Fabrication of superhydrophilic or superhydrophobic self-cleaning metal surfaces using picosecond laser pulses and chemical fluorination

Bioinspired superhydrophilic/phobic self-cleaning surfaces have recently drawn a lot of interest in both fundamental and applied research. A hybrid method to produce the self-cleaning property of micro/nanostructured surface using ultra-fast laser pulses followed by chemical fluorination is proposed. The typical micro/nanocomposite structures that form from microporous arrays and microgroove groups have been processed by picosecond laser on titanium alloy surface. The surface hydrophilic/phobic and self-cleaning properties of micro/nanostructures before and after fluorination with fluoroalkyl-silane were investigated using surface contact angle measurements. The results indicate that surface properties change from hydrophilic to hydrophobic after fluorination, and the micro/nanostructured surface with increased roughness contributes to the improvement of surface hydrophobicity. The micro/nanomodification can make the original hydrophilic titanium alloy surface more hydrophilic or superhydrophilic. It also can make an originally hydrophobic fluorinated titanium alloy surface more hydrophobic or superhydrophobic. The produced micro/nanostructured titanium alloy surfaces show excellent self-cleaning properties regardless of the fluorination treatment, although the fluorinated surfaces have slightly better self-cleaning properties. It is found that surface treatment using ultra-fast laser pulses and subsequent chemical fluorination is an effective way to manipulate surface wettability and obtain self-cleaning properties.     

高功率激光宽光谱减反膜的溶胶-凝胶旋转法制备工艺

 采用溶胶-凝胶法用旋转镀膜工艺在K9玻璃基片上制备出了SiO₂和有机硅单层减反膜以及有机硅-SiO₂双层减反膜。考察了旋转速度对SiO₂和有机硅单层膜的中心透射波长、膜层折射率等基本光学性质的影响，实验确定了双层膜的涂敷工艺。透射光谱测量表明，采用本文工艺条件制备的有机硅 SiO₂双层膜在430～800nm范围内透射率达99％以上。     

Heating of opaque surfaces by picosecond laser pulses

Received: 5 June 1997/Accepted: 13 June 1997     

高功率激光宽光谱减反膜的溶胶-凝胶旋转法制备工艺

采用溶胶-凝胶法用旋转镀膜工艺在K9玻璃基片上制备出了SiO2和有机硅单层减反膜以及有机硅-SiO2双层减反膜。考察了旋转速度对SiO2和有机硅单层膜的中心透射波长、膜层折射率等基本光学性质的影响,实验确定了双层膜的涂敷工艺。透射光谱测量表明,采用本文工艺条件制备的有机硅 SiO2双层膜在430～800nm范围内透射率达99％以上。     

Formation of antireflective surface structures on diamond films by laser patterning

Received: 29 September 1998/Accepted: 1 October 1998     

Preparation of broadband antireflective coating by sol-gel method

A sol-gel method for the preparation of silica coating that varied in refractive index is developed. Silicon dioxide sol is obtained by hydrolysis and co-condensation reactions occurred in acid-catalyzed system. Surface morphology, refractive index, and transmission spectrum of the samples are studied. The results of transmission spectra of single-sided coatings show that the average transmittance of the samples increases about 4% compared with the uncoated one in the spectra range from 400 to 1 200 nm in the case of vertical incidence. For the double-sided coating the maximum transmittance is 99% at the wavelength of 840 nm.     

Soft picosecond X-ray laser nanomodification of gold and aluminum surfaces

Experimental and theoretical investigations of aluminum (Al) and gold (Au) surface modification by soft X-ray laser pulse are presented. Well-polished samples of Al and Au are irradiated by ps-duration pulse with wavelength of 13.9 nm at the energy range of 24–72 nJ. Differences in the melting and the ablation processes for those materials are observed. It is shown that at low laser pulse energy, the nanoscale ripples on the surface may be induced by melting without following ablation. In that case, the nanoscale changes in the surface are caused by splash of molten metal under gradient of fluence. At higher laser pulse energy, the ablation process occurs and craters are formed on the surface. However, the melting determines the size of the modified surface at all ranges of the laser energies. For interpretation of experimental results, the atomistic simulations of melting and ablation processes in Al and Au are provided. The calculated threshold fluencies for melting and ablation are well consistent with measured ones.     

Fabrication of submicron structures by three-dimensional laser lithography

As a demonstration of unique capabilities of three-dimensional laser lithography, an example complex-shape microobject and photonic crystals with “woodpile” structure for the infrared spectral range are fabricated by this technique. Photonic dispersion relations for the woodpile structure are calculated for different values of the permittivity contrast and the filling factor.     

Fabrication of large-scale ultra-smooth metal surfaces by a replica technique

The IR double-resonance techniques IR/R2PI (infrared/resonant 2-photon ionization), IR/PIRI (infrared-photo-induced Rydberg ionization) and IR-photodissociation spectroscopy are valuable tools to investigate structure, vibrations, and dynamical processes of neutral and ionic hydrogen-bonded clusters containing aromatic molecules. In this paper we report on the application of the IR double-resonance techniques to determine the NH and OH stretching vibrations of 4-aminophenol and 4-aminophenol(H₂O)₁, both in the neutral (S₀) and ionic (D₀) ground state. All vibrational frequencies obtained for 4-aminophenol and the cluster are compared with the values obtained from ab initio and DFT calculations. In the S₀ state, a trans-linear arrangement of 4-aminophenol(H₂O)₁ is obtained containing an O-H·· O hydrogen bond. In the D₀ state an overlay of two spectra can be observed resulting from the trans-linear structure and a second structure which contains a N-H·· O hydrogen bond. The observation of these two structures within the ion is an interesting example of a rearrangement reaction in the ionic state. Received: 3 November 2000 / Accepted: 6 November 2000 / Published online: 9 February 2001     

Electronic excitations by chemical reactions on metal surfaces

Dissipation of chemical energy released in exothermic reactions at metal surfaces may happen adiabatically by creation of phonons or non-adiabatically by excitation of the electronic system of the metal or the reactants. In the past decades, the only direct experimental evidence for such non-adiabatic reactions has been exoelectron emission into vacuum and surface chemiluminescence which are observed in a special class of very exothermic reactions. The creation of e–h pairs in the metal has been discussed in many theoretical models but it was only recently that a novel experimental approach using Schottky diodes with ultrathin metal films makes direct measurement of reaction-induced hot electrons and holes possible. The chemical reaction creates hot charge carriers which travel ballistically from the metal film surface toward the Schottky interface and are detected as a chemicurrent in the diode. By now, such currents have been observed during adsorption of atomic hydrogen and deuterium on Ag, Cu and Fe surfaces as well as chemisorption of atomic and molecular oxygen, of NO and NO₂ molecules and of certain hydrocarbons on Ag. This paper reviews briefly exoelectron and chemiluminescence experiments and the concept of the Nørskov–Newns–Lundqvist model. The major part is devoted to the detection of chemically induced e–h pairs with thin metal film Si Schottky diodes by discussing the different influences on the chemicurrent magnitude and presenting experimental results predominantly with hydrogen and deuterium atoms. The experiments introduce a new method to investigate surface reaction kinetics and dynamics by use of an electronic device. In addition, the diodes may be used as selective reactive gas sensors.     

Fabrication of black multicrystalline silicon surface by nanosecond laser ablation

The optimal regimes for uniform texturing of a multicrystalline silicon (mc-Si) surface by pulsed laser radiation have been determined. The morphology and reflectance spectra of the texturized mc-Si have been studied. The laser-texturized mc-Si samples with reflectance of 2?C3% over a wide spectral region have been produced. The influence of subsequent chemical etching on the reflective properties of the texturized surface has been analyzed.     

Nanostructures fabricated on metal surfaces assisted by laser with optical near-field effects

Nanostructures on metal film surfaces have been written directly using a pulsed ultraviolet laser. The optical near-field effects of the laser were investigated. Spherical silica particles (500–1000 nm in diameter) were placed on metal films. After laser illumination with a single laser shot, nanoholes were obtained at the original position of the particles. The mechanism for the formation of the nanostructure patterns was investigated and found to be the near-field optical resonance effect induced by the particles on the surface. The size of the nanohole was studied as a function of laser fluence and silica particle size. The experimental results show a good agreement with those of the relevant theoretical calculations of the near-field light intensity distribution. The method of particle-enhanced laser irradiation allows the study of field enhancement effects as well as its potentialapplications for nanolithography. Received: 10 December 2002 / Accepted: 20 January 2003 / Published online: 28 May 2003 RID="*" ID="*"Corresponding author. Fax: +65-777/1349, E-mail: HUANG_Sumei@dsi.a-star.edu.sg     

Fabrication of grating structures by simultaneous multi-spot fs laser writing

Two-photon polymerisation is an established technique for the fabrication of three-dimensional microstructures. To date structures have mostly been developed using single beam serial writing. A novel approach to simultaneous multi-spot two-photon polymerisation, that uses a SiO₂ on glass Fraunhofer diffractive optical element to generate an array of beamlets, is described. A Ti:sapphire laser, with wavelength 790 nm, 80 MHz repetition rate, 100 fs pulse duration and an average power of 25 mW, was used to initiate two-photon polymerisation. The DOE, in combination with a high power microscope objective, efficiently transforms the laser beam into a linear array of four spots of equal intensity. The fabrication of a periodic transmission grating, using parallel processing with these four spots, is shown. The grating was written in a Zr-loaded resin prepared on a glass substrate using dip coating deposition of a Zr/PMMA hybrid prepared by the sol-gel method. The operation of the diffractive element and the performance of the diffraction grating are also discussed.     

Fabrication of large-area grating structures through laser ablation

A Grating-Interferometer setup is shown to be ideally suited for the fabrication of high quality periodic structures over large sample areas via laser ablation. Virtually perfect line structures with periods in the submicron range are easily obtained. The capabilities and limitations of the new setup are analyzed theoretically for nanosecond and femtosecond laser sources with different coherence properties. The theoretical predictions are verified experimentally for various sample materials.     

Femtosecond laser color marking of metal and semiconductor surfaces

Color marking of rough or smooth metal (Al, Cu, Ti) and semiconductor (Si) surfaces was realized via femtosecond laser fabrication of periodic surface nanorelief, representing one-dimensional diffraction gratings. Bright colors of the surface nanorelief, especially for longer electromagnetic wavelengths, were provided during marking through pre-determined variation of the laser incidence angle and the resulting change of the diffraction grating period. This coloration technique was demonstrated for the case of silicon and various metals to mark surfaces in any individual color with a controllable brightness level and almost without their accompanying chemical surface modification.     

Fabrication of 3D microfluidic structures inside glass by femtosecond laser micromachining

Femtosecond lasers have opened up new avenues in materials processing due to their unique characteristics of ultrashort pulse widths and extremely high peak intensities. One of the most important features of femtosecond laser processing is that a femtosecond laser beam can induce strong absorption in even transparent materials due to nonlinear multiphoton absorption. This makes it possible to directly create three-dimensional (3D) microfluidic structures in glass that are of great use for fabrication of biochips. For fabrication of the 3D microfluidic structures, two technical approaches are being attempted. One of them employs femtosecond laser-induced internal modification of glass followed by wet chemical etching using an acid solution (Femtosecond laser-assisted wet chemical etching), while the other one performs femtosecond laser 3D ablation of the glass in distilled water (liquid-assisted femtosecond laser drilling). This paper provides a review on these two techniques for fabrication of 3D micro and nanofluidic structures in glass based on our development and experimental results.     

Design of metamaterial surfaces with broadband absorbance

A simple design paradigm for making broadband ultrathin plasmonic absorbers is introduced. The absorber's unit cell is composed of subunits of various sizes, resulting in nearly 100% absorbance at multiple adjacent frequencies and high absorbance over a broad frequency range. A simple theoretical model for designing broadband absorbers is presented. It uses a single-resonance model to describe the optical response of each subunit and employs the series circuit model to predict the overall response. Validity of the circuit model relies on short propagation lengths of the surface plasmons.     

Fabrication of grating structures on silicon carbide by femtosecond laser irradiation and wet etching

A method for fabricating deep grating structures on a silicon carbide(SiC) surface by a femtosecond laser and chemical-selective etching is developed.Periodic lines corresponding to laser-induced structure change(LISC)are formed by femtosecond laser irradiation,and then the SiC material in the LISC zone is removed by a mixed solution of hydrofluoric acid and nitric acid to form grating grooves.Grating grooves with a high-aspect ratio of approximately 25 are obtained.To obtain a small grating period,femtosecond laser exposure through a phase mask was used to fabricate grating structures with a 1.07 μm period on the surface of the SiC.     

Observation of light propagation by holography with a picosecond pulsed laser

We demonstrate the propagation of a light pulse undergoing refraction and total refraction inside a glass block as well as diffraction at a grating. Observation of a frameless, continuous motion picture of the light propagation is possible by recording of hologram with a picosecond pulsed laser. It is shown that the direction of the pulse changes as a result of refraction, the pulse's speed decreases inside a glass block, and the pulse travels a zigzag path by total refraction. The pulse fronts of the diffracted light propagating parallel to the grating surface are also demonstrated.