In Situ TEM Near-Field Optical Probing of Nanoscale Silicon Crystallization

Abstract

Laser-based processing enables a wide variety of device configurations comprising thin films and nanostructures on sensitive, flexible substrates that are not possible with more traditional thermal annealing schemes. In near-field optical probing, only small regions of a sample are illuminated by the laser beam at any given time. Here we report a new technique that couples the optical near-field of the laser illumination into a transmission electron microscope (TEM) for real-time observations of the laser-materials interactions. We apply this technique to observe the transformation of an amorphous confined Si volume to a single crystal of Si using laser melting. By confinement of the material volume to nanometric dimensions, the entire amorphous precursor is within the laser spot size and transformed into a single crystal. This observation provides a path for laser processing of single-crystal seeds from amorphous precursors, a potentially transformative technique for the fabrication of solar cells and other nanoelectronic devices.

Laser processing and in-situ diagnostics for crystallization: from thin films to nanostructures

“…In the TEM experiment, we experienced significant uncertainty in producing the large sc-Si grain; more often, we had to apply non-deterministic number of laser pulses to reach the generation of the large tip crystal. Spontaneous nucleation could cause a stochastic behavior, 16 but our simulation did not detect such nucleation events in this case. We believe that this fortuity is rather related to the uncertain initial configuration of the apex crystallite(s).…”

“…This system enabled highly efficient in situ characterization of morphological evolution that repetitive laser irradiation induced. 16 As the overall duration of laser-induced crystallization processes was much shorter (at most, on the order of hundred nanoseconds) than that of our TEM image acquisition, tracing real-time growth of the individual grains was not possible. As an alternative approach, we conducted a numerical simulation in order to unveil the detailed mechanism of the laser-induced grain growth.…”

“…Recently, our team has developed an integrated TEM system (JEOL 3010) that is coupled with a near-field scanning optical microscopy (NSOM) fiber. 16 Figure 6 shows a schematic of the in situ TEM crystallization setup. Silicon nanopillars (diameter: 300~400 nm, length: 1.7~2 m) consisting of amorphous silicon (a-Si) -silicon oxide (~100 nm) -crystalline silicon layers were fabricated by a focused ion beam (FIB) technique.…”

“…This gap distance was carefully chosen to avoid unwanted interaction between the probe end and the sample as well as to assure uniformity of the beam profile. 16 The pulsed-laser beam was applied to the silicon pillar in the longitudinal direction. At the same time, an electron-beam was transmitted in the transverse direction for image scanning.…”

“…In contrast to our previous study where confined a-Si fully melted. 16 the laser heat could only affect the phase of the pillar extremity (that is, partial melting) due to the high aspect ratio of the initial a-Si structure. An increased laser power immediately ablated the structure or induced severe deformation.…”