Influence of l-alanine doping on crystalline perfection, SHG efficiency, optical and mechanical properties of KDP single crystals

Pure and l-alanine (LA) doped single crystals of potassium dihydrogen orthophosphate (KDP) were grown by slow evaporation solution technique (SEST) in aqueous solution at ambient temperature. Powder X-ray diffraction study was done to confirm the crystal system and lattice parameters of KDP. No additional phases were observed at all doping concentrations (1-7.5 mol%), which was further confirmed by FT-Raman spectroscopy analysis. The influence of LA doping on the crystalline perfection was assessed by high-resolution X-ray diffractometry (HRXRD) analysis. HRXRD studies revealed that the grown crystals could accommodate LA at the interstitial positions in the crystalline matrix of KDP up to some critical concentration without any deterioration in the crystalline perfection. Above this concentration, very low angle structural grain boundaries were developed and it seems that the excess LA above the critical concentration was segregated along the grain boundaries. The SHG efficiency was measured using the Kurtz powder technique. The relative SHG efficiency of the crystals was found to be increased with doping concentration up to 5 mol% and above this it decreases. Optical transmission study also revealed the same behavior with enhancement up to 5 mol% concentration and later decreased. The hardness values were found to be increased by increasing the doping concentration.     

Structural, optical and dielectric studies of glycinium trifluoroacetate single crystal

An organic material glycinium trifluoroacetate (GTFA) has been re-synthesized and large single crystals have been grown by solution technique. Complete structure of GTFA has been redetermined from single crystal XRD data. FTIR confirmed the presence of various functional groups. Melting point (152.44 °C), thermal stability and specific heat were studied from TG/ DTA and DSC. In UV absorption spectra, a lower cutoff value as 220 nm and a wide band gap as 4.86 eV for GTFA were observed. The dielectric studies, dielectric constant and loss were measured at different temperatures (30-90 °C) in the frequency range 100 Hz-2 MHz.     

Studies on the growth and characterization of tris (glycine) calcium(ΙΙ) dichloride—a nonlinear optical crystal

A systematic characterization of a novel nonlinear optical material tris (glycine) calcium(ΙΙ) dichloride (TGCC) is performed. The solubility and metastable zone width of TGCC were studied. TGCC single crystal of dimensions 34×23×5 mm³ was grown by the slow evaporation technique. Single crystal X-ray diffraction studies reveal that the crystal belongs to orthorhombic system. Energy dispersive X-ray analysis confirms the presence of elements in the crystal. Structural perfection of the as-grown single crystal was studied through multicrystal X-ray diffraction analysis. The thermal characteristics of TGCC were analyzed by thermogravimetric and differential thermal analysis and differential scanning calorimetry. The transmittance of TGCC crystal has been used to calculate the optical band gap of the crystal. Chemical etching studies of TGCC crystal was carried out. The dielectric and mechanical behavior of the crystals were analyzed. The second harmonic conversion property of TGCC was identified by the Kurtz and Perry powder technique and was observed to be higher than that of KDP.     

Synthesis,growth and characterization of l-threonine zinc acetate (LTZA) NLO single crystal

Single crystals of l-threonine zinc acetate (LTZA) were grown from an aqueous solution by slow evaporation technique. Single crystal X-ray diffraction analysis reveals that the crystal belongs to monoclinic system. The optical transmission study reveals the transparency of the crystal in the entire visible region and the cut off wavelength has been found to be 350 nm. The optical band gap is found to be 3.55 eV. The microhardness studies reveal the mechanical strength of the grown crystal. The dielectric constant and dielectric loss were carried out for the grown crystal. Photoconductivity measurements carried out on the grown crystal reveal the negative photoconducting nature.     

The chemistry of C2 perfluoroalkyl iodide on the Cu(1 1 1) single crystal surface

The thermal chemistry of perfluoroethyl iodide (C₂F₅I) adsorbed on Cu(1 1 1) has been investigated by temperature-programmed reaction/desorption (TPR/D), reflection-absorption infrared spectroscopy (RAIRS), and X-ray photoelectron spectroscopy (XPS). I 4d and F 1s XPS spectra show that dissociative adsorption of C₂F₅I to form the surface-bound perfluroethyl (Cu-C₂F₅) moieties occurs at very low temperature (T < 90 K), while the C-F bond cleavage in adsorbed perfluroethyl (Cu-C₂F₅) begins at ca. 300 K. XPS and TPR/D studies further reveal that the reactions of ^βCF₃^αCF_2(ad) on Cu(1 1 1) are strongly dependent on the surface coverage. At high coverages (?0.16 L exposure), the adsorbed perfluroethyl (Cu-C₂F₅) evolves, via α-F elimination, into the surface-bound tetrafluoroethylidene moieties (CuCF-CF₃) followed by a dimerization step to form octafluoro-2-butene (CF₃CFCFCF₃) at 315 K as gas product. The surface-bound (Cu-C₂F₅) decomposes preferentially, at low coverages (?0.04 L), via consecutive α-F abstraction to afford intermediate, trifluoroethylidyne (CuCCF₃), resulting in the final coupling reaction to yield hexafluoro-2-butyne (CF₃CCCF₃) at 425 K. However, at middle coverages (ca. 0.08-0.16 L exposure), the adsorbed perfluroethyl (Cu-C₂F₅) first experiences an α-F elimination and then prefers to loss the second F from β position to yield the intermediate of Cu-CF₂-CFCu (μ-η,η-perfluorovinyl), which may further evolve into hexafluorocyclobutene (CF₂CFCFCF₂) at 350 K through cyclodimerization reaction. Our results have also shown that the surface reactions to yield the products, CF₃CFCFCF₃ and CF₃CCCF₃, obey first-order kinetics, whereas the formation of CF₂CFCFCF₂ follows second-order kinetics.     

Synthesis,spectral, thermal and optical characterization of benzyltributylammonium trichlorobarium(II) monohydrate crystal

A new nonlinear optical semiorganic crystal, benzyltributylammonium trichlorobarium(II) monohydrate was grown by slow evaporation solution growth method at ambient temperature. The powder X-ray diffraction pattern of the crystal confirms its crystallinity. The absorption spectrum of the material shows a peak at 265 nm and no absorption observed in the entire visible region indicates that the compound can be used as a nonlinear optical material. The optical transmittance spectrum of the grown crystal shows a lower cut-off wavelength at 235 nm with transparency of 88%. Thermal stability of the crystal was studied by thermogravimetry-differential thermogravimetry and differential thermal analyses (TG-DTG and DTA). The differential scanning calorimetry (DSC) analysis shows thermal anomalies in the heating and cooling cycles that indicates the occurrence of a first order phase transition. The various characteristics absorption chemical bands and BaCl₃⁻ vibration were assigned through fourier transform infrared (FTIR) spectral analysis. The second harmonic generation efficiency (SHG) of the grown crystal was analyzed by Kurtz–Perry powder technique using Nd:YAG laser. The dielectric constant and dielectric loss of the compound decrease with increase in frequency.     

Studies on the optical and dielectric properties of a zinc thiourea chloride NLO single crystal

Single crystals of a nonlinear optical material, zinc thiourea chloride were grown by the slow evaporation technique. The crystal structure and lattice parameters of the grown crystal were determined by the single crystal X-ray diffraction studies. The single crystal XRD revealed that the material crystallized in a orthorhombic crystal system. Optical studies were carried out and it was found that the tendency of transmission observed from the specimen, with respect to the wavelength of light, is practically more suitable for opto-electronic applications. The optical band gap is found to be 4.30 eV. Optical constants such as the band gap, refractive index, reflectance, extinction coefficient and real (?_r) and imaginary (?_i) components of the dielectric constant and electric susceptibility were determined from the UV–vis–NIR spectrum. The dielectric constant and dielectric loss of zinc thiourea chloride were measured in the different frequency range from 50 Hz to 5 MHz at different temperatures. Further, electronic properties, such as valence electron plasma energy, Penn gap, Fermi energy and electronic polarizability of the grown crystal have been estimated.     

Synthesis,growth and physicochemical properties of an organometallic nonlinear optical crystal: Mercury cadmium chloride thiocyanate

SCN⁻ ligand based organometallic non-linear optical mercury cadmium chloride thiocyanate (MCCTC) crystals are grown from water plus methanol mixed solvent by slow evaporation technique. The grown crystals are confirmed by single crystal X-ray diffraction analysis. MCCTC exhibits a SHG efficiency which is nearly 17 times more than that of KDP. The dielectric constant, dielectric loss and ac conductivity measurements of the sample have been carried out for different frequencies (100 Hz to 5 MHz) and, temperatures (308–388 K) and the results are discussed. Photoconductivity study confirms that the title compound possesses negative photoconducting nature. The surface morphology of MCCTC was also investigated.     

Pd8Ni92(1 1 0) surface structure from surface X-ray diffraction. Surface evolution under hydrogen and butadiene reactants at elevated pressure

The (N × 1) reconstruction (N = 5-6) of the clean Pd₈Ni₉₂(1 1 0) surface has been investigated by surface X-ray diffraction. A good fit with experimental data collected under UHV conditions is obtained when introducing undulations in the outer dense rows, constituted mainly of Pd atoms which strongly segregate to the surface. This reconstruction can be regarded as a way to relax the strains induced on the bigger Pd surface atoms, at least partially. The modifications of the surface were studied under butadiene then hydrogen as well as during butadiene hydrogenation at elevated pressure at 300 K and the (N × 1) reconstruction was found to be still present. The main changes are observed under pure hydrogen and during butadiene hydrogenation.     

Adsorption of phenylalanine on single crystal rutile TiO2(1 1 0) surface

The adsorption of the aromatic amino acid, phenylalanine on a TiO₂ rutile (1 1 0) single crystal surface has been investigated with photoemission and NEXAFS (near edge X-ray absorption fine structure) spectroscopy. The results indicate initial adsorption via the carboxylate group in a bidentate configuration with the phenyl ring oriented at approximately 25° to the surface normal. The amino group remains as NH₂. Subsequent layers of phenylalanine appear to adsorb as neutral molecules with H-bonding between NH₂ and CO groups.     

Ultra-thin film growth of titanium dioxide on W(1 0 0)

We have employed low energy electron diffraction (LEED) and X-ray photoelectron spectroscopy to follow the epitaxial growth of thin films of TiO₂ on W(1 0 0). The films were grown both by metal vapour deposition of titanium onto the substrate in UHV with subsequent annealing in a low partial pressure of oxygen, and by metal vapour deposition in a low partial pressure of oxygen. LEED patterns showed the characteristic patterns of (1 1 0) oriented rutile. A systematic spot splitting was observed and attributed to a stepped surface. The calculated step height was found to be in good agreement with that expected for rutile TiO₂(1 1 0), 3.3 Å. Titanium core level shifts were used to identify oxidation states as a function of film thickness allowing the interpretation in terms of a slightly sub-stoichiometric interface layer in contact with the substrate. In combination with the LEED patterns, the film structure is therefore determined to be (1 1 0) oriented rutile with a comparable level of stoichiometry to UHV prepared bulk crystals. The ordered step structure indicates considerable structural complexity of the surface.     

Synthesis,spectral, thermal,optical and dielectric studies on 4-dimethylaminopyridinium picrate crystals

Single crystal of 4-dimethylaminopyridinium picrate was grown by slow evaporation solution growth method. The optical properties of the crystal were studied by using UV–vis absorption and transmittance studies. The emission spectrum indicates that the crystal shows green and red fluorescence emissions. The band gap energy of the crystal was calculated and it is found to be 2.05 eV. The thermal stability of the crystal was studied using thermogravimetry-differential thermal (TG-DTA) analyses. The thermal anomalies observed in the differential scanning calorimetry (DSC) heating and cooling cycles indicate the occurrence of a first order phase transition. FTIR spectrum was used to confirm the presence of various functional groups in the crystal. The synthesized crystal shows SHG efficiency 32 times greater than that of potassium dihydrogen phosphate (KDP). The dielectric constant and dielectric loss of the crystal decreases with increases in frequency.     

In situ X-ray analysis of solid/electrolyte interfaces: electrodeposition of Cu and Co on Si(1 1 1):H and GaAs(0 0 1) and corrosion of Cu3Au(1 1 1)

Electrochemical deposition of Cu and Co in monolayer amounts on hydrogen terminated Si(1 1 1) was studied ex situ and in situ by X-ray techniques. The X-ray beam was found to have a strong effect on the deposit causing desorption under the beam. Cu deposition on GaAs(0 0 1) from UHV is compared with electrodeposited Cu on the same surface, elucidating similarities and differences of electrochemical and UHV deposition. Roughening due to corrosion of Cu₃Au(1 1 1) is observed by crystal truncation scattering. The observed behaviour of passivation of this surface is explained by the formation of Au clusters, increasingly covering the surface at higher oxidation potential.     

Synthesis and characterization of semicarbazone of p-hydroxy-3-methoxy acetophenone (SPH3MA) single crystal

Single crystals of semicarbazone of p-hydroxy-3-methoxy acetophenone (SPH3MA) were grown by a slow evaporation solution growth technique at room temperature. This is the first report in the literature on the crystallization of SPH3MA. The cell parameters of the grown crystals were estimated by single crystal X-ray diffraction analysis. The various planes of reflection were identified from the XRD powder pattern. The presence of functional groups was identified from FTIR and ¹H NMR. The results were found to be in accordance with the structure of the crystal. The formation of charge transfer complex was confirmed by UV-vis-NIR spectroscopy. The thermal stability of the grown crystal was studied by thermal analysis.     

X-ray diffraction in AT-cut quartz single crystal at acoustic excitation at the fundamental frequency

X-ray diffraction on different atomic planes of an AT-cut quartz crystal is studied experimentally in the Laue geometry in case of excitation by acoustic waves at the first resonant (fundamental) frequency. Acoustic waves lead to an increase in the integral intensity of the reflection-diffracted beam. The amplification coefficients in reflection are measured in dependence on the amplitude of a.c. voltage applied to the crystal at the resonant frequency. The frontal distributions of the intensity of the beam diffracted in the reflection direction are obtained for different atomic planes.     

Relaxations in the 1 × 5 reconstruction of Pt(1 1 0)

Pt(1 1 0) is one of the most closely investigated metal surface structures because it displays a variety of “missing-row” reconstructions, which are only marginally stable. The ground state is usually found to have 1 × 2 translational symmetry, but a 1 × 3 form has also been seen. Between 1 × 2 and 1 × 3, a series of disordered structures has been recorded, which shows a slight preference for 1 × 5 periodicity. Under the preparation conditions used in this study, a stable 1 × 5 structure was found for Pt(1 1 0). Investigation by surface X-ray diffraction has led to a complete three-dimensional structure, which closely resembles an alternation of 1 × 2 and 1 × 3 unit cells. Pt(1 1 0) shows an interesting example of two “homometric” structures that are indistinguishable by diffraction, but are distinguishable by virtue of their subsurface relaxation pattern.     

The preparation of tridymite crystal by chemical processing

A new method for the synthesis of tridymite is reported in this article. When amorphous SiO₂ is treated with ethylene glycol for 3 h at 196°C and then filtered and washed with distilled water, tridymite is obtained. The transmission electron microscopy equipped with energy-dispersive X-ray spectroscopy (EDX), powder X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR) are used to characterize the crystal materials. The EDX shows the material is pure silica and The XRD pattern shows this silica is tridymite phase. In order to study the formation process of tridymite, all sorts of reaction conditions are discussed in detail. The products obtained at different conditions are characterized by XRD techniques. Finally, a reasonable mechanism is proposed.     

Growth and morphology of Cobalt thin films on Pd(1 1 1)

We report on the growth of thin Co films on Pd(1 1 1) at three different temperatures 180 K, 300 K, and 550 K. The structure and morphology was determined by scanning tunneling microscopy and low energy electron diffraction. The growth mode was found to vary with temperature. For 180 K and 300 K, we observed a tendency to double layer growth for the initial layers while at elevated temperatures, the initial film grows in single layer. For most conditions, non-ideal three-dimensional growth was observed. Two-dimensional growth was only found for growth temperature of 550 K and coverages above 5 ML. Depending on temperature, the Co islands at low coverages exhibit three principally different shapes: dendritic at 180 K, hexagonal at 300 K and triangular at 550 K. For growth at 550 K and coverages above 5 ML, the islands changed to an irregular shape. This transition is most likely responsible for the transition to 2D growth. Further, the large strain is relaxed by the creation of a dislocation network with mixed fcc and hcp stacking. Depending on the temperature and coverage, a hexagonal or a triangular network was observed. Finally, we have investigated the effect of annealing Co films prepared at 180 K and 300 K. Heating to 490 K leads to coarsening and intermixing.     

Soft X-ray appearance potential spectroscopy (SXAPS) study of TiO2(1 1 0)-1 × 2 and (0 0 1)-1 × 1 surfaces

A soft X-ray appearance potential spectroscopy (SXAPS) apparatus with high sensitivity was built to measure non-derivative spectra. SXAPS spectra (non-derivative) of Ti 2p and O 1s for TiO₂(1 1 0)-1 × 2 and (0 0 1)-1 × 1 surfaces have been measured using low incident currents (about 10 μA/cm²) and a photon counting mode. Density of empty states on Ti and O sites are deduced by self-deconvoluting the spectra. The self-deconvoluted SXAPS spectra are qualitatively similar to those measured by X-ray absorption spectroscopy (XAS). The Ti 2p_3/2 spectrum shows two strong peaks which correspond to t_2g and e_g states. For the O 1s spectrum two strong peaks near the threshold are also found which can be ascribed to O 2pπ and O 2pσ states. These results suggest that the spectra almost obey the dipole selection rule, so-called the “approximate dipole selection rule”. The SXAPS spectra of Ti 2p and O 1s for the (1 1 0) and (0 0 1) surfaces resemble qualitatively, which is consistent with the XAS results. The spectra measured on the (1 1 0)-1 × 2 surface at an incident angle of 45° off normal to the surface and on the (1 1 0) surface sputtered by Ar ions indicate that SXAPS is very sensitive to the surface electronic states.     

透射式柱面弯晶谱仪的单滤片能量刻度方法

根据布拉格衍射定律和晶层模型,推导了透射式柱面弯晶谱仪的三维衍射光路的理论公式,并利用该理论研究了谱仪测量光谱的能量刻度问题。在考虑了实验中谱仪与光源的准直度和记录介质放置姿态带来的误差后,发现利用多种滤片的K吸收边进行公式拟合得到弯晶谱仪能量刻度曲线的方法对低能X射线谱线的误差较大,进而提出了用单滤片通过理论公式模拟计算进行谱仪能量刻度的方法。通过对透射式柱面弯晶谱仪测量到的Ag靶X光机的实验光谱进行能量刻度,实现了用单滤片在线定标弯晶谱仪,验证了理论公式和能量刻度方法的正确性。