Ultrathin Crystal Research Articles

On classical and quantum effects at scattering of ultrarelativistic electrons in ultrathin crystal

Classical and quantum properties of scattering of ultrarelativistic electrons in ultrathin crystals are considered. A comparison is made of these two ways of study of scattering process. In classical consideration we remark the appearance of sharp peaks in angular distribution of scattered particles, that is treated as a manifestation of the rainbow scattering phenomenon, and in quantum case we show sharp peaks in the angular distribution that arise from the interference of single electrons on numerous crystal planes and can be expressed in terms of reciprocal lattice vectors. We show that for some parameters the quantum predictions substantially differ from the classical ones. The influence of beam divergence on the possibility of experimental observation of the studied effects is estimated.

Triple band‐notched UWB monopole antenna on ultra‐thin liquid crystal polymer based on ESCSRR

A triple band-notched UWB monopole antennas is presented for flexible electronics. To enhance the flexibility, ultra-thin liquid crystal polymer with 50 μm thickness is used as the substrate. The antennas are constituted by swallow tail radiation patch and trapezoid ground. Moreover, band-notched characteristic is realised by etching different sized elliptic single complementary split-ring resonators on the radiation patch. An improved triple band-notched UWB antenna with notched-frequency bands at 3.7–4.2 GHz, 5.15–5.35 GHz, and 5.725–5.825 GHz are designed by a novel capacitance compensation method. The measured radiation patterns indicate that the antennas are an omni-directional antenna both at flat and bent circumstances. The occupied area of antenna is 27 × 21 mm.

UWB flexible filter with low loss and excellent stopband performance

ABSTRACTThe compact UWB flexible filter with low loss and excellent stop band suppression on ultrathin liquid crystal polymer substrate is presented firstly. A uniform microstrip line connected with five pairs of stubs is used. The flexible filter with the pass band of 4.1–10.6 GHz. The measured minimum insertion loss is 0.76 dB at 5.4 GHz and the return loss is better than 11.3 dB. While the frequency is higher than 12.1 GHz, excellent high resistance band suppression is obtained. The bending behavior of the UWB flexible filter is analyzed. In case of R = 17.5 mm, the insertion loss is only improved by 0.004 dB and the return loss is optimized by 0.45dB. Good agreement is obtained between the flat and the bending. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:194–197, 2017

Improving time and space resolution in electro-optic sampling for near-field terahertz imaging

In this Letter, we present a significant improvement to time and space resolutions in electro-optic sampling (EO) for two-dimensional terahertz (THz) near-field imaging. Using a THz microscope, we readapt a recent EO sampling scheme based on optical probe spectrum filtering. Combined with an ultra-thin EO crystal, we achieve record broadband video-rate THz near-field imaging. Particularly, this new scheme improves the THz bandwidth, the imaging contrast, and the spatial resolution. To validate our method, we show THz near-field images ranging from 100 GHz to 4 THz with a spatial resolution up to λ/600 at 100 GHz. This demonstration positively affects the detection of intense THz pulses derived from the tilted-pulse-front excitation of lithium niobate and will accelerate our understanding of the interaction processes between electromagnetic waves and the conducting electrons of metallic interfaces.

44-2: Ultra-Thin High-Dichroic-Ratio Polarizer Generated by Photoalignment

A dichroic polarizer with a high dichroic ratio of up to 60 is achieved by photoalignment induced anisotropic azo dye ordering. The film thickness is well controlled in 200 nm, and it is 500 times thinner than a conventional iodine Polaroid polarizer, which is desirable for ultra-thin high performance liquid crystal display applications.

Nanoseed Assisted PVT Growth of Ultrathin 2D Pentacene Molecular Crystal Directly onto SiO2 Substrate

High order of molecular packing and perfect semiconductor/dielectric interface are two key factors to achieve high performance for organic field-effect transistors (OFET). Moreover, the thin crystal offers an improved efficiency of carrier injection for OFETs. To this aim, formation of thin and large single crystal directly on dielectrics is the basis to obtain the ideal crystal OFETs. Herein, we report the controlled growth of ultrathin 2D Pentacene (Pn) crystal via nanoseed assisted physical vapor transport (PVT) method grown directly on SiO2. The size, thickness, and density of Pn crystals are systematically studied. Potentially effective parameters such as initially lowered Pn coverage and decreased supersaturation with the aid of carrier gas flow were optimized to grow large, ultrathin 2D Pn crystalline flakes efficient for the fabrication of crystal OFETs. The typical size and thickness of as-grown Pn crystalline flakes can be controlled to be large and thin enough. Device of ultrathin crystal with ...

Mechanical exfoliation and Raman spectra of ultrathin PbI2 single crystal

In this paper, we report the successful fabrication of ultrathin PbI2 single crystal by mechanical exfoliation method after the realization of graphene. The properties of samples were investigated by X-ray diffraction, atomic force microscopy and Raman scattering. The XRD spectrum indicates that PbI2 crystal has hexagonal crystalline pattern with 2H type crystal structure. The thickness around 10nm about 15 layers of PbI2 single crystal verified by AFM was obtained. Five Raman bands with peaks at 73, 95, 111, 167, and 214cm−1 are observed with 532nm laser, while there are only four bands can be observed for laser 676.4nm and 514.5nm respectively. The results of ultrathin PbI2 single crystal will stimulate further theoretical calculations and experimental investigation of their fundamental properties and potential applications.

Design of band‐notched ultra wideband antenna for indoor and wearable wireless communications

Design of a tapered-slot ultra wideband (UWB) band-notched wearable antenna is presented in this study. The antenna operation covers the whole UWB frequency spectrum of 7.5 GHz ranging from 3.1 to 10.6 GHz, while rejecting the wireless local area network operation at 5.25 GHz band. The performance of the antenna is analysed through simulations and validated through measurements. The antenna makes use of ultra-thin liquid crystal polymer (LCP) substrate. The presented return loss and radiation pattern results show that the antenna offers excellent performance in the UWB frequency band in free space. Use of the LCP substrate makes the antenna to efficiently mitigate the bending effects. Moreover, the antenna performs well in on-body configurations and its working is little affected in adversely hot and humid weather conditions. Furthermore, it offers good on-body communication link and pulse fidelity. These features make the proposed antenna design a well-suited choice for hand-held and wearable UWB applications.

X‐band flexible bandpass filter based on ultra‐thin liquid crystal polymer substrate

The performance of an X-band flexible band-filter on ultra-thin liquid crystal polymer (LCP) substrate is investigated. The 50 µm-thick LCP substrate is adopted to enhance the flexibility of circuits. For the purpose of fabrication by the conventional printed circuit board process, copper-clad laminate with 18 µm thickness is selected. Excellent microwave transmission characterisation is demonstrated by measuring the microstrip line at flat and bending conditions. An X-band interdigital bandpass filter based on a half-wavelength microstrip line resonator is designed and fabricated for purpose of demonstration. The measured results at the flat condition show that the insertion loss is 2.1 dB at centre frequency of 9.4 GHz and the return loss is better than 20 dB at the designed band. The performance at the bending condition shows that the bending effect causes little deterioration to the performance at a different bending radius.

Solvent vapour mediated spontaneous healing of self-organized defects of liquid crystal films.

Ultrathin liquid crystal films showed a nematic to isotropic transition when exposed to solvent vapour for a short duration while a reverse isotropic to nematic transition was observed when the film was isolated from the solvent exposure. The phase transitions were associated with the appearance and fading of surface patterns as the solvent molecules diffused into and out of the film matrix, resulting in the destruction or restoration of the orientational order. A long-time solvent vapour exposure caused the dewetting of the film on the surface, which was demonstrated by the formation of holes and their growth in size with the progress of time. Even at this stage, withdrawal of the solvent exposure produced an array of nematic fingers, which nearly self-healed the dewetted holes. The change in contact angle due to the phase transition coupled with the imbalance of osmotic pressure across the contact line due to the differential rate of solvent evaporation from the film and the hole helped the fingers to grow towards the centre of the hole. The appearance of the fingers upon withdrawal of the solvent exposure and their disappearance upon exposure to solvent were also found to be a nearly reversible process. These findings could significantly contribute to the development of vapour sensors and self-healing surfaces using liquid crystal thin films.

Transitions between photoinduced macroscopic quantum states in 1T-TaS2 controlled by substrate strain

Controllable switching to and from metastable states of matter using electromagnetic fields could potentially revolutionize electronic logic and memory devices. Here, we investigate the effect of two-dimensional strain on switching between a photoinduced “hidden” state and a stable charge-ordered state in ultrathin 1T-TaS2 crystal films on different substrates, photoexcited by 35 fs laser pulses. The differential contraction of the sample and the substrate shows a very large and negative strain coefficient on the hidden state transition, implying that the stability of the hidden state could be markedly increased by tensile strain. Other transitions are not strongly affected by tensile strain.

Exotic X-ray back-diffraction: a path toward a soft inelastic X-ray scattering spectrometer

In this work, soft X-ray back-diffraction (XBD; X-ray diffraction at angles near and exactly equal to 90°) is explored. The experiment was conducted at the SXS beamline at Laboratorio Nacional de Luz Sincrotron, Brazil, at ∼3.2 keV. A high-resolution Si(220) multi-bounce back-diffraction monochromator was designed and constructed for this experiment. An ultra-thin Si(220) crystal (5 µm thick) was used as the sample. This ultra-thin crystal was characterized by profilometry, rocking-curve measurements and X-ray topography prior to the XBD measurements. It is shown that the measured forward-diffracted beam (o-beam) profiles, taken at different temperatures, are in close agreement with profiles predicted by the extended dynamical theory of X-ray diffraction, with the absence of multiple-beam diffraction (MBD). This is an important result for future studies on the basic properties of back-diffracted X-ray beams at energies slightly above the exact XBD condition (extreme condition where XBD is almost extinguished). Also, the results presented here indicate that stressed crystals behave like ideal strain-free crystals when used for low-energy XBD. This is mainly due to the large widths of XBD profiles, which lead to a low strain sensitivity in the detection of defects. This result opens up new possibilities for mounting spherical analyzers without degrading the energy resolution, at least for low energies. This is a path that may be used to construct a soft inelastic X-ray scattering spectrometer where different applications such as element-specific magnetic imaging tools could be explored.

Flux dynamics and angular distributions of relativistic electrons and positrons passing through a half-wave crystals

The simulation of trajectories, angular and spatial distributions of relativistic electrons and positrons (155 MeV – 1500 MeV) penetrating through an ultra-thin crystal (half-wave crystal – HWC) has been performed taking into account initial angular beam divergence. The results show similarities and differences with non-relativistic protons channeling in a HWC.

Coherent Production of Relativistic Singlet Ps Atoms by High Energy Photons and Electrons in Aligned Crystals – Revisited

Cross-sections of coherent production of relativistic (moving with relativistic velocities) singlet Ps atoms in the ultrathin crystal have been calculated and estimations of counting rates are obtained to propose the experiments.

Mirroring of 400 GeV/c protons by an ultra-thin straight crystal

Channeling is the confinement of the trajectory of a charged particle in a crystalline solid. Positively charged particles channeled between crystal planes oscillate with a certain oscillation length, which depends on particle energy. A crystal whose thickness is half the oscillation length for planar channeling may act as a mirror for charged particles. If the incident angle of the particle trajectory with the crystal plane is less than the critical angle for channeling, under-barrier particles undergo half an oscillation and exit the crystal with the reversal of their transverse momentum, i.e., the particles are “mirrored” by the crystal planes. Unlike the traditional scheme relying on millimeter-long curved crystals, particle mirroring enables beam steering in high-energy accelerators via interactions with micrometer-thin straight crystal. The main advantage of mirroring is the interaction with a minimal amount of material along the beam, thereby decreasing unwanted incoherent nuclear interactions. The effectiveness of the mirror effect for ultrarelativistic positive particles has been experimentally proven at external lines of CERN-SPS. The mirroring effect in a 26.5-μm-thick Si crystal has been studied in the experiment with a narrow beam of 400 GeV/c protons at the CERN-SPS. The reflection efficiency for a quasi-parallel beam is larger than 80%.

Vacuum filtration based formation of liquid crystal films of semiconducting carbon nanotubes and high performance transistor devices

In this paper, we report ultra-thin liquid crystal films of semiconducting carbon nanotubes using a simple vacuum filtration process. Vacuum filtration of nanotubes in aqueous surfactant solution formed nematic domains on the filter membrane surface and exhibited local ordering. A 2D fast Fourier transform was used to calculate the order parameters from scanning electron microscopy images. The order parameter was observed to be sensitive to the filtration time demonstrating different regions of transformation namely nucleation of nematic domains, nanotube accumulation and large domain growth.Transmittance versus sheet resistance measurements of such films resulted in optical to dc conductivity of σopt/σdc = 9.01 indicative of purely semiconducting nanotube liquid crystal network.Thin films of nanotube liquid crystals with order parameters ranging from S = 0.1–0.5 were patterned into conducting channels of transistor devices which showed high Ion/Ioff ratios from 10–19 800 and electron mobility values μe = 0.3–78.8 cm2 (V-s)−1, hole mobility values μh = 0.4–287 cm2 (V-s)−1. High Ion/Ioff ratios were observed at low order parameters and film mass. A Schottky barrier transistor model is consistent with the observed transistor characteristics. Electron and hole mobilities were seen to increase with order parameters and carbon nanotube mass fractions. A fundamental tradeoff between decreasing on/off ratio and increasing mobility with increasing nanotube film mass and order parameter is therefore concluded. Increase in order parameters of nanotubes liquid crystals improved the electronic transport properties as witnessed by the increase in σdc/σopt values on macroscopic films and high mobilities in microscopic transistors. Liquid crystal networks of semiconducting nanotubes as demonstrated here are simple to fabricate, transparent, scalable and could find wide ranging device applications.

In Vivo Silicon-Based Flexible Radio Frequency Integrated Circuits Monolithically Encapsulated with Biocompatible Liquid Crystal Polymers

Biointegrated electronics have been investigated for various healthcare applications which can introduce biomedical systems into the human body. Silicon-based semiconductors perform significant roles of nerve stimulation, signal analysis, and wireless communication in implantable electronics. However, the current large-scale integration (LSI) chips have limitations in in vivo devices due to their rigid and bulky properties. This paper describes in vivo ultrathin silicon-based liquid crystal polymer (LCP) monolithically encapsulated flexible radio frequency integrated circuits (RFICs) for medical wireless communication. The mechanical stability of the LCP encapsulation is supported by finite element analysis simulation. In vivo electrical reliability and bioaffinity of the LCP monoencapsulated RFIC devices are confirmed in rats. In vitro accelerated soak tests are performed with Arrhenius method to estimate the lifetime of LCP monoencapsulated RFICs in a live body. The work could provide an approach to flexible LSI in biointegrated electronics such as an artificial retina and wireless body sensor networks.

Precision mechanical design of an ultrahigh-resolution inelastic x-ray scattering spectrometer system with CDFDW optics at the APS

There are many scientific applications, especially involving topics related to the equilibrium atomic-scale dynamics of condensed matter, that require both a narrower and a steeper resolution function and access to a broader dynamic range than are currently available. To meet these important scientific needs, a prototype of a novel ultrahigh-resolution inelastic x-ray scattering spectrometer system has been designed and constructed at undulator-based beamline 30-ID at the Advanced Photon Source, Argonne National Laboratory. This prototype is designed to meet challenging mechanical and optical specifications for performing so-called CDFDW angular-dispersive x-ray crystal optics, which include a central ultra-thin CFW crystal and a pair of dispersing elements. The abbreviation CDFDW stands for: C – collimating crystal, D – dispersing-element crystal (two D-crystals are used in each CDFDW), F – anomalous transmission filter, and W – wavelength-selector crystal [1]. The mechanical design of the ultrahigh-resolution inelastic x-ray scattering spectrometer, as well as the preliminary test results of its precision positioning performance are presented in this paper.

Fabrication of a Bragg beam splitter for hard x-ray free-electron lasers

We report a fabrication method of an ultrathin silicon crystal as a beam splitter for the hard x-ray regime based on the Bragg diffraction operated in the symmetric Bragg geometry, and evaluation results of crystalline perfection at SPring-8. A sub-10-μm thick Si(511) crystal was fabricated with a reactive dry etching method using atmospheric-pressure plasma. Following the evaluation of topography and diffractometry, the crystal was found to be strain-free, and capable of splitting a monochromatic x-ray beam into two branches with almost 1:1 splitting ratio.

Growth of Ultrathin and Highly Efficient Organic Nonlinear Optical Crystal 4′-Dimethylamino-N-methyl-4-Stilbazolium p-Chlorobenzenesulfonate for Enhanced Terahertz Efficiency at Higher Frequencies

Growth of an ultrathin (thickness as low as 23 μm) organic nonlinear optical crystal of 4′-dimethylamino-n-methyl-4-stilbazolium p-chlorobenzenesulfonate (DASC) has been achieved by the slope nucleation method for generating THz waves with relatively higher efficiencies especially at higher frequencies. The propensity of lower solubility of this material in methanol solvent as compared to 4′-dimethylamino-n-methyl-4-stilbazolium tosylate (DAST) was favorably exploited to obtain these thin crystals. The DASC crystals thus obtained were studied for the generation of THz waves, and their efficiency was compared with DAST and zinc telluride (ZnTe) single crystals. The enhancement THz efficiency observed in thinner DASC could be attributed to better velocity matching and weaker absorption as compared to thicker crystals of the same material.