Optimization of large-area YBa_(2)Cu_(3)O_(7-δ)thin films by pulsed laser deposition for planar microwave devices

This paper presents high quality YBa_(2)Cu_(3)O_(7-δ)(YBCO)thin films on LaAlO_(3)substrate for microwave devices prepared by pulsed laser deposition(PLD).The double-sided YBCO films cover a large area and have been optimized for key parameters relevant to microwave device applications,such as surface morphology and surface resistance(R_(s)).This was achieved by improving the target quality and increasing the oxygen pressure during deposition,respectively.To evaluate the suitability of the YBCO films for microwave devices,a pair of microwave filters based on microstrip fabricated on films from this work and a commercial company were compared.The results show that the YBCO films in this work could completely meet the requirements for microwave devices.

Thickness modulation effect of CeO_2 layer for YBCO films grown by pulsed laser deposition

CeO2 film plays an essential role in nucleation and growth of YBa2 Cu3 O（7-x）（YBCO） films. In this work,the dependence of superconducting properties of YBCO on CeO2 films with different thicknesses was investigated,in order to achieve fabrication of high-performance YBCO coated conductors in industrial scale. The crystalline structure and morphology of CeO2 films with thickness ranging from 21 to 563 nm were systematically characterized by means of X-ray diffraction（XRD）, atomic force microscope（AFM） and reflection high-energy electron diffraction（RHEED）. Additional focus was addressed on evolution of the surface quality of CeO2 films with thickness increasing. The results show that at the optimal thickness of 221 nm, CeO2 film exhibits sharp in-plane and out-of-plane texture with full width of half maximum（FWHM） values of 5.9° and 1.8°, respectively, and smooth surface with a mean root-mean-square（RMS） roughness value as low as 0.6 nm. Combing RHEED and transmission electron microscope（TEM） cross-sectional analysis, it is found that nucleation and growth of CeO2 films at early stage remain in island growth mode with rougher surface,while further increasing the thickness beyond the optimal thickness leads to weak surface quality, consequently resulting in degradation of superconductor layers deposited subsequently. Eventually, a critical current density（Jc） as high as 4.6×10-6 A·cm-（-2）（77 K, self-field） is achieved on a YBCO film on a thickness-modulated CeO2/MgO/Y2 O3/Al2 O3/C276 architecture, demonstrating the advantages of CeO2 films as buffer layer in high-throughput manufacture of coated conductors.

气氛氧压对脉冲激光法制备的CeO_2/Si薄膜的结晶取向的影响

用脉冲激光镀膜法 ,在不同的温度和氧压条件下 ,在Si(10 0 )片上制备了一系列的CeO2 膜。X射线衍射分析表明 ,在较低的氧压下生长的CeO2 膜为 (111)取向 ,在较高的氧压下生长的膜则为 (10 0 )取向。研究表明 ,CeO2 膜的取向对氧压显示了独特的依赖性 ,氧压对控制膜的结晶取向具有十分重要的作用。讨论了氧压对CeO2 薄膜结晶取向影响的可能机理。

Density of states characterization of TiO_(2) films deposited by pulsed laser deposition for heterojunction solar cells

The application of titanium dioxide(TiO_(2))in the photovoltaic(PV)field is gaining traction as this material can be deployed in doping-free heterojunction solar cells with the role of electron selective contact.For modeling-based optimization of such contact,knowledge of the titanium oxide defect density of states(DOS)is crucial.In this paper,we report a method to extract the defect density through nondestructive optical measures,including the contribution given by small polaron optical transitions.The presence of both related to oxygen-vacancy defects and polarons is supported by the results of optical characterizations and the evaluation of previous observations resulting in a defect band fixed at 1 eV below the conduction band edge of the oxide.Solar cells employing pulsed laser deposited-TiO_(2)electron selective contacts were fabricated and characterized.The J-V curve of these cells showed,however,an S-shape,then a detailed analysis of the reasons for such behavior was carried out.We use a model involving the series of a standard cell equivalent circuit with a Schottky junction in order to explain these atypical performances.A good matching between the experimental measurements and the adopted theoretical model was obtained.The extracted parameters are listed and analyzed to shed light on the reasons behind the low-performance cells.

在金属基带上用激光脉冲沉积法制备帽子层CeO_2的研究

利用脉冲激光沉积法在带有Y2O3、YSZ隔离层的金属基带上制备了CeO2帽子层。主要讨论了温度、激光脉冲频率对CeO2隔离层的影响，用X射线θ～2θ扫描、Φ扫描对薄膜的取向和织构进行表征。结果表明在温度为610℃、激光频率为10Hz、1Pa氧压下制备的CeO2隔离层能有效地继承衬底的织构，平均平面内中扫描半高宽度为6．9°。扫描电镜可以观察到薄膜表面致密且无裂纹，原子力显微镜观测表面平均粗糙度在10nm以下。

Fabrication and Characterization of PLD-Grown Bismuth Telluride (Bi₂Te₃) and Antimony Telluride (Sb₂Te₃) Thermoelectric Devices

We report on the fabrication and characterization of multi-leg bismuth telluride (Bi2Te3) and antimony telluride (Sb2Te3) thermoelectric devices. The two materials were deposited, on top of SiO2/Si substrates, using Pulsed Laser Deposition (PLD). The SiO2 layer was used to provide insulation between the devices and the Si wafer. Copper was used as an electrical connector and a contact for the junctions. Four devices were built, where the Bi2Te3 and Sb2Te3 were deposited at substrate temperatures of 100°C, 200°C, 300°C and 400°C. The results show that the device has a voltage sensitivity of up to 146 μV/K and temperature sensitivity of 6.8 K/mV.

Embedding epitaxial VO_(2)film with quality metal-insulator transition to SAW devices

Epitaxial VO_(2)films grown by pulsed laser deposition(PLD)method with superior phase transition related switching characteristics are successfully embedded to SAW devices using concept of the“impedance loaded SAW sensor”.A resistance of VO2 sensor abruptly drops from 0.7 MΩto 90Ωwhen it is heated above~65℃and shows a narrow hysteresis loops when switching.Two designs of SAW devices are examined in which RF signal is reflected back from interdigital transducer(IDT)or a surface acoustic waves(SAW)is transferred through a coupler and the RF response is altered 2 and 3 times correspondingly upon the phase transition in VO2.In the proposed devices with external load,a SAW does not propagate via VO2 film and therefore is not attenuated which is beneficiary for wireless applications.Additionally,a SAW phase shift as great as 50°is induced to the SAW transferred through the coupler due to the phase transition in VO2.The proposed approach may boost the development of remotely controlled autonomous sensors,including those based on VO2 metamaterials and hybrid plasmonic structures for near IR/middle IR and sub-THz/THz applications.