The authors present the deposition of nanoscale droplets of Cr using femtosecond Ti:sapphire laser-induced forward transfer. Deposits around 300 nm in diameter, significantly smaller than any previously reported, are obtained from a 30 nm 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. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2386921͔The laser-induced forward transfer ͑LIFT͒ technique exists as a method for the direct writing of a wide variety of materials with a minimum achievable resolution around 1 m. 1 It is of particular interest due to the ability to pattern material in air and at room temperature onto virtually any substrate. 2 In recent years, significant study has been directed towards extending the range of materials that can be deposited using LIFT; metals, 3 oxides, 2 superconductors, 4 DNA, 5 proteins, 6 fungal spores, 7 polycrystalline Si, 8 and various important electronic and sensing materials 9 have all been transferred. In contrast, efforts to reduce the minimum achievable deposition dimensions have received comparatively little attention. LIFT using nanosecond pulsed lasers ͑ns-LIFT͒ typically produces depositions which at best reproduce the shape and size of the laser focal spot. 10 Femtosecond-LIFT ͑fs-LIFT͒ using an UV excimer laser has been shown to be capable of subspot size depositions with diameters around 0.5 m. 3 Recently, it was demonstrated that ns-LIFT could also be used to produce subspot size deposits by carefully controlling the laser fluence just above the threshold for material transfer. 11 In LIFT, a thin film of the material to be deposited ͑the "source film"͒ is coated onto one face of a transparent substrate ͑the "carrier"͒ and brought into close contact with another substrate ͑the "receiver"͒. A single laser pulse is then focused through the carrier onto the carrier-film interface, where it is absorbed in a shallow layer of the film ͓Fig. 1͑a͔͒. Conventionally, LIFT then occurs by vaporization of film material at the constrained interface, with the resultant pressure buildup propelling film material to the receiver. However, this is the case only for thicker films and high laser fluence; for thin films and fluence just above the threshold for material transfer, it is possible for LIFT to occur solely by melt-through of the source film ͓Fig. 1͑b͔͒. With precise control of the laser fluence, only the center of the melt front reaches the free surface of the film ͓Fig. 1͑c͔͒, allowing molten material under pressure to expand through an unconstrained, subspot size region. With ns-LIFT this process has been shown to facilitate sublaser spot size printing. 11 In this letter we demonstrate that the same process can occur with fs-LIFT...

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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.

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