Semiconductor and metal nanoparticles are known to possess excellent mechanical, electrical, and optical properties, but harnessing those novel properties for practical applications is impeded by the difficulty in depositing the nanoparticles into large two-dimensional thin films or three-dimensional structures. A new laser-assisted manufacturing process is developed for patterning and sintering nanoparticles to deposit semiconductor and conductor thin films. This technique has the ability to deposit various materials on rigid and flexible substrates such as paper and plastics for manufacturing flexible electronics.

Nanoscale patterns on rigid or flexible substrates are of considerable interest in modern nanophotonics and optoelectronics devices. Subwavelength structures are produced in this study by using a laser beam and microdroplets that carry nanoparticles to the deposition substrate. These droplets are generated from an aqueous suspension of nanoparticles by electrospray and dispensed through a conical hollow laser beam so that laser-droplet interactions occur immediately above the substrate surface. Each microdroplet serves the dual role as a nanoparticle carrier to the substrate and as a superlens for focusing the laser beam to a subwavelength diameter. This focused beam vaporizes the droplet and sinters the nanoparticles on the substrate. The deposition of subwavelength nanostructures and thin films on a silicon wafer are demonstrated in this paper. This process may be applied to produce novel nanophotonics and electronics devices involving a variety of subwavelength patterns including an ordered array of semiconductor nanoparticles.

Nanoelectrospray laser deposition (NELD) of nanoparticles (NPs) on various substrates has attracted considerable attention as a fast, cost-effective, and scalable technique for precise control of heating time and zone. In this work, NELD-assisted sintering of titanium dioxide (TiO2) NPs on borosilicate glass and quartz substrates is addressed. A 10.6μm CO2 laser was used for patterning and sintering titania nanoparticles in ambient air. The effects of laser dose and deposition process parameters on the morphological, structural, and optical characteristics of the sintered TiO2 patterns were characterized using optical microscopy, scanning electron microscopy, and x-ray diffraction. The results point out that the anatase phase was preserved after laser sintering, without the appearance of any TiO2 rutile traces. We show that the improvement in the morphological properties of TiO2 patterns is due to the laser sintering of a dense layer of ceramic with enhanced interconnectivity and connection between single nanoparticles. A theoretical model was developed to select the temperature required to sinter TiO2 nanoparticles and to correlate it with the laser power and scanning speed to prevent cracking on the substrate and sintered nanoparticles and also to get transparent TiO2 films. An optical transmittance of ∼91% was achieved. The experimental data were in accordance with the theoretical model, predicting the success of the model.

Annular laser beams provide a drilling mechanism that can be referred to as optical trepanning. In this paper an analytical two-dimensional model is developed for optical trepanning. The analysis accounts for conduction in the solid, vaporization, and convection due to the melt flow caused by an assist gas. Based on the model, the influences of pulse duration, laser-pulse length, pulse repetition rate, intensity profiles, and beam radius are investigated to examine their effects on the recast layer thickness, hole depth, and taper. Deeper cavity depth, thicker recast layer, and larger taper are obtained with the increase in the laser intensity. By using different types of intensity profiles, the nature of the hole taper can be modified, i.e., convergent or divergent holes can be produced. The effects of the inner radius of annular beams are more significant than other laser parameters. An increase in the inner radius reduces the hole taper and produces thinner recast layer and deeper cavity depth.