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.
• Dispersive element with 20 %
transmission for He I and II
• Patented zone plate arrangement
• Precise alignment with line of
sight viewport using LED
• Operating pressure down to
10-10 mbar range
• To be combined with HIS 13 & HIS 14 HD
• Integrated pumping port
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 FOCUS HIS Mono can be combined with the HIS 13 and HIS 14 HD VUV – lightsources.
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