S.M. Huang

Pulsed laser-assisted surface structuring with optical near-field enhanced effects

The effects of optical resonance and near field in the interaction of transparent particles on a substrate with laser light have been examined experimentally and theoretically. It is found that pits can be created at the contacting point between the particle and the metallic surface by laser irradiation (KrF,λ=248 nm) with a single pulse. The influence of the particle size and the laser fluence on the structuring of the surface has been investigated. The size of the particle ranges from 1.0 μm to 140 nm in diameter. The morphologies of the holes created have been characterized by an atomic force microscope and a scanning electron microscope. For constant laser fluence, the created hole is sensitive to the particle size. For higher-laser fluence, the corresponding hole becomes larger and deeper. With a low fluence of 300 mJ/cm2 and for 140 nm particles, the lateral dimensions of created pits can be down to 30 nm. With a high fluence of 750 mJ/cm2 and 1.0 μm particles, the diameter and the depth of created ...

Pulsed-laser assisted nanopatterning of metallic layers combined with atomic force microscopy

In this study, the nanostructure fabrication on metallic surfaces using a pulsed laser in combination with an AFM is reported. Nanopatterns such as pit and multilines were created. Dependence of pit apparent depth on the laser fluence and laser pulse numbers has been investigated. Chemical components of the modified features were analyzed by Auger electron spectroscopy ~AES!. The morphologies of created features were characterized by AFM and scanning electron microscope ~SEM!. Thermal expansion of the tip, the field enhancement underneath the tip and the sample heating were estimated. Experimental results and mechanisms of nanostructure formation are discussed. We hope that our experiments will contribute further to the study of mechanisms of the photoassisted nanoprocessing.

Raman spectroscopy of phenylcarbyne polymer films under pulsed green laser irradiation

The polycarbyne polymer films were coated on silicon substrates and then irradiated by a pulsed Nd:yttrium–aluminum–garnet laser (λ=532 nm) with various fluences in argon gas atmosphere. Significant changes in microstructures and chemical bonding (sp3/sp2) during laser treatment were investigated by Raman spectroscopy. At a laser fluence below 50 mJ/cm2, the Raman spectrum of the film was similar to that of the original polymer film. In a fluence range from 100 to 650 mJ/cm2, the thermal decomposition of the polymer occurred, resulting in upshift of G peak and downshift of the D peak both with narrower peak width. With increasing laser fluence from 650 to 950 mJ/cm2, both the G and D peaks downshifted simultaneously due to the thermal decomposition. The simultaneous downshift of both peaks indicated the increased sp3/sp2 ratio in the carbon film converted from the polymer. With increasing laser fluence in this range, the thermal decomposition also induced the narrowing of both peaks. The narrowing of both...

Ultraviolet and visible Raman spectroscopy characterization of chemical vapor deposition diamond films

Abstract Polycrystalline diamond films with different grain sizes (10 nm, 100 nm and 5 μm) were prepared by hot-filament chemical vapor deposition (HFCVD). The diamond films have been studied using ultraviolet (UV, 244 nm), visible (Vis, 514 nm) and (Vis, 633 nm), near-infrared, micro-Raman scattering. The fluorescence in the excited diamond film is found to change considerably with the incident photon energy. The scattering intensity of amorphous sp 2 -bonded carbon compared to the strength of the 1331 cm −1 Raman line from sp 3 -bonded diamond is found to vary considerably as functions of the grain size of diamond film and the incident photon energy. Possible models for the structures of amorphous sp 2 -bonded carbon and sp 3 -bonded diamond phases are discussed on the basis of the present Raman data. It is shown that UV Raman spectroscopy has provided significantly greater information than visible Raman spectroscopy in characterizing diamond phases.

Conversion of diamond clusters from a polymer by Nd:YAG pulsed laser (532 nm) irradiation

Abstract The phenylcarbyne polymer possesses a diamond-like structure. It is soluble in organic solvents and can easily form thin films on various substrates. Because of its special structure, this polymer can be converted into diamond-like carbon phases at atmospheric pressure by thermal decomposition. Here, we report on the growth of diamond films at room temperature by pulsed laser irradiation (Nd-YAG laser, 532 nm) of a polymer precursor in an argon atmosphere. The structures of films were investigated using Raman spectroscopy, which confirms the conversion of this polymer to diamond by the presence of a diamond characteristic peak at 1330 cm−1. The morphologies of the resulting samples were examined by scanning electron microscopy (SEM). The mechanism of diamond phase conversion from the polymer is discussed. It is proposed that the conversion to diamond phases may be related to the special diamond-like structure of the polymer, with the laser providing an efficient thermal source. The advantages of this method are simplicity, ease of operation, high efficiency, low-temperature deposition, low cost, and suitability to various substrates.

Electron field emission from polymer films treated by a pulsed ultraviolet laser

The poly(phenylcarbyne) polymer films were coated on silicon substrates and then irradiated by a pulsed ultraviolet laser (λ=248 nm) with various fluences (1–60 mJ/cm2) at an atmospheric pressure of nitrogen. The structures of the resulted films were investigated by Raman spectroscopy. The morphologies of the films were examined by scanning electron microscopy (SEM). The electron field emission properties of the films as cathodes were studied. Raman spectrum analysis and SEM results indicate that the polymer film is converted to nanoparticle carbon film with the laser fluence from 10 to 60 mJ/cm2. The conversion mechanism from the polymer to nanoparticle carbon and electron field emission mechanism from the converted carbon film is discussed. The converted carbon film showed better field emission properties, i.e., lower turn-on threshold emission field, higher emission current density, and higher emission light spot density with increasing laser fluence from 10 to 50 mJ/cm2. By increasing the laser fluenc...

OPTICAL RESONANCE AND NEAR-FIELD EFFECTS IN DRY LASER CLEANING

Optical problems, related to the particle on the surface, i.e. optical resonance and near-field effects in laser cleaning are discussed. It is shown that the small transparent particle with size by the order of the wavelength may work as a lens in the near-field region. This permits to focus laser radiation into the area with the sizes, smaller than the radiation wavelength. It leads to 3D effects in surface heating and thermal deformation, which influences the mechanisms of the particle removal.

Sub-50 nm nanopatterning of metallic layers by green pulsed laser combined with atomic force microscopy

Pulsed-laser assisted nanopatterning of metallic layers on silicon substrates under an atomic force microscope (AFM) tip has been investigated. A 532 nm Nd:YAG pulsed laser with a pulse duration of 7 ns was used. Boron doped silicon tips were used in contact mode. This technique enables the processing of structures with a lateral resolution down to 10 nm on gold and copper layers. Nanopatterns such as pit array and multilines with lateral dimensions between 10 and 50 nm and depths between 2.5 and 21 nm have been created. The experimental results and mechanism of the nanostructure formation are discussed. The created features were characterized by AFM, scanning electron microscope, and Auger electron spectroscopy. The apparent depth of the created pit has been studied as a function of laser intensity or laser pulse numbers. The dependence of nanoprocessing on the geometry parameters of the tip and on the optical and thermal properties of the processed sample has also been investigated. Thermal expansion of...

Laser-assisted nanofabrications on metal surfaces with optical near-field effects

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.

Unique Functional Micro/nano-structures Created by Femtosecond Laser Irradiation

Femtosecond (fs) laser application in three-dimensional (3D) optical recording is introduced. The laser irradiation on transparent glass and polymer matrix doped with fluorescent material is carried out, which changes the physical or chemical properties of the recording media and records information bits. With the change of the focusing positions inside the transparent substrates, 3D optical recording can be available for ultrahigh capacity data storage. Feasibility on fs laser drilling of poly-caprolactone (PCL) thin films for tissue engineering is investigated. It is found that precisely defined micro-hole arrays can be formed on the sample surfaces. Hydrophilic property of the processed samples is much improved, which provides good conditions for tissue cells to anchor on the man-made skin. Fs laser applications to form nanostructures on substrate surfaces are studied. Fs laser combination with near-field scanning optical microscopy (NSOM) to induce surface property modification in the sub 50-nm under NSOM tip and nanoparticles is also discussed.