Femtosecond (fs) laser pulses focused and confined inside the bulk of a material can deposit a volume energy density up to several MJ/cm3 in a sub-micron volume. This creates highly non-equilibrium, hot, dense and short-lived plasmas with conditions favorable for arrangement of atoms into unusual material phases. Singlecrystal silicon was exposed to strong shock waves induced by laser micro-explosion in confined geometry. The conditions of confinement were realized by focusing 170-fs pulses, with the energy up to 2.5 μJ, on a Si surface buried under a 10-μm thick SiO2-layer formed by oxidation of a Si-wafer. The generated intensity was 1015 W/cm2, well above the threshold for optical breakdown and plasma formation. The shock wave modified areas of the Si crystal were sectioned using a focused-ion beam and characterized with scanning electron microscopy. A void surrounded by a shock-wave-modified Si was observed at the Si/SiO2 boundary. The results demonstrate that confined micro-explosion opens up new perspectives for studies of high-pressure materials at the laboratory table-top expanding the laser-induced micro-explosion capabilities into the domain of non-transparent materials.
The development of organic electronic requires a non contact digital printing process. The European funded e-LIFT project investigated the possibility of using the Laser Induced Forward Transfer (LIFT) technique to address this field of applications. This process has been optimized for the deposition of functional organic and inorganic materials in liquid and solid phase, and a set of polymer dynamic release layer (DRL) has been developed to allow a safe transfer of a large range of thin films. Then, some specific applications related to the development of heterogeneous integration in organic electronics have been addressed. We demonstrated the ability of LIFT process to print thin film of organic semiconductor and to realize Organic Thin Film Transistors (OTFT) with mobilities as high as 4 10-2 cm2.V-1.s-1 and Ion/Ioff ratio of 2.8 105. Polymer Light Emitting Diodes (PLED) have been laser printed by transferring in a single step process a stack of thin films, leading to the fabrication of red, blue green PLEDs with luminance ranging from 145 cd.m-2 to 540 cd.m-2. Then, chemical sensors and biosensors have been fabricated by printing polymers and proteins on Surface Acoustic Wave (SAW) devices. The ability of LIFT to transfer several sensing elements on a same device with high resolution allows improving the selectivity of these sensors and biosensors. Gas sensors based on the deposition of semiconducting oxide (SnO2) and biosensors for the detection of herbicides relying on the printing of proteins have also been realized and their performances overcome those of commercial devices. At last, we successfully laser-printed thermoelectric materials and realized microgenerators for energy harvesting applications.
A comparative study of the ejection dynamic of organic materials by Laser-Induced Forward Transfer technique has
been performed using nanosecond and picosecond pulses for applications in plastic micro-electronics. The ejection of
organic materials has been carried out with various thicknesses and with and without a sacrificial metallic release layer
inserted between the substrate and the organic donor film. The advantage of this technique is to preserve organic layers
from being damaged by thermal and photochemical effects during the interaction. The dynamic of the process has been
investigated by shadowgraphic imaging during 1.5 μs after the laser irradiation, under atmospheric conditions. We have
determined the velocity of the transferred material and studied the influence of the metallic layer during the ejection
using a wide range of fluencies. The high directivity of the ejected material offers the possibilities of high spatial
resolution for the manufacture of micro-structures in non contact LIFT technique. The study of the influence of the
distance between the donor and acceptor substrates on the deposit functionality is discussed.