Influence of secondary ion bombardment on the composition, structure and surface properties of platinum thin films

Platinum (Pt) thin films were deposited by dual ion beam sputtering (DIBS) techniques on oxidized silicon substrates maintained at ambient temperature. Argon ions with energy of 1 keV and beam current of 15 mA were used to sputter the platinum target. The films during deposition were continuously bombarded by argon from a secondary argon ion source with ion energy of 150 eV and ion current density in the range 100–250 $\mu A/cm^2.$ The influence of the secondary ion beam parameters on the grain size, composition and surface morphology of the films were studied. X-ray diffraction (XRD) of all the films showed (1 1 1) orientation with other reflections being absent which is a stable structure for FCC crystals. The grain size of the Pt films prepared by DIBS at ambient temperature were found to be higher than those prepared at higher substrate temperature by low energy plasma sputtering. The presence of Ar impurities in the sputter deposited thin films is known to modify their properties. In this paper we report a method to control the Ar content in the films by secondary Ar ion bombardment of the growing films. The modification of the surface features by secondary ion beam current was studied by scanning tunneling microscope and is also presented in this paper. The surface analysis indicates a decrease in the surface roughness for the Pt films prepared at a secondary ion beam current density of 150 $\mu A/cm^2.

Characterization of bias magnetron-sputtered silicon nitride films

Influence of the deposition parameters and the substrate bias voltage on the optical, compositional and the surface properties of DC magnetron-sputtered silicon nitride thin films are studied. Silicon nitride thin films are deposited on silicon (100) and quartz substrates at different partial pressures of nitrogen and discharge currents. The variation in the refractive index and the optical band gap of these films is studied. Compositional variation has been studied using Rutherford backscattering spectroscopy (RBS). Silicon nitride thin films deposited at 3 \times 10^-^2 Pa partial pressure of nitrogen with $2.5 mA/cm^2$ cathode current density showed an optical band gap of 4.3 eV and refractive index of 2.04 (at 650 nm). Nitrogen to silicon ratio in the film is 1.31, and the roughness of the films is 2.3 nm. Substrate bias during deposition helped in changing the optical properties of the films. Substrate bias of -60V resulted in films having near stoichiometry with N/Si ratio 1.32, and the optical band gap, refractive index, and the roughness are 4.8 eV, 1.92 and 0.78 nm, respectively

Appearance of radial breathing modes in Raman spectra of multi-walled carbon nanotubes upon laser illumination

The Raman spectra of the multi-walled carbon nanotubes are studied with the laser power of 5–20 mW. We observe the Raman bands at not, vert, similar1352, 1581, 1607, and 2700 cm−1 with 5 mW laser power. As the laser power is increased to 10, 15 and 20 mW, the radial breathing modes (RBMs) of the single wall carbon nanotubes (SWNTs) appear in the range 200–610 cm−1. The diameter corresponding to the highest RBM is not, vert, similar0.37 nm, the lowest reported so far. The RBMs are attributed to the local synthesis of the SWNTs at the top surface of the samples at higher laser power.© Elsevie

Understanding the quantum size effects in ZnO nanocrystals

In the present work, we report the synthesis of high quality ZnO nanocrystals with sharp absorption edges in four different sizes, namely 3.0, 3.5, 4.7 and 5.4 nm, characterized by X-ray and electron diffraction, as well as transmission electron microscopy. The bandgaps of these samples, in conjunction with further data from the published literature, exhibit a systematic dependence on the nanocrystal size. In absence of any prior reliable theoretical resutls in the literature to understand this dependence quantitatively, we have analyzed for the first time, the electronic structure of bulk ZnO obtained from the full potential linearized augmented plane wave method using fatbands, density of states and partial density of states. The crystal orbital Hamiltonian population is obtained from linearized Muffin-Tin orbital band structure calculations to understand the range of hopping interactions relevant for an accurate description of the electronic structure. Using these analyses, a realistic tight binding model is proposed. Based on this model, we calculate the variation of the bandgap with the size of ZnO nanocrystals. These theoretical results agree well with all available data over the entire range of sizes, establishing the effectiveness of this approach

Structural damage on multiwalled carbon nanotubes and encapsulated single crystal nickel nanorods irradiated with Au+7 ions of 100 MeV

In the present work we report the results of the irradiation of the multiwalled carbon nanotubes samples with gold ions of 100 MeV. The damage on the tube walls and the encapsulated nickel filling inside was studied using high-resolution transmission electron microscopy (HRTEM). The irradiation produces localized planar defects on the tube walls and induces amorphization of the encapsulated nickel nanorods. It also results in decrease of the interplanar spacing of graphite walls as well as nickel (111) planes. As the nanotubes in our case are of 20-30 nm diameter, it is expected that the interaction with the tubes will be exclusively via electronic energy loss (dE/dx)(e) of the ion beam. The results on the damage of the tube walls and the nature of the generated defects are reported. (c) 2005 Elsevier B.V. All rights reserved

Reorientation of the crystalline planes in confined single crystal nickel nanorods induced by heavy ion irradiation

In a recent letter Tyagi [Appl. Phys. Lett. 86, 253110 (2005)] have reported the special orientation of nickel planes inside multiwalled carbon nanotubes (MWCNTs) with respect to the tube axis. Heavy ion irradiation has been performed with 1.5 MeV Au2+ and 100 MeV Au7+ ions on these nickel filled MWCNTs at fluences ranging from 10(12) to 10(15) ions/cm(2) at room temperature. Ion-induced modifications have been studied using high-resolution transmission electron microscopy. The diffraction pattern and the lattice imaging showed the presence of ion-induced planar defects on the tube walls and completely amorphized encapsulated nickel nanorods. The results are discussed in terms of thermal spike model. (c) 200

High-resolution transmission electron microscopy mapping of nickel and cobalt single-crystalline nanorods inside multiwalled carbon nanotubes and chirality calculations

The nickel and cobalt nanorods of the diameters in the range of 6 - 20 nm with lengths of 0.29 - 0.9 mu m are formed using multiwalled carbon nanotubes as templates. The nickel and cobalt nanorods as described in our letter are perfect single crystals inside the nanotube with their Miller planes inclined with respect to the tube axis in a particular fashion. The (111) planes of face-centered-cubic nickel and cobalt are inclined at angles 39.6 degrees and 39.4 degrees, respectively, while the hexagonal-closed-packed cobalt (002) planes incline at an angle 53.4 degrees. The inclination of these planes is studied in detail and results are discussed in terms of elastic energy and surface tension. The chirality of the carbon nanotubes, in intimate contact with the nanorod, is determined using the mapping of Ni and C atoms in a graphene sheet. We believe this could pave a way for synthesizing the tubes with known chirality. (c) 200

Axial buckling and compressive behavior of nickel-encapsulated multiwalled carbon nanotubes

In a recent report [Sun , Science 312, 1119 (2006)], the partially filled material inside multiwalled carbon nanotubes (MWNTs) was shown to have shrunk and deformed in the axial direction under 300 kV electron irradiation. In this experiment, 100 MeV Au7+ ion irradiation was performed to study the deformation and defects in uniformly nickel filled MWNTs with high-resolution transmission electron microscopy and Raman spectroscopy. We propose that high-pressure induced torsion in confined nickel could possibly result in successive compressions and expansions of the tubes, leading to axial buckling of MWNTs. The tangential Raman G band systematically upshifts as the ion fluence increases, attributed to the torsional strain. In contrast to a square root dependence of the buckling wavelength (lambda) on the radius (r) and thickness (t) of the tubes [lambda=3.5(rt)(1/2)], as predicted by theoretical models, the exponential fit of the data that assumes lambda proportional to e(root(r/t)) also produces an excellent fit

Single crystalline nickel nanorods inside carbon nanotubes: Growth behavior, structure, and magnetic properties

Nickel nanorods with diameters ranging from 5 to 10 nm, encapsulated inside the carbon nanotubes, are prepared using microwave plasma chemical vapor deposition. High-resolution transmission electron microscopy (HRTEM) studies reveal the perfect crystalline nature of the rods with of-spacing closely matching the (1111) interplanar spacing of Ni. The (1111) planes of the Ni nanorods are always aligned at 39.6° with respect to the graphite planes of the nanotubes. The cosine component of the d-spacing along the direction of the graphite planes is found to be 1.6 &ANGS;; exactly half the d-spacing between the graphite planes. The electron diffraction pattern shows clear spots corresponding to Ni structure. The field cooled and zero field cooled magnetization data reveal the reversibility of the magnetization of the Ni nanorods and show a blocking temperature of 195 K, which correspond to energy barrier of 0.4 eV/(V)

Multiwall carbon nanotubes from pyrolysis of tetrahydrofuran

Multiwalled carbon nanotubes have been prepared by pyrolysing tetrahydrofuran (THF) in the presence of nickelocene. Pyrolysis of the precursor mixture has been achieved at temperature as low as 600 degrees C. In this simple approach no carrier gas has been used. The yield of purified carbon nanotubes is found to be more than 65%. Characterization of the as-prepared and purified nanotubes are done by Xray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy and Raman spectra