Franck Rose

Real-time observation of FIB-created dots and ripples on GaAs

We report a phenomenological study of Ga dots and ripples created by a focused ion beam (FIB) on the GaAs(001) surface. Real-time observation of dot diffusion and ripple formation was made possible by recording FIB movies. In the case of FIB irradiation with a 40xa0nA current of Ga(+) ions accelerated under 40xa0kV with an incidence angle of θ = 30°, increasing ion dose gives rise to three different regimes. In Regime 1, dots with lateral sizes in the range 50-460xa0nm are formed. Dots diffuse under continuous sputtering. In Regime 2, dots self-assemble into Bradley and Harper (BH) type ripples with a pseudo-period of λ = 1150 ± 25xa0nm. In Regime 3, ripples are eroded and the surface topology evolves into microplanes. In the case of normal incidence, FIB sputtering leads only to the formation of dots, without surface rippling.

Atomically resolved observation of the quenched Si(111) surface with small amplitude dynamic force microscopy

Metastable reconstructed phases and highly disordered regions of the quenched Si(111) “1×1” phase with many silicon clusters were atomically resolved with a constant frequency mode of small amplitude dynamic force microscopy with the second flexural mode of a commercially available dynamic mode cantilever. Improved sensitivity due to the small amplitude dynamic force microscopy could operate at a relatively far distance from the sample surface with a given resolution and enable highly stable imaging with small interaction forces even on the Si(111) 1×1 metastable phases with silicon clusters. All of the individual atoms in the silicon cluster were atomically observed while avoiding deformations of the sample surface and the tip apex. In the case that the interaction forces of the imaging parameters were intently set to be ten times larger than those for stable imaging, arrangements of adatoms could easily be modified by mechanical interaction forces between the tip and the sample surface. The Si(111)-c(2×...

Suspended HOPG nanosheets for HOPG nanoresonator engineering and new carbon nanostructure synthesis

Suspended highly oriented pyrolytic graphite (HOPG) nanosheets (10?300?nm thick) were created by direct mechanical cleavage of a bulk HOPG crystal onto silicon micropillars and microtracks. We show that suspended HOPG nanosheets can be used to engineer HOPG nanoresonators such as membranes, bridges, and cantilevers as thin as 28 carbon atom layers. We measured by Doppler laser heterodyne interferometry that the discrete vibration modes of an HOPG nanosheet membrane and the resonance frequency of a FIB-created HOPG microcantilever lie in the MHz frequency regime. Moreover, a new carbon nanostructure, named nanolace, was synthesized by focused ion beam (FIB) sputtering of suspended HOPG nanosheets. Graphite nanosheets suspended on micropillars were eroded by a FIB to create self-oriented pseudo-periodical ripples. Additional sputtering and subsequent milling of these ripples led to the formation of honeycomb-like shaped nanolaces suspended and linked by ribbons.

Adsorption and combing of DNA on HOPG surfaces of bulk crystals and nanosheets : application to the bridging of DNA between HOPG/Si heterostructures

Controlled and reproducible combing of λ-phage DNA molecules can be realized in predetermined orientations on highly oriented pyrolitic graphite (HOPG) surfaces. Observations by atomic force microscopy (AFM) show that DNA adsorption onto HOPG surfaces leads to different hierarchical organizations such as balls, networks, films, and fractal structures. HOPG nanosheets (3.5–100xa0nm thick) were created by simply rubbing a HOPG crystal onto a silicon oxide surface, and then patterned with a focused ion beam (FIB) to fabricate HOPG/Si heterostructures (arrays of silicon micropillars and microtracks decorated on their top surface with HOPG nanosheets). The surface reactivity of HOPG nanosheets toward DNA is found to be the same as of HOPG bulk crystals. Finally, combing is used to attach and suspend bundles of approximately 20–50 DNA molecules between HOPG/Si heterostructures.

Application of capillary forces and stiction for lateral displacement, alignment, suspension and locking of self-assembled microcantilevers

We report the surface-tension-powered self-assembly (displacement, alignment, pulling down and locking) of microcantilevers. Capillary forces-assisted displacement is realized by compression of four arrays of springs linked to the opposite lateral sides of the cantilevers. After in-plane translation along the initial cantilever orientation, the microstructure is pulled down and locked on the substrate by stiction. Spring and capillary forces are described with a simple analytical model. Complete self-assembly occurs when the layout of the whole system (the cantilever with its traveling spring structure, the surrounding area and the local distribution of the liquid) is well designed. We show that the presence of a water meniscus trapped at a step edge in the vicinity of the tip end of a microcantilever could lead to stiction failure before traveling of the structure. Small beams (6 µm long) protruding over step edges were fabricated by adding a mechanically assisted displacement step (with a microneedle) to the self-assembly experiment.

Dynamic force microscopy study of the Ga-rich c(8×2) and As-rich c(4×4) reconstructions of the GaAs(001) surface

As-rich and Ga-rich GaAs(001) surfaces were studied with frequency-modulation dynamic force microscopy. By simply changing the parameters of argon sputtering and annealing during sample preparation, surfaces reconstructed with the As-rich c(4×4) phase or the Ga-rich c(8×2) phase could be obtained. True atomic resolution of the c(8×2) reconstruction is achieved by using constant frequency shift imaging. We show that tip functionalization allows selective species imaging. The presence at the tip apex of empty Ga dangling bonds or of fully filled As dangling bonds leads to selective atomic resolution of the As or Ga sublattices of the c(8×2) reconstructed surface, respectively. Our observations support the ζ model for the c(8×2) reconstruction (but no dimers were found) and the α model for the c(8×2) reconstruction (individual As–As dimers were resolved by dynamic force microscopy).