Applications:

Physical Vapor Deposition

• Film Production (sub-monolayer to thick film)
• Optical Coatings
• Molecular Beam Epitaxy

Molecular Beam Experiments

• Thermal Desorption Mass Spectrometry
• Heat of Vaporization Measurements
• Photoelectron Spectroscopy
• Electron Energy Loss Spectroscopy
• Laser Induced Fluorescence Spectroscopy

Description:

Comstock's KMB-237 Knudsen Cell depends on the principle of molecular effusion initially demonstrated by Knudsen in the early 1900s. Knudsen effusion occurs when two volumes are separated by an orifice and the mean free path of the effusing atoms of molecules is large in comparison with the dimensions of the orifice. Typically, a beam of neutrally charged species results. The intensity distribution of the beam follows the cosine rule. Knudsen effusion sources provide high reproducibility and consistent rates of vaporization. Comstock's KMB-237 Knudsen Cell provides a stable beam for gas-phase experimentation or for reproducible deposition of submonolayer to thick film coverages.

Comstock's Model KMB-237 is a carefully engineered Knudsen Cell designed for stable control throughout a wide temperature range. The KMB-237 is constructed of all UHV compatible materials. For temperatures below 1200 C, the KMB-237 uses a pyrolytic boron nitride encased graphite heater element.

For applications requiring temperatures ranging to 2000 C, the KMB-237 uses an optional tantalum heater element. All materials that outgas at temperatures up to 2000 C are eliminated from the heated zones in the tantalum heater. Multiple heat shields are used to minimize the power requirements for achieving high temperature.

Comstock's KMB-237 Knudsen Cell uses a water- or liquid nitrogen-cooled shroud to minimize contamination of the system. The shroud is constructed of highly reflective electropolished stainless steel for minimization of heat absorption and for reflecting radiation back onto the heater.

Crucible material choices include amorphous graphite, highly oriented pyrolytic graphite (HOPG), pyrolytic boron nitride, tantalum, molybdenum, and other machinable materials. The crucibles are easily loaded and replaced.

Comstock's KMB-237 Knudsen Cell uses a manual shutter mechanism that is operated outside the vacuum. A computer controlled mechanized shutter is optional. The standard source is mounted on a 4.5" stainless steel knife-edge flange (other flange types and sizes optional).

The temperature of the crucible is accurately measured using an imbedded type C thermocouple. A digital temperature controller with PID feedback circuit coupled to a phase-angle fired solid state relay is used to control the temperature of the crucible.

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