底温度为350-550℃。X光电子能谱（XPS）测试表明，在高真空下，电子束蒸发Al2O3固态源能获得化学配比接近蒸发源的Al2O3薄膜。X射线衍射（XRD）测试说明，不论衬底是硅还是多晶金刚石，当衬底温度为550℃时，PZT在Al2O3过渡层上呈现（222）取向的焦绿石相结构，当衬底是金刚石时，通过如下工艺：（1）较低温度（350℃）淀积；（2）空气氛围650℃快速退火5min，可以在Al2O3过渡层上获得高度（101）取向的钙钛矿结构的铁电相PZT薄膜，最后AFM测试显示，在硅衬底上，PZT薄膜的表面均方根粗糙度为9.78nm；而在多晶金刚石衬底上，PZT薄膜的表面均方根粗糙度为17.2nm。     

La2O3-doped BaTiO3 thin films obtained by pulsed laser deposition

Abstract

La²O³-doped barium titanate (BaTiO³) thin films have been obtained by pulsed laser deposition. The structure and quality of deposited films were characterized by X-ray diffraction and scanning electron microscopy. A smooth surface was obtained when the films were deposited in 30 Pa ambient oxygen. The composition (elements and oxides) of the thin films were close to those of the target. The layer obtained by pulsed laser deposition from a target of BaTiO³ doped with 0.5 at.% La exhibits good dielectric characteristics: capacitance 88 pF, Curie temperature 59°C and dielectrics loss, tanδ, 0.084.     

Microstructure and optical properties of Al2O3/ZrO2 nano multilayer thin films prepared by pulsed laser deposition

The aluminium oxide/zirconium oxide (Al₂O₃/ZrO₂) nanolaminate thin films (5/20 nm with 4 bilayers, 5/15 nm with 5 bilayers and 5/10 nm with 7 bilayers) were deposited on Si (100) and quartz substrates at an optimized oxygen partial pressure of 3 × 10⁻² mbar at room temperature using pulsed laser deposition. The multilayer films were characterized using X-ray diffraction, X-ray reflectivity, Atomic force microscopy and UV–Visible spectroscopy. The X-ray diffraction studies showed amorphous nature for 5/20 nm film, whereas 5/15 nm and 5/10 nm multilayers showed only tetragonal zirconia at room temperature. X-ray reflectivity studies showed the Kiessig fringes and Bragg peaks, indicating the well defined formation of individual layers and bilayer periodicity in the multilayer films. The AFM studies showed the RMS roughness values of 0.7 nm, 0.9 nm and 1.1 nm for 5/10 nm, 5/15 nm and 5/20 nm multilayers respectively. The optical performance of the combined Al₂O₃/ZrO₂ nanolaminates showed that the refractive indices of the films increased from 1.75 to 1.99 with the decrease of ZrO₂ layer thickness from 20 to 10 nm.     

Comparison of high-pressure dc-sputtering and pulsed laser deposition of superconducting YBa2Cu3O x thin films

Superconducting YBa₂Cu₃O_x thin films were deposited on NdGaO₃ (110) substrates using two different techniques: dc sputtering at high oxygen pressure and pulsed laser deposition. The structure, electrical properties, and surface morphology of the obtained films were compared. The superior crystal quality of dc-sputtered films fabricated at the same temperature and at oxygen pressure of the same range as for laser-deposited films can be explained by a lower deposition rate providing time for recrystallization processes. The re-evaporation becomes significant for dc sputtering at high deposition temperatures and results in Badeficient films. The high mobility of atoms on the surface of the growing film during laser deposition helps in the formation of smoothc-oriented areas of the film.     

Superconducting behavior of high-T c YBa2Cu3O7 thin films with BaO impurity produced by pulsed laser deposition

We have investigated the superconducting behavior of high-T _c YBa₂Cu₃O₇ (YBCO) thin films containing BaO impure phase produced by pulsed laser deposition. The thin films were characterized by the standard four-probe method, X-ray diffraction (XRD), and scanning electron microscopy (SEM). XRD showed that all these thin films contained BaO impurity, with thec-axis normal to the surface of the substrates. The presence of impurity existed from substrate temperatureT _s of 727 to 796°C. When these thin films with BaO impurity were measured under the magnetic fields, it was found that the critical current densityJ _c increased slightly with increase in magnetic fieldB within the range ofB≤500 G, in the case ofB perpendicular to thec-axis of the film.     

Origins of conductive losses at microwave frequencies in YBa2Cu3O7−δ/LaAlO3/YBa2Cu3O7−δ trilayers deposited by pulsed laser deposition

Oriented YBa₂Cu₃O_7?δ/LaAlO₃/YBa₂Cu₃O_7?δ trilayers were deposited by pulsed laser deposition (PLD) onto 〈100〉 MgO and LaAlO₃. Film thicknesses varied from 2000–5000 Å/ layer. A comparision of structure and transport data for the bottom and top superconducting layers indicated a slight decrease in film quality for the top superconducting layer. The critical temperature was lower for the top superconducting layer (90.5 vs. ～90 K) and the microwave surface resistance was higher (increasing from ～2 to 18 mω at 36 GHz, 20 K). The resistivity of the dielectric was estimated to be 10⁶ ω cm, and the loss tangent of the dielectric film at microwave frequencies had an upper limit of 0.01. Cross-sectional TEM analysis of the trilayer structure showed a high density of threading dislocations in the dielectric layer that appeared to nucleate at steps in the underlying superconducting layer. The threading dislocations may serve as conduction paths in the LaAlO₃ layer.     

Optical properties of Ag nanoparticles embedded Ba0.5Sr0.5TiO3 films prepared by alternating pulsed laser deposition

Nanocomposite thin films consisting of nanometer-sized Ag particles embedded in amorphous Ba0.5Sr0.5TiO3 matrix were prepared on fused silica substrates by an alternating pulsed laser deposition method. Their optical nonlinearities have been studied using the Z-scan method. The surface plasmon resonance (SPR) peak shifts to red and increases with the increasing the volume fraction of Ag in the nanocomposite films. The magnitude of the third-order nonlinear susceptibility of the nanocomposite with an Ag volume fraction of 3.3% was calculated to be approximately 2 x 10(-8) esu at the SPR wavelength.     

Optical and electrical properties between 0.4 and 12 microm for Sn-doped In2O3 films by pulsed laser deposition and cathode sputtering

Optical properties of Sn-doped In(2)O(3) (ITO) have been studied in the optical range of 0.4-12 microm. A deposition has been made on BK7 glass, magnesium fluoride, sapphire, and zinc sulfide substrates. The layers have been characterized by their optical properties, DC electrical sheet resistivity, and Hall mobility. Sheet resistivity lies in the range of 6.8-318 Omega/sq for thicknesses between 16 and 280 nm. The best carrier mobility is obtained on BK7 and sapphire substrates, up to approximately 50 cm(2)/V s. The material shows good infrared transparency in the 3-5 microm range on magnesium fluoride and 0.4-4 microm on sapphire, and it is usable for practical applications up to 12 microm on zinc sulfide. Simulations have been carried out for optical indices and spectra calculations. The Drude model has been used to exploit the results in either direction: from electrical measured data to the simulation of optical spectra and indices, and from measured optical spectra to simulated optical indices and electrical parameters (mobility, carrier density). Hall mobility is considered a worthy and convenient material quality criteria for materials aimed at optics.     

Charge-trapping characteristics of Al2O3/Cu/Al2O3 nanolaminate structures prepared through atomic layer deposition

The nanolaminate Al2O3/Cu/Al2O3 structures were constructed on p-type Si (001) substrates using atomic layer deposition (ALD) process with the aim to fabricating nonvolatile charge-trap memories. Low temperature Cu thin layers were deposited through plasma-enhanced atomic layre depositon of Cu aminoalkoxide (Cu(dmamb)2) combined with hydrogen plasma and Al2O3 layers were prepared by thermal atomic layer deposition of trimethylaluminum (TMA) combined with H2O. Nonvolatile features were confirmed using capacitance-voltage (C-V) measurements. The copper film functions as a charge-trapping layer and the Al2O3 thin layers were employed as tunneling and control oxide layers. Line shapes and binding energies of Cu metal and the thin layer of 6 nm Cu in nanolaminate structures were observed in the X-ray photoelectron spectroscopy (XPS) and high resolution transmission electron microscopy (TEM) image. The V(FB) shift width of the Al2O3 (28 nm)/Cu (6 nm)/Al2O3 (4.2 nm)/Si laminate structure is found to be 4.75 V in voltage sweeping between -10 and +10 V, leading to the trap density of 1.68 x 10(18) cm(-3).     

Nanoforest Nb2O5 photoanodes for dye-sensitized solar cells by pulsed laser deposition

Vertically aligned bundles of Nb(2)O(5) nanocrystals were fabricated by pulsed laser deposition (PLD) and tested as a photoanode material in dye-sensitized solar cells (DSSC). They were characterized using scanning and transmission electron microscopies, optical absorption spectroscopy (UV-vis), and incident-photon-to-current efficiency (IPCE) experiments. The background gas composition and the thickness of the films were varied to determine the influence of those parameters in the photoanode behavior. An optimal background pressure of oxygen during deposition was found to produce a photoanode structure that both achieves high dye loading and enhanced photoelectrochemical performance. For optimal structures, IPCE values up to 40% and APCE values around 90% were obtained with the N(3) dye and I(3)(-)/I(-) couple in acetonitrile with open circuit voltage of 0.71 V and 2.41% power conversion efficiency.     

中频反应磁控溅射沉积Al2O3薄膜中迟滞回线的研究

采用中频磁控反应溅射工艺进行氧化铝薄膜的沉积实验,对该工艺过程中溅射电压和沉积速率与氧流量的“迟滞回线”现象进行了研究。通过对实验现象的分析讨论,解释了薄膜沉积速率变化的原因。     

Defect microstructures in epitaxial PbZr0.2Ti0.8O3 films grown on (001) SrTiO3 by pulsed laser deposition

Transmission electron microscopy has been used to investigate the character and distribution of the microstructural features in epitaxial (001) ferroelectric PbZr_0.2Ti_0.8O₃ films grown on (001) SrTiO₃ substrates by pulsed laser deposition. The TEM observations revealed that the films were predominantly c-oriented with embedded a ₁- and a ₂-oriented domains lying on {101} planes. The substrate/film interfaces contained arrays of edge-type misfit dislocations and there were extraordinarily high densities ( ) of threading dislocations in the films. The character and distribution of these features are consistent with the following relaxation sequence. Firstly, the lattice misfit between the phases is accommodated at the growth temperature by the introduction of misfit dislocations at the edges of island nuclei, and some of these dislocations are forced away from the interface to form threading segments upon island coalescence. Next, the film adopts the c-orientation upon cooling through the Curie temperature with a ₁- and a ₂-oriented domains being formed to ameliorate the self-strain of the transformation. Finally, some redistribution of the embedded domains and misfit dislocations occurs in response to stresses caused by expansion coefficient differences. The impact of these defects on the electrical and electromechanical properties of epitaxial ferroelectric properties is discussed.     

Infrared and raman spectroscopic studies of optically transparent zirconia (ZrO2) films deposited by plasma-assisted reactive pulsed laser deposition

Plasma-assisted pulsed laser deposited zirconia (ZrO(2)) films were studied by Fourier transform infrared (FT-IR) and Raman spectroscopy for structural characterization and thermal stability in combination with optical characterization by spectroscopic ellipsometry and optical transmission measurements. Only the monoclinic ZrO(2) phase was positively identified from the infrared and Raman spectra of the as-deposited ZrO(2) films, which show excellent optical transparency from the ultraviolet to the near infrared as revealed by optical characterization. The as-deposited ZrO(2) films are free of any SiO(x) interfacial layer when deposited on silicon. The prepared ZrO(2) films exhibit good thermal stability in their structural, optical, and interfacial properties up to 900 °C. Upon annealing above 1100 °C, a silicon oxide interfacial layer forms due to the oxidation of the silicon substrate surface by the oxygen diffused from the oxide film to the silicon substrate at high temperatures.     

Fatigue behavior of SrBi2(Ta, Nb)2O9 ferroelectric thin films fabricated by pulsed laser deposition

The fatigue behavior for SBTN thin film capacitors with platinum electrodes (Pt/SBTN/Pt) on silicon wafers was investigated. Excellent electrical fatigue resistance was observed; the P _r during 10¹⁰ switching cycles did not display significant reduction. Optical fatigue becomes significant, however, with increasing illumination time to 50 s, the remanent polarization of the thin films shows about 78% reduction from its primary value. The optically induced polarization fatigue in SBTN films is due to trapping of photo-generated charge carriers at domain boundaries, resulting in polarization suppression. These results are helpful in understanding the fatigue-free response observed in electrical field, and are also necessary to fully characterize SBTN for memory applications.     

Flash-lamp-excited self-injection-seeded Q-switched Ti:Al(2)O(3) laser oscillator

A self-injection-seeded, flash-lamp-excited, Q-switched laser oscillator is presented. The laser comprises two resonators that are operated sequentially. The first resonator, which includes all the high insertion loss, damage prone, wavelength tuning, and line-narrowing components, is used to generate the seed signal. The second resonator is a low-loss, Q-switched resonator whose output wavelength and line width are controlled by the seed signal. Output pulses of energy as high as 325 mJ have been obtained that are tunable over a range of the order of 90 nm and with a bandwidth of the order of 0.05 nm.     

Synthesis of Al2O3 matrix composites by reactive infiltration

Reactive infiltration of a NiO-base blended powder with molten aluminium was attempted at 1673 K in order to obtain Al2O3 matrix composites containing a dispersion of Al3Ni, AlNi and/or AlNi3. The NiO powder was barely infiltrated by the molten aluminium after a 3600 s holding time at 1673 K. A continuous layer of Al2O3 was observed to exist at the infiltration front, which prevented any further infiltration. TiB2 particles were added to the NiO powder in order to absorb the heat of reaction between NiO and aluminium. When the TiB2 particle content in the [NiO+TiB2] powder blend was greater than 20 vol%, spontaneous infiltration occurred completely. Thus, it was shown that the addition of the TiB2 particles assisted in the spontaneous infiltration. The specimens produced by the in situ reaction consisted of Al2O3, TiB2 and Al3Ni. Al3Ni was mainly located between the TiB2 and Al2O3. The effect of the TiB2 addition on the infiltration kinetics was to decrease the maximum attainable temperature caused by the exothermic reaction. This in turn prevented the formation of a continuous Al2O3 film at the infiltration front. This resulted in the production of pathways for the infiltration of the molten aluminium and made possible the complete infiltration. This revised version was published online in November 2006 with corrections to the Cover Date.