Showing papers on "Single crystal published in 2011"
TL;DR: It is shown that geometrically well-defined graphene quantum dots can be synthesized on a ruthenium surface using C(60) molecules as a precursor, and Scanning tunnelling microscopy imaging suggests that the structures are formed through the ruthene-catalysed cage-opening of C( 60).
Abstract: The fragmentation of fullerenes using ions, surface collisions or thermal effects is a complex process that typically leads to the formation of small carbon clusters of variable size. Here, we show that geometrically well-defined graphene quantum dots can be synthesized on a ruthenium surface using C(60) molecules as a precursor. Scanning tunnelling microscopy imaging, supported by density functional theory calculations, suggests that the structures are formed through the ruthenium-catalysed cage-opening of C(60). In this process, the strong C(60)-Ru interaction induces the formation of surface vacancies in the Ru single crystal and a subsequent embedding of C(60) molecules in the surface. The fragmentation of the embedded molecules at elevated temperatures then produces carbon clusters that undergo diffusion and aggregation to form graphene quantum dots. The equilibrium shape of the graphene can be tailored by optimizing the annealing temperature and the density of the carbon clusters.
570 citations
TL;DR: In this paper, the authors used a combinatorial approach where targeted single-crystal compositions are obtained by a flexible, time saving, and cost-effective crystal growth technique.
Abstract: The Ce-doped (LuyGd1–x)3(Gay,Al1–y)5O12 single crystals were grown by the micropulling down method. Their structure and chemical composition were checked by X-ray diffraction (XRD) and electron probe microanalysis (EPMA) techniques. Optical, luminescent, and scintillation characteristics were measured by the methods of time-resolved luminescence spectroscopy, including the light yield and scintillation decay. Balanced Gd and Ga admixture into the Lu3Al5O12 structure provided an excellent scintillator where the effect of shallow traps was suppressed, the spectrally corrected light yield value exceeded 40 000 photons/MeV, and scintillation decay was dominated by a 53 ns decay time value which is close to that of Ce3+ photoluminescence decay. This study provides an excellent example of a combinatorial approach where targeted single-crystal compositions are obtained by a flexible, time saving, and cost-effective crystal growth technique.
459 citations
TL;DR: The time-dependent growth dynamics of the domains are studied and it is shown that the final continuous FLG film is polycrystalline, consisting of randomly connected single crystal domains.
Abstract: Hexagonal-shaped single crystal domains of few layer graphene (FLG) are synthesized on copper foils using atmospheric pressure chemical vapor deposition with a high methane flow. Scanning electron microscopy reveals that the graphene domains have a hexagonal shape and are randomly orientated on the copper foil. However, the sites of graphene nucleation exhibit some correlation by forming linear rows. Transmission electron microscopy is used to examine the folded edges of individual domains and reveals they are few-layer graphene consisting of approximately 5−10 layers in the central region and thinning out toward the edges of the domain. Selected area electron diffraction of individual isolated domains reveals they are single crystals with AB Bernal stacking and free from the intrinsic rotational stacking faults that are associated with turbostratic graphite. We study the time-dependent growth dynamics of the domains and show that the final continuous FLG film is polycrystalline, consisting of randomly co...
290 citations
TL;DR: The results suggested that topological superconductivity can be realized in Bi2Te3 due to the proximity effect between superconducting bulk states and Dirac-type surface states.
Abstract: We report a successful observation of pressure-induced superconductivity in a topological compound Bi2Te3 with Tc of ∼3 K between 3 to 6 GPa. The combined high-pressure structure investigations with synchrotron radiation indicated that the superconductivity occurred at the ambient phase without crystal structure phase transition. The Hall effects measurements indicated the hole-type carrier in the pressure-induced superconducting Bi2Te3 single crystal. Consequently, the first-principles calculations based on the structural data obtained by the Rietveld refinement of X-ray diffraction patterns at high pressure showed that the electronic structure under pressure remained topologically nontrivial. The results suggested that topological superconductivity can be realized in Bi2Te3 due to the proximity effect between superconducting bulk states and Dirac-type surface states. We also discuss the possibility that the bulk state could be a topological superconductor.
279 citations
TL;DR: The combination of advanced electron microscopy, spectroscopy and first-principles calculations can provide three-dimensional images of complex, multicomponent grain boundaries with both atomic resolution and chemical sensitivity and demonstrate that atomic-scale analysis of complex multicomponents structures in materials is now becoming possible.
Abstract: The ability to resolve spatially and identify chemically atoms in defects would greatly advance our understanding of the correlation between structure and property in materials. This is particularly important in polycrystalline materials, in which the grain boundaries have profound implications for the properties and applications of the final material. However, such atomic resolution is still extremely difficult to achieve, partly because grain boundaries are effective sinks for atomic defects and impurities, which may drive structural transformation of grain boundaries and consequently modify material properties. Regardless of the origin of these sinks, the interplay between defects and grain boundaries complicates our efforts to pinpoint the exact sites and chemistries of the entities present in the defective regions, thereby limiting our understanding of how specific defects mediate property changes. Here we show that the combination of advanced electron microscopy, spectroscopy and first-principles calculations can provide three-dimensional images of complex, multicomponent grain boundaries with both atomic resolution and chemical sensitivity. The high resolution of these techniques allows us to demonstrate that even for magnesium oxide, which has a simple rock-salt structure, grain boundaries can accommodate complex ordered defect superstructures that induce significant electron trapping in the bandgap of the oxide. These results offer insights into interactions between defects and grain boundaries in ceramics and demonstrate that atomic-scale analysis of complex multicomponent structures in materials is now becoming possible.
211 citations
TL;DR: In this paper, the authors used low-energy electron microscopy to investigate how graphene grows on smooth, clean Cu(111) and showed that surface diffusion limited by comparing simulations of the time evolution of island shapes with experiments.
Abstract: We use low-energy electron microscopy to investigate how graphene grows on Cu(111). Graphene islands first nucleate at substrate defects such as step bunches and impurities. A considerable fraction of these islands can be rotationally misaligned with the substrate, generating grain boundaries upon interisland impingement. New rotational boundaries are also generated as graphene grows across substrate step bunches. Thus, rougher substrates lead to higher degrees of mosaicity than do flatter substrates. Increasing the growth temperature improves crystallographic alignment. We demonstrate that graphene growth on Cu(111) is surface diffusion limited by comparing simulations of the time evolution of island shapes with experiments. Islands are dendritic with distinct lobes, but unlike the polycrystalline, four-lobed islands observed on (100)-textured Cu foils, each island can be a single crystal. Thus, epitaxial graphene on smooth, clean Cu(111) has fewer structural defects than it does on Cu(100).
205 citations
TL;DR: In this article, a porous cathode material consisting of interconnected single crystal LiNi1/3Co 1/3Mn1/ 3O2 (NCM) nanoparticles has been synthesized for lithium ion batteries.
Abstract: A porous cathode material consisting of interconnected single crystal LiNi1/3Co1/3Mn1/3O2 (NCM) nanoparticles has been synthesized for lithium ion batteries. Trace nitric acid is used as pH value adjuster to form honeycomb-shaped foam, and a novel stepwise crystallization process is employed to obtain NCM particles. The modified sol–gel process followed by an optimized crystallization process results in significant improvements in chemical and physical characteristics of the NCM particles. They consist of a fully-developed single crystal NCM with uniform composition and a porous NCM architecture with a reduced degree of fusion and a large specific surface area. These structural modifications in turn significantly enhance the electrochemical properties of the NCM cathode material, in terms of improved charge/discharge capacity, cyclic stability and rate capability.
203 citations
TL;DR: In this article, X-ray diffraction and electron probe microanalysis techniques are employed to check the structure and chemical composition of single crystals, and the authors show that balanced Gd and Ga admixture in the Y3Al5O12 structure can considerably increase scintillation efficiency.
Abstract: Ce-doped (YyGd1−y)3(GaxAl1−x)5O12 (x = 0, 1, 2, 3, 4 and y = 1, 2, 3) single crystals are grown by the micro-pulling down method. X-ray diffraction and electron probe microanalysis techniques are employed to check their structure and chemical composition, respectively. Optical and photoluminescence characteristics are measured and radioluminescence spectra, light yield and scintillation decay measurements are further made to evaluate the scintillation performance. We show that balanced Gd and Ga admixture in the Y3Al5O12 structure can considerably increase the scintillation efficiency, and the spectrally corrected light yield value exceeds 44000photonMeV −1 . Scintillation decay times approach that of Ce 3+ photoluminescence decay and an additional less intense slower component is also observed. Physical aspects of energy transfer process and 5d1 excited state depopulation are discussed. The micro-pulling down technique is shown as an ideal tool for a directed combinatorial search for targeted single crystal compositions to reveal those with the highest figure-of-merit for a given application field. (Some figures may appear in colour only in the online journal)
198 citations
TL;DR: In this paper, a simple hydrothermal process was used to synthesize CoFe 2− x Gd x O 4 (x = 0−0.25) nanoparticles with a doping amount of ≤ 0.25 and the peaks could be readily indexed to cubic spinel cobalt ferrite.
186 citations
TL;DR: The obtained SnS nanosheets exhibit excellent electrochemical properties which have promising applications in lithium ion batteries.
180 citations
TL;DR: In this paper, the authors analyzed the impact of a slight orthorhombic and monoclinic distortion of the Ni 50.2 Mn 28.3 Ga 21.5 at.
TL;DR: It is elucidate that the mismatch between the large Ce and small Al atoms frustrates the crystallization and causes amorphization, but a long-range fcc topological order still exists, and pressure induces electronic transition in Ce, which eliminates the mismatch and manifests the topological Order by the formation of a single crystal.
Abstract: Glass lacks the long-range periodic order that characterizes a crystal. In the Ce75Al25 metallic glass (MG), however, we discovered a long-range topological order corresponding to a single crystal of indefinite length. Structural examinations confirm that the MG is truly amorphous, isotropic, and unstrained, yet under 25 gigapascals hydrostatic pressures, every segment of a centimeter-length MG ribbon devitrifies independently into a face-centered cubic (fcc) crystal with the identical orientation. By using molecular dynamics simulations and synchrotron x-ray techniques, we elucidate that the mismatch between the large Ce and small Al atoms frustrates the crystallization and causes amorphization, but a long-range fcc topological order still exists. Pressure induces electronic transition in Ce, which eliminates the mismatch and manifests the topological order by the formation of a single crystal.
TL;DR: A large-size single crystal of nearly stoichiometric SrCoO(3) was prepared with a two-step method combining the floating-zone technique and subsequent high oxygen pressure treatment, indicative of the possible effect of orbital fluctuation in the intermediate spin ferromagnetic metallic state.
Abstract: A large-size single crystal of nearly stoichiometric SrCoO(3) was prepared with a two-step method combining the floating-zone technique and subsequent high oxygen pressure treatment. SrCoO(3) crystallizes in a cubic perovskite structure with space group Pm3m, and displays an itinerant ferromagnetic behavior with the Curie temperature of 305 K. The easy magnetization axis is found to be along the [111] direction, and the saturation moment is 2.5 µ(B)/f.u., in accord with the picture of the intermediate spin state. The resistivity at low temperatures (T) is proportional to T(2), indicative of the possible effect of orbital fluctuation in the intermediate spin ferromagnetic metallic state. Unusual anisotropic magnetoresistance is also observed and its possible origin is discussed.
TL;DR: Gold-core silica-shell nanoparticles (Au@SiO(2) NPs) boost the intensity of Raman scattering from molecules adsorbed on atomically flat surfaces and may open up new approaches for the characterization of adsorbates and reaction pathways on a wide range of smooth surfaces.
Abstract: We used shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) to systematically study the adsorption of pyridine on low-index Au(hkl) and Pt(hkl) single crystal electrodes. Our gold-core silica-shell nanoparticles (Au@SiO2 NPs) boost the intensity of Raman scattering from molecules adsorbed on atomically flat surfaces. The average enhancement factor reaches 106 for Au(110) and 105 for Pt(110), which is comparable to or even greater than that obtained for bare gold NPs (a widely adopted SERS substrate). 3D-FDTD simulations reveal that this large enhancement is due to the transfer of the “hotspots” from NP-NP gaps to NP-surface gaps. We also found that the SHINERS intensity strongly depends on the surface crystallographic orientation, with differences up to a factor of 30. Periodic DFT calculations and theoretical analysis of dielectric functions indicate that this facet-dependence is predominantly governed by the dielectric property of the surface. The results presented in this work may open up...
TL;DR: Large-area single crystal monolayer graphene is synthesized on Ni(111) thin films, which have flat terraces and no grain boundaries, and continuous millimeter-scale single domain graphene is obtained.
Abstract: Large-area single crystal monolayer graphene is synthesized on Ni(111) thin films, which have flat terraces and no grain boundaries. The flat single-crystal Ni films are heteroepitaxially grown on MgO(111) substrates using a buffer layer technique. Low-energy electron diffraction and various spectroscopic methods reveal the long-range single crystallinity and uniform monolayer thickness of the graphene. When transferred onto an insulating wafer, continuous millimeter-scale single domain graphene is obtained.
TL;DR: A selective etching phenomenon on {001} faceted anatase TiO(2) single crystal surfaces by HF and associated etching mechanism are reported and density functional theory calculations reveal that HF stabilizes the grown facets at low concentrations, but selectively destroys the growing facets at high concentrations.
TL;DR: First-principles DFT computation results show that Zn vacancies can induce intrinsic ferromagnetism in these undoped ZnS NWs and indicate that the magnetic moment of the ultrathin Zn S NWs can be increased by increasing the Zn vacancy concentration without significant energy cost.
Abstract: Highly uniform single crystal ultrathin ZnS nanowires (NWs) with 2 nm diameter and up to 10 μm length were fabricated using a catalyst-free colloidal chemistry strategy. The nanowires crystallized in hexagonal phase structure with preferential growth along the direction of the (001) basal plane. The strong polarity of the (001) plane composed of Zn cations or S anions drives the oriented attachment of ZnS nanocrystals (NCs) along this direction via electrostatic (or dipole) interaction. The ultrathin ZnS nanowires show intrinsic ferromagnetism at room temperature and other unusual properties related to its unique nature, such as large anisotropic lattice expansion, large blue-shift of UV–vis absorption band of the excition, and photoluminescence spectrum of the exciton band edge. First-principles DFT computation results show that Zn vacancies can induce intrinsic ferromagnetism in these undoped ZnS NWs. The main source of the magnetic moment arises from the unpaired 3p electrons at S sites surrounding the...
TL;DR: Hexagonal single crystal WO(3) nanorods with dominant (001) and (1 ̄10) facets were synthesized, which exhibited high adsorption capacities for organic dyes.
TL;DR: The magnetic properties of 1 and 2 were investigated, showing the existence of ferromagnetic interaction between the Co(II) atoms within the trinuclear subunit.
Abstract: A three-dimensional (3D) coordination polymer, [Co3(L)2(BTEC)(H2O)2]·2H2O [1, HL = 3,5-di(imidazol-1-yl)benzoic acid, H4BTEC = 1,2,4,5-benzenetetracarboxylic acid], with tfz-d topology has been hydrothermally synthesized. The framework of 1 has high thermal stability and exhibits single-crystal-to-single-crystal (SCSC) transformations upon removing and rebinding the noncoordinated and coordinated water molecules. X-ray crystallographic analyses revealed that the coordination geometry of Co(II) changes from octahedral to square pyramid upon dehydration, accompanying the appearance of one-dimensional (1D) open channels with dimensions of 2.0 × 2.8 A. The dehydrated form [Co3(L)2(BTEC)] (2) exhibits highly selective adsorption of water molecules over N2, CH3OH, and CH3CH2OH, which could be used as sensors for water molecules. Furthermore, the magnetic properties of 1 and 2 were investigated, showing the existence of ferromagnetic interaction between the Co(II) atoms within the trinuclear subunit.
TL;DR: In this paper, single crystals of l -leucine l leucinium picrate (LLLLP) were grown by the slow evaporation solution technique and the crystal system and lattice parameters were confirmed by single crystal XRD.
TL;DR: The AFM-based SMFS is extended to the investigation of polymer interactions in their condensed states (e.g., in polymer single crystals) and the corresponding extraction force obtained quantitatively by a good combination of atomic force microscopy and single-molecule force spectroscopy.
Abstract: A thiol-labeled single polyethylene oxide chain has been pulled out of its single crystal and the corresponding extraction force obtained quantitatively by a good combination of atomic force microscopy (AFM) imaging and AFM-based single-molecule force spectroscopy (SMFS). Our study extends the AFM-based SMFS to the investigation of polymer interactions in their condensed states (e.g., in polymer single crystals).
TL;DR: In this article, metal organic chemical vapor deposition on single crystal AlN substrates processed from AlN boules grown by physical vapor transport was used to obtain high crystalline quality of films and interfaces.
Abstract: AlN and AlGaN epitaxial films were deposited by metal organic chemical vapor deposition on single crystal AlN substrates processed from AlN boules grown by physical vapor transport. Structural, chemical, and optical characterization demonstrated the high crystalline quality of the films and interfaces.
TL;DR: In this paper, a series of near-infrared solid-state emitters based on the dicyanoisophorone electron acceptor group was synthesized and the solid state spectroscopic properties were studied by UV−visible absorption spectroscopy and fluorescence spectrographs and analyzed in light of single crystal structures obtained by X-ray diffraction.
Abstract: A series of near-infrared solid-state emitters based on the dicyanoisophorone electron acceptor group was synthesized. The solid-state spectroscopic properties were studied by UV−visible absorption spectroscopy and fluorescence spectroscopy and analyzed in light of the single crystal structures obtained by X-ray diffraction. This series of push−pull dipolar fluorophores differing only by the substituent groups on the donor end display interesting solid-state emission properties on crystal with an emission in the near-infrared ranging from 710 to 790 nm. The origin of the emission depends on the nature of the substituent groups that influence the crystal packing and trigger the formation of long chain of emitting aggregates.
TL;DR: In this paper, the authors synthesized the new Fe-based superconductor K0.8Fe2Se2 single crystal, which exhibited a sharp superconducting transition and the onset and zero-resistivity tempera-ture were estimated to be 33 and 31.8 K, respectively.
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 tempera-ture were estimated to be 33 and 31.8 K, respectively. A high upper critical field of 192 T was obtained. The anisotropy of superconductivity of K0.8Fe2Se2 was ∼3.6. Both the high upper critical field and comparably low anisotropy are advantageous for applications under a high magnetic field.
TL;DR: In this paper, high temperature hydrothermal syntheses, using calcium nitrate tetrahydrate, sodium dihydrogen phosphate and urea as precursors, and characterization of hydroxyapatite whiskers are reported.
TL;DR: In this paper, a platelet α-MoO 3 single crystal with dimensions of ∼1000 × 200 × 0.4 μm 3 has been grown on Si(1 0 0) substrates in a quartz tube reactor in air atmosphere by sublimation of molybdenum oxide at T=660 °C.
TL;DR: In this paper, as-prepared nanorods, nanobelts, and nanosheet Co3O4 samples are single crystalline and mesoporous in nature with a predominance of exposed high-energy (110) crystal planes.
Abstract: Co3O4 nanorods, nanobelts, nanosheets and cubic/octahedral nanoparticles have been successfully synthesized with tunable size from the nanoscale to the microscale, accompanied by a variation in the nature of the exposed crystal planes. The products are formed by thermal treatment of Co(CO3)0.5(OH)·0.11H2O nanorod, nanobelt, nanosheet and nanocubic/nanooctahedral precursors at 250 °C. Detailed characterization, including X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photo-electron spectroscopy (XPS), and nitrogen adsorption and desorption isotherms, revealed that the as-prepared nanorods, nanobelts, and nanosheet Co3O4 samples are single crystalline and mesoporous in nature with a predominance of exposed high-energy (110) crystal planes. They exhibited excellent electrochemical properties in supercapacitors, showing higher capacitance and better rate capability than conventional cubic/octahedral Co3O4 nanoparticles having exposed low-energy (100) and (111) planes. No decay in capacitance was observed when the scan rate was increased from 5 mV/s to 100 mV/s, or from 1 A/g to 10 A/g. The maximum value of the specific capacitance was calculated to be 162.8 F/g and the capacitance retention reached as high as 90%. Their excellent performance in supercapacitors is believed to result from the large-area exposure of active (110) crystal planes. The Co3O4 nanosheets showed the best performance due to their larger surface area and ability to provide a better pathway for charge transfer, and are promising electrode materials for application in practical supercapacitors. Open image in new window
TL;DR: This paper reports the synthesis of high-surface-area, singlecrystal-like anatase with controlled mesoporous network and preferential exposure of the highly active (001) planes of anatase, providing a new class of materials for catalysis, energy storage and conversion, and other applications.
Abstract: Titania represents the most widely used oxide semiconductor for photocatalysts and photovoltaics, and its performance is heavily governed by its surface area and the exposed crystal planes. To date, however, as-made TiO2 samples have been limited to the single crystals with low surface area or porous polycrystals exposing their less-active planes. We report herein the synthesis of high-surface-area, singlecrystal-like anatase with controlled mesoporous network and preferential exposure of the highly active (001) planes. This simple solution-growth method is readily extendable to the synthesis of other mesoporous single crystals beyond TiO2, providing a new class of materials for catalysis, energy storage and conversion, and other applications. The photocatalytic activity of TiO2 is generally dependent on its crystallography. For example, the (001) planes of anatase are much more active than the (101) planes, which are the most commonly observed and thermodynamically more stable crystalline planes in the anatase form. Significant effort has therefore been devoted to synthesize TiO2 crystals with preferential (001) plane exposure. As well as crystallographic control, equally important is building networks of pores within the crystals to increase the surface area and provide pore-dependent activity and selectivity. To date, although a large number of porous TiO2 have been made using sol–gel and softor hard-templating approaches, 8, 21,23–25] the current materials are limited to porous TiO2 with amorphous or polycrystalline frameworks that exhibit low photocatalytic activity and charge-transport capability. Herein, using a method of crystal oriented growth, we report the synthesis of highly active mesoporous, singlecrystal-like TiO2 (mesocages) with both preferential (001) plane exposure and controllable mesoporous networks. As illustrated in Figure 1, we started with precursor solutions containing SO4 2 ; solvothermal reactions generate TiO2 building crystals of which the (001) planes are preferably
TL;DR: Crystallographic data show that in both solvate complexes lead(II) binds six solvent molecules with the former complex being hemidirected whereas the latter is holodirected, as expected given their space-demanding characteristics and ligand-ligand intermolecular interactions.
Abstract: The coordination chemistry of lead(II) in the oxygen donor solvents water, dimethylsulfoxide (dmso, Me2SO), N,N-dimethylformamide (dmf), N,N-dimethylacetamide (dma), N,N′-dimethylpropyleneurea (dmpu), and 1,1,3,3-tetramethylurea (tmu), as well as in the sulfur donor solvent N,N-dimethylthioformamide (dmtf), has been investigated by extended X-ray absorption fine structure (EXAFS) and/or large angle X-ray scattering (LAXS) in solution, and by single crystal X-ray diffraction and/or EXAFS of solid hydrates and solvates. Lead(II) may either form hemidirected complexes with large bond distance distribution and an apparent gap for excess electron density, or holodirected ones with a symmetric coordination sphere with normal bond distance distribution, depending on the strength of antibonding lead 6s/ligand np molecular orbital interactions and ligand−ligand interactions. The crystallographic data show that the solid lead(II) perchlorate and trifluoromethanesulfonate hydrate structures are hemidirected, while t...
TL;DR: This study definitively proves the 1-D polymeric nature of the crystal structure and allows a description of the [Fe(Rtrz)(3)] chains, as well as of the anions and water implementation within the crystal lattice opening the possibility of subsequent investigations of the structure-property correlation within this peculiar family of spin transition compounds.