Valved Sulfur Source VSS

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
150 cm³ reservoir
Reservoir and valve are located ex vacuum Datasheet

Introduction

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.

Valve Characteristic — 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.

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.

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.

Application

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)

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.

Technical Data

General
Mounting flange	DN40CF (O.D. 2.75")
In-vacuum length L	220 mm or 287 mm
In-vacuum maximum total length TL	240 mm or 307 mm
Maximum airside length OL	459 mm
In-vacuum diameter D	36 mm
Maximum airside radius AR	300 mm
Shutter distance DS	15 mm
Shutter opening angle	90° ccw
Bakeout temperature	200°C
Cooling water flow	30-90 l/h
Weight	13 kg
Maximum chamber pressure	10^-5 mbar
Reservoir
Heater type	Industrial grade electrical heater
Temperature sensor	Pt100 class A
Operating temperature	100°C – 245°C
Outgassing temperature	Up to 300°C
Cooling	None
Reservoir capacity	150 cm³
Reservoir material	Stainless steel or Inconel
Valve
Heater type	Industrial grade electrical heater
Temperature sensor	Pt100 class A
Operating temperature	100°C – 295°C
Outgassing temperature	Up to 300°C
Cooling	None
Valve material	Stainless steel
Tube
Heater type	Ta wire filament
Thermocouple	W5%Re/W26%/Re (type C)
Operating temperature	200°C – 600°C
Outgassing temperature	Up to 600°C
Cooling	None
Tube material	PBN
Cracker
Heater type	Ta wire filament
Thermocouple	W5%Re/W26%/Re (type C)
Operating temperature	300°C – 1000°C
Outgassing temperature	Up to 1200°C
Cooling	Integrated water cooling shroud
Cracking insert material	PBN or graphite

Dimensions

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 Gasketdimensions .

Product	CF flange	Nominal capacity	Reservoir outer diameter	Cooling	Shutter*	Valve type	Valve control	UHV dimensions*** [mm]	max. electrical [W]/[A]	Power supply product code
		[cm³ ]	[mm ]					[mm]/[mm]	[W]/[A]	Product code
VSS	40 -	150 -	51 -	K	S -	RV -	MC -	LxxxD36	reservoir 80/2 valve 80/2 tube 100/5 cracker 150/8	PS 60-35 PS 60-35 PS 36-12** PS 36-12
VSS	40 -	150 -	51 -	K	S -	RV -	HC -	LxxxD36	reservoir 80/2 valve 80/2 tube 100/5 cracker 150/8	PS 60-35 PS 60-35 PS 36-12** PS 36-12
VSS	40 -	150 -	51 -	K	S -	TV -	PC -	LxxxD36	reservoir 80/2 valve 80/2 tube 100/5 cracker 150/8	PS 60-35 PS 60-35 PS 36-12** PS 36-12

* rotary shutter possible on same flange (option S) ** optional *** 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.