L-arginine Phosphate Monohydrate Single Crystals Research Articles

Crystal growth and optical characterization of chromium-doped l-arginine phosphate monohydrate

l-arginine phosphate monohydrate single crystals doped with Cr3+ ions (LAP:Cr) were grown by slow cooling method, with dimensions up to 10 × 10 × 8 mm3. Chromium ions induce a drastic reduction of overall growth rate and produce a drastic change in LAP growth morphology. The functional groups of LAP:Cr crystals were confirmed by FTIR analysis and compared with pure LAP. The optical band gap of LAP:Cr was determined from UV-VIS-NIR transmittance spectrum. Optical absorption spectrum at room temperature and 10 K was measured consisting of two large bands due to the 4A2 → 4T2 and 4A2 → 4T1 transitions and a narrower band attributed to the 4A2 → 2E spin-forbidden transition, characteristic of Cr3+ ions. Luminescence spectra of pure and Cr3+-doped samples were collected with excitation at wavelength of 350 nm and 335 nm. Emissions from host LAP matrix and Cr3+ ions were observed. Excited with 350 nm the spectra reveal a broad intense band from 21000 to 26000 cm−1 region due to electronic transition from LAP ligand. The emission spectra of doped sample present two broad bands centered at 12346 cm−1 and 13412 cm−1 from 2E → 4A2 and 4T2 → 4A2 transitions, characteristics of luminescence from Cr3+ ions. From these results the Racah and crystal-field Cr3+ parameters were evaluated and comparing with those obtained in similar systems.

Crystal growth, structural and thermal studies of amino acids admixtured l-arginine phosphate monohydrate single crystals

To study the improved characteristics of l-arginine phosphate monohydrate (LAP) crystals, amino acids mixed LAP crystals have been grown by slow cooling method. Amino acids like glycine, l-alanine, and l-valine have been selected for doping. Optical quality bulk crystals have been harvested after a typical growth period of about twenty days. The effect of amino acids in the crystal lattice and molecular vibrational frequencies of various functional groups in the crystals have been studied using X-ray powder diffraction and Fourier Transform infrared (FTIR) analyses respectively. Thermal behavior of the amino acids mixed LAP crystals have been studied from the TG and DTG analyses. High-resolution X-ray diffraction studies have been carried out to find the crystalline nature. Optical transmission studies have been carried out by UV–vis spectrophotometer. The cut off wavelength is below 240 nm for the grown crystals.

AFM study of the surface morphology of the {100} cleavage planes of L‐arginine phosphate monohydrate single crystals

AbstractSurface morphology of the {100} cleavage planes of L‐arginine phosphate monohydrate single crystals grown from aqueous solutions is described and discussed. Different from the previous studies, dislocations are not frequently detected and most of them don't have hollow cores on the emergence points. Various step patterns are also described. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

EPR and optical absorption studies of Cu 2+ doped l-arginine phosphate monohydrate single crystals — part II

The EPR spectra of Cu 2+ ion in l-Arginine phosphate monohydrate (LAP) at X-band frequencies at room temperature reveal the presence of two magnetically inequivalent interstitial Cu 2+ sites in the lattice. The principal values of the g- and A-tensors indicate rhombic symmetry around the Cu 2+ ion. From the direction cosines of the principal values of the g- and A- tensors, the orientations of the sites in the lattice have been identified. The bonding parameters were evaluated and the ground state wave function of Cu 2+ ion was constructed. The ground state is found to be an admixture of ∣ x 2− y 2〉 and ∣3 z 2− r 2〉 orbitals. The optical absorption studies show four bands centered at 9803, 10 753, 15 748 and 16 666 cm −1 confirming the rhombic symmetry around the Cu 2+ ion. Using the observed bands the crystal field parameters have been evaluated.

EPR and optical absorption studies of VO 2+ doped l-arginine phosphate monohydrate single crystals — part I

The electron paramagnetic resonance (EPR) studies on VO 2+ doped l-arginine phosphate monohydrate (LAP) single crystals at room temperature at X-band frequencies reveal the presence of two magnetically inequivalent VO 2+ sites occupying interstitial positions in the lattice with fixed orientations and show very high angular dependence. The principal values of the g and A tensors indicate that the electrostatic field around the VO 2+ ion is rhombic. The optical absorption spectra at room temperature show four absorption bands at 16 155, 14 775, 10 928 and 10 526 cm −1, characteristic of rhombic symmetry. From EPR and optical absorption data, the molecular orbital bonding coefficients ( β 2, ε 2, P and k) and the crystal field parameters have been evaluated.

Study of coloration, microbe inhibition during the growth of L-arginine phosphate monohydrate single crystals

During the growth of L-arginine phosphate monohydrate (LAP) single crystals, the problems of coloration and microbial contamination of the solution were investigated. It was found that the solution coloration can be prevented by conducting crystal growth at temperatures lower than 40°C and by inhibiting microbial growth. Compared to the known microbe inhibitors H 2O 2 and n-hexane, liquid paraffin shows advantages of long durability and convenience of usage for the growth of high-quality LAP single crystals.

AFM study of etching of cleaved {1 0 0} faces of L-arginine phosphate monohydrate single crystals I. Dislocation etch pits and step bunching

The formation of dislocation etch pits and the process of coalescence of dissolution steps composing the walls of dislocation etch pits on the etched {1 0 0} cleavage faces of L-arginine phosphate (LAP) single crystals was studied by using atomic force microscopy (AFM). The results show that (1) etch pits at edge and screw dislocations are formed by repeated two-dimensional nucleation mechanism, (2) the values of different slopes of etch pits in regions close to dislocation lines are due to differences in the stress fields of dislocations producing the etch pits, and that (3) the process of step bunching is statistical in nature.

AFM study of etching of cleaved {1 0 0} faces of L-arginine phosphate monohydrate single crystals II. Two-dimensional nucleation, formation of spiral elevations and decoration of dissolution layers

Observations on the formation of two-dimensional (2D) etch pits, the decoration of dissolution steps and the formation of dissolution spiral elevations on the etched {1 0 0} cleavage faces of L-arginine phosphate (LAP) single crystals made by using atomic force microscopy (AFM) are described and discussed. It was found that spiral elevations at the points of emergence of screw dislocations are formed during dissolution by the retreating of their elementary steps around decorated centres, and that there are gradients in undersaturation on the surface in the vicinity of spiral elevation centres, the maximum undersaturation being at spiral centres.

Observations of cleavage steps, slip traces and dislocation hollow cores on cleaved {100} faces of l-arginine phosphate monohydrate single crystals by atomic force microscopy

The results of an atomic force microscopy study of the nature of cleavage steps, observation of slip traces and formation of hollow cores at the centres of dislocations on the {100} faces of l-arginine phosphate monohydrate (LAP) single crystals grown from aqueous solutions are described and discussed. It was observed that: (1) most of the cleavage steps and all the slip traces are of elementary height, a = 1.085 nm; (2) the origin of a cleavage step may or may not have a hollow core; and (3) close to its origin, the curvature of a cleavage step may be positive or negative or may change from positive to negative. The results suggest that slip traces observed on the cleaved surfaces of LAP are formed during the cleavage process while the rounding and the rearrangement of elementary cleavage steps take place immediately after the occurrence of cleavage. Analysis of the results also shows that the dislocations responsible for the origin of hollow cores always represent a stress field state corresponding to a trapped solution of different local interface supersaturations.

Atomic force microscopic study of step bunching and macrostep formation during the growth of L-arginine phosphate monohydrate single crystals

The experimental results of the formation of step bunches and macrosteps on the {100} face of L-arginine phosphate monohydrate crystals grown from aqueous solutions at different supersaturations studied by using atomic force microscopy are described and discussed. It was observed that (1) the step height does not remain constant with increasing time but fluctuates within a particular range of heights, which depends on the region of step bunches, (2) the maximum height and the slope of bunched steps increases with growth time as well as supersaturation used for growth, and that (3) the slope of steps of relatively small heights is usually low with a value of about 8° and does not depend on the region of formation of step bunches, but the slope of steps of large heights is up to 21°. Analysis of the experimental results showed that (1) at a particular value of supersaturation the ratio of the average step height to the average step spacing is a constant, suggesting that growth of the {100} face of L-arginine phosphate monohydrate crystals occurs by direct integration of growth entities to growth steps, and that (2) the formation of step bunches and macrosteps follows the dynamic theory of faceting, advanced by Vlachos et al.

Study of growth dislocations in L-arginine phosphate monohydrate single crystals by chemical etching

The results of a study of the distribution of growth dislocations revealed on different faces of L-arginine phosphate monohydrate (LAP) crystals by selective etching in relation to the growth conditions of the crystals are described. It was found that (1) the dislocation density, ϱ, on a face is the highest in its central regions and depends on the supersaturation used for growth, and that (2) ϱ on different faces is different. The observations are discussed from the standpoint of the mechanism of generation of dislocations at the seed-crystal interface in the initial stages of regeneration of the seed and at the crystal-medium interface due to the formation of bunches of growth layers on the growing crystal faces during their development.

Growth habit and surface morphology of L-arginine phosphate monohydrate single crystals

The results of a study of the growth habit and the surface topography of L-arginine phosphate monohydrate (LAP) single crystals as a function of supersaturation are described and discussed. Apart from a change in the growth habit with supersaturation, it was observed that most of the as-grown faces of LAP exhibit isolated growth hillocks and macrohillocks and parallel bunched layers and that the formation of bunched layers is pronounced on faces showing macrohillocks. Observations of bunching of growth layers emitted by macrohillocks on the {100} faces revealed that, for the onset of bunching close to a macrospiral, there is a characteristic threshold distance whose value depends on the interstep distance and supersaturation, but is independent of step height. The theoretical habit of LAP deduced from PBC analysis showed that all faces exhibiting growth hillocks and macrohillocks are F faces. Analysis of the results on bunch formation revealed that growth of LAP takes place by the direct integration of growth entities at the growth steps, that the bunching is facilitated by an increasing value of the activation energy for their integration, and that the observed dependencies of threshold distance on interstep distance, supersaturation and step height are qualitatively in agreement with van der Eerden and Müller-Krumbhaar's theory of bunch formation.

On the formation of dislocation etch pits on L-arginine phosphate monohydrate single crystals

The results of the etching behaviour of different faces of L-arginine phosphate monohydrate (LAP) crystals in distilled water, methanol and ethanol are described. It was found that all the three solvents produce dislocation etch pits on different faces of LAP crystals, and that the capability of revelation of etch pits by a solvent on different faces depends on their crystallographic orientation. The observations are interpreted from the standpoint of Cabrera's thermodynamic theory of dislocation etch-pit formation.