Quantitative thermodynamic analysis of sublimation rates using an atomic force microscope

Atomic force microscopy (AFM) has been successfully used to study the activation energy for evaporation of pentaerythritol tetranitrate (PETN) nanoislands formed by spin coating. These islands are annealed isothermally in the temperature range of 30-70 degrees C for a given time and are scanned with AFM in contact mode at room temperature. The volume of these islands does not change significantly up to about 35-40 degrees C indicating that sublimation is not significant below 40 degrees C. Above 40 degrees C, the islands start shrinking, and the rate of weight loss is analyzed as a function of temperature. The activation energy of evaporation using AFM was found to be similar to that for bulk PETN crystals using thermogravimetric analysis (TGA) at higher temperatures (110-135 degrees C). These results demonstrate that AFM is a useful tool to measure thermodynamic properties with a nanoscale probe.     

Growth,geometrical analysis,FMO, MEP UV–vis,nonlinear optical and antibacterial properties of pure and 2-furoic acid doped Guanidinium carbonate single crystal

In the presence of distilled water, the adaption of the slow evaporation solution growth approach resulted in the successful development of single crystals of Pure and doped GC (FAGC). The cell characteristics of the produced FAGC crystals were investigated using single-crystal X-ray diffraction analysis. The theoretical analysis was carried out using the DFT method, and the HOMO-LUMO energy band difference was estimated. The Molecular optimized geometry, MEP and HOMO-LUMO energy distance were computed using the B3LYP level of theory using a 6-31G (d,p) basis set. The FT-IR spectrum probes the modes of vibration of various functional groups in pure and doped GC (FAGC) crystals. According to UV–visible NIR transmittance experiments, the formed crystal exhibits a high transmittance in the whole visible range. The relative SHG efficiency of pure and doped crystals (FAGC) was carried out by the Kurtz perry technique. The Antibacterial activity demonstrates that both the pure and the dopant have antibacterial action against dangerous microorganisms.     

The effect of nitric acid (HNO3) on growth,spectral, thermal and dielectric properties of triglycine sulphate (TGS) crystal

The effect of nitric acid (HNO₃) addition on the growth of triglycine sulphate (TGS) crystal has been studied from the aqueous solution for various concentrations of nitric acid. Significant changes in the crystal size and morphology have been observed in all the grown samples. Single crystal and powder X-ray diffraction analyses confirm the structure and cell parameter values of pure and HNO₃ doped TGS crystals. FT-Raman and FTIR spectra confirm the characteristics absorption bands of pure and HNO₃ doped TGS crystals. The composition of TGS crystals have been confirmed by CHNS analysis. Physical properties such as thermal, dielectric and mechanical studies have been performed for the pure and HNO₃ doped TGS crystals. The dielectric constants of the crystals have been studied as a function of frequency. The results suggest that the HNO₃ is doped into TGS crystal and that the doping increases its dielectric constant.     

Spectral, optical, and thermal studies of pure and Zn(II)-doped l-histidine hydrochloride monohydrate (LHHC) crystals

The influence of doping the transition metal Zn(II) on the growth, spectral, optical, and thermal properties of l-histidine hydrochloride monohydrate (LHHC) crystals grown by slow solvent evaporation method has been investigated. Structural characterizations of the grown crystals were carried out by single crystal X-ray diffraction analysis and it shows slight structural changes as a result of doping. The FT-IR spectral study reveals the presence of various functional groups and confirms the slight distortion of the structure of the crystals due to doping. The energy dispersive X-ray analysis reveals the incorporation of Zn(II) in the crystalline matrix of LHHC crystal. The UV?CVis spectral study was carried out to analyze the optical transmittance of the grown crystals and found that the transmittance is very high in the visible and UV regions for both pure and doped crystals. The second harmonic generation (SHG) for the grown crystals was confirmed by Nd:YAG laser. The scanning electron microscopy reveals the presence of defect centers and crystal voids. The thermal stability and purity of the grown crystals were analyzed by thermogravimetry, differential thermal analysis, and differential scanning calorimetry techniques.     

Order-disorder phase transition in p-terphenyl and p-terphenyl: tetracene doped crystals as studied by Raman spectroscopy

Phase transition in crystalline pure p-terphenyl and p-terphenyl: tetracene doped crystals was studied with Raman spectroscopy, for temperatures from 295 to 10 K. In particular, the torsional Raman vibrational mode with a “hard-core frequency” of 230.8 cm⁻¹ was investigated in its frequency and bandwidth dependence upon temperature. The results were analyzed based on an order-disorder model allowing the determination of the activation energies and orientational correlation times of the molecular diffusive process in the monoclinic (above 193 K) and triclinic (below 193 K) phases of the crystals. The activation energy is observed to decrease from the monoclinic to the triclinic phase, whereas the orientational correlation times increase, both in the undoped and the doped crystals. The doping of p-terphenyl with tetracene appears to affect the activation energy and the orientational correlation times in a different way in each phase.     

Imaging of crystal morphology and molecular simulations of surface energies in pentacene thin films

We have investigated the crystal growth of the organic semiconductor pentacene by complementing molecular simulations of surface energies with experimental images of pentacene films. Pentacene thin films having variations in thickness and grain size were produced by vacuum sublimation. Large (approximately 20 microm) faceted crystals grew on top of the underlying polycrystalline thin film. The films were characterized using optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Single crystals most commonly grew in a truncated diamond shape with the largest crystal face, (001), growing parallel to the substrate. Crystal morphologies and surface energies were calculated using force field-based molecular simulations. The (001) surface was found to have the lowest energy, at 76 mJ/m(2), which was consistent with experimental observations of crystal face size. It was demonstrated that the morphology of the large faceted crystals approached the equilibrium growth shape of pentacene. From contact angle measurements, the critical surface tension of textured pentacene thin films in air was determined to be 34 mJ/m(2).     

The Role of Liquid Water in Crystalline Hydrate Dehydration: Copper sulphate pentahydrate

Simultaneous Differential Thermal Analysis/Thermogravimetric experiments carried out on one large single crystal, several small single crystals and powdered crystals of pentahydrate copper sulphate have been used to demonstrate the role that retained liquid water plays in maintaining crystal morphology during dehydration. Measured activation energies for stepwise dehydration in the system show the presence of solution-based transformations provide lower energy paths for the dehydration steps and stress relieving mechanisms. Skeletal anhydrous crystals from large-sized pentahydrate copper sulphate have the same morphology as the starting crystal on complete dehydration at controlled heating rates as long as a solution phase is maintained within the crystal during decomposition. The athermal activation energies, in this work, are in agreement with those obtained by isothermal methods as long as coincident reaction paths for the two techniques are maintained. The literature has been reviewed in the light of this work and a three-stage process is presented to rationalise the conflicting information obtained by workers using a variety of different experimental techniques.This revised version was published online in November 2005 with corrections to the Cover Date.     

Growth and thermal kinetics of pure and cadmium doped barium phosphate single crystal

Non-isothermal kinetic parameter of pure and cadmium-doped barium phosphate single crystal grown by room temperature solution technique have been investigated. Single crystal X-ray diffraction establishes grown crystal to be orthorhombic in nature. Scanning electron microscopy supplemented with energy dispersive X-ray analysis was used to study the surface features and to find the exact stoichiometric composition of the grown crystal. Fourier transform infrared spectroscopy studies confirm the presence of various functional groups. The effect of cadmium doping on pure barium phosphate single crystal was studied using thermogravimetry analysis. Thermogravimetry studies shows that the pure crystal was stable up to a temperature of 330 °C whereas doped crystal was stable up to a temperature of 240 °C, i.e., pure crystals were more stable than doped ones. Various solid-state reaction kinetics, i.e., activation energy (E _a), frequency factor (Z), and entropy (ΔS*) was calculated out to find the mechanism of thermal decomposition at different stages for pure and cadmium doped barium phosphate.     

Molecular modelling of poly(aryl ether ketones). I. Aryl··aryl interactions in crystal structures

Summary Non-bonded potentials for the aryl interaction have been derived using crystal structure data of a number of small aromatic molecules. The potentials, based on atom-centred interactions, give an accurate reproduction of the benzene crystal geometry and sublimation energy when used in conjunction with coulombic energies evaluated using point atomic charges. An examination of the charge distribution on benzene suggested values of 0.13e (H) and -0.13e (C) to be suitable. The transferability of the potentials has been shown by prediction of crystal geometries and sublimation energies of other hydrocarbon molecules and, with additional interactions for the oxygen atom included, preliminary polymer crystal structure calculations have been carried out. These demonstrate the validity of the derived parameters by successfully predicting crystallographic unit cell dimensions and ring conformations in the poly(phenylene oxide) and poly(aryl ether ketone) crystals.     

Influence of Vo(II) doping on the thermal and optical properties of magnesium rubidium sulfate hexahydrate crystals

We have prepared pure and divalent vanadyl ion-doped magnesium rubidium sulfate hexahydrate crystals by using slow evaporation solution growth technique. It is interesting to observe that Vo(II) doping influences the physical properties of MRSH. Presence of Vo(II) ions in the doped specimen was confirmed by energy dispersive spectroscopy and electron paramagnetic resonance spectroscopy. FTIR studies reveal that the doping of vanadium ion has not altered the basic structure of MRSH. Scanning electron microscope studies of doped sample reveals that structure defect centers are formed in the crystals. Gradual decomposition patterns were observed for pure and doped specimens in thermogravimetry and differential thermogravimetry. The grown crystals were also characterized by powder X-ray diffraction. The second harmonic generation efficiency tested using Kurtz powder technique is not influenced by the added dopant.     

Thermal and optical properties of Cu(II)-doped magnesium rubidium sulfate hexahydrate crystals

Single crystals of pure and cupric ion (Cu(II))-doped magnesium rubidium sulfate hexahydrate (MRSH) were prepared by slow evaporation of saturated solution technique (SEST) and the influence of dopant Cu(II) on the MRSH crystals has been investigated. Incorporation of Cu(II) into the crystalline matrix was confirmed by energy dispersive spectroscopy (EDS) and electron paramagnetic resonance (EPR) spectroscopy. Thermogravimetric (TG) analysis of the doped sample reveals the faster rate of degradation. EPR spectrum of the MRSH both at room temperature and at 77 K indicates the presence of Cu(II) in the interstitial position. The grown crystals were also characterized by UV–VIS and IR spectroscopy. The surface morphology of the doped sample studied by scanning electron microscopy (SEM) indicates different morphology at various magnifications. The non-linear optical (NLO) property measured using second harmonic generation (SHG) efficiency test reveals that the non-linearity is not facilitated by doping of Cu(II).     

Specific properties of fine SnO<Subscript>2</Subscript> powders connected with surface segregation

The effect of surface segregation in Sb- and In-doped SnO₂ fine-grained powders has been analyzed in comparison with single-crystalline samples. The kinetics and thermodynamics of the Sb and In segregation processes were studied as a function of annealing temperature by X-ray photoelectron spectroscopy (XPS) after annealing in an oxygen-containing atmosphere. Significant differences between diffusion and segregation were revealed for doped powders and single crystals, obviously because of simultaneous diffusion and particle-growth processes proceeding during annealing of powders. For doped single crystals the thermodynamic equilibrium is approached after 24 h annealing above 850 °C and at 1000 °C for Sb and In, respectively. Higher effective activation energies of diffusion are observed for doped powders and the thermodynamic equilibrium is not achieved under technologically relevant annealing conditions. On the basis of dopant profile measurements anomalies in the electrical resistivity at 300 °C of Sb-doped SnO₂ powders annealed at 700 and 900 °C were attributed to an Sb-depleted zone formed beneath the segregated surface during the kinetic regime. To achieve optimum resistivity behavior for commercial application, inhomogeneous doping of powders must be avoided by appropriate preparation steps.     

Ions in liquid crystals doped with nanoparticles: conventional and counterintuitive temperature effects

The concentration of ions in liquid crystals with fully ionised ionic contaminants does not depend on the temperature. Nanoparticles dispersed in the same liquid crystals change the number of mobile ions through the temperature-dependent adsorption/desorption process. As a result, the concentration of ions in liquid crystal nanocolloids is a strong function of their temperature. This type of temperature dependence is governed by the values of the adsorption activation energy and desorption activation energy. A commonly observed scenario is an increase in the concentration of mobile ions in liquid crystal nanocolloids as their temperature goes up. In this article, an opposite effect is modelled. Under certain conditions, the concentration of ions in liquid crystal nanocolloids decreases with increasing temperature. This unusual behaviour is analysed considering liquid crystals doped with both 100% pure and contaminated nanoparticles.     

Effect of gamma-irradiation on the thermal decomposition of pure and doped (Ba2+ caesium bromate

Effect of γ-irradiation on the isothermal decomposition of pure and doped (Ba²⁺, 0.50 mol%) caesium bromate has been studied in the temperature range 633–673 K. It is indicated that though the pure and pure irradiated crystals are immune to decomposition, doped and doped irradiated crystals undergo decomposition rapidly. There is initial rapid gas evolution representing 1–2% reaction, which is completely eleminated in doped irradiated crystals. The other stages exhibited by the crystals are, (1) acceleratory and (2) decay stages. Presence of two decay stages (one short and one long) is indicated in the doped substance, and the short decay diminishes with increase in temperature and virtually remains absent at 673 K. The acceleratory as well as decay periods of doped and doped irradiated crystals are analysed according to Prout-Tompkins, Avrami-Erofeev and Contracting square models. The rate constants in all the stages increase with increase in temperature. The energy of activation for the acceleratory periods of both the substances are almost same (± 10 kJ/mol) irrespective of the kinetic equation employed. Similar is the case with decay stages. But the energy of activation of the decay stages are higher than those of the acceleratory stages. Microscopic observation reveals that the reaction begins essentially on surfaces by the rapid formation of an interface and is followed by the penetration of the interface into the crystallite. The melting of a eutectic formed between the product CsBr and the parent material causes a marked increase in the rate.     

Optical,piezoelectric and mechanical properties of xylenol orange doped ADP single crystals for NLO applications

Single crystals of pure and xylenol orange (XO; C₃₁H₃₂N₂O₁₃S) dye doped (0.01, 0.05 and 0.1 mol%) ammonium dihydrogen phosphate (ADP; NH₄H₂PO₄) were grown by slow evaporation method with the vision to improve the properties of pure ammonium dihydrogen phosphate crystal. The theoretical morphology of the grown crystals was drawn using Bravais–Friedel–Donnay–Harker (BFDH) law. The selective nature of xylenol orange dye to selectively stain the particular growth sectors of ADP crystal was studied. The structural analysis of as grown crystals was carried out using powder XRD study. The identification of the functional groups present in the ADP material was done using Fourier transform infrared (FTIR) spectroscopy. The linear optical study on pure and dye doped crystals was carried out using UV–vis–NIR spectroscopy. The optical band gap, extinction coefficient, refractive index and optical conductivity were calculated using the transmittance spectra for all the samples. In photoluminescence studies, the blue emission intensity got quenched and an orange emission at 597 nm was seen as a result of XO doping. The thermal stability and decomposition temperature of ADP crystal were found to decrease as an effect of dye doping. The piezoelectric charge coefficient, SHG conversion efficiency, mechanical strength and wettability were also enhanced as a result of XO dye doping.     

Structural, spectral, optical and dielectric properties of copper and glycine doped LAHCl single crystals

Cu2+ and glycine doped L-arginine monohydrochloride monohydrate (LAHCl) single crystals were grown by slow solvent evaporation technique. The grown single crystals were confirmed by X-ray diffraction study and the interaction of dopants with LAHCl molecule was identified in Fourier transform infrared spectra. The crystalline perfection of pure and doped crystals was analyzed by high resolution X-ray diffraction studies. Vickers microhardness and UV-visible spectroscopy were carried out respectively to study the mechanical stability and optical transmittance of pure and doped LAHCl single crystals. He-Ne laser of wavelength 632.8 nm was used to measure refractive index and birefringence of grown crystals. The second harmonic generation efficiency was also measured for pure and doped LAHCl single crystals using Nd:YAG laser.     

Application of the quartz crystal microbalance to the evaporation of colloidal suspension droplets

An investigation into the evaporation of sessile droplets of latex and clay particle suspensions is presented in this work. The quartz crystal microbalance (QCM) has been used to study the interfacial phenomena during the drying process of these droplets. Characteristic changes of the crystal oscillating frequency and crystal resistance (damping of the oscillating energy) have been observed and related to the different stages of the evaporation process. Measurements have been made for latex particle sizes from 1.9 to 10 microm and for rough and polished crystals using drops from 0.3 to 1.5 microL. The behavior of the QCM is shown to depend strongly on the size of particles present and on the morphology of the crystal surface. One of the most striking features is a drastic damping of the oscillation energy and corresponding rise in frequency observed during the final stages of evaporation, particularly for the clay suspensions.     

Effect of doping an organic molecule ligand on TGS single crystals

Good quality single crystals of thiourea-doped triglycinesulphate (TuTGS) a new semiorganic nonlinear optical (NLO) crystal has been successfully grown from aqueous solution by slow evaporation method. The solubilities under various solvents in different proportions have been studied. The structural characterization of the grown crystals was carried out by X-ray diffraction. The grown crystals were subjected to FTIR and Raman analyses for vibrational assignments. The optical absorption coefficient alpha was analysed and interpreted to be allowed in the direct transition. The values of allowed direct energy gap (Eg) for undoped and doped crystals were calculated. It was found that Eg values were decreased with organic molecule doping. The powder technique of Kurtz and Perry confirm the NLO property of the grown crystal.     

Thermal analysis,effect of dopants,spectral characterisation and growth aspects of KAP crystals

Potassium acid phthalate (KAP) which is also known as potassium hydrogen phthalate (KC₈H₅O₄), a semi-organic compound was grown from its aqueous solution only by slow evaporation method at room temperature. The effect of metallic salts HgCl₂ and PbCl₂ as dopants in the growth aspects, thermal properties and SHG efficiency of KAP were determined using UV-VIS, FTIR spectral studies, thermal (TG and DTA) analysis and NLO test. There is only one significant mass loss step on TG curve of pure and doped KAP crystal. DTA curve exhibit a higher peak temperature in case of doped KAP crystal compared to those of pure KAP crystals.     

Direct current conduction in ammonium perchlorate single crystals

The dc electrical conductivity of pure and doped ammonium perchlorate (AP) has been studied in two different crystal orientations, with the electric field applied perpendicularly to either (001) or (210) planes. The conductivity along the direction of the c axis was found to be lower than that normal to (210) by a factor of 5 to 10. The dc electrical conductivity of AP is decreased by Pb²⁺ ions but increased by SO^2?₄ and CrO^2?₄ ions. The conductivity of pure AP and of Pb²⁺-doped AP displays two regions with activation energies for conduction of 0.56 and 0.87 eV, respectively. The conductivity of the anion-doped crystals has a single activation energy, 0.66 eV for SO^2?₄ and 0.72 eV for CrO^2?₄. Exposure to ammonia enhances the conductivity of pure AP. A proton conduction mechanism is proposed that takes due regard of the structure of AP. The effect of the various additives on the conductivity are attributed to their influences on the formation of charge-carrying protons.