The electrical and magnetic properties of epitaxial orthorhombic YMnO3 thin films grown under various oxygen pressures

Orthorhombic YMnO₃ thin films were epitaxially grown on bare and LaNiO₃ buffered (0 0 1)-SrTiO₃ substrates by pulsed laser deposition under various oxygen pressures from 5 to 30 Pa. The crystal structure and microstructure of these films have been characterized by both X-ray diffractions and transmission electron microscopy. The leakage current, modeled as the space charge limited current (SCLC) mechanism, decreased significantly with the increase of oxygen content. It is further found that the magnetic property of films is greatly enhanced in YMnO₃ films grown under high oxygen pressure, which can be explained decreased oxygen vacancies. In addition, bipolar switching behavior was obtained only in the films grown under 30 Pa oxygen pressure, which is attributed to the decrease of voltage-driven oxygen vacancy migration.     

Ferromagnetism in epitaxial orthorhombic YMnO3 thin films

Epitaxial orthorhombic YMnO₃ thin films, (0 0 1) oriented, have been grown by pulsed laser deposition on (0 0 1)SrTiO₃ substrates. Their crystal structure and magnetic response have been studied in detail. Although bulk o-YMnO₃ is antiferromagnetic, our magnetic measurements reveal intriguing thermal hysteresis between the zero-field-cooled and field-cooled curves below the onset of the antiferromagnetic ordering temperature, thus signaling a more complex magnetic structure with net ferromagnetic moments. We discuss on the possible origin of this net magnetization and we have found a correlation of the magnetic response with the strain state of the films. We propose that substrate-induced strain modifies the subtle competition of magnetic interactions and leads to a non-collinear magnetic state that can thus be tuned by strain engineering.     

脉冲激光沉积温度及氧压对Bi2Sr2Co2Oy热电薄膜晶体结构与电输运性能的影响

利用脉冲激光沉积技术在c-Al₂O₃单晶基片上制备了Bi₂Sr₂Co₂O_y热电薄膜并研究了沉积温度和氧压对薄膜晶体结构及电输运性能的影响.在最佳沉积条件下制备的单相、c轴取向的Bi₂Sr₂Co₂O_y薄膜的室温电阻率ρ和塞贝克系数S分别为2.9mΩ/cm和110μupV/K,其功率因子S²/ρ好于在单晶样品上得到的值.此外,该薄膜在低温下表现出较强的负磁阻效应,在2K,9T时达到了40%.     

Material characterization of superconducting T′-Nd2CuO4 films synthesized by metal organic decomposition

Recently we have achieved superconductivity in T′-RE₂CuO₄ (RE = Pr, Nd, Sm, Eu, and Gd), films by metal organic decomposition (MOD). In this article, we first report the cation off-stoichiometry effect, which aims at screening out the possibility of hole doping by cation deficiencies. We also investigated the structure and microstructure of superconducting T′-Nd₂CuO₄ films synthesized by MOD. This investigation aims at elucidating why MOD-grown Nd₂CuO₄ films become superconducting whereas our previous Nd₂CuO₄ films grown by molecular beam epitaxy were not superconducting.     

室温生长MgO底层诱导(001)取向FePt薄膜的有序化过程对FePt成分的依赖

室温下通过磁控溅射在表面热氧化的Si基片上生长了MgO/Fe_xPt_100-x双层膜和Fe_xPt_100-x单层膜系列样品，Fe_xPt_100-x的原子成分x=48—68.研究了热处理前后不同成分FePt薄膜的晶体结构和磁性的变化，尤其是MgO底层的引入对FePt的晶体结构和磁性的影响 关键词： FePt(001)薄膜 0相')" href="#">L1₀相     

Laser spectroscopy of CaF2:Eu:Sm thin films grown by pulsed laser deposition

Thin films of CaF₂ co-doped with low concentrations of Eu and Sm ions were grown by pulsed laser deposition (PLD) using a KrF (λ=248 nm) as the ablation source. To the best of our knowledge, the work presented here is the first report of rare-earth-doped CaF₂ films grown by PLD with this source. Combined laser excitation-emission spectroscopy was used to map out electronic transitions of Eu³⁺ with ⁷F₀→⁵D₁ excitation and the ⁵D₀→⁷F₁ emission. At the low concentrations used here the crystal field center of cubic symmetry is dominant in the films that are same for laser targets. However, charge compensated centers are present in the bulk crystal precursor. The removal of the charge compensated centers in the films and the target is likely caused by the target preparation where high pressure and temperature were applied.     

Preparation, structures and photoluminescent enhancement of CdWO4-TiO2 composite nanofilms

For the first time, Cadmium tungstate (CdWO₄)-TiO₂ composite nanofilms on a glass substrate were prepared by means of the dip-coating technique, in which collodion was used as a dispersant and film-forming agent. The films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermo gravimetric and thermal analyses (TG/DTA), FTIR and photoluminescence (PL) methods, respectively. SEM and XRD characterization of these films indicated that CdWO₄ particles crystallized in a monoclinic wolframite-type structure whereas TiO₂ particles were Anatase phase; and both of them were well distributed in the nanofilms. FTIR spectra proved the presence of CdWO₄ on the nanofilms. Photoluminescent results showed that the emitting peak of CdWO₄ films blue shifted slightly relative to that of CdWO₄ crystal. Moreover, the PL intensity of CdWO₄-TiO₂ composite nanofilm was much higher than that of CdWO₄ nanofilm. We ascribed that the introduction of TiO₂ should be responsible for the PL enhancement.     

Anisotropic transport and optical properties of superconducting (La1-xSrx)2CuO4 single crystal thin films

An experimental study on the resistivity, Hall coefficient, upper critical field, and optical reflection and transmission characteristics is described for single-crystalline superconducting (La_1-xSr_x)₂CuO₄ thin films epitaxially grown on SrTiO₃ single crystal substrates by rf magnetron sputtering. These properties exhibit pronounced anisotropy between the c-axis direction and the Cu-O plane. The characteristics are consistently explained from the point of view of the two-diemensional (2D) electronic structure. The most noteworthy implication of the experimental results is that the transport along the c-axis is far from an itinerant picture. This leads to the idea that the superconductivity in the series of cuprate materials is caused by the 2D electronic system arising from the Cu-O planes, and some interactions between them, which is not possibly due to itinerant carriers.     

Growth of β-Ga2O3 nanorods by ammoniating Ga2O3/V thin films on Si substrate

This paper reports that/3-Ga2O3 nanorods have been synthesized by ammoniating Ga2O3 films on a V middle layer deposited on Si（111） substrates. The synthesized nanorods were confirmed as monoclinic Ga2O3 by x-ray diffraction,Fourier transform infrared spectra. Scanning electron microscopy and transmission electron microscopy reveal that the grown β-Ga2O3 nanorods have a smooth and clean surface with diameters ranging from 100 nm to 200 nm and lengths typically up to 2μm. High resolution TEM and selected-area electron diffraction shows that the nanorods are pure monoclinic Ga2O3 single crystal. The photoluminescence spectrum indicates that the Ga2O3 nanorods have a good emission property. The growth mechanism is discussed briefly.     

Synthesis of ZnAl<Subscript>2</Subscript>O<Subscript>4</Subscript>/α-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> complex substrates and growth of GaN films

With the solid phase reaction between pulsed-laser-deposited (PLD) ZnO film and α-Al₂O₃ substrate, ZnAl₂O₄/α-Al₂O₃ complex substrates were synthesized. X-ray diffraction (XRD) spectra show that as the reaction proceeds, ZnAl₂O₄ changes from the initial (111)-oriented single crystal to poly-crystal, and then to inadequate (111) orientation. Corresponding scanning electron microscope (SEM) images indicate that the surface morphology of ZnAl₂O₄ transforms from uniform islands to stick structures, and then to bulgy-line structures. In addition, XRD spectra present that ZnAl₂O₄ prepared at low temperature is unstable at the environment of higher temperature. On the as-obtained ZnAl₂O₄/α-Al₂O₃ substrates, GaN films were grown without any nitride buffer using light-radiation heating low-pressure MOCVD (LRH-LP-MOCVD). XRD spectra indicate that GaN film on this kind of complex substrate changes fromc-axis single crystal to poly-crystal as ZnAl₂O₄ layer is thickened. For the single crystal GaN, its full width at half maximum (FWHM) of X-ray rocking curve is 0.4°. Results indicate that islands on thin ZnAl₂O₄ layer can promote nucleation at initial stage of GaN growth, which leads to the (0001)-oriented GaN film.     

Role of crystal orientation on the magnetic properties of CoFe2O4 thin films grown on Si (1 0 0) and Al2O3 (0 0 0 1) substrates using pulsed laser deposition

We report the influence of crystal orientation on the magnetic properties of CoFe₂O₄ (CFO) thin films grown on single crystal Si (1 0 0) and c-cut sapphire (Al₂O₃) (0 0 0 1) substrates using pulsed laser deposition technique. The thickness was varied from 200 to 50 nm for CFO films grown on Si substrates, while it was fixed at 200 nm for CFO films grown on Al₂O₃ substrates. We observed that the 200 and 100 nm thick CFO-Si films grew in both (1 1 1) and (3 1 1) directions and displayed out-of-plane anisotropy, whereas the 50 nm thick CFO-Si film showed only an (1 1 1) orientation and an in-plane anisotropy. The 200 nm thick CFO film grown on an Al₂O₃ substrate was also found to show a complete (1 1 1) orientation and a strong in-plane anisotropy. These observations pointed to a definite relation between the crystalline orientation and the observed magnetic anisotropy in the CFO thin films.     

KrF pulsed laser deposition of La5Ca9Cu24O41 thin films on various substrates

Recent studies on single crystals of cuprate oxides containing spin chains and ladders have reported large anisotropic magnon-mediated thermal conductivity. A potential use of thin films of such materials could be in the thermal management of electronic devices for the guiding of unwanted heat to a heat sink. In this article, the pulsed laser deposition and characterization of La₅Ca₉Cu₂₄O₄₁ thin films on SrLaAlO₄, SrTiO₃, MgO, and Si substrates are reported for the first time. The films were grown using a pulsed UV laser (KrF, 248 nm) and various substrate temperatures up to 650 °C. The XRD spectra revealed successful target-film stoichiometric transfer and high texturing of the thin films with (0 k 0) preferred orientation.     

薄膜厚度对La1.85Sr0.15CuO4薄膜结构和超导电性的影响

使用直流同轴磁控溅射法,在SrTiO₃(STO)衬底上成功制备出c取向的La_1.85Sr_0.15CuO₄(LSCO)超导薄膜.通过电输运测量系统和X射线衍射仪研究了薄膜厚度对LSCO(x＝0.15)薄膜电学性质和晶体结构的影响.实验证明随着膜厚增加,(006)衍射峰的半高宽(Full Width at Half Maximum,FWHM)逐渐减小,薄膜的取向性增强,与此同时,薄膜的超导转变温 关键词： 1.85Sr_0.15CuO₄薄膜')" href="#">La_1.85Sr_0.15CuO₄薄膜 超导电性 晶体结构     

Deposition and stoichiometry control of Nd-doped gadolinium gallium garnet thin films by combinatorial pulsed laser deposition using two targets of Nd:Gd<Subscript>3</Subscript>Ga<Subscript>5</Subscript>O<Subscript>12</Subscript> and Ga<Subscript>2</Subscript>O<Subscript>3</Subscript>

We have demonstrated pulsed laser deposition of Nd-doped gadolinium gallium garnet on Y₃Al₅O₁₂ by the simultaneous ablation of two separate targets of Nd:Gd₃Ga₅O₁₂ (GGG) and Ga₂O₃. Such an approach is of interest as a method of achieving stoichiometry control over films whilst the growth parameters are kept constant and optimal for high quality crystal growth. We show here how the stoichiometry and resultant lattice parameter of a film can be controlled by changing the relative deposition rates from the two targets. Films have been grown with enough extra Ga to compensate for the deficiency that commonly occurs when depositing only from a GGG target. We have also grown crystalline GGG films with an enriched Ga concentration, and this unconventional approach to film stoichiometry control may have potential applications in the fabrication of films with advanced compositionally graded structures.     

磁控共溅射法制备的Zn2GeO4多晶薄膜结构及其光致发光研究

用射频磁控共溅射方法在不同温度的单晶硅基片上生长薄膜,然后在800℃真空环境下对薄膜进行退火处理,成功获得了结晶状态良好的Zn₂GeO₄多晶薄膜.利用X射线衍射(XRD),X射线光电子能谱(XPS)和原子力显微镜(AFM)对薄膜进行了结构、成分和形貌分析,研究了基片温度对三者的影响. 结果显示,当基片温度升高到400℃以上时,薄膜中的Zn₂GeO₄晶粒在(220)方向上显示出了明显的择优取向. 当基片温度在500—600℃范围内,有利于GeO₂结晶相的形成. XPS显示薄膜中存在着Zn₂GeO₄,GeO₂,GeO,ZnO四种化合态. 同时,随着基片温度的升高,晶粒尺寸增大且薄膜表面趋于平整. 薄膜的光致发光在绿光带存在中心波长为530和550nm两个峰,应该归因于主体材料Zn₂GeO₄中两个不同的Ge²⁺的发光中心. 关键词： 射频磁控溅射 2GeO₄')" href="#">Zn₂GeO₄ 荧光体     

Si基铁电Bi3.15Nd0.85Ti3O12多层薄膜的一致取向生长和性能的研究

采用脉冲激光沉积(PLD)技术，利用LSCO/CeO₂/YSZ多异质缓冲层，在Si(100)基 片上成功地制备了c轴一致取向的Bi_3.15Nd_0.85Ti₃O12(BNT)铁电薄膜.利用X射线衍射(XRD)和扫描电镜(SEM)分析测定了薄膜的相结构 、取向和形貌特征，考察了沉积温度和氧分压对BNT薄膜微结构、取向和形貌的影响，确定 了BNT薄膜的最佳沉积条件.对在优化的条件下制备得到的BNT薄膜的C-V曲线测试得到了典型 的蝴蝶形曲线，表明该薄膜具有较好的电极化反转存储特性.最后讨论了BNT薄膜铁电性能与 薄膜取向的相关性. 关键词： 3.15Nd_0.85Ti₃O₁₂')" href="#">Bi_3.15Nd_0.85Ti₃O₁₂ 铁电薄 膜 多层异质结 脉冲激光沉积     

Microstructural and domain effects in epitaxial CoFe2O4 films on MgO with perpendicular magnetic anisotropy

CoFe₂O₄ (CFO) epitaxial thin films of various thicknesses were grown on MgO substrates using the pulsed electron-beam deposition technique. The films have excellent in-plane coherence with the substrate, exhibit layer-by-layer growth and have well-defined thickness fringes in x-ray diffraction measurements. Atomic force microscopy (AFM) measurements indicate that misfit dislocations form in thicker films and the critical thickness for the dislocation formation is estimated. Perpendicular magnetic anisotropy in CFO due to epitaxial in-plane tensile strain from the substrate was found. A stripe-like domain structure in the demagnetized state is demonstrated using magnetic force microscopy (MFM), in agreement with previous predictions. Coercivity increased in thicker films, which is explained by domain wall pinning due to misfit dislocations at the CFO/MgO interface.     

Deposition of Na2WO4 films by ultrasonic spray pyrolysis: effect of thickness on the crystallographic and sensing properties

Na₂WO₄ films have been grown on Si (1 0 0) and glass substrate using ultrasonic spray pyrolysis. The films are prepared from aqueous solution containing Na₂WO₄·2H₂O at 475 °C temperature and characterized by XRD and SEM techniques and the chemical composition of the films have been verified by EDX and PIXE and its formula Na₂WO₄ is confirmed by XRD. The evolution of the crystallinity was studied as a function of film thickness ranging from 2500 to 4200 nm, which corresponds to a deposition time from 10 to 30 min, respectively. The crystalline quality was found to improve, where the grain size values increased with increasing thickness. Atomic Force Microscopy (AFM) was used to study the morphology evolution with the deposition time, where porous films were found due to the synthesis parameters, and a better sensing response to gases was developed with increasing thickness. Thus, this study demonstrates the possibility of utilizing Na₂WO₄ thick films as a sensor element for the detection of ethanol vapor at room temperature, where thicker films exhibit excellent ethanol vapor sensing properties with a maximum sensitivity at 25 °C in air atmosphere with fast response time.     

LiFePO4 thin films grown by pulsed laser deposition: Effect of the substrate on the film structure and morphology

Well crystallized and homogeneous LiFePO₄/C (LFPO) thin films have been grown by pulsed laser deposition (PLD). The targets were prepared by the sol-gel process at 600 °C. The structure of the polycrystalline powders was analyzed with X-ray powder diffraction (XRD) data. The XRD patterns were indexed having a single phase olivine structure (Pnma). LFPO thin films have been deposited on three different substrates: aluminum (Al), stainless steel (SS) and silicon (Si) by pulsed laser deposition (PLD). The structure of the films was analyzed by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM). It is found that the crystallinity of the thin films depends on the substrate temperature which was set at 500 °C. When annealed treatments were used, secondary phases were found, so, one step depositions at 500 °C were made.Stainless steel is demonstrated to be the best choice to act as substrate for phosphate deposition. LiFePO₄ thin films grown on stainless steel plates exhibited the presence of carbon, inducing a slight conductivity enhancement that makes these films promising candidates as one step produced cathodes in Li-ion microbatteries.     

Preparation, structure and ferromagnetic properties of the nanocrystalline Ti1-xMnxO2 thin films grown by radio frequency magnetron co-sputtering

This paper reported that the Mn-doped TiO2 films were prepared by radio frequency （RF） magnetron cosputtering. X-ray diffraction measurements indicate that the samples are easy to form the futile structure, and the sizes of the crystal grains grow big and big as the Mn concentration increases. X-ray photoemlssion spectroscopy measurements and high resolution transmission electron microscope photographs confirm that the manganese ions have been effectively doped into the TiO2 crystal when the Mn concentration is lower than 21%. The magnetic property measurements show that the Ti1-xMnxO2 （x = 0.21） films are ferromagnetic at room temperature, and the saturation magnetization, coercivity, and saturation field are 16.0 emu/cm^3, 167.5 × 80 A/m and 3740 × 80 A/m at room temperature, respectively. The room-temperature ferromagnetism of the films can be attributed to the new futile Ti1-xMnxO2 structure formed by the substitution of Mn^4＋ for Ti^4＋ into the TiO2 crystal .lattice, and could be explained by O vacancy （Vo）-enhanced ferromagnetism model.