Density of amorphous Si

Abstract

The density of amorphous Si has been measured. Multiple Si implants, at energies up to 8.0 MeV, were made through a contact mask to produce alternating amorphous/crystalline Si stripes with amorphous thicknesses up to ∼5.0 μm. For layers up to 3.4 μm (5 MeV), the amorphous Si is constrained laterally and deforms plastically. Above 5 MeV, plastic deformation of the surrounding crystal matrix is observed. Height differences between the amorphous and crystalline regions were measured for as-implanted, thermally relaxed, and partially recrystallized samples using a surface profilometer. Combined with ion channeling measurements of the layer thickness, amorphous Si was determined to be 1.8±0.1% less dense than crystalline Si (4.90×1022 atom/cm3 at 300 K). Both relaxed and unrelaxed amorphous Si show identical densities within experimental error (<0.1% density difference).

Latent ion tracks in amorphous silicon

“…Ion-implanted a-Si in a relaxed state has no measurable difference in mass density compared to as-implanted a-Si; however, during relaxation short-range ordering occurs where defects and dangling bonds are reduced in number, and the material moves structurally closer to an ideal continuous random network. 14,17,18 In addition to structural differences, relaxation yields an ≈150 K increase in melting temperature relative to that of as-implanted a-Si. 19,20 If the measured ion track diameter is representative of the maximum width of the molten zone along the ion trajectory, the increase in melting temperature for relaxed a-Si necessarily yields a decrease in ion track diameter.…”

Tuning the Er3+ sensitization by Si nanoparticles in nanostructured as-grown Al2O3 films

“…The areal density of Si NPs per layer can be estimated as ͓Si͔ / V NP ϫ , where ͓Si͔ is the areal density of Si as determined from the RBS measurements, V NP is the volume of an average NP calculated by assuming that they are spheres with an average diameter of 4.5Ϯ 0.5 nm, and is the density of amorphous Si. 16 The result of the calculation yields an areal density of NPs of ϳ3 ϫ 10 12 cm −2 , which is one order of magnitude less than the areal density of Er 3+ ions. Nevertheless the results should be analyzed taking into account the two-dimensional distribution in the Si NPs and the Er 3+ ion layer.…”

“…11,12 The Si areal density per layer is 7.0 ϫ 10 15 cm −2 , which is equivalent to an effective thickness of 1.4 nm, taking into account the density of the a-Si. 16 The total film thickness is 510Ϯ 10 nm and the s values determined for the films are 0, 4.0, 7.0, and 11.0Ϯ 0.5 nm, showing that a fine control of the deposited Al 2 O 3 has been achieved. Figure 2 shows an EFTEM image corresponding to the cross section of the film with s = 11 nm, filtered at the Si plasmon peak: The light contrast lines in the image correspond to the Si-rich regions in the film.…”

Microstructure of amorphous-silicon-based solar cell materials by small-angle x-ray scattering. Annual subcontract report, 6 April 1994--5 April 1995

“…The result that no voids are present in this type of pure a-Si allows us to rule out this mechanism for the known density deficit of 1.8&0.1% [40]. The most likely remaining mechanism is an increase in the average Si-Si bond length of 0.6% [56].…”

“…6 have been done with a-Sil,,Ge,:H alloys [15,16,26]. The observed density deficits compared to c-Si (2.329 g/cm3), pure a-Si (2.287 g/cm3) [40], c-Sil,,Ge, alloys [41], diamond (3.52 g/cd), graphite (2.26 g/cm3), or Sic (3.22 g/cm3) can be helpful in interpretation of the SAXS and in determining the average effect of H alloying.…”