ABSTRACT
In the interfacial superconductor Bi2Te3/Fe1+yTe, two dimensional superconductivity occurs in direct vicinity to the surface state of a topological insulator. If this state were to become involved in superconductivity, under certain conditions a topological superconducting state could be formed, which is of high interest due to the possibility of creating Majorana fermionic states. We report directional point-contact spectroscopy data on the novel Bi2Te3/Fe1+yTe interfacial superconductor for a Bi2Te3 thickness of 9 quintuple layers, bonded by van der Waals epitaxy to a Fe1+yTe film at an atomically sharp interface. Our data show highly unconventional superconductivity, which appears as complex as in the cuprate high temperature superconductors. A very large superconducting twin-gap structure is replaced by a pseudogap above ~12 K which persists up to 40 K. While the larger gap shows unconventional order parameter symmetry and is attributed to a thin FeTe layer in proximity to the interface, the smaller gap is associated with superconductivity induced via the proximity effect in the topological insulator Bi2Te3.
ABSTRACT
A highly aligned one-dimensional (1D) nanostructure was realized at the surface of Fe/ZnSe bilayers grown on GaAs(001) substrates through thermal annealing. These 1D nano-grooves were found to align along the [110] direction resulting in bent reflection high energy electron diffraction (RHEED) patterns when the sample was rotated relative to the e-beam. A model based on Ewald construction is presented to explain the unusual RHEED observation. The formation mechanism of this 1D nanostructure is possibly related to the minimization of surface energy, together with an Fe-Se exchange interaction and Fe-induced decomposition of several top ZnSe atomic layers during thermal annealing.
Subject(s)
Crystallization/methods , Iron/chemistry , Nanostructures/chemistry , Nanostructures/ultrastructure , Nanotechnology/methods , Selenium Compounds/chemistry , Zinc Compounds/chemistry , Hot Temperature , Macromolecular Substances/chemistry , Materials Testing , Molecular Conformation , Particle Size , Surface PropertiesABSTRACT
The structural characteristics and optical and electrical properties of molecular-beam-epitaxy (MBE) grown ZnS(0.8)Se(0.2) thin films on indium-tin-oxide (ITO) glass substrates were investigated in this work. The X-ray diffraction (XRD) results indicated that high quality polycrystalline ZnS(0.8)Se(0.2) thin film grown at the optimized temperature had a preferred orientation along the (111) planes. The transmission electron microscopy (TEM) cross-sectional micrograph of the sample showed a well defined columnar structure with lateral crystal dimension in the order of a few hundred angstroms. Ultraviolet (UV) photoresponsivity as high as 0.01 A/W had been demonstrated and for wavelengths longer than 450 nm, the response was down from the peak response by more than 3 orders of magnitude. The thin ZnS(0.8)Se(0.2) photosensor layer, with a wide energy gap and anisotropic electrical property, makes a transmission UV liquid crystal light valve (LCLV) with high resolution feasible.
ABSTRACT
MBE growth of ZnS(x)Se(1 - x) thin films on ITO coated glass substrates were carried out using ZnS and Se sources with the substrate temperature ranging from 270 degrees C to 330 degrees C . The XRD theta/2theta spectra resulted from these films indicated that the as-grown polycrystalline ZnS(x)Se(1 - x) thin films had a preferred orientation along the (111) planes. The evaluated crystal sizes as deduced from the FWHM of the XRD layer peaks showed strong growth temperature dependence, with the optimized temperature being about 290 degrees C. Both AFM and TEM measurements of these thin films also indicated a similar growth temperature dependence. High quality ZnS(x)Se(1 - x) thin film grown at the optimized temperature had the smoothest surface with lowest RMS value of 1.2 nm and TEM cross-sectional micrograph showing a well defined columnar structure.