This protocol aims explaining how to make a celadonite electron source. These sources have shown a long lifetime and their brightness are equivalent to that of filled emission metal tips. Using this celadonite electron source in a projection microscope, associated with an electrostatic lens, makes it possible to work with a large source object distance.
This prevents the source crash risk and image distortion by decreasing local field effect on the object. To begin this procedure, insert the source into stainless steel tube with an inner diameter of 90 micrometers. Insert a tungsten wire with a diameter of 50 micrometers into the tube and roll the tube under a knife blade to cut it to the required length.
Fix the source support underneath an optical microscope. Insert a 10 micrometer carbon fiber into the stainless steel tube. And glue the carbon fiber to the tube with silver lacquer.
Under a binocular microscope, use cutting tweezers to cut the fibers so that between 100 micrometers and three millimeters are left outside of the stainless steel tube. Next, grind the celadonite with a mortar and pestle. Weigh out 0.2 milligrams of celadonite powder, and dilute it in 10 milliliters of deionized water.
Place an ultrasound tip directly into the celadonite-containing water, and use an ultrasonic frequency of 30 kilohertz and a power of 50 watts for 30 seconds to break up the aggregates. To prepare the deposition environment, connect a capillary holder to a pressure controller. Maintain the capillary holder under an optical microscope with a multi-directional micro manipulator.
Place the support under the microscope with the carbon fiber facing the capillary holder. Next, fix a glass capillary in a polar jaw. Using table one of the text protocol, ensure that the polar parameters are set properly according to the patch pipet size, and pull a micro pipet with an internal end diameter between two to ten micrometers, to allow the dispersed celadonite to flow without obstruction.
Then, fill the micro pipet with the celadonite-containing water. Under the microscope, mount the micro pipet on the capillary holder, and align the micro pipet with the carbon fiber. Increase pressure on the wide end of the micro pipet, such that a drop forms at its exit without falling down.
Move the carbon fiber up to touch the drop, which will wet the apex of the carbon fiber. After this, retract the carbon fiber. Under a microscope, insert the source into the source support.
Install the source holder under the vacuum. Connect the carbon fiber and the object to two high-voltage electrical feed-throughs. Check the electrical continuity of each contact, and install the flange on the experimental setup.
After this, turn on the vacuum pumping. Connect a nanoammeter of a caliber in the microampere range between the object and the electrical ground. Increase the negative bias voltage applied to the source slowly at approximately one volt per second.
If the anode is one millimeter away from the source, the kickoff takes place at around two kilovolts when the intensity suddenly increases. Then, immediately decrease the voltage to stabilize the intensity by some hundred nanoamperes. At the beginning, the intensity can fluctuate over several orders of magnitude.
Intensity may fluctuate for several hours. Wait until the fluctuations decrease. Cut off the voltage when the fluctuations are lower than 10%To begin, use the rotating flange to turn the source towards the simple projection setup to observe the electron beam.
Use the micro manipulator to decrease the source-to-screen distance, and obtain the entire spot on the screen. Measure the source-to-screen distance. Take pictures of the screen by using the rotating flange to change the angle between the electron beam and the normal to the screen.
Plot the gray level intensity profile along one axis, and determine the emission radius at a given source-to-screen distance. Calculate the cone angle as outlined in the text protocol. After this, measure the emission intensity versus the voltage applied to the source with the intensity measured at the anode, and the voltage applied at the carbon fiber.
Create a Fowler-Nordheim plot to the celadonite source as outlined in the text protocol. The curve will show a decreasing straight line with saturation for highest voltage. The longest straight line is the signature of the field emission process.
To measure the source size, use the rotating flange to turn the source towards the electrostatic lens. Adjust the intensity to still have the signal at the highest magnification. Make a first magnification with L1, and then approach the object toward the source.
Finally, activate L2 to produce a projection image containing a huge fresnel diffraction pattern along the edge of an object. Measure the sharpest visible detail on the image on-screen, and calculate the source size as outlined in the text protocol. Several scanning electron micrograph images of celadonite deposited on carbon fibers, were obtained at 15 kilovolts or three kilovolts.
Sources exhibit one, sometimes two crystals at their apex. However, the use of the SEM involves another support for the carbon fiber, which is hard to mount and de-mount without breaking. It is safer to attempt direct electron emission.
Tests in a projection microscope show that every source prepared this way emits. The kickoff is required only once. Most of these sources show one single point source.
The emission profile indicates only one continuing image without any other spot. The Fowler-Nordheim plot exhibits 10 orders of magnitude straight and saturation at higher voltage. The saturation regime obtained for a given voltage depends on the structure, but the slope decreases systematically for higher current intensities from about 10 microamperes.
The source size is then estimated by measuring the smallest detail on the image produced. This image is the fresnel diffraction pattern of the object. Here, loss of interference fringes is attributed to the size of the source.
In this protocol, the most important is to obtain a single crystal of celadonite at the apex of a tiplied-shaped conductor, to be able to approach an object towards the source to image the subject. Likely the crucial step is where a small drop of the well-dosed celadonite-containing water, is deposited at the apex of the fiber. Using this celadonite electron source in a projection microscope equipped with an electrostatic lens allows working with a large source object distance.
This makes it possible to develop off-axis autographic techniques, to explore magnetic and electric fields around nanometric objects.
