We report on experimental activities on HiRES, a novel ultrafast electron diffraction beamline under development at LBNL. The instrument provides high-flux of relativistic electron pulses with sub-picosecond duration, which are then shaped in transverse and longitudinal phase space producing small spot sizes with femtosecond resolution. Alternatively beam shaping can be used to achieve large lateral coherence lengths for chemical and biological applications.
Recent work on laser-induced crystallization of thin films and nanostructures is presented. Characterization of the morphology of the crystallized area reveals the optimum conditions for sequential lateral growth in a-Si thin films under
high-pulsed laser irradiation. Silicon crystal grains of several micrometers in lateral dimensions can be obtained
Laser-induced grain morphology change is observed in silicon nanopillars under a transmission electron microscopy (TEM) environment. The TEM is coupled with a near-field scanning optical microscopy (NSOM) pulsed laser processing system. This combination enables immediate scrutiny on the grain morphologies that the pulsed laser
irradiation produces. The tip of the amorphous or polycrystalline silicon pillar is transformed into a single crystalline
domain via melt-mediated crystallization. The microscopic observation provides a fundamental basis for laser-induced
conversion of amorphous nanostructures into coarse-grained crystals.
A laser beam shaping strategy is introduced to control the stochastic dewetting of ultrathin silicon film on a foreign
substrate under thermal stimulation. Upon a single pulse irradiation of the shaped laser beam, the thermodynamically
unstable ultrathin silicon film is dewetted from the glass substrate and transformed to a nanodome. The results suggest that the laser beam shaping strategy for the thermocapillary-induced de-wetting combined with the isotropic etching is a
simple alternative for scalable manufacturing of array of nanostructures.
Recent research results are presented where lasers of different pulse durations and wavelengths have been coupled to
near-field-scanning optical microscopes (NSOMs) through apertured bent cantilever fiber probes and atomic force
microscope (AFM) tips in apertureless configurations. Experiments have been conducted on the surface modification of
metals and semiconductor materials. By combining nanoscale ablative material removal with subsequent chemical
etching steps, ablation nanolithography and patterning of fused silica and crystalline silicon wafers has been
demonstrated. Confinement of laser-induced crystallization to nanometric scales has also been shown. <i>In-situ</i> observation of the nanoscale materials modification was conducted by coupling the NSOM tips with a scanning electron
microscope (SEM). Nucleation and growth of semiconductor materials have been achieved by laser chemical vapor
deposition (LCVD) at the nanoscale level. Locally selective growth of crystalline silicon nanowires with controlled size,
heterogeneity and nanometric placement accuracy has been accomplished.