Showing papers on "Single crystal published in 2017"
TL;DR: It is shown that utilizing the below-bandgap absorption of perovskite single crystals can narrow down their effective optical bandgap without changing the composition, resulting in an efficiency of 17.8% for single crystal perovSKite solar cells.
Abstract: The efficiency of perovskite solar cells has surged in the past few years, while the bandgaps of current perovskite materials for record efficiencies are much larger than the optimal value, which makes the efficiency far lower than the Shockley-Queisser efficiency limit. Here we show that utilizing the below-bandgap absorption of perovskite single crystals can narrow down their effective optical bandgap without changing the composition. Thin methylammonium lead triiodide single crystals with tuned thickness of tens of micrometers are directly grown on hole-transport-layer covered substrates by a hydrophobic interface confined lateral crystal growth method. The spectral response of the methylammonium lead triiodide single crystal solar cells is extended to 820 nm, 20 nm broader than the corresponding polycrystalline thin-film solar cells. The open-circuit voltage and fill factor are not sacrificed, resulting in an efficiency of 17.8% for single crystal perovskite solar cells.
415 citations
265 citations
TL;DR: This work combines 3D atomic structure determination of crystal defects with DFT calculations, which is expected to advance the understanding of structure–property relationships at the fundamental level.
Abstract: Perfect crystals are rare in nature. Real materials often contain crystal defects and chemical order/disorder such as grain boundaries, dislocations, interfaces, surface reconstructions and point defects. Such disruption in periodicity strongly affects material properties and functionality. Despite rapid development of quantitative material characterization methods, correlating three-dimensional (3D) atomic arrangements of chemical order/disorder and crystal defects with material properties remains a challenge. On a parallel front, quantum mechanics calculations such as density functional theory (DFT) have progressed from the modelling of ideal bulk systems to modelling 'real' materials with dopants, dislocations, grain boundaries and interfaces; but these calculations rely heavily on average atomic models extracted from crystallography. To improve the predictive power of first-principles calculations, there is a pressing need to use atomic coordinates of real systems beyond average crystallographic measurements. Here we determine the 3D coordinates of 6,569 iron and 16,627 platinum atoms in an iron-platinum nanoparticle, and correlate chemical order/disorder and crystal defects with material properties at the single-atom level. We identify rich structural variety with unprecedented 3D detail including atomic composition, grain boundaries, anti-phase boundaries, anti-site point defects and swap defects. We show that the experimentally measured coordinates and chemical species with 22 picometre precision can be used as direct input for DFT calculations of material properties such as atomic spin and orbital magnetic moments and local magnetocrystalline anisotropy. This work combines 3D atomic structure determination of crystal defects with DFT calculations, which is expected to advance our understanding of structure-property relationships at the fundamental level.
259 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: In this article, the growth of CsPbBr3 single crystal was revealed to be of a 2D nucleation mechanism and the similarity of d values and octahedra arrangements along [101] and [020] orientations restricted single-crystal growth.
Abstract: Band gap tunable hybrid organic–inorganic lead halide perovskites (APbX3, A = CH3NH3+ and NH2CH═NH2+, and X = Cl, Br, or I) have attracted significant attention in optoelectronic- and photovoltaic-related fields on account of their outstanding optoelectronic properties. Single crystals of hybrid perovskites, such as CH3NH3PbI3 and CH3NH3PbBr3, were certified to be advantageous over thin films as photodetectors. However, their resistance toward heat and moisture hinders their future development. Fully inorganic perovskite CsPbBr3 stands a chance to fill the gap as a novel photodetector with perovskite structure. We revealed the growth of CsPbBr3 single crystal was of a 2D nucleation mechanism. Similarities of d values and octahedra arrangements along [101] and [020] orientations restricted single-crystal growth. Under optimized conditions, orthorhombic CsPbBr3 single crystals with (101) crystallographic facets were grown by using methyl alcohol as antisolvent from saturated DMSO solution. The optoelectroni...
219 citations
TL;DR: A novel Cu(II)-azolate metal-organic framework (MOF) with tubular pores undergoes a reversible single crystal to single crystal transition between neutral and anionic phases upon reaction with stoichiometric amounts of halide or pseudohalide salts, allowing loading of record amounts of charge-balancing Li+, Na+, and Mg2+ ions for MOFs.
Abstract: A novel Cu(II)–azolate metal–organic framework (MOF) with tubular pores undergoes a reversible single crystal to single crystal transition between neutral and anionic phases upon reaction with stoichiometric amounts of halide or pseudohalide salts. The stoichiometric transformation between the two phases allows loading of record amounts of charge-balancing Li+, Na+, and Mg2+ ions for MOFs. Whereas the halide/pseudohalide anions are bound to the metal centers and thus stationary, the cations move freely within the one-dimensional pores, giving rise to single-ion solid electrolytes. The respective Li+-, Na+-, and Mg2+-loaded materials exhibit high ionic conductivity values of 4.4 × 10–5, 1.8 × 10–5, and 8.8 × 10–7 S/cm. With addition of LiBF4, the Li+ conductivity improves to 4.8 × 10–4 S/cm. These are the highest values yet observed for MOF solid electrolytes.
199 citations
TL;DR: Time-resolved photoluminescence, transient reflection spectroscopy, and electrical transport measurements show that the CsPbBr3 epitaxial thin film has a slow charge carrier recombination rate, low surface recombination velocity, and low defect density of 1012 cm-3, which are comparable to those of cesium lead bromide perovskite single crystals.
Abstract: High-quality metal halide perovskite single crystals have low defect densities and excellent photophysical properties, yet thin films are the most sought after material geometry for optoelectronic devices. Perovskite single-crystal thin films (SCTFs) would be highly desirable for high-performance devices, but their growth remains challenging, particularly for inorganic metal halide perovskites. Herein, we report the facile vapor-phase epitaxial growth of cesium lead bromide perovskite (CsPbBr3) continuous SCTFs with controllable micrometer thickness, as well as nanoplate arrays, on traditional oxide perovskite SrTiO3(100) substrates. Heteroepitaxial single-crystal growth is enabled by the serendipitous incommensurate lattice match between these two perovskites, and overcoming the limitation of island-forming Volmer–Weber crystal growth is critical for growing large-area continuous thin films. Time-resolved photoluminescence, transient reflection spectroscopy, and electrical transport measurements show tha...
191 citations
TL;DR: SEM study confirm the formation of nanorods and single crystal nanosheets of very few nanometers in size and relaxed nanostructure formation and occurrence of confinement effect in Nd3+ doped PbI2 synthesized via microwave-assisted technique.
Abstract: Hexagonal single crystal nanosheets of Nd3+ doped PbI2 were effortlessly synthesized via microwave-assisted technique under a power of 700 W and in a duration of 15 minutes with a homogeneous morphology. X-ray diffraction, energy dispersive X-ray spectroscope, scanning electron microscope, FT-Raman, UV-Visible, photoluminescence and dielectric measurement were employed to study the product. High purity, single phase and presence of Nd3+ doping was confirmed. SEM study confirm the formation of nanorods and single crystal nanosheets of very few nanometers in size. Robust vibrational analysis has been carried out and the observed bands are assigned to the vibration modes of E21, A11, A12, 2E21 and 2E11, respectively. These bands are red-shifted when compare to the corresponding bulk values which indicate relaxed nanostructure formation and occurrence of confinement effect. The thickness of the synthesized single crystal nanosheets are found to be in the range of ~20 to 30 nm. The energy band gap was calculated and found to be 3.35, 3.34, 3.42 and 3.39 eV for pure, 1, 3 and 5% Nd3+ doped lead iodide, respectively. The clear blue luminescence has been observed at 440 nm and 466 nm when excited at 250 nm and 280 nm respectively. Dielectric and ac electrical conductivity was also measured and discussed.
189 citations
TL;DR: In this paper, an in situ synthetic strategy for the construct of carbon-doped TiO2 single crystal nanorods using cationic polystyrene spheres (CPS) as the precursors of the nanorod and carbon source via a facile hydrothermal route was proposed.
Abstract: Incorporating dopants into the TiO2 single crystals lattice is a big challenge because single crystal has a high crystallinity and the nucleation and growth of TiO2 single crystals is readily subjected to the interference of the dose of dopant precursors. Here, we propose an in situ synthetic strategy for the construct of carbon-doped TiO2 single crystal nanorods using CPS/TiO2 as the precursors of TiO2 nanorods and carbon source via a facile hydrothermal route. This technique involves the preparation of cationic polystyrene spheres (CPS), sequential deposition of TiO2 precursor, hydrothermal reaction, and the pyrolysis of CPS in a N2 atmosphere at 450 °C. The morphology and structure of as-prepared C-TiO2 single crystal nanorods were characterized by TEM, SEM, STEM Mapping, XRD, UV–vis spectroscopy, and XPS. All results confirm the carbon doping in the as-prepared TiO2 single crystal nanorods. As a result of unique microstructure, the resulting TiO2 exhibits remarkably visible-light photocatalytic efficiency for the degradation of organic pollutants including methylene blue (MB), Rhodamine B (RhB) and p-nitrophenol (PNP). Therefore, the current study provides a new insight for incorporating dopants into the TiO2 single crystals lattice.
180 citations
TL;DR: It is found that Br incorporation can effectively control the perovskite crystallization kinetics and reduce defect density to acquire high-quality single crystals with significant inhibition of δ-phase.
Abstract: The spontaneous α-to-δ phase transition of the formamidinium-based (FA) lead halide perovskite hinders its large scale application in solar cells. Though this phase transition can be inhibited by alloying with methylammonium-based (MA) perovskite, the underlying mechanism is largely unexplored. In this Communication, we grow high-quality mixed cations and halides perovskite single crystals (FAPbI3)1–x(MAPbBr3)x to understand the principles for maintaining pure perovskite phase, which is essential to device optimization. We demonstrate that the best composition for a perfect α-phase perovskite without segregation is x = 0.1–0.15, and such a mixed perovskite exhibits carrier lifetime as long as 11.0 μs, which is over 20 times of that of FAPbI3 single crystal. Powder XRD, single crystal XRD and FT-IR results reveal that the incorporation of MA+ is critical for tuning the effective Goldschmidt tolerance factor toward the ideal value of 1 and lowering the Gibbs free energy via unit cell contraction and cation ...
173 citations
TL;DR: In this article, it is revealed that melt-synthesized cesium tin iodide (CsSnI3) ingots containing high-quality large single crystal (SC) grains transcend these fundamental limitations.
Abstract: Sn-based perovskites are promising Pb-free photovoltaic materials with an ideal 1.3 eV bandgap. However, to date, Sn-based thin film perovskite solar cells have yielded relatively low power conversion efficiencies (PCEs). This is traced to their poor photophysical properties (i.e., short diffusion lengths (<30 nm) and two orders of magnitude higher defect densities) than Pb-based systems. Herein, it is revealed that melt-synthesized cesium tin iodide (CsSnI3) ingots containing high-quality large single crystal (SC) grains transcend these fundamental limitations. Through detailed optical spectroscopy, their inherently superior properties are uncovered, with bulk carrier lifetimes reaching 6.6 ns, doping concentrations of around 4.5 × 1017 cm−3, and minority-carrier diffusion lengths approaching 1 µm, as compared to their polycrystalline counterparts having ≈54 ps, ≈9.2 × 1018 cm−3, and ≈16 nm, respectively. CsSnI3 SCs also exhibit very low surface recombination velocity of ≈2 × 103 cm s−1, similar to Pb-based perovskites. Importantly, these key parameters are comparable to high-performance p-type photovoltaic materials (e.g., InP crystals). The findings predict a PCE of ≈23% for optimized CsSnI3 SCs solar cells, highlighting their great potential.
TL;DR: The exciton binding energy and reduced mass of single crystals of methylammonium lead triiodide using magneto-reflectivity at very high magnetic fields is accurately determined and almost identical to the value found in polycrystalline samples.
Abstract: We have accurately determined the exciton binding energy and reduced mass of single crystals of methylammonium lead triiodide using magneto-reflectivity at very high magnetic fields. The single crystal has excellent optical properties with a narrow line width of ∼3 meV for the excitonic transitions and a 2s transition that is clearly visible even at zero magnetic field. The exciton binding energy of 16 ± 2 meV in the low-temperature orthorhombic phase is almost identical to the value found in polycrystalline samples, crucially ruling out any possibility that the exciton binding energy depends on the grain size. In the room-temperature tetragonal phase, an upper limit for the exciton binding energy of 12 ± 4 meV is estimated from the evolution of 1s–2s splitting at high magnetic field.
TL;DR: A facile roll-printing method based on transfer of a perovskite ink solution via a patterned rolling mould to a heated substrate, where the solution crystallizes instantly with the immediate evaporation of the solvent, for the fabrication of large-scale, single-crystal CH3NH3PbI3 perovkite thin films.
Abstract: We report a facile roll-printing method, geometrically confined lateral crystal growth, for the fabrication of large-scale, single-crystal CH3NH3PbI3 perovskite thin films. Geometrically confined lateral crystal growth is based on transfer of a perovskite ink solution via a patterned rolling mould to a heated substrate, where the solution crystallizes instantly with the immediate evaporation of the solvent. The striking feature of this method is that the instant crystallization of the feeding solution under geometrical confinement leads to the unidirectional lateral growth of single-crystal perovskites. Here, we fabricated single-crystal perovskites in the form of a patterned thin film (3 × 3 inch) with a high carrier mobility of 45.64 cm2 V−1 s−1. We also used these single-crystal perovskite thin films to construct solar cells with a lateral configuration. Their active-area power conversion efficiency shows a highest value of 4.83%, which exceeds the literature efficiency values of lateral perovskite solar cells. Wafer-scale deposition of uniform metal halide perovskite single-crystals is a step towards commercialisation. Using geometrically-confined lateral crystal growth, Leeet al., report patterned thin films of highly-aligned single-crystals and achieve lateral solar cells with efficiencies up to 4.83%.
TL;DR: It is shown that a diamond single crystal with a diameter of ~90 mm and a weight of 155 carat can be grown from such a carbon film which initially consisted of 2 · 1013 individual grains.
Abstract: A detailed mechanism for heteroepitaxial diamond nucleation under ion bombardment in a microwave plasma enhanced chemical vapour deposition setup on the single crystal surface of iridium is presented. The novel mechanism of Ion Bombardment Induced Buried Lateral Growth (IBI-BLG) is based on the ion bombardment induced formation and lateral spread of epitaxial diamond within a ~1 nm thick carbon layer. Starting from one single primary nucleation event the buried epitaxial island can expand laterally over distances of several microns. During this epitaxial lateral growth typically thousands of isolated secondary nuclei are generated continuously. The unique process is so far only observed on iridium surfaces. It is shown that a diamond single crystal with a diameter of ~90 mm and a weight of 155 carat can be grown from such a carbon film which initially consisted of 2 · 1013 individual grains.
TL;DR: In this article, the effect of white light illumination on the electronic and chemical properties of mixed halide perovskite (CH3NH3PbI3−xClx) thin films and single crystals using photoelectron and absorption spectroscopy was investigated.
Abstract: This study investigates the effect of white light illumination on the electronic and chemical properties of mixed halide perovskite (CH3NH3PbI3−xClx) thin films and CH3NH3PbI3 single crystals using photoelectron and absorption spectroscopy. The pristine materials' surfaces are found to be n-type because of surface band bending due to the presence of donor levels, likely consisting of reduced lead (Pb0) that acts as surface traps. When illuminating the sample with white light (up to 1 sun), the valence features shifted to lower binding energy due to surface photovoltage, i.e., the bulk of the materials is much less n-type. However, the surface photovoltage is only partially reversible and vanishes for prolonged illumination time. Concomitantly, a high concentration of metallic Pb0 is found, which induces strong Fermi-level pinning and quenching of the surface photovoltage. This is accompanied also by the formation of PbI2 defects. Similar experiments on single crystals reveal the presence of a high concentration of reduced (metallic) Pb0 at the sample surface after cleaving. The present findings indicate that the chemical and electronic properties of perovskite films are very sensitive to white light illumination. Accounting for these light-induced material changes is important to fully understand its photophysical properties and for improving the lifetime of perovskite-based devices.
TL;DR: In this article, a series of perovskite single crystals with mixed organic cations (APbI3, A = CH3NH3+, MA+; or CH(NH2)2+, FA+) along the compositional space were synthesized via inverse temperature crystallization assisted by hydroiodic acid, where the quality of the crystals could be judiciously controlled by the thermodynamic process.
Abstract: Organic–inorganic hybrid perovskites with mixed organic cations and/or halides have attracted increasing attention due to their superior optoelectronic properties, which are tailorable for different applications. To obtain a deeper understanding of materials properties, single crystals are regarded as the best platform among various building blocks for fundamental study. Here, we synthesized a series of perovskite single crystals with mixed organic cations (APbI3, A = CH3NH3+, MA+; or CH(NH2)2+, FA+) along the compositional space, and conducted a systematic investigation to correlate the carrier behavior with the organic cations. The single crystals were synthesized via inverse temperature crystallization assisted by hydroiodic acid, where the quality of the crystals could be judiciously controlled by the thermodynamic process. It is found that the substitution of 15% MA+ in FAPbI3 single crystals stabilizes the phase with the best charge transport characteristics. Both photodetector and J–V measurements suggested that FA0.85MA0.15PbI3 single crystal exhibits suppressed ion migration compared with the counterpart FA0.15MA0.85PbI3 single crystal. These results represent an important step to highlight the role of organic cations in hybrid perovskite materials, which will further benefit fundamental understanding of materials and device optimization.
TL;DR: A viologen-based Borromean entangled porous framework was found to be sensitive to both CuKα and MoKα X-ray sources, showing rapid photochromic response and recovery within one minute, a potential candidate for practical indoor and outdoor applications.
Abstract: A viologen-based Borromean entangled porous framework was found to be sensitive to both CuKα and MoKα X-ray sources, showing rapid photochromic response and recovery within one minute. The X-ray-induced photochromic process is accompanied by a reversible single-crystal-to-single-crystal (SC-SC) structural transformation, an unprecedented phenomenon for X-ray sensitive materials. The complex can be further processed into portable thin films for detecting the dose of the X-ray exposure. Moreover, the photochromism can occur over a broad temperature range of 100-333 K, both in the form of single crystals and thin films, making it a potential candidate for practical indoor and outdoor applications.
TL;DR: In this paper, the authors provide guidance for the synthesis of single crystal NMC positive electrode materials that may be suitable for lithium-ion cells with high energy density and long lifetime.
Abstract: Single crystal Li[Ni0.5Mn0.3Co0.2]O2 materials in NMC532/artificial graphite cells have excellent long term charge-discharge cycle lifetime which greatly exceeds that of conventional NMC532 materials. There are a few patents from industry regarding the synthesis of single crystal NMC. In addition, there have only been a few reports in the academic literature showing that single crystal NMC with a grain size of ~2–5 μm having good electrochemical performance was successfully synthesized, but these workers used complex approaches. This work systematically studies the steps required to synthesize single crystal NMC materials. The key synthesis steps including the impact of the Li to transition metal ratio, sintering temperature, precursor size and sintering time are discussed. This work provides guidance for the synthesis of single crystal NMC positive electrode materials that may be suitable for lithium-ion cells with high energy density and long lifetime.
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: A sulfonated indium (In) metal organic framework (MOF) is reported with an anionic layered structure incorporating hydrogen-bonded dimethylammonium cations and water molecules, revealing a very high proton conduction value for low humidity and moderate temperature.
Abstract: A sulfonated indium (In) metal organic framework (MOF) is reported with an anionic layered structure incorporating hydrogen-bonded dimethylammonium cations and water molecules The MOF becomes amorphous in >60% relative humidity; however, impedance analysis of pelletized powders revealed a proton conduction value of over 10–3 S cm–1 at 25 °C and 40% RH, a very high proton conduction value for low humidity and moderate temperature Given the modest humidity stability of the MOF, triaxial impedance analyses on a single crystal was performed and confirmed bulk proton conductivity over 10–3 S cm–1 along two axes corroborating the data from the pellet
Abstract: The monolithic perovskite films with a single crystal cross profile are considered to be the ideal active layer for high efficiency perovskite solar cells (PSCs) owing to the minimization of defects and the maximization of charge carrier mobility. To date, how to prepare a high-quality monolithic perovskite film is still a challenge for PSCs. Here, we demonstrated a combined method via CH3NH3Cl (MACl) coordination and a heat assisted process (HAP) to grow a compact monolithic CH3NH3PbI3 (MAPbI3) film with an average grain size of 3.6 μm. The ordered intermediate phase framework of MAPbIxCly grew up from the bottom to the top on the heated substrate, avoiding the grain boundaries and pin-holes in the cross profile. According to the space charge limited current (SCLC), the trap density in the monolithic film was nearly an order of magnitude lower than that of the control samples, while the charge carrier mobility increased to 22.74 cm2 V−1 S−1, approaching that of the MAPbI3 single crystal. As a result, the power conversion efficiency (PCE) of the PSCs is increased from 13.26% to 18.34%. These results shed light on the preparation of high quality monolithic MAPbI3 films via retarding crystallization (MACl additive) and increasing the nucleation rate (HAP).
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 article, a simple alloying strategy by mixing methylammonium with formamidinium is developed to stabilize the FAPbI3 perovskite phase, hence achieving a highly stable mixed cation MA0.45FA0.55PbI 3 single crystal over a span of 14 months.
Abstract: Halide perovskite single crystal of cubic HC(NH2)2PbI3 (FAPbI3) having excellent optoelectronic properties, such as narrow bandgap, large absorption coefficient and superior thermal stability has caught a surge of attention as a promising material for production of high-performance optoelectronic devices. However, at room temperature, the self-transformation of cubic FAPbI3 perovskite phase to non-perovskite phase leaves a critical roadblock to its practical viability. Herein, a simple alloying strategy by mixing methylammonium with formamidinium is developed to stabilize the FAPbI3 perovskite phase, hence achieving a highly stable mixed cation MA0.45FA0.55PbI3 perovskite single crystal over a span of 14 months. The MA0.45FA0.55PbI3 single crystal exhibits exceptional optoelectronic properties like high carrier mobility of 271 ± 60 cm2 s−1 V−1 and long diffusion length up to 254 μm, which are twice the values for sole MAPbI3 or FAPbI3 crystals. In addition, the photodetector based on MA0.45FA0.55PbI3 single crystal exhibits low detection limit of about 1 nW cm−2, high ON–OFF ratio of ∼1000, short response time of less than 200 μs, and impressive stability under aging in dark for 4 months or continuous photo-switching test for 1000 s.
TL;DR: Inhomogeneity along with the coexistence of Li-rich and Li-poor phases are broadly observed on partially delithiated crystals, providing direct evidence for a concurrent nucleation and growth process instead of a shrinking-core or a particle-by-particle process.
Abstract: Understanding the reaction pathway and kinetics of solid-state phase transformation is critical in designing advanced electrode materials with better performance and stability. Despite the first-order phase transition with a large lattice mismatch between the involved phases, spinel LiMn1.5Ni0.5O4 is capable of fast rate even at large particle size, presenting an enigma yet to be understood. The present study uses advanced two-dimensional and three-dimensional nano-tomography on a series of well-formed LixMn1.5Ni0.5O4 (0≤x≤1) crystals to visualize the mesoscale phase distribution, as a function of Li content at the sub-particle level. Inhomogeneity along with the coexistence of Li-rich and Li-poor phases are broadly observed on partially delithiated crystals, providing direct evidence for a concurrent nucleation and growth process instead of a shrinking-core or a particle-by-particle process. Superior kinetics of (100) facets at the vertices of truncated octahedral particles promote preferential delithiation, whereas the observation of strain-induced cracking suggests mechanical degradation in the material.
TL;DR: Si-doped Ga2O3 thin films were fabricated by pulsed laser deposition on semi-insulating (010) and (0001) Al 2O3 substrates in this paper, showing single crystal, homoepitaxial growth as determined by high resolution transmission electron microscopy and x-ray diffraction.
Abstract: Si-doped Ga2O3 thin films were fabricated by pulsed laser deposition on semi-insulating (010) β-Ga2O3 and (0001) Al2O3 substrates. Films deposited on β-Ga2O3 showed single crystal, homoepitaxial growth as determined by high resolution transmission electron microscopy and x-ray diffraction. Corresponding films deposited on Al2O3 were mostly single phase, polycrystalline β-Ga2O3 with a preferred (20 1 ¯ ) orientation. An average conductivity of 732 S cm−1 with a mobility of 26.5 cm2 V−1 s−1 and a carrier concentration of 1.74 × 1020 cm−3 was achieved for films deposited at 550 °C on β-Ga2O3 substrates as determined by Hall-Effect measurements. Two orders of magnitude improvement in conductivity were measured using native substrates versus Al2O3. A high activation efficiency was obtained in the as-deposited condition. The high carrier concentration Ga2O3 thin films achieved by pulsed laser deposition enable application as a low resistance ohmic contact layer in β-Ga2O3 devices.
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: The authors combine accelerated abnormal grain growth and cyclic heat treatments to grow a superelastic shape memory alloy single crystal to 70 cm and ensure that the range of applications of shape memory alloys will spread beyond small-sized devices to large-scale components.
Abstract: Producing a single crystal is expensive because of low mass productivity. Therefore, many metallic materials are being used in polycrystalline form, even though material properties are superior in a single crystal. Here we show that an extraordinarily large Cu-Al-Mn single crystal can be obtained by abnormal grain growth (AGG) induced by simple heat treatment with high mass productivity. In AGG, the sub-boundary energy introduced by cyclic heat treatment (CHT) is dominant in the driving pressure, and the grain boundary migration rate is accelerated by repeating the low-temperature CHT due to the increase of the sub-boundary energy. With such treatment, fabrication of single crystal bars 70 cm in length is achieved. This result ensures that the range of applications of shape memory alloys will spread beyond small-sized devices to large-scale components and may enable new applications of single crystals in other metallic and ceramics materials having similar microstructural features. Growing large single crystals cheaply and reliably for structural applications remains challenging. Here, the authors combine accelerated abnormal grain growth and cyclic heat treatments to grow a superelastic shape memory alloy single crystal to 70 cm.
TL;DR: In this article, single and multiple slip activation, slip localization and microstructure-sensitive stress evolution have been examined using high-resolution digital image correlation to quantify the developing strain fields and the strain localization in both single and oligocrystals in fatigue.
TL;DR: In this article, a centimeter-sized organic-inorganic hybrid lead-based perovskite (MAPbI3) single crystal was obtained by using a modified fast and inverse-temperature growth method.
Abstract: A centimeter-sized organic–inorganic hybrid lead-based perovskite CH3NH3PbI3 (MAPbI3) single crystal was obtained by using a modified fast and inverse-temperature growth method. The optical properties of this single crystal at room and low temperatures were studied in terms of optical absorption and photoluminescence measurements. The single crystal exhibited optical properties with a band-gap of 1.53 eV, which is comparable to a reported value. The temperature-dependent UV-vis spectra of this perovskite single crystal showed a unique structural phase transition as the temperatures varied. The thermoelectric properties of this MAPbI3 single crystal were studied, showing that the Seebeck coefficient of 920 ± 91 μV K−1 almost remained unchanged from room temperature to 330 K and it progressively increased with the increase in temperature and reached 1693 ± 146 μV K−1 at 351 K. In contrast, there was no very clear trend for thermal conductivities with changes in temperature. The thermal conductivities were maintained between 0.30 and 0.42 W m K−1 in the temperature range of 298–425 K. These thermoelectric characteristics would be useful for potential thermoelectric applications if the electrical conductivity of this crystal is improved by tuning its composition.