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/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Low-macroscopic-field+electron+emission+from+carbon+films+and+other+electrically+nanostructured+heterogeneous+materials:+hypotheses+about+emission+mechanism.">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/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cold+field+emission+from+CVD+diamond+films+observed+in+emission+electron+microscopy.">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/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Low-threshold+cold+cathodes+made+of+nitrogen-doped+chemical-vapour-deposited+diamond.">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/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+new+surface+electron-emission+mechanism+in+diamond+cathodes.">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/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Field+emission+from+atomic+size+sources.">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/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Emission+properties+of+electron+point+sources.">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/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Brightness+measurements+of+nanometer-sized+field-emission-electron+sources.">Brightness measurements of nanometer-sized field-emission-electron sources.</a> Journal of Applied Physics. 73 (11), 7041-7045 (1993).</li><li>Rech, J. e. m., Grauby, O., Morin, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Low-voltage+electron+emission+from+mineral+films.">Low-voltage electron emission from mineral films.</a> Journal of Vacuum Science &amp; 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/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Source+of+low-energy+coherent+electron+beams.">Source of low-energy coherent electron beams.</a> Applied Physics Letters. 88, 023101 (2006).</li><li>Salan&#231;on, E., Daineche, R., Grauby, O., Morin, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Single+mineral+particle+makes+an+electron+point+source.">Single mineral particle makes an electron point source.</a> Journal of Vacuum Science &amp; Technology B. 33, 030601 (2015).</li><li>Prigent, M., Morin, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Charge+effect+in+point+projection+images+of+Ni+nanowires+and+I+collagen+fibres.">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>Salan&#231;on, E., Degiovanni, A., Lapena, L., Lagaize, M., Morin, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+low-energy+electron+point-source+projection+microscope+not+using+a+sharp+metal+tip+performs+well+in+long-range+imaging.">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>Salan&#231;on, E., Degiovanni, A., Lapena, L., Morin, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High+spatial+resolution+detection+of+low-energy+electrons+using+an+event-counting+method,+application+to+point+projection+microscopy.">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. 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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 p...

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 border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Carbon fiber filament</td>
			<td>Goodfellow</td>
			<td>C 005711&#160;&#160;</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&#160;</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&#160;</td>
			<td></td>
		</tr>
		<tr>
			<td>Piezo-electric actuators</td>
			<td>Mechonics</td>
			<td>MS30&#160;</td>
			<td></td>
		</tr>
		<tr>
			<td>Quartz capillary</td>
			<td>Sutter Instrument&#160;</td>
			<td>B100-75-15&#160;</td>
			<td></td>
		</tr>
		<tr>
			<td>Silver Lacquer</td>
			<td>DODUCO GmbH</td>
			<td>AUROMAL 38&#160;&#160;</td>
			<td></td>
		</tr>
		<tr>
			<td>Ultrasonic processor</td>
			<td>Hielscher / sonotrode MS3</td>
			<td>UP50H&#160;</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 pr...

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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 ...

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4.4K Views.  Aix-Marseille University, CNRS. 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.

Video: Preparing a Celadonite Electron Source and Estimating Its Brightness

Micro 3D Printing Using a Digital Projector and its Application in the Study of Soft Materials Mechanics

Buckling is a classical topic in mechanics. While buckling has long been studied as one of the major structural failure modes1, it has recently drawn new attention as a unique mechanism for pattern transformation. Nature is full of such examples where a wealth of exotic patterns are formed through mechanical instability2-5. Inspired by this elegant mechanism, many studies have demonstrated creation and transformation of patterns using soft materials such as elastomers and hydrogels6-11. Swelling gels are of particular interest because they can spontaneously trigger mechanical instability to create various patterns without the need of external force6-10. Recently, we have reported demonstration of full control over buckling pattern of micro-scaled tubular gels using projection micro-stereolithography (P&mu;SL), a three-dimensional (3D) manufacturing technology capable of rapidly converting computer generated 3D models into physical objects at high resolution12,13. Here we present a simple method to build up a simplified P&mu;SL system using a commercially available digital data projector to study swelling-induced buckling instability for controlled pattern transformation.
A simple desktop 3D printer is built using an off-the-shelf digital data projector and simple optical components such as a convex lens and a mirror14. Cross-sectional images extracted from a 3D solid model is projected on the photosensitive resin surface in sequence, polymerizing liquid resin into a desired 3D solid structure in a layer-by-layer fashion. Even with this simple configuration and easy process, arbitrary 3D objects can be readily fabricated with sub-100 &mu;m resolution.
This desktop 3D printer holds potential in the study of soft material mechanics by offering a great opportunity to explore various 3D geometries. We use this system to fabricate tubular shaped hydrogel structure with different dimensions. Fixed on the bottom to the substrate, the tubular gel develops inhomogeneous stress during swelling, which gives rise to buckling instability. Various wavy patterns appear along the circumference of the tube when the gel structures undergo buckling. Experiment shows that circumferential buckling of desired mode can be created in a controlled manner. Pattern transformation of three-dimensionally structured tubular gels has significant implication not only in mechanics and material science, but also in many other emerging fields such as tunable matamaterials.

We demonstrate controlled pattern transformation of swelling gel tubes by elastic instability. A simple projection micro stereo-lithography setup is built using an off-the-shelf digital data projector to fabricate three-dimensional polymeric structures in a layer-by-layer fashion. Swelling hydrogel tubes under mechanical constraint display various circumferential buckling modes depending on dimension.

Buckling is a classical topic in mechanics. While buckling has long been studied as one of the major structural failure modes1, it has recently drawn new ...

Scanning-probe Single-electron Capacitance Spectroscopy

The integration of low-temperature scanning-probe techniques and single-electron capacitance spectroscopy represents a powerful tool to study the electronic quantum structure of small systems - including individual atomic dopants in semiconductors. Here we present a capacitance-based method, known as Subsurface Charge Accumulation (SCA) imaging, which is capable of resolving single-electron charging while achieving sufficient spatial resolution to image individual atomic dopants. The use of a capacitance technique enables observation of subsurface features, such as dopants buried many nanometers beneath the surface of a semiconductor material1,2,3. In principle, this technique can be applied to any system to resolve electron motion below an insulating surface.
As in other electric-field-sensitive scanned-probe techniques4, the lateral spatial resolution of the measurement depends in part on the radius of curvature of the probe tip. Using tips with a small radius of curvature can enable spatial resolution of a few tens of nanometers. This fine spatial resolution allows investigations of small numbers (down to one) of subsurface dopants1,2. The charge resolution depends greatly on the sensitivity of the charge detection circuitry; using high electron mobility transistors (HEMT) in such circuits at cryogenic temperatures enables a sensitivity of approximately 0.01 electrons/Hz&frac12; at 0.3 K 5.

Scanning-probe single-electron capacitance spectroscopy facilitates the study of single-electron motion in localized subsurface regions. A sensitive charge-detection circuit is incorporated into a cryogenic scanning probe microscope to investigate small systems of dopant atoms beneath the surface of semiconductor samples.

The integration of low-temperature scanning-probe techniques and single-electron capacitance spectroscopy represents a powerful tool to study the ...

Using Neutron Spin Echo Resolved Grazing Incidence Scattering to Investigate Organic Solar Cell Materials

The spin echo resolved grazing incidence scattering (SERGIS) technique has been used to probe the length-scales associated with irregularly shaped crystallites. Neutrons are passed through two well defined regions of magnetic field; one before and one after the sample. The two magnetic field regions have opposite polarity and are tuned such that neutrons travelling through both regions, without being perturbed, will undergo the same number of precessions in opposing directions. In this case the neutron precession in the second arm is said to &#34;echo&#34; the first, and the original polarization of the beam is preserved. If the neutron interacts with a sample and scatters elastically the path through the second arm is not the same as the first and the original polarization is not recovered. Depolarization of the neutron beam is a highly sensitive probe at very small angles (&#60;50&#160;&#956;rad) but still allows a high intensity, divergent beam to be used. The decrease in polarization of the beam reflected from the sample as compared to that from the reference sample can be directly related to structure within the sample.
In comparison to scattering observed in neutron reflection measurements the SERGIS signals are often weak and are unlikely to be observed if the in-plane structures within the sample under investigation are dilute, disordered, small in size and polydisperse or the neutron scattering contrast is low. Therefore, good results will most likely be obtained using the SERGIS technique if the sample being measured consist of thin films on a flat substrate and contain scattering features that contains a high density of moderately sized features (30 nm to 5 &#181;m) which scatter neutrons strongly or the features are arranged on a lattice. An advantage of the SERGIS technique is that it can probe structures in the plane of the sample.

Progress has been made in utilizing spin echo resolved grazing incidence scattering (SERGIS) as a neutron scattering technique to probe the length-scales in irregular samples. Crystallites of [6,6]-phenyl-C61-butyric acid methyl ester have been probed using the SERGIS technique and the results confirmed by optical and atomic force microscopy.

The spin echo resolved grazing incidence scattering (SERGIS) technique has been used to probe the length-scales associated with irregularly shaped ...

Spatial Separation of Molecular Conformers and Clusters

Gas-phase molecular physics and physical chemistry experiments commonly use supersonic expansions through pulsed valves for the production of cold molecular beams. However, these beams often contain multiple conformers and clusters, even at low rotational temperatures. We present an experimental methodology that allows the spatial separation of these constituent parts of a molecular beam expansion. Using an electric deflector the beam is separated by its mass-to-dipole moment ratio, analogous to a bender or an electric sector mass spectrometer spatially dispersing charged molecules on the basis of their mass-to-charge ratio. This deflector exploits the Stark effect in an inhomogeneous electric field and allows the separation of individual species of polar neutral molecules and clusters. It furthermore allows the selection of the coldest part of a molecular beam, as low-energy rotational quantum states generally experience the largest deflection. Different structural isomers (conformers) of a species can be separated due to the different arrangement of functional groups, which leads to distinct dipole moments. These are exploited by the electrostatic deflector for the production of a conformationally pure sample from a molecular beam. Similarly, specific cluster stoichiometries can be selected, as the mass and dipole moment of a given cluster depends on the degree of solvation around the parent molecule. This allows experiments on specific cluster sizes and structures, enabling the systematic study of solvation of neutral molecules.

We present a technique that allows the spatial separation of different conformers or clusters present in a molecular beam. An electrostatic deflector is used to separate species by their mass-to-dipole moment ratio, leading to the production of gas-phase ensembles of a single conformer or cluster stoichiometry.

Gas-phase molecular physics and physical chemistry experiments commonly use supersonic expansions through pulsed valves for the production of cold ...

Flame Experiments at the Advanced Light Source: New Insights into Soot Formation Processes

The following experimental protocols and the accompanying video are concerned with the flame experiments that are performed at the Chemical Dynamics Beamline of the Advanced Light Source (ALS) of the Lawrence Berkeley National Laboratory1-4. This video demonstrates how the complex chemical structures of laboratory-based model flames are analyzed using flame-sampling mass spectrometry with tunable synchrotron-generated vacuum-ultraviolet (VUV) radiation. This experimental approach combines isomer-resolving capabilities with high sensitivity and a large dynamic range5,6. The first part of the video describes experiments involving burner-stabilized, reduced-pressure (20-80 mbar) laminar premixed flames. A small hydrocarbon fuel was used for the selected flame to demonstrate the general experimental approach. It is shown how species&#8217; profiles are acquired as a function of distance from the burner surface and how the tunability of the VUV photon energy is used advantageously to identify many combustion intermediates based on their ionization energies. For example, this technique has been used to study gas-phase aspects of the soot-formation processes, and the video shows how the resonance-stabilized radicals, such as C3H3, C3H5, and i-C4H5, are identified as important intermediates7. The work has been focused on soot formation processes, and, from the chemical point of view, this process is very intriguing because chemical structures containing millions of carbon atoms are assembled from a fuel molecule possessing only a few carbon atoms in just milliseconds. The second part of the video highlights a new experiment, in which an opposed-flow diffusion flame and synchrotron-based aerosol mass spectrometry are used to study the chemical composition of the combustion-generated soot particles4. The experimental results indicate that the widely accepted H-abstraction-C2H2-addition (HACA) mechanism is not the sole molecular growth process responsible for the formation of the observed large polycyclic aromatic hydrocarbons (PAHs).

Gas sampling from laboratory-scale flames with online analysis of all species by mass spectrometry is a powerful method to investigate the complex mixture of chemical compounds occurring during combustion processes. Coupled with tunable soft ionization via synchrotron-generated vacuum-ultraviolet radiation, this technique provides isomer-resolved information and potentially fragment-free mass spectra.

The following experimental protocols and the accompanying video are concerned with the flame experiments that are performed at the Chemical Dynamics ...

Electron Channeling Contrast Imaging for Rapid III-V Heteroepitaxial Characterization

Misfit dislocations in heteroepitaxial layers of GaP grown on Si(001) substrates are characterized through use of electron channeling contrast imaging (ECCI) in a scanning electron microscope (SEM). ECCI allows for imaging of defects and crystallographic features under specific diffraction conditions, similar to that possible via plan-view transmission electron microscopy (PV-TEM). A particular advantage of the ECCI technique is that it requires little to no sample preparation, and indeed can use large area, as-produced samples, making it a considerably higher throughput characterization method than TEM. Similar to TEM, different diffraction conditions can be obtained with ECCI by tilting and rotating the sample in the SEM. This capability enables the selective imaging of specific defects, such as misfit dislocations at the GaP/Si interface, with high contrast levels, which are determined by the standard invisibility criteria. An example application of this technique is described wherein ECCI imaging is used to determine the critical thickness for dislocation nucleation for GaP-on-Si by imaging a range of samples with various GaP epilayer thicknesses. Examples of ECCI micrographs of additional defect types, including threading dislocations and a stacking fault, are provided as demonstration of its broad, TEM-like applicability. Ultimately, the combination of TEM-like capabilities &#8211; high spatial resolution and richness of microstructural data &#8211; with the convenience and speed of SEM, position ECCI as a powerful tool for the rapid characterization of crystalline materials.

The use of electron channeling contrast imaging in a scanning electron microscope to characterize defects in III-V/Si heteroexpitaxial thin films is described. This method yields similar results to plan-view transmission electron microscopy, but in significantly less time due to lack of required sample preparation.

Misfit dislocations in heteroepitaxial layers of GaP grown on Si(001) substrates are characterized through use of electron channeling contrast imaging ...

Measurement of X-ray Beam Coherence along Multiple Directions Using 2-D Checkerboard Phase Grating

A procedure for a technique to measure the transverse coherence of synchrotron radiation X-ray sources using a single phase grating interferometer is reported. The measurements were demonstrated at the 1-BM bending magnet beamline of the Advanced Photon Source (APS) at Argonne National Laboratory (ANL). By using a 2-D checkerboard &#960;/2 phase-shift grating, transverse coherence lengths were obtained along the vertical and horizontal directions as well as along the 45&#176; and 135&#176; directions to the horizontal direction. Following the technical details specified in this paper, interferograms were measured at different positions downstream of the phase grating along the beam propagation direction. Visibility values of each interferogram were extracted from analyzing harmonic peaks in its Fourier Transformed image. Consequently, the coherence length along each direction can be extracted from the evolution of visibility as a function of the grating-to-detector distance. The simultaneous measurement of coherence lengths in four directions helped identify the elliptical shape of the coherence area of the Gaussian-shaped X-ray source. The reported technique for multiple-direction coherence characterization is important for selecting the appropriate sample size and orientation as well as for correcting the partial coherence effects in coherence scattering experiments. This technique can also be applied for assessing coherence preserving capabilities of X-ray optics.

The measurement protocol and data analysis procedure are given for obtaining transverse coherence of a synchrotron radiation X-ray source along four directions simultaneously using a single 2-D checkerboard phase grating. This simple technique can be applied for complete transverse coherence characterization of X-ray sources and X-ray optics.

A procedure for a technique to measure the transverse coherence of synchrotron radiation X-ray sources using a single phase grating interferometer is ...

Using Synchrotron Radiation Microtomography to Investigate Multi-scale Three-dimensional Microelectronic Packages

Synchrotron radiation micro-tomography (SR&#181;T) is a non-destructive three-dimensional (3D) imaging technique that offers high flux for fast data acquisition times with high spatial resolution. In the electronics industry there is serious interest in performing failure analysis on 3D microelectronic packages, many which contain multiple levels of high-density interconnections. Often in tomography there is a trade-off between image resolution and the volume of a sample that can be imaged. This inverse relationship limits the usefulness of conventional computed tomography (CT) systems since a microelectronic package is often large in cross sectional area 100-3,600 mm2, but has important features on the micron scale. The micro-tomography beamline at the Advanced Light Source (ALS), in Berkeley, CA USA, has a setup which is adaptable and can be tailored to a sample&#39;s properties, i.e., density, thickness, etc., with a maximum allowable cross-section of 36 x 36 mm. This setup also has the option of being either monochromatic in the energy range ~7-43 keV or operating with maximum flux in white light mode using a polychromatic beam. Presented here are details of the experimental steps taken to image an entire 16 x 16 mm system within a package, in order to obtain 3D images of the system with a spatial resolution of 8.7 &#181;m all within a scan time of less than 3 min. Also shown are results from packages scanned in different orientations and a sectioned package for higher resolution imaging. In contrast a conventional CT system would take hours to record data with potentially poorer resolution. Indeed, the ratio of field-of-view to throughput time is much higher when using the synchrotron radiation tomography setup. The description below of the experimental setup can be implemented and adapted for use with many other multi-materials.

For this study synchrotron radiation micro-tomography, a non-destructive three-dimensional imaging technique, is employed to investigate an entire microelectronic package with a cross-sectional area of 16 x 16 mm. Due to the synchrotron&#39;s high flux and brightness the sample was imaged in just 3 min&#160;with an 8.7 &#181;m spatial resolution.

Synchrotron radiation micro-tomography (SR&#181;T) is a non-destructive three-dimensional (3D) imaging technique that offers high flux for fast data ...

Printing Fabrication of Bulk Heterojunction Solar Cells and In Situ Morphology Characterization

Polymer-based materials hold promise as low-cost, flexible efficient photovoltaic devices. Most laboratory efforts to achieve high performance devices have used devices prepared by spin coating, a process that is not amenable to large-scale fabrication. This mismatch in device fabrication makes it difficult to translate quantitative results obtained in the laboratory to the commercial level, making optimization difficult. Using a mini-slot die coater, this mismatch can be resolved by translating the commercial process to the laboratory and characterizing the structure formation in the active layer of the device in real time and in situ as films are coated onto a substrate. The evolution of the morphology was characterized under different conditions, allowing us to propose a mechanism by which the structures form and grow. This mini-slot die coater offers a simple, convenient, material efficient route by which the morphology in the active layer can be optimized under industrially relevant conditions. The goal of this protocol is to show experimental details of how a solar cell device is fabricated using a mini-slot die coater and technical details of running in situ structure characterization using the mini-slot die coater.

Printing Fabrication of Bulk Heterojunction Solar Cells and In Situ Morphology Characterization

Here, we present a protocol to fabricate organic thin film solar cells using a mini-slot die coater and related in-line structure characterizations using synchrotron scattering techniques.

Polymer-based materials hold promise as low-cost, flexible efficient photovoltaic devices. Most laboratory efforts to achieve high performance devices ...

Measurement of Quantum Interference in a Silicon Ring Resonator Photon Source

Silicon photonic chips have the potential to realize complex integrated quantum information processing circuits, including photon sources, qubit manipulation, and integrated single-photon detectors. Here, we present the key aspects of preparing and testing a silicon photonic quantum chip with an integrated photon source and two-photon interferometer. The most important aspect of an integrated quantum circuit is minimizing loss so that all of the generated photons are detected with the highest possible fidelity. Here, we describe how to perform low-loss edge coupling by using an ultra-high numerical aperture fiber to closely match the mode of the silicon waveguides. By using an optimized fusion splicing recipe, the UHNA fiber is seamlessly interfaced with a standard single-mode fiber. This low-loss coupling allows the measurement of high-fidelity photon production in an integrated silicon ring resonator and the subsequent two-photon interference of the produced photons in a closely integrated Mach-Zehnder interferometer. This paper describes the essential procedures for the preparation and characterization of high-performance and scalable silicon quantum photonic circuits.

Silicon photonic chips have the potential to realize complex integrated quantum systems. Presented here is a method for preparing and testing a silicon photonic chip for quantum measurements.