Basically all discharge based laboratory sources for photo electron spectroscopy produce a range of different emission lines which compromise the signal to noise performance and generate unwanted „ghost peaks“ in the spectrum. A VUV monochromator allows to select one specific emission line out of the emission specta generated in the VUV lamp.
A dedicated monochromator is now available for our popular HIS 13 and HIS 14 HD VUV sources: The FOCUS HIS Mono is based on a patented zone plate arrangement to separate the two prominent lines He I (21.2 eV) and He II (40.8 eV) from the rest of the emission spectrum. In particular the He I – ß, ƴ and He II – ß satellites are removed.
The zone plate has different areas for the He I- and He II line respectively. A z-shift moves the relevant area into the light path. The reflection angle of the zone plate is energy dependent and an aperture cuts out the emission line of interest. A third area on the zone plate provides the path for visible light of a LED in order to adjust the beam spot position and spot shape on the sample.
A module for HIS 13 and HIS 14 HD
The drawings and measures of the HIS 14 HD with monochromator.
Spectral improvement with the monochromator
Photoelectron spectrum accross the Fermi edge of W (100) were acquired with and without monochromatized He I exitation. A zoom reveals photoelectron peaks generated by HeI-ß and HeI-ƴ satellites. With the monochromatized source the peaks induced by the satellites are removed. The spectra were measured with a FOCUS CSA analyzer.
The benefit to remove satellite induced ghost peaks becomes even more evident when looking at momentum microsocopy with kx – ky images as shown below with a PEEM with IEF ( Imaging Energy Filter) :
This table shows the technical specifications of the monochromated versions of our VUV sources.
|Model||HIS 13 Mono||HIS 14 HD Mono||HIS 14 HD 200 Mono|
|Photo current He I / He II||> 80/10 nA*||> 40 nA**/> 12 nA**||> 40 nA**/12 nA**|
|Useful gas discharge lines:|| He I/II||He I/II|| He I/II|
|Light spot diameter:||working distance depending||< 300µm||< 600µm|
|Photon line width|| < 2 meV ( He I radiation)||< 2 meV ( He I radiation)|| < 2 meV ( He I radiation)|
|Photon flux density:||working distance depending (unfocused source)||> 50 times compared to an unfocused source||> 13 times compared to an unfocused source|
|Pumping || 2-, 3- or 4- stage differential pumping||2-, 3- or 4- stage differential pumping|| 2-, 3- or 4- stage differential pumping|
|Working distance||spot size depending||ca. 70 mm||ca. 170 mm|
|Insertion depth:|| Customized (to be defined)||Customized (to be defined)|| Customized (to be defined)|
|Mounting flange||CF40||CF63 or CF100||CF40|
|Operating pressure|| Down to 10-11 mbar range||Down to 10-11 mbar range|| Down to 10-11 mbar range|
|Adjustment & Discharge control||Via backside viewport||Via backside viewport||Via backside viewport|
|Cooling:||Water cooling||Water cooling||Water cooling|
|Bake out temperature:||Up to 250°C||Up to 250°C||Up to 250°C|
|Plasma Ignition:|| Automatic||Automatic|| Automatic|
|Available Capillaries (mm):|| 0.8/1.2/1.7 (standard)||0.8/1.2/1.7 (standard)|| 0.8/1.2/1.7 (standard)|
**photo current with VUV diode