Single Crystal Research Articles

Lattice dynamics of Bi12GeO20 crystal: Polarized Raman scattering and first-principles analysis

Our paper presents a combined experimental and theoretical study of the lattice dynamics of Bi12GeO20 crystal. Polarized Raman spectra were measured in two x-ray oriented single crystals. In a crystal of cubic symmetry, phonon modes of A- and E-types are spectroscopically indistinguishable. Using a special experimental technique, we separated the phonon modes that transform according to A and E irreducible representations. Since the number of E-type lines observed in Raman scattering is higher than theoretically allowed by group theory, we performed a first-principles calculation of the Bi12GeO20 lattice dynamics to accurately identify the symmetry of phonon modes. All experimental lines observed in Raman scattering are classified according to irreducible representations of the cubic I23 group. Using samples of different thicknesses, 10 mm and 0.120 mm, we have demonstrated that the optical activity plays an insignificant role at Raman backscattering in Bi12GeO20 crystal.

Photoluminescence and scintillation properties of rare earth doped Lu2O3 single crystal grown by floating zone method

A series of Lu2O3 single crystals doped with rare earth (RE) ions (RE = Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb, dopant concentrations are 1 %) was synthesized by the floating zone method. Their photoluminescence (PL) and scintillation properties were evaluated. In PL, emissions due to 4f-4f transitions of trivalent rare earth ions were observed, and those doped with Nd3+, Eu3+, Tb3+ and Er3+ showed the highest emission intensities among the samples. As a scintillation property, those doped with Eu, Gd, and Dy showed a clear photoabsorption peak under 137Cs 662 keV γ-ray irradiation. Among them, the Eu3+-doped Lu2O3 showed the highest scintillation light yield of 67000 photons/MeV. The current work conducted the first systematic study of rare earth doped Lu2O3 single crystals grown by the floating zone method.

Theoretical-level insights on the molecular structures and LiCl dopant of carbon nitride single crystals for solar-driven overall water splitting

Addressing energy and environmental challenges requires sustainable technologies like photocatalytic overall water splitting (OWS) using graphitic carbon nitride (GCN). This study investigates the molecular structures and LiCl doping effects in GCN variants-poly(triazine imide) intercalated with LiCl (PTI/Li+Cl-), and heptazine-based crystalline GCN (HCCN)-to understand their suitability for OWS. Experimental results show that PTI/Li+Cl- exhibits superior OWS activity, producing 802.3 μmol h-1 gcat-1 of H₂ and 395.6 μmol h-1 gcat-1 of O₂, due to its active planes and favorable electron transfer. In contrast, HCCN shows high H₂ production but no O₂ release. Density functional theory calculations reveal that triazine structures are more favorable for oxygen evolution reaction (OER) while heptazine structures excel in hydrogen evolution reaction (HER). LiCl doping can enhance OWS performance by improving electronic conductivity and reducing reaction activation energy. The results encourage the combination of triazine and heptazine structures with LiCl doping to optimize OWS, offering a theoretical basis for designing efficient GCN-based photocatalysts.

Strong and pH dependent fluorescence in unprecedented anthra[2,3-d]imidazole derivatives

We here report the synthesis and characterization of three new molecules based on an unprecedented anthra [2,3-d]imidazole unit. The new heterocycle was unexpectedly formed while attempting to obtain 2,3-diacetamidoanthracene by reducing the corresponding anthraquinone molecules by sodium borohydride. The same reaction was successfully performed using two further different 2,3-diamidoanthraquinone derivatives, thus confirming its generality. The chemical identity of the novel molecules was also proved by realizing single crystals suitable for XRD diffraction and solving the crystalline structure of one of the prepared systems. All the molecules are strong blue emitters in ethanol, with fluorescence quantum yields around 0.40. Because of the acid-base properties of anthraimidazole ring, the optical response was investigated at different pH values. While slight differences were observed in acidic conditions, in the alkaline pH range we observed a dramatic change of the fluorescence spectra in a narrow pH range (from 11 to 13), with the color of the emission turning from blue to green. This feature makes the new class of derivatives here reported very promising as pH sensors working in strongly alkaline conditions.

Analysis on optical, thermal and third-order nonlinear properties of L-histidine hydrochloride monohydrate single crystal

This research contributes valuable insights into the understanding of third-order nonlinear optical effects in L-histidine hydrochloride monohydrate (LHHC) single crystal, offering a foundation for future work in optimizing its properties for practical applications in the field of nonlinear optics. It presents a systematic analysis into the LHHC crystal properties harvested by slow evaporation solution (SEST) method. Originally, structure of the compound was confirmed through single crystal x-ray diffraction and powder x-ray diffraction analysis. FTIR analysis was performed to get information about molecular composition of the compound. The assessment of the optical quality of LHHC single crystal was done by UV–Visible and photoluminescence spectroscopies. TG-DTA was employed to assess the stability of the single crystal under different temperature conditions. Z-scan technique, with an open aperture (OA) & closed aperture (CA) configuration, was employed to comprehensively explore the third-order nonlinear response of LHHC single crystal. The nonlinear absorption coefficient β is determined to be 5.32 × 10−10 cm W−1. The NLR index (n2) is calculated as −2.72 × 10−15 cm2 W−1.

Thermodynamic potential construction and biaxial stress analysis of K0.4Na0.6NbO3 single crystals

The macroscopic properties of piezoelectric materials can be profoundly influenced by stress. In this research, thermodynamic potential parameters of K0.4Na0.6NbO3 (KNN) single crystals have been experimentally quantified to assess the effects of stress. Leveraging the Landau thermodynamic potential theory, it has been identified that the application of biaxial tensile stress causes a significant elevation in both the piezoelectric property and phase transition temperature in KNN crystals. This transition remarkably extends their working range and improves the material's applicated potential. The coherence between these computational outcomes and experimental data—from the strategic growth of KNN single crystals with internal stress—underscores the reliability of our findings (dielectric constant from 213 to 1274, TO-T from 180 to 234 °C). Additionally, theoretical calculation predicts a potential enhancement in the piezoelectric capabilities of KNN single crystals. This study provides valuable insights for the growth of high-quality piezoelectric crystals and further promotes the application of lead-free piezoelectric materials.

Selenophosphate Pb2P2Se6 Single Crystals Growth by Chemical Vapor Transport (CVT) Method for Radiation Detection.

The heavy metal selenophosphate Pb2P2Se6emerges as a promising room-temperature X-ray/γ-ray detectors due to its high resistivity, robust radiation-blocking capability, and outstanding carrier mobility-lifetime product, etc. However, the high activity of phosphides poses significant impediment to the synthesis and single crystal growth. In this work, we have prepared high-quality Pb2P2Se6 single crystals with using the chemical vapor transport (CVT) method. The XRD analysis combined with EDS result confirmed the uniform composition of the resulting as-grown single crystals, while UV-Vis-NIR transmittance spectra revealed the bandgap of 1.89 eV. Selected area electron diffraction patterns indicated the crystal belonged to the P21/c(14) space group. Additionally, the Au/Pb2P2Se6/Au device is fabricated, which exhibits a robust X-ray response with a sensitivity of 648.61 μC·Gy-1·cm-2 at 400 V·mm-1 under 50 kVp. Notably, the device also excels in alpha particle detection, boasting a resolution of ~14.48% under a bias of 400 V bias. The hole mobility-lifetime product (µτ)h of Pb2P2Se6 is estimated to be ~2.58×10-5 cm2·V-1. The results underscore potential applications of Pb2P2Se6 crystal is in the field of the semiconductor radiation detectors.

DNA/BSA Binding and Antimicrobial Properties of Biguanide-Cu(II) Complexes.

The biguanide Cu(II) complexes [Cu(L1-4)2](ClO4)2 were synthesized and spectroscopic/analytical techniques were used to clarify their structures. Single crystals of complex [Cu(L4)2](ClO4)2 was obtained and its definite structure was determined by single crystal X-ray diffraction study. The complexes [Cu(L1-4)2](ClO4)2 were screened for their FSds-DNA interactions by using UV-Vis absorption and fluorescence spectroscopies. The complexes [Cu(L2)2](ClO4)2 and [Cu(L3)2](ClO4)2 were shown to exhibit higher affinity for binding DNA. Examining the EB-DNA interaction, it is believed that the complexes interact with DNA through a groove binding mechanism. The interaction of complexes with BSA were observed through the quenching of the fluorescence emission. Complexes [Cu(L2)2](ClO4)2 and [Cu(L3)2](ClO4)2 show moderate binding affinity to BSA through a static mode. Additionally, the Cu(II) complexes were screened for their antibacterial activities against various bacterial strains. Complexes showed potential antimicrobial activity against Salmonella typhimurium, Bacillus cereus, Salmonella typhimurium and S. aureus.

Evaluating Nondestructive Quantification of Composition Gradients in Metal-Organic Frameworks by MeV Ion Microbeam Analysis.

We evaluate a method to quantify composition depth gradients in intact metal-organic framework (MOF) single crystals and thereby derive diffusion coefficients of postsynthetically incorporated active sites by nondestructive ion-beam microanalysis. Zr-based UiO-67-bpy (bpy = 2,2'-bipyridine-5,5'-dicarboxylic acid) MOFs were synthesized on Si substrates and then metalated postsynthetically with NiCl2 for 2-48 h, resulting in different Ni depth distributions. Simultaneous micro-Rutherford backscattering spectrometry (μ-RBS) and micro-particle induced X-ray emission (μ-PIXE) analysis were used for the spatially resolved chemical analysis of the MOF single crystals. Qualitative assessment of the μ-RBS spectra indicated the presence of elemental depth gradients and hinted at the governing process of the postsynthetic Ni incorporation, in the present case, molecular diffusion. Quantitative evaluation of the resulting composition depth profiles directly provided the diffusion length and, thereby, the diffusion coefficient of the system. Virtual gradients caused by overhanging tips/edges of the truncated octahedral crystal shape are considered. Furthermore, in the case of insufficient probing depth for μ-RBS, μ-PIXE was still capable of providing qualitative information. In the present system the diffusion coefficient for NiCl2 is found to be (1.72 ± 0.18) × 10-16 m2s-1. The long-term stability of the synthesized and postsynthetically modified MOFs is proved by repeated measurements.

Nature of electrically detected magnetic resonance in highly nitrogen-doped 6H -SiC single crystals

This work focuses on unraveling electron paramagnetic resonance (EPR) and electrically detected magnetic resonance (EDMR) properties of n-type 6H silicon carbide (SiC) single crystals with high concentrations of uncompensated nitrogen (N) donors, which is essential for fundamental understanding of spin-related phenomena, developing spin-based devices, optimizing materials and devices, and advancing research in quantum information and spintronics. Utilizing low-temperature multifrequency EPR spectroscopy (9.4–395.12 GHz), we identified two intense signals labeled as S line and S1 line in the 6H-SiC crystals with ND–NA≈8×1018 and 4×1019cm−3. In addition, in 6H-SiC crystals with ND–NA≈8×1018cm−3, a low-intensity triplet from N donors substituting the quasicubic “k2” nonequivalent position (Nk2) was observed. The S line [g⊥=2.0029(2),g∥=2.0038(2)] was assigned to the exchange interaction of conduction electrons and Nk2, while the S1 line [g⊥=2.0030(2),g∥=2.0040(2)] is caused by the exchange spin coupling of localized N donors at the “k1” and “k2” positions. The S1 line was observed in high-frequency EDMR spectra of 6H-SiC with ND–NA≈8×1018cm−3, and its emergence was explained by an enhancement of the hopping conductivity due to the EPR-induced temperature increase mechanism. No EDMR spectra were found to occur in the 6H-SiC crystals with ND–NA≈4×1019cm−3, which is close to the critical donor concentration value for a semiconductor-metal transition. Thus it can be concluded that this N donor concentration is too high for the appearance of spin-dependent scattering and too low for the emergence of EPR-induced hopping mechanisms in 6H-SiC. Published by the American Physical Society 2024

Enhancing Two-Photon Excited Fluorescence of Metal-Organic Framework Single Crystals through Modulation of Inorganic Nodes.

Regulation of the two-photon excited fluorescence (TPEF) emission intensity and wavelength of metal-organic framework (MOF) crystals with similar constitutions presents a significant challenge. In this study, two MOFs, Zn-BTPPA and Cd3-BTPPA, were constructed using tetrakis(1,1'-biphenyl-4-carboxylic acid)-1,4-benzenediamine (H4BTPPA) as the organic ligand and mononuclear Zn and trinuclear Cd3 inorganic nodes, respectively. The incorporation of H4BTPPA within the MOF structures enables effective TPEF emission in both Zn-BTPPA and Cd3-BTPPA. The TPEF results show that Zn-BTPPA and Cd3-BTPPA exhibited strong emissions at 523 and 463 nm, respectively, when excited with a 780 nm laser. Moreover, Zn-BTPPA and Cd3-BTPPA exhibited much higher two-photon absorption cross sections, approximately 4.9 and 5.2 times higher than that of the reported dinuclear MOF, Cd2-BTPPA, with a similar composition, respectively. With different inorganic nodes, the stacking of chromophores, π···π interactions, and ligand geometry were found to correlate with the enhanced TPEF in Cd3-BTPPA and the blue-shifted TPEF in Zn-BTPPA. This work serves as an inspiration for designing efficient TPEF MOF materials based on the structure-property relationship.

Germanium Single Crystals for Photonics

Germanium (Ge) is a system-forming material of IR photonics for the atmospheric transparency window of 8–14 µm. For optics of the 3–5 µm range, more widespread silicon (Si), which has phonon absorption bands in the long-wave region, is predominantly used. A technology for growing Ge single crystals has been developed, allowing the production of precision optical parts up to 500 mm in diameter. Ge is used primarily for the production of transparent optical parts for thermal imaging devices in the 8–14 µm range. In addition, germanium components are widely used in a large number of optical devices where such properties as mechanical strength, good thermal properties, and climatic resistance are required. A very important area of application of germanium is nonlinear optics, primarily acousto-optics. The influence of doping impurities and temperature on the absorption of IR radiation in germanium is considered in detail. The properties of germanium photodetectors are reported, primarily on the effect of photon drag of holes. Optical properties in the THz range are considered. The features of optical properties for all five stable isotopes of germanium are studied. The isotopic shift of absorption bands in the IR region, caused by phonon phenomena, which was discovered by the authors for the first time, is considered.

Toward the reproducible fabrication of conductive ferroelectric domain walls into lithium niobate bulk single crystals

Ferroelectric domain walls (DWs) are promising structures for assembling future nano-electronic circuit elements on a larger scale since reporting domain wall currents of up to 1 mA per single DW. One key requirement hereto is their reproducible manufacturing by gaining preparative control over domain size and domain wall conductivity (DWC). To date, most works on DWC have focused on exploring the fundamental electrical properties of individual DWs within single-shot experiments, with an emphasis on quantifying the origins of DWC. Very few reports exist when it comes to comparing the DWC properties between two separate DWs, and literally nothing exists where issues of reproducibility in DWC devices have been addressed. To fill this gap while facing the challenge of finding guidelines for achieving predictable DWC performance, we report on a procedure that allows us to reproducibly prepare single hexagonal domains of a predefined diameter into uniaxial ferroelectric lithium niobate single crystals of 200 and 300 μm thickness, respectively. We show that the domain diameter can be controlled with an uncertainty of a few percent. As-grown DWs are then subjected to a standard procedure of current-limited high-voltage DWC enhancement, and they repetitively reach a DWC increase of six orders of magnitude. While all resulting DWs show significantly enhanced DWC values, their individual current–voltage (I–V) characteristics exhibit different shapes, which can be explained by variations in their 3D real structure reflecting local heterogeneities by defects, DW pinning, and surface-near DW inclination.

Morphology Control of Nanoporous Gold Through Selective Dissolution of Au–Ge Eutectic Microstructures

The synthesis of nanoporous gold (np‐Au) through the conventional method of dealloying a more reactive element from AuTherma alloys has been extensively studied and applied in various fields, particularly catalysis. Herein, a novel approach to creating droplet‐like np‐Au through the selective dissolution of Au–Ge eutectic microstructures is explored. This work reveals that adjusting the undercooling of the eutectic melt during solidification allows for the tuning of pore and ligament sizes. It is demonstrated that this undercooling can be modified, either directly or indirectly, by adjusting either the cooling rate or the heterogeneous nucleation site density of the eutectic melt. The findings, aligned with the model based on classical theory for eutectic solidification, elucidate the connection between the tuning of pore and ligament sizes in the eutectic microstructure and the undercooling of the eutectic melt. Importantly, it is established that this phenomenon is applicable across a variety of compositions, including hypereutectic, eutectic, and hypoeutectic. The ability to regulate pore and ligament size in single crystals of np‐Au droplets offers a novel approach to synthesizing catalytic np‐Au crystals with enhanced mechanical and thermal stability compared to conventional methods.

Orbital coupling of Pt single crystal via decoration of hetero-diatomic nickel-cobalt for efficient hydrogen evolution

Loading active metals in forms of single atoms or nanocluster is considered as an effective approach for designing catalysts with high atomic utilization efficiency. However, synthesis single atoms or clusters precisely in large quantities is a challenge. In this work, the isolated diatomic sites (Ni, Co) decorated single crystal Pt cluster were synthesized as efficient catalyst for hydrogen evolution. Adjacent Ni and Co atoms optimize the electronic structure of Pt single crystal, effectively lowering the water dissociation barrier and ensuring optimal binding strength of intermediates throughout the reaction process. As results, the mass activity of 2.087 A mg−1 was achieved under 200 mA cm−2, approximately 3 times than that of Pt/C. Theoretical calculations reveal that diatomic Ni, Co decorated Pt cluster reduces the energy barrier for breaking the OH-H bond, as well as facilitating the preferential adsorption and dissociation of H*. This work provides an opportunity for regulation electronic structure of catalytic via decoration single crystal cluster with diatomic sites and provides guidance for designing high efficiency electrocatalysts for promising applications.

Comparison on Hysteresis Loops and Dislocation Configurations in Fatigued Face-Centered Cubic Single Crystals

The aggregation and evolution of dislocations form different configurations, which are the preferred locations for fatigue crack initiation. To analyze the spatial distribution of the same dislocation configuration and the resulting configuration morphologies on different observation planes, several typical hysteresis loops and dislocation configurations in fatigued face-centered cubic single crystals with various orientations were compared. The crystal orientations of these specimens were determined by the electron back-scattering diffraction technique in a Cambridge S360 Scanning Electron Microscope. It is well known that dislocation ladder and wall structures, as well as patch and vein structures, are distributed on their respective observation planes, (12¯1) and (111). These correspond to the point defect direction and line defect direction of dislocations, respectively. Therefore, the wall structures on the (12¯1) and (111) planes consist of point defects and line defects, which can be defined as point walls and line walls, respectively. Furthermore, the walls on the (12¯1) plane consist of Persistent Slip Band ladders connected with each other, corresponding to the formation of deformation bands. The evolution of dislocation patterns follows a process from patch to ladder and from vein to wall. The formation of labyrinths and dislocation cells originates from the activation of different secondary slip systems. In one word, it can help us better understand the physical nature of metal fatigue and failure by studying the distribution and evolution of different configurations.

Optical tunning of high-luminescent iodine-substituted CsPb2(Br0.84I0.16)5 under pressure

Metal halide compounds hold significant interest for optoelectronics, given their substantial potential for solar cells and light-emitting applications. Low-dimensional (0D, 1D, and 2D) metal halide perovskites or perovskite-like compounds exhibit various compositions with soft lattices and modular optical properties. Thus, the finding of new strategies to further improve such properties is a current research challenge. In this scenario, the 2D perovskite-like compound CsPb2Br5 has attracted attention due to its structural stability and favorable optical properties. This study presents the pressure-induced structural phase transitions of the iodine substituted CsPb2(Br0.84I0.16)5. This substitution induces strong green photoluminescence in single crystals at ambient conditions. High-pressure optical and synchrotron X-ray diffraction experiments reveal a tetragonal-tetragonal structural phase transitions around 1 GPa, while the photoluminescence emission is quenched around 2.7 GPa. Additionally, a new high-pressure orthorhombic phase is identified in the iodine-doped compound beyond 4.5 GPa. Further analysis of structural features prove that the pressure dependent photoluminescence behavior is directly related to structural distortions observed upon pressure increase.

Anisotropic ferroelectric-shaped hysteresis loop and colossal permittivity in thermally treated rutile TiO2 single crystals

Space charge polarization is an unavoidable phenomenon in electronic components that leads to deterioration of electrical response. Hence manipulation and utilization of space charge polarization to improve electrical properties is a phenomenal task. In the present study, heating treatment produces oxygen vacancies, resulting in the crystal structures (i.e., modulated structure and intergrowth structure) and band gap are anisotropic, which in turn leads to anisotropic nonlinear polarization behavior and colossal permittivity. Quantitative analysis of the atomic-scale structure confirms the modulated structure and intergrowth structure are anisotropic. A modulated structure along a axis of rutile TiO2 with a width of six times that of a rutile crystal cell a is constructed through an intergrowth structure between rutile and srilankite TiO2 phases in rutile TiO2 single crystals, wherein space charges at the intergrowth structure give rise to ferroelectric-shaped hysteresis in heated TiO2 single crystals along [001] direction. Impedance spectra display three kinds of space charge polarizations (modulated structure, intergrowth structure, and electrode non-ohmic contact) contribute to the colossal permittivity along [001] direction. The space charge polarizations contribute to a colossal permittivity (∼45,000), high resistivity (∼1010 Ω cm), and ferroelectric-shaped P-E loop (remanent polarization: ∼17.1 μC/cm2, coercive field: ∼4.3 kV/cm) in the heated TiO2 single crystal along [001] direction, while a linear polarization behavior and permittivity value of 120 are obtained along [100] direction. The findings provide guidance for the utilization of space charge polarization in dielectric materials.

Low-loss plasmons in Weyl semimetals Mn3Sn

We report the optical reflectance measurement for Weyl semimetal Mn3Sn single crystal at room temperature. We observe a low-loss plasmon in the UV energy ranges. This low plasmonic loss is associated with a large electron scattering rate contributed by electron-electron interaction and scattering of conduction electrons by Mn atoms. The incorporation of more Mn atoms simultaneously adds more elastic scattering centers and increases the strength of electron-electron correlation which generates multiple plasmons with lower plasmonic loss in Mn3+xSn1-x. The UV tunable plasmonic properties in Mn3+xSn1-x have great potential for plasmonic and spintronic applications. We also discuss the plasmonic loss in Mn3Sn to the other conducting materials including correlated and non-correlated systems establishing the crucial role of electron correlation on the plasmonic loss. Our result suggests novel and effective strategies for obtaining lower plasmonic loss in the class of correlated materials.

Suppressing non-radiative recombination and tuning morphology via central core asymmetric substitution for efficient organic solar cells

It is necessary and challenging to achieve high-efficiency organic solar cells (OSCs) by suppressing nonradiative energy loss (ΔEnr) and fine-tuning active layer morphology through the delicate active material design. In this study, we design two asymmetric acceptors, a-CH-ThCl and a-CH-Th2Cl, featuring asymmetric conjugated substitutions on central cores via single bond linkages. Single crystals analysis indicate that these two acceptors exhibit intense J-aggregation induced by the asymmetric substitution, which favours for their high photoluminescence quantum yields and contributes to reducing non-radiative recombination. Meanwhile, the two asymmetric acceptors demonstrate enhanced miscibility and optimized morphology with the donor D18. Consequently, the binary device based on D18: a-CH-Th2Cl demonstrates an impressive efficiency of up to 19.10 % with a high open-circuit voltage of 0.935 V, attributed to the remarkably low ΔEnr of 0.179 eV and optimized morphology. These results provide an effective strategy for material design to optimize molecular packing, reduce non-radiative recombination and tune active layer morphology to achieve high-efficiency OSCs.