Alexandra Palla-Papavlu

Microfabrication of polystyrene microbead arrays by laser induced forward transfer

In this study we describe a simple method to fabricate microarrays of polystyrene microbeads (PS-μbeads) on Thermanox coverslip surfaces using laser induced forward transfer (LIFT). A triazene polymer layer which acts as a dynamic release layer and propels the closely packed microspheres on the receiving substrate was used for this approach. The deposited features were characterized by optical microscopy, scanning electron microscopy, atomic force microscopy, and Raman spectroscopy. Ultrasonication was used to test the adherence of the transferred beads. In addition, the laser ejection of the PS-μbead pixels was investigated by time resolved shadowgraphy. It was found that stable PS-μbeads micropatterns without any specific immobilization process could be realized by LIFT. These results highlight the increasing role of LIFT in the development of biomaterials, drug delivery, and tissue engineering.

Laser deposition and direct-writing of thermoelectric misfit cobaltite thin films

A two-step process combining pulsed laser deposition of calcium cobaltite thin films and a subsequent laser induced forward transfer as micro-pixel is demonstrated as a direct writing approach of micro-scale thin film structures for potential applications in thermoelectric micro-devices. To achieve the desired thermo-electric properties of the cobaltite thin film, the laser induced plasma properties have been characterized utilizing plasma mass spectrometry establishing a direct correlation to the corresponding film composition and structure. The introduction of a platinum sacrificial layer when growing the oxide thin film enables a damage-free laser transfer of calcium cobaltite thereby preserving the film composition and crystallinity as well as the shape integrity of the as-transferred pixels. The demonstrated direct writing approach simplifies the fabrication of micro-devices and provides a large degree of flexibility in designing and fabricating fully functional thermoelectric micro-devices.

Applications of laser printing for organic electronics

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.

Direct laser deposition of nanostructured tungsten oxide for sensing applications

Nanostructured tungsten trioxide (WO 3 ) thin films are deposited by pulsed laser deposition (PLD) and radio-frequency (RF) assisted PLD onto interdigitated sensor structures. Structural characterization by x-ray diffraction and Raman spectroscopy shows the WO 3 films are polycrystalline, with a pure monoclinic phase for the PLD grown films. The as-fabricated WO 3 sensors are tested for ammonia (NH 3 ) detection, by measuring the electrical response to NH 3 at different temperatures. Sensors based on WO 3 deposited by RF-PLD do not show any response to NH 3 . In contrast, sensors fabricated by PLD operating at 100 °C and 200 °C show a slow recovery time whilst at 300 °C, these sensors are highly sensitive in the low ppm range with a recovery time in the range of a few seconds. The microstructure of the films is suggested to explain their excellent electrical response. Columnar WO 3 thin films are obtained by both deposition methods. However, the WO 3 films grown by PLD are porous, (which may allow NH 3 molecules to diffuse through the film) whereas RF-PLD films are dense. Our results highlight that WO 3 thin films deposited by PLD can be applied for the fabrication of gas sensors with a performance level required for industrial applications.

Laser Structuring of Soft Materials: Laser-Induced Forward Transfer and Two-Photon Polymerization

This chapter discusses recent progress in 2D and 3D printing technologies, in particular laser-induced forward transfer and two-photon polymerization (TPP). We explore their potential for applications in micro-electronics, protein microarrays, sensors and biosensors, and tissue engineering. An overview of the factors that affect patterning, miniaturization and functionality is presented. A special focus is placed on laser direct writing via TPP for the fabrication of 3D vertical microtubes acting as microreservoirs for an osteogenic drug.

Surface acoustic wave biosensor based on odorant binding proteins deposited by laser induced forward transfer

In this paper, a biosensor for vapor phase detection of odorant molecules based on Surface Acoustic Wave (SAW) resonators is presented. The SAW resonators were coated with a wild-type odorant-binding protein from pig (wtpOBP) deposited by laser-induced forward transfer (LIFT). Two protein solutions, i.e. with 20% and 50% (v/v) glycerol, were deposited by LIFT changing the laser fluence and the printing morphology of droplets. The SAW biosensor was tested in nitrogen upon exposure to R-(-)-1-octen-3-ol (octenol) and R-(-)-carvone (carvone) vapors in the range of concentrations between 9 and 60 ppm. An uncoated device was used to compensate the responses due to variations in environmental parameters. The differential response curves showed a linear behavior in the tested range of concentrations and the obtained sensitivities were of 20.7 Hz/ppm and of 13.8 Hz/ppm, respectively, for octenol and carvone.