RESUMEN
This paper demonstrates replication of ultrafast laser-induced micro/nano surface textures on poly(dimethylsiloxane) (PDMS). The surface texture replication process reduces the processing steps for microtexturing while improving light trapping. Two methods are demonstrated to replicate surface microtexture, a simple mold method and an embossing method. The laser microtextured silicon and titanium surfaces with micro to nanoscale features have been successfully replicated. Optical characterization of the replicated microtextured PDMS surfaces is performed and the results agree with model predictions. The replicated microtextured PDMS film is applied on a silicon surface and optical characterization shows that surface reflectance can be suppressed over 55% compared to the control value.
RESUMEN
A low-cost pulsed N(2)-laser has been used to successfully demonstrate the formation of self-organized conical microtexture in Si. The process is demonstrated in vacuum environment to avoid the use of SF(6) gas and sulfur incorporation. The microtexture is formed with an average structure height of ~15 um, base diameter ~10 µm, and tip-to-tip separation ~8 µm. Energy dispersive x-ray spectroscopy of individual conelike structure shows that the material remains free from impurity incorporation. We have shown that the laser-induced-damage-related absorption can be successfully restored after an hour annealing at 1000 °C, making the material an ideal candidate for photovoltaic and other photonic applications.
RESUMEN
A femtosecond-laser-textured Si photodetector is reported. Broadband spectral optical response is detected from UV to NIR. A quantum efficiency of greater than 80% from 490 nm to 780 nm has been achieved. The quantum efficiency at 245 nm is 62%, which is comparable to UV-enhanced Si photodiodes. The bandwidth of a 250-µm-diameter device is 60 MHz.
RESUMEN
We report a phenomenon of spontaneous formation of self-organized 2D periodic arrays of nanostructures (protrusions) by directly exposing a silicon surface to multiple nanosecond laser pulses. These self-organized 2D periodic nanostructures are produced toward the edge as an annular region around the circular laser spot. The heights of these nanostructures are around 500 nm with tip diameter ~100 nm. The period of the nanostructures is about 1064 nm, the wavelength of the incident radiation. In the central region of the laser spot, nanostructures are destroyed because of the higher laser intensity (due to the Gaussian shape of the laser beam) and accumulation of large number of laser pulses. Optical diffraction from these nanostructures indicates a threefold symmetry, which is in accordance with the observed morphological symmetries of these nanostructures.
RESUMEN
The most successful metal implant materials currently have relatively smooth surfaces on the micron size scale, with most failures occurring after only 10 years. To move beyond this limiting time scale, texturing methods have been developed to modify the metal surface to enhance integration of the implant directly with surrounding bone. A flexible single-step ultrafast-laser texturing process has been developed that results in a surface texture that exhibits micron scale peaks and troughs with superimposed submicron and nano-scale features. The textured titanium samples remain completely hydrophilic with no measurable contact angle even after several weeks in normal atmosphere. An increase in mesenchymal stem cell number is observed over that on an untreated control titanium surface. Extensive formation of cellular bridges by stromal cells between pillars shows the favorable response of differentiated cells to the surface and the promotion of their attachment. Expression of the alkaline phosphatase and osteocalcin genes in human bone marrow cells were seen to increase on the textured surface. The development of this single-step method for creating micron, submicron, and nano-scale surface texture directly on metals makes a significant contribution to the goal of improving the integration and life span of joint replacement implants.