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Self-standing polycrystalline diamond films fabricated by chemical vapor deposition, which were transparent up to the intrinsic band edge of ∼5.5 eV, were implanted with boron negative dimer ions (B2-) of 60 keV at various fluences ranging from 1×1014 to 3×1017 B/cm2. Even at the lowest fluence of 1×1014 B/cm2, a weak color darkening was observed by the naked eye, indicating the optical absorption due to damage, not to implants. The subbandgap absorption tail increases with the fluence to the powers of ∼0.5 and ∼0.2 in the fluence regions lower and higher, respectively, than the transition fluence of ∼1×1016 B/cm2. The implanted regions also show large surface swelling of up to ∼60 nm in height. The swelling shows the same two-step power-law dependence with the same transition fluence. The same two-step power-law fluence dependence with the same transition fluence is also observed in the intensity of the defect Raman band around 1520 cm-1. From the good agreement between the estimated volume change due to graphitization and the measured swelling, the transition fluence is ascribed to the fluence where all the diamond structures in the implanted layer are transformed to graphitelike structures. [ABSTRACT FROM AUTHOR]

Kinetic behaviors of nanoparticle formation in LiNbO3 have been studied with negative Cu ion implantation and the effects on nonlinear optical properties have been discussed. Negative Cu ions of 60 keV are implanted into LiNbO3 disks at fluxes up to 50 μA/cm2. Ion-induced photon spectroscopy was applied to monitor the ion-substrate interactions and the nanoparticle morphology was studied by cross-sectional TEM. Metal precipitation behaviors as well as the matrix stability significantly depended on ion flux. In a flux range of 3–10 μA/cm2, LiNbO3 showed spontaneous formation of Cu nanocrystals of ∼10 nm, including nonspherical shape. Crystallinity of the LiNbO3 lattice implanted was sustained up to 3 × 1016 ions/cm2. The Cu nanoparticles in LiNbO3 showed a sub-picosec nonlinear optical response. However, significant Li-atom release to the vacuum was detected by ion-induced photon spectroscopy, indicating formation of a Li-depleted zone. Particularly above a flux of 30 μA/cm2, significant coarsening of Cu particles and amorphization of the LiNbO3 lattice occurred. The results indicate that metal nanoparticle formation in LiNbO3 is sensitive to the ion flux and that the optimization is requisite to fabricate well-defined nanocomposites. [Copyright &y& Elsevier]

Silica glass (SiO2) was implanted with 60 keV Zn+ ions to a fluence of 1.0×1017 ions/cm2, and the chemical states were investigated along the depth in as-implanted state by x-ray excited Auger electron spectroscopy and x-ray photoelectron spectroscopy. The metallic Zn and Zn2SiO4 phases were found to have, respectively, formed in the shallow and deep regions of the SiO2, whereas thermodynamics predicts the Zn phase only. Oxygen atoms in SiO2 are preferentially displaced to the deeper region because of the lighter mass. The excess oxygen in the deep region and athermal energy from the implantation drive the formation of Zn2SiO4. [ABSTRACT FROM AUTHOR]

Nanocrystals (NCs) of cuprous oxide (Cu2O), cupric oxide (CuO), and copper metal (Cu) are fabricated in silica glasses (SiO2) by implantation of 60 keV Cu- ions at different annealing conditions. At room temperature, Cu2O NCs show two sharp absorption peaks at 2.58 and 2.71 eV due to autoionized exciton states, and Cu NCs show a broad peak at ∼2.2 eV due to the surface plasmon resonance (SPR). With decreasing temperature down to 2.8 K, the peaks of Cu2O NCs become much narrower, while the SPR peak of Cu NCs keeps almost the same peak width. [ABSTRACT FROM AUTHOR]

Zinc-oxide (ZnO) nanoparticles (NPs) are fabricated in silica glasses (SiO2) by implantation of Zn+ ions of 60 keV up to 1.0×1017 ions/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 ∼3.25 eV. Cross-sectional transmission electron microscopy confirms the formation of ZnO NPs of 5–10 nm in diameter within the near-surface region of ∼80 nm thick and larger ZnO NPs on the surface. Under He–Cd laser excitation at λ=325 nm, an exciton luminescence peak centered at 375 nm with FWHM of 113 meV was observed at room temperature. [ABSTRACT FROM AUTHOR]

Abstract: Thermal annealing effects on Zn+ ion-implanted silica glass (a-SiO2) have been studied in order to control void formation. Void formation in a-SiO2 with Zn+ ion implantation and subsequent oxidation has been observed using transmission electron microscopy (TEM). Zn+ ions of 60keV were implanted into a-SiO2 to a fluence of 1.0×1017 ions/cm2. After the implantation, thermal annealing at 600 or 700°C for 1h in oxygen gas was conducted. In as-implanted state, metal Zn nanoparticles (NPs) of 10–15nm in diameter are formed in the depth region around the projected range. The size of the Zn nanoparticles increases after the annealing at 600°C in oxygen gas. Annealing in oxygen gas at 700°C for 1h caused two processes: (1) the migration of Zn atoms which formed Zn NPs in as-implanted state to the surface of the a-SiO2 substrate and (2) the transformation to the oxide phase on the substrate. The transportation of Zn NPs to the surface leaves voids of 10–25nm in diameter inside the a-SiO2. These results indicate that the oxidation at 700°C for 1h causes the migration of Zn atoms to the surface without diffusion and recombination of vacancies which form the voids. [Copyright &y& Elsevier]

Elongation of metal nanoparticles (NPs) embedded in silica (SiO2) 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 Xe14+ ions with an incident angle of 45°. The fluence ranged from 1.0×1011 to 5.0×1013 Xe/cm2, 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 5.0×1011 Xe/cm2 (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 5.0×1013 Xe/cm2. 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. [ABSTRACT FROM AUTHOR]

Abstract: Optical nonlinearity and dispersion were studied for Cu nanoparticle composite. Negative Cu− ions with 60keV were applied for implanting into SrTiO3 at a flux of 10μA/cm2 up to a total fluence of 1×1017 ions/cm2. The steady-state optical spectrum of Cu-implanted SrTiO3 showed a surface plasmon resonance resulting from the formation of nanoparticles. Transient transmission and reflection were measured by the pump–probe method with a femtosecond laser system. Optical nonlinearity originated from Cu:SrTiO3 nanoparticle composite and from SrTiO3 matrix overlap, in measured transient spectra. The nonlinear component of Cu:SrTiO3 composite was extracted from the transient spectra with the difference of time response. Nonlinear dielectric coefficient and dispersion around the surface plasmon resonance were derived from extracted transient spectra. The dispersion was compared with a local electric field factor. [Copyright &y& Elsevier]

Abstract: Surface recession due to sputtering under low-energy and high-fluence heavy-ion implantation makes shallower and broader depth profile of implanted ions than those calculated by conventional ion-range simulation-codes such as SRIM. Depth profiles of Zn atoms in silica glasses (SiO2) implanted with Zn+ ions of 60keV up to 1.0×1017 ions/cm2 were evaluated using both experimental methods as Rutherford backscattering spectrometry (RBS), sputtering depth-profiling by X-ray photoelectron spectroscopy (XPS), and an advanced numerical simulation code TRIDYN, which includes the sputtering loss effects. The TRIDYN code predicts the shallowing of the projectile range from ∼46 to ∼27nm with increasing the fluence up to 1×1017 ions/cm2, and very high-concentration (∼20at%) of Zn atoms close to the surface. However, RBS and XPS results exclude such high concentration close to the surface. These results suggest remarkable redistribution of Zn atoms from the nearer surface to the deeper region during the implantation. In fact, Zn-atom concentration near the surface and that near the projectile range are, respectively, lower and higher than those by the SRIM code predictions. [Copyright &y& Elsevier]

Abstract: Spectra of the optical transmission and ion-induced photon emission (IIPE) of LiNbO3 were measured during implantation of 60keV Cu- ions at ion fluxes from 1 to 50μA/cm2 up to a fluence of 2×1017ions/cm2. The optical transmission in the range of surface plasmon resonance (SPR) and the IIPE are good monitors of the nanocomposite formation and the chemical composition change, respectively. Copper atoms precipitate at fluences lower than 6×1015ions/cm2. Further formation of nanocomposite comprises two easily distinguishable stages: the slope of fluence dependencies of SPR abruptly decreases at about 1017ions/cm2. Lithium-depleted regions are created in the substrates, and concentration of Nb increases. The formation of nanocomposite is most efficient at a flux of 1μA/cm2. [Copyright &y& Elsevier]