Laboratory of Cathodoluminescence Microscopy
head: Przemysław Gorzelak
e-mail: przemyslaw.gorzelak@gmail.com
CL-Form (link)
Laboratory Regulations (link)
Cathodoluminescence microscopy enables analysis of light emitted by a luminescent material when excited by an electron source. Cathodoluminescence can reveal impurities of trace elements and hidden or cryptic textures in minerals that normally are not detected under optical microscopy.
The basic research instrument of the Laboratory is the Lumic HC5-LM cathodoluminescence microscope with a hot cathode. The possibility of adjusting the power of the pure electron beam allows for obtaining much higher quality luminescence images compared to cold cathode microscopes. The microscope is coupled with the UV-VIS spectroscopic system by Princeton Instruments (Acton Series SP-2356), and an air-cooled, color CCD camera KAPPA DX 40-285 CL. The design of the device is based on the OLYMPUS optical microscope equipped with four achromatic objectives (magnifications 2.5x, 5x, 10x and 20x) and monocular and trinocular attachments. The most important modification of the microscope is the stage, which in the case of HC5-LM is formed by a conical vacuum chamber equipped with a lid with a lead glass window. The vacuum of < 10-5 mbar is provided by a vacuum pump system, i.e. a rotary pump and a turbomolecular pump. The actual microscope stage moved by external adjustment screws and an electron gun is located at the base of the chamber.
A sample properly prepared for measurement is a very thin, uncovered petrographic thin section (approx. 20 micrometers thick), sputtered with a carbon coating several nanometers thick and placed with the exposed side towards the base of the cone. An electron beam emitted by an electron gun with the so-called hot cathode (thermocathode) is directed at this surface. The thermocathode emits electrons when heated to a high temperature (emission via thermonuclear radiation). Compared to traditional cold cathode cathodoluminescence microscopes, which emit electrons without external heating, the hot cathode microscope offers much greater possibilities of regulating a pure electron beam (the cold cathode emits cations in addition to electrons).
Sample preparation, measurements
The size of the thin sections should correspond exactly to the dimensions of 27 x 46 mm, i.e. the size of a standard petrographic glass slide, while the thickness of the polished object should not exceed 25 micrometers. In rare cases, depending on the method of preparing the sections and the type of resin used, part of the sample may peel off during the examination, for which the laboratory is not responsible. Visible damage to the cut surface ("burning") may occur during longer observation without changing the position of the examined area, therefore, usually when working in cathodoluminescence mode, the selection of the examined area must be done very quickly (a dozen or so seconds).