Arsenic

Species	Binding energy / eV	Charge Ref	Ref
As Metal	41.5		2,3
GaAs	40.9		3
As₂O₃	44.9	C 1s (284.8 eV)	4
As₂O₅	46.2	C 1s (284.8 eV)	4
NiAs	41.1	C 1s (284.8 eV)	5

Common As(3d_5/2) Binding Energies

Species	Binding energy / eV	Charge Ref	Ref
As Metal	41.5		2,3
GaAs	40.9		3
As₂O₃	44.9	C 1s (284.8 eV)	4
As₂O₅	46.2	C 1s (284.8 eV)	4

Common As(3d_5/2) Binding Energies

Arsenic is primarily analysed using the As(3d) region, which can overlap with the Ta(5p_1/2) signal. Generally observed as an oxide or in GaAs, the As(3d) region has a spin-orbit splitting of 0.7 eV, with an intensity ratio of 0.7, as opposed to the expected 0.67.

Recording the As(2p_3/2) region is useful also and demonstrates oxide thickness as a function of kinetic energy (see below)

Figure 1: The As(3d) and As(2p3/2) regions of an as received GaAs sample. Green = elemental, blue = oxide

Experimental Advice

It has been reported that As₂O₃ sublimes in vacuum [1], whereas As⁵⁺ may under go some degredation by XPS analysis to yield As³⁺, so rapid analysis and/or summation of multi-point analysis may be required.

The As LMM Auger peaks when recorded with a Al source encompass a wide energy range (500 – 250 eV) and therefore overlap with many other photoemission lines, so care should be taken in analysis. This can be seen in the spectra below of As₂O₅.

Figure 2: Expansion of the survey spectrum for As2O5, showing the As LMM structure in the highlighted area

Fitting Advice

Due to the difficulties mentioned above, it is therefore common to use the modified auger parameter (α‘) to assign chemistry, values for which may be found in table 1. To find auger parameters of many more compounds, see reference 5 from Mark Biesinger.

Species	Modified auger parameter / eV	Ref
Cu	1851.2	2
Cu₂O	1849.4	3
CuO	1851.5	4
Cu(OH)₂	1853.1	5
CuCl	1847.8	5
CuCl₂	1850.2	5
CuSO₄	1851.4	5

Table 1: Modified auger parameters for Cu species

The modified auger paramater may also provide insight into specific nanoparticle chemistry via estimation of the relaxation energy (r).⁽⁶⁾ This may be defined as half the change in the modified auger parameter compared to bulk Cu (equation 1).⁽⁷⁾

r = 0.5 * (|1851.2 – α‘) Equation 1

Copper nanoparticles may evidence increased relaxation energies when an decreased number of copper atoms are screening the core-hole (i.e. smaller nanoparticles)⁽¹⁾ or due to a decrease in the polarizability of the support.⁽⁸⁾

Copper metal does not exhibit a high degree of asymmetry, due to it’s largely filled d-band. A lineshape of LA(1.05, 110) can be used to give a good fit for Cu metal.