Third-order nonlinear optical response of Cu/Ag nanoclusters by ion implantation under 1064 nm laser excitation

The evolution of nanoclusters in sequentially ion-implanted Cu/Ag into silica glasses has been studied. The doses for implantation (×10¹⁶ ions/cm²) were 5Cu/5Ag, 5Cu/10Ag and 5Cu/15Ag, respectively. The microstructural properties of the nanoclusters are characterized by optical absorption spectra and transmission electron microscopy (TEM). Fast nonlinear optical refraction and nonlinear optical absorption coefficients were measured at 1064 nm of wavelength using Z-scan technique. Results in this project indicate that different optical nonlinearities could be selectively obtained at the near-infrared region of 1064 nm of wavelength by changing the metal ingredient percentage in silica.     

Photoluminescence properties of impurity-doped ZnS nanocrystals fabricated by sequential ion implantation

We have studied photoluminescence (PL) spectrum and dynamics of Cu- and Al-doped ZnS (ZnS:Cu,Al) nanocrystals fabricated by sequential implantation of Zn⁺, S⁺, Cu⁺, and Al⁺ ions into Al₂O₃ matrices. These samples exhibit intense green PL under UV light excitation. The space- and time-resolved PL measurements show that the broad green PL is due to the donor–acceptor (DA) pair luminescence of single ZnS:Cu,Al nanocrystals.     

Influence of Cu ion implantation on the microstructure and cathodoluminescence of ZnS nanostructures

The microstructure and optical properties of as-synthesized and Cu ion implanted ZnS nanostructures with branched edges are studied by using high-resolution transmission electron microscope (TEM) and spatially-resolved cathodoluminescence measurement. Obvious crystalline deterioration has been observed in Cu-doped ZnS nanostructures due to the invasion of Cu ions into ZnS lattice. It was found that the optical emissions of ZnS nanostructures can be selectively modified through the control of Cu ion dose and subsequent heat treatment. An increase of Cu dopant content will lead to an apparent red-shift of the intrinsic band-gap emission in the UV range and the broadening of defect-related emission in visible range. The influences of Cu ion implantation on the microstructure and related optical properties were discussed.     

Potential for size reduction of AlGaAs optical channel waveguide structures fabricated by focused ion beam implantation and oxidation

Optical channel waveguides formed by focused ion beam (FIB) implantation-induced mixing of AlGaAs multiple quantum well structures and subsequent oxidation of the mixed regions have the potential of significantly reducing the size of integrated photonic waveguide structures. Since FIB implantation is a direct write process characterized by nanoscale precision, we suggest its use for forming channel waveguides having nanoscale (submicrometer) widths. Calculations presented for such channel waveguides show reductions in size by at least an order of magnitude are possible for directional couplers and other structures involving curved channel waveguide sections. Such size reductions would allow the realization of significantly higher levels of device integration than are now currently possible.     

Structural and photoluminescence properties of Si nanoclusters obtained by ion implantation into Si3N4 films

In the present paper we report structural and photoluminescence (PL) results from samples obtained by Si implantation into stoichiometric silicon nitride (Si₃N₄) films. The Si excess was introduced in the matrix by 170 keV Si implantation performed at different temperatures with a fluence of Φ=1×10¹⁷ Si/cm². The annealing temperature was varied between 350 and 900 °C in order to form the Si precipitates. PL measurements, with a 488 nm Ar laser as an excitation source, show two superimposed broad PL bands centered around 760 and 900 nm. The maximum PL yield is achieved for the samples annealed at 475 °C. Transmission electron microscopy (TEM) measurements show the formation of amorphous nanoclusters and their evolution with the annealing temperature.     

Nonlinear optical properties of Cu nanoclusters by ion implantation in silicate glass

Metal nanocluster composite glass prepared by 180 keV Cu ions into silica with dose of 1 × 10¹⁷ ions/cm² has been studied. The microstructural properties of the nanoclusters were analysed by optical absorption spectra and transmission electron microscopy (TEM). Third-order nonlinear optical properties of the nanoclusters were measured at 1064 nm and 532 nm excitations using Z-scan technique. The nonlinear refraction index, nonlinear absorption coefficient, and the real and imaginary parts of the third-order nonlinear susceptibility were deduced. The mechanisms responsible for the nonlinear response were discussed. Absolute third-order nonlinear susceptibility χ⁽³⁾ of this kind of sample was determined to be 2.1 × 10⁻⁷ esu at 532 nm and 1.2 × 10⁻⁷ esu at 1064 nm, respectively.     

Influence of helium implantation of optical fibre faceplates on acid etching

In order to achieve preferential etching of a structured multi-component glass fibreoptic faceplate the surface has been ion implanted to enhance the differences in chemical reactivity of the various glass constituents. While HF dissolution is enhanced at silicate glass components due to ion beam electronic excitation, changes in the glass stability of the heavy metal fibre core due to nuclear collision damage were evident at the end of the ion penetration range after HNO₃ acid attack.     

Effect of Cr implantation on structural and optical properties of AlN thin films

Molecular beam epitaxy (MBE) grown AlN thin layer on sapphire substrates have been implanted with Cr⁺ ions for various dose from 10¹³ to 10¹⁵ cm⁻². The analyses were carried out by an X-ray diffractometer (XRD), Raman spectroscopy, a spectrophotometer and spectroscopic ellipsometry (SE) for structural and optical analyses. E₂(high) and A₁(LO) Raman modes of AlN layer have been observed and analyzed. The behavior of Raman shift and the variation in intensity and in peak width of Raman modes as a function of ions flux are explained on the basis of chromium substituting aluminum atom and implantation-induced lattice damage. Both Raman and X-ray analyses reveal that the incorporation of chromium atoms increases in the host lattice with the increasing of Cr ions fluence. The band gap energy was determined by using transmission spectra. It was found that the band gap energy decreases as the ion dose increases. The band gap of the unimplanted AlN is 6.02 eV and it decreases down to 5.92 eV for the Cr⁺-implanted AlN with a ion dose of 1×10¹⁵ cm⁻². Optical properties such as optical constants of the samples were examined by using a spectroscopic ellipsometer. It was observed that the refractive index (n) decreases with the increasing of ion dose.     

Effect of N ion implantation on the optical properties of an organometallic complex—Zinc cadmium thiocyanate single crystal

A highly efficient non-linear optical organometallic compound zinc cadmium thiocyanate (ZCTC) single crystal was grown by solvent evaporation method. The as grown single crystals were implanted with 45 keV N⁵⁺ ions having energy at various fluencies of 1 × 10¹⁵, 5 × 10¹⁵, 1 × 10¹⁶ and 5 × 10¹⁶ ions/cm². The surface modification induced by the ion implantation was studied using scanning electron microscopy. The UV spectrum shows an increase in absorbance with the increase in the dosage of the ions implanted. There is a red shift in the cut off wavelength due to implantation which may be attributed to the lattice damage produced during implantation. From the Raman spectra, it is observed that there is no shift in the peak positions or any extra peaks due to implantation confirming that the nitrogen ions are not substituted into the lattice. The FWHM, area and intensity of the Raman peak corresponding to CN stretching vibration were calculated and the influence of ion implantation on these parameters was discussed. The effect of implantation on the PL spectra was analysed and discussed in detail. The change in refractive index of the sample due to implantation was reported.     

Double optical waveguide in Cu-doped KNSBN crystal formed by MeV boron ion implantation

We reported for what is to be believed the first time a double optical waveguide in a Cu-doped potassium sodium strontium barium niobate (KNSBN) crystal formed by double boron ion implantation. The energy and dose of B⁺ and B³⁺ ions were (3+6) MeV and (2+2)×10¹⁴ ions/cm², respectively. The refractive index profile of the waveguide showed a double-barrier confined shape, which suggested the formation of a two-layer waveguide structure. The two waveguide layers were with thickness of 2.6 and 2 μm, respectively, which was in a good agreement with the parameters obtained from transport and range of ions in matter 98 (TRIM) code simulation. The nuclear energy loss distribution of the MeV B ions implanted into this crystal had a similar shape to that of the waveguide index profile, which means an inherent relationship between the waveguide formation and the energetic energy deposition.     

Controlled gold doping of silicon by using ion implantation

A new technology is suggested to dope silicon devices with gold for carrier life time adjustment with high accuracy and reproducibility. Ion implantation is used to dope the sample with a well defined total amount of gold. This gold dose is redistributed by high temperature anneal. A computer simulation of gold diffusion and experimental radio tracer results show that highly accurate gold doping can be obtained in bulk material when temperatures around 1000 C are applied during the redistribution anneal. Damage free surfaces must be used to reduce the gold content gettered in surfaces.     

Nonlinear optical properties in double-sided nonlinear media with Z-scan technique based on the Huygens——Fresnel principle

We present a theoretical model to analyse the propagation of a Gaussian laser beam through double-sided nonlinear media. This model is based on the Huygens--Fresnel diffraction integral method. This theoretical model is not only consistent with the cascade structure model for a small nonlinear phase-shift but also can be used for a large nonlinear phase-shift. It has been verified that it is suitable to characterize the double-sided nonlinear media compared with the cascade structure model. A good agreement between the experimental data and the results from the theoretical model is obtained. It will be useful for the design of multi-sided nonlinear materials.     

Excess Si concentration dependence of the photoluminescence of Si nanoclusters in SiO2 fabricated by ion implantation

A method for the fabrication of luminescent Si nanoclusters in an amorphous SiO₂ matrix by ion implantation and annealing, and the detailed mechanisms for the photoluminescence are reported. We have measured the implanted ion dose, annealing time and excitation energy dependence of the photoluminescence from implanted layers. The samples were fabricated by Si ion implantation into SiO₂ and subsequent high-temperature annealing. After annealing, a photoluminescence band below 1.7 eV has been observed. The peak energy of the photoluminescence is found to be independent of annealing time and excitation energy, while the intensity of the luminescence increases as the annealing time and excitation energy increase. Moreover, we found that the peak energy of the luminescence is strongly affected by the dose of implanted Si ions especially in the high dose range. These results indicate that the photons are absorbed by Si nanoclusters, for which the band-gap energy is modified by the quantum confinement effects, and the emission is not simply due to direct electron–hole recombination inside Si nanoclusters, but is related to defects probably at the interface between Si nanoclusters and SiO₂, for which the energy state is affected by Si cluster–cluster interactions. It seems that Si nanoclusters react via a thin oxide interface and the local concentrations of Si nanoclusters play an important role in the peak energy of the photoluminescence.     

Effect on polarization control in 850 nm vertical cavity surface emitting laser fabricated by H ion inclined implantation using tungsten wire as mask

Polarization character measurements on VCSEL devices, fabricated by ion inclined implantation with various parameters using tungsten wire as mask, were performed. The effect of polarization mode control was observed in these devices with square injected current aperture formed by distributed ion during implantation. Moreover, the effect depended on the size of the square injected current aperture. The device with highest polarization mode suppression ratio (PMSR) up to 14 dB was obtained, which kept the operation of linear polarization state at 3.4I_th injected current. The further optimization to obtain the better polarization control effect is available. What the most valuable is that the mechanism of polarization control effect is completely self-formed during device processing. Furthermore, this method is the simplest technique to apply in industry, as much as we know.     

Picosecond nonlinear optical response of Ba0.5Sr0.5TiO3 thin films fabricated by pulsed laser deposition

Well-crystallized Ba_0.5Sr_0.5TiO₃ thin films with good surface morphology were prepared on MgO(1 0 0) substrates by pulsed laser deposition technique at a deposition temperature of 800 °C under the oxygen pressure of 2 × 10⁻³ Pa. X-ray diffraction and atomic force microscopy were used to characterize the films. The full width at half maximum of the (0 0 2) Ba_0.5Sr_0.5TiO₃ rocking curve and the root-mean-square surface roughness within the 5 μm × 5 μm area were 0.542° and 0.555 nm, respectively. The nonlinear optical properties of the films were determined by a single beam Z-scan method at a wavelength of 532 nm with laser duration of 55 ps. The results show that Ba_0.5Sr_0.5TiO₃ thin films exhibit a fast third-order nonlinear optical response with the nonlinear refractive index and nonlinear absorption coefficient being n₂ = 5.04 × 10⁻⁶ cm²/kW and β = 3.59 × 10⁻⁶ (m/W), respectively.     

Cu-Ni alloy nanocluster formation by ion implantation in silicate glasses: Structure and optical properties

Sequential ion implantation (copper and nickel) in silica and soda-lime glasses has been performed. The formation of copper-nickel alloy nanocluster in the glass host has been evidenced by synchrotron radiation-based techniques, namely X-ray diffraction and absorption spectroscopy. The nanocrystals' lattice parameter value was estimated, indicating the formation of Cu₅₅Ni₄₅ alloy particles. Optical absorption spectra are also discussed. Received 6 May 1999 and Received in final form 22 September 1999     

Stabilization of organic thin film transistors by ion implantation

We report on the effects of low energy ion implantation (N and Ne) in the reduction and control of the degradation of pentacene organic thin film transistors (OTFTs) due to the exposure to atmosphere (i.e. oxygen and water). We have observed that a controlled damage depth distribution preserves the functionality of the devices, even if ion implantation induces significant molecular structure modifications, in particular a combination of dehydrogenation and carbonification effects. No relevant changes in the pentacene thin film thickness have been observed. The two major transport parameters that characterize OTFT performance are the carrier mobility and the threshold voltage. We have monitored the effectiveness of this process in stabilizing the device by monitoring the carrier mobility and the threshold voltage over a long time (over 2000 h). Finally, we have assessed by depth resolved X-ray Photoemission Spectroscopy analyses that, by selectively implanting with ions that can react with the hydrocarbon matrix (e.g. N⁺), it is possible to locally modify the charge distribution within the organic layer.     

Effect of boron ion implantation on the structural, optical and electrical properties of ZnSe thin films

Zinc Selenide (ZnSe) thin films were deposited onto well cleaned glass substrates using vacuum evaporation technique under a vacuum of 3×10⁻⁵ mbar. The prepared ZnSe samples were implanted with mass analyzed 75 keV B⁺ ions at different doses ranging from 10¹² to 10¹⁶ ions cm⁻². The composition, thickness, microstructures, surface roughness and optical band gap of the as-deposited and boron-implanted films were studied by Rutherford backscattering (RBS), grazing incidence X-ray diffraction, Atomic force microscopy, Raman scattering and transmittance measurements. The RBS analysis indicates that the composition of the as-deposited and boron-implanted films is nearly stoichiometric. The thickness of the as-deposited film is calculated as 230 nm. The structure of the as-deposited and boron-implanted thin films is cubic. It is found that the surface roughness increases on increasing the dose of boron ions. In the optical studies, the optical band gap value decreases with an increase of boron concentration. In the electrical studies, the prepared device gave a very good response in the blue wavelength region.     

绝缘体中金属离子注入合成纳米颗粒的理论研究

理论上提出了利用离散电子态来计算绝缘体中金属纳米颗粒Fermi能级的方法,给出了金属纳米颗粒的能级结构,并得到了依据金属纳米颗粒等离子体共振峰计算金属纳米颗粒尺寸的新公式.该理论可解释相关现象,通过实验初步验证了该理论的正确性. 关键词： 离子注入 金属纳米颗粒 绝缘体 Fermi能级     

Third-order nonlinear optical properties of multiwalled carbon nanotubes modified by CdS nanoparticles

CdS nanoparticles were coated on the side wall of multiwalled carbon nanotubes (MWCNTs) by a wet chemical synthesis approach via noncovalent functionalization of MWCNTs with poly(diallyldimethylammonium chloride) (PDDA). The as-prepared material was characterized by X-ray diffraction (XRD), UV–vis absorption, fluorescence and transmission electron microscopy (TEM). The results indicated that CdS nanoparticles were uniformly coated on the surface of MWCNTs. Third-order optical nonlinearity of the as-prepared material was studied with the Z-scan technique with picosecond laser pulses at 532 nm. The Z-scan curve revealed that CdS nanoparticle-modified MWCNTs exhibited negative nonlinear refraction index and positive absorption coefficient. The real part and imaginary part of the third-order nonlinear susceptibility χ⁽³⁾ were calculated to be −4.9 × 10⁻¹² and 6.8 × 10⁻¹³ esu, respectively.