Anharmonicity and the Temperature Dependence of the Forbidden (222) Reflection in Silicon

The temperature dependence of the integrated intensity of the forbidden (222) reflection in silicon has been measured from 4 to 900 °K. The results indicate that the (222) intensity at room temperature is due almost entirely to charge asymmetries introduced by the covalent bonds. However, the temperature dependence may be due to a combination of bond vibrations and anharmonicity in the atom motions. From estimates of the anharmonic contribution, and the observed temperature dependence, there is evidence that the thermal motion of the covalent bond may be different from that of the core electrons. The absolute intensity of the (222) was also measured and is consistent with $F\left(222\right)=1.46\mathrm{}\pm 0.04$.