Phase transformations of 100nm Ge1Sb4Te7 films induced by single 130fs pulse at 800nm have been investigated with time-resolved microscope. With an average fluence of 30mJ/cm2, a reflective intensity increase was observed within 1ps in 100nm as-deposited Ge1Sb4Te7 films after excitation by intense femtosecond pulse, which was consistent to an electronically induced non-thermal phase transformation. XRD measurement confirmed that single femtosecond pulse could induce crystalline marks in 100nm as-deposited Ge1Sb4Te7 films. Our results indicated that single femtosecond pulse could trigger both crystalline and amorphous phase in 100nm Ge1Sb4Te7 films. The fluence for crystallization was higher than that for amorphization.
A method for surface metallization on transparent substrate with laser induced plasma deposition was described. A laser beam goes through the transparent substrate first and then irradiates on a metal target behind. For laser fluence above ablation threshold for the target, the generated plasma flies forward at a high speed to the substrate and induces metal materials deposition on its rear side surface and even doping into the substrate. The diffusion distribution of metallic particles was measured with Time of Flight Secondary Ion Mass Spectrometer (TOF-SIMS). Electrically conducting films are formed on the substrate with laser beam scanning. The near 1Ω/Square lower resistivity can be formed with precise control of the processing parameters. Laser fluence, pulse repetition rate and scanning speed, distance between the substrate and metal target and overlapping of the metal lines. This technology can be used to form electrodes, resistors, LCD or electronic circuits on the transparent substrates.
Laser assisted nanofabrication for surface nanopatterning is investigated. To overcome the limitation of light wavelength, pulsed lasers were applied to combine with atomic force microscope (AFM) and nanoparticle self-assembled mask to achieve sub-30 nm patterning on the metallic surfaces. The mechanisms of the formation of nanostructure patterns are discussed. Progress on numerical simulation and physical modeling of laser assisted nanofabrication has been demonstrated. The method of AFM tip or particle enhanced laser irradiation allows the study of field enhancement effects as well as its potential applications for nanolithography.
The feasibility of multilayered optical data storage is examined in glass, quartz, polycarbonate and a rhodamine B and Au (III) doped PMMA medium by using a focused 800 nm, 100-fs pulsed laser. Refractive-index or fluorescent data patterns are recorded by use of an objective to focus laser pulses inside these transparent medium. The laser pulse produces a submicrometer-diameter structurally altered region in the material. For glass, quartz and polycarbonate materials, we record binary information by writing such bits in multiple planes and read it out with a microscope. We demonstrate data storage and retrieval with 0.6-μm in-plane bit spacing and 10-μm interplane spacing (100 Gbits/cm3). Scanning electron microscopy (SEM) are used to characterize structural changes in these materials. For the rhodamine B and Au (III) doped PMMA medium, fluorescent spectra are measured before and after laser treatment. Writing three-dimensional data bit inside the transparent medium based on a multi-photon absorption process is expected to become a useful method used to fabricate optical memory with both an ultra-high storage density and an ultra-high storage density and an ultra-high recording speed.
Laser directly writing of nanostructures on metal film surfaces with optical near field effects has been investigated. Spherical silica particles (500-1000 nm) were placed on metal films. After laser illumination with a pulsed ultraviolet laser, naoholes were obtained at the original position of the particles. The mechanism of the formation of nanostructure pattern was investigated and found to be the near-field optical resonance effect induced by particles on the surface. The size of the nanohole has been studied as a function of laser fluence and silica particle size. A comparison with relative theoretical calculations of near-field light intensity distribution showed good agreement with the experiment results. The method of particle enhanced laser irradiation allows the study of field enhancement effects as well as its potential applications for nanolithography.
For 10 previous years dry laser cleaning has been analyzed in the frame of 1D model with homogeneous surface heating. This model gave qualitative description of the process and was sufficient for initial studies. Nevertheless further examinations show that 1D model is in one-two order magnitudes discrepancy with experiment. The problem is that the particle on the surface produces non-homogeneous distribution of laser intensity. For example, a small transparent particle can work as a near-field lens. This produces nonstationary 3D distribution of temperature and nonstationary 3D thermal deformations of the surface. 3D model is qualitatively different from the 1D model (the latest does not permit the inward motion of the surface). In some region of parameters 3D model predicts a result close to the experimental one (for small particles, typically smaller than 1 micrometers ). With higher particle size intensity under the surface becomes so strong that the particle is removed by the flux of evaporated material.
Laser microprocessing has been extensively studies with applications in microelectronics, data storage and photonics. In addition to the fundamental aspects of laser materials interactions, we have investigated various applications of laser microprocessing in different areas. Laser cleaning has been studies systematically both theoretically and experimentally for dry surface cleaning and steam surface cleaning. This technology has been applied for cleaning magnetic head, magnetic sliders, suspension, laser mold cleaning and laser deflash for IC packages. Laser texturing and related processes such as laser bumping, laser tagging have been studied for magnetic recording applications. The other laser works include real-time monitoring of laser surface processing, laser-induced controllable periodic structures, laser nanopatterning by scanning probe microscope tip-enhanced laser irradiation. The further prospects of using laser microprocessing for applications in formation of ultrashallow (less than 50 nm) pn junction for next-generation MOS devices, laser generation of Si nanoparticles for quantum-dot flash memory and light emission devices are addressed.
Diamond-like polymer, poly(phenylcarbyne), films were irradiated by pulsed UV laser ((lambda) equals 248 nm) at an atmospheric pressure of nitrogen. The morphologies of the resulting samples were examined by scanning electron microscopy (SEM). The structures of the resulting films were investigated by Raman spectra and X-ray diffraction (XRD). The electron field emission properties of the films were investigated. The results indicate that the polymer is converted into nano-particle carbon films by pulsed laser irradiation. The converted carbon film shows good field emission properties, such as low turn-on threshold emission field, high emission current density and high emission light spot density. Field emission images from the converted carbon films have been demonstrated. The mechanisms of both carbon cluster conversion from the polymer and field emission of the converted carbon film have been discussed.
The phenylcarbyne polymer possesses a diamond-like structure. Because of its special structure, this polymer can be converted into diamond-like carbon phases at atmospheric pressure by thennal decomposition. In this article, we report on the growth of hydrogenated amoiphous carbon films (a-C:H) films by pulsed laser (KrF excimer, λ =248 mn) ablation of a phenylcarbyne polymer target under vacuum. a-C:H films were deposited with various laser fluences and at different
substrate temperatures. Chemical and siructural characteristics of these films were analysed using X-ray-excited Auger electron spectroscopy (XAES), photoelectron loss spectroscopy (PELS), and Ranian speciroscopy. It was found that the fourfold-coordinated component increases with laser fluence at 80°C or increases with temperature increasing from 25°C to 60°C at a fluence of 1 x 1O9cm2. When the deposition temperature is increased from 60°C to 200°C at a fluence of 1 x 109 W/cm2, the graphitic component increases. The variation in chemical structures of these films is explained in terms of the changes in the fraction of sp2-bonded clusters and changes in the termination of the gmphitic clusters and sp3-bonded
networks by hydrogen in the a-C:H films.