Welcome to WSI
Williamsburg Scientific Instruments
Your partner for in-situ and experimendo Surface Analysis with Near Ambient Pressure (NAP) capability
WSI develops and sells components and systems for surface analysis, performing at much higher pressures than standard equipment. Our products aim to raise the operating vacuum pressure for surface analysis into a range as close as possible to Near Ambient Pressure (NAP). At present, NAP spectroscopies typically performed by optical methods such as Infrared, X-ray diffraction and Surface Plasmon Spectroscopy operate at atmospheric pressure; however, many surface interactions take place at lower environmental pressure and require some vacuum, especially when working with gaseous components. This lower pressure range is called Near Ambient Pressure (NAP) referring to a pressure range starting roughly at 0.1 Torr up to 100 Torr or higher.
Only a few analysis techniques can presently reach this pressure range, as described later. For reference, the pressure at Mount Everest is ~0.3 atmosphere (260 Torr, mostly O2, N2, H2O) and on the Mars surface ~0.3 atmosphere (260 Torr mostly CO2).
WSI offers new modular components, such as electron and ion sources, energy analyzers and detectors, able to operate in such a high pressure range. The high pressure capability operation is achieved by multiple vacuum steps, which keep a suitable operating pressure inside the components and by mainly using optical designs better adapted for use in higher vacuum pressures. Each application has specific requirements, such as the use of different gaseous mixtures, and thus the operating range will strongly depend upon the actual experimental conditions.
There is no universal answer to the question: ‘How far in pressure can an experiment be conducted?’. More precisely, the use of light gases reduces the electron scattering effects but also reduces the overall pumping speed. Many such intricate relationships exist in operating at higher vacuum pressures. The WSI team can provide specific recommendations to customers in designing a vacuum chamber and operating a NAP system.
Combining available NAP electron sources and detectors provides the following techniques:
| Technique | Acronym | NAP- Energy Analyzer | NAP- Electron Source | X-Ray Detector | Optical Spectro-meter |
| Auger Electron Spectroscopy | AES | Y | Y | ||
| Reflection High Electron Energy Diffraction | RHEED | Y | |||
| Reflection Electron Energy Loss Spectroscopy | REELS | Y (at lower energy) | Y | ||
| Cathodoluminescence | CLS | Y | Y | ||
| X-ray spectroscopy | XRS XRF | Y | Y | ||
| Optical Spectroscopy | IR Spectroscopy | Y | |||
| Synchrotron Radiation | AES XRF | Y | Y | Y |
The different techniques are used in different maximum pressure ranges.
The vacuum system can vary from UHV up to atmosphere, but each spectroscopy will operate at different pressure limits. The vacuum system should be designed to allow fast pumping in order to rapidly adjust the pressure according to the technique in use.
Electron and Ion sources can operate up to several 10 Torr. The X-Ray analyzer runs at up to a small fraction of the atmospheric pressure. High energy electron guns equipped with vacuum window can work at almost normal pressure. Auger electron analyzers have a more complex optical system and are presently limited into the 100 mTorr range.
A major requirement for all components is that the distance between sample and source (Working Distance, WD) must be kept short enough to ensure results. NAP components usually keep the WD in a 3-10 mm range, thus still allowing easy sample positioning, and tilt to optimize beam geometry.
Various combinations of the modular components are possible to build a NAP analysis system best adapted to the user’s goals. Some applications like RHEED, XRS, or CLS combined for Optical Spectroscopy require a simple vacuum chamber. Combining a NAP-electron source with the NAP Auger Spectrometer for operando surface analysis to study corrosion, catalysis with material deposition requires a more complex vacuum system. Many combinations are possible. WSI can assist you in determining the feasibility of a specific design.
The WSI NAP vacuum system includes a load and transfer chamber attached to a compact analysis / process chamber with multiple access flanges to accommodate sources and instruments. For instance, RHEED, XRS, AES and ports for Optical Spectroscopy (Infrared, Cathodoluminescence, Synchrotron radiation, etc.), provide sample preparation, material deposition, gas inlets and viewports for observation.
There are 3 ways to upgrade laboratory equipment to a NAP capability:
- Upgrade an existing vacuum system. The NAP sources and analyzers can often be custom adapted to an existing chamber; the chamber itself being upgraded with consequent pumping capability.
- Attach a NAP chamber to an existing vacuum system. A transfer line is generally a premium choice for adding a NAP system.
- Stand-alone NAP process & analysis system. A fast loading chamber provides easy sample exchange. The chamber is equipped with access ports for components and viewports for optical spectroscopy. A Vacuum transfer case can be used to carry sample between vacuum systems. The chamber can be attached to a synchrotron facility for soft X-ray excitation.