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Structural modifications in InP(111) due to 1.5 MeV implantation of Sb have been characterized using first-order and second-order Raman spectroscopy. With both longitudinal optical (LO) and transverse optical (TO) modes allowed for InP(111), we have investigated the evolution of both these modes as a function of fluence. Investigations of both the first and second-order Raman modes indicate the presence of tensile stress in the lattice after implantation, which increases with fluence. Results show a coexistence of nanocrystalline InP regions and amorphous zones in the lattice. Consequently phonon confinement is observed and phonon confinement model (PCM) has been applied here to estimate the coherence length and the size of nanocrystalline zones in InP lattice after implantation. Nanocrystalline zones as small as 35 Å have been observed here. A LO phonon-plasmon coupled mode, due to the charge layer in the vicinity of the surface, has also been observed. This coupled mode becomes sharper and more intense with increasing fluence. For high fluences, crystalline to amorphous phase transition has also been observed. First and second-order LO modes have been utilized to estimate the electron-phonon coupling strengths. The coupling strength is observed to decrease as the nanocrystalline zones, in the implanted lattice, become smaller. [ABSTRACT FROM AUTHOR]

Nickel cobaltite nano-flower was synthesized via temperature dependent co-precipitation techniques and its single phase formation, vibrational spectra and nanostructured with flower-like morphology were confirmed by XRD, FTIR, Raman and TEM micrographs. The electrical transport properties and conduction mechanism of NiCo 2 O 4 were studied first time using complex impedance spectroscopy in frequency range 100 Hz-1 MHz and wide temperature range 25 °C-300 °C. Poor grain relaxation was observed from RT to 75 °C whereas interface (both grain boundary and electrode effect) plays a dominant role above 75 °C are ascertained from Nyquist plot of impedance and modulus spectra. The utmost dielectric constant (6.8 × 10 2 ) and loss (540) was observed at high temperature (300 °C) and low frequency (100 Hz) regime and gradually diminished with high-frequency evolution and low-temperature approach. Finally, the ac and dc conduction mechanism were examined individually in details by the help of hooping relaxation model and overlapping large polaron tunneling (OLPT) concept for supercapacitor application. The calculated value of activation energy for dc conduction (0.63 eV) is larger than ac conduction (0.36 eV) as the ac conductivity is thermally activated. [ABSTRACT FROM AUTHOR]

The Hg 5d5/2 and 5d3/2 cross sections and branching ratios were measured in the photon energy range between 26 and 105 eV for Hg overlayers on Ag (100) and Cu (100). The branching ratios deviate from the nonrelativistic statistical value of 1.5, reaching values of 8.0. Data are presented that establish a direct relationship between the branching ratio and the long-range crystallographic structure of the Hg overlayers. This relationship is a consequence of the formation of a band structure from the shallow mercury 5d eigenstates. [ABSTRACT FROM AUTHOR]

An exotic condensation of DNA molecules is observed on the nanostructured ZnO surface. The ZnO nanostructures (NS) fabricated by thermal vapor deposition technique were associated with a large number of oxygen vacancies on the surface. These oxygen vacancies induced changes in the DNA conformation which further reflected through changes in the persistence length of the DNA molecules. This indicates a reinforcement of the bonds and binding in both the phosphate and the base regions of the DNA molecules with the positively charged core vacancy sites on the ZnO nanostructured surface through strong interaction mediated via long-range electrostatic forces which effectively reduced the end-to-end distance of the λ-DNA molecule. This strongly suggests a transition of the λ-DNA molecule through structural modification into a more compact higher-order fractal dimension from its native state. [Display omitted] • Condensation of DNA molecule observed on ZnO surface. • Oxygen vacancies initiate the chemical adsorption of DNA molecules onto the Oxide surface. • Higher order transition of the biomolecule observed on Nanopatterned oxide surface. [ABSTRACT FROM AUTHOR]

Abstract: Temporal evolution of nano dots fabricated, in off-normal geometry but in the absence of rotation, on InP(111) surfaces by 3keV Ar ion sputtering is reported here. After 10min of sputtering, self-assembled nano dots with mean diameter of 24±4nm display square short range weak ordering. Fully developed square celled arrays of dots with mean diameter of 90±26nm, are seen beyond the non-linear coarsening regime at the critical time of 40min. Inverse coarsening of dots in conjunction with surface smoothening, never seen in earlier studies of dot evolution, is observed beyond the critical time. [Copyright &y& Elsevier]

Abstract: We have investigated the topography and the radial separation distribution of the InP(111) surfaces after 1.5MeV Sb2+ implantation. Power spectral density has been evaluated by utilizing the scanning probe microscopy (SPM) images of the MeV implanted InP(111) surfaces. We find that the exponent, n, increases up to the fluence of 1×1014 ions/cm2 and is found to be n =4.36 at this fluence suggesting that the diffusion processes are crucially determining the evolution of InP surface. For higher fluences a slight decrease in n is seen. We have also studied the radial separation distribution of the nanostructures that form on the InP(111) surfaces after MeV Sb implantation. The radial separation distributions, for all the fluences, collapse on a curve. Moreover, although for Sb fluence of 1×1011 ions/cm2 the nanostructures are randomly distributed on the InP surface, for higher fluences a clustering of nanostructures at r ≈〈R〉, suggesting a non-uniform distribution of nanostructures is observed. The clustering may be a result of surface diffusion or strain. [Copyright &y& Elsevier]

Abstract: We have investigated the formation of nanosized structures on InP(111) surfaces after 1.5MeV Sb implantation. Scanning probe microscope (SPM) has been utilized to investigate the size, height and the density distributions of the nanostructures as a function of ion fluence. We observe nanostructures smaller than 100nm and lower than 4nm at all fluences. Moreover in large nanostructures we observe agglomeration of several smaller structures. We have also investigated the rms surface roughness of the InP(111) surfaces after MeV implantations. [Copyright &y& Elsevier]

We have employed in parallel the Catalyst HypoGen pharmacophore modeling approach and the variable selection k-nearest neighbor quantitative structure–activity relationship (kNN QSAR) method to model a diverse data set of p38 mitogen-activated protein (MAP) kinase inhibitors. The HypoGen pharmacophore model, developed from a novel automated training set selection protocol, identified chemical functional features that were characteristic of the active compounds and differentiated the active from the inactive inhibitors. The kNN QSAR modeling employed topological descriptors and afforded predictive QSAR models with consistently high values of both leave-one-out cross-validated R2 for the training set and predictive R2 for the test set. The results of both modeling approaches were sensitive to the selection of the training and test sets used for model development and validation. The resulting Catalyst pharmacophore and kNN QSAR models can be used concurrently for rapid virtual screening of chemical databases to identify novel p38 MAP kinase inhibitors. [Copyright &y& Elsevier]

We investigate the effect of high-energy ion irradiation (HEII) on the dopant behaviour for a 1.5 MeV Sb implantation in Si(1 0 0). For HEII, 8 MeV carbon ions were utilized. In addition to exploring the Sb substitution, distribution and diffusion, after HEII, Si lattice damage has also been studied. Effects of annealing, both prior to and after HEII, have also been investigated. Techniques of Rutherford backscattering spectrometry and channeling (RBS/C) have been applied to understand the dopant behaviour as well as the damage and crystallization of Si lattice. The results show that the vacancy (V) supersaturation created during HEII promotes a high (93%) Sb substitution and a low Si damage after a 400 °C anneal. This is an anomalous result as the SPEG of Si is expected at 600 °C. Enormous redistribution of Sb is observed indicating that the dopant defect interactions become crucial after HEII. In-diffusion of Sb is noticed at higher temperatures. Sb diffusion or redistribution is not observed in the absence of HEII. Results indicate that the excess V after HEII can control the dopant behaviour as well as the Si lattice damage. [Copyright &y& Elsevier]

We have studied the dopant substitution and the lattice damage after 1.5 MeV Sb implantation in Si(1 0 0). The effects of high-energy ion irradiation (HEII) on the Sb substitution and the Si damage have also been investigated. Vacancy super-saturation after HEII promotes high Sb substitution as well as stimulates Si regrowth after 400 °C anneal. The crystallinity of Si lattice as well as the Sb substitution however deteriorates after higher temperature anneals. In addition an inward Sb diffusion is also observed. With low-temperature annealing treatment prior to HEII, a good Sb substitution is observed after 800 °C. In addition, no dopant diffusion and a reduced overall damage is evidenced after 800 °C anneal. Techniques of RBS/C have been applied to investigate the dopant substitution and lattice damage for different irradiation conditions. Multiple scattering formalism has been utilized to extract the damage profiles from RBS/C data. [Copyright &y& Elsevier]

Here we study the roughening behavior, scaling properties and the wetting nature of the Silicon surfaces that have been irradiated with 3 keV Ar ions. These surfaces illustrate the formation of nanostructures and ripples, which evolve at higher fluences. The scaling studies have been applied to understand the evolution of the surfaces. Height- Height correlation method has been utilized to extract important scaling parameters, and the derived Hurst exponents (H) indicate these surfaces to be of self-affine type. The derived correlation lengths (ξ) reflect long ranged correlations on the surface and evolution of the nanostructures. The nano-patterned surfaces show near hydrophobic behavior, which gets further enhanced with increasing irradiation. [ABSTRACT FROM AUTHOR]

We have investigated the dopant behavior of 1.5 MeV implanted Sb in Si(100) both prior to and following irradiation with 8 MeV C[sup +] ions. The irradiation stimulates the regrowth in silicon lattice and induces a high Sb substitution of 93% after a thermal anneal of 400 °C. At higher temperatures, a significant Sb diffusion towards the amorphous/crystalline interface is detected in the ion-irradiated sample. It is suggested that the vacancy supersaturation produced during ion irradiation is dominantly responsible for the significant modification of dopant substitution, redistribution, and diffusion. Point defects created during precipitation also seem to influence the dopant diffusion. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have studied the surface modifications as well as the surface roughness of the InP(111) surfaces after 1.5 MeV Sb ion implantations. A scanning probe microscope has been utilized to investigate the ion-implanted InP(111) surfaces. We observe the formation of nanoscale defect structures on the InP surface. The density, height, and size of the nanostructures have been investigated here as a function of ion fluence. The rms surface roughness, of the ion implanted InP surfaces, has also been investigated. Raman-scattering results demonstrate that at the critical fluence, where the decrease in surface roughness occurs, the InP lattice becomes amorphous. [ABSTRACT FROM AUTHOR]

We investigate here the structural phase transformation and electrical resistive switching properties of TiO 2 thin films (80 nm) after their self-ion implantation with 50 keV Ti + ions at several fluences. UV-Raman, grazing incidence x-ray diffraction (GIXRD), transmission electron microscopy, x-ray photoelectron spectroscopy, and atomic force microscopy techniques have been utilized to investigate the modifications in thin films. Both, the as-grown and ion implanted, films display mixed phases of rutile (R) and anatase (A). Surprisingly, however, a phase transition from A to R is observed at a critical fluence, where some anatase content transforms into rutile. This A to R transformation increases with additional fluence. The critical fluence found by GIXRD is slightly smaller (1 × 10 13 ions/cm 2) than from UV-Raman (1 × 10 14 ions/cm 2), indicating the first initiation of phase transformation probably in bulk. All the films contain anatase in nanocrystalline form also and the phase transformation seems to take place via aggregation of anatase nanoparticles. Thin films also show the presence of oxygen vacancies (O V) Ti 3 + , whose number grows with fluence. These O V as well as thermal spikes created during Ti + ion implantation are also crucial for the A-R transition. After implantation at the highest fluence, TiO 2 thin films show bipolar resistive switching behavior. The development of conducting filaments, formed by the migration of many oxygen vacancies generated during ion implantation, can be responsible for this behavior. [ABSTRACT FROM AUTHOR]

Surfaces bombarded with low energy ion beams often display development of self assembled patterns and quasi-periodic structures. Kinetic Monte Carlo simulations have been performed to describe ion sputtered Tantalum surfaces. A weak nonlinearity in the relaxation process has been introduced and the results show that the positive Schwoebel barrier, produced by the nonlinear Hamiltonian, is necessary in describing ion bombarded Tantalum surfaces. Furthermore, their scaling exponents suggest presence of a class other than KPZ. [ABSTRACT FROM AUTHOR]

We present photoabsorption (PA) response and resistive switching (RS) behavior of ZnO thin films that were ion implanted, at many fluences, with 50 keV Ti ions. Photoluminescence (PL), X-ray photoelectron spectroscopy (XPS), UV–Visible spectroscopy and conductive- Atomic Force Microscopy (c-AFM) have been utilized to study the role of oxygen vacancies (O V) in the evolution of the PA and RS properties. Grazing incidence X-ray diffraction (GIXRD) and Raman Scattering results suggest an improvement in the crystallinity of the films with ion fluence. Enhancement in oxygen vacancy, with fluence, appears to be responsible for higher photo response in the UV–Vis range. Additionally, engineering of bandgap, exhibiting systematic reduction in bandgap- energy with fluence, introduces enhanced absorption in visible regime. For the films implanted at the highest fluence, an asymmetric RS behavior is observed. A Switching behavior, from a high resistance state to a low resistance state, is demonstrated under positive bias conditions. However, for negative bias conditions a rectifying nature is seen. Oxygen vacancies play a crucial role in the modulation of PA response as well as in RS mechanism. Migration of these oxygen vacancies contribute to the formation of conducting filament which may be crucial for the observation of RS phenomenon at the highest fluence. [ABSTRACT FROM AUTHOR]

The nanoscale patterns created on the ZnO(0001) surfaces during atom beam irradiation have been investigated here for their photo absorption response. Preferential sputtering, during irradiation, promotes Zn-rich zones that serve as the nucleation centers for the spontaneous creation of nanostructures. Nanostructured surfaces with bigger (78 nm) nanodots, displaying hexagonal ordering and long ranged periodic behavior, show higher photo absorption and a ~0.09 eV reduced bandgap. These nanostructures also demonstrate higher concentration of oxygen vacancies which are crucial for these results. The enhanced photo-response, as observed here, has been achieved in the absence of any dopant elements. [ABSTRACT FROM AUTHOR]

Abstract: An attempt has been made to prepare MgO nano-crystallites through decomposition of sol–gel derived magnesium oxalate dihydrate in air, oxygen and nitrogen ambient at 500, 600, 800, and 1000°C for 2h each and study them with regard to their phase, average crystallite size, morphology, and photoluminescence (PL) behaviour. They are shown to possess f.c.c. (NaCl-type) structure with lattice parameter a∼4.211Å, average crystallite size in the range of 3.0–73.5nm, 〈111〉 preferred orientation at decomposition temperature of 500°C (in nitrogen and oxygen ambient), and a distorted rod-like morphology. The PL peaks observed around 395 and 440nm have been assigned to 2T1u→2A1g and 3B1u→1Ag transitions associated with the relaxation of excited states of F+- and F2 2+-centres, respectively. Further, the emission band intensity is found to depend on decomposition temperature and gas ambient, crystallite size, and their morphology. However, in nitrogen ambient above 800°C, several other PL peaks observed at 491.8, 501.8, 503.5, 509.3, 561.5, and 563.0nm arise due to aggregates of F centres and/or extra energy levels created in the energy band gap by nitrogen incorporation. A mechanism for nitrogen trapping in MgO has been suggested. Further, emission intensity depends on both colour centres and surface states. [Copyright &y& Elsevier]

Superconductors are the only experimentally accessible systems with spontaneously broken gauge symmetries which support topologically nontrivial defects, namely string defects. We propose two experiments whose aim is the observation of the dense network of these strings thought to arise, via the Kibble mechanism, in the course of a spontaneous symmetry breaking phase transition. We suggest ways to estimate the order of magnitude of the density of flux tubes produced in the phase transition. This may provide an experimental check for the theories of the production of topological defects in a spontaneously broken gauge theory, such as those employed in the context of the early Universe. [ABSTRACT FROM AUTHOR]

Two dimensional nanostructures have been created on the rutile TiO2 (110) surfaces via ion irradiation technique. Enhanced anomalous photo- absorption response is displayed, where nanostructures of 15 nm diameter with 0.5 nm height, and not the smaller nanostructures with larger surface area, delineate highest absorbance. Comprehensive investigations of oxygen vacancy states, on ion- irradiated surfaces, display a remarkable result that the number of vacancies saturates for higher fluences. A competition between the number of vacancy sites on the nanostructure in conjunction with its size is responsible for the observed anomalous photo-absorption. [ABSTRACT FROM AUTHOR]

The surface dynamics of TiO 2 thin films, evolving under the implantation of 50 keV Ti ions, have been investigated. The morphological evolution, as investigated with atomic force microscopy, delineates a surface smoothening by ion implantation.The nanoscale structures at surfaces also undergo a size reduction. Scaling formalism has been applied to understand this temporal and spatial dynamics by estimating the scaling exponents (α , β and γ) via Height-height correlation function (HHCF) and power spectral density (PSD) investigations. The roughness exponent α (0.5 < α < 1) indicates these ion irradiated surfaces to be of self affine nature. Also, they evolve into locally smoother surfaces with increasing fluence. Negative growth exponent (β) also delineates surface smoothening. Exponent, γ , is observed to increase from ~ 2 at lower ion fluences to 2.5 at the highest fluence. This behavior suggests that diffusion is predominantly controlling the dynamical evolution of the ion irradiated TiO 2 surfaces at the highest fluence, similar to that in the bulk case. [ABSTRACT FROM AUTHOR]

Conjugated hybrid nanostructured Cu2O-ZnO has been grown via the single-step coelectrodeposition (CED) technique. Though ZnO nanostructures grown alone by electrodepostion technique do not exhibit any glucose sensing, the CED-grown Cu2O-ZnO nanostructures show non-enzymatic glucose sensing and amperometric behavior with a good sensitivity of 441.2 μ A mM− 1 cm− 2, linear range of 0.02–1 mM and low detection limit of 0.13 μ M (S/N = 3) along with a fast response time (less than 3 s). The CED growth process leads to development of conjugated hybrid nanostructured Cu2O-ZnO that presents an excellent template for non-enzymatic glucose sensing. [ABSTRACT FROM AUTHOR]

The role of N/F co-doping on the defect-driven room-temperature d0 ferromagnetism in group-I element Li doped ZnO nanowire arrays has been investigated. The ferromagnetic signature of pristine ZnO nanowires has enhanced significantly after Li doping but the Li-N co-doping has found to be more effective in the stabilization and enhancement in room-temperature ferromagnetism in ZnO nanowires. Saturation magnetization in Li-doped ZnO nanowires found to increase from 0.63 to 2.52 emu/g and the Curie temperature rises up to 648 K when 10 at. % N is co-doped with 6 at. % Li. On the other hand, Li-F co-doping leads to exhibit much poor room-temperature ferromagnetic as well as visible luminescence properties. The valance state of the different dopants is estimated by x-ray photoelectron spectroscopy while the photoluminescence spectra indicate the gradual stabilization of Zn vacancy defects or defect complexes in presence of No acceptor states, which is found to be responsible for the enhancement of intrinsic ferromagnetism in ZnO:Li matrix. Therefore, the Li-N co-doping can be an effective parameter to stabilize, enhance, and tune zinc vacancy-induced room-temperature d0 ferromagnetism in ZnO nanowires, which can be an exciting approach to prepare new class of spintronic materials. [ABSTRACT FROM AUTHOR]

The dynamics of TiO surfaces evolving under 60 keV Ar ions have been explored here. Dynamic scaling ansatz, height–height correlation (HHC) model and power spectral density (PSD) model have been applied to investigate the growth mechanisms. The surfaces are growing under non-equilibrium growth processes and three separate domains of evolution have been noticed. Early time growth of the surfaces can be characterized by roughness exponent, –0.74, and growth exponent,. Dominance of diffusion is also noticed with Edward Wilkinson (EW) growth scaling. In the next time regime, non-local instabilities get incorporated, due to sputter-induced nanostructuring of the surfaces, resulting in a rapid surface roughening with a high value of β. The surface roughness saturates in late time regime. [ABSTRACT FROM AUTHOR]

Abstract Aligned ZnO nanorods (NRs) were synthesized by a simple and inexpensive hydrothermal method. Morphological, structural, photoabsorbance and photoluminescence studies have been carried out using field emission scanning electron microscopy (FE-SEM), grazing incidence X-ray diffraction (GIXRD), Raman, UV–visible and Photoluminescence spectroscopy. Results show that crystallinity and alignment of ZnO NRs lead to good photocatalytic activity in the presence of visible light. The Photoluminescence spectra revealed a decrease in the UV emission, suggesting a reduced recombination of the photo generated carriers. The visible region emission is due to the surface oxygen vacancies. Increase of charge separation rate observed from emission spectra and the vacancy related sub-bands in the absorbance spectra are together responsible for the enhanced visible light photocatalytic activity of ZnO NRs. Vertically aligned 1-D morphology of ZnO NRs and the presence of oxygen vacancy states assist in the visible light photocatalytic degradation of Methylene Blue dye. Highlights • Preparation of aligned ZnO nanorods by hydrothermal method. • Morphological, structural and photoabsorbance characterizations of ZnO nanorods. • An enhanced photo absorption in the visible region was observed for ZnO nanorods. • PL results show decrease in e-h recombination for aligned nanorods. • Good crystallinity, alignment of ZnO NRs and oxygen vacancies lead to good photocatalytic activity in the presence of visible light. [ABSTRACT FROM AUTHOR]

Abstract This paper reports the structural, morphological and optical properties of undoped and cobalt doped (1, 10 atomic wt% Co) ZnO thin films on glass substrates prepared by a simple cost effective sol-gel spin coating technique. The effect of cobalt doping on the optical properties like transmittance, refractive index, extinction coefficient, etc. was investigated. X-ray diffraction (XRD) and Raman spectra confirm the formation of wurtzite ZnO structure with (100) as the preferred orientation. Atomic force microscopy (AFM) images of ZnO and Co-doped ZnO films show smooth surfaces with a uniform distribution of spherical grains on the surface. The morphological changes from undoped to doped samples are more evident from the correlation images obtained using MATLAB software. All the films show more than 80% of transparency in the entire visible region while 10% Co-doped ZnO film has the highest transparency (>94%). Spectroscopic ellipsometry was used to study the refractive index and extinction coefficient which indicates the highest refractive index and lower extinction coefficient for 10% Co-doped ZnO thin films. High transparency in the visible region along with a high refractive index and lower extinction coefficient in Co-doped ZnO films can be useful for optoelectronic devices. Highlights • Effect of doping in the morphology of the samples is studied first time by correlation images obtained by using MATLAB software. • Highest transmittance (∼94%) as well as high refractive index and low attenuation coefficient of 10% cobalt doped ZnO sample can be useful for optoelectronic device applications. • Preferential growth of our films is along (100) orientation which is very difficult to grow. [ABSTRACT FROM AUTHOR]

Abstract Nickel-zinc oxide (Ni-ZnO) nanoparticles were synthesized via low-cost sol-gel auto combustion route using ethylene glycol as a reducing agent. The structural and surface morphological analysis were confirmed by XRD, FESEM and TEM micrographs which exhibits pure phase formation, unit cell crystal structure and inhomogeneous grain growth in nm range (43.20 nm). The EDXS elemental mappings and SAED patterns exposed the presence of the fundamental element with stoichiometric ratios and double phase formation of Ni-ZnO nanocomposite. The dielectric and conduction mechanism were characterized by impedance, modulus, dielectric and conductance spectra with frequency and temperature evolution. The suppressed Nyquist plot of impedance and modulus with temperature demonstrates the curtailment of grain boundary resistance and dominance of grain contribution. The dielectric constant and loss both lessened with high-frequency evolution and utmost value of dielectric constant 300 was observed at 95 °C. The ion hopping conduction mechanism (Nearest neighbor hopping and Variable range hopping) was proposed to explain its conduction processes and activation energy (1.02 eV) of dc conduction was calculated from Arrhenius plot. Finally, the direct and indirect optical band gap of Ni-ZnO was estimated from UV-DRS absorption spectra using Kubelka-Munk equation. [ABSTRACT FROM AUTHOR]

Abstract The topographic evaluation of the nano-scale pattern, on ZnO (001) surface, and its scaling properties have been investigated here after low energy atom beam irradiation. Preferential sputtering promotes the formation of Zn-rich zones near the surface that serve as the nucleation centers for the spontaneous nanostructure growth. The rms roughness (σ) however increases with irradiation fluence and displays power law behaviour, σ ∼ t β , for t < t c (crossover time) but saturates at longer time scale. In the case of t > t c , σ is independent of irradiation time but interestingly follows the power law behaviour σ ∼ L α , where L is the size of image used in analysis. The morphology of the surfaces has also been investigated using the height-height correlation and power spectral density methods. The observed values of growth (β) and roughness (α) exponents indicate a scaling behavior that is induced by the disordered but well-defined geometry of the nanostructures. [ABSTRACT FROM AUTHOR]

Highlights • This study investigates the magnetic properties of rutile TiO 2 implanted with cobalt ions. • SPM behavior here is highly anisotropic coupled with magneto-crystalline anisotropy of the Ti 1−x Co x O 2. • The Co nanoclusters possess an easy and hard axis of magnetization. • The M-T variation reveals the prominent role of dipole and inter-cluster exchange interaction. • Highly anisotropic nature of the SPM presents applications in magnetic switching devices. Abstract The present study investigates the magnetic properties of single crystal rutile TiO 2 (110) implanted with cobalt ions for fluences between 5 × 1016 and 1 × 1017 ions/cm2 with energy of 200 keV. The temperature and field dependent magnetization for magnetic fields along [0 0 1] and [ 1 1 ¯ 0 ] directions of the as implanted TiO 2 crystals show anisotropic super-paramagnetic behaviour due to formation of Co (hcp) nano-clusters unlike the complete ferromagnetic behaviour from previous reports. The ZFC and FC magnetization curves show a much higher blocking temperature ( T B ) along [ 1 1 ¯ 0 ] with values ranging from 30 to 150 K, while for field along [0 0 1] shows a lower T B ranging from 8 to 70 K. The magnetization isotherms above T B show a sharper rise and universal scaling behaviour, for field along [ 1 1 ¯ 0 ] direction. At 2 K, M - H curves show hysteresis behaviour similar of easy and hard axis of a ferromagnet. The magnetic anisotropy of Co nano clusters are coupled by the magneto crystalline anisotropy of secondary phases of cobalt with TiO 2 , thus indicating the highly oriented nature of the Co clusters. Role of dipole interactions and inter cluster exchange interactions have also been discussed. [ABSTRACT FROM AUTHOR]

The present work investigates the radiation damage, amorphization and structural modifications that are produced by ion–solid interactions in TiO 2 crystals during 200 keV Cobalt ion implantation. RBS/C and GIXRD have been utilized to evaluate the damage in the host lattice as a function of ion fluence. Multiple scattering formalism has been applied to extract the depth dependent damage distributions in TiO 2 (1 1 0). The results have been compared with the MC simulations performed using SRIM-2013. RBS/C results delineate a buried amorphous layer at a low fluence. Surprisingly, ion induced dynamic activation produces a recovery in this damage at higher fluences. This improvement interestingly occurs only in deep regions (60–300 nm) where a systematic lowering in damage with fluence is observed. Formation of Co-Ti-O phases and generation of stress in TiO 2 lattice can also be responsible for this improvement in deep regions. In contrast, surface region (0–60 nm) indicates a gradual increase in damage with fluence. Such a switch in the damage behavior creates a cross point in damage profiles at 60 nm. Surface region is a sink of vacancies whereas deep layers are interstitial rich. However, these regions are far separated from each other resulting in an intermediate (100–150 nm) region with a significant dip (valley) in damage which can be characterized by enhanced recombination of point defects. The damage profiles thus indicate a very complex behavior. MC simulations, however, present very different results. They depict a damage profile that extends to a depth of only 150 nm, which is only about half of the damage- width observed here via RBS/C. Moreover, MC simulations do not indicate presence of any valley like structure in the damage profile. The complex nature of damage distribution observed here via RBS/C may be related to the high ionic nature of the chemical bonds in the TiO 2 lattice. [ABSTRACT FROM AUTHOR]

Dynamic Scaling studies have been performed here to investigate the morphological surface evolution of single crystal TiO 2 (110) surfaces after they are implanted with Cobalt ions. These ion irradiated surfaces develop via non-equilibrium growth processes and display rough interfaces with height fluctuations that demonstrate self-affine behavior. The scaling exponents like Roughness exponent ( α ), Growth Exponent ( β ), dynamic exponent (z) and structure factor constant ( γ ) have been derived here by applying height-height correlation as well as structure factor analysis techniques and show that diffusion plays a pivotal role in the evolution of these self-affine surfaces created after Cobalt ion irradiation. [ABSTRACT FROM AUTHOR]

Au nanoparticles embedded In 2 O 3 thin films (In 2 O 3 :Au) were grown by DC reactive sputtering method in three different target configurations. Presence of Au in In 2 O 3 matrix was confirmed by glancing angle X-ray diffraction (GXRD) and transmission electron microscopy (TEM). Crystallite sizes of Au were obtained by Debye-Scherrer formula from GXRD data. Localized surface plasmon resonance was observed for In 2 O 3 :Au samples from optical absorption measurement at peak value of ~ 550 nm and inferred red shift of resonance peak towards the increasing crystallite size. Rutherford backscattering spectrometry (RBS) studies of selected samples on Si substrate showed minor In diffusion and absence of Au diffusion into the Si substrate. X-ray photoelectron spectroscopy (XPS) studies revealed that the chemical state of Au is neutral. The samples with high Au content exhibited persistent photoconductivity due to the sub band gap absorption indicating the introduction of sub band gap trap levels in In 2 O 3 . [ABSTRACT FROM AUTHOR]

Present study investigates the photoabsorption properties of single crystal rutile TiO 2 (110) surfaces after they have been implanted with low fluences of cobalt ions. The surfaces, after implantation, demonstrate fabrication of nanostructures and anisotropic nano-ripple patterns. Creation of oxygen vacancies (Ti 3+ states), development of cobalt nano-clusters as well as band gap modifications have also been observed. Results presented here demonstrate that fabrication of self organized nanostructures, upon implantation, along with the development of oxygen vacancies and ligand field transitions of cobalt ion promote the enhancement of photo-absorbance in both UV (∼2 times) and visible (∼5 times) regimes. These investigations on nanostructured TiO 2 surfaces can be important for photo-catalysis. [ABSTRACT FROM AUTHOR]

Present study demonstrates an enhancement in thermoelectric power of 10% Ag doped PbTe (PbTe:Ag) thin films when irradiated with 200 keV Ar ion. X-ray diffraction showed an increase in crystallinity for both PbTe and PbTe:10Ag nano-composite films after Ar ion irradiation due to annealing of defects in the grain boundaries. The preferential sputtering of Pb and Te ions in comparison to Ag ions resulted in the formation of nano-dots. This was further confirmed by X-ray photoelectron spectroscopy (XPS). Such an enhancement in thermoelectric power of irradiated PbTe:10Ag films in comparison to pristine PbTe:10Ag film is attributed to the decrease in charge carrier concentration that takes part in the transport process via restricting the tunneling of carriers through the wider potential barrier formed at the interface of nano-dots. [ABSTRACT FROM AUTHOR]

Scaling properties of TiO(110) surfaces, after irradiation with 3 keV Ar ions, have been investigated here. Ion irradiation leads to the spontaneous formation of self-assembled Ti-rich nanostructures (NS) as well as Tivacancy states. The NS thus formed are elliptical in shape and exhibit a shape transformation to less elliptical nature at high fluences. Scaling studies also reflect this transition. Scaling studies further reveal that the surfaces are self-affine in nature and with increasing fluence the regions of correlated structures, or fluctuations, spread and become bigger. This is connected to the formation of bigger NS, causing long-ranged correlations on the surface. On the other hand, at short length scales, the surfaces become less jagged as reflected by the roughness exponent of irradiated surfaces. [ABSTRACT FROM PUBLISHER]

[Display omitted] • Adsorption of plasmid DNA on SiOx and nanostructured-SiOx (nano-SiOx) substrates. • XPS shows DNA binds on nano-SiOx with Si⋯O⋯N & Si⋯N states, but with only Si⋯O⋯N on SiOx. • Emphasizes participation of nitrogenous DNA bases for adsorption on nano-SiOx and SiOx. • DFT used for studying adsorption of DNA base, on SiOx and nano-SiOx. • Electrostatic interaction and charge transfer from substrate to nitrogen bases. The adsorption of DNA on SiO x and nanostructured-SiO x substrates has been investigated here in order to understand their binding behaviour. The XPS results indicate that DNA binding on nanostructured-SiO x introduces chemical states like Si⋯O⋯N and Si⋯N. On the other hand, on SiO x surface only Si⋯O⋯N state is observed. Formation of Si⋯O⋯N and Si⋯N states emphasize the dominant participation of nitrogenous DNA bases during the adsorption as well as transport of charge carriers. We complement the experimental findings with first principles DFT investigations on the linkage of DNA base, adenine, with SiO x and nanostructured-SiO x , respectively. DFT results show that linkage appears to occur via electrostatic interaction and charge transfer from the substrate to the nitrogen bases of DNA. The molecular electrostatic potential maps, highest occupied molecular orbitals and lowest unoccupied molecular orbitals support the experimental findings. These results will be important for biosensing applications. [ABSTRACT FROM AUTHOR]

Present study explores the observation of topological non-hexagonal rings (NHR) and Stone Wale (SW) defects by Raman experiments in both single (SLG) and multi-layer graphene (MLG) after they are irradiated with 100–300 eV Ar ions. Although predicted by theoretical studies, here it is experimentally shown that graphene SW/NHR defects have a signature in Raman. Broad bandwidth of the pertinent Raman features suggests the presence of more than one SW/NHR defect mode, in agreement with the DFT studies. Variations in the SW/NHR related Raman mode intensities demonstrate the annihilation of these topological defects at higher energies. Behavior of Raman allowed G and 2D excitations, as well as the disorder-activated D, D' and G* lines, has also been investigated in SLG and MLG. These indicate an evolution of defects in graphene with ion irradiation, as well as presence of a transition state beyond which the Raman modes are dominated by a rise in sp3 content. Correlation of these aspects with the SW/NHR Raman provide significant insight into ion induced evolution of graphene. The direct observation of SW/NHR defects by Raman spectroscopy could be important in promoting exploration of rich topological aspects of Graphene in various fields. [Display omitted] • Observing Stone Wale/Non-hexagonal ring (SW/NHR) defects in graphene by Raman. • Predicted by theory, SW/NHR observed here first time by Raman experiments. • Irradiation ion energy (100–300 eV) affects disorder modes in Raman. • Transition stage, in energy 100–150 eV, in single and multilayers (SLG, MLG). • SW/NHR Raman mode is significant for studying topological aspects of Graphene. [ABSTRACT FROM AUTHOR]

Nanostructures (NS) have been fabricated on rutile TiO 2 (1 1 0) single crystal surfaces using Ar ion beam sputtering technique. Pronounced quantum confinement effects in TiO 2 nanodots lead to reduction in optical reflectance and bandgap widening. Moreover, a direct correlation between the size of NS and magnetic behavior is observed. This suggests that the size of NS plays crucial role in the evolution of magnetic nature. Though the smallest (∼5 nm) NS display superparamagnetic (SPM) behavior, ferromagnetism is observed for larger nanostructures. Single domain nature of TiO 2 quantum dots is responsible for the observed SPM behavior. [ABSTRACT FROM AUTHOR]

We have investigated TiO 2 films prepared by pulsed laser deposition method on Si(1 1 1) surface using X-ray diffraction (XRD), Raman Spectroscopy, X-ray Photoelectron Spectroscopy (XPS), Atomic Force Microscopy (AFM) and ion beam sputtering techniques. Our XRD data along with Raman indicated that the deposited TiO 2 is in anatase phase. The binding energy position of Ti 2p also supports the anatase phase formation. AFM topography of as deposited film indicates the formation of non uniform TiO 2 growth with the formation of voids on Si(1 1 1) substrate. After sputtering with argon ion beam, surface erosion occurs and voids have disappeared. The Ti 2p core level of sputtered TiO 2 exhibits the formation of Ti 2 O 3 , TiO and pure Ti on the surface. High binding energy shoulder of O 1s peak becomes sharp after sputtering. Ti LMM Auger peaks become broader after sputtering but no shift in kinetic energy is observed. [ABSTRACT FROM AUTHOR]

Cu/Ni bilayer has been prepared by thermal evaporation of pure Cu and Ni metals onto Si(100) surface in high vacuum; it was sputtered using argon ion beam in ultra-high vacuum. The ion beam-induced surface and interface modification was investigated using X-ray photoelectron spectroscopy and atomic force microscopy techniques. The deposited sample exhibits the formation of CuO nano-structures of size 40 nm on Cu surface and after sputtering with argon ion beam at a fluence of 5 × 10 ions/cm, the surface exhibits a mound structure with an average size of about 100 nm. Interestingly, with sputtering at higher fluence of 2⋅4 × 1 0 ions/cm, the surface exhibits broad pits of sizes ranging from 100 to 300 nm with an average depth of 10 nm. Bottom surface of these pits contains Ni atoms. The Cu 2 p peak exhibits a shift of 0⋅3 eV towards high binding energy and also a large asymmetry of 0⋅11 after sputtering at high fluence compared with pure copper. These changes are attributed to Cu-Ni interactions at the interface. [ABSTRACT FROM AUTHOR]

[Display omitted] • Facile and scalable chemical synthesis of Au@α-Fe2O3 nanostructure. • Interface modified strategy to self-assemble the as-synthesized Au@Fe2O3 nanostructures on graphene substrate. • Au@α-Fe2O3/graphene exhibited excellent photocatalytic activity under visible-light. • Amphoteric catalytic activity in degradation of cationic as well as anionic dyes. • The Au@α-Fe2O3/graphene catalyst exhibited a highly stability and recyclability. We report a simple interface modified strategy to self-assemble the as-synthesized Au@Fe 2 O 3 nano structures by facile chemical synthesis route on graphene substrate (AFG) fo r substrate mediated photo-catalytic dye degradation. The substrate modification, film formation, photo induced charge transfer mechanism and the physico-chemical properties of the AFG has been systematically analysed using different analytical techniques. The alteration in light absorption capacity and band gap of the hybrid with respect to the individuals have been observed using diffuse reflectance spectroscopy. Moreover, the broad absorption in the visible range and squeeze in band gap of the hybrid from 2.3 to 1.97 eV confirms the ability of the hybrid and the intention of hybridization for visible light-responsive photo-catalysis. Additionally, interesting superparamagnetic behaviour of the hybrid and its magnetic separation ability has been explored. Further, the applicability, repeatability and versatility of this AFG hybrid material in catalytic degradation of different dyes in presence of visible light have been analysed. This AFG catalyst exhibits excellent photocatalytic activity against the decolouration of the both cationic and anionic dyes. A systematic study in the photo-catalytic degradation behaviour, kinetic of degradation and the postulated mechanism has been proposed. [ABSTRACT FROM AUTHOR]

Here, we report the cation vacancy-induced room-temperature ferromagnetism (RTFM), photoluminescence (PL) and electrical properties of different group-IA alkali-metal (Li, Na, K)-doped ZnO thin films fabricated by pulse laser deposition. The experimental evidence indicates that the Zn vacancies are responsible for the visible green luminescence and RTFM in the alkali-doped ZnO films. The alkali-metal ions are found to have a crucial role in the formation and stabilization of the Zn vacancies and also to introduce the p-type conductivity to mediate the long-range ferromagnetic interaction in the films. The Li-doped ZnO films are found to exhibit the most intense green luminescence due to the presence of a large concentration of Zn vacancies and consequently, they exhibited the strongest RTFM with the highest saturation moment (MS) and Curie temperature (TC). The concentration of the Zn vacancy as well as the carrier (hole) density of the alkali-doped ZnO films decrease gradually when the alkali-dopants are varied from Li to Na, then to K, resulting in a decrease in both the MS and TC. This study demonstrates that the alkali elements are promising dopants to stabilize and tune high temperature FM in ZnO which can be an exciting way to prepare a new class of ZnO-based magnetic semiconductors. [ABSTRACT FROM AUTHOR]

An enhanced biocompatibility from nanodot patterned TiO2 surfaces, fabricated by ion beam sputtering, has been observed here through its interaction with plasmid DNA. Investigations of the persistence length and the areal conformation of DNA show that the biocompatibility increases with ion fluence. Presence of nanostructures and increased surface roughness, in conjugation with higher oxygen vacancy sites that promote charge transfer from DNA moiety, are responsible for the increased hydrophilicity and biocompatibility of the patterned surfaces. [ABSTRACT FROM AUTHOR]