Effect of argon implantation on solid-state dewetting: control of size and surface density of silicon nanocrystals.

Thermally induced solid-state dewetting of ultra-thin films on insulators is a process of prime interest, since it is capable of easily forming nanocrystals. If no particular treatment is performed to the film prior to the solid-state dewetting, it is already known that the size, the shape and the density of nanocrystals is governed by the initial film thickness. In this paper, we report a novel approach to control the size and the surface density of silicon nanocrystals based on an argon-implantation preliminary surface treatment. Using 7.5 nm thin layers of silicon, we show that increasing the implantation dose tends to form smaller silicon nanocrystals with diameter and height lower than 50 nm and 30 nm, respectively. Concomitantly, the surface density is increased by a factor greater than 20, going from 5 µm-2 to values over 100 µm-2.

Measuring the lifetime of silicon nanocrystal solar cell photo-carriers by using Kelvin probe force microscopy and x-ray photoelectron spectroscopy.

We report the first measurements of photo-carrier lifetimes in silicon nanocrystal-based third generation solar cells by Kelvin force microscopy and x-ray photoelectron spectroscopy under modulated frequency light illumination. A high concentration of active defects at the interface between the nanocrystals and silicon oxide matrix may be passivated by annealing under hydrogen. We found that the carrier lifetime, τ, is τ = 7 × 10(-5) s and τ = 3.5 × 10(-5) s within 10% accuracy for the hydrogen passivated and non-passivated nanocrystals, respectively. We used an exponential model to confirm the experimental potential measurements and to estimate photo-carrier lifetimes.

Numerical simulations for a quantitative analysis of AFM electrostatic nanopatterning on PMMA by Kelvin force microscopy.

Electrostatic nanopatterning of electret thin films by atomic force microscopy (AFM) has emerged as an alternative efficient tool for the directed assembly of nano-objects on surfaces. High-resolution charge imaging of such charge patterns can be performed by AFM-based Kelvin force microscopy (KFM). Nevertheless, quantitative analysis of KFM surface potential mappings is not trivial because of side-capacitance effects induced by the tip cone and the cantilever of the scanning probe. In this paper, we developed numerical simulations of KFM measurements taking into account these artifacts, so as to estimate the actual surface charge density of square charge patterns (nominal sizes ranging from 100 nm to 10 microm) written by AFM into polymethylmethacrylate (PMMA) thin films. This work revealed that, under our conditions, such charge patterns exhibit a surface charge density between 1.5 x 10(-3) and 3.8 x 10(-3) C m(-2), depending on the assumed depth of injected charges. These results are crucial to quantify the actual electric field generated by such charge patterns and thus the electrostatic forces responsible for the directed assembly of nano-objects onto these electrostatic traps.