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In this present article, we report the organization of the room temperature nematic liquid crystalline (NLC) phase of MBBA [N-(4-methoxybenzylidene)-4-butylaniline] in the presence of gold nanoparticles (AuNPs), which are synthesized in situ within the MBBA matrix without using any separate reducing, stabilizing, or capping unit. The imine nitrogen (C=N) of MBBA is capable of donating its non-bonding electrons and, therefore, we explore the possibility that this could reduce the Au precursor (HAuCl4, 3H2O) to generate AuNPs within the MBBA matrix and form a stable MBBA–AuNP composite. The role duality of MBBA is evident in our synthesis process, acting as an active site to reduce Au precursor to generate AuNPs as well as to provide support to synthesized AuNPs as a soft template so that synthesis and assembly can happen concomitantly. The AuNPs formed in this process comprise mostly faceted spherical particles at higher concentrations of precursor, as evident from TEM and SEM investigations, and the size of the AuNPs was observed to be increasing with precursor concentration. The most important aspect that has emerged from our study is the organization of the NLC phase during AuNP production, which is clearly manifested through the evolution of ordered textures, significant enhancements in the isotropization temperature, associated enthalpies, and perceptible modifications in the optical properties of NLC. All these collective phenomena are indicative of AuNP assisted phase ordering in MBBA. The observed macroscopic phase ordering is well corroborated with our findings from microscopic investigations, which provide deep molecular insight regarding such phenomena. [ABSTRACT FROM AUTHOR]

ZnS quantum dots (QDs) with cubic phase have been prepared by mechanical alloying the stoichiometric mixture of Zn and S powders at room temperature in a planetary ball mill under Ar. Initially, an amorphouslike thin wurtzite (hexagonal) shell is formed on major zinc-blende (cubic) core after 3.5 h of milling and, in the course of milling up to 20 h, strain free single phase (cubic) QDs are formed with ∼4.5 nm in size. These ball-milled QDs contain different kinds of stacking faults and the Rietveld analysis of x-ray powder diffraction data reveals their concentration in milled samples. Though the high resolution transmission electron microscope (HRTEM) images could not detect the presence of the wurtzite phase but confirm the presence of cubic phase, core-shell structure, and different kinds of stacking faults in ball-milled samples. The particle size of QDs and their distributions obtained from Rietveld analysis agree well with the observations of HRTEM images. [ABSTRACT FROM AUTHOR]

Ion-irradiation-induced modifications of a periodic Pt/C multilayer system containing a small amount of Fe have been analyzed by transmission electron microscopy and grazing incidence x-ray diffraction (GIXRD) studies. The multilayer stack with 16 Pt/C layer pairs (period of 4.23 nm) was fabricated on a glass substrate. A 2 MeV Au2+ ion beam was rastered on the sample to obtain uniformly irradiated strips with fluences from 1×1014 to 1×1015 ions/cm2. Ion irradiation has been found to cause preferential migration of Fe towards Pt layers [Bera et al., Nucl. Instrum. Methods Phys. Res. B 212, 530 (2003)]. Cross-sectional transmission electron microscopy (XTEM) shows considerable atomic redistribution for irradiation at the highest ion fluence (1×1015 ions/cm2). This structure is composed of small clusters. Phase separation and cluster formation processes are discussed. Periodic multilayers have periodicity only in the direction normal to the multilayer surface. However, Fourier transform (FT) of the XTEM images of the sample irradiated at the highest fluence shows extra off-normal Fourier components of superlattice periodicities arising due to ion irradiation. These extra spots in the FT are due to preferential length scales in intercluster separation in three dimensions. With a proper understanding of this phenomenon it may be possible to fabricate useful three-dimensional self-assembled structures of nanoclusters. Our high resolution transmission electron microscopy and GIXRD results reveal the formation of an FePt alloy. As FePt is a magnetic alloy, our observation raises the possibility of fabrication of ion-beam induced magnetic nanocluster lattices. [ABSTRACT FROM AUTHOR]

Nanoisland gold films, deposited by vacuum evaporation of gold onto Si(100) substrates, were irradiated with 1.5 MeV Au2+ ions up to a fluence of 5×1014 ions cm-2 and at incidence angles up to 60° with respect to the surface normal. The sputtered particles were collected on carbon-coated grids (catcher grid) during ion irradiation and were analyzed with transmission electron microscopy and Rutherford backscattering spectrometry. The average sputtered particle size and the areal coverage are determined from transmission electron microscopy measurements, whereas the amount of gold on the substrate is found by Rutherford backscattering spectrometry. The size distributions of larger particles (number of atoms/particle, n>=1000) show an inverse power law with an exponent of ∼-1 in broad agreement with a molecular-dynamics simulation of ion impact on cluster targets. [ABSTRACT FROM AUTHOR]

We report on swift heavy-ion-beam-induced epitaxial crystallization of a buried Si3N4 layer. We observe good epitaxial crystallization at 200 °C, which is a much lower temperature than that required for the conventional solid phase epitaxial growth. High-resolution transmission electron microscopy and selected area diffraction patterns have been used to study the 100-MeV Ag8+-ion-beam-induced epitaxial growth of the Si3N4 layer. A possible mechanism of recrystallization is discussed on the basis of synergetic effects of electronic and nuclear energy-loss processes along the trajectory of the swift heavy ions at elevated temperatures. [ABSTRACT FROM AUTHOR]

We report on room-temperature synthesis of nanodimensional Au-Ge alloy on Si surface by ion-beam mixing of nanoislands of Au and Ge. Synthesis of such surface nanoalloys could be the basis of making nanodimensional contacts towards miniaturization of microelectronic devices. The nanoislands of Au and Ge were grown by UHV electron beam evaporation technique on Si (100) surface and were irradiated by 1.5 MeV Au2+ ions over a fluence range of 5×1012–1×1015 ions cm-2. High-resolution transmission electron microscopy has been employed to study the formation of Au-Ge alloy in the form of nanoislands. Formation of such surface alloy nanoislands has been discussed in the light of ion-matter interaction in nanometer scale regime. [ABSTRACT FROM AUTHOR]

We report on interface modification in Co/Ge bilayer system using 100 MeV Au7+ ion irradiation at different temperatures and fluences. Irradiation induced changes occurring across the Co/Ge interface are studied by Rutherford backscattering spectrometry and cross-sectional transmission electron microscopy. Although Au irradiation at low temperature does not show any interface mixing, formation of a thin (∼3–4 nm) Co–Ge alloy layer has been observed after room temperature irradiation to a fluence of 1×1014 ions cm-2. This mixing has been discussed on the basis of synergetic effects of nuclear and electronic energy loss processes in the bilayer system. [ABSTRACT FROM AUTHOR]

Megaelectron volts ion-induced effects for discontinuous gold nanoislands and for continuous gold films on silicon substrate have been studied. Irradiation was carried out with 1.5 MeV Au2+ ions at room temperature to various fluences. Cross-sectional transmission electron microscopy and Rutherford backscattering spectrometry are used to study the ion-beam mixing in Au/Si systems. At a fluence of 1×1014 ions cm-2, a material push-in effect and a metastable Au-Si phase formation have been observed for Au nanoislands, while no push in or mixing has been observed for the case of continuous films. The mixed phase of Au-Si system is found to be crystalline in nature. The material push- in and ion-beam mixing effects that are observed in case of nanoislands appear to be due to combined effect of capillary driving force, ion-induced viscous flow, and ion-induced energy spike effects. [ABSTRACT FROM AUTHOR]

Copper oxide nanoparticles of median diameter 17 nm were synthesized by a chemical method. By subjecting these to a reduction treatment at 373 K for a duration extending to 1 h copper shells of thicknesses in the range 2–6.5 nm were grown. Optical absorption measurements were carried out on these core-shell structured nanosystems in the temperature range 274–343 K. Analyses of the data show that below a shell thickness of 3 nm the copper shell conductivity has a value below the Mott’s minimum metallic conductivity and shows a semiconducting behavior. Electrical conductivity measurements on pellets of the nanostructured powders show a resistivity variation at low temperatures with activation energies in satisfactory agreement with those obtained from the optical studies. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

One-dimensional arrays of nanoparticles of silver and copper, respectively, have been grown within a silicate glass by an electrodeposition process. Silver-silica nanocomposites were prepared using a melt quenched glass whereas sol-gel derived glass was used for the synthesis of copper-silica nanocomposites. The metal particle diameters had values ranging from 1.5 to 20 nm. The composite structures exhibited a diodelike current-voltage characteristic in the temperature range 300 to 160 K for silver containing nanocomposites and at around 280 K for copper containing nanocomposites. The diode action is believed to be caused by the presence of metal-semiconductor nanojunctions in these glass—the typical number of such junctions being 60. The rather narrow range of temperature for diode action as observed in copper-silica nanocomposites is ascribed to the easy breakup of the metal nanoarrays because of the sol-gel derived medium of silica glass in which the metal phase was grown. The metal particles of diameter ∼2 nm constituted the semiconducting phase in these nanojunctions. [ABSTRACT FROM AUTHOR]

Abstract We have investigated the evolution of magnetic behavior with ion fluence in ion irradiation of a Si/Ni/Si sandwich system. An oscillatory behavior of the saturation magnetic moment and the coercive field has been observed with increasing ion fluence. As reported earlier, with increasing ion fluence, this system also shows an oscillatory amorphization and recrystallization of the Si substrate on which the Ni layer was grown. Ion beam induced Ni redistribution, associated with the oscillatory behavior of amorphization and recrystallization of Si, appears to be responsible for the oscillatory magnetic behavior in the sandwich structure. Highlights • Evolution of the magnetic behavior with fluence of ion irradiation is studied on a Si/Ni/Si sandwich system. • A novel oscillatory behavior of saturation magnetic moment and coercive field with ion fluence has been observed. • The oscillatory magnetic behavior arises from the ion-fluence-dependent redistridution of Ni in the Si/Ni/Si sandwich system. [ABSTRACT FROM AUTHOR]

Ion-beam-induced amorphization and recrystallization are well-known phenomena. At a constant ion flux, there is a substrate temperature T R such that, for T < T R the irradiation produces amorphization, whereas for T > T R , it produces recrystallization. However, both the processes do not happen at a given substrate temperature. Here we present a novel phenomenon of ion fluence dependent oscillatory amorphization and recrystallization in silicon at room temperature in a Si(5 nm)/Ni(15 nm)/Si system. Before the deposition of Ni on Si, a buffer Si layer was deposited on the Si substrate. Ion irradiation was carried out with 1 MeV Si + ions in the fluence range 1 × 10 14 –3 × 10 17 ions/cm 2 . At a fluence of 5 × 10 16 ions/cm 2 , Si is amorphous up to a depth of ∼1.4 μm. However, at a fluence of 1 × 10 17 ions/cm 2 two narrow bands of recrystallized (rc) Si are formed within the amorphized Si. At 2 × 10 17 ions/cm 2 these rc-Si bands become amorphous again. At 3 × 10 17 ions/cm 2 the broader rc band reappears. This oscillatory amorphization/recrystallization behaviour is Ni-mediated. Energy dispersive X-ray map of Ni shows Ni accumulation at the top of the rc-Si bands. The top of the broader rc band is actually the buffer-Si/substrate-Si interface. TRIM simulation shows the appearance of a Ni-displacement-induced vacancy peak at the position of the narrow rc-Si band. Accumulation of Ni in these regions is associated with the recrystallization process. The Ni layer, with incorporation of Si, also passes through amorphization and recrystallization. At the highest fluence η-NiSi nanocrystals are formed in the Ni layer. [ABSTRACT FROM AUTHOR]

Nanocrystalline carbonated HAp powder has been synthesized successfully within 2 h by mechanical alloying the stoichiometric mixture of CaCO 3 , CaHPO 4 ·2H 2 O at room temperature under open air. To observe the sintering behavior of HAp the as-milled sample is sintered at different temperatures. The amorphous HAp phase (~14 vol%) in as-synthesized sample transforms completely to crystalline HAp after sintering at 700 °C and after sintering the sample at 800 °C, the crystalline HAp partially transforms to β-TCP phase. Presence of low content of β-TCP phase in HAp powder could be useful in artificial hard tissue applications. Increase in sintering temperature up to 1000 °C results in enhancement of decomposition rate of HAp into β-TCP phase. Microstructure characterization in terms of lattice imperfections and relative phase abundances in non-sintered and all sintered samples are made both by analyzing the respective XRD patterns using Rietveld's structure refinement method as well as TEM images. The growth mechanism of β-TCP from crystalline HAp phase has been proposed based on structure and microstructure characterizations of sintered samples. [ABSTRACT FROM AUTHOR]

Cadmium sulphide (CdS) thin film was prepared by successive ion layer adsorption and reaction (SILAR) technique using ammonium sulphide as anionic precursor. Characterization techniques of XRD, SEM, TEM, FTIR and EDX were utilized to study the microstructure of the films. Structural characterization by x-ray diffraction reveals the polycrystalline nature of the films. Cubic structure is revealed from X-ray diffraction and selected area diffraction (SAD) patterns. The particle size estimated using X-ray line broadening method is approximately 7 nm. Instrumental broadening was taken into account while particle size estimation. TEM shows CdS nanoparticles in the range 5–15 nm. Elemental mapping using EFTEM reveals good stoichiometric composition of CdS. Characteristic stretching vibration mode of CdS was observed in the absorption band of FTIR spectrum. Optical absorption study exhibits a distinct blue shift in band gap energy value of about 2.56 eV which confirms the size quantization. [ABSTRACT FROM AUTHOR]

Single phase nanocrystalline hydroxyapatite (HAp) powder has been synthesized by mechanical alloying the stoichiometric mixture of CaCO3 and CaHPO4 powders in open air at room temperature, for the first time, within 2h of milling. Nanocrystalline hexagonal single crystals are obtained by sintering of 2h milled sample at 500°C. Structural and microstructural properties of as-milled and sintered powders are revealed from both the X-ray line profile analysis and transmission electron microscopy. Shape and lattice strain of nanocrystalline HAp particles are found to be anisotropic in nature. Particle size of HAp powder remains almost invariant up to 10h of milling and there is no significant growth of nanocrystalline HAp particles after sintering at 500°C for 3h. Changes in lattice volume and some primary bond lengths of as-milled and sintered are critically measured, which indicate that lattice imperfections introduced into the HAp lattice during ball milling have been reduced partially after sintering the powder at elevated temperatures. We could achieve ~96.7% of theoretical density of HAp within 3h by sintering the pellet of nanocrystalline powder at a lower temperature of 1000°C. Vickers microhardness (VHN) of the uni-axially pressed (6.86MPa) pellet of nanocrystalline HAp is 4.5GPa at 100gm load which is close to the VHN of bulk HAp sintered at higher temperature. The strain-hardening index (n) of the sintered pellet is found to be >2, indicating a further increase in microhardness value at higher load. [ABSTRACT FROM AUTHOR]

Abstract: The nanostructured (Ti0.9Si0.1)N powder has been mechanosynthesized by ball-milling the elemental stoichiometric mixture of α-Ti(0.9mol fraction) and Si (0.1mol fraction) powders at room temperature under nitrogen atmosphere. After 1h of milling, the α-Ti (hcp) phase partially transformed to metastable β-Ti (cubic) phase and the initiation of (Ti0.9Si0.1)N (fcc) phase is noticed. Completely stoichiometric nanocrystalline (Ti0.9Si0.1)N phase is obtained after 7h of milling. Microstructure of unmilled and ball-milled powders is characterized by analyzing their XRD patterns employing the Rietveld structure refinement method and by HRTEM images. The analysis reveals the inclusion of Si and nitrogen atoms into the Ti lattice on the way to formation of (Ti0.9Si0.1)N phase. Presence of Si and nitrogen in the ball milled powders is also confirmed from EDX spectra. The average size of almost monodispersed spherical particles of (Ti0.9Si0.1)N is ~4nm. Optical band gaps of TiN and TiSiN powders are measured from UV–vis absorption spectra and it has been found that the optical band gap of highly insulating TiN nanoparticles (band gap ~5.56eV) can be substantially reduced towards semiconductors (band gap ~3.96eV) by incorporating a small amount of Si into TiN matrix. [Copyright &y& Elsevier]

Preliminary results of growth of thin diamond film in a recently installed 3 kW capacity microwave plasma activated CVD (MW-PACVD) system are being reported. The films were deposited on Si (100) substrate at 850°C using methane and hydrogen mixture at 1·5 kW MW power. The grown polycrystalline films were characterized by micro-Raman, transmission electron microscope (TEM), spectrophotometer and atomic force microscope (AFM). The results were compared with that of a thicker diamond film grown elsewhere in a same make MW-PACVD system at relatively higher power densities. The presence of a sharp Raman peak at 1332 cm confirmed the growth of diamond, and transmission spectra showed typical diamond film characteristics in both the samples. Typical twin bands and also a quintuplet twinned crystal were observed in TEM, further it was found that the twinned region in thin sample composed of very fine platelet like structure. [ABSTRACT FROM AUTHOR]

Here we report the role of ion irradiation in the field emission characteristics of aligned multiwalled carbon nanotubes (MWNTs). Aligned MWNTs show improvement in field emission characteristics under low dose 70 Mev Ni6+ ion irradiation. But field emission current density reduces for the higher dose due to adsorption of amorphous carbon and melting as well damage of carbon nanotubes (CNTs). High resolution transmission electron microscopic (HRTEM) analysis has been carried out to find the morphological changes due to ion irradiation leading to modifications in field emission characteristics. At low dose formation of dangling bond, cross-linking between different layers, exposure of buried emission sites and reduction of mutual shielding are responsible for the enhancement in field emission characteristics. [ABSTRACT FROM AUTHOR]

Abstract: Thermal stability of thin Pt/Cr/Co multilayers and the subsequent changes in their structural, magnetic, and magneto-optical properties are reported. We observe CoCrPt ternary alloy phase formation due to annealing at temperatures about 773K, which is accompanied by enhancement in the coercivity value. In addition, 360° domain wall superimposed on a monodomain like background has been observed in the pristine multilayer, which changes into a multidomain upon annealing at 873K. [ABSTRACT FROM AUTHOR]

Abstract: We report on the structural characterization of short period type-II InAs/GaSb superlattices (SLs) adapted for mid-infrared detection. These structures, grown by molecular beam epitaxy (MBE) on n-type GaSb substrates, are made up of 10 InAs monolayers (MLs) and 10 GaSb MLs and a strain balanced condition is obtained by inserting an InSb ML at the interface between InAs and GaSb in each superlattice''s period. From cross-sectional transmission electron microscopy (TEM) measurements, the interface structure is analysed in detail. Very homogeneous and smooth InAs and GaSb layers all over a 50 periods SL structure are observed and high-resolution images bring out the InSb ML inserted between InAs and GaSb. Room temperature absorbance spectroscopy measurements have been performed on strain-compensated SLs including 50, 100, 300 and 400 periods, for a total absorption zone thickness of 0.32, 0.64, 1.92 and 2.56μm, respectively. The spectra display reproducible and well-defined features with an absorption coefficient varying between 2×103 and 4×103 cm−1 in the 3–5μm mid-infrared domain, a sign of high-quality samples suitable for detection. [Copyright &y& Elsevier]

Polycrystalline fullerene (C60) films prepared on hydrogen-passivated Si(1 1 1) substrates were irradiated by 2 MeV protons with fluences ranging from 6×1015 to 1×1017 ions/cm2. Ferromagnetic-like ordering is reported for samples irradiated with a fluence of 6×1015 ions/cm2 [S. Mathew et al., arxive:cond-mat/0503315]. Raman spectroscopy results indicate an enhancement of the characteristic Ag and Hg modes of C60 after irradiation, especially for the fluence 6×1015 ions/cm2. High-resolution transmission electron microscopy and transmission electron diffraction results show the crystalline nature of both as-deposited and irradiated films in the fcc structure. Stability of the fullerite structure under the above irradiation condition is discussed. [ABSTRACT FROM AUTHOR]

Abstract: Single crystalline Si(100) substrates were irradiated with 1.0MeV N+ ions at elevated temperature to synthesize silicon on insulator materials and to understand the nature of the amorphous region and the defect layer. The RBS-channeling spectra show a sharp amorphous–crystalline interface at a depth of ∼500nm, around half of the mean projected range (R p). Beyond the R p a heavily damaged layer has been observed. Micro-Raman spectra show the development of a large amount of stress in the damage free crystalline region. The variation of peak position and FWHM indicates that the surface crystalline quality improves as the implantation temperature increases up to 450°C. The microstructures underneath the surface and interface regions are studied by cross-sectional TEM. We proposed that the ratio of the concentration of vacancies (N v) and number of nitrogen atoms (N N) coming to rest beyond R p plays a major role in the formation of damage free near surface region during high temperature implantation. [Copyright &y& Elsevier]

Abstract: This paper reports on swift heavy ion beam induced epitaxial crystallization of a buried Si3N4 layer. Transmission electron microscopy and selected area diffraction patterns are used to study the epitaxial growth of the buried Si3N4 layer. We observe good epitaxial crystallization at 150°C and 200°C, respectively, for 70MeV Si and 100MeV Ag ions at an ion fluence of 1×1014 ionscm−2. The fact that recrystallization is achieved at a lower temperature for Si ions is attributed to the higher ratio (one order of magnitude) of the electronic to nuclear energy loss values compared to that of Ag ions. The possible role of the electronic and nuclear energy loss processes in the mechanism of recrystallization has also been discussed. [Copyright &y& Elsevier]

Abstract: Au nanoparticles, prepared by thermal evaporation under high vacuum condition on Si substrate, are irradiated with Au ions at different ion energies. During ion irradiation, embedding of nanoparticles as well as ejection of nanoclusters is observed. Ejected particles due to sputtering are collected on carbon-coated grids. Both the grids and the ion-irradiated samples are analyzed with transmission electron microscopy (TEM) and Rutherford backscattering spectrometry (RBS). Size distribution of the sputtered Au clusters on the TEM grids for different ion energy regimes are presented. In the case of low energy (32keV) ions, where the nuclear energy loss is dominant, sputtering is less as compared to medium energy (1.5MeV). In the high-energy regime (100MeV), where the electronic energy loss is dominant, sputtering is found to be maximum. [Copyright &y& Elsevier]

Abstract: We report on swift heavy ion beam induced epitaxial crystallization of a buried Si3N4 layer. High-resolution transmission electron microscopy and selected area diffraction patterns are used to study the 70MeV Si5+ ion beam induced epitaxial growth of the Si3N4 layer. We observe good epitaxial crystallization at 150°C, which is a much lower temperature as compared to the conventional solid phase epitaxial growth. A possible mechanism of recrystallization is discussed on the basis of formation of vacancies along the track of the swift heavy ion and their migration at elevated temperatures during irradiation. [Copyright &y& Elsevier]

Abstract: Based on the potential need of making nano-dimensional contact materials for successful miniaturization of nanoscale devices, we have attempted to synthesize nano-dimensional alloys on the surface of a material. This method has been termed as nanomixing. In this paper, we report on formation of nano-dimensional Au–Ge alloy islands by ion beam mixing of island thin films of Au and Ge. The nanoislands of Au and Ge were grown by UHV electron beam evaporation technique on Si(100) surface covered with a thin native oxide layer and were irradiated later on by different energetic ions (viz. 1.5MeV Au, 800keV Ar and 800keV Xe) at room temperature over a fluence range of 1×1014–2×1016 ionscm−2. We have carried out high-resolution transmission electron microscopic study to confirm the formation of Au–Ge alloy in the form of nanoislands. [Copyright &y& Elsevier]

Abstract: Strain at surfaces and interfaces play an important role in the optical and electronic properties of materials. MeV ion-induced strain determination in single crystal silicon substrates and in Ag (nanoisland)/Si(111) at surface/interfaces has been carried out using transmission electron microscopy (TEM) and surface-sensitive X-ray diffraction. Irradiation has been carried out with 1.5MeV Au2+ ions at various fluences and impact angles. Selected area electron diffraction (SAED) and lattice imaging (using TEM) has been used to determine the strain at surface and interfaces. Preliminary results on the use of surface-sensitive asymmetric X-ray Bragg reflection method have been discussed. The TEM results directly indicate a contraction in the silicon lattice due to ion-induced effects. The nanoislands have shadowed the ion beam resulting in lesser strain beneath the island structures in silicon substrates. High-resolution lattice imaging has also been used to determine the strain in and around amorphization zones caused by the ion irradiation. [Copyright &y& Elsevier]

Abstract: Tailoring of nanostructures with energetic ion beams has become an active area of research leading to the fundamental understanding of ion–solid interactions at nanoscale regime and with possible applications in the near future. Rutherford backscattering spectrometry (RBS), high resolution transmission electron microscopy (HRTEM) and asymmetric X-ray Bragg-rocking curve experimental methods have been used to characterize ion-induced effects in nanostructures. The possibility of surface and sub-surface/interface alloying at nano-scale regime, ion-beam induced embedding, crater formation, sputtering yield variations for systems with isolated nanoislands, semi-continuous and continuous films of noble metals (Au, Ag) deposited on single crystalline silicon will be reviewed. MeV-ion induced changes in specified Au-nanoislands on silicon substrate are tracked as a function of ion fluence using ex situ TEM. Strain induced in the bulk silicon substrate surface due to 1.5MeV Au2+ and C2+ ion beam irradiation is determined by using HRTEM and asymmetric Bragg X-ray rocking curve methods. Preliminary results on 1.5MeV Au2+ ion-induced effects in nanoislands of Co deposited on silicon substrate will be discussed. [Copyright &y& Elsevier]

Abstract: We have deposited Ag on hydrogen passivated Si(1 0 0) surfaces under high vacuum conditions at room temperature. The deposition, followed by annealing at 250 C for 30 min, produced silver islands of an average lateral size  nm. Depositing a small amount of Pb prior to Ag deposition reduced the average island size to  nm. A small amount of Pb, initially present at the Ag–Si interface, is found to be segregating to the surface of Ag after annealing. Both these aspects, namely, reduction of the island size and Pb floating on the Ag surface conform to the surfactant action of Pb. Samples have been characterized by transmission electron microscopy (TEM) and Rutherford backscattering spectroscopy (RBS). A selective etching process that preferentially removes Pb, in conjunction with RBS, was used to detect surface segregation of Pb involving depth scales below the resolution of conventional RBS. The annealing and etching process leaves only smaller Ag islands on the surface with complete removal of Pb. Ag growth in the presence of Pb leads to smaller Ag islands with a narrower size distribution. [Copyright &y& Elsevier]

MeV ion induced mixing in the nanoscale regime for Au and Ag nanoislands on silicon substrates has been studied. Au and Ag nanoislands are grown on silicon substrates at room temperature and irradiated with 1.5-MeV Au2+ ions at various fluences. Cross-sectional high-resolution transmission electron microscopy and Rutherford backscattering spectrometry (RBS) are used to study the ion-beam mixing in Au/SiOx/Si and Ag/SiOx/Si systems. We observe a metastable mixed phase for the Au–Si system at a fluence of 1×1014 ions cm-2, while no mixed phase is formed for the Ag–Si system. For both Au–Si and Ag–Si systems, a part of the islands is pushed into the substrate. The mixed phase of the Au–Si system is found to be crystalline in nature. The higher eutectic temperature and lower heat of mixing of the Ag–Si system compared to the Au–Si system could be responsible for the lack of mixing and silicide formation in the Ag–Si system. [ABSTRACT FROM AUTHOR]

Very thin films of gold deposited on silicon substrates form isolated nano-island structures due to the non-wetting nature of gold. Thick films are more homogeneous and do not have the isolated island structures. Thin gold films of various thicknesses (≈0.4–21.4 nm) are deposited under high vacuum condition and irradiated with 1.5 MeV Au2+ ions. The sputtered particles are collected on catcher grids (carbon coated) during the irradiation and are analyzed with transmission electron microscopy (TEM) and Rutherford backscattering spectrometry (RBS). The average sputtered particle size is determined from TEM measurements, whereas the amount of gold on the catcher grid is found by RBS. The average sputtered particle size from thin (up to a thickness of ≈2 nm) discontinuous films is larger compared to the average particle size from thick continuous films. The coverage of the sputtered particles on the catcher grids is also discussed. Energy spike and its distribution in the nano-islands is proposed to be the main reason for the variation in the particle size and the coverage of the sputtered particles on the catcher grid. [Copyright &y& Elsevier]

Formation of Au0.6Ge0.4 alloy on Si (1 0 0) substrate has been observed upon irradiating Au/Ge bilayer with 120 MeV Au ions and subsequent vacuum annealing at 360 °C. Transmission electron microscopy measurements on irradiated and vacuum annealed Au/Ge samples show a possibility of formation of oriented Au0.6Ge0.4 alloy, in agreement with X-ray diffraction data. These measurements reveal that although 120 MeV Au irradiation alone can not lead to a large scale mixing, it acts as a seed by forming nanoislands of Au0.6Ge0.4 alloy. Further post-irradiation annealing leads to vigorous intermixing of Au and Ge followed by the formation of large, closely packed and oriented Au0.6Ge0.4 islands. These results have been discussed on the basis of irradiation induced effects followed by subsequent thermal annealing. [Copyright &y& Elsevier]

This paper reports on the formation of Ni2Ge alloy through interface modification of Ni/Ge bilayer structure using 100 MeV Au-ion irradiation at different temperatures and fluences. Compositional analysis and calculation of mixing efficiency were performed by Rutherford backscattering spectrometry. High resolution cross-sectional transmission electron microscopy was carried out for thickness determination and structure determination. Alloy formation has been discussed on the basis of swift heavy ion irradiation induced effects. [Copyright &y& Elsevier]

Transmission electron microscopy (TEM), atomic force microscopy (AFM) and Rutherford backscattering spectrometry (RBS) have been used to study the modification of Au nanoislands, grown on silicon substrates under high vacuum condition by MeV self-ion irradiation. Upon irradiation with 1.5 MeV Au2+ ions, interesting observations were found for the nanoislands in comparison with continuous films: (i) higher probability of crater formation, (ii) larger sputtered particle size as well as coverage and (iii) enhanced sputtering yield. Crater formation has been studied as a function of impact angle at a fluence of 1 × 1014 ions cm−2 and we found that crater formation is prominent at high impact angles (i.e. at glancing angle geometry). AFM has been used to determine the crater formation, TEM to study the sputtered particles as well as craters and RBS has been used to determine the sputtering yield from the nanoisland and continuous films. [Copyright &y& Elsevier]

The amorphization due to MeV Au2+ ion implantation in Si(1 1 1) has been studied using Rutherford backscattering spectrometry/channeling (RBS/C) and transmission electron microscopy (TEM) methods. 1.5 MeV Au2+ ions were implanted into Si(1 1 1) substrates at various fluences at low currents (0.02–0.04 μA cm−2) while the samples were kept at room temperature. The RBS/C results for as-implanted specimen shows the onset fluence for amorphization to be &ap;5×1013 ions cm−2 which is much lower than the fluence reported earlier. Selected area diffraction (TEM) for a sample implanted at a of 1×1014 ions cm−2 confirms the occurrence of the amorphization. Earlier, amorphization studies by Alford and Theodore, using 2.4 MeV gold ions in silicon (1 0 0) reported a threshold fluence of 1.8×1015 ions cm−2 for amorphization when the implantation was carried out at higher currents (0.2–5 μA cm−2) [J. Appl. Phys. 76 (1994) 7265]. The nuclear energy loss (Sn) for 1.5 MeV gold ions in silicon is &ap;13% greater than the value for 2.4 MeV and cannot be the sole reason for lower threshold fluence for the amorphization. The amorphization at a relatively lower fluence for the low current implantations could be possible due to reduction in the dynamical annealing effects. [Copyright &y& Elsevier]

The unique properties of the noncommon-atom InAs/GaSb short-period-superlattices (SPSL) strongly depend on the interface structure. These interfaces are characterized using transmission electron microscopy (TEM). The compositional sharpness is obtained from the comparison of the experimental contrast in g002 two-beam dark-field TEM images with simulated intensity profiles, which are calculated assuming that the element distribution profiles are described by sigmoidal functions. The interfacial intermixing, defined by the chemical width, is obtained for SPSL with different periods and layer thicknesses, even in the extreme case of nominally less than 3 ML thick InAs layers. Nominal 1 ML InSb layers intentionally inserted are also identified. [ABSTRACT FROM AUTHOR]

Room temperature irradiation of InSb(111) by 60 keV Ar+-ions at normal (0°) and oblique (60°) angles of incidence led to the formation of nanoporous structure in the high fluence regime of 1 x 1017 to 3 x 1018 ions cm-2 . While a porous layer comprising of a network of interconnected nanofibers was generated by normal ion incidence, evolution of plate-like structures was observed for obliquely incident ions. Systematic studies of composition and structure using energy dispersive x-ray spectroscopy, Raman spectroscopy, x-ray photoelectron spectroscopy, Raman mapping, grazing incidence x-ray diffraction, and cross-sectional transmission electron microscopy revealed a high degree of oxidation of the ion-induced microstructures with the presence of In2O3 and Sb2O3 phases and presence of nanocrystallites within the nanoporous structures. The observed structural evolution was understood in terms of processes driven by ion-induced defect accumulation within InSb. [ABSTRACT FROM AUTHOR]

Room temperature implantation of 60 keV Ar+-ions in GaSb to the fluences of 7×1016 to 3×1018 ions cm-2 is carried out at two incidence angles, viz 0° and 60°, leading to formation of a nanoporous layer. As the ion fluence increases, patches grow on the porous layer under normal ion implantation, whereas the porous layer gradually becomes embedded under a rough top surface for oblique incidence of ions. Grazing incidence x-ray diffraction and cross-sectional transmission electron microscopy studies reveal the existence of nanocrystallites embedded in the ion-beam amorphized GaSb matrix up to the highest fluence used in our experiment. Oxidation of the nanoporous layers becomes obvious from x-ray photoelectron spectroscopy and Raman mapping. The correlation of ion-beam induced structural modification with photoluminescence signals in the infrared region has further been studied, showing defect induced emission of additional peaks near the band edge of GaSb. [ABSTRACT FROM AUTHOR]

The layered nanosheets exhibit a variety of physical and optical properties originating from amalgamation of intra- and inter- layer electronic interactions, which makes them promising materials for advanced devices with varsatile controlling channels. In particular, the dilute magnetic semiconductor multilayered nanosheets have promising optical, electrical and magnetic properties that have been less explored so far. Here, the spin permissible optical properties from solvothermally grown Mn doped CdSe (thickness ~2.26 nm) multilayered nanosheets are reported on. The presence of multi-phase magnetic orderings with a sharp ferromagnetic transition at temperature ~48 K pertinent to the stabilization and co-existence of Mn2+ and Mn3+ based local phases have been observed from the (Cd,Mn)Se layered nanosheets corroborating to the x-ray absorption near edge structure, electron paramagnetic resonance, Raman scattering and magnetic measurements. The optical absorption and photoluminescence (PL) studies at room temperature affirm wide array of optical properties in the visible regime corresponding to the band edge and intriguing dopant-phase mediated spin approved transitions. The circularly polarized magneto-PL and life time analysis exhibits the spin-polarized fast radiative transitions confirming the presence of spin-active electronic states. [ABSTRACT FROM AUTHOR]

Abstract This paper reports the tunability of magnetic domains and its correlation with depth-resolved microstructure in 100 nm thick Gd-Fe films after rapid thermal processing. The as-deposited films are amorphous in nature and display elongated periodic stripe domains, signifying the development of perpendicular magnetic anisotropy. Rapid thermal processing at 550 o C for different time intervals viz. 5, 10, 15 and 20 min induces the crystallization of Fe over the amorphous Gd-Fe matrix and the presence of wider reaction zone has been evidenced at the film-substrate interface. While the magnetization measurements reveal a spin re-orientation along the plane of the film surface, the stripe domains are no longer observed for the processed films. 3D micromagnetic simulations have been performed to complement the experimental findings. The consideration of in-plane tilt of anisotropy axis along with anisotropy reduction successfully demonstrate the experimentally observed changes in magnetic properties and domain structure. Graphical abstract Image 1 Highlights • Ferrimagnetic Gd-Fe amorphous thin films display nano-scale periodic stripe domains. • RTP for different time intervals results in the nucleation of iron on the surface. • RTP results in a spin re-orientation from perpendicular to the plane of the film. • Anisotropy modification and its in-plane tilt explains the observed results. [ABSTRACT FROM AUTHOR]

Applying Le Chatelier's principle, a one-pot synthesis method is reported that generates highly anisotropic hedgehog gold nanoparticles (HHogGNPs), undemanding of a preformed seed or surfactant. These non-toxic HHogGNPs are potent candidates for nanomedicinal applications owing to their broad-band plasmon tunability, gigantic Raman enhancement and remarkable retention in a highly salted physiological environment. [ABSTRACT FROM AUTHOR]

Abstract: In the present investigation, high-energy milling was carried out to synthesize ultrafine Al–Cu alloy powder from elemental Al and Cu powder. Elemental Al and Cu powders were milled in a high-energy planetary mill at a speed of 300rpm and at 10:1 ball to powder weight ratio. Milling was carried out for 50h in wet condition to prevent undue oxidation and agglomeration. Powder particles were characterized by X-ray diffraction (XRD), particle size analyzer, scanning electron microscope (SEM), and transmission electron microscope (TEM). It is found from XRD that nanostructured Al–Cu alloy prepared by high-energy milling resulted in a grain size of around 6.0nm and lattice strain of about 1.43%. It is also found that the average particle size is around 4.0μm after 50h of milling. TEM shows that particles are irregular in shape and their size is around 200–300nm. To study the dispersion stability, alloy powders were dispersed in de-ionized water and then zeta potential were measured at different pHs. The zeta potential value of the Al–Cu dispersion increases numerically from 49.00 (pH 4.96) to −90.60 (pH 9.50) when oleic acid is added. It is evident from different zeta potential values that stability is improved by the addition of oleic acid into the dispersion. [ABSTRACT FROM AUTHOR]

Germanium exhibits a remarkable effect when subjected to high energy heavy ions irradiation. A synergic effect of high electronic energy loss (Se=16.4 keV nm–1) and nuclear energy loss (Sn=0.1 keV nm–1) of 100MeV Ag ions irradiation in Ge is presented. The results show that crystalline Ge is insensitive to the ionizing part of energy loss whereas thermal spike generated in the damaged Ge leads to the formation of porous structure. Further, an unusual high sputtering of the porous structure opens up the sub-surface voids to show the surface pattern. We explore the role of electron and phonon confinement to explain this effect. [ABSTRACT FROM AUTHOR]

Open volume formation, their growth and shape evolution in Ge by two step ion beam processing are meticulously analyzed and presented in this paper. In the first step, a continuous damaged Ge (d-Ge) layer of ∼1.2 μm thickness is prepared by multiple energy Ar ion implantations in single crystalline Ge (c-Ge) with damage formation of ∼7 DPA. Doppler broadening spectroscopy (DBS) which is highly sensitive to vacancy type defects indicates the formation of 5% open volume in d-Ge layer as compared to c-Ge. The high resolution transmission electron microscopic (HRTEM) studies show that the d-Ge layer consists of nano-crystallites of size ∼1–2 nm. In the second step, d-Ge layer is further irradiated using 100 MeV Ag ions at room temperature. After this irradiation, a substantial volume expansion is detected with the help of a stylus profiler. The volume expansion is observed to be due to the formation of open volume which is restricted to d-Ge only as characterized by DBS at low irradiation fluences and by cross-section scanning electron microscopy (XSEM) and HRTEM at higher irradiation fluences. Microscopic analysis shows that the voids grow in size and change in shape from spherical to prolate spheroid with increasing ion fluence while void density ∼2 × 10 12 cm −3 remains almost invariant of ion fluence. The major axis of prolate spheroid is observed to be aligned approximately along the direction of strain which is confirmed by irradiation at two different angles (0° and 45°). Relative swelling and aspect ratio increase with fluence and tend to saturate at higher fluences. These results are explained on the basis of thermal spike model which indicates that temperature within ion track reaches above melting point of Ge only in disordered phase. The voids are restricted to only d-Ge as formation of voids along ion track is due to melting and re-solidification. The shape change of voids and alignment in strain direction is a consequence of ‘ion hammering’ effect. [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]

In this work we report the fabrication of both pristine Mn2O3 and Mn2O3–Au composite thin films on an indium tin oxide (ITO) substrate by a one-step novel co-electrodeposition technique. From the electron microscopy study, we observed that these two films are morphologically different. The main aim of this study is to understand the effect of the nanostructure and metal integration on the electrochemical charge storage properties of these two films. Since a charge storage mechanism is possible through faradic red-ox reaction and non-faradic double layered process, electrochemical characterization and frequency response analysis indicate better charge storage properties of the composite system over pristine Mn2O3. The Mott–Schottky analysis is used for the charge carrier estimation which provides the electronic properties of both the samples. Besides the mechanism of the co-electrodeposition technique, we also discuss in detail the material characterization of both pristine Mn2O3 and Mn2O3–Au composite samples using XRD, EELS and electron microscopy analysis. To the best of our knowledge, the electrochemical properties of the Mn2O3–Au composite sample are reported here for the first time. [ABSTRACT FROM AUTHOR]

We have achieved giant enhancement of magnetoresistance (MR) by the formation of La0.67Sr0.33MnO3 (LSMO)-Pr0.67Ca0.33MnO3 (PCMO) core-shell nanostructure. Astonishingly, 1143% enhancement of MR in the core-shell nanostructure has been observed with respect to the parent PCMO nanoparticles at 100 K and 2 T magnetic field. The observed giant enhancement is the result of significantly weaken the charge ordered state in the created ferromagnetic-charge ordered core-shell nano structure. Our study clearly indicates a method to achieve huge enhancement of magnetoresistance that can eventually give rise artificially created superior materials important for magnetic field sensor technology. [ABSTRACT FROM AUTHOR]