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...

Discs of solid material have been forward transferred from thin films on transparent carrier substrates using femtosecond Ti:sapphire laser-induced forward transfer (fs-LIFT) with a triazene polymer dynamic release layer (DRL). The fluence threshold for fs-LIFT was found to be only ≈ 20% of the DRL ablation threshold at the laser wavelength. This decrease is attributed to ultrafast shock-wave generation in the constrained polymer layer under femtosecond irradiation being the driving force for fs-LIFT with the polymer DRL. The result is very different from the nanosecond regime, where the LIFT threshold is observed to be slightly above the polymer ablation threshold. White-light continuum generation in a carrier substrate is observed and its influence on the fs-LIFT process is discussed.

A novel technique for the laser-induced forward transfer (LIFT) of material in solid phase from a thin film precursor is presented. Multiple, sub-threshold energy femtosecond pulses are used to lessen the adhesion of a donor film to a support substrate to facilitate forward transfer of solid 'pellets' of donor material to a receiver. A relatively higher intensity outer ring is added to the transfer laser pulses, by means of the near-field diffraction pattern of a circular aperture, to define the area for transfer in the donor film and allow for more reproducible pellet shapes. This technique has been termed Ballistic Laser-Assisted Solid Transfer (BLAST).

The laser-induced forward transfer process of solid ceramic donor materials ͑gadolinium gallium oxide and ytterbium doped yttrium aluminium oxide͒ was studied using triazene polymer as a sacrificial layer by means of a time-resolved nanosecond-shadowgraphy technique. The dependence of the ablation dynamics and quality of the ejected donor material on the laser fluence and thickness of the sacrificial and donor layers were investigated and discussed.

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