I. Zergioti

Nanodroplets deposited in microarrays by femtosecond Ti:sapphire laser-induced forward transfer

The authors present the deposition of nanoscale droplets of Cr using femtosecond Ti:sapphire laser-induced forward transfer. Deposits around 300nm in diameter, significantly smaller than any previously reported, are obtained from a 30nm thick source film. Deposit size, morphology, and adhesion to a receiver substrate as functions of applied laser fluence are investigated. The authors show that deposits can be obtained from previously irradiated areas of the source material film with negligible loss of deposition quality, allowing subspot size period microarrays to be produced without the need to move the source film.

Femtosecond laser microprinting of biomaterials

This Letter demonstrates a laser rapid prototyping method that can be used for fabricating high-density resolution patterns of biomaterials. Ultraviolet femtosecond laser pulses have been used for directly printing a wide range of biomaterials in complicated patterns and structures. The ultrashort laser pulses reduce the thermal effects, thus allowing the effective deposition of sensitive biomaterials at high spatial resolution for microfabricating patterns. We present the microprinting of different biomaterial patterns, such as DNA (deoxyribonucleic acid) and proteins, with spatial resolution down to 50μm and we demonstrate that they maintain their properties and biological functions and, thus, can be practically used as biosensors.

Laser-Induced Fluorescence in Artwork Diagnostics: An Application in Pigment Analysis

The applicability of laser-induced fluorescence (LIF) spectroscopy as a nondestructive analytical technique for artwork diagnostics is investigated. In this work, LIF is employed in the examination of a set of cadmium sulfide- and cadmium selenide sulfide-based pigments in a series of oil painting test samples. Fluorescence spectra of the oil colors are recorded upon pulsed laser excitation at 532, 355 (Nd:YAG), and 248 nm (KrF excimer). The technique is shown to be suitable for differentiating among the various cadmium pigments used in this study and, furthermore, to be capable of identifying individual components in mixtures of these pigments on the basis of their characteristic fluorescence emission. Future prospects and the potential for the extension of LIF from a research laboratory technique into a conservators tool for artwork diagnostics are discussed.

Liquid phase direct laser printing of polymers for chemical sensing applications

This letter demonstrates the direct laser printing of polymers on capacitive micromechanical arrays for the realization of a chemical sensor. Each sensor of a single chip array is composed of a thin Si membrane covered by a chemically sensitive polymer layer by means of a direct laser printing technique. We present the high spatial resolution deposition of three different sensitive polymer materials by the liquid phase laser induced forward transfer process. We also show that the optimum sensitivity of the sensors can be achieved by varying the percentage of the coverage of the sensors’ membranes with the polymer.

Ultraviolet femtosecond, picosecond and nanosecond laser microstructuring of silicon: structural and optical properties

The effect of laser pulse duration on the morphology, composition, crystallinity and optical properties of self-organized Si microcones fabricated using 248 nm laser pulses (500 fs, 5 ps and 15 ns) in an SF(6) atmosphere, is presented in this paper. Despite distinct differences in the morphology, the Si cones show similar structure and composition independently of the laser pulse duration used: a core of single-crystalline Si, covered by a few hundred nanometer thick, sulfur-doped nanocrystalline Si layer, where no amorphous Si is present. The obtained features exhibit strong below-bandgap absorptance, making them excellent candidates for Si based photodetectors with improved spectral response.

Microdeposition of metals by femtosecond excimer laser

Abstract Microablation and transfer of thin metal films using ultrashort, ultraviolet laser radiation has been studied. A KrF excimer laser (λ=248 nm) having 500-fs pulse duration is coupled to a high-power image projection micromachining workstation. The laser irradiation is focused onto thin Cr films through the supporting transparent quartz substrates. Single pulses are used to completely remove the metal film. The ablated material is transferred onto a receiving target glass substrate placed parallel to the source film. Experiments were conducted in a miniature vacuum cell under a pressure of 10−1 Torr. The distance between the source and target surfaces is variable from near-contact to several hundreds of microns. Serial writing of well-defined metal lines and isolated dots, is accomplished using the x–y sample micropositioning system. Optical microscopy and surface profilometry showed deposition of highly reproducible and well-adhering features of a few microns in width for a source–target distance in the neighborhood of 10 μm. The short pulse length limits thermal diffusion, thereby enabling superior definition of the deposited features. Metal patterns were also directly deposited via a parallel-mode mask projection scheme. In a first demonstration of this method, deposited diffractive structures were shown to produce high-quality computer-generated holograms.

Capacitive microsystems for biological sensing

The growing interest in personalized medicine leads to the need for fast, cheap and portable devices that reveal the genetic profile easily and accurately. To this direction, several ideas to avoid the classical methods of diagnosis and treatment through miniaturized and label-free systems have emerged. Capacitive biosensors address these requirements and thus have the perspective to be used in advanced diagnostic devices that promise early detection of potential fatal conditions. The operation principles, as well as the design and fabrication of several capacitive microsystems for the detection of biomolecular interactions are presented in this review. These systems are micro-membranes based on surface stress changes, interdigitated micro-electrodes and electrode-solution interfaces. Their applications extend to DNA hybridization, protein-ligand binding, antigen-antibody binding, etc. Finally, the limitations and prospects of capacitive microsystems in biological applications are discussed.

Silicon electron emitters fabricated by ultraviolet laser pulses

In this letter we consider the effect of laser pulse duration on the surface morphology and the field emission properties of silicon structured by UV laser pulses. In three different pulse duration regimes ranging from sub-ps to ns, we altered the morphology of the fabricated silicon microspike arrays. The field emission properties of the microspike arrays were influenced by the morphological changes exhibiting a reduction of the emission threshold field to 2.5V∕μm for 15ns laser pulses. The ability of tuning the field emission properties of laser-fabricated silicon microspike arrays makes them excellent candidates for use as field emission cathodes.

Effect of processing parameters on the properties of hydroxylapatite films grown by pulsed laser deposition

Abstract Thin films of hydroxylapatite (HA) (Ca10(PO4)6(OH)2) were created on Ti substrates by KrF laser ablation. The layers were deposited in vacuum, in pure H2O vapours (pressure, 2 × 10−3 to 2 × 10−1 mbar) and in an Ar-H2O vapour mixture. The influence of the laser energy density ET (3 J cm−2, 13 J cm−2) and substrate temperature Ts (500–760 °C) on the film parameters was studied. Two different processes were used for HA target preparation. Films and targets were characterized by Rutherford backscattering (RBS) analysis, particle induced X-ray emission (PIXE), X-ray diffraction (XRD), scanning electron microscopy (SEM) and Knoop microhardness and scratch tests. For lower Ts and higher ET, the Ca/P ratio in the films was similar to that in the HA target. Crystalline HA peaks were found preferentially in the films deposited in the presence of Ar-H2O vapours. Time of flight (TOF) spectra of the plasma plume from the HA target were also analysed.

Polymer/carbon nanotube composite patterns via laser induced forward transfer

Direct and high spatial resolution printing of polymer/carbon nanotube (CNT) composite layers has been demonstrated by means of laser induced forward transfer (LIFT). Laser irradiation of composite target materials, such as poly(acrylic acid)/CNT and polyvinylpyrrolidone/CNT, enabled dry deposition of well resolved composite pixels onto glass substrates. The dispersion of the CNT into the deposited composite pixels was investigated by transmission electron microscopy. The LIFT technique was also employed for the accurate deposition of polymer/CNT composite pixels onto aluminum microelectrodes for the fabrication of chemical sensors based on polymer/CNT compounds.