Association

3.4. Ex situ characterization techniques 51
Figure 3.16.: HAXPES experiment at the P09 beamline at PETRA III (a). (b): Geometry of an MCD
measurement. A remanent magnetization of the thin film parallel or antiparallel with respect to
the incoming light is induced by a removable permanent magnet. (c): The sample temperature
is directly measured at the sample plate using a thermocouple (design courtesy F. Okrent).
3.4.4. Depth-selective profiling with HAXPES
A suitable measure of the sampling depth in solids from which photoelectrons carry information
to the detector is based on the so-called information depth (ID). We define the information
depth as the probing depth from which 95% of the emitted photoelectrons originate,
thus I(λ,α)| top
ID
/
I(λ,α)|
top
∞
I(λ,α) ∣ ∣ ∣
top
bottom = C
∑
layers i
95%, whereas
∫ top i
exp
bottom i
(
−z
λ i cosθ
)
dz, (3.10)
where I denotes the spectral intensity, z the depth in the heterostructure from the surface, λ
the effective attenuation length, 84 θ the off-normal emission angle, and C a sample-specific
parameter. For example, using an excitation energy hν = 4 keV, we can obtain an information
depth of approximately 20 nm for valence level photoemission peaks.
see MCD results in Ch. 4.