Search

Ni:SiO(2) granular films have been prepared by atom beam sputtering technique under ambient conditions. These films have been subsequently annealed at 200-600 degrees C temperature. GAXRD and TEM analyses show the growth of Ni particles and improvement in crystallinity with increase in annealing temperature. Selected area electron diffraction and XPS analyses show the presence of a small quantity of NiO phase in addition to metallic Ni. Room temperature magnetic measurements indicate that the films annealed at lower temperatures (

There are several confronting reports of room temperature ferromagnetic (FM) ordering in bulk as well as thin films of dilutely doped or even some undoped semiconductors. We have synthesized and characterized dilute Mn-doped (2 and 4%) ZnO pellets. SQUID measurements confirm that the 2% Mn sample shows the FM ordering above the room temperature and the FM contribution coming mainly from the bulk. However, the ordering gets completely quenched for 4% Mn doping. Upon cooling down the 2%, Mn-doped sample shows further enhancement in the magnetic properties while the 4% sample did not show any FM ordering down to 5 K. The powerful X-ray photoemission spectroscopy (XPS) was employed to compare the electronic structure of these two samples. The XPS results show that the manganese shifts toward the higher valence state upon Mn doping while there is no change in the zinc and oxygen valence. The atomic concentration of divalent Mn state is found to be dominant in the ferromagnetic sample For. the non-ferromagnetic sample, a larger contribution of higher oxidation Mn states is present that is correlated to the suppressed ferromagnetism. Interestingly, the oxygen content is also found to be higher in the 4% Mn sample than that in the 2% Mn sample that has been attributed to the charge neutrality of the samples. The present study provides evidence that the magnetization originates neither from any precipitating secondary phase nor from the oxygen content but the Mn2+ state plays a significant role for the FM properties in the Mn-doped ZnO system. (C) 2008 Elsevier B.V. All rights reserved.

The effect of high electronic energy deposition on the structure, surface topography, optical properties, and electronic structure of cadmium sulfide (CdS) thin films have been investigated by irradiating the films with 100 MeV Ag+7 ions at different ion fluences in the range of 1012–1013 ions/cm2. The CdS films were deposited on glass substrate by thermal evaporation, and the films studied in the present work are polycrystalline with crystallites preferentially oriented along (002)-H direction. It is shown that swift heavy ion (SHI) irradiation leads to grain agglomeration and hence an increase in the grain size at low ion fluences. The observed lattice compaction was related to irradiation induced polygonization. The optical band gap energy decreased after irradiation, possibly due to the combined effect of change in the grain size and in the creation of intermediate energy levels. Enhanced nonradiative recombination via additional deep levels, introduced by SHI irradiation was noticed from photoluminescence (PL) analysis. A shift in the core levels associated with the change in Fermi level position was realized from XPS analysis. The chemistry of CdS film surface was studied which showed profound chemisorption of oxygen on the surface of CdS.

Temperature dependent magnetic and electronic properties of electron beam evaporated Fe/Al multilayer samples (MLS) with an average composition of Fe0.70A10.30 (MLS-A) and Fe0.50Al0.50 (MLS-B) have been investigated. A ferromagnetic behaviour in MLS-A and nonmagnetic behaviour in MLS-B is obtained after annealing the multilayers at 400 °C. The different magnetic behaviours can be interpreted in terms of constant increase of Fe-3d and Al-3sp hybridization accompanied by an increased de-localization of the d-electrons participating in the strong bonding of Fe with Al leading to formation of different Fe–Al phases (Fe3Al in MLS-A) and (FeAl in MLS-B) as suggested from valence band photoemission and X-ray diffraction measurements.

A study of growth, structure, and properties of $Eu_2O_3$ thin films were carried out. Films were grown at $500-600^o C$ temperature range on Si(100) and fused quartz from the complex of $Eu(acac)_3$. Phen by low pressure metalorganic chemical vapor deposition technique which has been rarely used for $Eu_2O_3$ deposition.These films were polycrystalline. Depending on growth conditions and substrates employed, these films had also possessed a parasitic phase. This phase can be removed by post-deposition annealing in oxidizing ambient. Morphology of the films was characterized by well-packed spherical mounds. Optical measurements exhibited that the bandgap of pure $Eu_2O_3$ phase was 4.4 eV. High frequency 1MHz capacitance–voltage (C–V) measurements showed that the dielectric constant of pure $Eu_2O_3$ film was about 12. Possible effects of cation and oxygen deficiency and parasitic phase on the optical and electrical properties of $Eu_2O_3$ films have been briefly discussed.

X-ray topographic studies of growth sector geometry in {110} sections of large potash alum crystals confirm the occurrence of growth rate dispersion of the {100} growth fronts. Contrary to previous speculations that this variation arises as a consequence of the refraction of screw dislocations in and out of these sectors we show that the dispersion occurs even in the absence of this effect and despite the presence of continuously propagating edge dislocations in the sectors. Strain mapping using double crystal diffractometry yields a strong correlation between increase of lattice strain along the sector and cessation of growth. This leads to the speculation that the potential cause of the growth rate dispersion is the absorption of undetectable amounts of impurities at the growth interface to generate the observed strain which in turn influences the growth rate (or vice versa). This speculation is in agreement with other observations of the influence of lattice strain on crystal growth.

A novel in-situ system for the investigation of the structural nature of the crystal/solution interface is presented. A combination of synchrotron radiation and high resolution X-ray diffraction enables the growth interface to be studied under a thick overlayer of saturated solution. Data on the growth and dissolution of the (100) crystal surface of ADP under 6 mm of thick saturated solution is presented which indicates the existence of an ordered layer at the crystal/solution interface. Kinetic studies reveal this interfacial layer to be highly labile.

A novel configuration ITO/n-OVC CuIn3Se5/p-CIS/In solar cell has been fabricated by multisource vacuum co-evaporation technique on soda lime glass substrates. The pn junction is formed with ordered vacancy compound as the n counter part for the p type CuInSe2. The structural, compositional, hall coefficient, optical and electrical properties of the p and n layers have been studied respectively by X-ray diffraction, Energy Dispersive Analysis of X rays, optical absorbance and conductivity measurements. Current density-Voltage measurements enabled the determination of efficiency of the device.

We investigated Ag and Pd MNN Auger transitions in AgPdx alloys with low Pd concentrations using high-resolution x-ray excited Auger electron spectroscopy. The Ag MNN Auger profile exhibits composition-dependent kinetic energy shifts and also broadening. The Auger kinetic energy shift varies as the square root of the Pd concentration in the alloy, and the highest value of the shift observed for AgPd is about 0.27 eV. The fine structure observed in the Ag MNN Auger transition is independent of composition, but the Pd MNN Auger transition exhibits dramatic changes in intensities of fine features. The Ag MNN Auger transition exhibits a predominantly atomic character, whereas the Pd MNN Auger profile changes from quasi-atomic to band behavior with an increase in Pd concentration.

The diffusion behavior of arsenic (As) and gallium (Ga) atoms from semi-insulating GaAs (SI-GaAs) into ZnO films upon post-growth annealing vis-à-vis the resulting charge compensation was investigated with the help of x-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy. The films, annealed at 600 ºC and 700 ºC showed p-type conductivity with a hole concentration of 1.1 × 1018 cm−3 and 2.8 × 1019 cm−3 respectively, whereas those annealed at 800 ºC showed n-type conductivity with a carrier concentration of 6.5 × 1016 cm−3. It is observed that at lower temperatures, large fraction of As atoms diffused from the SI-GaAs substrates into ZnO and formed acceptor related complex, (AsZn–2VZn), by substituting Zn atoms (AsZn) and thereby creating two zinc vacancies (VZn). Thus as-grown ZnO which was supposed to be n-type due to nonstoichiometric nature showed p-type behavior. On further increasing the annealing temperature to 800 ºC, Ga atoms diffused more than As atoms and substitute Zn atoms thereby forming shallow donor complex, GaZn. Electrons from donor levels then compensate the p-type carriers and the material reverts back to n-type. Thus the conversion of carrier type took place due to charge compensation between the donors and acceptors in ZnO and this compensation is the possible origin of anomalous conduction in wide band gap materials.

Core and valence level spectra of (Sm0.50Ca0.50)MnO3 are reported. The spectral weight of the valence band has a peak 6 eV below Fermi level. Comparative analysis with the similar class of compounds suggests that width of the valence band is low for this compound. Semiconductor type behaviour of this compound is qualitatively predicted using the features of valence band and core level spectra.

The technique of synchrotron radiation X-ray reflectivity is presented and its application to the non-destructive characterisation of polymer thin films outlined. The technique is applied to an investigation of the structure of polyphenylene thin films prepared on indium/tin oxide coated glass substrates. Samples synthesised from carbonate-based precursors have a higher density than those prepared from acetate-based precursors. Possible molecular origins are discussed.

In this article, we report GaAs metal-oxide-semiconductor (MOS) capacitors with a metal organic chemical vapor deposited ultrathin (1.5 nm) pseudomorphic InP interface passivation layer (IPL) and a thin (5 nm) ZrO2 high-k dielectric. Reduction of the surface states on InP passivated GaAs surfaces was observed from the photoluminescence study. The x-ray photoelectron spectra confirmed the dramatic reduction of GaAs native oxides (Ga-O and As-O) from the interface of ZrO2 and p-GaAs, implying that the Fermi level at the high-k/GaAs interface can be unpinned with good interface quality. As a result, very low values of interface trap density (1.1 × 1011 cm−2 eV−1) and hysteresis (8.21 mV) were observed. The same was done for directly deposited ZrO2 on GaAs surface to understand the efficacy of InP interface passivation layer on GaAs MOS devices. A systematic capacitance-voltage and current density-voltage studies were performed on bothAl/ZrO2/InP/p-GaAs and Al/ZrO2/p-GaAs structures. It was found that inserti...

TiO2 and Co-doped TiO2 (CTO) thin films deposited at various oxygen partial pressures by pulsed laser deposition exhibit room temperature ferromagnetism (RTFM) independent of their phase. Films deposited at 0.1 mTorr oxygen partial pressure show a complete rutile phase confirmed from glancing angle x-ray diffraction and Raman spectroscopy. At the highest oxygen partial pressure, i.e. 300 mTorr, although the TiO2 film shows a complete anatase phase, a small peak corresponding to the rutile phase along with the anatase phase is identified in the case of CTO film. An increase in O to Ti/(Ti+Co) ratio with increase in oxygen partial pressure is observed from Rutherford backscattering spectroscopy. It is revealed from x-ray photoelectron spectroscopy (XPS) that oxygen vacancies are found to be higher in the CTO film than TiO2, while the valency of cobalt remains in the +2 state. Therefore, the CTO film deposited at 300 mTorr does not show a complete anatase phase unlike the TiO2 film deposited at the same partial pressure. We conclude that RTFM in both films is not due to impurities/contaminants, as confirmed from XPS depth profiling and cross-sectional transmission electron microscopy (TEM), but due to oxygen vacancies. The magnitude of moment, however, depends not only on the phase of TiO2 but also on the crystallinity of the films.

Here, we report the development of a simple, small, fast heating, and portable, homemade, inert gas (Ar) atmospheric annealing setup. Instead of using a conventional heating element, a commercial soldering rod having an encapsulated fast heating heater is used here. The sample holder is made of a block of stainless steel. It takes 200 s to reach 700 °C, and 10 min to cool down. The probability of oxidation or surface contamination has been examined by means of x ray photoelectron spectroscopy of virgin Cu sample after annealing at 600 °C. In addition, we compare the annealing of a hydrogenated carbon nitride film (HCN(x)) in both a conventional vacuum and our newly developed ambient Ar atmosphere setup.

Aluminum (Al)/zirconium oxide (ZrO2)/GaAs metal-oxide-semiconductor (MOS) capacitors were fabricated on p-GaAs. The carrier concentration of n-GaAs was varied by metal organic chemical vapor deposition. The ZrO2 gate dielectrics were prepared by the sol-gel process and then spin-coated onto GaAs substrates. Three different thicknesses of the ZrO2 layer, viz., 25, 40 and 50 nm, were used to study the effect of oxide thickness on different MOS parameters. Sulfur (S) passivation of the GaAs surface was done to control the interface state densities before ZrO2 deposition. It was found that S passivation resulted in both low hysteresis and high accumulation capacitance of the device. Frequency dependent studies on the dielectric characterizations were made in the frequency range of 10 kHz–1 MHz. It was found that within this frequency range dispersion of the oxide capacitance was 2%/decade. It was observed that interface trap densities (Dit) increased with an increase in the carrier concentration of n-GaAs fro...

The evolution of reversible room temperature ferromagnetism (RTFM) has been investigated in Co- and Fe-doped (5% each) and non-doped CeO2 polycrystalline samples. Specimens with different oxygen vacancy (VO) concentration including the (i) as-synthesized, (ii) hydrogenated and (iii) re-annealed in air were investigated using SQUID magnetometry, x-ray diffraction and x-ray photoelectron spectroscopy. The influence of the electronic properties on the RTFM was examined/analysed systematically. Our findings confirm that the ferromagnetism observed in CeO2 originates due to the oxygen vacancies, supporting the VO mediated ferromagnetic exchange mechanism. Additionally, the cationic (cerium and transition metal) valence states play a crucial role.

The influence of hydrogen and vacuum annealing on the structural, electronic, and magnetic properties of Ni-doped ZnO pellets viz. Zn0.95Ni0.05O has been investigated using x-ray diffraction (XRD), magnetization, resistance measurements, and x-ray photoelectron spectroscopy (XPS). Rietveld refinement of the XRD patterns confirms that all the polycrystalline samples possess wurtzite type hexagonal structure with no evidence of secondary phases. The superconducting quantum interference device magnetometry measurements exhibit a paramagnetic state for the as-synthesized Zn0.95Ni0.05O. However, the post annealing in H2 as well as in vacuum, drive it to a ferromagnetic state at 300 K. The obtained values of coercivity are 177 and 270 Oe, and the saturation magnetizations are 1.67 and 1.91 emu/g, respectively, for the H2 and vacuum annealed samples. Temperature dependent magnetization results show that the Curie temperatures are nearly the same (∼550 K) for both the annealed samples. Resistance of the annealed ...

We present low-temperature infrared measurements of magnetite (Fe3O4) thin films on Si (111) substrate across the Verwey transition temperature (TV). The line parameters of the most intense t1u mode observed in the Fourier transform infra red spectrum of the film is studied as a function of temperature. We observe that mode frequency increases abruptly at 130 K, and full width at half maxima of the mode increases abruptly at 113 K. The observations point out that structural transition may start earlier at 130 K than the actual Verwey transition (121 K) and that complete at 113 K. These results are consistent with the higher transition temperature as observed in resistivity and magnetization measurements.

Electronic and magnetic properties of Co-doped TiO2 polycrystalline pellets (Ti0.95Co0.05O2) have been investigated using x-ray diffraction, x-ray photoemission, magnetization, and resistance measurements. The as-synthesized and hydrogenated specimens crystallize in the anatase type tetragonal structure containing very small (∼4.4%) rutile phase. The dopant ions of Co are found to be divalent and well incorporated into TiO2 lattice, substituting the Ti site within the anatase phase, with no evidence of metallic Co or any other oxides of Co. The Co doping induces a weak ferromagnetic ordering in the diamagnetic TiO2 host matrix. Interestingly, when the Co-doped TiO2 is annealed in hydrogen atmosphere, it shows a giant enhancement in magnetization. However, an extended reheating in air causes this H-induced magnetization to vanish and the sample regains the as-prepared status. Our findings indicate that ferromagnetism originates from the doped matrix rather than any magnetic clusters and strongly correlated...

The effect of low energy (300 eV) argon plasma treatment on the morphology of polycarbonate was studied by means of contact angle measurement, X-ray photoelectron spectroscopy (XPS), Vickers' micro hardness indentation and atomic force microscopy (AFM). The surface free energy (SFE) changes from 38.5 mJ/m2 to 74.9 mJ/m2 on increasing the treatment time and the corresponding contact angle was changed from 63° to 17°, which shows the enhancement in surface adhesion. The XPS analysis shows the increase of the C-O and C=O functional groups upon treatment. The Vickers' micro hardness was studied in the load range 10-500 gf. The micro hardness of the film increases with the treatment time. Atomic force microscopy (AFM) reveals that average surface roughness increases from 7.0 nm to 27.2 nm as treatment time increases.

The surfaces of polycarbonate films were treated by nitrogen plasma, in order to understand the effect of low energy ions on the surface modification of polycarbonate. The modified samples were characterized by micro-hardness tester, optical micrograph/atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and FTIR spectroscopy. It was observed that the hardness of the film increases as fluence increases. This may be attributed to the cross-linking effect as corroborated with FTIR spectra. XPS analysis indicates that chemical bonding on the surface of the film, especially C=O, C-O and C-C/C-H functional groups, was found to change due to plasma treatment. AFM analysis reveals that average surface roughness increases from 5.9 nm to 42.7 nm as fluence increases.

We report the results of electronic and magnetic properties of poly-crystalline Zn1-xMxO (M = Co and Mn) pellets studied by XRD, VSM and XPS. The specimens were synthesized by solid state reaction method using high purity oxides. Samples exhibit Wurtzite hexagonal symmetry and show interesting magnetic properties. The Co (5%) doped sample prepared by heating in air shows a paramagnetic state in agreement with several claims. But the sample prepared by heating in Ar atmosphere depicts ferromagnetic ordering. Addition of 2% Mn in it further enhances its magnetic moment. The specimens ZnCoO (Ar heated) and ZnCoMnO were hydrogenated at 550°C that caused a significant change in their magnetization. The Co doped ZnO shows a robust increment in the magnetic moment but the Mn doping does not seem to respond to hydrogenation. O 1s XPS results show clear evidence of oxygen depletion for the samples prepared by heating in Ar atmosphere and a further depletion upon hydrogenation. Results suggest oxygen vacancies as the basic origin for room temperature ferromagnetism in doped ZnO.

An analysis has been carried out of the genesis and character of growth dislocations present in all growth sectors of single crystals of potash alum. The crystals, grown from seeded solutions by the temperature lowering method under conditions of low supersaturation, presented the well-developed forms: {111} dominant, {100} and {110}. Growth dislocations formed predominately during refacetting of the edges and corners of the seed, rounded during preparation and insertion into the supersaturated solution. From here they become refracted into the {111} sectors which proved to be the most defective. Smaller numbers of dislocations form at the {111}, {100} and {110} seed interfaces and propagate in these sectors. In crystals of inferior quality, a number of inclusions were found predominantly in the fast growing {100} sectors which become the source of additional dislocations. Dislocations present in the original seed did not propagate across the interface into the developing crystal. Dislocations of all characters were observed. The principal Burgers vectors were found to be left angle bracket100right-pointing angle bracket, left angle bracket110right-pointing angle bracket and left angle bracket111right-pointing angle bracket.

Potassium titanyl phosphate (KTP) is a relatively new nonlinear optical material with excellent combination of physical properties. This paper presents the combined etching and X-ray topographic studies carried out on KTP crystals with a view to characterizing their defects. KTP crystals employed in this investigation were grown from flux. Optical microscopic study of habit faces revealed growth layers and growth hillocks on (100) and (011) faces respectively. Etching of (011) habit faces proved that growth hillocks corresponded to the emergence point of dislocation out crops on these faces. The suitability of the new etchant to reveal dislocation was confirmed by etching the matched pairs obtained by cleaving. The defects present in the crystal were also studied by X-ray topography. The defect configuration in these crystals is characteristic of crystals grown from solution. The dislocations arc predominantly linear with their origin either at the nucleation centre or inclusions. In general, grown crystals were found to have low dislocation density and often large volumes of crystals free from dislocation could be obtained.

The wide band gap semiconductor ZnO when doped with a very low percent of some transition metal ions can exhibit above room temperature ferromagnetism, transforming it into a unique compound for spin-electronic applications. In the present work we have compared the electronic structure of two polycrystalline Zn1-xMnxO pellets (for x=0.02 and 0.04), prepared by low temperature processing, and carefully characterized. The Rietveld refinement of the XRD patters established that the samples have the ZnO lattice with ZnS type Wurtzite hexagonal symmetry and no detectable impurities. The samples exhibit distinctly different magnetic properties. The pure ZnO pellet shows a diamagnetic behaviour, the 2% sample displayed a clear FM ordering at 300 K while the 4% sample did not show any ordering even upon cooling. Their electronic structure has been investigated using x-ray absorption and x-ray photoemission spectroscopy with an aim to find out how the changes in the electronic structure can correlate to the magnetic properties in such diluted magnetic semiconductor materials. The results show that most of the Mn ions of the ferromagnetic sample are in the divalent state. For the higher Mn percent nonmagnetic sample, a larger contribution of higher oxidation Mn states are dominant and the oxygen content also increases. The two factors can be correlated to the suppressed ferromagnetism, though it is hard to exactly predict that which of these two factors weighs more.

The electronic structure of BaPbO3 and Ba2PbO4 was investigated using photoemission, x-ray diffraction (XRD) and tight binding linear muffin tin orbital (TB-LMTO) band structure techniques. BaPbO3 is a base material for all Pb based superconductors. Rietveld analysis of the XRD data suggested that BaPbO3 is an orthorhombically distorted perovskite with Imma space group and Ba2PbO4 possesses tetragonal structure with I4/mmm space group. LMTO calculations indicated an insulating ground state for Ba2PbO4 with a band gap of 1.3 eV and a metallic ground state for BaPbO3. Ultraviolet photoemission results agree well with the LMTO calculations. The Pb–O1–Pb bond angle in the basal plane is a key parameter in deciding the electronic structure of these compounds. The Pb 4f and O 1s core levels of BaPbO3 exhibited asymmetry on the high binding energy side of the peak, indicating that both Pb and O contribute to the density of states at the Fermi edge. The core levels of Ba2PbO4 did not exhibit asymmetry. Core level asymmetry can be used to probe the local density of states at EF.

The authors regret that an error occurred in section (4) of the above published article. On page 9, in the fourth sentence of the second paragraph 'smaller' should be replaced with 'larger'. Thus, the corrected sentence should now read 'However, the Pr–O2 distance 2.95 A is seen to be much larger compared to the corresponding distance 2.41 A in the case of 10% Pr substitution at the Y site, calculated by Peng et al [9].'

Photoinduced interdiffusion was observed with above band gap light in nanolayered Se/As2S3 films. It is discussed in terms of the optical parameters such as band gap, Urbach edge (E-e) [F. Urbach, Phys. Rev. 92, 1324 (1953)], and B-1/2 (Tauc's parameter) [J. Tauc , Phys. Status Solidi 15, 627 (1966)]. Experimental data of B-1/2 and E-e for as-prepared samples do not show clear correlation implied by the Mott-Davis model [N. F. Mott and E. A. Davis, Electronic Process in Non-crystalline Materials (Clarendon, Oxford 1979), p. 287]. It is also shown that the optical parameters can be changed with a change in the Se sublayer thickness. Variations of these optical parameters as a function of modulation period and photoinduced interdiffusion were discussed in terms of the quantum confinement effect and changes in the valence and conduction bands. We proposed a model to explain the mechanism of Se diffusion in As2S3, which suggests that diffusion takes place through the wrong bonds. X-ray photoelectron spectroscopy (XPS) is used to investigate the chemical alternations in the bonding. The proposed model was supported by the XPS data.

Using a combination of growth kinetics and X-ray topographic studies an assessment has been made of the role of growth dislocations in the growth process on the {111} and {110} surfaces of seeded potash alum single crystals.{111} Growth sectors contain few dislocations which initiate at the seed interface. Most growth dislocations enter these sections at later stages of growth from adjacent {110} and {100} sections. These dislocations appear to have little influence on the growth process, the kinetics and mechanism being defined at an early stage of growth to give a constant growth rate.The {110} sectors contain dislocations of all types which initiate at the seed crystal interface and influence the growth process. Identification of the numbers of different types of growth dislocation and the correlation of their density with growth rate shows no distinct and regular variation of growth rate with the number of screw and/or mixed dislocations. Edge dislocations must be included in the total to yield a regular and potentially dominant influence. Studies of the supersaturation dependence of the growth rate of {110} faces yields a behaviour consistent with growth by a two-dimensional nucleation mechanism.This is additional evidence to that already noted in growth of the {100} sectors for a strong contributory role of edge dislocations to crystal growth in some sectors of this material.

X-ray topographic studies have been made of the formation, propagation and character of growth dislocations in the {100} growth sectors of potash alum crystals grown from cut and polished seeds in a kinetic growth cell. Under the conditions of growth used (supersaturation 0.1–6.4%) all dislocations were found to be of pure edge character. As the sectors propagated, the area of the face initially remained constant but then decreased. As the decrease occurred many of the dislocations intersected the growth sector boundaries and became refracted into the adjacent {111} growth sectors. In parallel with the loss of these dislocations from this sector, the growth rate of the facet decreased and became variable. This association is consistent with the contention that the emergent ends of dislocations of pure edge character can act as nucleation centres for crystal growth. Further, more definite proof for such a role was obtained by examining the growth rates of {100} growth sectors containing different numbers of growth edge dislocations, but in the early, constant growth region. The growth rate was found to increase with increasing edge dislocation density. This evidence confirms that edge as well as screw dislocations play a significant role in the crystal growth process.

Single crystals of K, Rb and Cs perchlorates have been grown by the counter diffusion of the respective ions and ClO 4 − through the gel medium. Studies on nucleation, growth kinetics, morphological aspects and purity are discussed in this paper. The dielectric constant, e b, as well as loss measured along the longest axis, exhibits an anomaly at the transition temperature, T t, in all the three crystals. It is found that the peak values of T t are approximately 800, 100 and 53 in K, Rb and Cs perchlorates, respectively. The dielectric anomaly and the large value of e b in the cubic phase are discussed in terms of the degree of disorder of the ClO 4 − group and the possible contribution from defects.

An examination has been made of the regrowth of fractured and strained crystals in an effort to define the potential influence of attrition on the defect structure of a regrown crystal and hence on its growth rate. The primary consequence of regrowth is the development of lattice strain at the newly formed interface. The degree of strain depends on the nature of the original damage and the rate of refacetting. The strain may be released plastically by the formation of dislocations or it may be retained. The dislocations so formed can contribute to the growth process and enhance the growth rate in proportion to the number formed. Elastic strain leads to a reduction in growth rate. Thus the distribution of dislocation and strain in different crystals could lead to growth rate dispersion. The possibility that similar processes could contribute to growth rate dispersion in micro-crystals is discussed.

This investigation deals with the effect of growth temperature on the microstructure, nitrogen content, and crystallinity of C–N nanotubes. The X-ray photoelectron spectroscopic (XPS) study reveals that the atomic percentage of nitrogen content in nanotubes decreases with an increase in growth temperature. Transmission electron microscopic investigations indicate that the bamboo compartment distance increases with an increase in growth temperature. The diameter of the nanotubes also increases with increasing growth temperature. Raman modes sharpen while the normalized intensity of the defect mode decreases almost linearly with increasing growth temperature. These changes are attributed to the reduction of defect concentration due to an increase in crystal planar domain sizes in graphite sheets with increasing temperature. Both XPS and Raman spectral observations indicate that the C–N nanotubes grown at lower temperatures possess higher degree of disorder and higher N incorporation.

The paper reports a very efficient and reproducible technique for room temperature crystallization of titanium dioxide in a record time of 5 minutes, by application of alternating voltage square pulses. The well aligned tubular formation of crystalline nanotubes is confirmed through various characterizations and the mechanism of crystallization is explained based on the pulse induced electrophilic-nucleophilic reaction. This ultrafast pulsed crystallization method provides a viable alternative for the widely used post fabrication thermal annealing and is highly applicable in device fabrication.