Crystal Growth & Design最新文献

A cationic perylene salt was synthesized by chemical oxidation through treatment of perylene with triethyloxonium hexachloroantimonate in dichloromethane and characterized by single crystal X-ray diffraction as [(C₂₀H₁₂)₂]^•+(SbCl₆)⁻. EPR spectrometry confirmed the formation of an organic radical with a g-factor of 2.0024. X-ray diffraction analysis revealed a 1D column stacking of perylene molecules with alternating interplanar distances of 3.255(2)–3.340(2) Å and 3.409(2)–3.466(3) Å, indicative of the dimer formation within infinite π-stacks. Within a dimer, a large π-surface overlap and a slight loss of planarity for perylene were also observed. As these structural characteristics are consistent with pancake bonding for a perylene dimer, further insights into bonding were sought with the help of density functional theory. The calculations revealed that the pancake interaction contributes significantly to the stabilization of the stacked perylene dimer, providing approximately 8.0–10.0 kcal/mol per pair. Further stabilization is achieved by an even distribution of the positive charge in the monocationic dimer. A direct comparison with the close analogue revealed the critical role of the solid-state packing effects in achieving a higher degree of overlap between the perylene monomers in the title product.

The AZO/Cu/AZO heterogeneous interface is prepared to improve the optoelectronic property of AZO as Cu intercalation is introduced. The experimental results show that the Cu layer is at 8 nm, the (002) peak intensity of the sample reaches the maximum, the crystallization quality is the best, the roughness is the lowest, and the transmittance and conductivity have better values. In the meantime, the simulation results show that the interface of AZO/Cu is bonded, and the conductivity of AZO/Cu is higher than that of AZO, but the transmittance is the opposite. This is consistent with the experimental results. The research implies that we can design efficient optoelectronic properties with an AZO/Cu/AZO heterogeneous interface by adjusting Cu intercalation.

Traditionally, off-line measurements via image analysis or laser diffraction methods are used to analyze the crystal product. It is often beneficial to extract crystal samples intermittently during the crystallization process to better understand the complex dynamics in batch and continuous crystallization. However, frequent invasive product sampling can lead to undesired disturbances in the process dynamics. Various process analytical technologies have been developed for in situ monitoring of crystallization systems; however, obtaining quantitative crystal size distribution (CSD) information from these is challenging. While in the case of traditional concentration monitoring tools system-specific calibration is an accepted standard procedure, most image analysis-based techniques attempt to provide direct measurement of CSD information. To obtain a fast and accurate in situ image analysis measurement of particle size for a high aspect ratio crystallization system, a systematic off-line image analysis calibration methodology was performed to model off-line Malvern Morphologi image analysis results. An image analysis algorithm was calibrated to extract size distribution data from in situ images of varying sizes and solid concentrations. Using a genetic algorithm, the various methods and parameters in the image analysis algorithm were automatically optimized by minimizing the size distribution error between the model and the off-line image analysis measurement. Trends observed in the calibrated parameters were then fitted to continuous functions depending on solid density to be able to adapt to changes in the solid loading. The algorithms were then validated with a different particle data set with a known solid loading. Last, to demonstrate the proof of concept in sensor fusion and online application, the adaptive image analysis algorithm was coupled with a UV/vis sensor and tested on a dynamic data set to predict the size distribution with varying solid loadings throughout the crystallization process due to dissolution, nucleation, and growth.

Indium nitride (InN) is a low-band-gap semiconductor with unusually high electron mobility, making it suitable for IR-range optoelectronics and high-frequency transistors. However, the development of InN-based electronics is hampered by the metastable nature of InN. The decomposition temperature of InN is lower than the required growth temperature for most crystal growth techniques. Here, we discuss growth of InN films and epitaxial layers by atomic layer deposition (ALD), a growth technique based on self-limiting surface chemical reactions and, thus, inherently a low-temperature technique. We describe the current state of the art in ALD of InN and InN-based ternary alloys with GaN and AlN, and we contrast this to other growth technologies for these materials. We believe that ALD will be the enabling technology for realizing the promise of InN-based electronics.

Indium nitride (InN) is a low-band-gap semiconductor with unusually high electron mobility, making it suitable for IR-range optoelectronics and high-frequency transistors. This potential is hampered by the breakdown temperature of InN, which is lower than the required growth temperature for most crystal growth techniques. We describe the current state of the art in atomic layer deposition (ALD) of InN and InN-based ternary alloys with GaN and AlN and argue that ALD will be the technology for realizing the promises of InN-based electronics.

High-quality GaAs on the c-plane sapphire has been achieved by employing a two-step growth technique, multiple annealing, and an AlAs nucleation layer using molecular beam epitaxy (MBE). The effect of growth parameters, namely, growth temperature, As₂ flux, and low-temperature layer growth temperature (LTLGT) in two-step growth have been investigated. In all of the grown samples, the epitaxial orientation of the film is GaAs (111)A. Unlike the homoepitaxial GaAs (111)A MBE growth, where increasing the As₂ flux improves the film quality, here the lowest As₂ flux resulted in the best film quality. Very low LTLGT resulted in highly twinned material and film surface with many pits. Growth temperature also plays an important role, as seen by the exceptional structural and optical properties of samples grown at 650 °C, but at the cost of the rough film surface. We have observed low-temperature photoluminescence (PL) for all of the samples. However, for the first time, to the best of our knowledge, room-temperature PL (RT-PL) has been demonstrated from a heteroepitaxial GaAs (111)A film. This result is important because RT-PL from the epitaxial GaAs/c-plane sapphire will lead to the fabrication of GaAs laser on sapphire, which is an important functionality to realize photonic circuits on the sapphire platform.

Amorphous calcium phosphate (ACP) has been widely reported as a metastable precursor during the mineralization of calcium phosphates in bone and enamel. Although the influence of fluoride on the crystallization of hydroxyapatite (HAP) has been extensively investigated, the mineralization pathways of ACP in the presence of fluoride are not fully understood. Here, using a combination of in situ monitoring and ex situ characterizations, we show that fluoride exhibits little effect on the formation and particle size of ACP nanospheres from a supersaturated calcium phosphate solution. However, the stability of ACP increases with increasing concentration of free fluoride ions in solution. We show that the aggregation of ACP nanospheres into larger spheres is an important step during ACP crystallization, which drives the nucleation of plate-like nanocrystals on the surface of ACP nanospheres and induces subsequent crystallization of ACP via a dissolution-recrystallization pathway. In the presence of fluoride, the aggregation of ACP nanospheres and the nucleation of crystalline phases are retarded, thus stabilizing the amorphous phase. In addition, fluoride promotes the formation rod-like crystals on the surface of ACP nanospheres, which grow both outward from solution ions and inward from ACP nanospheres. These results significantly improve our understanding of the mineralization pathways of ACP and explain the inhibitory effect of fluoride during ACP crystallization.

Crystalline orientation control is of great importance for the optoelectronic applications of perovskite single crystals due to their structural anisotropy. Herein, we develop an ionic liquid, named methylammonium difluoroacetate (MA2FAc), as a growth solvent to fabricate multifarious methylammonium-based perovskite single crystals. Typically, it can easily achieve preferably oriented growth of high-quality MAPbI₃ single crystals with (002) facet exposition. Benefiting from the superior charge carrier properties along the [001] direction, a bias-modulating broadband/narrowband switchable photodetector is proposed, which exhibits a broadband specific detectivity D* of 1.1 × 10¹¹ Jones under 0.1 V and a narrowband D* of 9.0 × 10⁹ Jones with a full width at half-maximum (fwhm) of 31 at 810 nm merely under 0.25 mV, respectively. Theoretical calculations and experimental analysis reveal that the difluoromethyl substitution can simultaneously regulate solvation characteristics of the acetate anion as well as crystallization kinetics of perovskite single crystals. In light of the universal solvent utilization of MA2FAc, this work provides a new perspective in the solution growth process of high-quality methylammonium based perovskite single crystals.