Senthil Theppakuttai

Marangoni effect in nanosphere-enhanced laser nanopatterning of silicon

We report a Marangoni effect in nanosphere-enhanced laser direct nanopatterning of silicon surface. A monolayer of nanosphere array was formed on the silicon substrate by self-assembly. A 248-nm excimer laser was used to irradiate the sample surface. Due to optical field enhancement between the nanosphere and the substrate, the silicon surface was locally melted. The molten material was redistributed due to surface tension forces, resulting in the formation of a nanodent array. The morphology of the nanodents changed from bowl-type to “Sombrero” with increase of laser intensity as a result of a Marangoni effect that arises due to the competition between a thermocapillary force and a chemicapillary force acting on the molten material.

Nanoscale surface modification of glass using a 1064 nm pulsed laser

We report a method to produce nanopatterns on borosilicate glass by a Nd:yttrium–aluminum–garnet laser (10 ns, 1064 nm), using silica nanospheres. Nonlinear absorption of the enhanced optical field between the spheres and glass sample is believed to be the primary reason for the creation of nanofeatures on the glass substrate. By shining the laser beam from the backside of the glass sample, the scattering effects are minimized and only the direct field enhancement due to the spheres is utilized for surface patterning. To confirm this, calculations based on the Mie scattering theory were performed, and the resulting intensity as a function of scattering angles are presented. The nanofeatures thus obtained by this method are 350 nm in diameter and the distance between them is around 640 nm, which is same as the size of spheres used.

Localized laser transmission bonding for microsystem fabrication and packaging

This paper reports a method using localized laser heating to bond silicon and glass wafers directly. A pulsed Nd:YAG laser (1064 nm, 12 ns) is transmitted through the glass wafer and absorbed by the silicon wafer. Bonding is realized when the glass wafer is in immediate contact with the silicon wafer. A continuous wave He-Ne laser (633 nm, 20 mW) is used for probing the transient melting and resolidification of the silicon surface upon pulsed laser heating. This transmission bonding process is conducted locally while the entire wafer is maintained at a low temperature, which is especially useful in fabricating or packaging temperature-sensitive materials or devices. The bonded areas are studied in detail using a scanning electron microscope (SEM) and a chemical analysis is done to understand the bonding mechanism. Numerical simulation is also carried out using the finite element method to predict the local temperature change of both the glass wafer and the silicon wafer during laser heating.

Submicron ripple formation on glass surface upon laser-nanosphere interaction

Submicron ripples have been observed on a borosilicate glass surface when irradiated by a nanosecond Nd: yttritium–aluminum–garnet laser (10 ns, 1064 nm), using silica nanospheres. The ripples thus obtained do not satisfy Rayleigh’s diffraction condition in that (a) the ripple spacing is different from the value predicted by the classical model, (b) the spacing is independent of the incident angle, and (c) the orientation is not always perpendicular to the laser polarization. Also, the ripple characteristics are not dependent on the diameter of the spheres used and the ripples have almost the same periodicity irrespective of the experimental parameters. Photoionization followed by a self-organization process due to nonlinear absorption of the enhanced optical field between the spheres and glass sample is believed to be the primary reason for the creation of ripples on the glass substrate.

Analytical and Experimental Investigation of Laser-Microsphere Interaction for Nanoscale Surface Modification

An investigation on the features created on a silicon substrate by the irradiation of nanospheres on the substrate surface with a pulsed laser is presented. Silica nanospheres of diameter on the order of laser wavelength are deposited on silicon substrate and irradiated with a pulsed Nd: YAG laser. As a result, nanofeatures are created on the surface by the melting and resolidification of silicon. The experiment is repeated for different laser wavelengths (532 nm, and 355 nm), sphere diameters (640 nm, and 1.76 μm) and laser energies, and the effect of each of these parameters on the features created are studied. An analytical model based on Mie Theory complements the results. The model includes all evanescent terms and does not rely on either far field or size-parameter approximations. The predicted intensity distributions on the substrate indicate a strong near field enhancement confined to a very small area (nanometer scale). The results correlate well with the feature geometries obtained in the experiment.Copyright

Direct, parallel nanopatterning of silicon carbide by laser nanosphere lithography

A technique to create nanopatterns on hard-to-machine bulk silicon carbide (SiC) with a laser beam is presented. A monolayer of silica (SiO 2 ) spheres of 1.76-µm and 640-nm diameter are deposited on the SiC substrate and then irradiated with an Nd:YAG laser of 355 and 532 nm. The principle of optical near-field enhancement between the spheres and substrate when irradiated by a laser beam is used for obtaining the nanofeatures. The features are then characterized using a scanning electron microscope and an atomic force microscope. The diameter of the features thus obtained is around 150 to 450 nm and the depths vary from 70 to 220 nm.

Experimental Investigation and Numerical Simulation of Glass-Silicon Bonding by Localized Laser Heating

In this paper, we report a method to bond silicon and glass wafers directly using localized laser heating (pulsed Nd:YAG laser, 1064 nm, 12 ns). Laser energy was transmitted through the glass wafer and absorbed by the silicon wafer, resulting in a localized high temperature area. Pressure was applied upon the silicon and glass wafers to ensure immediate contact and good heat conduction between them. Scanning electron microscope (SEM) and chemical analysis were used to study bonding area and bonding mechanism. Numerical simulation was carried out in parallel using finite element method to predict the local temperature change of both the glass wafer and the silicon wafer during laser heating. The simulation was validated to some extent by the matching of melting time, which was obtained by using an additional probing laser (He-Ne, 633 nm, 20 mW) during the transient melting and re-solidification of the silicon. This bonding process is conducted locally while the entire wafer is maintained at room temperature, making it advantageous over traditional anodic bonding or fusion bonding.© 2003 ASME

Excitation of Surface Plasmons with Gold Microspheres

** † ‡ A pulsed laser is used to produce surface plasmon excitation in a monolaye r of gold (Au) spheres to nanopattern a silicon substrate. An electrodynamic model accompanies the experimental data, based on the numerical solution to the complete Maxwells equations including near - and far -field effects and reflection from the substrat e. The Drude -employed finite difference time domain method describes the deformation and enhancement of the laser pulse around the boundary of a Au sphere and the resulting intensity distribution incident upon the substrate . The effect of incident laser a ngle on plasmon generation and lithographic potential is studied.

Direct-patterning of silicon carbide by nanosphere-assisted pulsed laser

Optical near-field enhancement obtained between the spheres and substrate by irradiating with laser beam can be used for nano-patterning the hard-to-machine bulk silicon carbide (SiC). For this study a monolayer of silica (SiO2) spheres of 1.76 µm and 640 nm diameter are deposited on the SiC substrate and then irradiated with an Nd:YAG laser of wavelength 355 nm and 532 nm. Scanning electron microscope and atomic force microscope are used to characterize the features. It was found that the features obtained were having diameters around 150 to 450 nm and the depths varying from 70 to 220 nm.Optical near-field enhancement obtained between the spheres and substrate by irradiating with laser beam can be used for nano-patterning the hard-to-machine bulk silicon carbide (SiC). For this study a monolayer of silica (SiO2) spheres of 1.76 µm and 640 nm diameter are deposited on the SiC substrate and then irradiated with an Nd:YAG laser of wavelength 355 nm and 532 nm. Scanning electron microscope and atomic force microscope are used to characterize the features. It was found that the features obtained were having diameters around 150 to 450 nm and the depths varying from 70 to 220 nm.

Nanosphere-Assisted Direct-Patterning of Silicon Carbide by a Nanosecond Pulsed Laser

A strategy wherein the optical near-field enhancement between the spheres and substrate obtained by irradiating with laser beam is used for nano-patterning the hard-to-machine bulk silicon carbide (SiC). For this study a monolayer of silica (SiO2 ) spheres of 1.76 μm and 640 nm diameter are deposited on the SiC substrate and then irradiated with an Nd:YAG laser of wavelength 355 nm and 532 nm. Scanning electron microscope and atomic force microscope are used to characterize the features. It was found that the features obtained were having diameters around 150 to 450 nm and the depths varying from 70 to 220 nm.Copyright