An apparatus for imaging liquids, cells, and other wet samples in the scanning electron microscopy

We present a technique of scanning electron microscopy that is adapted to the study of wet samples. The wet environment is protected in a small chamber enclosed by a membrane, which is thin enough for energetic electrons to go through and interact with the sample studied. We detail both the technique and the general mechanisms of signal formation in the imaging of samples through a membrane. We first describe our setup and the properties required for the membrane, the main element in this method. Some simple measurements for its characterization are given, guiding the choice of material and thickness. We then go on to describe the capabilities of the technique in imaging a variety of different samples. We evaluate the accessible contrast and resolution, and the current needed to obtain them. Low contrast samples can be imaged with an improvement in resolution over optical microscopy. High contrast samples like gold markers labeling a biological cell can be imaged with a resolution of the order of 10 nm. The resolution depends on the location of the particle in the sample: the closer to the membrane, the better the resolution. We believe such a result opens up potential applications for routine experiments in biology, and expect this new technique to find numerous applications in domains where liquid samples are investigated such as soft materials science. (C) 2004 American Institute of Physics.