CCD camera in J. Heyrovský Institute of Physical Chemistry

Main page▹References	22.3.2007 \|

Demanding scientific experiments require hi-tech equipment. Scientists at J. Heyrovský Institute of Physical Chemistry use G2CCD camera to visualize images from field emission microscope. This microscopic technique displays the surface on fluorescent screen by electrons emitted from the sample in the presence of high-voltage electric field (10⁷ V/cm). Lateral resolution of this technique is approximately 2 nm (2x10^-6 mm). Field emission image is quite dim and requirements for its digitization are high. Astronomical CCD camera with very high quantum efficiency, 16-bit digitization, low noise, fast USB interface and ability to integrate light during long exposures perfectly fits their needs.

G2CCD-0400 camera is equipped with ordinary SLR camera lens, pointing to the microscope screen in the ultra high vacuum chamber. Camera is attached to the microscope body using custom-made arm. Exposure times vary within seconds, so it is not necessary to cool the CCD chip below freezing point—the KAF chip generates approx. 1 electron per second per pixel at 0 deg.C.

G2CCD-0400 Camera on the Field Emission Microscope

Experiment results

The following images show the progress of experiment focused to examination of growth and thermal stability of very thin palladium layer on the tungsten sample covered by tungsten oxide. The sample is prepared from 0.2 mm thin tungsten wire etched to very sharp tip.

The sample holder with tungsten tip prepared for experiment

The images below show field emission images of the tip during experiment. Field of view covers 800 nm (0.000,8 mm) diameter—camera shows approx. 1.5 nm per pixel. All images are displayed in false colors to enhance subtle details.

The first figure shows the clean surface of the tungsten monocrystal.

The second frame shows the sample surface after mild oxidation.

Then a very thin layer—only 0.3 nm—of palladium is evaporated on the tungsten oxide surface cooled to 78 K.

The sample is then heated to approx. 350 and 500 K. After heating to 350 K (left image) palladium layer forms island with cross shape influenced by tungsten oxide support. Additional heating to 500 K (right image) probably cause encapsulation of palladium by tungsten oxide (the image is similar to bare oxidized tungsten before palladium evaporation).

All images on this page are courtesy of Ing. Jan Plsek, PhD., J. Heyrovský Institute of Physical Chemistry, Prague