Bare Crystal Research Articles

Subsurface Spectroscopy of Thermal Degradation Inside an Inert Plastic Bonded Explosive (PBX) Simulant Using Feedback-Assisted Wavefront Shaping.

We characterize the subsurface thermal degradation of an inert analog of high-explosive molecular crystals (Eu:Y(acac)3(DPEPO)) (EYAD) embedded inside of a plastic bonded explosive simulant using feedback-assisted wavefront shaping-based fluorescence and Raman spectroscopies. This technique utilizes wavefront shaping to focus pump light inside a heterogeneous material onto a target particle, which significantly improves its spectroscopic signature. We find that embedding the EYAD crystals in the heterogeneous polymer results in improved thermal stability, relative to bare crystal measurements, with the crystal remaining fluorescent to >612 K inside of the heterogeneous material, while the bare crystal's fluorescence is fully quenched by 500 K. We hypothesize that this improvement is due to the polymer restricting the effects of EYAD melting, which occurs at 400 K and is the primary mechanism for spectroscopic changes in the temperature range explored.

Identification of hydrated phases in ALPO4-5, and explanation of their effect on the water sorption and dynamics

A sequence of phases between structural phases in ALPO4-5, commencing from the 4-coordinated aluminum atoms (tetrahedra) in the bare crystal, up to the formation of 6-coordinated (octahedra), and 5-coordinated (bipyramids) aluminum atoms upon the progressive increase of the sorbate water loading, was identified by means of density functional theory calculations, combined with Rietveld refinement of our measured XRD patterns, and produced a crystallographic information file (CIF) at 313 K and relative humidity 81.5%. We modeled the thermodynamics of the sorbed water at progressively increasing chemical potentials via grand canonical Monte Carlo computations, and explained, on the basis of the formed phases, the hysteresis loop which appears in the gravimetrically measured isotherms of the literature during the sorption-desorption cycles. Molecular dynamics simulations predicted the impact of the existence of hydrated phases on the sorbate water diffusivity; collective diffusivities at the linear response regime were also calculated and thereby, transport coefficients.

A hybrid analytical–numerical method for full energy peak efficiency calibration of a NaI detector

A hybrid analytical–numerical method is proposed to determine the Full Energy Peak Efficiency (FEPE) of a NaI bare crystal for a point γ-source in the energy range 48–2040 keV. The efficiency is calculated at all possible source locations with respect to the detector and at a maximum Source-to-Detector (S–D) distance of 50 cm. The method combines an analytical formula used for total efficiency calculation with numerically calculated Peak-to-Total (P/T) ratios. The FEPE efficiencies are calculated by integrating the combined analytical formula. A computer code is written using the C programming language to solve the integration using Simpson’s rule. The calculated values of the FEPE are found to be in agreement with these calculated using the Monte Carlo (MC) method with a maximum relative difference of about 2.5%. The main advantage of the proposed method is the extremely reduced runtime of calculation in comparison with the MC method.

Enhancement of the second harmonic signal of nonlinear crystals by self-assembled gold nanoparticles.

In second harmonic generation (SHG), the energy of two incoming photons, e.g., from a femtosecond laser, can be combined in one outgoing photon of twice the energy, e.g., by means of a nonlinear crystal. The SHG efficiency, however, is limited. In this work, the harvested signal is maximized by composing a hybrid system consisting of a nonlinear crystal with a dense coverage of plasmonic nanostructures separated by narrow gaps. The method of self-assembled diblock-copolymer-based micellar lithography with subsequent electroless deposition is employed to cover the whole surface of a lithium niobate (LiNbO3) crystal. The interaction of plasmonic nanostructures with light leads to a strong electric near-field in the adjacent crystal. This near-field is harnessed to enhance the near-surface SHG signal from the nonlinear crystal. At the plasmon resonance of the gold nanoparticles, a pronounced enhancement of about 60-fold SHG is observed compared to the bare crystal within the confocal volume of a laser spot.

A Study of NaI(Tl) crystal encapsulation using organic scintillators for the dark matter search

Scintillating NaI(Tl) crystals are used for various rare decay experiments, such as dark matter searches. However, the hygroscopicity of NaI(Tl) crystals makes the construction of crystal detectors in these experiments challenging. Therefore, the crystal requires a tight encapsulation to prevent from air contact. More importantly, in a low radioactivity measurement, identification of external radiations and surface contamination is crucial to characterize the origin of total crystal radioactivities. Studies for the NaI(Tl) crystal encapsulation with active organic scintillator vetoes have been performed to mitigate the above-mentioned issues simultaneously. A bare crystal is directly coupled with liquid and plastic scintillators to tag external radiations that penetrate from the outer part of the crystal. We report the pulse shape discrimination between organic scintillator and the crystal scintillator in a single detector setup and their long-term stability.

Electro-optic sensor for static fields

A sensor has been developed for low frequency and DC electric fields E. The device is capable of measuring fields with varDelta mathrm{E}= 4 (1) V/cm resolution. It is based on a Y-cut Z-propagation lithium niobate electro-optic crystal. For a particular commercially available bare crystal, we achieved an in air time constant tau _mathrm{c}(mathrm air)= 6.4(1.8) h for the decay of the electro-optic signal. This enables field monitoring for several hours. As an application, we demonstrated that a constant electric field E^{mathrm{ext}} = 640 V/cm applied via external electrodes to a particular spherical glass container holding an Xe/He gas mixture decays inside this cell with a time constant tau _{E}^{mathrm{glass}} = 2.5(5) h. This is sufficient for the needs of experiments searching for a permanent electric dipole moment in ^{129}Xe. An integrated electric field sensor has been constructed which is coupled to a light source and light detectors via optical fibers. The sensor head does not contain any electrically conducting material.

PEALD of SiO2 and Al2O3 Thin Films on Polypropylene: Investigations of the Film Growth at the Interface, Stress, and Gas Barrier Properties of Dyads.

A study on the plasma-enhanced atomic layer deposition of amorphous inorganic oxides SiO2 and Al2O3 on polypropylene (PP) was carried out with respect to growth taking place at the interface of the polymer substrate and the thin film employing in situ quartz-crystal microbalance (QCM) experiments. A model layer of spin-coated PP (scPP) was deposited on QCM crystals prior to depositions to allow a transfer of findings from QCM studies to industrially applied PP foil. The influence of precursor choice (trimethylaluminum (TMA) vs [3-(dimethylamino)propyl]-dimethyl aluminum (DMAD)) and of plasma pretreatment on the monitored QCM response was investigated. Furthermore, dyads of SiO2/Al2O3, using different Al precursors for the Al2O3 thin-film deposition, were investigated regarding their barrier performance. Although the growth of SiO2 and Al2O3 from TMA on scPP is significantly hindered if no oxygen plasma pretreatment is applied to the scPP prior to depositions, the DMAD process was found to yield comparable Al2O3 growth directly on scPP similar to that found on a bare QCM crystal. From this, the interface formed between the Al2O3 and the PP substrate is suggested to be different for the two precursors TMA and DMAD due to different growth modes. Furthermore, the residual stress of the thin films influences the barrier properties of SiO2/Al2O3 dyads. Dyads composed of 5 nm Al2O3 (DMAD) + 5 nm SiO2 exhibit an oxygen transmission rate (OTR) of 57.4 cm3 m-2 day-1, which correlates with a barrier improvement factor of 24 against 5 when Al2O3 from TMA is applied.

Reconfigurable Phononic-Crystal Circuits Formed by Coupled Acoustoelastic Resonators

Reconfigurable phononic circuits can be created by the selective fluid filling of holes in a solid phononic crystal. For frequencies within a complete band gap of the bare phononic crystal, the filled holes become cavities that sustain acoustoelastic defect modes. Those cavities couple evanescently with a strength that depends on their separation. We investigate the dispersion relation and the transmission properties of coupled-resonator acoustoelastic waveguides formed by a chain of cavities. While the dispersion relation is strongly dependent on the separation between cavities, transmission properties are only weakly dependent on the details of the phononic circuit for a fixed separation. Furthermore, depending on the polarization of the source of waves, defect modes can be excited selectively. As a result, rather arbitrary phononic circuits can be created, such as multiply bent waveguides or wave splitters.

Theory of substrate-directed heat dissipation for single-layer graphene and other two-dimensional crystals

We present a theory of the phononic thermal (Kapitza) resistance at the interface between graphene or another single-layer two-dimensional (2D) crystal (e.g., ${\mathrm{MoS}}_{2})$ and a flat substrate, based on a modified version of the cross-plane heat transfer model by Persson, Volokitin, and Ueba [J. Phys.: Condens. Matter 23, 045009 (2011)]. We show how intrinsic flexural phonon damping is necessary for obtaining a finite Kapitza resistance and also generalize the theory to encased single-layer 2D crystals with a superstrate. We illustrate our model by computing the thermal boundary conductance (TBC) for bare and ${\mathrm{SiO}}_{2}$-encased single-layer graphene and ${\mathrm{MoS}}_{2}$ on a ${\mathrm{SiO}}_{2}$ substrate, using input parameters from first-principles calculation. The estimated room temperatures TBC for bare (encased) graphene and ${\mathrm{MoS}}_{2}$ on ${\mathrm{SiO}}_{2}$ are 34.6 (105) and 3.10 (5.07) ${\mathrm{MW}\phantom{\rule{0.16em}{0ex}}\mathrm{K}}^{\ensuremath{-}1}{\mathrm{m}}^{\ensuremath{-}2}$, respectively. The theory predicts the existence of a phonon frequency crossover point, below which the low-frequency flexural phonons in the bare 2D crystal do not dissipate energy efficiently to the substrate. We explain within the framework of our theory how the encasement of graphene with a top ${\mathrm{SiO}}_{2}$ layer introduces new low-frequency transmission channels, which significantly reduce the graphene-substrate Kapitza resistance. We emphasize that the distinction between bare and encased 2D crystals must be made in the analysis of cross-plane heat dissipation to the substrate.

Removal of triphenylmethane dyes by calcium carbonate–lentinan hierarchical mesoporous hybrid materials

An inorganic–organic hybrid material with hierarchical mesoporous structure was prepared by involving lentinan (LTN) into CaCO3 crystal using a simple method at mild condition. The characterization of CaCO3–LTN hybrid materials indicated that it has higher surface area, more adsorption sites and better dispersion in water compared to bare CaCO3 crystal due to rich organic ligands of LTN and hierarchical structure.CaCO3–LTN hybrid materials was applied to the removal of triphenylmethyl dyes (TPMs) including crystal violet (CV), malachite green (MG) and aniline blue (AB). A powerful adsorption capability of the hybrid materials to dyes was observed, and moreover, it was found that a very rapid and efficient oxidative degradation of dyes by H2O2 can be achieved in the assist of CaCO3–LTN hybrid materials due to the reactants concentrated into its plentiful and negative charged pores. CV, MG, and AB can be complete decolorized by H2O2+CaCO3–LTN after 30min, 10min, and 2min, respectively. Moreover, cation dyes, besides TPMs, were also suitable to be treated by this H2O2+CaCO3–LTN system. These results ensure the CaCO3–LTN hybrid material a promising candidate for treatment of effluent of textile industry.

Photonic crystals with plasmonic patterns: novel type of the heterostructures for enhanced magneto-optical activity

A multilayer structure consisting of a magnetophotonic crystal with a rare-earth iron garnet microresonator layer and plasmonic grating deposited on it was fabricated and studied in order to combine functionalities of photonic and plasmonic crystals. The plasmonic pattern allows excitation of the hybrid plasmonic-waveguide modes localized in dielectric Bragg mirrors of the magnetophotonic crystal or waveguide modes inside its microresonator layer. These modes give rise to the additional resonances in the optical spectra of the structure and to the enhancement of the magneto-optical effects. The Faraday effect increases by about 50% at the microresonator modes while the transverse magneto-optical Kerr effect demonstrates pronounced peculiarities at both hybrid waveguide modes and microresonator modes and increases by several times with respect to the case of the bare magnetophotonic crystal without the metal grating.

A Study on Wafer and Feature Size

the paper introduced the bare silicon crystal how to become a wafer .then, it told the processing of wafers to produce integrated circuits .Today, most integrated circuits (ICs) are made of silicon. every integrated circuit is tested and functional and formed a dies. At last , the article explain feature size and the number of gross die per wafer (DPW).

Efficient terahertz emission, detection, and ultrafast switching using one-dimensional photonic crystal microcavity

We demonstrated the terahertz (THz) emission and detection properties and ultrafast switching effect using a one-dimensional photonic crystal microcavity with a semiconductor. Using this structure as the emission source and electro-optic crystal, the THz emission and detection efficiencies were enhanced to several times relative to bare GaP crystal. The results of experimental and theoretical calculation using the transfer matrix method agree very well. Moreover, ultrafast switching effects were also observed using carrier excitation and recombination of the semiconductor after the optical pump. Finally, we demonstrated ultrafast THz switching with a response time of the order of 1 ps.

Quartz crystal microbalance for comparison of calcium phosphate precipitation on planar and rough phospholipid bilayers

The planar and rough phospholipid bilayers at the surfaces of quartz crystal and titania-modified quartz crystal were fabricated via the surface modification, respectively, and characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), cyclic voltammetry (CV) and piezoelectric measurement. The formation of calcium phosphate on planar and rough phospholipid bilayers was investigated in detail using in situ quartz crystal microbalance (QCM) and X-ray diffraction (XRD) techniques. The obtained results showed that the calcium phosphate precipitation was closely related to the roughness and surface potential of phospholipid bilayers. Compared with planar phospholipid bilayers, the rough phospholipid bilayers exhibited a higher deposition rate of calcium phosphate. The presence of anionic phosphatidylserine (PS) in phosphatidylcholine (PC)/PS phospholipid induced PC/PS surface with negative charge, thus showing significantly enhanced calcium phosphate precipitation.

An electrodeless quartz crystal resonator integrated with UV/Vis spectroscopy for the investigation of the photodecomposition of methylene blue

The photodecomposition of organic molecules (methylene blue) was investigated using an integrated system consisting of a UV–vis spectrometer and an electrodeless quartz crystal microbalance (EL-QCM). ZnO nanorods were directly grown on a bare quartz crystal and methylene blue was coated onto the nanorods by drop-casting. Ring-type remote electrodes were used to enable the transmission of light. As the coated methylene blue was photo decomposed by UV light, the changes in mass and light transmittance were measured with the EL-QCM and UV–vis spectrometer respectively. These simultaneous measurements revealed that the rate of change in optical transmission is greater than that of the mass in the early stage of photodecomposition, which indicates that the structural degradation of methylene blue is dominant in the early stage. In contrast, the changes in light transmittance were linearly proportional to those in mass during the later stages, which is attributed to the mineralization of methylene blue.

Fabrication And Characterization Of Photonic Crystal Slow Light Waveguides And Cavities

Slow light has been one of the hot topics in the photonics community in the past decade, generating great interest both from a fundamental point of view and for its considerable potential for practical applications. Slow light photonic crystal waveguides, in particular, have played a major part and have been successfully employed for delaying optical signals(1-4) and the enhancement of both linear(5-7) and nonlinear devices.(8-11) Photonic crystal cavities achieve similar effects to that of slow light waveguides, but over a reduced band-width. These cavities offer high Q-factor/volume ratio, for the realization of optically(12) and electrically(13) pumped ultra-low threshold lasers and the enhancement of nonlinear effects.(14-16) Furthermore, passive filters(17) and modulators(18-19) have been demonstrated, exhibiting ultra-narrow line-width, high free-spectral range and record values of low energy consumption. To attain these exciting results, a robust repeatable fabrication protocol must be developed. In this paper we take an in-depth look at our fabrication protocol which employs electron-beam lithography for the definition of photonic crystal patterns and uses wet and dry etching techniques. Our optimised fabrication recipe results in photonic crystals that do not suffer from vertical asymmetry and exhibit very good edge-wall roughness. We discuss the results of varying the etching parameters and the detrimental effects that they can have on a device, leading to a diagnostic route that can be taken to identify and eliminate similar issues. The key to evaluating slow light waveguides is the passive characterization of transmission and group index spectra. Various methods have been reported, most notably resolving the Fabry-Perot fringes of the transmission spectrum(20-21) and interferometric techniques.(22-25) Here, we describe a direct, broadband measurement technique combining spectral interferometry with Fourier transform analysis.(26) Our method stands out for its simplicity and power, as we can characterise a bare photonic crystal with access waveguides, without need for on-chip interference components, and the setup only consists of a Mach-Zehnder interferometer, with no need for moving parts and delay scans. When characterising photonic crystal cavities, techniques involving internal sources(21) or external waveguides directly coupled to the cavity(27) impact on the performance of the cavity itself, thereby distorting the measurement. Here, we describe a novel and non-intrusive technique that makes use of a cross-polarised probe beam and is known as resonant scattering (RS), where the probe is coupled out-of plane into the cavity through an objective. The technique was first demonstrated by McCutcheon et al.(28) and further developed by Galli et al.(29).

MOD growth of epitaxial cerium oxide buffer layer on LAO substrates for fabrication of c-axis oriented YBCO

Epitaxial cerium oxide (CeO2) buffer layer has been grown on lanthanum aluminate (LAO) single crystal substrates for fabrication of c-axis oriented YBa2Cu3O7−x (YBCO). Precursor solution of cerium acetylacetonates with viscosity of 0.6 centipoises was spin coated on the 1×1 cm area LAO substrates. The calcination was carried out by very slow ramp (1°C per minute) until the final temperature of 500°C in oxygen flow to remove most of the organic compounds. The final heat treatment has been done at 780°C by a ramp of 20° per minute in gas flow of mixed argon–oxygen with 5 Pa partial pressure of oxygen. The thickness of the deposited CeO2 buffer layer was 20 nm. Then, 100 nm thick YBCO film was deposited by sputtering on the CeO2 buffered LAO substrate. Another film with same deposition conditions was also fabricated on the bare LAO crystal for comparison. The scanning electron microscopy (SEM) and X-ray diffraction characterisations show a/b axis YBCO decreases significantly when using the CeO2 buffered LAO instead of the bare LAO. R–T and Jc measurements of the samples are also reported. Superconducting transition width of the fabricated film on the substrate with CeO2 buffer layer is less than 0.4 K and the Jc of the fabricated film is above 3.5 MA/cm2.

Enhancement of terahertz detection efficiency in electro‐optical sampling using Fabry‐Perot microcavity structure

AbstractWe have fabricated a Fabry‐Perot (FP) microcavity in the THz region with a GaP crystal as the cavity layer by using a simple stacking method. We utilized the FP cavity structure as the electro‐optic (EO) material for THz wave detection in the EO sampling of THz time domain spectroscopy. We observed three‐fold enhancement in the THz detection efficiency in the FP cavities as compared to the bare GaP crystal at the frequencies of resonant modes and stopband edges. This enhancement in THz detection efficiency is caused by the incidental THz electric field enhancement effect in the FP cavity. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Enhancement and suppression of terahertz emission by a Fabry-Perot cavity structure with a nonlinear optical crystal

We have fabricated Fabry-Perot (FP) cavities in the THz region with a ZnTe crystal as a cavity layer by a simple stacking method. We observed more than a three times enhancement of the THz emission intensity in the FP cavities compared with the bare ZnTe crystal at the frequencies of the resonant modes and stopband edges. On the other hand, suppression of the THz emission occurs at frequencies in the stopband. The enhancement and suppression of the THz emission are caused by the modification of the optical density of state in the FP cavities compared to the vacuum.

Attenuated Total Reflection Surface-Enhanced Infrared Absorption Microspectroscopy for Identification of Small Thin Layers on Material Surfaces

Attenuated total reflection surface-enhanced infrared absorption microspectroscopy (micro-ATR-SEIRA) was developed for the identification of sub-mm size and nm-thick layers on material surfaces by using gold island films deposited on the surface of micro-ATR crystals. A thin layer of triphenyl phosphate (TPP) on a poly(tetrafluoroethylene) (PTFE) membrane filter was used to evaluate the enhancement of the absorption bands. Three types of crystals: diamond, silicon, and germanium, were evaluated. Diamond gave the greatest enhancement with a 12 nm thick gold island film. The enhancement factor was 200 times compared to bare diamond crystal, whereas it was 10 times for germanium crystal. This variation of enhancement factor according to crystal types was presumed to be due to the morphology of the gold films on the crystals. We also obtained an enhanced ATR map over an area of approximately 2 x 6 mm for a thin layer (approximately 1 nm thick) of di-2-ethylhexylphthalate on PTFE using gold-coated hexagonal silicon micro-ATR crystals. This micro-ATR-SEIRA technique has major potential for analyzing small and thin substances on material surfaces.