SCREEN_APERTURE

SCREEN_APERTURE defines the aperture (in degrees) of the acceptance cone of the LEED screen. This, in turn, determines the highest-order beams that will be visible in the LEED experiment.

Default: SCREEN_APERTURE = 110 (i.e., the one of the ErLEED optics)

Syntax:

SCREEN_APERTURE = 95

Acceptable values: integer/floating point number between 0 and 180

Note

A beam with indices \((h, k)\) and corresponding in-plane reciprocal vector \(\mathbf{g} = h \mathbf{a}^* + k \mathbf{b}^*\) is visible at energy \(E\) (in electronvolts) if \(\theta <\) SCREEN_APERTURE \(/ 2\), where \(\sin{\theta} = \frac{\hbar g}{\sqrt{2 m_e e E}}\). Here \(e\) and \(m_e\) are the elementary charge and electron mass respectively.