A low-energy electron point-source projection microscope not using a sharp metal tip performs well in long-range imaging

Abstract

A low-energy electron point-source projection microscope that uses a metal/insulator structure as source instead of a sharp metal needle is presented. By combining this source with an electron optical lens and a high spatial resolution image detector, performances comparable to those of a normal electron projection microscope are easily accessible and presented here. The accessible electron energy range extends from 100eV to 1000eV. In the example presented here, instead of the usual near-field source-object distance, long-range imaging at a distance of about 600µm is achieved. 1-Introduction The normal low-energy electron point-source projection microscope [1,2,3,4] is a lensless system where an electron point source illuminates a perforated object, and the "physical shadow" of the object is recorded on a more distant fluorescent screen. The so-called physical shadow corresponds to the interference between the reference wave that comes directly from the source and the object wave that results from object scattering. This Fresnel interference pattern is an electronic hologram of the object. Numerical reconstruction yields an image of the object in its position during the recording [5,6,7].The projection microscope is known to reach a magnification of about 10 5 with an experimental spatial resolution of about 1nm [8,9,10]. These

Preparing a Celadonite Electron Source and Estimating Its Brightness

“…The electron celadonite source is now regularly used in a low-energy electron point-source projection microscope, associated with an Einzel lens system. Because of the high brightness of the source, at this large working distance of 600µm, a resolution of about 30nm is generally obtained [12]. In point-projection microscopes, working at a so large source-object distance is comfortable and is really advantageous.…”

“…A simple short projection setup with a fluorescent screen allows for low magnification projection. The second setup involves an electrostatic lens and a dual microchannel-plate / fluorescent screen assembly for the strongest magnifications [12]. In fact, information available on each projection image is used to under-estimate the brightness: the smallest detail in the record [13].…”

“…However, we recently showed that the celadonite source emitter combined with an Einzel lens performs comparably to a classic point-source projection microscope. The long-range imaging thus made accessible even limits the charge effect [11] on the object and the image distortions involved [12,13]. The celadonite source also presents major advantages compared to sharp metal tips.…”

Bright sources under the projection microscope: using an insulating crystal on a conductor as electron source

“…However, this source is not an ultra-thin tip; it is situated at the end of a carbon fiber of = 10µm diameter, and the approach is therefore limited to some tens of micrometers [9]. For this reason, a new point-projection microscope was realized, comprising a micro-manipulator, a double electrostatic Einzel lens, and a double micro-channel plate detector [10]. These modifications enabled us to achieve a source size of s = 1.5nm according to the interferometric measurement described above.…”

“…We will see in this article that a projection microscope is perfectly suited to characterizing sources and in particular their size, whatever the emitted particles [4,5]. An electron source consisting of an insulating crystal deposited on a carbon fiber, as described in several articles [6,7,8,9,10], was characterized with these methods and will be described here.…”