MBE Components, Valved Sulfur Source VSS


Valved Sulfur Source


VSS 40-150-51-KS-RV-MC valved sulfur cracker on DN40CF (O.D. 2.75") mounting flange with 150 cm³ reservoir, integrated cooling shroud with shutter
  • Provides sulfur flux rates for R&D applications on a DN40CF flange

  • Flux regulation and on/off control by motorized valve

  • UHV-tight valve

  • Water-cooled cracker with beam shaping nozzle

  • 12 cm³ or 150 cm³ reservoir

  • Reservoir and valve are located ex vacuum

Download IconData Sheet


The Valved Sulfur Source VSS aims at R&D applications where valve controlled small or medium flux rates of high vapor pressure materials are required.

This cell comes with a water-cooled cracker that reaches temperatures up to 1400°C. The cracker and injector building blocks are identical with our established TCC design. As shown for TCC, the thermal cross talk between the cracker and reservoir are almost negligible. See figure on the right for a schematic overview of the VSS cell. 

The reservoir and the valve are both located ex vacuum. This offers a huge benefit for reloading the reservoir or maintenance work, which can be done without venting the chamber. The reservoir and valve are heated by industrial grade electrical heaters and are both temperature controlled with high accurate Pt100 thermometers. In order to achieve the highest possible cleanliness all critical welds for the valve and reservoir are prepared by electron beam welding.

VSS schematic
Schematic of VSS

1 case, 2 vacuum chamber
3 stepper motor for valve regulation
4 material reservoir, 5 valve
6 PBN injector tube, 7 cracker insert, 8 shutter 
9 electrical heater, 10 water cooling

The VSS is designed for reservoir temperatures up to 250°C and works smoothly down to 100°C. The internal thermal design ensures ideal temperature gradients for trouble free operation. To ensure maximum process control this cell offers four independent heating circuits (reservoir, valve, pipe, cracker). However, depending on application the cell can be operated by using three circuits only.

The VSS is equipped with a high precision stepper motor that controls the valve. Hence, flux modulations in the order of two magnitudes are typically obtainable. For other applications pneumatic and manual valve control is also available.

There are two different valve types available for the VSS, namely a high throughput variation with higher overall throughput and one valve with smaller throughput but finer flux regulation characteristics. See the figure on the right for information about valve characteristic.

click to enlarge image

Valve characteristic for
0.18 mbar (~145°C sulfur vapour pressure) and
0.25 mbar (~150°C sulfur vapour pressure)
valve inlet pressure. Inlet gas is air.



A source concept like this is used for high vapor pressure materials, which form atom clusters. Typical evaporation elements are S and Se.

The in-vacuum length of the VSS is either 220 mm or 287 mm. Other in vacuum lengths are achievable using application specific spacers.

By default the cracker insert will be made from pyrolytic boron nitride, which will ensure efficient cracking for sulfur and selenium.

The following figure shows an example of a short operating cycle of the VSS.

typical operating circle

Temperature / time chart for an operation example of the VSS 40-150-51. The shown temperature curves can be separated in three procedure steps: heat up (0-140 min), growth window (140-145 min) and cool down (145 min – 220 min)


Technical data

Port to chamber DN40CF (2.75” O.D.)
In vacuum diameter 36 mm
Bakeout temperature 200°C
Shutter opening angle 90° ccw
Cooling water flow 30-60 l/h
Weight 13 kg (VSS 40-150-51-KS-RV-P-MC-L220D36)
Surface temperature typical 60°C,
maximum 90°C (touch protection available)
Heater type industrial grade electrical heater 80 W / 42 V
Temperature sensor Pt100 Class A 3-wire configuration
Operating temperature 100 - 250 °C
Maximum temperature 300°C
Cooling none
Capacity options 150 cm³
12 cm³
Heater type industrial grade electrical heater 80 W / 42 V
Temperature sensor Pt100 Class A 3-wire configuration
Operating temperature 100-250 °C
Maximum temperature 270°C
Cooling none
Types high throughput version (Option: -TV)
fine regulation version (Option: -RV)
Control options motorized (Option: -MC)
pneumatic (Option: -PC)
manual (Option: -HC)
Injector pipe
Length of tube 220 mm or 287 mm
Heater type tantalum wire filament
Cooling none
Operating temperature 200-400°C
Temperature sensor W5%Re/W26%Re (type C)
Options integrated rotary shutter (-S)
Operating temperature 300 - 1200°C
Maximum temperature 1400°C
Heater type tantalum wire filament
Temperature sensor W5%Re/W26%Re (type C)
Cooling integrated water cooling shroud
Cracking insert PBN or graphite



schematic drawing VSS

Schematic drawing of a Valved Sulfur Source VSS

(drawing shows VSS 40-150-51-KS-RV-MC)


Specific data

For general information on CF mounting flanges see Flange and Gasket dimensions.

[cm3] [mm] [mm] / [mm] Product code
VSS 40 - 150 - 51 - K S - RV - MC - LxxxD36 1 x PS 30-10¹
2 x PS 75-2
VSS 40 - 150 - 51 - K S - RV - HC - LxxxD36 1 x PS 30-10¹
2 x PS 75-2
VSS 40 - 150 - 51 - K S - TV - PC - LxxxD36 1 x PS 30-10¹
2 x PS 75-2
* rotary shutter possible on same flange (option S) 1 Power supplies for cracker heater; for optional pipe heater an additional PS 30-10 power supply is needed
*** specify UHV length L with order
(L = 220 mm or L = 287 mm)


Typical accessories

- Motorized Valve Control Unit MVCU

- Rotary Shutter Module RSM


Product code:

e.g. VSS 40-150-51-KS-RV-MC-L220D36

is a valved sulfur cracker source on DN40CF flange with 150 cm³ nominal reservoir capacity, integrated cooling shroud and shutter, fine regulation valve and motorized valve control, in-vacuum length 220 mm and outer diameter 36 mm.