Material:Silicon

Silicon is crystalline solid with a diamond cubic crystal structure. Silicon wafers are frequently used as substrates for samples used in GISAXS. Si wafers make ideal substrates because they are very smooth at the atomic/nano scale, and are also very flat across larger (macroscale) distances. Note, however, that sample preparation (e.g. spin coating) may stress the wafer and 'kink' it, with effects that can be visible in GISAXS and especially reflectivity experiments.

Scattering

Because silicon is normally a single-crystal, it leads to no discernible peaks on the detector unless the crystal lattice is aligned to satisfy the Bragg condition (i.e. the Ewald sphere must intercept a peak in the reciprocal lattice).

Properties

• Density: 2.3290 g/cm³
• Neutron SLD: 2.074×10⁻⁶ Å⁻²

Material	density (g/cm3)	X-ray energy (keV)	X-ray wavelength (Å)	critical angle (°)	qc (Å−1)	SLD (10−6Å−2)
Si	2.3290	2.0	6.20	0.824	0.0291	16.89
		4.0	3.10	0.451	0.0319	20.28
		8.0	1.55	0.224	0.0317	20.07
		12.0	1.03	0.149	0.0317	19.92
		16.0	0.77	0.112	0.0316	19.84
		24.0	0.52	0.07426	0.0315	19.77

Wafer transmission

Silicon is often used as a substrate. The transmission of a 'standard' (500 μm) Si wafer is:

Material	density (g/cm3)	X-ray energy (keV)	X-ray wavelength (Å)	transmission
Si	2.3290	2.0	6.20	0.000
		4.0	3.10	3×10−23
		8.0	1.55	0.0007
		9.0	1.38	0.006
		12.0	1.03	0.11
		16.0	0.77	0.39
		24.0	0.52	0.75

See Also

• Wikipedia: Silicon