Showing papers on "Single crystal published in 2010"

Epitaxial graphene on Cu(111).

Abstract: The growth of graphene on single crystal Cu(111) has been achieved by thermal decomposition of ethylene in an ultrahigh vacuum chamber for the first time. The structural and electronic properties of graphene on Cu(111) have been investigated by scanning tunneling microscopy and spectroscopy. The nucleation of monolayer islands and two predominant domain orientations have been observed, which lead to the formation of numerous domain boundaries with increasing coverage. These results reveal that reducing the density of domain boundaries is one challenge of growing high-quality graphene on copper.

Rigid Pillars and Double Walls in a Porous Metal-Organic Framework: Single-Crystal to Single-Crystal, Controlled Uptake and Release of Iodine and Electrical Conductivity

Abstract: A highly stable pillared and double-walled zinc(II) metal-organic framework with regular nanochannels displays single-crystal to single-crystal transformation upon desolvation and a large quantity of iodine uptake, controlled release, and electrical conductivity elevation due to synergy between the iodine guests and the host framework.

Comparison of Graphene Growth on Single-Crystalline and Polycrystalline Ni by Chemical Vapor Deposition

Abstract: We report a comparative study and Raman characterization of the formation of graphene on single crystal Ni (111) and polycrystalline Ni substrates using chemical vapor deposition (CVD). Preferential formation of monolayer/bilayer graphene on the single crystal surface is attributed to its atomically smooth surface and the absence of grain boundaries. In contrast, CVD graphene formed on polycrystalline Ni leads to a higher percentage of multilayer graphene (≥3 layers), which is attributed to the presence of grain boundaries in Ni that can serve as nucleation sites for multilayer growth. Micro-Raman surface mapping reveals that the area percentages of monolayer/bilayer graphene are 91.4% for the Ni (111) substrate and 72.8% for the polycrystalline Ni substrate under comparable CVD conditions. The use of single crystal substrates for graphene growth may open ways for uniform high-quality graphene over large areas.

Crystal Structure and Electrochemical Properties of A2MPO4F Fluorophosphates (A = Na, Li; M = Fe, Mn, Co, Ni)†

Abstract: We report new solid state and hydrothermal synthetic routes to (Li,Na)2FePO4F that incorporate carbon-containing additives and result in good electrochemical properties of this Li (or Na) ion electrode material. Single crystal X-ray diffraction analysis of Na2FePO4F prepared by flux growth confirms the unusual structural features of this compound that include pairs of face-sharing metal octahedra and [6 + 1] coordination of the sodium ions. Facile Na−Li ion-exchange occurs upon reflux with lithium salts, upon electrochemical cycling in a cell (vs. Li), and also in a cell simply equilibrated at OCV. The material does not exhibit typical two-phase behavior on electrochemical cycling. A combination of a redox process which occurs with little structural strain, and ion scrambling give rise to a solid solution-like sloping voltage profile on charge−discharge, although localization of the Fe2+/3+ in the mixed valence single phase intermediate, Na1.5FePO4F drives a very small structural distortion. Temperature-d...

Trap density of states in small-molecule organic semiconductors: A quantitative comparison of thin-film transistors with single crystals

Abstract: We show that it is possible to reach one of the ultimate goals of organic electronics: producing organic field-effect transistors with trap densities as low as in the bulk of single crystals. We studied the spectral density of localized states in the band gap [trap density of states (trap DOS)] of small-molecule organic semiconductors as derived from electrical characteristics of organic field-effect transistors or from space-charge-limited current measurements. This was done by comparing data from a large number of samples including thin-film transistors (TFT's), single crystal field-effect transistors (SC-FET's) and bulk samples. The compilation of all data strongly suggests that structural defects associated with grain boundaries are the main cause of ``fast'' hole traps in TFT's made with vacuum-evaporated pentacene. For high-performance transistors made with small-molecule semiconductors such as rubrene it is essential to reduce the dipolar disorder caused by water adsorbed on the gate dielectric surface. In samples with very low trap densities, we sometimes observe a steep increase in the trap DOS very close $(l0.15\text{ }\text{eV})$ to the mobility edge with a characteristic slope of 10--20 meV. It is discussed to what degree band broadening due to the thermal fluctuation of the intermolecular transfer integral is reflected in this steep increase in the trap DOS. Moreover, we show that the trap DOS in TFT's with small-molecule semiconductors is very similar to the trap DOS in hydrogenated amorphous silicon even though polycrystalline films of small-molecules with van der Waals-type interaction on the one hand are compared with covalently bound amorphous silicon on the other hand.

Growth and structure of crystalline silica sheet on Ru(0001)

Abstract: Thin SiO₂ films were grown on a Ru(0001) single crystal and studied by photoelectron spectroscopy, infrared spectroscopy and scanning probe microscopy. The experimental results in combination with density functional theory calculations provide compelling evidence for the formation of crystalline, double-layer sheet silica weakly bound to a metal substrate.

How Grain Growth Stops: A Mechanism for Grain-Growth Stagnation in Pure Materials

Abstract: The thermodynamic equilibrium state of crystalline materials is a single crystal; however, polycrystalline grain growth almost always stops before this state is reached. Although typically attributed to solute drag, grain-growth stagnation occurs, even in high-purity materials. Recent studies indicate that grain boundaries undergo thermal roughening associated with an abrupt mobility change, so that at typical annealing temperatures, polycrystals will contain both smooth (slow) and rough (fast) boundaries. Mesoscale grain-growth models, validated by large-scale polycrystalline molecular dynamics simulations, show that even small fractions of smooth, slow boundaries can stop grain growth. We conclude that grain-boundary roughening provides an alternate stagnation mechanism that applies even to high-purity materials.

Growth Strategy and Physical Properties of the High Mobility P-Type CuI Crystal

Abstract: Acquiring stable binary wide band-gap semiconductor (WBS) materials with high p-type mobility is essential for the development of WBS optoelectronic devices. CuI is a p-type WBS material with a large band gap (3.1 eV) and high exciton binding energy (62 meV). However, the semiconductor characteristics of the CuI single crystal are unknown due to the lack of a large sized and high quality crystal. Our approach focuses on the design of the mineralizer for the hydrothermal method to effectively control the growth habit and the impurity concentration in the crystal. A large size (15 mm × 10 mm × 1 mm) and high quality CuI single crystal is obtained by using a new mineralizer (NH4I + KI). The crystal shows high p-type mobility (43.9 cm2·V−1·S1−). The strong and sharp band-edge emission at 410 nm indicates that the interband excitonic transition dominates the optical response in the spectrum. Such a binary crystalline material may open the way to new applications in optoelectronic devices.

Very strong intrinsic flux pinning and vortex avalanches in (Ba,K)Fe2As2 superconducting single crystals

Abstract: We report that the (Ba,K)Fe2As2 crystal with Tc =3 2 K shows a pinning potential, U0, as high as 104 K, with U0 showing very little field dependence. The (Ba,K)Fe2As2 single crystals become isotropic at low temperatures and high magnetic fields, resulting in a very rigid vortex lattice, even in fields very close to Hc2. The isotropic rigid vortices observed in the two-dimensional (2D) (Ba,K)Fe2As2 distinguish this compound from 2D high-Tc cuprate superconductors with 2D vortices. The vortex avalanches were also observed at low temperatures in the (Ba,K)Fe2As2 crystal. It is proposed that it is the K substitution that induces both almost isotropic superconductivity and the very strong intrinsic pinning in the (Ba,K)Fe2As2 crystal.

Lattice, elastic, polarization, and electrostrictive properties of BaTiO3 from first-principles

Abstract: Predicting the domain structures and properties in both bulk single crystal and thin film ferroelectrics using the phase-field approach requires the knowledge of fundamental mechanical, electrical, and electromechanical coupling properties of a single-domain state. In this work, the elastic properties and structural parameters of cubic single crystals as well as tetragonal, orthorhombic, and rhombohedral BaTiO3 single domain states are obtained using first-principles calculations under the local density approximation. The calculated lattice constants, bulk modulus, and elastic constants are in good agreement with experiments for both the cubic paraelectric phase and the low-temperature ferroelectric phases. Spontaneous polarizations for all three ferroelectric phases and the electrostrictive coefficients of cubic BaTiO3 are also computed using the Berry’s phase approach, and the results agree well with existing experimentally measured values.

The Thermosalient Phenomenon. “Jumping Crystals” and Crystal Chemistry of the Anticholinergic Agent Oxitropium Bromide

Abstract: The anticholinergic agent oxitropium bromide possesses rich crystal chemistry, most remarkably exhibiting a strong thermosalient effect ("jumping crystal" effect), a mechanical property with potential applications in organic-based actuators. The thermosalient effect, manifested in forceful jumps of up to several centimeters, was investigated by a combination of structural, microscopic, spectroscopic, and thermoanalytical techniques, providing data on which to base a proposed mechanism for the phenomenon. Direct observation of the effect in a single crystal and structure determination of both phases revealed that the jumping of the crystals is a macroscopic manifestation of a highly anisotropic change in the cell volume. The cell distortion is accompanied by a conformational change of the oxitropium cation, which triggers increased separation between the ion pairs in the lattice at nearly identical separation between the cation and the anion within each ion pair. At the molecular level, the cation acts as a molecular shuttle composed of two rigid parts (epoxy-aza-tricyclic-nonyl portion and phenyl ring) that are bridged by a flexible ester linkage. The structure of the rigid, inert aza-tricyclic portion remains practically unaffected by the temperature, suggesting a mechanism in which the large, thermally accumulated strain is transferred over the ester bridge to the phenyl ring, which rotates to trigger the phase transition. Mechanistic details of the higher temperature solid-state phenomena are also presented. The high-temperature phase can also be obtained by grinding or UV irradiation of the room-temperature phase. In addition, if it is irradiated with UV light in the presence of KBr, the high-temperature phase undergoes intramolecular photochemical rearrangement. Heating the high-temperature phase to slightly below the melting temperature results in an additional solid-state reaction that results in the conversion of the salt to a mixture of neutral compounds.

Ligand exchanges and selective catalytic hydrogenation in molecular single crystals

Abstract: Chemical reactions inside single crystals are likely to be highly selective, but examples of single crystal to single crystal (SC-SC) transformations are uncommon, because crystallinity is difficult to retain following the rearrangement of atoms in the solid state. The most widely studied SC-SC transformations involve solvent exchange reactions in porous coordination polymers or metal-organic frameworks, which take advantage of the robust polymeric networks of the hosts. Examples of reactions occurring within molecular organic crystals generally involve photo-induced reactions, such as the coupling of alkenes or alkynes within the crystal. For nonporous molecular inorganic or organometallic crystals, single-crystal transformations involving the formation or cleavage of metal-ligand bonds are rare; known examples usually involve ligand loss from the single crystal and reversible religation, a process sometimes accompanied by decay of the single crystal to a microcrystalline powder. Here we report a series of SC-SC transformations that involve the interchange of multiple small gaseous ligands (N(2), CO, NH(3), C(2)H(4), H(2) and O(2)) at an iridium centre in molecular single crystals of a pincer Ir(I) complex. The single crystal remains intact during these ligand-exchange reactions, which occur within the crystal and do not require prior ligand extrusion. We reveal a selective catalytic transformation within a nonporous molecular crystal: pincer iridium single crystals ligated with nitrogen, ethylene or hydrogen show selective hydrogenation of ethylene relative to propylene (25:1) when surface sites are passified by CO.

Quantum phase transitions in single-crystal Mn 1 − x Fe x Si and Mn 1 − x Co x Si : Crystal growth, magnetization, ac susceptibility, and specific heat

Abstract: We report the magnetization, ac susceptibility, and specific heat of optically float-zoned single crystals of Mn1-xFexSi and Mn1-xCoxSi for temperatures down to $\sim$2 K and magnetic fields up to 9 T. The suppression of the helimagnetic transition temperature T1 above a critical composition x1, as seen in the magnetization, ac susceptibility, and specific heat, suggests the existence of a quantum phase transition at x1. A Vollhardt invariance at a temperature T2$>$T1, which may be attributed to the Dzyaloshinsky-Moriya (DM) spin-orbit interactions, is also suppressed with increasing x and vanishes above a concentration x2, where x2$>$x1. When suppressing the effects of the DM interactions in an applied magnetic field, the magnetization for sufficiently large fields shares the signatures expected of an underlying putative ferromagnetic quantum critical point for a critical concentration xc, where x1$<$xc$<$x2. As a function of normalized concentration x/xc, where xCoc$\approx$0.084 and xFec$\approx$0.192, the properties of Mn1-xFexSi and Mn1-xCoxSi are essentially identical with x1/xc$\approx$0.78 and x2/xc$\approx$1.17. Taken together, our study identifies Mn1-xFexSi and Mn1-xCoxSi as model systems in which the influence of DM interactions on ferromagnetic quantum criticality may be studied.

Single‐Crystal to Single‐Crystal Cross‐Linking of an Interpenetrating Chiral Metal–Organic Framework and Implications in Asymmetric Catalysis

Abstract: Metal–organic frameworks (MOFs) have received extensive interest in the past decade because of their interesting properties. MOFs exhibit exceptional gas-uptake capacity owing to their extreme porosity. The ability to incorporate desired functional groups allows MOFs to perform in a variety of applications, such as catalysis, chemical sensing, and drug delivery. In particular, MOFs represent ideal candidates as heterogeneous catalysts by simultaneously imparting porosity and introducing catalytic sites into MOFs. Unlike other catalyst heterogenization strategies, the MOF-derived heterogeneous catalysts can remain singlecrystalline, thus providing a unique opportunity for detailed structural interrogation and therefore delineating the relationships between the MOF structures and their catalytic activities and selectivities. Moderate hydrolytic and thermal stabilities of most MOFs limit the scope of reactions that can be heterogeneously catalyzed by MOFs. We have recently focused our efforts on the design of chiral porous MOFs for heterogeneous asymmetric catalysis as most asymmetric catalytic reactions are carried out under mild conditions in aprotic solvents. In order for chiral MOFs to be useful asymmetric catalysts, they must possess large nanometer-scale open channels for the facile transport of sterically demanding substrates and products. We have recently synthesized isoreticular chiral MOFs based on tetracarboxylate bridging ligands derived from 1,1’-bi-2-naphthol (BINOL) and copper paddle-wheel secondary building units (SBUs), and observed the remarkable dependence of the enantioselectivities of the addition of Et2Zn to aromatic aldehydes on the MOF openchannel sizes. In order to expand the scope of applications of such chiral tetracarboxylate ligands, and to further understand the relationships between framework structures and catalytic activities, we have used these ligands in combination with other metal-connecting points or metal-cluster SBUs. Herein we report the synthesis and characterization of two interpenetrating chiral MOFs [Zn2(L)(dmf)(H2O)]·2EtOH·4.3DMF·H2O (1, where L is (R)-2,2’-diethoxy-1,1’-binaphthyl-4,4’,6,6’-tetrabenzoate) and [Zn2(L’)(dmf)(H2O)]·2EtOH·4.3DMF·4 H2O (2, L’= (R)-2,2’-dihydroxy-1,1’-binaphthyl-4,4’,6,6’-tetrabenzoate), which are constructed from dizinc SBUs and chiral tetracarboxylate ligands. More importantly, we observed unprecedented single-crystal to single-crystal crosslinking of the two interpenetrating networks in 2 by Ti(OiPr)4 to lead to intermolecular [Ti(BINOLate)2] complexes that exhibit modest enantioselectivity in catalyzing the addition of diethylzinc to aromatic aldehydes to afford chiral secondary alcohols. This result provides unambiguous structural identification of an immobilized homogeneous catalyst and has significant implications in rational design of MOF-based heterogeneous asymmetric catalysts. MOF 1 was synthesized by heating a mixture of ZnI2 and (R)-H4L in DMF/EtOH at 90 8C for five days, while MOF 2 was produced by heating ZnI2 and (R)-H4L’ in DMF/EtOH at 100 8C for one week (Scheme 1). The formulae of 1 and 2 were established by single-crystal X-ray diffraction studies, NMR analysis, and thermogravimetric analysis (TGA).

Laser-induced melting of a single crystal gold sample by time-resolved ultrafast relativistic electron diffraction

Abstract: We report the experimental demonstration of time-resolved relativistic electron diffraction. Single shot diffraction patterns from a single crystal gold sample were recorded using ultrashort 3.5 MeV electron bunches from a radio frequency photoinjector. By scanning the pump pulse time-delay, we studied the Bragg peaks amplitude change due to the laser-induced melting of the sample. The observed time scale matches the one predicted using a simple two temperature model of the heating of the thin foil. Time-resolved relativistic electron diffraction using megaelectronvolt electron beams with 107 particles in 100 fs bunch length opens exciting possibilities in ultrafast structural dynamics.

High-Performance Single Crystal Organic Field-Effect Transistors Based on Two Dithiophene-Tetrathiafulvalene (DT-TTF) Polymorphs

Abstract: Solution prepared single crystal organic field-effect transistors (OFETs) combine low-cost with high performance due to structural ordering of molecules. However, in organic crystals polymorphism is a known phenomenon, which can have a crucial influence on charge transport. Here, the performance of solution-prepared single crystal OFETs based on two different polymorphs of dithiophene-tetrathiafulvalene, which were investigated by confocal Raman spectroscopy and X-ray diffraction, are reported. OFET devices prepared using different configurations show that both polymorphs exhibited excellent device performance, although the -phase revealed charge carrier mobility between two and ten times higher in accordance to the closer stacking of the molecules.

The development of morphology and structure in hexagonal vaterite

Abstract: Inspired by the remarkable shapes and properties of CaCO(3) biominerals, many studies have investigated biomimetic routes aiming at synthetic equivalents with similar morphological and structural complexity. Control over the morphology of CaCO(3) crystals has been demonstrated, among other methods, by the use of additives that selectively allow the development of specific crystal faces, while inhibiting others. Both for biogenic and biomimetic CaCO(3), the crystalline state is often preceded by an amorphous precursor phase, but still limited information is available on the details of the amorphous-to-crystalline transition. By using a combination of cryoTEM techniques (bright field imaging, cryo-tomography, low dose electron diffraction and cryo-darkfield imaging), we show for the first time the details of this transition during the formation of hexagonal vaterite crystals grown in the presence of NH(4)(+) ions. The formation of hexagonal plate-like vaterite occurs via an amorphous precursor phase. This amorphous phase converts into the crystalline state through a solid state transformation in which order and morphology develop simultaneously. The mineral initially develops as polycrystalline vaterite which transforms into a single crystal directed by an NH(4)(+)-induced crystal plane that acts as a templating surface.

One-pot low temperature solution synthesis, magnetic and microwave electromagnetic properties of single-crystal iron submicron cubes

Abstract: Large quantities of single-crystal iron submicron cubes with controllable dimensions and surface structures were synthesized by a facile low-temperature solution reduction approach under normal atmosphere. The influence of kinetic parameters such as NaOH concentration, reaction temperature, reaction time, species of solvents and reducing agents, etc. on the morphology, size and crystal structure of the as-synthesized products were investigated in detail. The resultant products experience multistep phase transformations and morphology evolutions from Fe(OH)2 nanosheets, to weak crystalline Fe3O4 ultrafine particles and to high crystalline Fe cubes. It is believed that both the control over the quasi-equilibrium crystal nucleation and growth rate by adjusting kinetic parameters, and the selective interaction between ethylenediamine and various crystallographic planes of bcc iron play crucial roles in the formation of the slightly truncated cubes with {100} planes at the sides and small {111} planes on the corners. The as-synthesized iron cubes exhibit a strong and wide resonance behavior for the imaginary permittivity and imaginary permeability over the frequency range of 2–14 GHz as a result of the submicron size and anisotropy morphology. The paraffin-based composites containing 26 vol% iron submicron cubes show good electromagnetic wave absorbing characteristics and the reflection loss values less than −20 dB are obtained in the frequency range of 6.5–18.0 GHz when the thickness of the composites is 1.0–2.5 mm, suggesting that the iron submicron cubes synthesized here are promising as a strong-absorption, thin-thickness, light-weight and low-cost microwave absorber.

Metal-insulator transition characteristics of VO2 thin films grown on Ge(100) single crystals

Abstract: Phase transitions exhibited by correlated oxides could be of potential relevance to the emerging field of oxide electronics. We report on the synthesis of high-quality VO2 thin films grown on single crystal Ge(100) substrates by physical vapor deposition and their metal-insulator transition (MIT) properties. Thermally triggered MIT is demonstrated with nearly three orders of magnitude resistance change across the MIT with transition temperatures of 67 °C (heating) and 61 °C (cooling). Voltage-triggered hysteretic MIT is observed at room temperature at threshold voltage of ∼2.1 V for ∼100 nm thickness VO2 films. Activation energies for electron transport in the insulating and conducting states are obtained from variable temperature resistance measurements. We further compare the properties of VO2 thin films grown under identical conditions on Si(100) single crystals. The VO2 thin films grown on Ge substrate show higher degree of crystallinity, slightly reduced compressive strain, larger resistance change a...

High-Performance Organic Field-Effect Transistors from Organic Single-Crystal Microribbons Formed by a Solution Process

Abstract: Intensive research has been carried out on one-dimensional (1D) organic electronics in recent years because of their highly tunable energy levels and good processability, their low-cost fabrication, flexibility, etc. In the ever ongoing quest for enhanced performance in the microelectronics industry, organic 1D materials with high carrier mobilities for both holes and electrons are required. High-performance organic field-effect transistors (OFETs), photo-transistors, and complementary inverters have been successfully demonstrated based both on vacuumprocessed and solution-processed organic 1D nanoor microstructures. Hu and co-workers fabricated single-crystal nanoribbon OFETs and achieved a hole mobility of 0.6 cmV 1 s 1 using copper phthalocyanine (CuPc) and an electron mobility of 0.1 cmV 1 s 1 using copper hexadecafluorophthalocyanine (F16CuPc). [2a,2c] Bao reported a p-channel mobility as high as 0.27 cmV 1 s 1 based on hexathiapentacene (HTP) nanowires developed in the same group. ] Kim et al. fabricated FETdevices based on triisopropylsilylethynyl pentacene (TIPS-PEN) microbelts that showed a hole mobility as high as 1.4 cmV 1 s . Most recently, Bao has achieved an electron mobility of 1.4 cmV 1 s 1 using an n-channel organic nanowire. Nevertheless, fabricating 1D organic structures with mobilities higher than 1 cmV 1 s 1 remains a challenge, especially for solution-processed, self-assembled, and dispersed nanoand microwires. Physical vapor and vacuum deposition are widely used for the fabrication of high-quality organic single crystals and the production of highly crystallized organic films. OFETs based on vapor-phase fabricated single crystals and films generally exhibit a higher performance than their counterparts based on solution-processed small molecules or polymers. The major obstacles for high-performance OFETs lie in the interface between the organic compound and the dielectric layer, and

Influence of TCP phase and its morphology on creep properties of single crystal nickel-based superalloys

Abstract: By means of the measurement of creep curves and SEM, TEM observation, an investigation has been made into the influences of the element Re and TCP phase on the creep properties of the single crystal nickel-based superalloys. Results show that, during aging of the containing/free Re superalloys, the slice-like TCP phase identified as μ phase is precipitated along the 〈1 1 0〉 orientation on {1 1 1} planes. As the aging time prolongs, the quantities of the slice-like μ phase precipitated in the alloys increase, no spheroidized feature of μ phase is detected in 6%W alloy, but the slice-like μ phase in 4.5%Re alloy is transformed into the sphere-like morphology. During aging, the evolution process of the strip-like μ phase consists of the inhomogeneous coarsening, the appearance of the groove and the decomposition of the one in the interval distance. The higher chemical potential in the strip-like μ phase with the groove acts as the driving force for promoting the diffusion of the solute atoms, which results in the strip-like μ phase dissolved and the groove deepened up to separation to form the sphere-like morphology. During creep, the stress concentration generates easily in the regions near the strip-like μ phase, and promotes the initiation and propagation of the cracks, which is the main reason of reducing the creep lifetime of 6%W alloy to a great extent, but the stress concentration does not easily generate in the regions near the sphere-like μ phase, this is the main reason of reducing the creep lifetime of 4.5%Re alloy to a small extent.

Large inverse magnetocaloric effect in Ni45Co5Mn37.5In12.5 single crystal above 300 K

Abstract: A large inverse magnetocaloric effect has been observed in a Ni45Co5Mn37.5In12.5 single crystal at room temperature. Magnetothermal measurements performed at different magnetic fields reveal a nonmagnetic to ferromagnetic transition correlated with the austenite-martensite phase transformation. The Heusler single crystal shows a large entropy change of 30 J/Kg K at an applied magnetic field of 7 T during the first-order magnetostructural transition at 355 K. It leads to a net refrigerant capacity of 267 J/Kg at 7 T, which is very encouraging for magnetic refrigeration applications.

Transport properties of the new Fe-based superconductor KxFe2Se2 (Tc = 33 K)

Abstract: We synthesized the new Fe-based superconductor K0.8Fe2Se2 single crystals. The obtained single crystal exhibited a sharp superconducting transition, and the onset and zero-resistivity temperature was estimated to be 33 and 31.8 K, respectively. A high upper critical field of 192 T was obtained. Anisotropy of superconductivity of K0.8Fe2Se2 was ~3.6. Both the high upper critical field and comparably low anisotropy are advantageous for the application under high magnetic field.