Thin Crystals Research Articles

Comprehensive Application of XFEL Microcrystallography for Challenging Targets in Various Organic Compounds.

There is a growing demand for structure determination from small crystals, and the three-dimensional electron diffraction (3D ED) technique can be employed for this purpose. However, 3D ED has certain limitations related to the crystal thickness and data quality. We here present the application of serial X-ray crystallography (SX) with X-ray free electron lasers (XFELs) to small (a few μm or less) and thin (a few hundred nm or less) crystals of novel compounds dispersed on a substrate. For XFEL exposures, two-dimensional (2D) scanning of the substrate coupled with rotation enables highly efficient data collection. The recorded patterns can be successfully indexed using lattice parameters obtained through 3D ED. This approach is especially effective for challenging targets, including pharmaceuticals and organic materials that form preferentially oriented flat crystals in low-symmetry space groups. Some of these crystals have been difficult to solve or have yielded incomplete solutions using 3D ED. Our extensive analyses confirmed the superior quality of the SX data regardless of crystal orientations. Additionally, 2D scanning with XFEL pulses gives an overall distribution of the samples on the substrate, which can be useful for evaluating the properties of crystal grains and the quality of layered crystals. Therefore, this study demonstrates that XFEL crystallography has become a powerful tool for conducting structure studies of small crystals of organic compounds.

Phase-engineered synthesis of atomically thin te single crystals with high on-state currents

Multiple structural phases of tellurium (Te) have opened up various opportunities for the development of two-dimensional (2D) electronics and optoelectronics. However, the phase-engineered synthesis of 2D Te at the atomic level remains a substantial challenge. Herein, we design an atomic cluster density and interface-guided multiple control strategy for phase- and thickness-controlled synthesis of α-Te nanosheets and β-Te nanoribbons (from monolayer to tens of μm) on WS2 substrates. As the thickness decreases, the α-Te nanosheets exhibit a transition from metallic to n-type semiconducting properties. On the other hand, the β-Te nanoribbons remain p-type semiconductors with an ON-state current density (ION) up to ~ 1527 μA μm−1 and a mobility as high as ~ 690.7 cm2 V−1 s−1 at room temperature. Both Te phases exhibit good air stability after several months. Furthermore, short-channel (down to 46 nm) β-Te nanoribbon transistors exhibit remarkable electrical properties (ION = ~ 1270 μA μm−1 and ON-state resistance down to 0.63 kΩ μm) at Vds = 1 V.

Measurement of the surface susceptibility of single-layer atomic crystal by the photonic spin Hall effect in momentum space

Fast and robust measurement of the surface susceptibility is still in urgent need for investigation and application of atomically thin crystals. In this work, we propose an effective method to measure the surface susceptibility of single-layer graphene by detecting the photonic spin Hall effect in momentum space. At a graphene interface, the beam separations with different spin states contain an angular component due to the existence of surface susceptibility. By implementing a postselection with real weak value in our scheme, the contribution of the spatial spin-Hall shift is excluded and the angular one is amplified for detection. It is demonstrated that treating the angular shift as a pointer allows for a reliable determination of the surface susceptibility. Our method may pave a way for the optical parameter characterization of two-dimensional atomic crystals via angular metrology.

Dense Stacking of Millimeter‐Sized Perovskite Single Crystals for Sensitive and Low‐Bias Hard X‐Ray Detection

AbstractMetal halide perovskite single crystals are promising for hard X‐ray detection, but growth of large‐sized thin single crystals and inhibition of halide ion migration under high bias are challenging. Herein, the preparation of dense stacking of oriented millimeter‐sized perovskite single crystals with capability of large‐area fabrication, controlled thickness, and high ion migration activation energy (Ea)is reported. The oriented growth results in absence of grain boundaries parallel with the substrates, leading to large carrier mobility‐lifetime (µτ) product of 2.7 × 10−3 cm2 V−1, which is comparable to values of many perovskite bulk single crystals. Under low bias, hard X‐ray detectors exhibit high sensitivity of 1.2 × 104 µC Gy−1 cm−2 and low detection limit of 87.5 nGy s−1, which are comparable to those of many single‐crystal hard X‐ray detectors under high bias. Moreover, combination of low bias and high Ea results in weak halide ion migration and small dark current drift of 3.2 × 10−4 nA cm−1 s−1 v−1. Benefited from the superior detector performance, high‐contrast hard X‐ray imaging can be obtained at a low dose rate of 1.26 µGy s−1. The work may promote the application of perovskite hard X‐ray detectors in practical imaging area.

High Sensitivity and Ultra-Broad-Range NH3 Sensor Arrays by Precise Control of Step Defects on The Surface of Cl2-Ndi Single Crystals.

Vapor sensors with both high sensitivity and broad detection range are technically challenging yet highly desirable for widespread chemical sensing applications in diverse environments. Generally, an increased surface-to-volume ratio can effectively enhance the sensitivity to low concentrations, but often with the trade-off of a constrained sensing range. Here, an approach is demonstrated for NH3 sensor arrays with an unprecedentedly broad sensing range by introducing controllable steps on the surface of an n-type single crystal. Step edges, serving as adsorption sites with electron-deficient properties, are well-defined, discrete, and electronically active. NH3 molecules selectively adsorb at the step edges and nearly eliminate known trap-like character, which is demonstrated by surface potential imaging. Consequently, the strategy can significantly boost the sensitivity of two-terminal NH3 resistance sensors on thin crystals with a few steps while simultaneously enhancing the tolerance on thick crystals with dense steps. Incorporation of these crystals into parallel sensor arrays results in ppb-to-% level detection range and a convenient linear relation between sheet conductance and semi-log NH3 concentration, allowing for the precise localization of vapor leakage. In general, the results suggest new opportunities for defect engineering of organic semiconductor crystal surfaces for purposeful vapor or chemical sensing.

Light-induced edge-excitation of two-dimensional surface polaritons in atomically thin crystals

We theoretically investigate the light-induced excitation of two-dimensional surface polaritons (2DSPs) at the edge of atomically thin crystals. Through our analytic model based on the coupled mode theory, we achieve a precise and quantitative description of light interaction with the crystal's edge. Our model unveils three notable properties associated with the edge-excitation of 2DSPs. Firstly, under strong confinement conditions (i.e., polariton momentum significantly surpassing free-space photon momentum), the amplitude of edge-excited 2DSPs exhibits a cosine dependency on the incident angle. Secondly, the amplitude reaches a saturation point at a specific value as polariton momentum increases, depending on the incident angle. Lastly, we demonstrate that the edge-excitation of 2DSPs entails the generation of induced unbounded waves near the edge, leading to peak oscillations due to the interference between the 2DSPs and the unbounded waves.

Surface effect on the phase separation in thin liquid crystal film as seen from a mean-field approach

The effect of the interplay between attractive nonlocal surface interactions and attractive pair long-range intermolecular couplings on molecular structures of liquid crystals confined in thin cells with flat solid surfaces has been studied. It has been shown, in the framework of the extended McMillan′s mean field theory, that in the confined LC system a complex orientational and translational ordering of molecules can be induced. Several scenarios of the formation of local smectic A, nematic, and isotropic phases have been shown to coexist in a certain temperature range. Due to the nonlocality of the surface interaction, an unexpected complexity of the spatial arrangement of these local phases along the direction of the normal to the surface may exhibit itself.

Lattice strain-induced high-performance low-operating-voltage organic field-effect transistors by solution-sheared organic single crystal

This work employs lattice strain engineering to enhance OFET performance. By modulating the shear speed of solution shearing, lattice strain is induced in the C8-BTBT crystals, leading to a reduction in π–π stacking distance and thinner crystals.

Reproduction Experiments of Radial Pyroxene Chondrules Using a Gas-jet Levitation System under Reduced Conditions

Reproduction experiments of radial pyroxene (RP) chondrules were carried out using an Ar–H2 or Ar gas-jet levitation system in a reducing atmosphere in order to simulate chondrule formation in the protoplanetary disk. The experiments reproduced RP-chondrule textures, consisting of sets of thin pyroxene crystals and mesostasis glass between crystals. However, iron partition coefficients between pyroxene and glassy mesostasis (DFe =Fe mol%pyroxene/Fe mol%mesostasis) in natural RP chondrules were much higher than that in the experimentally reproduced RP chondrules. The high DFe in natural RP chondrules suggests that iron was removed from the mesostasis melt at high temperatures after the growth of pyroxene crystals. We found that many small iron-metal inclusions had formed in the mesostasis glass, indicating that FeO in the high-temperature melt of mesostasis was reduced to metallic iron, and iron in the mesostasis diffused into the newly formed metal inclusions. The formation of the iron-metal inclusions in the mesostasis was reproduced by our experiments in a reducing atmosphere, confirming that DFe in natural RP chondrules increased after the growth of RP crystals. Therefore, the DFe of RP chondrules can be an indicator to constrain cooling rates and redox states during chondrule formation.

Near room temperature multilevel resistive switching memory with thin film ionic liquid crystals

Multilevel operation of nonvolatile resistive random-access memory devices was demonstrated using thin films of an ionic liquid crystal, 1-dodecyl-3-methylimidazolium tetrafluoroborate ([C12mim][BF4]), as a resistive switching layer.

Polarization Based Out-Coupling for Cavity Based X-ray FELs

Cavity Based X-ray Free-Electron Lasers (CBXFELs) promise fully 3D coherent, very brilliant and shot-to-shot stable X-ray pulses. For CBXFELs the X-ray radiation is trapped in an X-ray optical cavity, which is formed using Bragg-reflecting crystal mirrors. As is the case for laser systems in the optical regime, a major question for the CBXFELs is how to couple out the radiation from the cavity. Possibilities range from employing semi-transparent thin crystals, over manipulation of the electron phase space density to cavity dumping schemes. In this work, making use of the strong polarization of Bragg reflection shall be studied for out-coupling. As the radiation does not change its polarization during Bragg reflection, reflection in the direction of the polarization vector is suppressed. By adjusting the 3D orientation of the crystals with respect to the polarization axis of a linearly polarized undulator, or vice versa, the transmission through the crystals can be tailored to some degree independently of the crystal thickness.

Twisted 2D Materials – A New Era in Condensed Matter Physics

Atomically thin crystals have changed our understanding of materials. With all their atoms exposed at the surface, it has become possible to tune their properties without altering their chemical composition, by means such as strain, electric-fields, or substrate engineering, resulting in new states of matter [1,2].

Electrochemical exfoliation of 2D materials beyond graphene.

After the discovery of graphene in 2004, the field of atomically thin crystals has exploded with the discovery of thousands of 2-dimensional materials (2DMs) with unique electronic and optical properties, by making them very attractive for a broad range of applications, from electronics to energy storage and harvesting, and from sensing to biomedical applications. In order to integrate 2DMs into practical applications, it is crucial to develop mass scalable techniques providing crystals of high quality and in large yield. Electrochemical exfoliation is one of the most promising methods for producing 2DMs, as it enables quick and large-scale production of solution processable nanosheets with a thickness well below 10 layers and lateral size above 1 μm. Originally, this technique was developed for the production of graphene; however, in the last few years, this approach has been successfully extended to other 2DMs, such as transition metal dichalcogenides, black phosphorous, hexagonal boron nitride, MXenes and many other emerging 2D materials. This review first provides an introduction to the fundamentals of electrochemical exfoliation and then it discusses the production of each class of 2DMs, by introducing their properties and giving examples of applications. Finally, a summary and perspective are given to address some of the challenges in this research area.

Electrochemical Intercalation and Exfoliation of CrSBr into Ferromagnetic Fibers and Nanoribbons.

Recent studies dedicated to layered van der Waals crystals have attracted significant attention to magnetic atomically thin crystals offering unprecedented opportunities for applications in innovative magnetoelectric, magneto-optic, and spintronic devices. The active search for original platforms for the low-dimensional magnetism study has emphasized the entirely new magnetic properties oftwo dimensional (2D) semiconductor CrSBr. Herein, for the first time, the electrochemical exfoliation of bulk CrSBr in a non-aqueous environment is demonstrated. Notably, crystal cleavage governed by the structural anisotropy occurred along two directions forming atomically thin and few-layered nanoribbons. The exfoliated material possesses an orthorhombic crystalline structure and strong optical anisotropy, showing the polarization dependencies of Raman signals. The antiferromagnetism exhibited by multilayered CrSBr gives precedence to ferromagnetic ordering in the revealed CrSBr nanostructures. Furthermore, the potential application of CrSBr nanoribbons is pioneered for electrochemical photodetector fabrication and demonstrates its responsivity up to 30µAcm-2 in the visible spectrum. Moreover, the CrSBr-based anode for lithium-ion batteries exhibited high performance and self-improving abilities. This anticipates that the results will pave the way toward the future study of CrSBr and practical applications in magneto- and optoelectronics.

Cluster-Based Approach Utilizing Optimally Tuned TD-DFT to Calculate Absorption Spectra of Organic Semiconductor Thin Films.

The photophysics of organic semiconductor (OSC) thin films or crystals has garnered significant attention in recent years since a comprehensive theoretical understanding of the various processes occurring upon photoexcitation is crucial for assessing the efficiency of OSC materials. To date, research in this area has relied on methods using Frenkel-Holstein Hamiltonians, calculations of the GW-Bethe-Salpeter equation with periodic boundaries, or cluster-based approaches using quantum chemical methods, with each of the three approaches having distinct advantages and disadvantages. In this work, we introduce an optimally tuned, range-separated time-dependent density functional theory approach to accurately reproduce the total and polarization-resolved absorption spectra of pentacene, tetracene, and perylene thin films, all representative OSC materials. Our approach achieves excellent agreement with experimental data (mostly ≤0.1 eV) when combined with the utilization of clusters comprising multiple monomers and a standard polarizable continuum model to simulate the thin-film environment. Our protocol therefore addresses a major drawback of cluster-based approaches and makes them attractive tools for OSC investigations. Its key advantages include its independence from external, system-specific fitting parameters and its straightforward application with well-known quantum chemical program codes. It demonstrates how chemical intuition can help to reduce computational cost and still arrive at chemically meaningful and almost quantitative results.

Molten pool free surface solidification behavior in laser remelted near-β titanium alloy

Free surface solidification (FSS) is a common physical phenomenon that has been found by various studies in metallurgy field while targeted studies are rare. This work investigated special structure and formation mechanism of surface grains generated by free surface solidification through laser remelting a near-β titanium alloy Ti-5Al-5Mo-5V-1Cr-1Fe (Ti-55,511). A thin layer crystal film covers molten pool surface through two-dimensional constrained solidification, which can be classified into flake-like crystal film located at molten pool edge and lotusleaf-like crystal film at molten pool center. Numerous cells grow from overflowing melt chill zone around molten pool edge and undergo two-dimensional constrained growth on surface, forming flake-like crystal films. TiNx particles formed from surface melt and N2 reaction can act as heterogeneous crystal nuclei, forming lotusleaf-like crystal films, whose secondary dendrite arm growth direction transforms from 〈100〉 of primary dendrite arm to 〈110〉. Equiaxed lotusleaf-like crystal films and columnar flake-like crystal films have a competitive growth relationship. Inward growth cells growing from two kinds crystal films form flake-like surface grains and central surface grains, respectively. This study can provide FSS theoretical guidance for laser additive manufacturing and surface modification.

Diffraction-based nonlinear model for the design of broadband adiabatic up-conversion imaging.

In recent years, mid-infrared parametric upconversion imaging, a nonlinear optical method that involves converting mid-infrared light into visible images, has significantly advanced and has shown considerable potential for various applications, including biomedical imaging and remote sensing. While diffraction-based parametric upconversion imaging modeling in standard thin birefringence crystals have been addressed, the numerical framework developed so far fails to address long aperiodic poled crystals. Specifically, diffraction-based analysis of the recent broadband adiabatic frequency upconversion imaging, which allows simultaneous image upconversion of extremely broadband signals is still lacking. Here, we introduce a diffraction-based numerical simulation framework for predicting the evolution of the nonlinear image/signal generation in upconversion imaging systems. This generalized framework can handle both periodically and aperiodically poled crystal designs. Specifically, the model captures faithfully and addresses the varying image magnification arising from upconversion at a Fourier plane of a multiwavelength object. The numerical simulations are validated by experimental measurements of broadband upconversion 3-5 µm mid-IR images to the visible-NIR, showing a good agreement. Moreover, the model allows the exploration of the trade-offs in the spectral span when moving to the full visible range. Our numerical framework will be useful for the interpretation of experimental results obtained in an imaging setting with nonlinear optical elements.

Microstructural and mechanical properties of additive manufactured 2319 aluminum alloy annular-shaped components: As-built and multistage heat treatment

A novel multistage aging heat-treatment method was applied to investigate the microstructural evolution and properties of an additive-manufactured 2319 aluminum alloy. The microstructure and mechanical properties were analyzed, and the results revealed that the as-built annular-shaped components were characterized by an alternating distribution of thin equiaxed crystals, dendrites, and coarse columnar crystals. The microstructure occurs recrystallization and the average grain size decreased after the two-stage aging treatment. The maximum texture strength in the selected area increased after the two-stage aging treatment, and the angle grain boundaries were evenly distributed. Solid solution plus aging could significantly improve ultimate tensile strength and hardness. The tensile fracture morphology was typical of ductile fracture. Two-stage aging exhibited a higher corrosion resistance.

Insight on MWW siliceous zeolites: From 2D precursors toward 3D structure

ITQ-1 layered zeolites, with MWW framework, were prepared using different synthesis and calcination procedures and fully characterized by means of X-ray diffraction, scanning electron microscopy, N2 sorption and vibrational and nuclear magnetic resonance spectroscopies. Exploring different compositions of the precursor gel, the role of the Organic Structure Directing Agent (OSDA) was definitely disclosed. We proved that the concentration of OSDA in the synthesis gel affects the short-range crystalline order of zeolite crystals. In particular, diluted precursor gels led to the formation of low-density materials in the form of hollow spheres, with partially disordered layers, thinner crystals and high defectivity. In general, all ITQ-1 samples had the same crystalline structure but different morphology, either rose-like or hollow spheres. Moreover, the calcination procedure had an impact on the structural defects of the ITQ-1 zeolite: the higher the removal rate of the OSDA, the higher the defectivity degree of the zeolite.

Hall effect in the MnBi2Te4 crystal using silicon nitride nanomembrane via contacts

Utilizing an interplay between band topology and intrinsic magnetism, the two-dimensional van der Waals (vdW) system MnBi2Te4 provides an ideal platform for realizing exotic quantum phenomena and offers great opportunities in the emerging field of antiferromagnetic spintronic technology. Yet, the fabrication of MnBi2Te4-based nanodevices is hindered by the high sensitivity of this material, which quickly degrades when exposed to air or to elevated temperatures. Here, we demonstrate an alternative route of fabricating vdW-MnBi2Te4-based electronic devices using the cryogenic dry transfer of a printable circuit embedded in an inorganic silicon nitride membrane. The electrical connections between the thin crystal and the top surface of the membrane are established through via contacts. Our magnetotransport study reveals that this innovative via contact approach enables exploring the MnBi2Te4-like sensitive 2D materials and engineering synthetic heterostructures as well as complex circuits based on the two-dimensional vdW systems.