Swift heavy-ion irradiation of elemental metal nanoparticles (NPs) embedded in amorphous SiO 2 induces a spherical to rodlike shape transformation with the direction of NP elongation aligned to that of the incident ion. Large, once-spherical NPs become progressively more rodlike while small NPs below a critical diameter do not elongate but dissolve in the matrix. We examine this shape transformation for ten metals under a common irradiation condition to achieve mechanistic insight into the transformation process. Subtle differences are apparent including the saturation of the elongated NP width at a minimum sustainable, metal-specific value. Elongated NPs of lesser width are unstable and subject to vaporization. Furthermore, we demonstrate the elongation process is governed by the formation of a molten ion-track in amorphous SiO 2 such that upon saturation the elongated NP width never exceeds the molten ion-track diameter. Ion-solid interactions during swift heavy-ion irradiation (SHII) are dominated by inelastic processes in the form of electron excitation and ionization while, in contrast, the influence of elastic processes such as ballistic displacements is negligible. Macroscopically, amorphous SiO 2 (a-SiO 2 ) undergoes a volume-conserving anisotropic deformation when subjected to SHII such that thin freestanding layers contract and expand, respectively, in directions parallel and perpendicular to that of the incident ion [1]. The viscoelastic model [2,3], based on a transient thermal effect, successfully explains this so-called ion hammering. Microscopically, energy is deposited along the ion path, from incident ion to matrix electrons, and is then dissipated within a narrow cylinder of material surrounding the ion path. The heat flow in both the electron and lattice subsystems is well described as functions of time and radial distance by the inelastic thermal spike (i-TS) model [4,5]. When the temperature of the lattice exceeds that required for melting, the material along the ion path is molten and upon quenching an ion track is formed. Recently, we measured the molten ion-track diameter in a-SiO 2 as a function of electronic stopping power [6]. The ion-track radial density distribution consisted of an under-dense core and over-dense shell (relative to unirradiated material), the formation of which was attributed to a quenched-in pressure wave emanating from the ion-track center [6].Elemental metal nanoparticles (NPs) embedded in a-SiO 2 and subjected to SHII can undergo an intriguing shape transformation where once-spherical NPs become progressively more rodlike with the direction of elongation aligned along that of the incident ion. This phenomenon has been reported for several metals under a wide range of SHII conditions, with Refs. [7][8][9][10][11][12][13][14][15][16][17] citing selected examples. Freestanding metallic NPs irradiated under comparable conditions do not change shape, demonstrating the embedding a-SiO 2 matrix must have a role in the shape transformation process [8,17]. An unambiguous ...

The room-temperature photoluminescence (PL) of Tb3+ ions has been studied. The Tb ions were implanted into 200 nm thick SiO2 on Si wafers. To achieve a uniform Tb distribution, the implantations were performed at 50, 100, and 190 keV to a total dose of 8.8×1014–1.3×1016 ions/cm2, resulting in Tb concentrations of 0.18–2.7 at. %. The PL spectrum consists of sharp lines due to the Tb3+ intra-4f transitions and a broadband due to SiO2 defects. The samples were annealed at temperatures ranging from 600 to 1050 °C. Up to 900 °C, the annealing procedure improves the PL yield; at temperatures higher than 1000 °C, the PL yield drops again at high dose. The PL spectra show noticeable influence of Tb–Tb crossrelaxation, which favors the green PL over the blue PL.

Silica glass implanted with Zn ions of 60keV to 1.0×1017ions∕cm2 was annealed in oxygen gas to form ZnO nanoparticles (NPs). In as-implanted state, the implanted Zn atoms form Zn metallic NPs inside of the silica. After annealing at 600°C, ZnO NPs form on the surface, while Zn metallic NPs still remain in the deep region. At 700°C, most of Zn atoms move to the surface to form the droplet-shaped ZnO NPs which show two photoluminescence bands, i.e., an exciton band at 375nm and a defect band at ∼500nm. The defect band almost disappears in the samples annealed at 600°C, which include both ZnO NPs and Zn NPs.

Zinc-oxide (ZnO) nanoparticles (NPs) are fabricated in silica glasses (SiO2) by implantation of Zn+ ions of 60 keV up to 1.0×1017ions∕cm2 and following thermal oxidation. After the oxidation at 700 °C for 1 h, the absorption in the visible region due to Zn metallic NPs disappears and a new absorption edge due to ZnO appears at ∼3.25eV. Cross-sectional transmission electron microscopy confirms the formation of ZnO NPs of 5–10 nm in diameter within the near-surface region of ∼80nm thick and larger ZnO NPs on the surface. Under He–Cd laser excitation at λ=325nm, an exciton luminescence peak centered at 375 nm with FWHM of 113 meV was observed at room temperature.

Elongation of metal nanoparticles (NPs) embedded in silica (SiO 2 ) induced by swift heavy-ion (SHI) irradiation, from spheres to spheroids, has been evaluated mainly by transmission electron microscopy (TEM) at high fluences, where tens to thousands of ion tracks were overlapped each other. It is important to clarify whether the high fluences, i.e., track overlaps, are essential for the elongation. In this study the elongation of metal NPs was evaluated at low fluences by linearly polarized optical absorption spectroscopy. Zn NPs embedded in silica were irradiated with 200-MeV Xe 14+ ions with an incident angle of 45• . The fluence ranged from 1.0 × 10 11 to 5.0 × 10 13 Xe/cm 2 , which corresponds to the track coverage ratio (CR) of 0.050 to 25 by ion tracks. A small but certain dichroism was observed down to 5.0 × 10 11 Xe/cm 2 (CR = 0.25). The comparison with numerical simulation suggested that the elongation of Zn NPs was induced by nonoverlapping ion tracks. After further irradiation each NP experienced multiple SHI impacts, which resulted in further elongation. TEM observation showed the elongated NPs whose aspect ratio (AR) ranged from 1.2 to 1.7 at 5.0 × 10 13 Xe/cm 2 . Under almost the same irradiation conditions, Co NPs with the same initial mean radius showed more prominent elongation with AR of ∼4 at the same fluence, while the melting point (m.p.) of Co is much higher than that of Zn. Less efficient elongation of Zn NPs while lower m.p. is discussed.

a b s t r a c tNitrides of high-entropy alloys (TiHfZrNbVTa)N were fabricated using cathodic-vacuum-arc-vapordeposition method. Morphology and topology of the surface of the coatings, roughness, elemental and phase composition, microstructure and mechanical properties were investigated. Dependence of deposition parameters on surface morphology and elemental composition was demonstrated. Influence of the heavy negative charged Au À ions implantation on phase structure, microstructure and hardness of nitride (TiHfZrNbVTa)N coatings was investigated.

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wileyonlinelibrary.com FULL PAPERapproach to increase the effi ciency of the photoconversion processes consists on integrating plasmonic metal nanostructures with semiconductor materials [4][5][6][7] Plasmonic nanostructures can improve photocatalytic processes via: [ 8 ] (i) intrinsic charge separation mechanisms (builtin potentials) that occur at metal-semiconductor junctions (Schottky contacts), (ii) strong confi nement of electromagnetic energy at the surface of the metal nanoparticles, which leads to enormous energy densities at the near-fi eld regions of the metallic nanostructures and (iii) the emission of hot charge-carriers from the metal nanoparticles into the semiconductor material. [9][10][11] Plasmon related phenomena originate from the light-driven collective oscillation of electrons at the surface of metallic nanostructures. The resonance frequencies at which these oscillations take place are largely controlled by the geometry of the metallic nanostructures. One of the simplest structures that exhibits localized surface plasmon resonances are metal nanowires ( Figure 1 ): these structures consist of metal stripes with particle plasmon resonances that depend on the width and height of the wire in addition to the period of the wire array (gratings). These particle plasmon resonances can be excited with light polarized perpendicular to the wire length and occur in the visible region of the spectrum for width and heights in the order of a few tens of nanometers for Au.Under particular illumination conditions and for specifi c grating periods, these nanowire gratings can exhibit [ 12 ] resonances involving coupling of energy into complex waves supported by the grating and Rayleigh-type anomalies due to the emergence of a grating order at grazing angle.Rayleigh anomalies are easy to understand for the simple case of a 1D nanowire grating deposited on a substrate (see diagram of Figure 1 b). For normal incidence, conservation of momentum k inc on the incident medium dictates that 2 inc 2 2 k k k n t = − (1)where n and t denote the normal and transverse components of the total momentum resulting from the interaction of light with the grating (see diagram of Figure 1 ). The transverse component (for normal incidence) is given by integer multiples ( m ) of the momentum imparted by the grating (2π/ p ):One key process in plasmon-enhanced photocatalysis is the transfer of hot charge-carriers from metal nanostructures into photocatalytically active materials. This process is secondary to the initial step of light absorption by the metal nanostructures. Light absorption in these structures can be controlled by designing complex geometries with tailored optical cross-sections.Here, a study on one of the simplest nanostructures exhibiting plasmon resonances is presented: 1D gratings of metal wires. Results on the effect of the periodicity of these arrays are presented on the resonant absorption of light and on the hot charge-carrier transfer to a supporting TiO 2 thin fi lm. This charge transfer process is monitor...