Growth of 〈1 0 0〉 directed ADP crystal with slotted ampoule

Good quality ammonium dihydrogen phosphate single crystals have been grown by: (i) Sankaranarayanan–Ramasamy (SR) method and (ii) SR method with slotted ampoule. The grown crystals were subjected to UV–Vis spectroscopy, high-resolution X-ray diffractometer, dielectric, piezoelectric and laser damage threshold studies. Compared to the (1 0 0) plane of the conventional method grown ADP crystal and 〈1 0 0〉 directed SR method grown ADP crystal, the crystal grown by SR method with slotted ampoule has higher growth rate, higher optical transparency, high crystalline perfection, low dielectric loss, high piezoelectric charge coefficient and high laser damage threshold due to diffusion of segregated impurities away from the growing crystal in the slotted ampoule growth.     

Synthesis of porous Cu-BTC with ultrasonic treatment: Effects of ultrasonic power and solvent condition

Cu-BTC (BTC = 1,3,5-benzenetricarboxylate) metal organic framework (MOF) was synthesized using different solvent conditions with ultrasonic treatment. Solvent mixtures of water/N,N-dimethylformamide (DMF), water/ethanol were used for the reactions with or without a variety of bases under 20 kHz ultrasonically treated conditions. Prepared crystals were purified through 30 min of sonication to remove unreacted chemicals. Treatment time and ultrasonic power effects were compared to get optimum synthetic condition. The characterization of MOF powders was performed by scanning electron microscopy, X-ray powder diffraction, infrared-spectroscopy, thermo-gravimetric analysis and specific surface determination using the BET method. Isolated crystal yields varied with different solvent and applied ultrasonic power conditions. A high isolated crystal yield of 86% was obtained from water/ethanol/DMF solvent system after 120 min of ultrasonic treatment at 40% power of 750 W. Different solvent conditions led to the formation of Cu-BTC with different surface area, and an extremely high surface area of 1430 m²/g was obtained from the crystals taken with the solvent condition of water:DMF = 70:30.     

Growth and size control in anti-solvent crystallization of glycine with high frequency ultrasound

Antisolvent crystallization of glycine was performed under ultrasonic irradiation of 1.6 MHz. The irradiation enhanced both the growth of α-glycine crystal and the uniformity in the crystal size. The degree of both enhancement effects increased with increasing ultrasonic power. While under the irradiation of 20 kHz ultrasound, no growth enhancement was observed, but the crystal size reduced as was reported in the literature. To elucidate the mechanism of growth enhancement, another experiment was designed and conducted to avoid the effect of nucleation from the sonocrystallization. The result suggests that the ultrasound enhances the incorporation of microcrystals to larger crystals. Probably, the collision between solid particles is intensified by the disturbance characterized by the high frequency ultrasound. The crystal growth was modeled with an apparent reaction of microcrystal and larger crystal. The result of the growth experiment was successfully predicted with a rate equation for pseudo first order reaction with a single parameter of rate constant. The rate constant linearly increased with the ultrasonic power. The analysis enables quantitative evaluation of the ultrasonic effect on the crystal growth.     

Effects of growth temperature modulated by HCl flow rate on the surface and crystal qualities of thick GaN by HVPE

We studied the influence of the growth temperature and HCl flow rate on the morphological evolution of crack-free thick GaN films by using a home-made horizontal hydride vapor phase epitaxy on sapphire substrates. Optical difference microscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), and cathodoluminescence (CL) were carried out to reveal the surface property of the GaN epilayer. It was found that the higher growth temperature is a key factor to obtain mirror, colorless and flat GaN surface. However, this key effect of temperature was modulated by HCl flow rate (HCl > 15 sccm). The surface RMS roughness was reduced from 206 to 2.51 nm for 10 μm × 10 μm scan area when GaN was grown at 1070 °C with HCl flow rate up to 30 sccm. These samples also reduced their (0 0 0 2) FWHM result from 1000 to 300 arcsec and showed a strong near-band-edge peak in CL spectra. Results indicated that growth temperature influence growth velocities on different crystalline planes, which will lead to the different morphologies obtained. High growth temperature can improve the lateral growth rate of vertical {1 1 ? 2 0} facets and reduce the vertical growth rate of top {0 0 0 1} facet combined with higher HCl flow rate, which leads to completely coalescence of surface.     

Effect of power ultrasound on crystallization characteristics of magnesium ammonium phosphate

Magnesium ammonium phosphate (MAP) crystallization could be utilized for the recovery of phosphorus from wastewater. However, the effectiveness of the recovery is largely determined by the crystallization process, which is very hard to be directly observed. As a result, a specific ultrasonic device was designed to investigate the crystallization characteristics of MAP under various ultrasonic conditions. The results demonstrated that the metastable zone width (MZW) narrowed along with the rising of the ultrasonic power. Similarly, for the 6 mM MAP solution, with the ultrasonic power gradually enhanced from 0 W to 400 W, the induction time was shortened from 340 s to 38 s. Meanwhile, the crystallization rate was accelerated till the power reached 350 W, and then remained a constant value. It can be observed from the scanning electron microscopy (SEM), the MAP crystal became bigger in size as well as the crystal size distribution (CSD) became broad and uneven, with the increase of ultrasonic power. The results indicate that the crystallization process enhanced by power ultrasound could be used as an effective method to eliminate and recover the phosphorus from wastewater.     

Linear and nonlinear optical properties of N-(3-nitrophenyl) acetamide single crystals

Optically transparent nonlinear optical bulk single crystal of N-(3-nitrophenyl) acetamide (3NAA) of dimension 7 mm × 6 mm × 5 mm has been grown from its aqueous solution by slow solvent evaporation technique. The grown crystal was characterized by powder X-ray diffraction to confirm the crystal structure. Investigation has been carried out to assign the vibrational frequencies of the grown crystals by Fourier Transform Infrared Spectroscopy and FT-NMR technique. Thermal behaviour of the grown crystals was studied by thermogravimetric analysis. The second harmonic generation efficiency of 3NAA was determined by Kurtz and Perry powder technique. The optical absorption study confirms the suitability of the crystal for device applications. The mechanical properties of the grown crystals have been studied using Vickers microhardness tester. Dielectric, microhardness and photoconductivity studies also carried out for the grown sample.     

Investigation of hillocks formation on (1 0 0) HgCdTe layers grown by MOCVD on GaAs epi-ready substrates

In this paper we present the recent progress in the growth of (1 0 0) HgCdTe epilayers using metal organic chemical vapour deposition on GaAs epi-ready substrates. Particular progress has been achieved in the reduction of macro-defects known as “hillocks”, revealed on the surface of HgCdTe epilayers with (1 0 0) crystallographic orientation. The large-scale defects can arise from such sources as poor substrate processing, dust and remnants from previous deposition, and non optimal parameters of nucleation and growth process. In our experiment, hillocks density was decreased to <10² cm⁻² by proper choice of the growth parameters.Obtained epilayers are suitable for device fabrication. So far, significant improvements has been obtained in photoconductors operated at near-room temperatures. Devices fabricated from (1 0 0) HgCdTe have about one order of magnitude higher voltage responsivity than their (1 1 1) B counterparts.     

Mechanical characteristics of solution grown potassium zinc chloride crystals doped with lithium ions

Results of indentation-induced hardness testing studies on potassium zinc chloride crystals doped with Li⁺ ions, leading to an understanding of their mechanical behaviour, are presented. The Vickers hardness of these crystals for (1 0 0), (0 1 0) and (0 0 1) planes in the load range 20–160 g were studied. Load-independent values of hardness are estimated for the three crystallographic planes by applying Hays-Kendall’s and Li-Bradt models. The results showed that: (1) for the three crystallographic planes the load-independent hardness obtained by Li-Bradt model is higher than that predicted by Hays-Kendall’s, approach; (2) the load independent hardness of the (0 0 1) plane is higher than that of both (1 0 0) and (0 1 0) planes, (3) the values of load-independent hardness depend on Li⁺ concentrations in the K₂ZnCl₄ crystals, (4) the variations of crack length and crack morphology are described for studied crystal planes.     

Experimental measurements of the energetics of surface reactions

Microcalorimetric measurements of the adsorption energies of well-defined surface species are reviewed, using selected examples mainly from our own group to demonstrate the types of information that can be achieved with this technique. The adsorption energies of molecules on single crystal transition metal surfaces to produce well-characterized molecular or dissociated adsorbates allow determination of the standard enthalpies of formation of key catalytic reaction intermediates. The adsorption energies for metal atoms during metal thin-film growth allow quantitative estimates of metal-substrate bond energies, metal film/substrate adhesion energies and the energetic costs associated with lattice mismatch during thin film growth. Results for several metals on MgO(1 0 0) reveal that they bind weakly to terrace sites. Metals from the right side of the periodic table also bind weakly to step and kink sites (although more strongly than on terraces), whereas alkali and alkaline earth metals bind very strongly to these defects. At 300 K, metals tend to form 2D or 3D clusters nucleated on MgO(1 0 0) defects, via a transiently adsorbed precursor (mobile adatoms on terraces). Calorimetric measurement of the energy of metal atoms in supported 3D metal nanoparticles as a function of particle size reveals a very strong size dependence below 6 nm diameter. Metal atoms also adsorb weakly on polymer surfaces and nucleate 3D metal particles, sometimes in kinetic competition with migration to and strong reaction with the more reactive, subsurface organic functional groups. Measurements of the energies for adsorbed proteins on calcium phosphate crystals, which have been structurally characterized by NMR, reveal extremely weak binding dominated by the entropy gained from release of organized water. These experimental measurements of the energies of well-defined adsorbates serve as benchmarks against which to compare theoretical computations for accuracy, thus enabling improvement upon quantum mechanical methods. Comparisons of calorimetric adsorption energies on single crystal surfaces with state-of-the-art DFT calculations show that the latter can often be in substantial (?20%) error.     

Epitaxial growth of well-ordered ultra-thin Al2O3 film on NiAl (1 1 0) by a single-step oxidation

Well-ordered ultra-thin Al₂O₃ films were grown on NiAl (1 1 0) surface by exposing the sample at various oxygen absorption temperatures ranging from 570 to 1100 K at dose rates 6.6 × 10⁻⁵ and 6.6 × 10⁻⁶ Pa. From the results of low-energy electron diffraction (LEED), Auger electron spectrometer (AES) and X-ray photon spectroscopy (XPS) observations, it was revealed that oxidation mechanism above 770 K is different from well-known two-step process. At high temperature, oxidation and crystallization occurred simultaneously while in two-step process oxidation and crystallization occurred one after another. At high-temperature oxidation well-ordered crystalline oxide can be formed by a single-step without annealing. Well-ordered Al₂O₃ layer with thickness over 1 nm was obtained in oxygen absorption temperature 1070 K and a dose rate 6.6 × 10⁻⁶ Pa at 1200 L oxygen.     

Studies on the optical and mechanical properties of non-linear optical 3-aminophenol orthophosphoric acid (3-amphph) single crystal

Single crystals of semiorganic material 3-aminophenol orthophosphoric acid (denoted as 3-amphph) of size 29 × 17 × 4 mm³ have been grown by the slow evaporation of an aqueous solution of deionized water at 50 °C. The crystal belongs to orthorhombic system with the non centrosymmetric space group P2₁2₁2₁. The lattice parameter values of 3-amphph crystal are a = 4.481(2) Å, b = 9.782(4) Å and c = 18.326(4) Å. The grown crystals are subjected to single crystal XRD studies to identify its morphology and structure. Optical transmittance and second harmonic generation of the grown crystals have been studied by UV–Vis–NIR spectrum and Kurtz powder technique respectively. The transmittance of 3-amphph crystal has been used to calculate the refractive index n, the extinction coefficient k, reflectance R and both the real (?_r) and imaginary (?_i) components of the dielectric constant as a function of wavelength. The optical band gap of 3-amphph is 4.05 eV with direct transition. The anisotropic mechanical behavior of 3-amphph has been analyzed using Vickers microhardness test. The mechanism of growth is revealed by carrying out chemical etching using water as etchant.     

Kinetics and thermodynamics of sucrose crystallization from pure solution at different initial supersaturations

Growth rates of sucrose crystallization from pure solutions of initial relative supersaturation levels between 0.094 and 0.181 were studied in agitated crystallizer at 313.13 K. Birth and spread model was applicable for the obtained growth rate data in this range of supersaturation and used to estimate the principal growth parameters. The estimated interfacial free energy varied inversely with supersaturation from 0.00842 to 0.00461 J/m², respectively. The obtained kinetic coefficient changed with the initial supersaturation from 9.45 × 10^? 5 to 2.79 × 10^? 7 m/s. The corresponding radius of the 2D (two dimensional) critical nucleus varied from 7.47 × 10^? 9to 1.46 × 10^? 9 m. Predominance of surface integration or volume diffusion mechanism during the growth process was assessed using the calculated activation free energies of the 2D nucleation process. An acceptable confirmation of the calculated radius of the critical 2D nucleus was found using atomic force microscopy (AFM) technique. The calculated interfacial free energy between the saturated sucrose solution and the crystal surface was found to be 0.02325 J/m².     

Comparative study on the effects of different annealing conditions on the surface morphology,crystallinity, and optical properties of ZnO micro/nanoparticle-based discs

The effects of annealing parameters on the surface morphology, crystallinity, and optical properties of ZnO disc were investigated. Variations in the annealing temperatures and gas flow rates were found to have a profound impact; grain growth was enhanced even at the low annealing temperature of only 400 °C. SEM and AFM revealed smooth and uniform grain growth after annealing treatment, especially at 800 °C. A unique secondary growth of ZnO nanoparticles and multilayer grain growth that have not been reported elsewhere were also observed. The annealing treatment was also found to improve grain crystallinity as illustrated by the lowering of intrinsic compressive stress based on the XRD lattice constant and FWHM data. The PL spectra of the M-Disc showed a huge band edge emission at 371–376 nm. In contrast, the N-Disc exhibited a dominant and broad visible PL emission in the green band with peaks at 519–533 nm. These peaks were attributed to a very high concentration of structural defects (oxygen vacancies and zinc/oxygen interstitials). The annealing conditions had a significant effect on the properties of ZnO. Increased percentage of oxygen in the O/Ar from 50% to 100% did not change the M-Disc spectra. However, the XRD pattern of the N-Disc revealed that the (0 0 2) peak intensity decreased, the position of the (1 0 1) peak slightly shifted toward a higher angle, and the FWHM of the (1 0 1) peak improved. The experimental results showed that thermal annealing could enhance the different properties of ZnO discs.     

Magnetostriction of Tb–Dy–Fe alloy with different crystal axes orientation

Based on the principle of energy minimum, magnetostriction of Tb–Dy–Fe alloy with different crystal axes under different compressive stress has been calculated using a three-dimensional anisotropy domain rotation model. Simulated results show that the magnetostriction property of 〈1 1 1〉-oriented single crystal is the best; saturation magnetostriction up to 2378 ppm has been obtained under compressive prestress of 24 MPa, which is very close to the experiment results. Saturation magnetostriction properties of 〈1 1 2〉-oriented and 〈1 1 0〉-oriented single crystal are very close under lower compressive prestress, while the 〈1 1 0〉-oriented ones have higher magnetostriction than 〈1 1 2〉-oriented ones under higher compressive prestress. In lower magnetic field, 〈1 1 0〉-oriented crystals achieve jump effect (1018 ppm at 715 Oe under 10 MPa) prior to 〈1 1 2〉-oriented ones, which indicates that it has fairly better low-magnetic field properties. These results agree well with the experimental results in previous literatures.     

Growth and electrical characterization of type II InAs/GaSb superlattices for midwave infrared detection

Herein, we report a type II InAs/GaSb superlattice structure (SLS) grown on GaSb(1 0 0) substrates by molecular beam epitaxy (MBE) and its electrical characterization for mid-wavelength infrared detection. A GaSb buffer layer was grown under optimized SLS growth conditions, which can decrease the occurrence of defects for similar pyramidal structures. The complications associated with these conditions include oxide desorption of the substrate, growth temperature of the SLS, the V/III ratio during superlattice growth and the shutter sequence. High-resolution X-ray diffraction (HRXRD) shows the sixth satellite peak, and the period of the SLS was 52.9 Å. The atomic force microscopy (AFM) images indicated that the roughness was less than 2.8 nm. High-resolution transmission electron microscopy (HRTEM) images indicated that the SLS contains few structural defects related to interface dislocations or strain relaxation during the growth of the superlattice layer. The photoresponse spectra indicated that the cutoff wavelength was 4.8 μm at 300 K. The SLS photodiode surface was passivated by a zinc sulfide (ZnS) coating after anodic sulfide.     

Cathodoluminescence microcharacterization of forsterite in the chondrule experimentally grown under super cooling

Cathodoluminescence (CL) of laboratory forsterite chondrules has been characterized to clarify the formation process of chondrules and related mechanism of the crystal growth in a supercooled melt. Color CL image of the experimentally grown forsterite exhibits significant blue luminescence in the main branches of the interior structure of lab-chondrule, which reflects to the anisotropy of crystallization. A new CL band centered at 450–525 nm (2.76–2.36 eV) in blue to green region might be assigned to a microdefect-related center, which is a diagnostic peak for the forsterite that was formed due to the rapid growth as high as ～10 mm/s or higher from a supercooled melt.     

AFM study of a SiC film grown on Si(1 0 0) surface using a C2H4 beam

A 3C-silicon carbide (SiC) thin film grown on a Si(1 0 0) surface using an ethylene (C₂H₄) molecular beam has been studied by atomic force microscopy. At the center of the irradiation area of the ethylene beam, the shape of the SiC islands was rectangular, the average length of which was 74.5 nm and the average height was 13.1 nm. Each SiC island consists of the SiC particles with the average diameter of 17 nm. Just inside of the boundary region of the beam irradiation, the average size and height of the islands decreased to 50.1 and 8.2 nm, respectively. Just outside of the boundary region, the average size and height decreased to 17.7 and 5.1 nm, respectively. The average reaction probabilities at the above three points were estimated to be 0.14, 0.27 and 2.7%, respectively. New growth mode of the crystal growth is proposed (particles gathering island mode).     

Characteristics of silicon oxide thin films prepared by sol electrophoretic deposition method using tetraethylorthosilicate as the precursor

Silicon dioxide films were prepared on p-type Si (1 0 0) substrates by sol electrophoretic deposition (EPD) using tetraethylorthosilicate (TEOS) at low temperature. According to the variation of sol dipping conditions, we estimated the characteristics of SiO₂ films, such as composition, surface morphology, wet etch rate, breakdown voltage, etc. The growth rate of the film increased linearly with increasing TEOS quantity in solution. It increased exponentially with the increase in deposition time, and the film thickness was saturated at approximately 200 nm on hydrophilic Si surface after more than 6 days. The growth rate of the EPD SiO₂ films on the hydrophobic Si surface was much lower than that of the film on the hydrophilic Si surface.     

Photodiode properties of molecular beam epitaxial InSb on a heavily doped substrate

Photodiodes of InSb were fabricated on an epitaxial layer grown using molecular beam epitaxy (MBE). Thermal cleaning of the InSb (0 0 1) substrate surface, 2° towards the (1 1 1) B plane, was performed to remove the oxide. Photodiode properties of МВЕ-formed epitaxial InSb were demonstrated. Zero-bias resistance area product (R₀A) measurements were taken at 80 K under room temperature background for a pixel size of 100 μm × 100 μm. Values were as high as 4.36 × 10⁴ Ω/cm², and the average value of R₀A was 1.66 × 10⁴ Ω/cm². The peak response was 2.44 (A/W). The epitaxial InSb photodiodes were fabricated using the same process as bulk crystal InSb diodes with the exception of the junction formation method. These values are comparable to the properties of bulk crystal InSb photodiodes.     

Exploring surface processes by coaxial impact-collision ion scattering spectroscopy and time-of-flight elastic recoil detection analysis

The usefulness of coaxial impact-collision ion scattering spectroscopy and time-of-flight elastic recoil detection analysis for in situ surface analysis, especially for elucidation of surface processes, is demonstrated by taking the following studies as examples: (1) self-restoration processes of oxygen vacancies at vacuum-annealed TiO₂(1 1 0) surface, (2) effects of Mn incorporation on MBE growth of GaMnN film, (3) growth process in hydrogen-surfactant mediated epitaxy of Ge/Si(0 0 1), and (4) structure analysis of the Si(0 0 1)2×3-Ag surface.