Oxford Applied Research

X-Ray Monochrometer


In many XPS applications monochromated X-ray sources have important advantages over standard X-ray sources

Spectral interpretation is made easier due to the narrow energy width, better signal to background and the removal of Bremsstrahlung radiation and satellites.

However in a conventional monochromator, these advantages are coupled with intrinsically low transmission.

By incorporating a large area crystal matrix on a toroidal substrate, the VSW MX10 Monochromator has greatly increased transmission. This gives superior sensitivity but does not compromise performance. Together these resolution features allow the MX10 to be used routinely in the widest range of XPS applications, including small area XPS.

 

  • Large 700mm Rowland Circle for high performance
  • Micro focus source producing high flux density into 1.2mm diameter.
  • Modified toroidal geometry
  • Large solid angle (0.1 steradian) for maximum intensity
  • Multiple crystal design for accurate focusing
  • High stability crystal backplane
  • Precision micrometer crystal and source adjustment for optimum tuning
  • High power 600W
  • Integral X-ray transparent window for contamination free operation in UHV
  • BIS option


The MX10 monochromator consists of a microfocus x ray source and crystal assembly in a vacuum housing.

The geometry is based on a 700 mm diameter Rowland circle for high performance with a multiple toroidal array of quartz 1010 crystals.

The Bragg angle is 78.5 degrees to produce monochromated Al K alpha radiation (1486.6eV). A large solid angle for maximum intensity is produced of 0.1 steradian. Maximum power is 600 watts.

The housing contains a removable transparent window for contamination free operation.

 

MX10 Mechanical Details

Crystals 1O1O Quartz
Crystal substrate        
Precision engineered, high stability
Crystal alignment Precision micrometers on 3 axes
Anode matrix Aluminium
Power maximum 600W
Anode voltage 15kV
Bakeout Up to 1500C
Source cooling Water (200C maximum) @ 70L/HR
Source alignment

Linear positioning

 

Routine High Sensitivity

The high transmission of the VSW monochromator means that wide ranging survey scans can be realised in only a few minutes. The survey scan was acquired in 13.5 minutes, with a peak count rate of 900 kc/s in the Ag 3d5/2 peak.

This spectrum demonstrates the monochromator's suitability for XPS studies of polymers. The instrumental resolution is narrower than the observed linewidths of the Mylar Cls peak

High resolution
Many samples must be studied at the highest resolution to enable subtle peak shapes or chemical shifts to be accurately measured, or to resolve closely spaced peaks.

In this spectrum, the Ag3d5/2 peak has a width of 0.48eV yet with a peak count rate in excess of 30,000 cps, it was acquired in under 17 minutes

The spectrum of crystalline Silicon (100) shows the Si 2p spin orbit doublet (split by only 0.6eV), with a FWHM resolution of 0.36eV in the raw data. Peak shifts in this material reflect the chemical state and give vital information in semiconductor material research.

The low intensities of the 4d band and the Fermi edge in Silver require a combination of high sensitivity, high resolution and high signal to background as demonstrated here. The Fermi edge is measured as only 0.24eV wide (20:80%).

The spectrum of crystalline Silicon (100) shows the Si 2p spin orbit doublet (split by only 0.6eV), with a FWHM resolution of 0.36eV in the raw data. Peak shifts in this material reflect the chemical state and give vital information in semiconductor material research.

Very weak signals are normally experienced in small area XPS because of the reduced area of analysis. However, even in these circumstances, the VSW MX10 X-Ray Monochromator enables superb data to be obtained.

For example this survey spectrum was obtained using the CLASS 150's Variable Magnification facility and has a resolution of 0.8eV from an area of 150um diameter, yet took only 28 minutes to collect.