Film-thickness-dependent conduction in ordered Si quantum dot arrays

Silicon core-mesoporous shell carbon spheres as high stability lithium-ion battery anode

An innovative and simple synthesis strategy of silicon nanoparticle (Si NP) core covered by mesoporous shell carbon (MSC) structure is demonstrated. The Si core@MSC (SCMSC) composite is developed for addressing the issues for Si anode material in lithium ion batteries (LIBs) such as high volume expansion and low electrical conductivity. Significant improvement in the electrochemical performance for the SCMSC anode is observed compared with bare Si anode. The SCMSC composite delivers an initial specific capacity of 2450 mAh g^-1 at 0.166 A g^-1 with Coulombic efficiency of 99.2% for 100 cycles. Compared to bare Si anode, the SCMSC anode exhibits much higher Li storage capacity, superior cyclability, and good rate capability, highlighting the advantages of hierarchical MSC in the SCMSC structure.

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.

Morphological and nanostructural features of porous silicon prepared by electrochemical etching

Porous layers were produced on a p-type (100) Si wafer by electrochemical anodic etching. The morphological, nanostructural and optical features of the porous Si were investigated as functions of the etching conditions. As the wafer resistivity was increased from 0.005 to 15 Ω·cm, the etched region exhibited 'sponge', 'mountain' and 'column'-type morphologies. Among them, the sponge-type structured sample showed the largest surface area per unit volume. Silicon nanocrystallites, 2.0 to 5.3 nm in size, were confirmed in the porous layers. The photoluminescence peaks varied in the wavelength range of 615 to 722 nm. These changes in the maximum peak position were related to the size distribution of the Si crystallites in the porous silicon. The doping levels of the wafers significantly affect the size distribution of the Si crystallites as well as the light-emitting behavior of the etched Si, which contains nanoscale Si crystallites.