Dynamics of fast pattern formation in porous silicon by laser interference

Abstract

Patterns are fabricated on 290 nm thick nanostructured porous silicon layers by phase-mask laser interference using single pulses of an excimer laser (193 nm, 20 ns pulse duration). The dynamics of pattern formation is studied by measuring in real time the intensity of the diffraction orders 0 and 1 at 633 nm. The results show that a transient pattern is formed upon melting at intensity maxima sites within a time <30 ns leading to a permanent pattern in a time <100 ns upon solidification at these sites. This fast process is compared to the longer one (>1 μs) upon melting induced by homogeneous beam exposure and related to the different scenario for releasing the heat from hot regions. The diffraction efficiency of the pattern is finally controlled by a combination of laser fluence and initial thickness of the nanostructured porous silicon layer and the present results open perspectives on heat release management upon laser exposure as well as have potential for alternative routes for switching applications.

Dynamics of laser induced metal nanoparticle and pattern formation

“…It becomes clear that T1(t) starts at the same time as T0(t) starts decreasing, i.e., upon melting of the film. This result suggests that a transient pattern due to the alternation of liquid/solid metal as reported earlier for porous silicon 17 has most likely been formed at this very early stage. Once aggregation/coalescence starts (minimum of T0(t)), T1(t) mirrors T0(t), i.e., it increases fast until it undergoes a change of slope at approximately the same time than T0 and needs a time >1 ls to reach the final level.…”

“…Further details can be found elsewhere. 17 A He-Ne laser beam pulsed to %1 ls by means of an acousto-optic modulator and focused at the irradiated area at a) rpelaez@io.cfmac.csic.es 0003-6951/2015/106(6)/061914/5/$30.00 V C 2015 AIP Publishing LLC 106, 061914-1 %33 off its normal was synchronized with the irradiation laser pulse in order to record in real time and simultaneously the reflectivity and transmission of the sample upon homogeneous beam exposure. The signals are collected by two fast photodiodes and recorded with a two-channel fast oscilloscope that is triggered by the signal provided by a photodiode collecting a small fraction of the pump beam thus defining the origin of the time scale (it is %3 ns earlier than the time at which the pump pulse reaches its maximum at the most).…”

“…The application of this type of measurements to study the dynamics of pattern formation has only very recently applied to patterns produced in porous silicon. 17 Figure 4(a) shows the transients recorded in the 5.9 nm thick sample and while the vertical scale for the signal in order 0 (T0(t)) corresponds to the intensity normalized to the initial, that in order 1 (T1(t)) is the intensity recorded in mV since initial value is cero. The vertical scales have been chosen in order to overlap both final and initial levels, the former been indicated by a single horizontal line.…”

“…Further details can be found elsewhere. 17 A He-Ne laser beam pulsed to %1 ls by means of an acousto-optic modulator and focused at the irradiated area at a)…”

Real‐Time 3D Visualization of the Formation of Micrograting Structures Upon Direct Laser Interference Patterning of Ge

“…This technique has been applied to the study of the formation of periodic topography patterns in porous silicon films and bulk silicon upon DLIP. [22,23] In the present work, we further develop this technique to the study of the formation dynamics of complex topography patterns in crystalline Ge, yielding quantitative real-time 3D visualization of the formation of grating structures with submicron feature sizes. The results obtained reveal the nature and quantify the dynamics of the underlying mechanisms responsible for the structure formation.…”