Showing papers on "Crystal published in 2017"
TL;DR: In this paper, the authors present the experimental observation of a discrete time crystal in an interacting spin chain of trapped atomic ions and apply a periodic Hamiltonian to the system under many-body localization conditions, and observe a subharmonic temporal response that is robust to external perturbations.
Abstract: Spontaneous symmetry breaking is a fundamental concept in many areas of physics, including cosmology, particle physics and condensed matter. An example is the breaking of spatial translational symmetry, which underlies the formation of crystals and the phase transition from liquid to solid. Using the analogy of crystals in space, the breaking of translational symmetry in time and the emergence of a 'time crystal' was recently proposed, but was later shown to be forbidden in thermal equilibrium. However, non-equilibrium Floquet systems, which are subject to a periodic drive, can exhibit persistent time correlations at an emergent subharmonic frequency. This new phase of matter has been dubbed a 'discrete time crystal'. Here we present the experimental observation of a discrete time crystal, in an interacting spin chain of trapped atomic ions. We apply a periodic Hamiltonian to the system under many-body localization conditions, and observe a subharmonic temporal response that is robust to external perturbations. The observation of such a time crystal opens the door to the study of systems with long-range spatio-temporal correlations and novel phases of matter that emerge under intrinsically non-equilibrium conditions.
970 citations
TL;DR: The experimental demonstration of an electrostatic-doping-driven phase transition between the hexagonal and monoclinic phases of monolayer molybdenum ditelluride (MoTe2), which opens up new possibilities for developing phase-change devices based on atomically thin membranes.
Abstract: Monolayers of transition-metal dichalcogenides (TMDs) exhibit numerous crystal phases with distinct structures, symmetries and physical properties. Exploring the physics of transitions between these different structural phases in two dimensions may provide a means of switching material properties, with implications for potential applications. Structural phase transitions in TMDs have so far been induced by thermal or chemical means; purely electrostatic control over crystal phases through electrostatic doping was recently proposed as a theoretical possibility, but has not yet been realized. Here we report the experimental demonstration of an electrostatic-doping-driven phase transition between the hexagonal and monoclinic phases of monolayer molybdenum ditelluride (MoTe2). We find that the phase transition shows a hysteretic loop in Raman spectra, and can be reversed by increasing or decreasing the gate voltage. We also combine second-harmonic generation spectroscopy with polarization-resolved Raman spectroscopy to show that the induced monoclinic phase preserves the crystal orientation of the original hexagonal phase. Moreover, this structural phase transition occurs simultaneously across the whole sample. This electrostatic-doping control of structural phase transition opens up new possibilities for developing phase-change devices based on atomically thin membranes.
556 citations
TL;DR: A dopant compensation in alloyed OIHP single crystals is reported to overcome limitations of device noise and charge collection, enabling γ-ray spectrum collection at room temperature.
Abstract: Organic–inorganic halide perovskites (OIHPs) bring an unprecedented opportunity for radiation detection with their defect-tolerance nature, large mobility–lifetime product, and simple crystal growth from solution. Here we report a dopant compensation in alloyed OIHP single crystals to overcome limitations of device noise and charge collection, enabling γ-ray spectrum collection at room temperature. CH3NH3PbBr3 and CH3NH3PbCl3 are found to be p-type and n-type doped, respectively, whereas dopant-compensated CH3NH3PbBr2.94Cl0.06 alloy has over tenfold improved bulk resistivity of 3.6 × 109 Ω cm. Alloying also increases the hole mobility to 560 cm2 V−1 s−1, yielding a high mobility–lifetime product of 1.8 × 10−2 cm2 V−1. The use of a guard ring electrode in the detector reduces the crystal surface leakage current and device dark current. A distinguishable 137Cs energy spectrum with comparable or better resolution than standard scintillator detectors is collected under a small electric field of 1.8 V mm−1 at room temperature. Hybrid organic–inorganic perovskite single crystals with optimized combination of Cl and Br ions are used to fabricate γ-ray detectors operating at room temperature and competing with the performance of sodium iodide scintillators.
426 citations
TL;DR: By investigating the molecular packing arrangement in single crystals, it is found that the packing style of the compact face to face favors of long phosphorescence lifetime and high photoluminescence efficiency, with the lifetime up to 748 ms observed in the crystal of CPM.
Abstract: Long-lived phosphorescence at room temperature (RTP) from pure organic molecules is rare. Recent research reveals various crystalline organic molecules can realize RTP with lifetimes extending to the magnitude of second. There is little research on how molecular packing affecting RTP. Three compounds are designed with similar optical properties in solution, but tremendously different solid emission characteristics. By investigating the molecular packing arrangement in single crystals, it is found that the packing style of the compact face to face favors of long phosphorescence lifetime and high photoluminescence efficiency, with the lifetime up to 748 ms observed in the crystal of CPM ((9H-carbazol-9-yl)(phenyl)methanone). Theoretical calculation analysis also reveals this kind of packing style can remarkably reduce the singlet excited energy level and prompt electron communication between dimers. Surprisingly, CPM has two very similar single crystals, labeled as CPM and CPM-A, with almost identical crystal data, and the only difference is that molecules in CPM-A crystal take a little looser packing arrangement. X-ray diffraction and cross-polarization under magic spinning 13 C NMR spectra double confirm that they are different crystals. Interestingly, CPM-A crystal shows negligible RTP compared to the CPM crystal, once again proving that the packing style is critical to the RTP property.
328 citations
27 Apr 2017
TL;DR: A brief overview of binary transition metal dihalides and trihalides is given, summarizing their crystallographic properties and long-range-ordered magnetic structures, focusing on those materials with layered crystal structures and partially filled d-shells as discussed by the authors.
Abstract: Materials composed of two dimensional layers bonded to one another through weak van der Waals interactions often exhibit strongly anisotropic behaviors and can be cleaved into very thin specimens and sometimes into monolayer crystals. Interest in such materials is driven by the study of low dimensional physics and the design of functional heterostructures. Binary compounds with the compositions M X 2 and M X 3 where M is a metal cation and X is a halogen anion often form such structures. Magnetism can be incorporated by choosing a transition metal with a partially filled d-shell for M, enabling ferroic responses for enhanced functionality. Here a brief overview of binary transition metal dihalides and trihalides is given, summarizing their crystallographic properties and long-range-ordered magnetic structures, focusing on those materials with layered crystal structures and partially filled d-shells required for combining low dimensionality and cleavability with magnetism.
294 citations
TL;DR: In this article, the design and hydrothermal crystal growth of double perovskite Cs2AgInCl6 was investigated in detail, including crystal structure, morphology related to the crystal growth habit, band structure, optical properties, and stability.
Abstract: The discovery of lead-free double perovskites provides a feasible way of searching for air-stable and environmentally benign solar cell absorbers. Herein we report the design and hydrothermal crystal growth of double perovskite Cs2AgInCl6. The crystal structure, morphology related to the crystal growth habit, band structure, optical properties, and stability are investigated in detail. This perovskite crystallized in a cubic unit cell with the space group Fm3m and is composed of [AgCl6] and [InCl6] octahedra alternating in a ordered rock-salt structure, and the as-obtained crystal size is dependent on the hydrothermal reaction time. Cs2AgInCl6 is a direct gap semiconductor with a wide band gap of 3.23 eV obtained experimentally and 3.33 eV obtained by DFT calculation. This theoretically predicted and experimentally confirmed optical gap is a prototype of the band gaps that are direct and optically allowed except at the single high-symmetry k-point, which didn't raise interest before but have potential applications in future technologies. Cs2AgInCl6 material with excellent moisture, light and heat stability shows great potential for photovoltaic and other optoelectronic applications via further band gap engineering.
274 citations
TL;DR: In this article, the fabrication of large-area, high-quality 2D tellurium (tellurene) using a substrate-free solution process was reported. But the fabrication method suffers from a variety of drawbacks, including limitations in crystal size and stability.
Abstract: The reliable production of two-dimensional crystals is essential for the development of new technologies based on 2D materials. However, current synthesis methods suffer from a variety of drawbacks, including limitations in crystal size and stability. Here, we report the fabrication of large-area, high-quality 2D tellurium (tellurene) using a substrate-free solution process. Our approach can create crystals with a process-tunable thickness, from monolayer to tens of nanometres, and with lateral sizes of up to 100 um. The chiral-chain van der Waals structure of tellurene gives rise to strong in-plane anisotropic properties and large thickness dependent shifts in Raman vibrational modes, which is not observed in other 2D layered materials. We also fabricate tellurene field-effect transistors, which exhibit air-stable performance at room temperature for over two months, on off ratios on the order of 106 and field-effect mobilities of around 700 cm2 per Vs. Furthermore, by scaling down the channel length and integrating with high-k dielectrics, transistors with a significant on-state current density of 1 A mm-1 are demonstrated.
256 citations
TL;DR: Filtschew et al. as mentioned in this paper presented an ab initio density functional theory (DFT) study of the vibrational properties of ceria focusing on the interpretation of Raman spectra of polycrystalline powder samples, with vibrational bands in the frequency region between 250 and 1200 cm-1.
Abstract: Cerium oxide is an important material for catalytic and fuel cell applications. We present an ab initio density functional theory (DFT) study of the vibrational properties of ceria focusing on the interpretation of Raman spectra of polycrystalline powder samples, with vibrational bands in the frequency region between 250 and 1200 cm–1. The model systems include the oxidized CeO2 as well as the reduced CeO2–x and Ce2O3 bulk materials together with the CeO2(111) and oxygen defective CeO2–x(111) surfaces. The experimentally observed band at 250 cm–1 is assigned to a surface mode of the clean CeO2(111) surface, in agreement with our Raman spectra of ceria (CeO2) powders with varying crystal size (Filtschew, A.; Hofmann, K.; Hess, C., J. Phys. Chem. C 2016, 120, 6694). The reduced model systems display signature vibrational bands in the 480–600 cm–1 region associated with the presence of oxygen defects and reduced Ce3+ ions. In the high-frequency region between 800 and 900 cm–1, characteristic peroxide (O22–) ...
241 citations
TL;DR: Direct electron-microscopic observations of deposition growth of aligned ice crystals on feldspar, an atmospherically important component of mineral dust, are reported and molecular-scale computer simulations indicate that this alignment arises from the preferential nucleation of prismatic crystal planes of ice on high-energy surface planes of feldSpar.
Abstract: Ice formation on aerosol particles is a process of crucial importance to Earth’s climate and the environmental sciences, but it is not understood at the molecular level. This is partly because the nature of active sites, local surface features where ice growth commences, is still unclear. Here we report direct electron-microscopic observations of deposition growth of aligned ice crystals on feldspar, an atmospherically important component of mineral dust. Our molecular-scale computer simulations indicate that this alignment arises from the preferential nucleation of prismatic crystal planes of ice on high-energy (100) surface planes of feldspar. The microscopic patches of (100) surface, exposed at surface defects such as steps, cracks, and cavities, are thought to be responsible for the high ice nucleation efficacy of potassium (K)–feldspar particles.
240 citations
TL;DR: An ingenious space-limited inverse temperature crystallization method is first demonstrated to the in situ synthesis of 120 cm2 large-area CH3 NH3 PbBr3 crystal film on fluorine-doped tin oxide (FTO) glass, which enables a broad linear response range of 10-4 -102 mW cm-2 and high narrow response under low bias -1 V.
Abstract: Organometal trihalide perovskites have been attracting intense attention due to their enthralling optoelectric characteristics. Thus far, most applications focus on polycrystalline perovskite, which however, is overshadowed by single crystal perovskite with superior properties such as low trap density, high mobility, and long carrier diffusion length. In spite of the inherent advantages and significant optoelectronic applications in solar cells and photodetectors, the fabrication of large-area laminar perovskite single crystals is challenging. In this report, an ingenious space-limited inverse temperature crystallization method is first demonstrated to the in situ synthesis of 120 cm2 large-area CH3 NH3 PbBr3 crystal film on fluorine-doped tin oxide (FTO) glass. Such CH3 NH3 PbBr3 perovskite crystal film is successfully applied to narrowband photodetectors, which enables a broad linear response range of 10-4 -102 mW cm-2 , 3 dB cutoff frequency (f 3 dB ) of ≈110 kHz, and high narrow response under low bias -1 V.
239 citations
TL;DR: High-mobility atomically thin Bi2O2Se semiconductor, a typical non-neutral layered crystal without a standard vdWs gap, was synthesized via a facial chemical vapor deposition method, showing excellent controllability for thickness, domain size, nucleation site, and crystal-phase evolution.
Abstract: Non-neutral layered crystals, another group of two-dimensional (2D) materials that lack a well-defined van der Waals (vdWs) gap, are those that form strong chemical bonds in-plane but display weak out-of-plane electrostatic interactions, exhibiting intriguing properties for the bulk counterpart. However, investigation of the properties of their atomically thin counterpart are very rare presumably due to the absence of efficient ways to achieve large-area high-quality 2D crystals. Here, high-mobility atomically thin Bi2O2Se, a typical non-neutral layered crystal without a standard vdWs gap, was synthesized via a facial chemical vapor deposition (CVD) method, showing excellent controllability for thickness, domain size, nucleation site, and crystal-phase evolution. Atomically thin, large single crystals of Bi2O2Se with lateral size up to ∼200 μm and thickness down to a bilayer were obtained. Moreover, optical and electrical properties of the CVD-grown 2D Bi2O2Se crystals were investigated, displaying a size...
TL;DR: In this article, two porous ZnO nanosheets with different exposed crystal facets (0001) and (10 1 ¯ 0) were designed and synthesized by a facile hydrothermal route.
Abstract: Herein, we focused on the effects of exposed crystal planes on the gas sensing property of ZnO. For this purpose, we designed and synthesized two porous ZnO nanosheets with different exposed crystal facets (0001) and (10 1 ¯ 0) by a facile hydrothermal routes. The characterization results show that both the porous nanosheets have a near specific surface area about 7.5 m2/g, thickness about 100 nm, diameter about 5 μm and pore size of tens of nanometers. However, their dominating exposed crystal facets are (0001) and (10 1 ¯ 0), respectively. When employed them as sensing materials in gas sensors, porous ZnO nanosheets with dominating exposed (0001) facet exhibit a superior sensitivity than the (10 1 ¯ 0) one. The enhanced gas response is attributed to a large amount of oxygen vacancy defects and unsaturated dangling bonds existing in the ZnO nanosheets with exposed crystal facet (0001), which is favorable for the adsorption of gas molecular on the sensor surface and result in improvement of the gas response. Finally, the calculation of the chemisorption energy of oxygen on ZnO crystal facets also proves the reactive-facet-enhanced gas sensitivity.
TL;DR: 2D Fe2Si nanosheet, one counterpart of Hapkeite mineral discovered in meteorite with novel magnetism is proposed on the basis of first-principles calculations and has a high thermodynamic stability and its 2D lattice can be retained at the temperature up to 1200 K.
Abstract: Searching experimental feasible two-dimensional (2D) ferromagnetic crystals with large spin-polarization ratio, high Curie temperature and large magnetic anisotropic energy is one key to develop next-generation spintronic nanodevices. Here, 2D Fe2Si nanosheet, one counterpart of Hapkeite mineral discovered in meteorite with novel magnetism is proposed on the basis of first-principles calculations. The 2D Fe2Si crystal has a slightly buckled triangular lattice with planar hexacoordinated Si and Fe atoms. The spin-polarized calculations with hybrid HSE06 function method indicate that 2D Fe2Si is a ferromagnetic half metal at its ground state with 100% spin-polarization ratio at Fermi energy level. The phonon spectrum calculation and ab initio molecular dynamic simulation shows that 2D Fe2Si crystal has a high thermodynamic stability and its 2D lattice can be retained at the temperature up to 1200 K. Monte Carlo simulations based on the Ising model predict a Curie temperature over 780 K in 2D Fe2Si crystal, ...
TL;DR: In this article, a dual solution-shearing method utilizing the semiconductor concentration region close to the solubility limit was developed, which successfully generated large area and high performance semiconductor monolayer crystals on the millimeter scale.
Abstract: This work innovatively develops a dual solution-shearing method utilizing the semiconductor concentration region close to the solubility limit, which successfully generates large-area and high-performance semiconductor monolayer crystals on the millimeter scale. The monolayer crystals with poly(methyl methacrylate) encapsulation show the highest mobility of 10.4 cm2 V−1 s−1 among the mobility values in the reported solution-processed semiconductor monolayers. With similar mobility to multilayer crystals, light is shed on the charge accumulation mechanism in organic field-effect transistors (OFETs), where the first layer on interface bears the most carrier transport task, and the other above layers work as carrier suppliers and encapsulations to the first layer. The monolayer crystals show a very low dependency on channel directions with a small anisotropic ratio of 1.3. The positive mobility–temperature correlation reveals a thermally activated carrier transport mode in the monolayer crystals, which is different from the band-like transport mode in multilayer crystals. Furthermore, because of the direct exposure of highly conductive channels, the monolayer crystal based OFETs can sense ammonia concentrations as low as 10 ppb. The decent sensitivity indicates the monolayer crystals are potential candidates for sensor applications.
TL;DR: A strategy is outlined for the design of hand-twisted helical crystals, a new type of bendable crystals in which plastic behavior is seen with a fair degree of isotropic character in the crystal packing.
Abstract: A strategy is outlined for the design of hand-twisted helical crystals. The starting point in the exercise is the one-dimensional (1D) plastic crystal, 1,4-dibromobenzene, which is then changed to a 1D elastic crystal, exemplified by 4-bromophenyl 4′-chlorobenzoate, by introduction of a molecular synthon −O–CO– in lieu of the supramolecular synthon Br···Br in the precursor. The 1D elastic crystals are next modified to two-dimensional (2D) elastic crystals, of the type 4-bromophenyl 4′-nitrobenzoate where the halogen bonding and C–H···O hydrogen bonding are well-matched. Finally, varying the interaction strengths in these 2D elastic crystals gives plastic crystals with two pairs of bendable faces but without slip planes. Typical examples are 4-chlorophenyl and 4-bromophenyl 4′-nitrobenzoate. This type of 2D plasticity represents a new type of bendable crystals in which plastic behavior is seen with a fair degree of isotropic character in the crystal packing. The presence of two sets of bendable faces, gene...
TL;DR: The structural and photophysical characteristics of MAPbBr3 single crystals prepared using the inverse temperature crystallization method are evaluated using temperature-dependent X-ray diffraction and optical spectroscopy to reveal the effect of the desorption/adsorption of gas molecules on the crystal surface on the PL lifetimes.
Abstract: The structural and photophysical characteristics of MAPbBr3 single crystals prepared using the inverse temperature crystallization method are evaluated using temperature-dependent X-ray diffraction (XRD) and optical spectroscopy. Contrary to previous research reports on perovskite materials, we study phase transitions in crystal lattice structures accompanied with changes in optical properties expand throughout a wide temperature range of 300–1.5 K. The XRD studies reveal several phase transitions occurred at ~210 K, ~145 K, and ~80 K, respectively. The coexistence of two different crystallographic phases was observed at a temperature below 145 K. The emission peaks in the PL spectra are all asymmetric in line shape with weak and broad shoulders near the absorption edges, which are attributed to the Br atom vacancy on the surface of the crystals. The time-resolved PL measurements reveal the effect of the desorption/adsorption of gas molecules on the crystal surface on the PL lifetimes. Raman spectroscopy results indicate the strong interplays between cations and different halide atoms. Lastly, no diamagnetic shift or split in emission peaks can be observed in the magneto-PL spectra even at an applied magnetic field up to 5 T and at a temperature as low as 1.5 K.
TL;DR: In this paper, the formation process for the regular decahedron BiVO4 crystals prepared by a convenient hydrothermal method was investigated, and the phase was transformed from tetragonal zircon type to monoclinic sheelite type.
Abstract: Precise control of the morphology and crystalline structure of semiconductor-based photocatalyst is crucial for improving the efficiency of solar energy conversion system. In this work, taking BiVO4 semiconductor photocatalyst as an example, we investigated the formation process for the regular decahedron BiVO4 crystals prepared by a convenient hydrothermal method and found that the synthesis is undergoing a dissolution–recrystallization process, concomitantly, the phase was transformed from tetragonal zircon type to monoclinic sheelite-type. By controlling the kinetics of crystal growth for BiVO4 through regulating acidity of the reaction solution, we rationally tune the morphology of monoclinic BiVO4 from regular decahedron crystals to short rod-like particles, particularly precisely modulate the proportion of {010}/{011} facets for the decahedron BiVO4. By tuning the crystalline phase and morphologies of BiVO4 crystal, we found that the photocatalytic water oxidation activity for the well-defined BiVO4...
TL;DR: The discussion shows that high-pressure study can be used as an effective means to tune the structure and properties of all-inorganic halide perovskites.
Abstract: Perovskite photovoltaic materials are gaining sustained attention because of their excellent photovoltaic properties and extensive practical applicability. In this Letter, we discuss the changes in the structure and optical properties of CsPbBr3 under high pressure. As the pressure increased, the band gap initially began to red shift before 1.0 GPa followed by a continuous blue shift until the crystal was completely amorphized. An isostructural phase transition at 1.2 GPa was determined by high-pressure synchrotron X-ray and Raman spectroscopy. The result could be attributed to bond length shrinkage and PbBr6 octahedral distortion under high pressure. The amorphization of the crystal was due to the severe distortion and tilt of the PbBr6 octahedron, leading to broken long-range order. Changes in optical properties are closely related to the evolution of the crystal structure. Our discussion shows that high-pressure study can be used as an effective means to tune the structure and properties of all-inorgan...
TL;DR: An experimental study of epitaxial Te deposited on highly oriented pyrolytic graphite (HOPG) by molecular-beam epitaxy using density functional theory calculations reveals rectangular surface cells with the cell size consistent with the theoretically predicted β-tellurene.
Abstract: Monolayer tellurium (Te) or tellurene has been suggested by a recent theory as a new two-dimensional (2D) system with great electronic and optoelectronic promises. Here we present an experimental study of epitaxial Te deposited on highly oriented pyrolytic graphite (HOPG) by molecular-beam epitaxy. Scanning tunneling microscopy of ultrathin layers of Te reveals rectangular surface cells with the cell size consistent with the theoretically predicted β-tellurene, whereas for thicker films, the cell size is more consistent with that of the [100] surface of the bulk Te crystal. Scanning tunneling spectroscopy measurements show that the films are semiconductors with the energy band gaps decreasing with increasing film thickness, and the gap narrowing occurs predominantly at the valence-band maximum (VBM). The latter is understood by strong coupling of states at the VBM but a weak coupling at conduction band minimum (CBM) as revealed by density functional theory calculations.
TL;DR: It is demonstrated that a crystal appears within a noncrystalline particle assembling lysozyme on an ASP or a container wall, highlighting the role of heterogeneous nucleation.
Abstract: Nucleation, the primary step in crystallization, dictates the number of crystals, the distribution of their sizes, the polymorph selection, and other crucial properties of the crystal population. We used time-resolved liquid-cell transmission electron microscopy (TEM) to perform an in situ examination of the nucleation of lysozyme crystals. Our TEM images revealed that mesoscopic clusters, which are similar to those previously assumed to consist of a dense liquid and serve as nucleation precursors, are actually amorphous solid particles (ASPs) and act only as heterogeneous nucleation sites. Crystalline phases never form inside them. We demonstrate that a crystal appears within a noncrystalline particle assembling lysozyme on an ASP or a container wall, highlighting the role of heterogeneous nucleation. These findings represent a significant departure from the existing formulation of the two-step nucleation mechanism while reaffirming the role of noncrystalline particles. The insights gained may have significant implications in areas that rely on the production of protein crystals, such as structural biology, pharmacy, and biophysics, and for the fundamental understanding of crystallization mechanisms.
TL;DR: A brief overview of binary transition metal dihalides and trihalides is given, summarizing their crystallographic properties and long-range-ordered magnetic structures, focusing on those materials with layered crystal structures and partially filled d-shells.
Abstract: Materials composed of two dimensional layers bonded to one another through weak van der Waals interactions often exhibit strongly anisotropic behaviors and can be cleaved into very thin specimens and sometimes into monolayer crystals. Interest in such materials is driven by the study of low dimensional physics and the design of functional heterostructures. Binary compounds with the compositions MX2 and MX3 where M is a metal cation and X is a halogen anion often form such structures. Magnetism can be incorporated by choosing a transition metal with a partially filled d-shell for M, enabling ferroic responses for enhanced functionality. Here a brief overview of binary transition metal dihalides and trihalides is given, summarizing their crystallographic properties and long-range-ordered magnetic structures, focusing on those materials with layered crystal structures and partially filled d-shells required for combining low dimensionality and cleavability with magnetism.
TL;DR: An acid/base co-modulation strategy to the large-scale synthesis of monodisperse UiO-66 crystals with acetic acid for modulating crystal shape and with triethylamine as a base for controlling the nucleation of crystallization and tuning the formation of missing linker defects via promoting presumably the singe deprotonation of terephthalic acid linkers is reported.
Abstract: Beyond their pore structures and surface chemistry, precise controls over other attributes of metal–organic frameworks (MOFs) such as shapes, sizes, and defects are also favorable to their fundamental studies and applications but still remain challenging. Herein, we reported an acid/base co-modulation strategy to the large-scale synthesis of monodisperse UiO-66 crystals with acetic acid for modulating crystal shape and with triethylamine (TEA) as a base for controlling the nucleation of crystallization and tuning the formation of missing linker defects via promoting presumably the singe deprotonation of terephthalic acid linkers. The obtained monodisperse MOF crystals have a well-defined octahedral shape, tunable sizes ranging from ∼500 nm to ∼2 μm, and high thermal stability. Their assembled-monolayers are responsive to methanol vapor with the crystal size-dependent and defect-relevant sensing performances.
TL;DR: In this paper, a creative electronic dynamic gradient (EDG) method was used to grow a CsPbBr3 single crystal with a perfect single crystal preferentially orienting in the (110) direction and met the basic demand of its applications.
Abstract: As a typical representative of all-inorganic lead halide perovskites, cesium lead bromide (CsPbBr3) has attracted significant attention in the context of photovoltaics and other optoelectronic applications in recent years. In this paper, CsPbBr3 single crystal growth was conducted by a creative electronic dynamic gradient (EDG) method. The crystal structure was systematically investigated using scientific instruments and equipment. X-ray diffraction techniques, including X-ray diffraction (XRD), temperature-dependent X-ray powder diffraction and the X-ray rocking curve, were used to identify the phase and to investigate phase transition rules. Electron diffraction techniques, including high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) and electron backscatter diffraction (EBSD), were used to investigate the crystal micro-structure. The final results indicated that the grown CsPbBr3 crystal was a perfect single crystal preferentially orienting in the (110) direction and met the basic demand of its applications.
TL;DR: P polarization-resolved optical transmission and photoluminescence spectroscopy of excitons in 1T'-ReSe2 pave the way for polarization-sensitive applications, such as optical logic circuits operating in the infrared spectral region.
Abstract: Atomically thin materials such as graphene or MoS2 are of high in-plane symmetry. Crystals with reduced symmetry hold the promise for novel optoelectronic devices based on their anisotropy in current flow or light polarization. Here, we present polarization-resolved optical transmission and photoluminescence spectroscopy of excitons in 1T′-ReSe2. On reducing the crystal thickness from bulk to a monolayer, we observe a strong blue shift of the optical band gap from 1.37 to 1.50 eV. The excitons are strongly polarized with dipole vectors along different crystal directions, which persist from bulk down to monolayer thickness. The experimental results are well reproduced by ab initio calculations based on the GW-BSE approach within LDA+GdW approximation. The excitons have high binding energies of 860 meV for the monolayer and 120 meV for bulk. They are strongly confined within a single layer even for the bulk crystal. In addition, we find in our calculations a direct band gap in 1T′-ReSe2 regardless of crysta...
TL;DR: The synthesis of a gold nanocluster is synthesized whose composition is determined to be Au60S6(SCH2Ph)36 by using electrospray ionization mass spectrometry and single crystal X-ray crystallography (SCXC), and the fourth crystallographic closest-packed pattern, termed 6H left-handed helical (6HLH) arrangement, which results in the distinct loss of solid photoluminescence of amorphous Au 60S6
Abstract: Metal nanoclusters have recently attracted extensive interest not only for fundamental scientific research, but also for practical applications. For fundamental scientific research, it is of major importance to explore the internal structure and crystallographic arrangement. Herein, we synthesize a gold nanocluster whose composition is determined to be Au60S6(SCH2Ph)36 by using electrospray ionization mass spectrometry and single crystal X-ray crystallography (SCXC). SCXC also reveals that Au60S6(SCH2Ph)36 consists of a fcc-like Au20 kernel protected by a pair of giant Au20S3(SCH2Ph)18 staple motifs, which contain 6 tetrahedral-coordinate μ4-S atoms not previously reported in the Au-S interface. Importantly, the fourth crystallographic closest-packed pattern, termed 6H left-handed helical (6HLH) arrangement, which results in the distinct loss of solid photoluminescence of amorphous Au60S6(SCH2Ph)36, is found in the crystals of Au60S6(SCH2Ph)36. The solvent-polarity-dependent solution photoluminescence is also demonstrated. Overall, this work provides important insights about the structure, Au-S bonding and solid photoluminescence of gold nanoclusters.
TL;DR: The spin-polarized second harmonic generation (SHG) of the recently synthesized CaCoSO single crystal is performed based on the calculated electronic band structure and the microscopic first hyperpolarizability, βijk, is calculated.
Abstract: The spin-polarized second harmonic generation (SHG) of the recently synthesized CaCoSO single crystal is performed based on the calculated electronic band structure. The calculation reveals that the spin-up (↑) channel of CaCoSO possesses a direct energy gap (Γv-Γc) of about 2.187 eV, 1.187 eV (Kv-Kc) for the spin-down (↓) channel and an indirect gap (Γv-Kc) of about 0.4 eV for the spin-polarized CaCoSO single crystal. The linear optical properties obtained reveal that the recently synthesized crystal exhibits considerable anisotropy with negative uniaxial anisotropy and birefringence favor to enhance the SHG. We have calculated the three non-zero tensor components of the SHG and found the is the dominat component, one with a large SHG of about (d33 = 6.936 pm/V at λ = 1064 nm), the half value of KTiOPO4 (KTP). As the values of (↑) (↓) 1.187 eV> spin-polarized gap 0.4 eV; therefore, a smaller energy gap gives better SHG performance. Furthermore, the microscopic first hyperpolarizability, βijk, is calculated.
TL;DR: In this paper, the edge-defined film-fed growth (EFG) technique was utilized to grow the (100)-oriented β-Ga2O3 single crystal substrate that shows good crystal quality characterized by X-ray diffraction and high resolution transmission electron microscope.
Abstract: The Pt/β-Ga2O3 Schottky barrier diode and its temperature-dependent current-voltage characteristics were investigated for power device application. The edge-defined film-fed growth (EFG) technique was utilized to grow the (100)-oriented β-Ga2O3 single crystal substrate that shows good crystal quality characterized by X-ray diffraction and high resolution transmission electron microscope. Ohmic and Schottky electrodes were fabricated by depositing Ti and Pt metals on the two surfaces, respectively. Through the current-voltage (I-V) measurement under different temperature and the thermionic emission modeling, the fabricated Pt/β-Ga2O3 Schottky diode was found to show good performances at room temperature, including rectification ratio of 1010, ideality factor (n) of 1.1, Schottky barrier height (ΦB) of 1.39 eV, threshold voltage (Vbi) of 1.07 V, ON-resistance (RON) of 12.5 mΩ·cm2, forward current density at 2 V (J@2V) of 56 A/cm2, and saturation current density (J0) of 2 × 10−16 A/cm2. The effective donor c...
TL;DR: In this article, the chemical vapor deposition (CVD) growth of atomic-layer SnS2 with a large crystal size and uniformity was reported, with an octahedral lattice made of two atomic layers of sulfur and one atomic layer of tin.
Abstract: Two-dimensional layers of metal dichalcogenides have attracted much attention because of their ultrathin thickness and potential applications in electronics and optoelectronics. Monolayer SnS2, with a band gap of ~2.6 eV, has an octahedral lattice made of two atomic layers of sulfur and one atomic layer of tin. Till date, there have been limited reports on the growth of large-scale and high quality SnS2 atomic layers and the investigation of their properties as a semiconductor. Here, we report the chemical vapor deposition (CVD) growth of atomic-layer SnS2 with a large crystal size and uniformity. In addition, the number of layers can be changed from a monolayer to few layers and to bulk by changing the growth time. Scanning transmission electron microscopy was used to analyze the atomic structure and demonstrate the 2H stacking poly-type of different layers. The resultant SnS2 crystals is used as a photodetector with external quantum efficiency as high as 150%, suggesting promise for optoelectronic applications.
TL;DR: The synthesis and characterization of CsPb2 Br5 bulk single crystals are presented, which enabled the material's optical features to be clarified, and it is shown that the material exhibits 3.1 eV indirect band gap with no emission in the visible spectrum.
Abstract: CsPb2Br5 is a ternary halogen-plumbate material with close characteristics to the well-reported halide perovskites. Owing to its unconventional two-dimensional structure, CsPb2Br5 is being looked at broadly for potential applications in optoelectronics. CsPb2Br5 investigations are currently limited to nanostructures and powder forms of the material, which present unclear and conflicting optical properties. In this study, we present the synthesis and characterization of CsPb2Br5 bulk single crystals, which enabled us to finally clarify the material's optical features. Our CsPb2Br5 crystal has a two-dimensional structure with Pb2Br5− layers spaced by Cs+ cations, and exhibits approximately 3.1 eV indirect band gap with no emission in the visible spectrum.
TL;DR: In this paper, single crystals of the birefringent material Ba2Ca(B3O6)2 (BCBO) with dimensions up to 40 × 28 × 10 mm3 were successfully grown by top-seeded solution growth (TSSG) method from B2O3-NaF flux.
Abstract: Single crystals of the birefringent material Ba2Ca(B3O6)2 (BCBO) with dimensions up to 40 × 28 × 10 mm3 were successfully grown by top-seeded solution growth (TSSG) method from B2O3–NaF flux. It exhibits high transmittance in the range of 190–3000 nm with UV cutoff of 178 nm, which is much shorter than that (189 nm) of the commercial UV birefringent crystal, the high-temperature phase of BaB2O4 (α-BBO). Meanwhile, BCBO crystal has large birefringence (Δn = no – ne = 0.2524–0.0862) in the wavelength range from 178 to 3000 nm and without phase transition from room temperature to the melting point. A prototype of Glan–Taylor polarizer made from BCBO crystal showed an optical extinction ratio of 104:1, which is comparable to those of commercial birefringence crystals. The experimental results demonstrate that the BCBO crystal can be a new promising birefringent crystal for UV, especially the sub-200 nm deep-UV range.