We greatly acknowledge the contributions by Shuang-Yan Lang and H&#233;ctor D. Abru&#241;a who provided samples for our research. This work was supported by the National Science Foundation (NSF) (DMR-1654596) and made use of the Cornell Center for Materials Research Facilities supported by the NSF under Award Number DMR-1719875.

1. Prepare the sample and transfer into the SEM chamber
<ol>
	<li>Set up the microscope
	<ol>
		<li>For systems that convert between room temperature and cryogenic equipment, install the cryo-SEM stage and anticontaminator according to the equipment manufacturer&#8217;s instructions and evacuate the SEM chamber.</li>
		<li>Adjust the gas injection system (GIS) platinum source so that when inserted it sits approximately 5 mm further away from the sample surface compared to typical room temperature experiments. This position needs to be optimized for each system to ensure even coating of the sample surface. On the FIB used here, this is done by loosening a set screw on the side of the GIS source and rotating the collar 3 turns clockwise.</li>
		<li>Set the GIS temperature to 28 &#176;C, open the shutter and vent for 30 s at this temperature to clear out excess material. Do this at room temperature, as the organometallic will coat any cold surface.</li>
		<li>Move the stage to the proper position for loading of the sample shuttle from the preparation chamber into the SEM (this will vary by system).</li>
		<li>Allow the SEM chamber to evacuate for a minimum of 8 h, to establish a low enough vacuum (typically about 4E-6 Torr) to minimize ice contamination during the experiment.</li>
	</ol>
	</li>
	<li>Set up the cryogenic preparation station
	<ol>
		<li>Evacuate the vacuum isolated lines for 8 h prior to use.</li>
		<li>Before cooling the microscope, flow dry nitrogen gas through the gas lines for about 15 min. This should be done at approximately 5 L/min, or the maximum flow rate of the system. This flushes moisture out of the system to mitigate the formation of ice in the lines upon cooling, which can impede the flow of gas.</li>
		<li>While still flowing gas at the maximum flow rate, close off the valve for the vacuum isolated lines, then transfer the heat exchanger into the liquid nitrogen Dewar.</li>
		<li>Set the temperature of the SEM and prep stages to -175 &#176;C, and the temperature of the anticontaminators to -192 &#176;C. Wait until all elements have reached the set temperature to proceed.</li>
	</ol>
	</li>
	<li>Vitrify the sample.
	<ol>
		<li>Fill the nitrogen dual pot slusher. Start by filling the main volume of the pot, then fill the volume surrounding it to reduce nitrogen bubbling. Continue adding more liquid nitrogen to each as needed until boiling stops.</li>
		<li>Seal the slusher with the lid and start the slush pump. Continue pumping until the liquid nitrogen starts solidifying.</li>
		<li>Start venting the slush pot. For air sensitive materials like lithium batteries, this is a good time to prepare the sample for plunge freezing.</li>
		<li>Once the pressure is high enough to allow the pot to be opened, quickly but gently set the sample in the nitrogen, and wait at least until the boiling has ceased around the sample to proceed. Remove all tools from the liquid nitrogen at this point to reduce the chances of ice contamination.&#160;</li>
		<li>If the slush pot is less than half full, add more liquid nitrogen.</li>
		<li>Transfer the sample to the SEM shuttle. Place any tools needed to secure or transfer the sample in the liquid nitrogen pot and allow them to fully cool, i.e., wait at a minimum until the LN2 stops boiling around each tool, before touching the sample or shuttle. Extended exposure to atmosphere, especially when humid, can cause ice crystals to form in the liquid nitrogen, so it is best to do this step quickly.</li>
		<li>Attach the shuttle to the transfer rod. As with other tools, pre-cool the end of the rod in the LN2 before touching the shuttle.</li>
		<li>Pump on the slush pot and watch the pressure. Lift the sample up out of the liquid nitrogen and seal it off in the vacuum chamber of the transfer system just before the nitrogen starts to freeze. Typically, this can be done by lifting the shuttle up when the pressure is ~8 mbar.</li>
		<li>Quickly transfer to the airlock of the prep chamber and pump on the transfer system. Open the transfer system&#8217;s vacuum chamber as soon as the airlock pressure is low enough for this to be done without much force.</li>
		<li>Once the prep chamber can be opened, quickly transfer the sample shuttle into the chamber and place on the cooled prep stage. Retract the transfer rod and close the airlock door.</li>
		<li>At this point, a ~5-10 nm gold-palladium layer can be sputtered onto the sample surface to mitigate charging. Typical starting values are 10 mA for 10 s, though these parameters should be adjusted for each system. Alternatively, one can image the uncoated surface, assess the extent of charging, and transfer back into the prep chamber to sputter coat.</li>
		<li>Re-open the airlock, connect the transfer rod and wait 1 min for the end of the rod to cool down. Then, open the valve to the main SEM chamber and transfer the sample shuttle as quickly and smoothly as possible onto the cooled SEM stage. Retract the transfer rod and store it under vacuum to prevent ice contamination in case it is needed again. 
		CAUTION: Liquid nitrogen can cause injury if exposed to skin. Handle with care while wearing the appropriate personal protective equipment. Do not place in a sealed container, as evaporation can cause pressure build-up.</li>
	</ol>
	</li>
</ol>
2. Image the sample surface and locate features
NOTE: The time required to set up to start imaging is usually sufficient to allow the sample to reach thermal equilibrium on the cryo-stage, especially if both stages in the prep-chamber and the SEM chamber are cooled to the same temperature and the transfer time of the shuttle from one stage to the other is minimized.
<ol>
	<li>Set the beam parameters prior to imaging, starting with a moderate voltage (~5 kV) and moderate current (~0.4 nA). For especially delicate samples, users may want to reduce these values, and more robust samples may tolerate higher voltage and current.&#160;</li>
	<li>Image the surface starting at low magnification (100x), focus and do any steps required by the instrument. For example, on the FIB user here, the measured working distance must be linked to the stage position. Assess the sample for changes in contrast or shape before focusing at higher magnifications to reduce charging.</li>
	<li>Bring the sample to approximately eucentric height and take another relatively low magnification image (100-200x).</li>
	<li>Select a sacrificial test region with the vitrified liquid and identify potential issues due to beam damage or charging. Start imaging at 100x magnification for 5 s, then increase the magnification to about 1,000x and image for another 5 s, then reduce the magnification to 100x, collect one image and pause the beam. If the region exposed at high magnification has changed contrast, the sample may be damaging or charging, and users should again consider adjusting the beam parameters or re-sputter coating. For a more detailed procedure see reference18.</li>
	<li>Search the sample for the regions of interest. This process will vary considerably by sample and may require some experimentation. Features which extend significantly above the surrounding surface will likely cause the vitrified liquid to be similarly raised, while other features may be hidden.
	<ol>
		<li>If the features of interest cannot be located, an EDX map may help. With the sample still oriented normal to the electron beam, follow the EDX mapping procedure described in step 4.</li>
	</ol>
	</li>
	<li>As features of interest are located, save both low and high magnification images of the surface as well as the stage position.</li>
	<li>Repeat to locate as many sites as desired.</li>
	<li>Select a region to image first and align that area to eucentric height following the instrument&#8217;s protocol.</li>
	<li>Tilt the sample so the surface is normal to the direction of the platinum GIS needle, and insert the GIS needle. Warm it to 28 &#176;C and open the valve for ~2.5 min, then retract the source. This should produce a uniform layer of uncured organometallic platinum, and the user can briefly image the sample surface to confirm even coverage. The deposition time will vary between instruments and should be adjusted to ensure an even layer 1-2 &#956;m thick.</li>
	<li>Tilt the sample shuttle towards the FIB source and expose the organometallic platinum to a 30 kV ion beam at 2.8 nA, 800x magnification for 30 s. Image with the electron beam to verify that the surface is smooth and lacks any signs of charging.</li>
</ol>
3. Prepare cross-sections
<ol>
	<li>Take a snapshot of the sample surface using the ion beam at 30kV and a lower bulk milling current (~2.8 nA), identify the feature of interest and measure out the rough placement of the cross-section. Trenches milled using about 2.8 nA can be placed 1 &#956;m away from the final cross-section and should extend past either side of the feature of interest by a few microns. Side windows (see 3.2) should be placed with one edge roughly flush with the desired final cross-section.</li>
	<li>Create a side window for x-rays prior to milling the main trenches to reduce redeposition.
	<ol>
		<li>Draw a Regular Cross Section rotated 90&#176; relative to where the trench will be. Orientation will depend on the configuration of each EDX detector; place the shallow end of this trench towards the EDX detector. In the instrument software used here, this rotation is done by clicking the Advanced tab for the pattern and entering a rotation angle, measured counterclockwise.</li>
		<li>Re-size the rotated pattern to maximize the number of x-rays to exit the cross-section&#8217;s surface, nominally 10 &#956;m square. The size will depend on the detector geometry, and often smaller windows will suffice. Users can expedite the procedure by determining the minimum size of this trench.</li>
	</ol>
	</li>
	<li>Create a Regular Cross Section just large enough to reveal the feature of interest. This can be done quickly by using a high current (~2.8 nA) to create one trench, lowering the current to clean up, or more slowly by working only at a lower current (~0.92 nA).
	<ol>
		<li>Take a snapshot of the sample surface using the ion beam at 30 kV and the desired current (see Discussion for selection of current). Identify the feature of interest and finalize the placement of the trench done in 3.1
		<ol>
			<li>The trench dimensions will vary by sample, but a typical size is 25 &#956;m x 20 &#956;m. Both dimensions must be large enough to allow the entire feature of interest to be visible; x will determine the width of the cross section, while y will limit how far down into the trench the electron beam can see. Ensure that there is 1 &#956;m of material left between the edge of this trench and the desired final cross-section.</li>
		</ol>
		</li>
		<li>Set the z-depth to 2 &#956;m with the milling application set to silicon and begin milling using the software, but regularly pause the process and image the cross-section using the electron beam, then resume milling as needed.</li>
		<li>Repeat this process until the trench is much deeper than the feature of interest, typically 10-20 &#956;m deep. Samples containing multiple materials will often have highly variable milling times and may need more or less time than the 1 &#956;m depth setting will estimate. Record the amount of time needed to create the rough trench to guide the depth used in 3.4.</li>
	</ol>
	</li>
	<li>Create a final clean cross-section
	<ol>
		<li>Lower the ion beam current to approximately 0.92 nA and take a snapshot. Verify the location of the feature of interest: if step 3.1.3 was done correctly, there will be about 1 &#956;m of material remaining to be milled away.</li>
		<li>Draw a Cleaning Cross Section using the FIB software. Overlap this cleaning window with the pre-made trench by at least 1 &#956;m to help mitigate redeposition.</li>
		<li>Set the z-depth, using the observations from step 3.3.3 to determine the value. For example, if half of the time was used on a 1 &#956;m depth, re-set the depth to 0.5 &#956;m.</li>
		<li>Let the cleaning cross section run uninterrupted. When finished, image the cleaned cross-section using the electron beam.</li>
	</ol>
	</li>
</ol>
4. Perform EDX mapping 
<ol>
	<li>Select the appropriate beam conditions for the sample (see Discussion for details)</li>
	<li>Orient the sample to maximize x-ray counts. Each instrument will have an ideal working height for EDX; ensure that the feature of interest is at this height. Tilt such that the incident electron beam is as close to normal to the surface of interest as possible.</li>
	<li>Insert the EDX detector and determine the appropriate process time. For highly beam sensitive samples, it may be necessary to test these conditions on a sacrificial region of the sample prior to mapping the site of interest.
	<ol>
		<li>In the detector&#8217;s software, go to Microscope Setup and start the electron beam image, then hit record. This will measure the count rate and dead time.</li>
		<li>Record both the average dead time and count rate. The ideal dead time will vary between detectors, but for the Oxford X-max 80 typical values range between 15-25. Lower values will give better resolution, and higher values correspond to higher count rates.</li>
		<li>If the deadtime needs to be adjusted, change the EDX time constant (also known as Process Time). A lower process time will give a lower deadtime, and vice versa. Repeat until the deadtime is in the desired range.</li>
		<li>Confirm that the count rate is reasonable. Lower count rates (1,000 counts/s and lower) will require longer acquisition times, which increases the likelihood that maps will be distorted by sample drift. If the count rate is too low, consider increasing the beam current and voltage, or increasing the process time.</li>
	</ol>
	</li>
	<li>Once the detector conditions have been established, collect the electron beam image.
	<ol>
		<li>Go to Image Setup and select the bit depth and image resolution, typically 8 bit and either 512 x 448 or 1024 x 896.</li>
		<li>Adjust the imaging conditions for the EDX software. Often the imaging conditions are calibrated differently in the EDX software than in the SEM&#8217;s own software, and magnification, brightness and contrast will need to be adjusted accordingly. In INCA hit the record button on the site of interest window, adjust the image as needed, then record another image, iterating as needed.</li>
	</ol>
	</li>
	<li>Adjust the mapping setup in the EDX software.
	<ol>
		<li>Select the X-ray Map resolution, Spectrum Range, Number of Channels, and the Map Dwell Time. The resolution of the EDX map must be lower than the electron image (typically 256 x 224), and the energy range can be as low as the beam energy used. Typically, the maximum number of channels are used, and the dwell time is set to 400 &#956;s.</li>
		<li>In the EDX software, select the area to map over. This can be done either by selecting the whole field of view, or by selecting a smaller region on the electron beam image which may expedite the process.</li>
	</ol>
	</li>
	<li>Start acquiring the EDX map. Allow this to run until a sufficient number of counts are collected (see the discussion below). In the elemental maps window, pre-processed maps are displayed, and if features start to blur during this process it is a sign the sample is either drifting or being damaged. In this case, consider stopping the map and using the SEM software to determine the problem.</li>
	<li>When the map is complete, save the EDX map as a data cube, which is a 3D array with an axis for both spatial coordinates in the image, and an axis for energy.</li>
</ol>

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The authors have nothing to disclose.

The cryogenic preparation method described here is important and must be done correctly for the chemistry and morphology to be preserved8. The foremost concern is freezing the sample quickly since this is what allows the liquid to be vitrified8. If the sample cools too slowly, liquids may crystalize resulting in a change in morphology6. To prevent crystallization, slush nitrogen is used in this procedure, as it reduces the Leidenfrost effect and acce...

Interfaces between solids and liquids play a vital role in the function of energy materials such as batteries, fuel cells, and supercapacitors1,2,3. While characterizing the chemistry and morphology of these interfaces could play a central role in improving functional devices, doing so has presented a substantial challenge1,3,4. Liquids are incompatible with the high vacuum environments needed for many common characterization techniques, such as x-ray photoemission spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy2. Historically, the solution has been to remove the liquid from the device, but this comes at the expense of potentially damaging delicate structures at the interface2,4 or modifying morphology3. In the case of batteries, especially those which employ highly reactive alkali metals, this physical damage is compounded by chemical degradation upon exposure to air5.
This paper describes cryo-SEM and focused ion beam (FIB) as a method for preserving and characterizing solid-liquid interfaces. Similar methods have been shown to preserve the structure of cells in biological samples6,7,8, energy devices5,9,10,11,12 and nanoscale corrosion reactions13,14,15. The crux of the technique is to vitrify the sample via plunge freezing in slush nitrogen prior to transfer into the microscope where it is placed onto a cryogenically cooled stage. Vitrification stabilizes the liquid in the vacuum of the microscope while avoiding the structural deformations associated with crystallization6,8. Once in the microscope, a dual beam system allows nanoscale imaging with the electron beam, and preparation of cross-sections with the focused ion beam. Lastly, chemical characterization is enabled via Energy Dispersive X-ray (EDX) mapping. Altogether, cryo-SEM/FIB can preserve the native structure of a solid-liquid interface, create cross-sections, and provide both chemical and morphological characterization.
In addition to providing a general workflow for cryo-SEM and EDX mapping, this paper will describe a number of methods to mitigate artifacts from milling and imaging. Often vitrified liquids are delicate and insulating, making them prone to charging as well as beam damage8. While a number of techniques have been established to reduce these unwanted effects in specimens at room-temperature16,17,18, several have been modified for cryogenic applications. In particular, this procedure details application of conductive coatings, first a gold-palladium alloy, followed by a thicker platinum layer. Additionally, instructions are provided to help users identify charging when it occurs and adjust the electron beam conditions to mitigate the accumulation of charge. Lastly, although beam damage has many characteristics in common with charging, the two can occur independent of one another16, and guidelines are provided for minimizing beam damage during the steps where it is most likely.
While dual-beam SEM/FIB is not the only electron microscopy tool to have been adapted for cryogenic operation, it is particularly well-suited for this work. Often realistic devices like a battery are on the scale of several centimeters in size, while many of the features of interest are on the order of microns to nanometers, and the most meaningful information can be contained in the cross-section of the interface4,5,19. Although techniques like Scanning Transmission Electron Microscopy (STEM) combined with Electron Energy Loss Spectroscopy (EELS) enable imaging and chemical mapping down to the atomic scale, they require extensive preparation to make the sample sufficiently thin to be electron transparent, dramatically limiting throughput3,4,19,20,21,22. Cryo-SEM, by contrast, allows for the rapid probing of interfaces in macroscopic devices, such as the anode of a lithium metal battery coin cell, albeit at a lower resolution of tens of nanometers. Ideally, a combined approach that leverages the advantages of both techniques is applied. Here, we focus on higher throughput cryogenic FIB/SEM techniques.
Lithium metal batteries were used as the primary test case for this work, and they demonstrate the broad utility of cryo-SEM techniques: they feature delicate structures of scientific interest4,5,9,10,11,12, have broadly varying chemistry to be revealed via EDX2, and cryogenic techniques are required to preserve the reactive lithium5,21. In particular, the uneven lithium deposits known as dendrites, as well as the interfaces with the liquid electrolyte are preserved and can be imaged and mapped with EDX4,5,12. Additionally, lithium typically would oxidize during preparation and form an alloy with gallium during milling, but the preserved electrolyte prevents oxidation and cryogenic temperatures mitigate reactions with gallium5. Many other systems (energy devices especially) feature similarly delicate structures, complex chemistries and reactive materials, so the success of cryo-SEM on the study of lithium metal batteries can be considered a promising indication that it is suitable for other materials as well.
The protocol uses a dual-beam FIB/SEM system fitted with a cryogenic stage, a cryogenic preparation chamber and a cryogenic transfer system, as detailed in the&#160;Table of Materials. For preparing the cryo-immobilized samples there is a workstation with a &#34;slush pot,&#34; which is a foam insulated pot that sits in a vacuum chamber in the station. The foam insulated dual pot slusher contains a primary nitrogen chamber and a secondary chamber which surrounds the former and reduces boiling in the main part of the pot. Once filled with nitrogen, a lid is placed over the pot and the whole system can be evacuated to form slush nitrogen. A transfer system featuring a small vacuum chamber is used to transfer the sample under vacuum to the preparation or &#34;prep&#34; chamber of the microscope. In the prep chamber the sample can be kept at -175 &#176;C and sputter coated with a conductive layer, such as a gold-palladium alloy. Both the prep chamber and the SEM chamber feature a cryogenically cooled stage for holding the sample, and an anticontaminator to adsorb contaminants and to prevent ice buildup on the specimen. The whole system is cooled with nitrogen gas that flows through a heat exchanger submerged in liquid nitrogen, and then through the two cryo-stages and two anticontaminators of the system.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>INCA EDS</td>
			<td>Oxford instruments</td>
			<td></td>
			<td>Control software for X-max 80</td>
		</tr>
		<tr>
			<td>PP3010T Cryo-preparation system</td>
			<td>Quorum Technologies, Inc.</td>
			<td></td>
			<td>FIB/SEM cryogenic preparation system. Includes pumping station, transfer rod system, preparation (prep) chamber, cryogenic stages, sample shuttles&#160;</td>
		</tr>
		<tr>
			<td>Strata 400 DualBeam System&#160;</td>
			<td>FEI Co. (now Thermo Fisher Scientific)</td>
			<td></td>
			<td>Dual beam FIB/SEM</td>
		</tr>
		<tr>
			<td>X-Max 80</td>
			<td>Oxford Instruments</td>
			<td></td>
			<td>80mm2 EDX detector</td>
		</tr>
		<tr>
			<td>xT Microscope Control</td>
			<td>FEI Co. (now Thermo Fisher Scientific)</td>
			<td></td>
			<td>Software for controlling FEI Strata&#160;</td>
		</tr>
	</tbody>
</table>

nanoscale characterization of liquid-solid interfaces by coupling cryo-focused ion beam milling with scanning electron microscopy and spectroscopy

Physical and chemical processes at solid-liquid interfaces play a crucial role in many natural and technological phenomena, including catalysis, solar energy and fuel generation, and electrochemical energy storage. Nanoscale characterization of such interfaces has recently been achieved using cryogenic electron microscopy, thereby providing a new path to advancing our fundamental understanding of interface processes.
This contribution provides a practical guide to mapping the structure and chemistry of solid-liquid interfaces in materials and devices using an integrated cryogenic electron microscopy approach. In this approach, we pair cryogenic sample preparation which allows stabilization of solid-liquid interfaces with cryogenic focused ion beam (cryo-FIB) milling to create cross-sections through these complex buried structures. Cryogenic scanning electron microscopy (cryo-SEM) techniques performed in a dual-beam FIB/SEM enable direct imaging as well as chemical mapping at the nanoscale. We discuss practical challenges, strategies to overcome them, as well as protocols for obtaining optimal results. While we focus in our discussion on interfaces in energy storage devices, the methods outlined are broadly applicable to a range of fields where solid-liquid interface play a key role.

This method has been developed on a dual FIB/SEM system equipped with a commercially available cryogenic stage, anticontaminator, and preparation chamber. For details, see the table of materials. We have primarily tested this method on lithium metal batteries with a number of different electrolytes, but the method is applicable to any solid-liquid interface that will endure the amount of dose applied during EDX mapping.
Figure 1&#160;illustrates the various compon...

Watch this Scientific Journal Video about Nanoscale Characterization of Liquid-Solid Interfaces by Coupling Cryo-Focused Ion Beam Milling with Scanning Electron Microscopy and Spectroscopy at JoVE.com

Nanoscale Characterization of Liquid-Solid Interfaces by Coupling Cryo-Focused Ion Beam Milling with Scanning Electron Microscopy and Spectroscopy

Cryogenic Focused Ion Beam (FIB) and Scanning Electron Microscopy (SEM) techniques can provide key insights into the chemistry and morphology of intact solid-liquid interfaces. Methods for preparing high quality Energy Dispersive X-ray (EDX) spectroscopic maps of such interfaces are detailed, with a focus on energy storage devices.

Physical and chemical processes at solid-liquid interfaces play a crucial role in many natural and technological phenomena, including catalysis, solar ...

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3.3K Views.  Cornell University. Cryogenic Focused Ion Beam (FIB) and Scanning Electron Microscopy (SEM) techniques can provide key insights into the chemistry and morphology of intact solid-liquid interfaces. Methods for preparing high quality Energy Dispersive X-ray (EDX) spectroscopic maps of such interfaces are detailed, with a focus on energy storage devices.

Video: Nanoscale Characterization of Liquid-Solid Interfaces by Coupling Cryo-Focused Ion Beam Milling with Scanning Electron Microscopy and Spectroscopy

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 ...

Speciation and Bioavailability Measurements of Environmental Plutonium Using Diffusion in Thin Films

The biological uptake of plutonium (Pu) in aquatic ecosystems is of particular concern since it is an alpha-particle emitter with long half-life which can potentially contribute to the exposure of biota and humans. The diffusive gradients in thin films technique is introduced here for in-situ measurements of Pu bioavailability and speciation. A diffusion cell constructed for laboratory experiments with Pu and the newly developed protocol make it possible to simulate the environmental behavior of Pu in model solutions of various chemical compositions. Adjustment of the oxidation states to Pu(IV) and Pu(V) described in this protocol is essential in order to investigate the complex redox chemistry of plutonium in the environment. The calibration of this technique and the results obtained in the laboratory experiments enable to develop a specific DGT device for in-situ Pu measurements in freshwaters. Accelerator-based mass-spectrometry measurements of Pu accumulated by DGTs in a karst spring allowed determining the bioavailability of Pu in a mineral freshwater environment. Application of this protocol for Pu measurements using DGT devices has a large potential to improve our understanding of the speciation and the biological transfer of Pu in aquatic ecosystems.

The technique of diffusive gradients in thin films (DGT) is proposed for speciation studies of plutonium. This protocol describes diffusion experiments probing the behavior of Pu(IV) and Pu(V) in presence of organic matter. DGTs deployed in a karstic spring allow assessment of the bioavailability of Pu.

The biological uptake of plutonium (Pu) in aquatic ecosystems is of particular concern since it is an alpha-particle emitter with long half-life which can ...

Ohmic Contact Fabrication Using a Focused-ion Beam Technique and Electrical Characterization for Layer Semiconductor Nanostructures

Layer semiconductors with easily processed two-dimensional (2D) structures exhibit indirect-to-direct bandgap transitions and superior transistor performance, which suggest a new direction for the development of next-generation ultrathin and flexible photonic and electronic devices. Enhanced luminescence quantum efficiency has been widely observed in these atomically thin 2D crystals. However, dimension effects beyond quantum confinement thicknesses or even at the micrometer scale are not expected and have rarely been observed. In this study, molybdenum diselenide (MoSe2) layer crystals with a thickness range of 6-2,700 nm were fabricated as two- or four-terminal devices. Ohmic contact formation was successfully achieved by the focused-ion beam (FIB) deposition method using platinum (Pt) as a contact metal. Layer crystals with various thicknesses were prepared through simple mechanical exfoliation by using dicing tape. Current-voltage curve measurements were performed to determine the conductivity value of the layer nanocrystals. In addition, high-resolution transmission electron microscopy, selected-area electron diffractometry, and energy-dispersive X-ray spectroscopy were used to characterize the interface of the metal&#8211;semiconductor contact of the FIB-fabricated MoSe2 devices. After applying the approaches, the substantial thickness-dependent electrical conductivity in a wide thickness range for the MoSe2-layer semiconductor was observed. The conductivity increased by over two orders of magnitude from 4.6 to 1,500 &#937;&#8722;1 cm&#8722;1, with a decrease in the thickness from 2,700 to 6 nm. In addition, the temperature-dependent conductivity indicated that the thin MoSe2 multilayers exhibited considerably weak semiconducting behavior with activation energies of 3.5-8.5 meV, which are considerably smaller than those (36-38 meV) of the bulk. Probable surface-dominant transport properties and the presence of a high surface electron concentration in MoSe2 are proposed. Similar results can be obtained for other layer semiconductor materials such as MoS2 and WS2.

We describe the approaches for the device fabrication and electrical characterization of molybdenum diselenide (MoSe2) layer semiconductor nanostructures with different thicknesses. In addition, the fabrication of ohmic contacts for MoSe2-layer nanocrystals by the focused-ion beam deposition method using platinum (Pt) as a contact metal is described.

Layer semiconductors with easily processed two-dimensional (2D) structures exhibit indirect-to-direct bandgap transitions and superior transistor ...

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 ...

Studying Dynamic Processes of Nano-sized Objects in Liquid using Scanning Transmission Electron Microscopy

Samples fully embedded in liquid can be studied at a nanoscale spatial resolution with Scanning Transmission Electron Microscopy (STEM) using a microfluidic chamber assembled in the specimen holder for Transmission Electron Microscopy (TEM) and STEM. The microfluidic system consists of two silicon microchips supporting thin Silicon Nitride (SiN) membrane windows. This article describes the basic steps of sample loading and data acquisition. Most important of all is to ensure that the liquid compartment is correctly assembled, thus providing a thin liquid layer and a vacuum seal. This protocol also includes a number of tests necessary to perform during sample loading in order to ensure correct assembly. Once the sample is loaded in the electron microscope, the liquid thickness needs to be measured. Incorrect assembly may result in a too-thick liquid, while a too-thin liquid may indicate the absence of liquid, such as when a bubble is formed. Finally, the protocol explains how images are taken and how dynamic processes can be studied. A sample containing AuNPs is imaged both in pure water and in saline.

This protocol describes the operation of a liquid flow specimen holder for scanning transmission electron microscopy of AuNPs in water, as used for the observation of nanoscale dynamic processes.

Samples fully embedded in liquid can be studied at a nanoscale spatial resolution with Scanning Transmission Electron Microscopy (STEM) using a ...

Precision Milling of Carbon Nanotube Forests Using Low Pressure Scanning Electron Microscopy

A nanoscale fabrication technique appropriate for milling carbon nanotube (CNT) forests is described. The technique utilizes an environmental scanning electron microscope (ESEM) operating with a low pressure water vapor ambient. In this technique, a portion of the electron beam interacts with the water vapor in the vicinity of the CNT sample, dissociating the water molecules into hydroxyl radicals and other species by radiolysis. The remainder of the electron beam interacts with the CNT forest sample, making it susceptible to oxidation from the chemical products of radiolysis. This technique may be used to trim a selected region of an individual CNT, or it may be used to remove hundreds of cubic microns of material by adjusting ESEM parameters. The machining resolution is similar to the imaging resolution of the ESEM itself. The technique produces only small quantities of carbon residue along the boundaries of the cutting zone, with minimal effect on the native structural morphology of the CNT forest.

Low pressure scanning electron microscopy in a water vapor ambient is used to machine nanoscale to microscale features in carbon nanotube forests.

A nanoscale fabrication technique appropriate for milling carbon nanotube (CNT) forests is described. The technique utilizes an environmental scanning ...

A Novel Method for In Situ Electromechanical Characterization of Nanoscale Specimens

Electrically assisted deformation (EAD) is increasingly being used to improve the formability of metals during processes such as sheet metal rolling and forging. Adoption of this technique is proceeding despite disagreement concerning the underlying mechanism responsible for EAD. The experimental procedure described herein enables a more explicit study compared to previous EAD research by removing thermal effects, which are responsible for disagreement in interpreting previous EAD results. Furthermore, as the procedure described here enables EAD observation in situ and in real time in a transmission electron microscope (TEM), it is superior to existing post-mortem methods that observe EAD effects post-test. Test samples consist of a single crystal copper (SCC) foil having a free-standing tensile test section of nanoscale thickness, fabricated using a combination of laser and ion beam milling. The SCC is mounted to an etched silicon base that provides mechanical support and electrical isolation while serving as a heat sink. Using this geometry, even at high current density (~3,500 A/mm2), the test section experiences a negligible temperature increase (&#60;0.02 &#176;C), thus eliminating Joule heating effects. Monitoring material deformation and identifying the corresponding changes to microstructures, e.g. dislocations, are accomplished by acquiring and analyzing a series of TEM images. Our sample preparation and in situ experiment procedures are robust and versatile as they can be readily utilized to test materials with different microstructures, e.g., single and polycrystalline copper.

A Novel Method for In Situ Electromechanical Characterization of Nanoscale Specimens

Isolating electrical and thermal effects on electrically assisted deformation (EAD) is very difficult using macroscopic samples. Metallic sample micro- and nanostructures together with a custom test procedure have been developed to evaluate the impact of applied current on the formation without joule heating and evolution of dislocations on these samples.

Electrically assisted deformation (EAD) is increasingly being used to improve the formability of metals during processes such as sheet metal rolling and ...

Focused Ion Beam Fabrication of LiPON-based Solid-state Lithium-ion Nanobatteries for In Situ Testing

Solid-state electrolytes are a promising replacement for current organic liquid electrolytes, enabling higher energy densities and improved safety of lithium-ion (Li-ion) batteries. However, a number of setbacks prevent their integration into commercial devices. The main limiting factor is due to nanoscale phenomena occurring at the electrode/electrolyte interfaces, ultimately leading to degradation of battery operation. These key problems are highly challenging to observe and characterize as these batteries contain multiple buried interfaces. One approach for direct observation of interfacial phenomena in thin film batteries is through the fabrication of electrochemically active nanobatteries by a focused ion beam (FIB). As such, a reliable technique to fabricate nanobatteries was developed and demonstrated in recent work. Herein, a detailed protocol with a step-by-step process is presented to enable the reproduction of this nanobattery fabrication process. In particular, this technique was applied to a thin film battery consisting of LiCoO2/LiPON/a-Si, and has further been previously demonstrated by in situ cycling within a transmission electron microscope.

Focused Ion Beam Fabrication of LiPON-based Solid-state Lithium-ion Nanobatteries for In Situ Testing

A protocol for the fabrication of electrochemically active LiPON-based solid-state lithium-ion nanobatteries using a focused ion beam is presented.

Solid-state electrolytes are a promising replacement for current organic liquid electrolytes, enabling higher energy densities and improved safety of ...

Single-Digit Nanometer Electron-Beam Lithography with an Aberration-Corrected Scanning Transmission Electron Microscope

We demonstrate extension of electron-beam lithography using conventional resists and pattern transfer processes to single-digit nanometer dimensions by employing an aberration-corrected scanning transmission electron microscope as the exposure tool. Here, we present results of single-digit nanometer patterning of two widely used electron-beam resists: poly (methyl methacrylate) and hydrogen silsesquioxane. The method achieves sub-5 nanometer features in poly (methyl methacrylate) and sub-10 nanometer resolution in hydrogen silsesquioxane. High-fidelity transfer of these patterns into target materials of choice can be performed using metal lift-off, plasma etch, and resist infiltration with organometallics.

We use an aberration-corrected scanning transmission electron microscope to define single-digit nanometer patterns in two widely-used electron-beam resists: poly (methyl methacrylate) and hydrogen silsesquioxane. Resist patterns can be replicated in target materials of choice with single-digit nanometer fidelity using liftoff, plasma etching, and resist infiltration by organometallics.

We demonstrate extension of electron-beam lithography using conventional resists and pattern transfer processes to single-digit nanometer dimensions by ...