Recent Submissions

  • Lattice deformation in epitaxial Fe3O4 films on MgO substrate studied by polarized Raman spectroscopy∗

    Yang, Yang; Zhang, Qiang; Mi, Wenbo; Zhang, Xixiang (Chinese Physics B, IOP Publishing, 2020-05-25) [Article]
    The lattice structures of epitaxial Fe3O4 films deposited on MgO were studied systematically using polarized Raman spectroscopy as a function of film thickness, where interesting phenomena were observed. Firstly, the spectral conflict to the Raman selection rules (RSRs) was observed under cross sectional configuration, which can be attributed to the tetragonal deformation in the growth direction due to the lattice mismatch between Fe3O4 and MgO. Secondly, the blue-shift and broadening of Raman peaks evidenced the decrease of the tensile strain in Fe3O4 film with decreased thickness. Thirdly, distinct from the other Raman modes, the lowest T 2g mode exhibited asymmetric lineshape, which can be interpreted using the spatial correlation model. The increased correlation length introduced in the model can well explain the enhanced peak asymmetry feature with decreasing thickness. These results provide useful information for understanding the lattice structure of epitaxial Fe3O4 film.
  • Effect of surface roughness on the anomalous Hall effect in Fe thin films

    Zhang, Qiang; Zheng, Dongxing; Wen, Yan; Zhao, Yuelei; Mi, Wenbo; Manchon, Aurelien; Boulle, Olivier; Zhang, Xixiang (Physical Review B, American Physical, 2020-04-01) [Article]
    Surface roughness plays an important role on the magnetotransport properties of thin films, especially in ultrathin films. In this work, we prepared Fe thin films with various surface roughness by using different seed layers and studied the electrical transport and anomalous Hall effect. By tuning surface roughness scattering, the longitudinal resistivity (ρxx) measured at 5 K increases by one order of magnitude and the corresponding anomalous Hall resistivity (ρAHE) increases by three times with increasing roughness. The intrinsic, skew-scattering, and side-jump contributions to ρAHE were separated from our data. The anomalous Hall angle depends on the surface roughness, which may be of importance to the material engineering for achieving large spin Hall angle.
  • Ultra miniaturized InterDigitated electrodes platform for sensing applications

    Wang, Z.; Syed, A.; Bhattacharya, S.; Chen, X.; Buttner, Ulrich; Iordache, Gheorghe; Salama, Khaled N.; Ganetsos, Th; Valamontes, E.; Georgas, A.; Raptis, Ioannis; Oikonomou, P.; Botsialas, A.; Sanopoulou, M. (Microelectronic Engineering, Elsevier BV, 2020-02-08) [Article]
    InterDigitated Electrodes (IDEs) is a generic platform for a wide range of diverse applications with their implementation in sensing modules being a major one. We propose the use of IDCs with deep sub-micron critical dimension; equally spaced electrodes of 200 nm width for enhanced sensing performance and also the method of fabrication thereof. The transducer configuration was studied theoretically with a finite element method simulation by using COMSOL Multiphysics. The miniaturization of the IDEs up to 200 nm critical dimension with an adequate sensing area for the deposition of the polymeric materials is considered beneficial in terms of sensitivity gain. The IDCs were designed to deliver capacitance values of few pF in order to be compatible with already developed miniaturized low-power readout electronics. The transducers fabrication is performed with conventional microelectronic/micromachining processing and then coated with several semi-selective polymeric films. Besides the fabrication of multiple sensor arrays (chips) on the same silicon wafer, the miniaturization offers the integration with the readout electronics on the same chip. The evaluation of the sensing performance of the semi-selective polymer coated sensors is performed upon exposure to vapours of pure and binary mixtures of VOCs and humidity in various concentrations. The sensors demonstrate high sensitivity to the examined analytes as a result of the miniaturization, while their semi-selectivity is a key for applications in complex vapour environment discrimination.
  • Direct imaging of an inhomogeneous electric current distribution using the trajectory of magnetic half-skyrmions

    Zhang, Senfu; Zhang, Xichao; Zhang, Junwei; Ganguly, Arnab; Xia, Jing; Wen, Yan; Zhang, Qiang; Yu, Guoqiang; Hou, Zhipeng; Wang, Wenhong; Peng, Yong; Xiao, Gang; Manchon, Aurelien; Kosel, Jürgen; Zhou, Yan; Zhang, Xixiang (Science Advances, American Association for the Advancement of Science (AAAS), 2020-02-08) [Article]
    The direct imaging of current density vector distributions in thin films has remained a daring challenge. Here, we report that an inhomogeneous current distribution can be mapped directly by the trajectories of magnetic half-skyrmions driven by an electrical current in Pt/Co/Ta trilayer, using polar magneto-optical Kerr microscopy. The half-skyrmion carries a topological charge of 0.5 due to the presence of Dzyaloshinskii-Moriya interaction, which leads to the half-skyrmion Hall effect. The Hall angle of half-skyrmions is independent of current density and can be reduced to as small as 4° by tuning the thickness of the Co layer. The Hall angle is so small that the elongation path of half-skyrmion approximately delineates the invisible current flow as demonstrated in both a continuous film and a curved track. Our work provides a practical technique to directly map inhomogeneous current distribution even in complex geometries for both fundamental research and industrial applications.
  • Understanding the Origin of Selective Reduction of CO2 to CO on Single-Atom Nickel Catalyst.

    He, Shi; Ji, Dong; Zhang, Junwei; Novello, Peter; Li, Xueqian; Zhang, Qiang; Zhang, Xixiang; Liu, Jie (The journal of physical chemistry. B, American Chemical Society (ACS), 2019-12-27) [Article]
    Electrochemical reduction of CO2 to CO offers a promising strategy for regulating the global carbon cycle and providing feedstock for the chemical industry. Understanding the origin that determines the faradaic efficiency (FE) of reduction of CO2 to CO is critical for developing a highly efficient electrocatalyst. Here, by constructing a single-atom Ni catalyst on nitrogen-doped winged carbon nanofiber (NiSA-NWC), we find that the single-atom Ni catalyst possesses the maximum CO FE of over 95% at -1.6 V vs Ag/AgCl, which is about 30% higher than the standard Ni nanoparticles on the same support. The Tafel analysis reveals that the single-atom Ni catalyst has a preferred reduction of CO2 to CO and a slower rate for the hydrogen evolution reaction. We propose that the domination of singular Ni1+ electronic states and limited hydrogen atom adsorption sites on the single-atom Ni catalyst lead to the observed high FE for CO2 reduction to CO.
  • Hybrid organic–metal oxide multilayer channel transistors with high operational stability

    Lin, Yen-Hung; Li, Wen; Faber, Hendrik; Seitkhan, Akmaral; Hastas, Nikolaos A.; Khim, Dongyoon; Zhang, Qiang; Zhang, Xixiang; Pliatsikas, Nikolaos; Tsetseris, Leonidas; Patsalas, Panos A.; Bradley, Donal; Huang, Wei; Anthopoulos, Thomas D. (Nature Electronics, Springer Science and Business Media LLC, 2019-12-16) [Article]
    Metal oxide thin-film transistors are increasingly used in the driving backplanes of organic light-emitting diode displays. Commercial devices currently rely on metal oxides processed via physical vapour deposition methods, but the use of solution-based processes could provide a simpler, higher-throughput approach that would be more cost effective. However, creating oxide transistors with high carrier mobility and bias-stable operation using such processes has proved challenging. Here we show that transistors with high electron mobility (50 cm2 V−1 s−1) and operational stability can be fabricated from solution-processed multilayer channels composed of ultrathin layers of indium oxide, zinc oxide nanoparticles, ozone-treated polystyrene and compact zinc oxide. Insertion of the ozone-treated polystyrene interlayer passivates electron traps in the channel and reduces bias-induced instability during continuous transistor operation over a period of 24 h and under a high electric-field flux density (2.1 × 10−6 C cm−2). Furthermore, incorporation of the pre-synthesized aluminium-doped zinc oxide nanoparticles enables controlled n-type doping of the hybrid channels, providing additional control over the operating characteristics of the transistors.
  • Current-Induced Helicity Reversal of a Single Skyrmionic Bubble Chain in a Nanostructured Frustrated Magnet.

    Hou, Zhipeng; Zhang, Qiang; Zhang, Xichao; Xu, Guizhou; Xia, Jing; Ding, Bei; Li, Hang; Zhang, Senfu; Batra, Nitin M; Da Costa, Pedro M. F. J.; Liu, Enke; Wu, Guangheng; Ezawa, Motohiko; Liu, Xiaoxi; Zhou, Yan; Zhang, Xixiang; Wang, Wenhong (Advanced materials, Wiley, 2019-11-21) [Article]
    Helicity indicates the in-plane magnetic-moment swirling direction of a skyrmionic configuration. The ability to reverse the helicity of a skyrmionic bubble via purely electrical means has been predicted in frustrated magnetic systems; however, it has been challenging to observe this experimentally. The current-driven helicity reversal of the skyrmionic bubble in a nanostructured frustrated Fe3 Sn2 magnet is experimentally demonstrated. The critical current density required to trigger the helicity reversal is 109 -1010 A m-2 , with a corresponding pulse-width varying from 1 µs to 100 ns. Computational simulations reveal that both the pinning effect and dipole-dipole interaction play a crucial role in the helicity reversal process.
  • Competition between Electronic and Magnonic Spin Currents in Metallic Antiferromagnets

    Wen, Yan; Zhuo, Fengjun; Zhao, Yuelei; Li, Peng; Zhang, Qiang; Manchon, Aurelien; Zhang, Xixiang (Physical Review Applied, American Physical Society (APS), 2019-11-13) [Article]
    We investigate the spin-orbit torque in a Ta/Ir−Mn/Cu/Ni−Fe multilayer heterostructure and relate it to spin current transmission through the Ir−Mn layer. We identify several spin current transport regimes as a function of the temperature and the thickness of the Ir−Mn layer. To interpret this experiment, we develope a drift-diffusion model accounting for both electron and magnon transport in the heterostructures. This model allows us to discriminate between the contributions of electrons and magnons to the total spin current in Ir−Mn. We find that the electron-magnon spin convertance is one order of magnitude larger than the interfacial electronic spin conductance, while the magnon diffusion length is about ten times longer than the electronic spin relaxation length. This study demonstrates that magnonic spin transport dominates over electronic spin transport even in disorder metallic antiferromagnets.
  • Weak antilocalization effect and high-pressure transport properties of ScPdBi single crystal

    Zhang, Junli; Hou, Zhipeng; Zhang, Chenhui; Chen, Jie; Li, Peng; Wen, Yan; Zhang, Qiang; Wang, Wenhong; Zhang, Xixiang (Applied Physics Letters, AIP Publishing, 2019-10-25) [Article]
    Half-Heusler compounds have attracted considerable attention due to their fantastic physical properties that include topological effects,Weyl fermions, unusual magnetism, and superconductivity. Herein, the transport properties of half-Heusler ScPdBi single crystals are studiedacross a wide temperature range and different magnetic fields. From the field-dependent magnetoresistance, we observe a clear weak antiloc-alization (WAL) effect below 200 K in the low magnetic-field region. The angle-dependent magnetoconductance and the ultralarge prefactoraextracted from the Hikami-Larkin-Nagaoka equation reveal that the WAL effect is a 3D bulk effect caused by strong spin–orbit coupling.We further studied the magnetotransport properties of the single crystal upon application of hydrostatic pressure and found that the energygap of ScPdBi increases gradually as the hydrostatic pressure increases. Density functional theory calculations confirm that applying hydro-static pressure decreases the lattice parameters and, consequently, enlarges the bandgap
  • Negative differential resistance and magnetotransport in Fe3O4/SiO2/Si heterostructures

    Liu, Xiang; Mi, Wenbo; Zhang, Qiang; Zhang, Xixiang (Applied Physics Letters, AIP Publishing, 2019-06-17) [Article]
    The electronic transport and magnetotransport properties of Fe3O4/SiO2/Si heterostructures were investigated with a current source. Negative differential resistance is observed in Fe3O4/SiO2/p-Si heterostructures. The measurement circuit with four electrodes that I+ (I−) and V+ (V−) came into contact with the Fe3O4 (Si) layer introduces an in-plane transport into the heterostructures. By decreasing the temperature, the in-plane conductive channel switches from Fe3O4 to p-Si. However, the in-plane current is still carried by Fe3O4 in Fe3O4/SiO2/n-Si heterostructures. The formation of an accumulation layer in p-Si facilitates conductive channel switching (CCS), while the depletion layer in n-Si hampers the CCS. At 150 K, a magnetic-field-independent magnetoresistance (MR) in Fe3O4/SiO2/p-Si heterostructures manifests the conductive channel in the space charge region of p-Si. A positive MR generated from the increased electronic scattering in a trapezoidal space charge region reshaped by the magnetic field has been detected.
  • Giant nonvolatile manipulation of magnetoresistance in magnetic tunnel junctions by electric fields via magnetoelectric coupling

    Chen, Aitian; Wen, Yan; Fang, Bin; Zhao, Yuelei; Zhang, Qiang; Chang, Yuansi; Li, Peisen; Wu, Hao; Huang, Haoliang; Lu, Yalin; Zeng, Zhongming; Cai, Jianwang; Han, Xiufeng; Wu, Tao; Zhang, Xixiang; Zhao, Yonggang (Nature Communications, Springer Nature, 2019-01-16) [Article]
    Electrically switchable magnetization is considered a milestone in the development of ultralow power spintronic devices, and it has been a long sought-after goal for electric-field control of magnetoresistance in magnetic tunnel junctions with ultralow power consumption. Here, through integrating spintronics and multiferroics, we investigate MgO-based magnetic tunnel junctions on ferroelectric substrate with a high tunnel magnetoresistance ratio of 235%. A giant, reversible and nonvolatile electric-field manipulation of magnetoresistance to about 55% is realized at room temperature without the assistance of a magnetic field. Through strain-mediated magnetoelectric coupling, the electric field modifies the magnetic anisotropy of the free layer leading to its magnetization rotation so that the relative magnetization configuration of the magnetic tunnel junction can be efficiently modulated. Our findings offer significant fundamental insight into information storage using electric writing and magnetic reading and represent a crucial step towards low-power spintronic devices.
  • Manipulating the Topology of Nanoscale Skyrmion Bubbles by Spatially Geometric Confinement

    Hou, Zhipeng; Zhang, Qiang; Xu, Guizhou; Zhang, Senfu; GONG, CHEN; Ding, Bei; Li, Hang; Xu, Feng; Yao, Yuan; Liu, Enke; Wu, Guangheng; Zhang, Xixiang; Wang, Wenhong (ACS Nano, American Chemical Society (ACS), 2019-01-03) [Article]
  • A Proof-of-Concept for Gas-Entrapping Membranes (GEMs) Derived from Water-loving 3 SiO2/Si/SiO2 Wafers for Green Desalination

    Das, Ratul; Arunachalam, Sankara; Ahmad, Zain; Manalastas, Edelberto; Syed, Ahad; Buttner, Ulrich; Mishra, Himanshu (Journal of Visualized Experiment, 2019) [Article]
    Desalination through direct contact membrane distillation (DCMD) process exploits water repellent membranes to robustly separate counterflowing streams of hot and salty seawater from cold and pure water, thus, allowing only the pure water vapor to transport across. To achieve this feat, commercial DCMD membranes are derived from or coated with perfluorocarbons such as polytetrafluoroethylene (PTFE) and polyvinylidene difluoride (PVDF). However, perfluorocarbons are limiting due to their high cost, non-biodegradability, and vulnerability to harsh operational conditions. Here, we unveil a new class of membranes - gas entrapping membranes (GEMs) - that can robustly entrap air on immersion in water due to their surface architecture rather than surface chemistry. This work demonstrates the proof-of concept for GEMs using intrinsically wetting silicon wafers with a thermally grown oxide layer (SiO2) as the model system; the contact angle of water on SiO2 is θo ≈ 40° . GEMs comprise arrays of pores whose diameters increase abruptly, i.e., with a 90° 64 turn, at the inlets and outlets(also known as “reentrant” edges). Protocols for the microfabrication of silica-GEMs that entails designing, photolithography, chrome sputtering, isotropic and anisotropic etching, among other steps are presented below. The efficacy of GEMs is underscored by the fact that silica membranes with simple cylindrical pores spontaneously imbibed water (in < 1 s), whereas the air entrapped in silica-GEMs underwater was intact even after six weeks (>106 69 s). While the choice of SiO2/Si wafers for GEMs was limited to demonstrating the proof-of-concept, we hope that the design concepts presented here might advance the rational design of scalable GEMs using inexpensive wetting materials for desalination and beyond.
  • Rendering SiO2/Si surfaces omniphobic by carving gas-entrapping microtextures comprising 2 reentrant and doubly reentrant cavities or pillars

    Arunachalam, Sankara; Domingues, Eddy; Das, Ratul; Nauruzbayeva, Jamilya; Buttner, Ulrich; Syed, Ahad; Mishra, Himanshu (Journal of Visualized Experiments, 2019) [Article]
    We present microfabrication protocols for rendering intrinsically wetting materials repellent to liquids (omniphobic) by creating gas-entrapping microtextures (GEMs) on them comprising cavities and pillars with reentrant and doubly reentrant features. Specifically, we use SiO2/Si as the model system and share protocols for two-dimensional (2D) designing, photolithography, isotropic/anisotropic etching techniques, thermal oxide growth, piranha cleaning, and storage towards achieving those microtextures. Even though the conventional wisdom indicates that roughening intrinsically wetting surfaces (θo < 90°) renders them even more wetting (θr < θo < 90°) GEMs demonstrate liquid repellence despite the intrinsic wettability of the substrate. For instance, despite the intrinsic wettability of silica, θo ≈ 40°, for the water/air system and θo ≈ 20° for hexadecane/air system, GEMs comprising cavities entrap air robustly on immersion in those liquids, and the apparent contact angles for the droplets areθr ≈ 90°. The reentrant and doubly reentrant features in the GEMs stabilize the intruding liquid meniscus thereby trapping the liquid-solid-vapor system in metastable air-filled states (Cassie states) and delaying wetting transitions to the thermodynamically-stable fully-filled state (Wenzel state) by, for instance, hours to months. Similarly, SiO2/Si surfaces with arrays of reentrant and doubly reentrant micropillars demonstrate extremely high contact angles (θr ≈ 150°–160°) and low contact angle hysteresis for the probe liquids, thus characterized as superomniphobic. However, on immersion in the same liquids, those surfaces dramatically lose their superomniphobicity and get fully-filled within <1 s. To address this challenge, we present protocols for hybrid designs that comprise arrays of doubly reentrant pillars surrounded by walls with doubly reentrant profiles. Indeed, hybrid microtextures entrap air on immersion in the probe liquids. To summarize, the protocols described here should enable the investigation of GEMs in the context of achieving omniphobicity without chemical coatings, such as perfluorocarbons, which might unlock the scope of inexpensive wetting materials for applications as omniphobic materials. Silica microtextures could also serve as templates for soft materials.
  • Vertically Aligned Graphene-based Thermal Interface Material with High Thermal Conductivity

    Wang, Nan; Chen, Shujing; Nkansah, Amos; Wang, Qianlong; Wang, Xitao; Chen, Miaoxiang; Ye, Lilei; Liu, Johan (2018 24rd International Workshop on Thermal Investigations of ICs and Systems (THERMINIC), Institute of Electrical and Electronics Engineers (IEEE), 2018-12-31) [Conference Paper]
    High density packaging in combination with increased transistor integration inevitably leads to challenging power densities in terms of thermal management. Here, a novel highly thermal conductive and lightweight graphene based thermal interface materials (GT) was developed for thermal management in power devices. Composed by vertically graphene structures, GTs provide a continuous high thermal conductivity phase along the path of thermal transport, which lead to outstanding thermal properties. The highest through-plane thermal conductivity GTs reaches to 1000 W/mK, which is orders of magnitude higher than conventional TIMs, and even outperforms the pure indium by over ten times. In addition, a thin layer of indium metal that coated on the surface of GTs can easily form alloys with many other metals at a relatively low reflow temperature. Therefore, GTs, as an excellent TIM, can provide complete physical contact between two surfaces with minimized the contact resistance. The measured total thermal resistance and effective thermal conductivity by using 300 m thick GTs as TIM between two copper blocks reaches to ~ 3.7 Kmm2 /W and ~ 90 W/mK, respectively. Such values are significantly higher than the randomly dispersed composites presented above, and show even better thermal performance than pure indium bonding. In addition, GTs has more advantages than pure indium bonding, including low weight (density < 2 g/cm3), low complexity during assembly and maintainability. The resulting GTs thus opens new opportunities for addressing large heat dissipation issues in form-factor driven electronics and other high power driven systems.
  • Single crystal hybrid perovskite field-effect transistors

    Yu, Weili; Li, Feng; Yu, Liyang; Niazi, Muhammad Rizwan; Zou, Yuting; Corzo Diaz, Daniel Alejandro; Basu, Aniruddha; Ma, Chun; Dey, Sukumar; Tietze, Max Lutz; Buttner, Ulrich; Wang, Xianbin; Wang, Zhihong; Hedhili, Mohamed N.; Guo, Chunlei; Wu, Tao; Amassian, Aram (Nature Communications, Springer Nature, 2018-12-17) [Article]
    The fields of photovoltaics, photodetection and light emission have seen tremendous activity in recent years with the advent of hybrid organic-inorganic perovskites. Yet, there have been far fewer reports of perovskite-based field-effect transistors. The lateral and interfacial transport requirements of transistors make them particularly vulnerable to surface contamination and defects rife in polycrystalline films and bulk single crystals. Here, we demonstrate a spatially-confined inverse temperature crystallization strategy which synthesizes micrometre-thin single crystals of methylammonium lead halide perovskites MAPbX3 (X = Cl, Br, I) with sub-nanometer surface roughness and very low surface contamination. These benefit the integration of MAPbX3 crystals into ambipolar transistors and yield record, room-temperature field-effect mobility up to 4.7 and 1.5 cm2 V−1 s−1 in p and n channel devices respectively, with 104 to 105 on-off ratio and low turn-on voltages. This work paves the way for integrating hybrid perovskite crystals into printed, flexible and transparent electronics.
  • PicoTesla magnetic tunneling junction sensors integrated with double staged magnetic flux concentrators

    He, Guanyang; Zhang, Yiou; Qian, Lijuan; Xiao, Gang; Zhang, Qiang; Santamarina, Carlos; Patzek, Tadeusz; Zhang, Xixiang (Applied Physics Letters, AIP Publishing, 2018-12-10) [Article]
    Ultra-sensitive solid-state magnetic sensors are in strong demand in many applications where currently available sensors are inadequate. We have used high performance magnetic tunneling junction (MTJ) sensors and pushed the magnetic sensing limit to a high level. We have incorporated double-staged magnetic flux concentrators, one on the MTJ chip level and the other on a more macroscopic level, to amplify the external field of interest. With this approach and undergoing a process of optimization on the flux concentrators, we have increased the sensitivity of the MTJ sensor by a large factor of 517 to 775.4%/Oe in terms of magnetoresistance response. The coercivity of the sensor is only 0.12 Oe. We have achieved a detectable field limit of 30 pT/Hz⎯⎯⎯⎯⎯√ at 10 kHz. We have presented the noise spectrum and the sensitivity spectrum up to a maximum frequency of 100 kHz.
  • A DNA-mimic contact-active functional group for antifouling ultrafiltration membranes

    Wang, Xinbo; Cheng, Hong; Hong, Pei-Ying; Zhang, Xixiang; Lai, Zhiping (Chemosphere, Elsevier BV, 2018-10-27) [Article]
    Despite advanced materials and techniques to reduce the fouling issue of membranes, 10–30% of the cost of ultrafiltration (UF) processes have been spent on membrane cleaning. Particularly in water treatment, the traditional heavy metal-based method is challenged due to its environmental pollution risk and increasing public health awareness. Here, we report the synthesis of a metal-free contact-active antifouling and antimicrobial membrane by covalently functionalizing a commercial polyacrylonitril (PAN) UF membrane with 2,4-diamino-1,3,5-triazine (DAT) via a one-step catalyst-free hydrothermal [4 + 2] cyclization of dicyandiamide reaction. The proposed mechanism of the antimicrobial activity of the DAT-functionalized membrane is through strong attraction between the DAT groups and the microbial membrane protein via strong hydrogen bonding, leading to microbial membrane disruption and thus microbe death. A high water flux and good reusability of the membrane against protein in a UF experiment were achieved. The low cost, easy availability of the compounds, as well as the facile reaction offer a high potential of the membrane for real applications in ultrafiltration.
  • Reduction and Increase in Thermal Conductivity of Si Irradiated with Ga+ via Focused Ion Beam

    Alaie, Seyedhamidreza; Ghasemi Baboly, Mohammadhosein; Jiang, Ying Bing; Rempe, Susan B.; Anjum, Dalaver H.; Chaieb, Saharoui; Donovan, Brian Francis; Giri, Ashutosh; Szwejkowski, Chester J; Gaskins, John Thomas; Elahi, Mirza; Goettler, Drew; Braun, Jeffrey L.; Hopkins, Patrick E.; Leseman, Zayd Chad (ACS Applied Materials & Interfaces, American Chemical Society (ACS), 2018-10-03) [Article]
    Focused Ion Beam (FIB) technology has become a valuable tool for the microelectronics industry and for the fabrication and preparation of samples at the micro/nanoscale. Its effects on the thermal transport properties of Si, however are not well understood, nor do experimental data exist. This paper presents a carefully designed set of experiments for the determination of the thermal conductivity of Si samples irradiated by Ga+ FIB. Generally, the thermal conductivity decreases with increasing ion dose. For doses of >1016 (Ga+/cm2), a reversal of the trend was observed due to recrystallization of Si. This report provides insight on the thermal transport considerations relevant to engineering of Si nanostructures and interfaces fabricated or prepared by FIB.
  • Observation of superconductivity in structure-selected Ti2O3 thin films

    Li, Yangyang; Weng, Yakui; Zhang, Junjie; Ding, Junfeng; Zhu, Yihan; Wang, Qingxiao; Yang, Yang; Cheng, Yingchun; Zhang, Qiang; Li, Peng; Lin, Jiadan; Chen, Wei; Han, Yu; Zhang, Xixiang; Chen, Lang; Chen, Xi; Chen, Jingsheng; Dong, Shuai; Chen, Xianhui; Wu, Tao (NPG Asia Materials, Springer Nature, 2018-06-06) [Article]
    The search for new superconductors capable of carrying loss-free current has been a research theme in condensed matter physics for the past decade. Among superconducting compounds, titanates have not been pursued as much as Cu (3d) (cuprate) and Fe (3d) (pnictide) compounds. Particularly, Ti-based compounds or electron systems with a special 3d filling are thought to be promising candidates as high-T superconductors, but there has been no report on such pure Ti-based superconducting titanates. With the advent of thin-film growth technology, stabilizing new structural phases in single-crystalline thin films is a promising strategy to realize physical properties that are absent in the bulk counterparts. Herein, we report the discovery of unexpected superconductivity in orthorhombic-structured thin films of TiO, a 3d electron system, which is in strong contrast to the conventional semiconducting corundum-structured TiO. This is the first report of superconductivity in a titanate with a pure 3d electron configuration. Superconductivity at 8 K was observed in the orthorhombic TiO films. Leveraging the strong structure-property correlation in transition-metal oxides, our discovery introduces a previously unrecognized route for inducing emergent superconductivity in a newly stabilized polymorph phase in epitaxial thin films.

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