The power of in situ pulsed laser deposition synchrotron characterization for the detection of domain formation during growth of Ba0.5Sr0.5TiO3 on MgO

A highly sophisticated pulsed laser deposition (PLD) chamber has recently been installed at the NANO beamline at the synchrotron facility ANKA (Karlsruhe, Germany), which allows for comprehensive studies on the PLD growth process of dielectric, ferroelectric and ferromagnetic thin films in epitaxial oxide heterostructures or even multilayer systems by combining in situ reflective high‐energy diffraction with the in situ synchrotron high‐resolution X‐ray diffraction and surface diffraction methods. The modularity of the in situ PLD chamber offers the opportunity to explore the microstructure of the grown thin films as a function of the substrate temperature, gas pressure, laser fluence and target–substrate separation distance. Ba_0.5Sr_0.5TiO₃ grown on MgO represents the first system that is grown in this in situ PLD chamber and studied by in situ X‐ray reflectivity, in situ two‐dimensional reciprocal space mapping of symmetric X‐ray diffraction and acquisition of time‐resolved diffraction profiles during the ablation process. In situ PLD synchrotron investigation has revealed the occurrence of structural distortion as well as domain formation and misfit dislocation which all depend strongly on the film thickness. The microstructure transformation has been accurately detected with a time resolution of 1 s. The acquisition of two‐dimensional reciprocal space maps during the PLD growth has the advantage of simultaneously monitoring the changes of the crystalline structure as well as the formation of defects. The stability of the morphology during the PLD growth is demonstrated to be remarkably affected by the film thickness. A critical thickness for the domain formation in Ba_0.5Sr_0.5TiO₃ grown on MgO could be determined from the acquisition of time‐resolved diffraction profiles during the PLD growth. A splitting of the diffraction peak into two distinguishable peaks has revealed a morphology change due to modification of the internal strain during growth.     

Axial distribution of plasma fluctuations,plasma parameters,deposition rate and grain size during copper deposition

Floating potential fluctuations, plasma parameters and deposition rate have been investigated as a function of axial distance during deposition of copper in direct current (DC) magnetron sputtering system. Fluctuations were analyzed using phase space, power spectra and amplitude bifurcation plots. It has been observed that the fluctuations are modified from chaotic to ordered state with increase in the axial distance from cathode. Plasma parameters such as electron density (n_e), electron temperature (T_e) and deposition rate (D_r) were measured and correlated with plasma fluctuations. It was found that more the deposition rate, greater the grain size, higher the electron density, higher the electron temperature and more chaotic the oscillations near the cathode. This observation could be helpful to the thin film technology industry to optimize the required film.     

Deposition of quaternary sputtered CIGS nanorods via glancing angle deposition

Nanostructured materials have become an attractive alternative to their thin film and bulk counterparts in photovoltaic and photoconductivity research. This is mainly attributed to their superior optical and electrical properties. Light trapping in vertically aligned nanostructures results in high optical absorption and provides enhanced carrier collection by utilizing a fully depleted p–n‐junction between the anode and cathode via an isolated ”capping” construction. The combination of these two features can potentially lead to the development of high efficiency nanostructured devices including solar cells, photodiodes, and photodetectors. Optical absorption proper ties of nanorod arrays of CuIn_x Ga_1–xSe₂ (CIGS), a p‐type semiconductor with a wide band gap ranging from 1.0 eV to 1.7 eV, are compared to their thin film counterpart. Utilizing an RF sputtering system, a quaternary target, and glancing angle deposition (GLAD) technique, vertical arrays of CIGS nanorods were fabricated while conventional films were fabricated by normal incidence deposition. Scanning electron microscopy (SEM) images indicated a successful growth of CIGS nanorods. Optical absorption was found to be strongly altered by the presence of the nanorod structures through spectroscopic reflectometry. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

An off‐axis magnetron‐sputtering system for in situ studies of artificial superlattices growth by synchrotron radiation scattering

A sputtering chamber for the growth of artificial superlattices of oxide‐based materials is described. The chamber is designed to fit into a standard Huber eight‐circle diffractometer. The chamber serves for investigation with synchrotron radiation of growth characteristics of oxide‐based artificial superlattices in situ. Two Be windows of large area in the vacuum chamber enable measurement of reflections of X‐rays at entrance and exit angles up to ～50°. Large perpendicular momentum transfers are practical with this apparatus. The possibility of investigating X‐ray scattering in situ is demonstrated by observation of the effects of the modulation length and the stacking period on the growth characteristics of BaTiO₃/LaNiO₃ artificial superlattices.     

Thin film solid oxide fuel cells

We have investigated the deposition of 91% ZrO₂ − 9% Y₂O₃ thin films by a variety of sputtering techniques for the application as electrolytes in thin film solid oxide fuel cells. The deposition by RF sputtering was accomplished by using an oxide target of the desired composition. The deposition rate in these initial tests was limited to 0.5 μm/hr and the morphology of the film was substantially modified by deposition rate and substrate temperature. Using DC magnetron sputtering we deposited metallic films from a metallic target with the desired chemical composition. We introduced oxygen into the sputtering chamber to reactively deposit the desired 91% ZrO₂ − 9% Y₂O₃ thin films; however, we encountered problems with target oxidation and growth rate reproducibility. We subsequently demonstrated that controlled oxidation of the metallic films could result in adhering, non porous yttria stabilized zirconia films. Paper presented at the 3rd Euroconference on Solid State Ionics, Teulada, Sardinia, Italy, Sept. 15–22, 1996     

Drop‐coating deposition Raman spectroscopy of liposomes

Drop‐coating deposition Raman (DCDR) spectroscopy was tested as a potential technique for studying liposomes at very low sample concentrations. We used model liposomes prepared either from 1,2‐distearoyl‐sn‐glycero‐3‐phospocholine or from soybean asolectin, which is composed of various lipids and thus represents a good model of natural membranes. In both cases, deposited samples formed a dried drop with a circular shape with a ring of concentrated liposomes at the edge. Spectral mapping showed that maximum Raman intensity originated from the inner part of the edge ring, while Raman signal gradually decreased in both radial directions. The Raman spectra exhibited excellent reproducibility of spectral characteristics at different locations in the drop, indicating similar conformation and ordering of hydrocarbon lipid chains in the sample. Our results suggest that DCDR spectroscopy can be used for studying lipids in situ, and sensitivity of this technique is at least two orders of magnitude higher than that of conventional Raman microscopy. Copyright © 2011 John Wiley & Sons, Ltd.     

高择优取向铌酸锶钡薄膜的射频磁控溅射制备

采用溶胶-凝胶法在(100)Si单晶上预先制备出掺钾(K)的铌酸锶钡(SBN)缓冲层,利用射频磁控溅射法在缓冲层KSBN上沉积出高择优取向的铌酸锶钡薄膜,获得了磁控溅射法制备择优取向铌酸锶钡薄膜的相关工艺参数,研究发现,KSBN缓冲层能够很有效地克服衬底与SBN薄膜之间较大的晶格失配,在氧气氩气的比例为1∶2,工作气压为10 Pa,溅射功率300 W,衬底温度300℃,退火温度为800℃的工艺条件下,能够获得c轴高度择优取向的铌酸锶钡铁电薄膜.利用X射线衍射仪,原子力显微镜等仪器分析了薄膜 关键词： 磁控溅射 高择优取向 p-n结效应     

Electrical and structural properties of In-doped ZnO films deposited by RF superimposed DC magnetron sputtering system

Zinc-indium-oxide (ZIO) films were deposited on non-alkali glass substrates by RF superimposed DC magnetron sputtering with a ZIO (9.54 wt% In₂O₃ content) high-density, sintered target at room temperature. The electrical, structural and optical properties of the ZIO films deposited with different sputtering parameters were examined. The total power for RF superimposed DC magnetron sputtering was 80 W. The RF power ratio in the total sputtering power was changed from 0 to 100% in steps of 25%. The ZIO films deposited with a 100% RF discharge showed the lowest resistivity, 1.28×10⁻³ Ω cm, due to the higher carrier concentration. The ZIO film deposited at 50% RF power showed a relatively larger grain size and smaller FWHM. XPS suggested an increase in the level of In³⁺ substitution for Zn²⁺ in the ZnO lattice with increasing RF/(DC+RF) due to the low damage process. The average transmittance of all ZIO films in the visible light region was >80%. The increasing RF power portion of the total sputtering power led to a broadening of the optical band gap, which was attributed to the increase in carrier density according to Burstein-Moss shift theory.     

Deposition of Ag nanostructures on TiO2 thin films by RF magnetron sputtering

Ag nanostructures on TiO₂ films were deposited by RF magnetron sputtering under variable deposition parameters, such as DC potential, RF-power and total pressure. The concentration, shape, and distribution of the deposited nanostructures and continuous Ag films on thin films of TiO₂ can be tailored by careful variation of the deposition parameters. Controllable clusterlike, islandlike and film Ag structures on TiO₂ film were obtained, respectively. DC potential was found as an appropriate parameter to tailor the change of Ag nanostructure and the overall Ag amount. The compositions, nanostructures and morphologies of nanocomposite films appreciably influence the optical response.     

Effect of synthesis conditions on the properties of Fe-Al-N thin films

The magnetic properties, microstructure, and morphology of Fe-Al-N films that are deposited by reactive rf sputtering and synthesized in situ, ex situ (deposition followed by annealing), and by thermal crystallization of amorphous films are studied. The FeAlN films synthesized ex situ offer the highest soft-magnetic properties. The films produced by thermal crystallization offer the highest thermal stability.     

Spatial variations in the stoichiometry of sputtered YBaCuO thin films: theory and experiment

A Monte Carlo simulation of the sputtering process is applied to the problem of the thickness and stoichiometry variations in the sputtering of YBaCuO superconducting targets. The theory predicts no strong spatial variations in stoichiometry due to the different scattering behaviour of the various constituents of the superconductor. The theory is compared with a systematic experimental study using both RF and DC sputtering in either argon or oxygen gases. The ratios Ba: Y and Cu: Y were determined as a function of radial distance by inductively coupled plasma analysis (ICP). In argon, both DC and RF sputtering gave a thickness distribution in reasonable agreement with theory. In oxygen, RF sputtering gave a thickness distribution very different to theory and gave no net deposition in an annular central region. Stoichiometry variations are interpreted in terms of etching processes. The role of oxygen ions in etching is discussed and a case made for the importance of oxygen positive ions in RF sputtering in oxygen.     

Thin SiC<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> layers prepared by hybrid laser–magnetron deposition

Thin SiC _x films were fabricated by hybrid laser–magnetron deposition system. KrF excimer laser was used for deposition of carbon and magnetron at the same time for sputtering of Si species. Films were fabricated in argon/hydrogen ambient with and without additional RF discharge. The substrate temperature was changed up to 700°C. Films topology, crystallinity, composition, chemical bonds and optical emission spectra were studied. Films were smooth and amorphous. Films of thickness 400–1000 nm were fabricated. Adhesion moved from 8 to 14 N, depending on deposition conditions.     

The influence of implanted xenon on the sputtering yield of silicon

Following implantation labeling with either 200 or 270 keV Xe⁺ the sputtering yield of silicon bombarded with 20 keV Xe⁺ has been determined in situ by means of the backscattering technique (Y = 3.0 ± 0.3 (atoms/ion)). Yield enhancement by up to 60% was observed in cases where the implantation-induced xenon concentrations exceeded the saturation concentration during sputtering. The effect is attributed to (i) an increase in energy deposition at the surface introduced by pronounced xenon loading of the target and (ii) lowering of the surface binding energy. As a consequence the energy dependence of the xenon sputtering yield of silicon is expected to be strongly affected by the energy dependence of the xenon saturation concentration in silicon. Available experimental data support this idea.     

Quick X‐ray reflectivity using monochromatic synchrotron radiation for time‐resolved applications

A new technique for the parallel collection of X‐ray reflectivity (XRR) data, compatible with monochromatic synchrotron radiation and flat substrates, is described and applied to the in situ observation of thin‐film growth. The method employs a polycapillary X‐ray optic to produce a converging fan of radiation, incident onto a sample surface, and an area detector to simultaneously collect the XRR signal over an angular range matching that of the incident fan. Factors determining the range and instrumental resolution of the technique in reciprocal space, in addition to the signal‐to‐background ratio, are described in detail. This particular implementation records ～5° in 2gθ and resolves Kiessig fringes from samples with layer thicknesses ranging from 3 to 76 nm. The value of this approach is illustrated by showing in situ XRR data obtained with 100 ms time resolution during the growth of epitaxial La_0.7Sr_0.3MnO₃ on SrTiO₃ by pulsed laser deposition at the Cornell High Energy Synchrotron Source (CHESS). Compared with prior methods for parallel XRR data collection, this is the first method that is both sample‐independent and compatible with the highly collimated, monochromatic radiation typical of third‐generation synchrotron sources. Further, this technique can be readily adapted for use with laboratory‐based sources.     

Paschen curve approach to investigate electron density and deposition rate of Cu in magnetron sputtering system

In this work, Paschen curve for argon gas was obtained during copper deposition using a DC magnetron sputtering system. Five process parameters of Paschen curve were used to obtain the electron density and deposition rate of the deposited nanostructured thin films. Plasma parameter such as electron density was correlated with the deposition rate. It is observed that a minimum deposition rate was obtained for the plasma process parameter corresponding to the Paschen minimum. This investigation helps to understand and optimize the quality of nanostructured thin films depending on the process parameters.     

Electrochemical in situ surface enhanced Raman spectroscopic characterization of a trinuclear ruthenium complex,Ru‐red

To study the fate of a molecular di‐μ‐oxo‐bridged trinuclear ruthenium complex, [(NH₃)₅Ru–O–Ru(NH₃)₄–O–Ru(NH₃)₅]⁶⁺, also known as Ru‐red, during the electro‐driven water oxidation reaction, electrochemical in situ surface enhanced Raman spectroscopy (SERS) investigations have been conducted on an electrochemically roughened gold surface in acidic condition. It was previously described that on a basal plane pyrolitic graphite electrode in 0.1 M H₂SO₄ aqueous solution, Ru‐red undergoes one electron oxidative conversion into a stable higher oxidation state ruthenium complex, Ru‐brown, at <1.0 V (vs normal hydrogen electrode (NHE)), and this leads to water oxidation and dioxygen release, but the fate of Ru‐red during electrochemistry was not studied in much detail. In this investigation, Ru‐red dispersed in acid electrolyte and immobilized on a roughened gold electrode without Ru‐red in solution has been subjected to anodic controlled potential experiments, and in situ SERS was carried out at various potentials in succession. The electrochemical SERS data obtained for Ru‐red are also compared with in situ SERS results of an electrodeposited ruthenium oxide thin film on the Au disk. Our study suggests that on a gold electrode in sulfuric acid solution containing Ru‐red, one electron oxidative conversion of Ru‐red to a higher oxidation state ruthenium compound, Ru‐brown, occurs at ca. 0.74 V (vs NHE), as supported by the electrochemical in situ SERS experiments. Moreover, at higher potentials and on Au disk, the Ru‐red / Ru‐brown are not stable and slowly decompose or electro‐oxidize leading to deactivation of the tri‐ruthenium catalytic system in acidic medium. Copyright © 2013 John Wiley & Sons, Ltd.     

Influence of deposition pressure and power on characteristics of RF-Sputtered Mo films and investigation of sodium diffusion in the films

Mo films deposited by DC sputtering are widely used as back contact in CIGS and CZTS based thin film solar cells. However, there have been only a few studies on the deposition of Mo films by RF sputtering method. In this context, Mo films on SLG substrates were prepared as a function of deposition pressure and power by using RF magnetron sputtering method to contribute to this shortcoming. Mo films were deposited at 250 °C substrate temperature by using 20, 15, 10 mTorr Ar pressures at 120 W RF power and 10 mTorr Ar pressure at 100 W RF power. Structural, morphological and reflectivity properties of RF-sputtered Mo films were clarified by XRD, AFM, FE-SEM and UV–Vis measurements. In addition, due to sodium incorporation from SLG substrate to the absorber layer through Mo back contact layer is so essential in terms of improving the conversion efficiency values of CIGS and CZTS thin film solar cell devices, the effects of Na diffusion in the films were analyzed with SIMS depth profile. The electrical properties of the films such as mobility, carrier density and resistivity were determined by Hall Effect measurements. It was found that Mo films prepared at 120 W, 10 mtorr and 250 °C substrate temperature and then annealed at 500 °C for 30 min, had resistivity as low as 10⁻⁵ Ω cm, as well as higher amount of Na incorporation than other films.     

Surface passivation of crystalline silicon by sputter deposited hydrogenated amorphous silicon

This letter shows that intrinsic hydrogenated amorphous silicon (a‐Si:H) films deposited by RF magnetron sputtering can provide outstanding passivation of crystalline silicon surfaces, similar to that achieved by plasma enhanced chemical vapour deposition (PECVD). By using a 2% hydrogen and 98% argon gas mixture as the plasma source, 1.5 Ω cm n‐type FZ silicon wafers coated with sputtered a‐Si:H films achieved an effective lifetime of 3.5 ms, comparable to the 3 ms achieved by PECVD (RF and microwave dual‐mode). This is despite the fact that Fourier transform infrared spectroscopy measurements show that sputtering and PECVD deposited films have very different chemical bonding configurations. We have found that film thickness and deposition temperature have a significant impact on the passivation results. Self‐annealing and hydrogen plasma treatment during deposition are likely driving forces for the observed changes in surface passivation. These experimental results open the way for the application of sputtered a‐Si:H to silicon heterojunction solar cells. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

磁控溅射沉积薄膜实验参数优化光谱诊断

采用磁控溅射仪、Omni-λ300系列光栅光谱仪、CCD数据采集系统和光纤导光系统等构成的等离子体光谱分析系统,采集了以Cu和Al为靶材、氩气为工作气体,射频磁控溅射法沉积硅基薄膜时的等离子体发射光谱。以CuⅠ324.754 nm,CuⅠ327.396 nm,CuⅠ333.784 nm,CuⅠ353.039 nm,AlⅠ394.403 nm和AlⅠ396.153 nm为分析线,研究了Cu和Al等离子体发射光谱强度随溅射时间、溅射功率、靶基距和气体压强等实验参数的变化。并与射频磁控溅射沉积薄膜实验参数的选择进行对比,表明发射光谱法对射频磁控溅射薄膜生长条件的优化有着很好的指导作用。     

Ab‐initio calculations and structural studies of (SiTe)2(Sb2Te3)n (n: 1, 2, 4 and 6) phase‐change superlattice films

(SiTe)₂(Sb₂Te₃)_n phase‐change superlattices were investigated theoretically and experimentally. Ab‐initio first principle simulations predicted that the (SiTe)₂(Sb₂Te₃)_n structures are stable and possess a Dirac semimetal‐like band structure. Calculation of the Z₂ invariant indicated that the structure was topologically nontrivial. (SiTe)₂(Sb₂Te₃)_n superlattice structures derived from first‐principles were successfully fabricated on a Si substrate by RF‐magnetron sputtering. XRD and TEM indicated that the superlattice films were highly oriented with the 00X planes of Sb₂Te₃ and the superlattice normal to the substrate surface. The (SiTe)₂(Sb₂Te₃)_n superlattice is suggested as new material system for interfacial phase‐change memory applications. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)