The authors would like to thank Marjorie Sweetko for improving the English of this article.

1. Preparation of the source
NOTE: In our microscope, the source-support is composed of a machinable glass ceramic plate from which emerges 1 cm of a stainless-steel tube of 90 &#181;m internal diameter with an electrical connection on the plate.
<ol>
	<li>Preparation of the fiber
	<ol>
		<li>Fix the source support under an optical microscope.</li>
		<li>Insert the 10 &#181;m carbon fiber into the stainless-steel tube. Glue the carbon fiber to the tube with silver lacquer.</li>
		<li>Cut the fiber with a cutting tweezers (under a binocular microscope) so that between 100 &#181;m and 3 mm are left outside the stainless-steel tube. 
		NOTE: The carbon fiber is brittle; leaving more than 1 cm outside the tube will increase the chance of the structure breaking during manipulation.</li>
	</ol>
	</li>
	<li>Celadonite-containing water preparation
	<ol>
		<li>Grind the celadonite with a mortar and pestle.</li>
		<li>Weigh 0.2 mg of celadonite powder and dilute in 10 mL of deionized water.</li>
		<li>Use an ultrasound tip directly in the 10 mL of celadonite-containing water to break the aggregates. Typically, use an ultrasonic frequency of 30 kHz for a power of 50 W over 30 s.</li>
	</ol>
	</li>
	<li>Preparation of the deposition environment
	<ol>
		<li>Connect a capillary holder to a pressure controller.</li>
		<li>Maintain the capillary holder under an optical microscope with a multidirectional micro-manipulator.</li>
		<li>Place the support with the carbon fiber facing the capillary holder under the optical microscope.</li>
	</ol>
	</li>
	<li>Celadonite deposition
	<ol>
		<li>Pull a micropipette with an internal-end diameter of 2-10 &#181;m to allow the dispersed celadonite to flow without obstruction.
		<ol>
			<li>Fix a glass capillary in the puller jaw. Ensure the right puller parameters according to patch pipette size (Table 1). Fill the micropipette with the celadonite-containing water.</li>
		</ol>
		</li>
		<li>Mount the micropipette on the capillary holder under the microscope. Align the micropipette and the carbon fiber under the optical microscope.</li>
		<li>Approach the micropipette, to a distance of 2-10 &#181;m from the apex of the carbon fiber.</li>
		<li>Apply progressive pressure on the wide entry to the micropipette. Typically, apply 100 mbar so that a drop forms at the tip but does not fall. This drop wets the apex of the carbon fiber.</li>
		<li>Retract the micropipette.</li>
	</ol>
	</li>
</ol>
2. Kicking-off the source
NOTE: In our microscope, the source-support is fixed on a manual rotating flange also carrying the piezo-electric actuator that moves (100 nm resolution, 25 mm range), with an electrical command, the object relative to the source (See Figure 2). This object plays the role of an electrical anode for electron emission; it is generally electrically grounded and placed in front of the source. In our experiment, voltages are hand controlled with different power supplies.
<ol>
	<li>Install the source holder under vacuum.</li>
	<li>Connect the carbon fiber and the object to two high-voltage electrical feedthroughs.</li>
	<li>Check electrical continuity of contacts everywhere: anode-object, lens and screen; turn on the vacuum pumping.</li>
	<li>Connect a nano-ammeter of a caliber in the &#181;A range between the object and the electrical ground.</li>
	<li>Increase the negative bias voltage applied to the source slowly, at approximately 1 V/s. If the anode is 1 mm away from the source, the kick-off takes place at about 2 kV. Intensity suddenly increases.</li>
	<li>Decrease the voltage to stabilize the intensity at some hundred nA. At the beginning, intensity can fluctuate over several orders of magnitude.</li>
	<li>Leave the system fluctuating for several hours, until fluctuations decrease. Cut off the voltage when fluctuations are lower than 10%.</li>
</ol>
3. Source characterization
NOTE: We present a way to probe the source characteristics. To estimate the source brightness, two projection microscopes are used. In these setups, the shadow of an object is observed on a fluorescent screen placed farther away (Figure 2). The source (cathode) and the object (anode) are mounted on a micro-manipulation flange and can rotate together in the projection plane. 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 magnifications12. Information available on each projection image is used to under-estimate the brightness: the smallest detail in the record13. This smallest visible detail depends on the apparent source-size, that includes the source-size geometrical blur, the vibrations between the object and the source, and the detector resolution.
<ol>
	<li>Measurement of the cone angle
	<ol>
		<li>Turn the source towards the simple projection setup, with the rotating flange, to observe the electron beam.</li>
		<li>Decrease the source-to-screen distance, with the manual micro-manipulator, to obtain the entire spot on the screen; then, measure the source-to-screen distance, D.</li>
		<li>Take pictures of the screen by changing the angle between the electron beam and the normal to the screen, with the rotating flange.</li>
		<li>Plot the gray-level intensity profile along one axis and determine the emission radius, R at a given source-to-screen distance, D (Figure 3).</li>
		<li>Calculate the cone angle: <img src="/files/ftp_upload/59513/59513eq1.jpg" /> with R, the emission radius at a given source-to-screen distance, D.</li>
	</ol>
	</li>
	<li>Measurement of the Fowler-Nordheim plot
	<ol>
		<li>Measure the emission intensity versus the voltage applied to the source: I(V) with I the intensity measured at the anode and V the voltage applied at the carbon fiber.</li>
		<li>Plot <img src="/files/ftp_upload/59513/59513eq2.jpg" />. The curve shows a decreasing straight line with saturation for highest voltage. An example is given in Figure 4. The longest straight line is the signature of the field emission process.</li>
	</ol>
	</li>
	<li>Measurement of the source size
	<ol>
		<li>Turn the source towards the electrostatic lens, with the rotating flange.</li>
		<li>Produce a projection image containing a huge Fresnel diffraction pattern along an edge of an object: magnification of about 20,000x is required. In our microscope, this is possible with a source-to-object distance of some 100 &#181;m, fixed with the piezo-actuators, and an Einzel electrostatic lens.</li>
		<li>Measure the sharpest visible detail on the image on the screen (Figure 5). 
		NOTE: The sharpest fringe-to-fringe distance, &#948;, is used.</li>
		<li>Calculate the source size: <img src="/files/ftp_upload/59513/59513eq3.jpg" />.</li>
	</ol>
	</li>
</ol>

<ol><li>Forbes, R. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Low-macroscopic-field+electron+emission+from+carbon+films+and+other+electrically+nanostructured+heterogeneous+materials%3A+hypotheses+about+emission+mechanism%5BTitle%5D)+AND+%22Solid-State+Electronics%22%5BJournal%5D)">Low-macroscopic-field electron emission from carbon films and other electrically nanostructured heterogeneous materials: hypotheses about emission mechanism.</a> Solid-State Electronics. 45, 779-808 (2001).</li>
<li>Wang, C., Garcia, A., Ingram, D. C., Lake, M., Kordesch, M. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Cold+field+emission+from+CVD+diamond+films+observed+in+emission+electron+microscopy%5BTitle%5D)+AND+%22Electronics+Letters%22%5BJournal%5D)">Cold field emission from CVD diamond films observed in emission electron microscopy.</a> Electronics Letters. 27, 1459(1991).</li>
<li>Okano, K., Koizumi, S., Ravi, S., Silva, P., Amaratunga, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Low-threshold+cold+cathodes+made+of+nitrogen-doped+chemical-vapour-deposited+diamond%5BTitle%5D)+AND+%22Nature%22%5BJournal%5D)">Low-threshold cold cathodes made of nitrogen-doped chemical-vapour-deposited diamond.</a> Nature. 381, 140-141 (1996).</li>
<li>Geis, M. W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((A+new+surface+electron-emission+mechanism+in+diamond+cathodes%5BTitle%5D)+AND+%22Nature%22%5BJournal%5D)">A new surface electron-emission mechanism in diamond cathodes.</a> Nature. 393, 431-435 (1998).</li>
<li>Horch, S., Morin, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Field+emission+from+atomic+size+sources%5BTitle%5D)+AND+%22Journal+of+Applied+Physics%22%5BJournal%5D)">Field emission from atomic size sources.</a> Journal of Applied Physics. 74 (6), 3652-3657 (1993).</li>
<li>Muller, H. U., Volkel, B., Hofmann, M., Woll, C., Grunze, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Emission+properties+of+electron+point+sources%5BTitle%5D)+AND+%22Ultramicroscopy%22%5BJournal%5D)">Emission properties of electron point sources.</a> Ultramicroscopy. 50 (1), 57-64 (1993).</li>
<li>Qian, W., Scheinfein, M. R., Spence, J. C. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Brightness+measurements+of+nanometer-sized+field-emission-electron+sources%5BTitle%5D)+AND+%22Journal+of+Applied+Physics%22%5BJournal%5D)">Brightness measurements of nanometer-sized field-emission-electron sources.</a> Journal of Applied Physics. 73 (11), 7041-7045 (1993).</li>
<li>Rech, J. em, Grauby, O., Morin, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Low-voltage+electron+emission+from+mineral+films%5BTitle%5D)+AND+%22Journal+of+Vacuum+Science+%26+Technology+B%22%5BJournal%5D)">Low-voltage electron emission from mineral films.</a> Journal of Vacuum Science & Technology B. 20 (1), 5-9 (2002).</li>
<li>Daineche, R., Degiovanni, A., Grauby, O., Morin, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Source+of+low-energy+coherent+electron+beams%5BTitle%5D)+AND+%22Applied+Physics+Letters%22%5BJournal%5D)">Source of low-energy coherent electron beams.</a> Applied Physics Letters. 88, 023101(2006).</li>
<li>Salançon, E., Daineche, R., Grauby, O., Morin, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Single+mineral+particle+makes+an+electron+point+source%5BTitle%5D)+AND+%22Journal+of+Vacuum+Science+%26+Technology+B%22%5BJournal%5D)">Single mineral particle makes an electron point source.</a> Journal of Vacuum Science & Technology B. 33, 030601(2015).</li>
<li>Prigent, M., Morin, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Charge+effect+in+point+projection+images+of+Ni+nanowires+and+I+collagen+fibres%5BTitle%5D)+AND+%22Journal+of+Physics+D%3A+Applied+Physics%22%5BJournal%5D)">Charge effect in point projection images of Ni nanowires and I collagen fibres.</a> Journal of Physics D: Applied Physics. 34 (8), 1167-1177 (2001).</li>
<li>Salançon, E., Degiovanni, A., Lapena, L., Lagaize, M., Morin, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((A+low-energy+electron+point-source+projection+microscope+not+using+a+sharp+metal+tip+performs+well+in+long-range+imaging%5BTitle%5D)+AND+%22Ultramicroscopy%22%5BJournal%5D)">A low-energy electron point-source projection microscope not using a sharp metal tip performs well in long-range imaging.</a> Ultramicroscopy. 200, 125-131 (2019).</li>
<li>Salançon, E., Degiovanni, A., Lapena, L., Morin, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((High+spatial+resolution+detection+of+low-energy+electrons+using+an+event-counting+method%2C+application+to+point+projection+microscopy%5BTitle%5D)+AND+%22Review+of+Scientific+Instruments%22%5BJournal%5D)">High spatial resolution detection of low-energy electrons using an event-counting method, application to point projection microscopy.</a> Review of Scientific Instruments. 89, 043301(2018).</li>
<li>Swanson, L. W., Crouser, L. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Total-Energy+Distribution+of+Field-Emitted+Electrons+and+Single-Plane+Work+Functions+for+Tungsten%5BTitle%5D)+AND+%22Physical+Review%22%5BJournal%5D)">Total-Energy Distribution of Field-Emitted Electrons and Single-Plane Work Functions for Tungsten.</a> Physical Review. 163, 622(1967).</li>
</ol>

The authors have no competing financial interests.

This protocol is not critical because the geometry of the source at a microscopic scale changes from one source to another one. The difficulty is that since a carbon fiber is brittle, its cutting can lead to an inappropriate length. An adequate length is about 500 &#181;m; the microscopic shape of the cut is not crucial. The critical step is to have a very small number of crystals (ideally one) deposited on the apex of a conductive wire. Adapting the crystal concentration with the deposited volume is the most important point. If too many crystals aggregate, emission is damped. Here, we describe a way to manage this. Due to the kick-off procedure, if a small number of crystals are deposited, only one of them is finally responsible for the emission. Another requirement is to build a protruding structure in order to approach the anode and to obtain a directive emission. This cannot be achieved if celadonite-crystals were deposited on a carbon film as in previous studies.
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 600 &#181;m, a resolution of about 30 nm is generally obtained12. In point-projection microscopes, working at such a large source-object distance is comfortable and is advantageous. Moreover, such large working distances avoid any field effects on the object. The high emission intensities provided by this source enable image acquisition at a video rate of about 500 images/s, and the robustness of the source is a practical advantage over classic field emission metal tips. Except in our microscope, this recently developed source has not yet been used in another microscope. The emission instabilities previously measured could be problematic for a scanning microscope. Although these instabilities are observable during point-projection imaging, the emission location is stable, making image averaging possible. Compared to classic metal-tip sources for identical magnification, holograms obtained with the present source are identical but obtained for a much larger working distance. Ultimate spatial resolution is presently an open experimental problem.

Metal/insulator structures used for electron emission have been studied for almost 20 years due to their low macroscopic field1. The electric field involved is only of the order of some V/&#181;m2,3,4, in contrast to the V/nm required for classic field emission with sharp metal tips5,6,7. This probably explains the starting plasma discharges that are so useful in electron source technologies. Some years ago, we sought to explore this low field emission by depositing films of natural insulators on electron transmission carbon layers8. Celadonite, an insulator mineral found in the basalt of the Parana Traps in the mines of Ametista di Sul in Brazil, was chosen.
When celadonite is ground, the crystal shape is a rectangular slab with micrometric dimensions and a thickness of less than 100 nm (typically: 1,000 nm x 500 nm x 50 nm). It is perfectly flat and recognizable in scanning electron microscopy (Figure 1). The film is formed by deposition of a celadonite-containing water droplet on the carbon layer. As applied voltage increases, it emits electrons following a Fowler-Nordheim regime with intensity saturation for the highest voltages. A study using a diaphragm in a projection system showed that one emitter is a point-like source9. However, using this large film with a diaphragm to select the source did not exploit the potential of the point-source. For example, the point-sources commonly used in low-energy electron point-source projection microscopy allow a source-to-object distance of about 100 nm. However, such a source-to-object distance would be out of the question with a film. Finding a way to isolate one crystal so as to be able to move something towards this electron source was a challenge. Our solution was first, to use a 10 &#181;m carbon fiber: depositing the droplet at the apex of the fiber necessarily limits the number of celadonite crystals. Second, we decided to limit droplet size: a micropipette with a tip end of about 5 &#181;m is filled with celadonite-containing water and pressure is applied at the entrance of the micropipette to create a small drop to wet the apex of the fiber. The protocol details the full source preparation process.
The resulting source is a coaxial point-source allowing good alignment between the source, the object and the electron optical system10. Because its 10 &#181;m diameter is still wider than ultra-sharp tips, the source-to-object distance is limited to some tens of micrometers. 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 effect11 on the object and the image distortions involved12,13. The celadonite source also presents major advantages compared to sharp metal tips. It is robust: the point-source is under the crystal and thus protected against sputtering. The source can operate under relatively high pressure: it was tested at 10-2 mbar during some minutes. Yet its lifetime and its stability remain dependent on the right vacuum conditions. We usually employ the celadonite source at 10-8 mbar and obtain a lifetime of months.
This article is intended to help all those wishing to use the celadonite source to produce a coherent electron beam.

<table><tbody><tr><td>Carbon fiber filament</td><td>Goodfellow</td><td>C 005711&amp;nbsp;&amp;nbsp;</td><td></td></tr><tr><td>Carbon fiber filament</td><td>Mitsubishi Chemical</td><td>DIALEAD</td><td></td></tr><tr><td>Carbon fiber filament</td><td>Solvay</td><td>THORNEL P25</td><td></td></tr><tr><td>Carbon fiber filament</td><td>Zoltek</td><td>PX35 Continuous Tow</td><td></td></tr><tr><td>Celadonite</td><td></td><td></td><td>Verona Green earth / pigment</td></tr><tr><td>Dual-stage microchannel plate and fluorescent screen assembly</td><td>Hamamatsu</td><td>F2225-21S</td><td></td></tr><tr><td>Flow controller</td><td>Elveflow</td><td>OB1&amp;nbsp;</td><td></td></tr><tr><td>Machinable glass ceramic</td><td>Macor</td><td></td><td></td></tr><tr><td>Micropipette Puller</td><td>Sutter Instruments</td><td>P2000&amp;nbsp;</td><td></td></tr><tr><td>Piezo-electric actuators</td><td>Mechonics</td><td>MS30&amp;nbsp;</td><td></td></tr><tr><td>Quartz capillary</td><td>Sutter Instrument&amp;nbsp;</td><td>B100-75-15&amp;nbsp;</td><td></td></tr><tr><td>Silver Lacquer</td><td>DODUCO GmbH</td><td>AUROMAL 38&amp;nbsp;&amp;nbsp;</td><td></td></tr><tr><td>Ultrasonic processor</td><td>Hielscher / sonotrode MS3</td><td>UP50H&amp;nbsp;</td><td></td></tr></tbody></table>

preparing a celadonite electron source and estimating its brightness

The electron celadonite source described here performs well in a low-energy electron point-source projection microscope in long-range imaging. It presents major advantages compared to sharp metal tips. Its robustness affords a lifetime of months and it can be used under relatively high pressure. The celadonite crystal is deposited at the apex of a carbon fiber, maintained itself in a coaxial structure ensuring a spherical beam shape and easy mechanical positioning to align the source, the object and the electron-optical system axis. There is a single crystal deposition via generation of celadonite-containing water droplets with a micropipette. Scanning electron microscopy observation can be performed to verify the deposition. However, this adds steps and therefore increases the risk of damaging the source. Thus, after preparation, the source is usually inserted directly under vacuum in the projection microscope. A first high voltage supply provides the kick-off needed to start the electron emission. The field emission process involved is then measured: it has already been observed for dozens of electron sources prepared in this way. The brightness is under-estimated through an over-estimation of source size, intensity at one energy and cone angle measured in a projection system.

Several scanning electron micrographies of carbon fibers prepared as detailed in protocol were obtained in an SEM at 15 kV. Sources exhibit one, sometimes two, crystals at their apex (Figure 1). However, the use of the SEM involves another support for the carbon fiber, which is hard to mount and demount without breaking. It is safer to attempt direct electron emission. Tested in a projection microscope (Figure 2), every source prepared this way emitted. The kick-off is required only once. With old sources, sometimes, a kick-off can be used for another source.
Most of these sources show one single point source (Figure 3): the emission profile indicates only one continuing image without any other spot. The beam has a cone angle of about 1srd.
The Fowler-Nordheim plot exhibits 10 orders of magnitude straight and saturation at higher voltage (Figure 4). The saturation regime obtained for a given voltage depends on the structure, but the slope decreases systematically for higher current intensities from about 10 &#181;A.
Energy distribution is not measured here, because the energy resolution is not good enough to obtain better accuracy than a few eV by simply biasing the entrance of the detector. Another point is that highly structured fringe patterns can be observed in some holograms rejecting a large energy distribution that would blur such patterns. Since the process involved is the Fowler-Nordheim regime, energy distribution close to 250 meV is expected14.
The source size is 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 (Figure 5); this is a way to over-estimate this measurement. In this case, the source radius is smaller than 4nm <img src="/files/ftp_upload/59513/59513eq4.jpg" />. Finally, the brightness of the source is obtained, <img src="/files/ftp_upload/59513/59513eq5.jpg" />. The method presented here under-estimates the brightness because the source size is necessarily smaller.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/59513/59513fig1.jpg" /> 
Figure 1: Carbon fiber with celadonite deposited on it (green arrow), observed with a scanning electron microscope. Inset: Typical close-up of a celadonite crystal. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/59513/59513fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/59513/59513fig2.jpg" /> 
Figure 2: Experimental setup. The projection electron microscope using a celadonite on carbon source and an electrostatic lens; and the simple projection setup. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/59513/59513fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/59513/59513fig3.jpg" /> 
Figure 3: Measurement of the cone angle. (a) Schematic setup with the projection-distance D = 5 cm and, &#945;, the angle between the carbon fiber and the normal of the screen; &#945; is manually changed to observe the emission pattern (c) and to measure the emission profile, along the blue dashed line, obtained on the screen for &#945; = 0&#176; (b). Note that the projection of the grid appears in the profile as a null intensity but clearly, the profile intensity is Gaussian with an extension of about 5 cm. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/59513/59513fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/59513/59513fig4.jpg" /> 
Figure 4: Fowler-Nordheim plot of a celadonite source. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/59513/59513fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/59513/59513fig5.jpg" /> 
Figure 5: Measurement of the sharpest detail in the image to over-estimate the source size. The profile (a) is plotted along the white line in the image (b). (c) is a detail of (b). <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/59513/59513fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>heat</td>
			<td>filament</td>
			<td>velocity</td>
			<td>delay</td>
			<td>pull</td>
		</tr>
		<tr>
			<td>450</td>
			<td>3</td>
			<td>5</td>
			<td>200</td>
			<td>120</td>
		</tr>
		<tr>
			<td>350</td>
			<td>4</td>
			<td>40</td>
			<td>200</td>
			<td>0</td>
		</tr>
	</tbody>
</table>
Table 1: Pulling parameters to obtain an internal-end diameter of 2-10 &#181;m.

Watch this Scientific Journal Video about Preparing a Celadonite Electron Source and Estimating Its Brightness at JoVE.com

Preparing a Celadonite Electron Source and Estimating Its Brightness

The article presents a protocol to prepare a celadonite source and estimate its brightness for use in a long-range imaging low-energy electron point-source projection microscope.

The electron celadonite source described here performs well in a low-energy electron point-source projection microscope in long-range imaging. It presents ...

preparing-a-celadonite-electron-source-and-estimating-its-brightness

Nanyang Technological University

Research

JoVE Journal

Engineering

4.5K Views.  Aix-Marseille University, CNRS. Dit protocol is bedoeld om uit te leggen hoe je een celadontische elektronenbron maakt. Deze bronnen hebben aangetoond een lange levensduur en hun helderheid zijn gelijk aan die van gevulde emissie metaal tips. Met behulp van deze celadoniet elektronenbron in een projectiemicroscoop, geassocieerd met een elektrostatische lens, maakt het mogelijk om te werken met een grote bron object afstand.Dit voorkomt het risico op een broncrash en beeldvervorming door het lokale veldeffect op het o...

Video: Preparing a Celadonite Electron Source and Estimating Its Brightness

Characterization of Electrode Materials for Lithium Ion and Sodium Ion Batteries Using Synchrotron Radiation Techniques

Intercalation compounds such as transition metal oxides or phosphates are the most commonly used electrode materials in Li-ion and Na-ion batteries. During insertion or removal of alkali metal ions, the redox states of transition metals in the compounds change and structural transformations such as phase transitions and/or lattice parameter increases or decreases occur. These behaviors in turn determine important characteristics of the batteries such as the potential profiles, rate capabilities, and cycle lives. The extremely bright and tunable x-rays produced by synchrotron radiation allow rapid acquisition of high-resolution data that provide information about these processes. Transformations in the bulk materials, such as phase transitions, can be directly observed using X-ray diffraction (XRD), while X-ray absorption spectroscopy (XAS) gives information about the local electronic and geometric structures (e.g.&#160;changes in redox states and bond lengths). In situ experiments carried out on operating cells are particularly useful because they allow direct correlation between the electrochemical and structural properties of the materials. These experiments are time-consuming and can be challenging to design due to the reactivity and air-sensitivity of the alkali metal anodes used in the half-cell configurations, and/or the possibility of signal interference from other cell components and hardware. For these reasons, it is appropriate to carry out ex situ experiments (e.g.&#160;on electrodes harvested from partially charged or cycled cells) in some cases. Here, we present detailed protocols for the preparation of both ex situ and in situ samples for experiments involving synchrotron radiation and demonstrate how these experiments are done.

We describe the use of synchrotron X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) techniques to probe details of intercalation/deintercalation processes in electrode materials for Li-ion and Na-ion batteries. Both in situ and ex situ experiments are used to understand structural behavior relevant to the operation of devices

Intercalation compounds such as transition metal oxides or phosphates are the most commonly used electrode materials in Li-ion and Na-ion batteries. ...

Integrating a Triplet-triplet Annihilation Up-conversion System to Enhance Dye-sensitized Solar Cell Response to Sub-bandgap Light

The poor response of dye-sensitized solar cells (DSCs) to red and infrared light is a significant impediment to the realization of higher photocurrents and hence higher efficiencies. Photon up-conversion by way of triplet-triplet annihilation (TTA-UC) is an attractive technique for using these otherwise wasted low energy photons to produce photocurrent, while not interfering with the photoanodic performance in a deleterious manner. Further to this, TTA-UC has a number of features, distinct from other reported photon up-conversion technologies, which renders it particularly suitable for coupling with DSC technology. In this work, a proven high performance TTA-UC system, comprising a palladium porphyrin sensitizer and rubrene emitter, is combined with a high performance DSC (utilizing the organic dye D149) in an integrated device. The device shows an enhanced response to sub-bandgap light over the absorption range of the TTA-UC sub-unit resulting in the highest figure of merit for up-conversion assisted DSC performance to date.

An integrated device, incorporating a dye-sensitized solar cell and triplet-triplet annihilation up-conversion unit was produced, affording enhanced light harvesting, from a wider section of the solar spectrum. Under modest irradiation levels a significantly enhanced response to low energy photons was demonstrated, yielding a record figure of merit for dye-sensitized solar cells.

The poor response of dye-sensitized solar cells (DSCs) to red and infrared light is a significant impediment to the realization of higher photocurrents ...

Detection and Recovery of Palladium, Gold and Cobalt Metals from the Urban Mine Using Novel Sensors/Adsorbents Designated with Nanoscale Wagon-wheel-shaped Pores

Developing low-cost, efficient processes for recovering and recycling palladium, gold and cobalt metals from urban mine remains a significant challenge in industrialized countries. Here, the development of optical mesosensors/adsorbents (MSAs) for efficient recognition and selective recovery of Pd(II), Au(III), and Co(II) from urban mine was achieved. A simple, general method for preparing MSAs based on using high-order mesoporous monolithic scaffolds was described. Hierarchical cubic Ia3d wagon-wheel-shaped MSAs were fabricated by anchoring chelating agents (colorants) into three-dimensional pores and micrometric particle surfaces of the mesoporous monolithic scaffolds. Findings show, for the first time, evidence of controlled optical recognition of Pd(II), Au(III), and Co(II) ions and a highly selective system for recovery of Pd(II) ions (up to ~95%) in ores and industrial wastes. Furthermore, the controlled assessment processes described herein involve evaluation of intrinsic properties (e.g., visual signal change, long-term stability, adsorption efficiency, extraordinary sensitivity, selectivity, and reusability); thus, expensive, sophisticated instruments are not required. Results show evidence that MSAs will attract worldwide attention as a promising technological means of recovering and recycling palladium, gold and cobalt metals.

Because of the importance and extensive use of palladium, gold and cobalt metals in high-technology equipment, their recovery and recycling constitute an important industrial challenge. The metal recovery system described herein is a simple, low-cost means for the effective detection, removal, and recovery of these metals from the urban mine.

Developing low-cost, efficient processes for recovering and recycling palladium, gold and cobalt metals from urban mine remains a significant challenge in ...

Low-energy Cathodoluminescence for (Oxy)Nitride Phosphors

Nitride and oxynitride (Sialon) phosphors are good candidates for the ultraviolet and visible emission applications. High performance, good stability and flexibility of their emission properties can be achieved by controlling their composition and dopants. However, a lot of work is still required to improve their properties and to reduce the production cost. A possible approach is to correlate the luminescence properties of the Sialon particles with their local structural and chemical environment in order to optimize their growth parameters and find novel phosphors. For such a purpose, the low-voltage cathodoluminescence (CL) microscopy is a powerful technique. The use of electron as an excitation source allows detecting most of the luminescence centers, revealing their luminescence distribution spatially and in depth, directly comparing CL results with the other electron-based techniques, and investigating the stability of their luminescence properties under stress. Such advantages for phosphors characterization will be highlighted through examples of investigation on several Sialon phosphors by low-energy CL.

Low-energy Cathodoluminescence for OxyNitride Phosphors

An excellent chemical and luminescence stabilities of (oxy)nitride phosphors present it as an promising alternative to currently used sulfide and oxide phosphors. In this paper, we present the way to investigate its local luminescence properties using low-energy cathodoluminescence (CL).

Nitride and oxynitride (Sialon) phosphors are good candidates for the ultraviolet and visible emission applications. High performance, good stability and ...

Chemistry

In Depth Analyses of LEDs by a Combination of X-ray Computed Tomography (CT) and Light Microscopy (LM) Correlated with Scanning Electron Microscopy (SEM)

In failure analysis, device characterization and reverse engineering of light emitting diodes (LEDs), and similar electronic components of micro-characterization, plays an important role. Commonly, different techniques like X-ray computed tomography (CT), light microscopy (LM) and scanning electron microscopy (SEM) are used separately. Similarly, the results have to be treated for each technique independently. Here a comprehensive study is shown which demonstrates the potentials leveraged by linking CT, LM and SEM. In depth characterization is performed on a white emitting LED, which can be operated throughout all characterization steps. Major advantages are: planned preparation of defined cross sections, correlation of optical properties to structural and compositional information, as well as reliable identification of different functional regions. This results from the breadth of information available from identical regions of interest (ROIs): polarization contrast, bright and dark-field LM images, as well as optical images of the LED cross section in operation. This is supplemented by SEM imaging techniques and micro-analysis using energy dispersive X-ray spectroscopy.

In Depth Analyses of LEDs by a Combination of X-ray Computed Tomography CT and Light Microscopy LM Correlated with Scanning Electron Microscopy SEM

A workflow for comprehensive micro-characterization of active optical devices is outlined. It contains structural as well as functional investigations by means of CT, LM and SEM. The method is demonstrated for a white LED which can be still be operated during characterization.

In failure analysis, device characterization and reverse engineering of light emitting diodes (LEDs), and similar electronic components of ...

Comprehensive Characterization of Extended Defects in Semiconductor Materials by a Scanning Electron Microscope

Extended defects such as dislocations and grain boundaries have a strong influence on the performance of microelectronic devices and on other applications of semiconductor materials. However, it is still under debate how the defect structure determines the band structure, and therefore, the recombination behavior of electron-hole pairs responsible for the optical and electrical properties of the extended defects. The present paper is a survey of procedures for the spatially resolved investigation of structural and of physical properties of extended defects in semiconductor materials with a scanning electron microscope (SEM). Representative examples are given for crystalline silicon. The luminescence behavior of extended defects can be investigated by cathodoluminescence (CL) measurements. They are particularly valuable because spectrally and spatially resolved information can be obtained simultaneously. For silicon, with an indirect electronic band structure, CL measurements should be carried out at low temperatures down to 5 K due to the low fraction of radiative recombination processes in comparison to non-radiative transitions at room temperature. For the study of the electrical properties of extended defects, the electron beam induced current (EBIC) technique can be applied. The EBIC image reflects the local distribution of defects due to the increased charge-carrier recombination in their vicinity. The procedure for EBIC investigations is described for measurements at room temperature and at low temperatures. Internal strain fields arising from extended defects can be determined quantitatively by cross-correlation electron backscatter diffraction (ccEBSD). This method is challenging because of the necessary preparation of the sample surface and because of the quality of the diffraction patterns which are recorded during the mapping of the sample. The spatial resolution of the three experimental techniques is compared.

The optical, electrical, and structural properties of dislocations and of grain boundaries in semiconductor materials can be determined by experiments performed in a scanning electron microscope. Electron microscopy has been used to investigate cathodoluminescence, electron beam induced current, and diffraction of backscattered electrons.

Extended defects such as dislocations and grain boundaries have a strong influence on the performance of microelectronic devices and on other applications ...

Fabrication of Fully Solution Processed Inorganic Nanocrystal Photovoltaic Devices

We demonstrate a method for the preparation of fully solution processed inorganic solar cells from a spin and spray coating deposition of nanocrystal inks. For the photoactive absorber layer, colloidal CdTe and CdSe nanocrystals (3-5 nm) are synthesized using an inert hot injection technique and cleaned with precipitations to remove excess starting reagents. Similarly, gold nanocrystals (3-5 nm) are synthesized under ambient conditions and dissolved in organic solvents. In addition, precursor solutions for transparent conductive indium tin oxide (ITO) films are prepared from solutions of indium and tin salts paired with a reactive oxidizer. Layer-by-layer, these solutions are deposited onto a glass substrate following annealing (200-400 &#176;C) to build the nanocrystal solar cell (glass/ITO/CdSe/CdTe/Au). Pre-annealing ligand exchange is required for CdSe and CdTe nanocrystals where films are dipped in NH4Cl:methanol to replace long-chain native ligands with small inorganic Cl- anions. NH4Cl(s) was found to act as a catalyst for the sintering reaction (as a non-toxic alternative to the conventional CdCl2(s) treatment) leading to grain growth (136&#177;39 nm) during heating. The thickness and roughness of the prepared films are characterized with SEM and optical profilometry. FTIR is used to determine the degree of ligand exchange prior to sintering, and XRD is used to verify the crystallinity and phase of each material. UV/Vis spectra show high visible light transmission through the ITO layer and a red shift in the absorbance of the cadmium chalcogenide nanocrystals after thermal annealing. Current-voltage curves of completed devices are measured under simulated one sun illumination. Small differences in deposition techniques and reagents employed during ligand exchange have been shown to have a profound influence on the device properties. Here, we examine the effects of chemical (sintering and ligand exchange agents) and physical treatments (solution concentration, spray-pressure, annealing time and annealing temperature) on photovoltaic device performance.

This protocol describes the synthesis and solution deposition of inorganic nanocrystals layer by layer to produce thin film electronics on non-conductive surfaces. Solvent-stabilized inks can produce complete photovoltaic devices on glass substrates via spin and spray coating following post-deposition ligand exchange and sintering.

We demonstrate a method for the preparation of fully solution processed inorganic solar cells from a spin and spray coating deposition of nanocrystal ...

Fabrication of White Light-emitting Electrochemical Cells with Stable Emission from Exciplexes

The authors present an approach for fabricating stable white light emission from polymer light-emitting electrochemical cells (PLECs) having an active layer which consists of blue-fluorescent poly(9,9-di-n-dodecylfluorenyl-2,7-diyl) (PFD) and &#960;-conjugated triphenylamine molecules. This white light emission originates from exciplexes formed between PFD and amines in electronically excited states. A device containing PFD, 4,4&#39;,4&#39;&#39;-tris[2-naphthyl(phenyl)amino]triphenylamine (2-TNATA), Poly(ethylene oxide) and K2CF3SO3 showed white light emission with Commission internationale de l&#39;&#233;clairage (CIE) coordinates of (0.33, 0.43) and a Color Rendering Index (CRI) of Ra = 73 at an applied voltage of 3.5 V. Constant voltage measurements showed that the CIE coordinates of (0.27, 0.37), Ra of 67, and the emission color observed immediately after application of a voltage of 5 V were nearly unchanged and stable after 300 sec.

The authors present a method for fabricating stable white-light-emitting electrochemical cells utilizing emission from exciplexes formed between a blue-emitting fluorene polymer and aromatic amines.

The authors present an approach for fabricating stable white light emission from polymer light-emitting electrochemical cells (PLECs) having an active ...

Analysis of Minerals Produced by hFOB 1.19 and Saos-2 Cells Using Transmission Electron Microscopy with Energy Dispersive X-ray Microanalysis

This video presents the use of transmission electron microscopy with energy dispersive X-ray microanalysis (TEM-EDX) to compare the state of minerals in vesicles released by two human bone cell lines: hFOB 1.19 and Saos-2. These cell lines, after treatment with ascorbic acid (AA) and &#946;-glycerophosphate (&#946;-GP), undergo complete osteogenic transdifferentiation from proliferation to mineralization and produce matrix vesicles (MVs) that trigger apatite nucleation in the extracellular matrix (ECM).
Based on Alizarin Red-S (AR-S) staining and analysis of the composition of minerals in cell lysates using ultraviolet (UV) light or in vesicles using TEM imaging followed by EDX quantitation and ion mapping, we can infer that osteosarcoma Saos-2 and osteoblastic hFOB 1.19 cells reveal distinct mineralization profiles. Saos-2 cells mineralize more efficiently than hFOB 1.19 cells and produce larger mineral deposits that are not visible under UV light but are similar to hydroxyapatite (HA) in that they have more Ca and F substitutions.
The results obtained using these techniques allow us to conclude that the process of mineralization differs depending on the cell type. We propose that, at the cellular level, the origin and properties of vesicles predetermine the type of minerals.

We present a protocol to compare the state of minerals in vesicles released by two human bone cell lines: hFOB 1.19 and Saos-2. Their mineralization profiles were analyzed by Alizarin Red-S (AR-S) staining, ultraviolet (UV) light visualization, transmission electron microscopy (TEM) imaging and energy dispersive X-ray microanalysis (EDX).

This video presents the use of transmission electron microscopy with energy dispersive X-ray microanalysis (TEM-EDX) to compare the state of minerals in ...

Quantitative Atomic-Site Analysis of Functional Dopants/Point Defects in Crystalline Materials by Electron-Channeling-Enhanced Microanalysis

A novel elemental and chemical analysis scheme based on electron-channeling phenomena in crystalline materials is introduced, where the incident high-energy electron beam is rocked with the submicrometric pivot point fixed on a specimen. This method enables us to quantitatively derive the site occupancies and site-dependent chemical information of impurities or intentionally doped functional elements in a specimen, using energy-dispersive X-ray spectroscopy and electron energy-loss spectroscopy attached to a scanning transmission electron microscope, which is of significant interest to current materials science, particularly related to nanotechnologies. This scheme is applicable to any combination of elements even when the conventional Rietveld analysis by X-ray or neutron diffraction occasionally fails to provide the desired results because of limited sample sizes and close scattering factors of neighboring elements in the periodic table. In this methodological article, we demonstrate the basic experimental procedure and analysis method of the present beam-rocking microanalysis.

We provide a general outline of quantitative microanalysis methods for estimating the site occupancies of impurities and their chemical states by taking advantage of electron-channeling phenomena under incident electron beam-rocking conditions, which reliably extract information from minority species, light elements, oxygen vacancies, and other point/line/planar defects.

Preparing a Celadonite Electron Source and Estimating Its Brightness

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