The temperature dependence of the conduction mechanism in thin films of ϳ8 nm diameter silicon nanocrystals is investigated using Al/ Si nanocrystal/ p-Si/ Al diodes. A film thickness of 300 nm is used. From 300 to 200 K, space charge limited current, in the presence of an exponential distribution of trapping states, dominates the conduction mechanism. Using this model, a trap density N t = 2.3 ϫ 10 17 cm −3 and a characteristic trap temperature T t = 1670 K can be extracted. The trap density is within an order of magnitude of the nanocrystal number density, suggesting that most nanocrystals trap single or a few carriers at most.
We investigate the temperature dependence of conduction in size-controlled silicon nanocrystals. The nanocrystals are ϳ8 nm in diameter, covered by ϳ1.5 nm thick SiO 2 shells. In 300 nm thick films for temperatures T from 30 to 200 K, the conductivity follows a ln͑͒ vs 1 / T 1/2 dependence. This may be associated with either percolation-hopping conductance or Efros-Shklovskii variable range hopping. Assuming hopping sites only on the nanocrystals, the data agree well with the percolation model.
We demonstrate highly directional etching in silicon 100 nm in diameter with an aspect ratio of 160 with no spiking on the pore walls using magnetic-field-assisted anodization. The relationship between the surface geometry of a silicon electrode and its highly directional etching properties have been investigated. Specifically, we show that the pore shape and pore wall orientation are not determined by the surface pattern but by the etching mechanisms specific to the magnetic-field-assisted anodization. These etching mechanisms enable highly directional and high aspect ratio etching at diameters below 100 nm in scale.
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