SEM: JEOL JSM-6490LV
The JEOL JSM-6490LV is a variable pressure scanning electron microscope (SEM). It produces a magnified image of a sample by scanning a focused electron beam across the surface of a sample and observing various signals produced when the electrons interact with the sample. By reducing the size of the scan, the magnification is increased. Almost any solid material can be observed using the SEM. Because of the variable pressure abilities of the SEM it is possible to observe insulating materials directly without the need for a conductive coating. It is also possible to observe biological materials without the need for extensive sample preparation.
Variable pressure operation of the SEM allows for a lower vacuum to exist at the sample than is traditionally required. By "leaking" air into the sample chamber it is possible to directly observe samples that have been frozen or are otherwise wet, oily or non-conductive. Traditionally, extensive sample preparation methods have been required to make hydrated samples ready for SEM observation. With the advent of variable pressure operation, sample preparation is simplified to simply freezing the sample and placing it in the microscope. Variable pressure operation also provides a positively ionized gas immediately above the sample. This source of positive ions works to dissipate the negative charge that accumulates on the sample surface during SEM observation and can interfere with image collection. This means that non-conductive samples can be imaged without application of a conductive coating. The JSM-6490LV is equipped with two imaging detectors useable in a variable-pressure environment. The backscattered electron detector images backscattered electrons that originate deeper within the sample, where contrast is dependent on the average atomic number of the sample. The variable pressure secondary electron (VPSE) detector images secondary electrons produced very near the sample surface and contrast is dependent on surface topography.