Miniature Knudsen-Cell (K-Cell)

Benefits of the WKC3 Knudsen Cell
 

• Intrinsically stable evaporation rate
• Controlled deposition of wide range of materials
• Compact design
• Flexibility to change materials
• Operating temperature up to 1500°C
• Integral shutter
• Integral watercooling jacket

Principle of Operation

The Miniature K-cell provides the ideal tool for reproducibly depositing small area thin films of material, with coverages ranging from sub-monolayer to continuous films. The material to be deposited is heated to provide a suitable vapour pressure in an isothermal enclosure. Molecular effusion from an aperture in the end of the cell gives rise to a cosine intensity distribution. The deposition rate is extremely stable, being determined by the temperature of the enclosure which is accurately controlled using a thermocouple and temperature Controller.

The K-cell is engineered to provide a compact, self contained cell enabling the researcher to have a convenient controllable deposition source. The entire cell, incorporating the furnace with water or liquid nitrogen cooling, electrical leadthroughs and a bellows-sealed shutter assembly, is mounted on a 35CF (2.75 inch OD) flange. This compact arrangement allows the cell to pass down a 35 mm bore tubulation.

The furnace of the K-cell is designed as a removable cartridge which contains the crucible, heater element and heat shields. The crucible is heated by a Tantalum foil element which is isolated with Pyrolytic Boron Nitride (PBN) shields. The central crucible is Graphite with an embedded thermocouple for accurate temperature measurement. The position of this thermocouple has been selected to track accurately the internal furnace temperature to provide high stability and reproducibility.

This design gives a stable high temperature furnace for controlled deposition of a wide range of materials. For maximum versatility, a PBN or alumina liner may be fitted into the main furnace. The PBN and alumina crucibles are supplied with removable apertures to define and limit the output beam. The unique cartridge design gives additional flexibility to the user since either the furnace or just the liner may easily be replaced when the deposition of a different material is required.
 

Three cell flange

For studies where simultaneous or sequential deposition of different materials is required the compact design of the Miniature K-cell allows a group of three cells to be mounted on a 10OCF (6" OD) flange. In this configuration the cells target a common area 130 mm from the shutter.

Power and temperature control of the WKC3 Knudsen Cell

To provide a stable deposition rate the temperature of the furnace must be regulated. The K-cell Controller uses a microprocessor managed three term PID (Proportional, Integral, Differential) Controller to determine the required power level and to provide excellent temperature stability. Changes in the cell temperature are simply achieved by changing the set temperature digitally displayed on the Controller.

K-Cell Specifications:
 

Max operating temp	1500°C
Heating	Tantalum foil heating element
Bakeout	Bakeable to 250°C
Typical power at 1500°C	125 W
Apertures	1 mm dia. Standard  (other sizes on request)
Crucibles:
Very Fine Grain Graphite
Density	1.82 g/cm3
Open Porosity	8%
Capacity	0.5 cm3
Pyrolytic Boron Nitride (PBN) liner
Density	2.15 g/cm3
Open Porosity	0%
Capacity	0.4 cm3

Ordering Information:
 

WKC3 Knudsen Cell
Body and shutter assembly	KC3-BODY
Standard Graphite furnace with (W-3%Re/W-25%Re) thermocouple	KC3-GRA-W3
Optional Graphite furnace with (Pt/Pt-13%Rh) thermocouple	KC3-GRA-R
PBN linerand apertures	KC3-PBN
PBN apertures (x2)	KC3-PBN-CAP
Graphite aperture (x1)	KC3-GRA-CAP
3-Cell 100CF flange	KC3-3F
Power and temperature control
Control unit	250-PTC
Connection lead	KC3-PTC-2 (2 metre) KC3-PTC-4 (4 metre)