Flat Crystal Research Articles

Dual‐exterior surface modification of layered double hydroxides and its application in flame retardant biobased poly(trimethylene terephthalate)

AbstractThe overall target of this research was to design a dual‐exterior surface chemical modification of eco‐friendly layered double hydroxides (LDH‐S@PA) using calcium stearate and phytic acid (PA) containing‐rich phosphorus to synchronously boost the dispersibility in the polymer matrix and the flame retardancy. Microstructure, surface chemical environments and morphologies of LDH‐S@PA were characterized. It was found that the target product with the hydrophobic surface was successfully prepared. The basic morphologies of LDH‐S@PA exhibited thin flat crystals composed of multi‐sheet with hexagonally arranged spots. Meanwhile, the thermal stability of LDH‐S@PA was improved. Significantly, after adding LDH‐S@PA into biobased poly(trimethylene terephthalate) (PTT) via melting‐blending, LDH‐S@PA exhibited a higher dispersity in the PTT matrix and the PTT/LDH‐S@PA composite with 20 wt% loading achieved 29.8% limiting oxygen index value and possessed V‐0 rating in UL‐94 test, revealing LDH‐S@PA dramatically enhanced the flame retardancy of the PTT. The flame retarded mechanism of LDH‐S@PA in PTT was discussed based on gaseous and condensed phase analysis. In addition, the incorporation of LDH‐S@PA improved the mechanical properties of the composites. This facile and straightforward approach for dual‐surface modification LDHs holds promise as flame retardant formulations for polymer in future applications.

Single‐Crystal Capacitive Sensors with Micropatterned Electrodes via Space‐Confined Growth of the Metal–Organic Framework HKUST‐1

AbstractThe polyhedral shape and fragile nature of single crystals of metal–organic frameworks (MOFs) hinder their processing using standard microfabrication techniques. As a result, the fabrication of surface patterns and microelectrodes on MOF single crystals is challenging, which limits both the direct electrical interrogation of crystals in research and their integration into optical and electrical devices. Herein, a new strategy to readily fabricate surface‐embossed micropatterns and surface‐embedded gold electrodes on MOF single crystals using a space‐confined, one‐step solvothermal synthesis is demonstrated. This method is based on the confined growth of the MOF crystal around prefabricated metal patterns with different adhesion strengths to the growth surface, producing features as small as 5 µm. As a proof of concept, micropatterns are created on flat single crystals of the MOF HKUST‐1, exhibiting the function as a diffraction grating. Additionally, a single‐crystal HKUST‐1 capacitive gas sensor with surface‐embedded electrodes that serves as a stable platform for the investigation of ethanol diffusion in the MOF pores is fabricated. The space‐confined fabrication strategy is promising for the integration of fragile MOF single crystals in various optical and electrical devices.

Position dispersive X-ray fluorescence

A novel scanning-free wavelength dispersive X-ray fluorescence spectrometer has been developed by combining low power X-ray tubes with X-ray optics. The X-rays are focused to a single point on the sample and then dispersed onto a flat diffracting crystal where they are spread depending on their energy through Bragg's law of diffraction onto a silicon strip detector. Throughout this study, the proposed method is referred to as Position Dispersive X-ray Fluorescence (PDXRF). The X-ray emission spectra of vanadium and copper as well as, CuO, CuS2 and V2O5 were measured. In the spectrometer energy resolutions of 3.14 eV and 8.94 eV FWHM were measured for V and Cu when measuring over a range of 4.8–5.8 keV and 6.2–9.1 keV respectively. The Kβ line shapes were fitted with a series of Voigt profiles and the energies and intensities of the Kβ valence transition peak, Kβ2,5, were determined. There was also sufficient variation in the intensity ratio of Kβ2,5/Kβ1,3 that the oxygen and sulphur compounds of V and Cu could be successfully observed and measured. The result demonstrates that this experimental setup is capable of measuring the Kβ line shape at resolutions of a few eV, allowing for chemical state analysis to be performed on 3d transition metals and their compounds such as the measurement of redox reactions to aid in battery development.

Rutile facet-dependent fibrinogen conformation: Why crystallographic orientation matters

Previous studies implied that single crystalline rutile surfaces have the ability to guide the functionality of adsorbed blood plasma proteins. However, a clear relation between the rutile crystallographic orientation and conformation of adsorbed proteins is still missing. Here, we examine the adsorption characteristics of human plasma fibrinogen (HPF) on atomically flat single rutile crystals with (110), (100), (101) and (001) facets. By direct visualization of individual protein molecules through atomic force microscopy (AFM) imaging, the distinct conformations of HPF were determined depending on rutile surface crystallographic orientation. In particular, dominant trinodular and globular conformation was found on (110) and (001) facets, respectively. The observed variations of HPF conformation were reasoned from the surface water contact angle and surface energy point of view. By analyzing AFM-based force measurements, statistically significant changes in surface energies of rutile surfaces covered with HPF were determined and linked to HPF conformation. Furthermore, the facet-dependent structural rearrangement of HPF was indirectly confirmed through deconvolution of high-resolution X-ray photoelectron spectroscopy (XPS) carbon and nitrogen spectra. The globular, and thus native-like HPF conformation observed on (001) facet, was reflected in the lowest level of amino group formation. We propose that the mechanism behind the crystallographic orientation-induced HPF conformation is driven by the facet-specific surface hydrophilicity and energy. From the biomedical material perspective, our results demonstrate that the conformation of HPF can be guided by controlling the crystallographic orientation of the underlying material surface. This might be beneficial to the field of titanium-based biomaterials design and development.

Electronic gap stability of two-dimensional tin monosulfide phases: Towards optimal structures for electronic device applications

It is well known that tin monosulfide is a potential environment-friendly solar cell material that maximizes light-energy conversion efficiency, given its band gap at the peak of the solar emission spectrum. However, the presence of Sn and S vacancies at the surface of SnS hinders the performance of these solar cells. In the present work, we have prepared tin sulfide platelets on graphite using vapor phase deposition under a known temperature gradient. Remarkably, we observe two types of growth modes: (i) a dominant one with platelet-like flat crystals and (ii) a less favorable one, formed by spiral terraces. Both structures present a chemical composition compatible with SnS. Using scanning tunneling microscopy (STM) and spectroscopy (STS), we observe that, whereas flat SnS platelets exhibit fluctuations in the band gap and doping, spiral platelets exhibit stable, homogeneous band gap, and negative doping. Using selected area electron diffraction (SAED), we determine that, whereas the platelets of the unstable phase are associated with the common orthorhombic structure of SnS, the minor stable spiral platelets are polycrystalline and are in the metastable cubic phase. The production of this less favorable phase on large surface areas is of potential interest for the production of more efficient tin sulfide-based solar cells. In addition, our analysis of solar cell materials using STM/STS and SAED provides a framework for the rapid determination of the suitability and applicability of 2D materials for other potential optoelectronic applications.

Calibration method for parabolic reflector measurement by using reverse Hartmann test.

Careful calibration of system geometric position and camera errors is crucial to achieve high testing accuracy for large-scale aspherical surfaces. We propose a geometrical optical calibration method for increasing the overall accuracy of a large-scale reverse Hartmann test system to realize the parabolic reflector measurement. By using a flat crystal, a mask with uniform holes and an external pinhole aperture in front of the camera, camera lens distortions and keystone distortion, as well as system geometry correspondence between LCD screen, camera, and reflecting point on the test surface, are determined accurately. We experimentally demonstrated that the proposed calibration method achieves high slope detection accuracy for a large-scale parabolic reflector: tens of microradians within 1620(H)×850(V)mm2.

Design of α/β-Hybrid Peptide Ligands of α4β1 Integrin Equipped with a Linkable Side Chain for Chemoselective Biofunctionalization of Microstructured Materials.

Arg-Gly-Asp (RGD)-binding integrins, e.g., αvβ3, αvβ1, αvβ5 integrins, are currently regarded as privileged targets for the delivery of diagnostic and theranostic agents, especially in cancer treatment. In contrast, scarce attention has been paid so far to the diagnostic opportunities promised by integrins that recognize other peptide motifs. In particular, α4β1 integrin is involved in inflammatory, allergic, and autoimmune diseases, therefore, it represents an interesting therapeutic target. Aiming at obtaining simple, highly stable ligands of α4β1 integrin, we designed hybrid α/β peptidomimetics carrying linkable side chains for the expedient functionalization of biomaterials, nano- and microparticles. We identified the prototypic ligands MPUPA-(R)-isoAsp(NHPr)-Gly-OH (12) and MPUPA-Dap(Ac)-Gly-OH (13) (MPUPA, methylphenylureaphenylacetic acid; Dap, 2,3-diamino propionic acid). Modification of 12 and 13 by introduction of flexible linkers at isoAsp or Dap gave 49 and 50, respectively, which allowed for coating with monolayers (ML) of flat zeolite crystals. The resulting peptide–zeolite MLs were able to capture selectively α4β1 integrin-expressing cells. In perspective, the α4β1 integrin ligands identified in this study can find applications for preparing biofunctionalized surfaces and diagnostic devices to control the progression of α4β1 integrin-correlated diseases.

Study of the Relationship between the Edge Effect and the Phenomenon of Focusing X-Rays in Flat Crystals

Study of the Relationship between the Edge Effect and the Phenomenon of Focusing X-Rays in Flat Crystals

Tungsten Ditelluride: Synthesis, Structure, and Magnetoresistance Property

AbstractTungsten ditelluride (WTe2) is arising as an attractive material in magnetoresistance (MR) properties filed. The magnetoresistance properties of WTe2 makes it an ideal material for its magnetoresistive heads of computer and magnetic sensor device applications. So far, people have developed various controlled synthesis methods to produce large‐quantity uniform flat WTe2 crystals. Nevertheless, none of the methods are sustainable, some methods use reducing gases, and some use very long heat preservation, and the process is very complicated. Here, a mild and fast self‐flux method is described for WTe2 synthesis that can avoid producing reducing gases. After conducting structural and physical tests, it is found that annealing time is critical for WTe2 structure formation. Long annealing time improves the crystallinity of WTe2 and makes its texture more obvious, increasing the conductivity of WTe2. Therefore, it will lead to the anomalous nonsaturating positive magnetoresistance with different field dependent behaviors, reaching the ultrastrong magnetoresistive value of 1040% at 5 K and 14 T. The results provide a sustainable approach for uniform WTe2 crystal synthesis, which will benefit the large‐quantity production of WTe2 magnetoresistive materials.

Two-dimensional hole gas in organic semiconductors.

A highly conductive metallic gas that is quantum mechanically confined at a solid-state interface is an ideal platform to explore non-trivial electronic states that are otherwise inaccessible in bulk materials. Although two-dimensional electron gases have been realized in conventional semiconductor interfaces, examples of two-dimensional hole gases, the counterpart to the two-dimensional electron gas, are still limited. Here we report the observation of a two-dimensional hole gas in solution-processed organic semiconductors in conjunction with an electric double layer using ionic liquids. A molecularly flat single crystal of high-mobility organic semiconductors serves as a defect-free interface that facilitates two-dimensional confinement of high-density holes. A remarkably low sheet resistance of 6 kΩ and high hole-gas density of 1014 cm-2 result in a metal-insulator transition at ambient pressure. The measured degenerate holes in the organic semiconductors provide an opportunity to tailor low-dimensional electronic states using molecularly engineered heterointerfaces.

Detailed diffraction imaging of x-ray optics crystals with synchrotron radiation

Rocking curve topography at the Advanced Photon Source's beamline 1-BM measures the x-ray reflection from large (many cm2) flat crystals on a sub-mm scale with microradian angular resolution. The (011̄1) reflection at 8 keV is uniform across the crystal and close to theory for three thick quartz wafers well-polished with increasingly finer grit. However, the reflection is non-uniform for some ∼0.1 mm thin, bendable crystals that are made flat by optical contact with a flat substrate. These thin crystals are bent to serve in certain x-ray diagnostics of plasmas, and similar non-uniformities could then occur in bent crystals as well. The same detail in x-ray reflection in bent crystals is unachievable with the existing topography setup: One way to get the desired resolution is with a standard microfocusing approach.

Water friction in nanofluidic channels made from two-dimensional crystals

Membrane-based applications such as osmotic power generation, desalination and molecular separation would benefit from decreasing water friction in nanoscale channels. However, mechanisms that allow fast water flows are not fully understood yet. Here we report angstrom-scale capillaries made from atomically flat crystals and study the effect of confining walls’ material on water friction. A massive difference is observed between channels made from isostructural graphite and hexagonal boron nitride, which is attributed to different electrostatic and chemical interactions at the solid-liquid interface. Using precision microgravimetry and ion streaming measurements, we evaluate the slip length, a measure of water friction, and investigate its possible links with electrical conductivity, wettability, surface charge and polarity of the confining walls. We also show that water friction can be controlled using hybrid capillaries with different slip lengths at opposing walls. The reported advances extend nanofluidics’ toolkit for designing smart membranes and mimicking manifold machinery of biological channels.

Analytical solution of crystal diffraction intensity* *Project supported by the National Natural Science Fundation of China (Grant Nos. 11775203 and 12075219) and the ChinaAcademy of Engineering Physics (CAEP) Foundation (Grant No. CX20210019).

Plasma density and temperature can be diagnosed by x-ray line emission measurement with crystal, and bent crystals such as von Hamos and Hall structures are proposed to improve the diffraction brightness. In this study, a straightforward solution for the focusing schemes of flat and bent crystals is provided. Simulations ith XOP code are performed to validate the analytical model, and good agreements are achieved. The von Hamos or multi-cone crystal can lead to several hundred times intensity enhancements for a 200 upmu mplasma source. This model benefits the applications of the bent crystals.

基于平面平晶的单次自相关仪标定技术研究

基于平面平晶的单次自相关仪标定技术研究

Out-of-plane corrugations in graphene based van der Waals heterostructures

Graphene, the first truly two-dimensional material isolated, is never perfectly flat. Even when it is sandwiched between other atomically flat crystals, it still slightly ripples. These out-of-plane corrugations, deformations of the graphene layer into the third dimension, have profound implications on graphene's properties. They reduce the mobility of electrons moving within graphene just like bumps on a road slow down a car. Here, the authors demonstrate the presence of such corrugations by studying the quantum mechanical phase electrons acquire in the presence of a magnetic field.

Inkjet‐Printed Conductive ITO Patterns for Transparent Security Systems

AbstractIndium tin oxide (ITO) is a transparent conducting material that is widely used in devices where high transparency of the electrodes is required, such as flat panel and liquid crystal displays, touch panels, smart windows, and many others. ITO layers are deposited on a large scale by magnetron sputtering and then structured by lithography to define desired patterns of transparent electrodes. Here, a method for direct printing of transparent conductive patterns from ITO nanoparticle ink is communicated. The method combines inkjet printing with fast flash lamp annealing whereby the main novelty is to use an additional layer of a colored organic dye onto printed ITO to increase light absorption. The dye coating is instantly heated together with the underlying ITO layer by a light pulse, leading to an instant rise of the surface temperature, which is translated into improved optoelectronic properties of the ITO layers. Inkjet‐printed ITO patterns processed with the dye‐assisted flash lamp annealing exhibit a transmittance of up to 88% at 550 nm and resistivity of 3.1 × 10−3 Ω cm. Transparent touch‐sensing trackpad and capacitive touch sensors are demonstrated based on the printed ITO patterns, which can be utilized in transparent security systems and other transparent Internet‐of‐Things devices.

Dislocation screening in crystals with spherical topology.

Whereas disclination defects are energetically prohibitive in two-dimensional flat crystals, their existence is necessary in crystals with spherical topology, such as viral capsids, colloidosomes, or fullerenes. Such a geometrical frustration gives rise to large elastic stresses, which render the crystal unstable when its size is significantly larger than the typical lattice spacing. Depending on the compliance of the crystal with respect to stretching and bending deformations, these stresses are alleviated either by a local increase of the intrinsic curvature in proximity of the disclinations or by the proliferation of excess dislocations, often organized in the form of one-dimensional chains known as "scars." The associated strain field of the scars is such as to counterbalance the one resulting from the isolated disclinations. Here we develop a continuum theory of dislocation screening in two-dimensional closed crystals with genus one. Upon modeling the flux of scars emanating from a given disclination as an independent scalar field, we demonstrate that the elastic energy of closed two-dimensional crystals with various degrees of asphericity can be expressed as a simple quadratic function of the screened topological charge of the disclinations, at both zero and finite temperature. This allows us to predict the optimal density of the excess dislocations as well as the minimal stretching energy attained by the crystal.

Flat Glass or Crystal Dome Aperture? A Year-Long Comparative Analysis of the Performance of Light Pipes in Real Residential Settings and Climatic Conditions

This paper presents the first comparative study of its type of the performance of light pipes with different types of apertures: a flat glass versus a bohemian crystal dome. Measurements were taken at 20-minute intervals over a period of one year in the bathrooms of two newly built identical houses of the same orientation located in Manchester, UK. The comparative analysis of the data collected for both light pipes types reveals that the crystal domed aperture consistently outperforms the flat glass one. Furthermore, the difference in the recorded horizontal illuminance is most marked during the winter months and at the end of the one-year experiment, indicating that the crystal dome has better performance for low incident winter light and higher resistance for the long term effect of weathering and pollution. This study provides strong evidence based on long term real measurements. Such evidence informs architects’ decisions when weighing up the aesthetic considerations of a flat glass aperture versus the higher illumination levels afforded by a crystal dome aperture with higher resistance to weathering and pollution.

Intrinsic Capacitance of Molybdenum Disulfide.

The metallic, 1T polymorph of molybdenum disulfide (MoS2) is promising for next-generation supercapacitors due to its high theoretical surface area and density which lead to high volumetric capacitance. Despite this, there are few fundamental works examining the double-layer charging mechanisms at the MoS2/electrolyte interface. This study examines the potential-dependent and frequency-dependent area-specific double-layer capacitance (Ca) of the 1T and 2H polymorphs of MoS2 in aqueous and organic electrolytes. Furthermore, we investigate restacking effects and possible intercalation-like mechanisms in multilayer films. To minimize the uncertainties associated with porous electrodes, we carry out measurements using effectively nonporous monolayers of MoS2 and contrast their behavior with reduced graphene oxide deposited layer-by-layer on atomically flat graphite single crystals using a modified, barrier-free Langmuir-Blodgett method. The metallic 1T polymorph of MoS2 (Ca,1T = 14.9 μF/cm2) is shown to have over 10-fold the capacitance of the semiconducting 2H polymorph (Ca,2H = 1.35 μF/cm2) near the open circuit potential and under negative polarization in aqueous electrolyte. However, under positive polarization the capacitance is significantly reduced and behaves similarly to the 2H polymorph. The capacitance of 1T MoS2 scales with layer number, even at high frequency, suggesting easy and rapid ion penetration between the restacked sheets. This model system allows us to determine capacitance limits for MoS2 and suggest strategies to increase the energy density of devices made from this promising material.

Pick and Place Distributed Feedback Lasers Using Organic Single Crystals

AbstractOrganic single crystals are of interest for optoelectronic applications due to their highly ordered molecular stacking and small defect concentration, giving the possibility of high mobility and luminescence efficiency. To achieve lasing in large flat single crystals, a simple “pick and place” method of mounting organic single crystals onto distributed feedback gratings is demonstrated. Efficient lasing is achieved with three kinds of active organic single crystals, indicating the potential for broad application of the method for making single crystal lasers using distributed feedback gratings. Detailed investigations of the anisotropic refractive index and waveguide simulations further confirm that distributed feedback can provide efficient ways of fabricating organic single crystal lasers.