4.3.1 Overview

Table 4.1: Summary of scattering properties measured using a 390eV per atom O $^{+}_{2}$ molecular primary beam at 82 $\ensuremath{°}$ angle of incidence. $^{1}$ data taken from [14 ].

	Reflection	FWHM [deg]
Surface	Efficiency [%]	$\;$ Azimuthal	$\; \; \; \; \;$ Polar
CrO - [MgF $_{2}$ -Cr] $_{x}$ - TiO $_{2}$ - Si substrate	8.5	>20	>20
WO - [MgF $_{2}$ -Cr] $_{x}$ - TiO $_{2}$ - Si substrate	8.5	>20	>20
W - MgF $_{2}$ - TiO $_{2}$ - Si substrate (top)	8	20	14.5
W - MgF $_{2}$ - TiO $_{2}$ - Si substrate (bottom)	15	18	13
10ÅAl - 1400ÅMgF $_{2}$ - Si substrate	6	>20	>20
50ÅAl - 1400ÅMgF $_{2}$ - Si substrate	8	>20	>20
CVD diamond on Si	24	17	12
MgO (100) single crystal	-	>20	16
Ta foil polycrystalline	7.5	>20	13
Ta(110) single crystal	-	16	10
W (110) single crystal $^{1}$	32	8	8

Table 4.1 depicts a summary of the measured reflection properties obtained with a 390eV per atom O $^{+}_{2}$ molecular primary beam. Figure 4.2 depicts the energy dependence of the scattering off the CVD diamond sample. The scattering improves significantly when the energy is lowered from 748eV to 193eV per incident atom. The scattering gets more specular as the beam energy is lowered (Figure 4.3 ). A similar effect was observed on the MgO (100) sample. The scattering from this sample was much wider probably due to the heating cycle executed prior to the angular scattering measurements (Figure 4.4 ).

Table 4.2 depicts a summary of the NPD relative detection efficiencies for start surfaces where secondary electron yield data (Chapter 3 ) was available.

**Figure 4.2:** Energy dependent scattering of O $^{+}_{2}$ off CVD diamond at 82 $\ensuremath{°}$ angle of incidence. Only the neutral charge state fraction is shown in these plots due to better statistics. The scattering of the negatively ionized charge state fraction does not differ significantly.
$\resizebox*{!}{0.8\textheight}{\includegraphics{diamond_scattering.eps}}$

**Figure 4.3:** Summary of the energy dependence of scattering O $^{+}_{2}$ primary particles off a CVD diamond surface shown in Figure 4.2 .
$\resizebox*{!}{0.35\textheight}{\includegraphics{diamond_energy_scatt.eps.eps}}$

**Figure 4.4:** Energy dependence of the FWHM scattering angle when scattering O $^{+}_{2}$ primary particles off a MgO (100) surface at 82 $\ensuremath{°}$ angle of incidence. The surface was already relatively rough as it had suffered from previous experiments but the more specular scattering at lower energies is clearly visible.
$\resizebox*{!}{0.35\textheight}{\includegraphics{mgo_energy_scatt.eps.eps}}$

Table 4.2: Summary of the NPD relative detection efficiencies for different start surfaces. A 390 eV per atom O $_{2}^{+}$ primary beam was used at 82 $\ensuremath{°}$ angle of incidence. For time dependent secondary electron yields initial values were taken, values after a prolonged beam exposition are given in parenthesis. $^{1}$ after exposition to air. $^{2}$ data taken from [14 ].

Surface	Reflection efficiency $\sigma$ [%]	Secondary electron yield $\gamma$	NPD relative detection efficiency $\epsilon$ [%]
CrO - [MgF $_{2}$ -Cr] $_{x}$ - TiO $_{2}$ - Si substrate	8.5	0.55	2.3
WO - [MgF $_{2}$ -Cr] $_{x}$ - TiO $_{2}$ - Si substrate	8.5	0.42	1.9
W - MgF $_{2}$ - TiO $_{2}$ - Si substrate (top)	8	0.45	1.9
W - MgF $_{2}$ - TiO $_{2}$ - Si substrate (bottom)	15	0.45	3.5
10Å Al - 1400Å MgF $_{2}$ - Si substrate $^{1}$	6	0.55 (0.15)	1.7 (0.52)
50Å Al - 1400Å MgF $_{2}$ - Si substrate $^{1}$	8	0.6 (0.15)	2.4 (0.69)
CVD diamond on Si	24	0.9	14.0
Ta foil polycrystalline	7.5	0.78	2.8
W (110) single crystal $^{2}$	32	0.52	8.5

4. 3.1 Overview