XL30 ESEM

A Unique Solution for Problematic Sample Observation at High Resolution

The XL30 ESEM-FEG offers high resolution secondary electron imaging at pressures as high as 10 Torr and sample temperatures as high as 1,000°C. This means that wet, oily, dirty, outgassing and non-conductive samples can be examined in their natural state without significant sample modification or preparation. The XL30 ESEM-FEG is the first Scanning Electron Microscope (ESEM®) to employ the stable, high brightness Schottky Field Emission Source for outstanding observation performance of potentially problematic samples for conventional high vacuum SEMs.

Key Benefits:

• True secondary electron imaging at 10 Torr chamber pressure
• No charging of non-conductive samples
• Low-Z materials
• Observation of contaminating samples
• Porous material observation
• BC stability < 1% / hour, Schottky emitter
• Hydrated samples remain fully stable
• No coating interference
• Phase transitions
• Hydration processes
• Oxidation/corrosion
• Stress testing

These benefits of the ESEM-FEG are realized by eliminating the high vacuum requirements of SEMs in the microscope chamber. This is done by separating the vacuum environment in the chamber from the high vacuum environment in the column and FEG source area. Two Pressure Limiting Apertures (PLAs) separate the microscope chamber from the FEG column. The three regions created by these PLAs are separately pumped. This causes a graduated vacuum from 10 Torr in the chamber (above the vapour pressure of water) to 10-8 Torr in the middle region of the column down to 10-10 Torr in the emission chamber.

The actual chamber pressure is controlled from a MS Windows graphical user interface. Low vacuum and conventional high vacuum modes can be selected from this user interface as can the chamber pressure in Wet mode (using water vapour) and Aux mode (using any other gas.) The pressure can be displayed in units of Torr, millibar or Pascals and set in increments of 0.1 Torr, 0.1 millibar or 10 Pascals.

Employing the "WET" Chamber Mode
Although basically any gas can be used in the microscope chamber, water vapour is used in the standard "Wet" ESEM mode. Not only does water vapour allow observation of hydrated specimens in their natural state but also provides an optional cooling stage, liquid to vapour transitions and vice-versa for in situ (de)hydration experiments that can be performed within the SEM environment.

The presence of gas in the chamber produces two important effects. These are induced intrinsic signal amplification and charge neutralization.

Secondary electrons emitted by the sample accelerate in the detector field as imposed by the detector. There they collide with gas molecules. This collision results in ionization of the gas, creating positive ions and additional secondary electrons called environmental secondary electrons. The repetition of this process results in a proportional cascade amplification of the original secondary electron signals that are strong enough to be detected. The positive ions are attracted to the sample surface as negative charge gathers from the beam on the insulated specimen surface. This is how the positive ions effectively suppress charging artefacts. Charge suppression allows the imaging of non-conductive samples in their natural, uncoated state, with a free choice of accelerating voltages.

The Role of the GSED Detector in Outstanding ESEM® Performance
The gaseous secondary electron detector (GSED) is mounted below the final lens assembly to permit secondary electron imaging in a gaseous environment. The primary function of the GSED is to discriminate the noise forming electrons so that image quality and resolution are comparable to that of conventional high vacuum FEG-SEMs. Image quality and high resolution are achieved by a suppressor electrode and a detector ring. The detector is constructed as a printed circuit board and is easily removed to clean contaminants from the sample. The shape and size of the ring mean that most backscattered electrons and type III secondary electrons, primarily responsible for noise in the image, are isolated by the electrode. Most other secondary electrons are detected by the detector ring. Optional detectors that can be used on the XL30 FEG-ESEM are the conventional secondary electron, Scintillator backscattered electron and specimen current detectors.

Exceptional X-ray analysis in the XL30 ESEM-FEG
Direct benefits for X-ray analysis are given with the XL30 ESEM-FEG, since charging is no longer the case and interference of sample coatings is no longer an issue. This means that analysis at higher accelerating voltages on non-conductive samples is finally realized.

The two important benefits in X-ray analysis with the XL30 ESEM-FEG of uncoated specimen are:
1. No X-ray lines from the coating interfere with the characteristic X-ray spectrum generated in the specimen. The absence of conductive coatings rids the potential absorption and interference artefacts.
2. X-ray analysis is performed at high beam energies. No charging artefacts means the operator is free to choose any acceleration voltage for optimal X-ray analysis.

The XL30 ESEM-FEG: Microscopy and Lab in One
The ESEM-FEG's extraordinary capabilities of performing and recording in-situ experiments extend research to areas it has never before been able to reach. For the first time, dynamic experiments can be carried out and recorded under ambient levels of light. This is because, unlike the Everhart-Thornley secondary electron detector of conventional SEMs, the gaseous secondary electron detector (GSED) is not light or heat sensitive. With the optional heating stage, samples can be heated, crystallized or melted while they are in the microscope chamber. The entire process can also be reversed without having to remove the sample from the chamber. This permits continuous observation and recording of in-situ experiments with a resolution never before seen. The ESEM-FEG vacuum automatically stabilizes the chamber pressure even if the sample outgases during experimentation.

For booking this instrument or other enquiries

Tel (0191) 222 7058

or email acma@ncl.ac.uk

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