We acknowledge the services of Stanley Flegler, Carol Flegler, and Abigail Tirrell at the MSU Center for Advanced Microscopy. We thank Ray Clark and Mark Wilson for technical assistance with the set-up of the electrochemical etching apparatus. Earlier contributions from Anne Benjamin, Georg Bollen, Rafael Ferrer, David Lincoln, Stefan Schwarz and Adrian Valverde, and technical assistance from John Yurkon are also acknowledged. This work was partially supported by the National Science Foundation contract no. PHY-1102511 and PHY-1307233, Michigan State University and the Facility for Rare Isotope Beams, and Central Michigan University.

1. Electrochemical Etching
<ol>
	<li>Experimental set-up
	<ol>
		<li>Apparatus 
		Note: The electrochemically etching set-up requires a standard 0 - 30 V direct current (DC) benchtop power supply and appropriate cables, a separatory funnel, a wide base glass beaker, and standard rod and utility clamp with electrically insulating grips. Small screws, insulated stand-offs, and alligator clips will also be required. Additional items, described below and shown in the picture of the etching apparatus in Figure 1, must be fabricated.
		<ol>
			<li>Make a tungsten rod holder from an approximately 100 mm long 6 mm diameter aluminum rod. Drill a 0.5 mm diameter approximately 8 mm deep hole in the center, and make a tapped hole for a 4-40 screw in the side to hold the rod in place.</li>
			<li>Make a counter electrode from an approximately 100 mm x 30 mm x 3 mm thick copper plate with an approximately 75 mm x 20 mm x 1.5 mm deep reservoir milled into it, and a 1.5 mm diameter hole in the center. Attach approximately 15 mm long insulated stand-offs to the backside of the counter electrode.</li>
			<li>Make an FEP catcher by drilling a 6 mm diameter 8 mm deep hole into an approximately 75 x 20 x 20 mm copper block.</li>
		</ol>
		</li>
		<li>Preparation of tungsten rod
		<ol>
			<li>Use wire clippers to cut the 0.5 mm diameter tungsten rods into approximately 25 mm lengths.</li>
			<li>Clean the rods in acetone in an ultrasonic bath for 15 min.</li>
			<li>Rinse the rods with deionized water.</li>
		</ol>
		</li>
		<li>Etching solution 
		Caution: NaOH solution is a corrosive alkali solution-NFPA 704 label: Flammability (0), Health (3), Instability/Reactivity (0), Special (COR)-and can cause chemical burns if it comes in contact with the skin or eyes. Inhalation of fumes can cause irritation and burns to the respiratory tract. When handling NaOH solution, wear chemical splash goggles and face shield to protect the eyes, and gloves and an apron to protect the skin. Perform the etching procedure in a fume hood or wear a respirator. Care should be taken when performing step 1.1.3.1 to produce the diluted NaOH solution. This process is highly exothermic and can release heat that may cause burns or ignite flammables, and could cause the solution to splash out of the container.
		<ol>
			<li>Make a 1.5 M NaOH solution by combining 30 ml of 50% by weight NaOH solution with 370 ml of deionized water to make a 400 ml total volume.</li>
			<li>Fill a separatory funnel with the NaOH solution.</li>
		</ol>
		</li>
		<li>Cut-off circuit 
		Note: If the DC power supply is to be operated manually, then the operator will turn the power supply off once the tungsten rod has etched all the way through (see 1.2.2). In case of manual operation, skip to step 1.2. For automatic cut-off of the DC power supply, the cut-off circuit (shown in Figure 2 and described below), should be constructed. Here, we implement the computer control using a DAQ card.
		<ol>
			<li>Connect an ammeter in series with the DC power supply.</li>
			<li>Connect two resistors, R1 and R2 in series and place in parallel with the tungsten rod/counter electrode etching leg of the circuit. (Nominal values for R1 and R2 are R1 = 5&#160;k&#937;&#160;and R2 = 10 k&#937;.)</li>
			<li>Monitor the voltage across one of the resistors with an analog-to-digital convertor (ADC) and suitable computer control software, e.g., LabVIEW. The monitored voltage, Vmon, can be related to the voltage across both resistors and hence, the voltage across the etching leg, Vetch, via 
			(4) <img alt="Equation 19" src="/files/ftp_upload/54030/54030eq19.jpg" />, 
			where the voltage is being monitored across R1.</li>
			<li>Connect a low resistance resistor, RL = 1 &#937;, in series in the etching circuit. Use a second channel on the ADC to record the voltage across this resistor. The etching current is then found via ietch &#8776; VL/RL. (Only about 1 mA flows throw the monitor leg of the circuit.)</li>
			<li>In software, create a program to output a 5 V TTL signal from the digital input/output channel (DI/O) when either the etching voltage increases above a set-value, or the etching current drops below a set value, indicating that the tungsten rod has etched all the way through. These values depend on the etching current and NaOH solution molarity being used and should be determined with a test run of the experiment.</li>
			<li>As shown in Figure 2, arrange for the 5 V TTL signal to open a relay to stop the current flow.</li>
		</ol>
		</li>
	</ol>
	</li>
</ol>
<img alt="Figure 2" src="/files/ftp_upload/54030/54030fig2.jpg" /> 
Figure 2. Schematic of etching circuit. A schematic drawing of the etching circuit used to provide the constant DC etching current. The current is determined by monitoring the voltage across a low resistance resistor and the voltage is recorded by monitoring the voltage across a high resistance resistor using an ADC. A computer program monitors the current and provides a 5 V output signal to a relay that opens the etching circuit once the current drops below a specified value. <a href="https://www.jove.com/files/ftp_upload/54030/54030fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<ol start="2">
	<li>Etching procedure
	<ol>
		<li>Apparatus preparation
		<ol>
			<li>Set up the apparatus as shown in Figure 1, with the copper FEP catcher block placed inside the wide base glass beaker and the copper cathode located above it, spaced off by the insulating stand-offs.</li>
			<li>Set the current on the DC power supply to the desired value, typically 200 mA.</li>
			<li>Place a tungsten rod in the holder and connect the positive terminal of the DC power supply to the 4-40 holding screw with an alligator clip.</li>
			<li>Insert the tungsten rod through the hole in the copper cathode so that approximately 12 mm of the tungsten rod passes through the hole.</li>
			<li>Connect the negative terminal of the power supply to the copper cathode with another alligator clip.</li>
		</ol>
		</li>
		<li>Etching
		<ol>
			<li>Manually adjust the drip rate of the separatory funnel to match the drip rate through the hole, about 1 drip every 3 sec. Wait for the reservoir in the copper cathode to become full.</li>
			<li>Turn on the DC power supply to begin etching.</li>
			<li>If operating in manual mode, turn off the DC power supply once the bottom part of the tip etches all the way through and drops off. If operating with an automatic shut-off switch, the etching current will be cut-off automatically once the rod etches through.</li>
		</ol>
		</li>
	</ol>
	</li>
</ol>
2. Characterization of Field Emission Points
<ol>
	<li>Inspection of tips
	<ol>
		<li>Carefully remove the bottom tip from the catcher block using pliers or tweezers. Remove the upper tip from the tungsten rod holder by loosening the 4-40 screw and gently pulling the upper tip out with the pliers or tweezers.</li>
		<li>Rinse with acetone and then with deionized water.</li>
		<li>Examine with an optical microscope. Tips should be seen to taper to a fine point. Those that do not, e.g., because they are bent or do not have a regular cone structure, should be discarded. Figure 3 shows an example of (a) a good tip and (b) a bent tip.</li>
		<li>Store tips in a desiccator.</li>
	</ol>
	</li>
</ol>
<img alt="Figure 3" src="/files/ftp_upload/54030/54030fig3.jpg" /> 
Figure 3. Optical image of FEP tips. Picture of (a) a good tip and (b) a bad tip, as viewed through an optical microscope. <a href="https://www.jove.com/files/ftp_upload/54030/54030fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<ol start="2">
	<li>Scanning Electron Microscope (SEM) Imaging
	<ol>
		<li>For SEM Imaging, secure FEP tips to a conducting holder using conducting tape or by screwing them to it (e.g., see Figure 4) and image in a SEM according to manufacturer&#39;s protocol at magnifications of approximately 1,800X and 37,000X to view the cone of the tip and the end of the tip, respectively.</li>
	</ol>
	</li>
</ol>
<img alt="Figure 4" src="/files/ftp_upload/54030/54030fig4.jpg" /> 
Figure 4. FEP holder for SEM imaging. A picture of (a) the top and (b) the bottom of the holder used to secure FEPs while imaging with the SEM. <a href="https://www.jove.com/files/ftp_upload/54030/54030fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" src="/files/ftp_upload/54030/54030fig5.jpg" /> 
Figure 5. Field emission apparatus. Schematic of the apparatus used to apply a HV to the FEPs while under vacuum to produce an electron beam. The electron beam current is monitored on the Faraday cup with a picoammeter. <a href="https://www.jove.com/files/ftp_upload/54030/54030fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<ol start="3">
	<li>Field Emission Tests
	<ol>
		<li>Apparatus 
		Note: For the field emission tests the following, or similar, equipment is required: a 6-way 6&#34; conflat flange cross to serve as a vacuum chamber, three 6&#34; to 2 &#190;&#34; conflat flange zero length adaptors, an SHV (safe high voltage) feedthrough on a 2 &#190;&#34; conflat flange, a BNC feedthrough on a 2 &#190;&#34; conflat flange, a linear feedthrough on a 2 &#190;&#34; conflat flange, a 6&#34; conflat flange window, a 6&#34; conflat flange blank off, a turbo vacuum pump mounted to a 6&#34; conflat flange, and a backing pump (e.g., a scroll pump) for the turbo. A high voltage (HV) power supply capable of delivering up to -5 kV is required to bias the FEP, and a picoammeter is required to monitor the electron current emitted from the FEP and collected on a Faraday cup, see e.g., 13. In lieu of a Faraday cup, a simple conducting collection plate can be used. A schematic of the field emission set-up is shown in Figure 5.
		<ol>
			<li>Make a second tungsten rod holder (see step 1.1.1.1). In the opposite end of the holder to the FEP drill a 1 mm diameter hole and drill and tap a hole in the side of the rod for a 4-40 screw to secure it to the vacuum side of the SHV feedthrough.</li>
			<li>Set-up the field emission apparatus as shown in Figure 5. The Faraday cup should be about 2 cm from the end of the FEP.</li>
			<li>Connect the HV supply to the SHV feedthrough that the FEP holder is attached to, and connect the picoammeter to the BNC feedthrough that the Faraday cup is attached to.</li>
			<li>Pump down the set-up to a pressure of 10-6 mbar or below.</li>
		</ol>
		</li>
		<li>Field emission
		<ol>
			<li>Gradually increase the bias on the FEP and monitor the electron beam current on the Faraday cup with a picoammeter. When field emission begins, a current will be observed on the picoammeter.</li>
			<li>Increase the HV in incremental steps (of around 50 V) and record the average electron beam current on the picoammeter at each step. (This process can be computer controlled e.g., by a LabVIEW program if desired, or can be done manually). Keep the electron beam current below 1 &#956;A.</li>
		</ol>
		</li>
		<li>Conditioning
		<ol>
			<li>Condition the tip by operating in field emission mode at 5 nA for 1 hr.</li>
			<li>Repeat the current vs HV scan of 2.3.2.2.</li>
		</ol>
		</li>
	</ol>
	</li>
</ol>

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B. 9, 601-608 (1990).</li><li>Shi, W., Redshaw, M., Myers, E. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Atomic+masses+of+32,33S,+84,86Kr,+and+129,132Xe+with+uncertainties+0.1+ppb.">Atomic masses of 32,33S, 84,86Kr, and 129,132Xe with uncertainties 0.1 ppb.</a> Phys. Rev. A. 72, 022510 (2005).</li><li>Van Dyck, R. S., Zafonte, S. L., Van Liew, S., Pinegar, D. B., Schwinberg, D. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ultraprecise+Atomic+Mass+Measurement+of+the+&#945;+particle+and+4He.">Ultraprecise Atomic Mass Measurement of the &#945; particle and 4He.</a> Phys. Rev. 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B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Decapitation+of+tungsten+field+emitter+tips+during+sputter+sharpening.">Decapitation of tungsten field emitter tips during sputter sharpening.</a> Surf. Sci. 339, L925-L930 (1995).</li></ol>

The authors have nothing to disclose.

We have described straightforward procedures to electrochemically etch sharp field emission points (FEPs) in a NaOH solution, and to test the FEPs by operating them in field emission mode. The etching procedure described is a variation of existing techniques-the lamella drop-off technique7,8 and the floating layer technique9,10. However, we found it to be more convenient and reliable to implement than the aforementioned methods.
Before starting the etching procedure, to m...

Sharp tips or points have long been used in microscopy applications, such as the field ion microscope (FIM)1 and the scanning tunneling microscope (STM)2, and a range of techniques for producing sharp tips of various materials have been developed3. These sharp tips can also be operated as field emission points (FEPs) by applying a high voltage to them, and serve as a convenient electron beam source. One application of such as source is ion production via electron impact ionization (EII). The FEP is particularly advantageous in applications where temperature fluctuations produced by thermal emitters are undesirable. For example, ion production via EII of background gas or vapor in high precision Penning traps4,5.
A simple method for fabricating FEPs is to electrochemically etch tungsten rods in a sodium hydroxide (NaOH) solution. This technique is relatively straightforward to implement with modest equipment and has been shown to be quite reproducible and reliable. A number of methods are described in the literature and improvements to these techniques continue to appear6. Here we describe a method for the electrochemical etching of tungsten tips in a NaOH solution. Our method is a variation of the lamella drop-off technique7,8 and the floating layer technique9,10. Like these two methods it enables the production of two tips from a single etching procedure. A picture of the experimental apparatus for etching the tips is shown in Figure 1.
<img alt="Figure 1" src="/files/ftp_upload/54030/54030fig1.jpg" /> 
Figure 1. Etching apparatus. Photograph of the experimental apparatus used for electrochemical etching of tungsten rods with NaOH solution. <a href="https://www.jove.com/files/ftp_upload/54030/54030fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Electrochemical etching of tungsten in the aqueous NaOH base occurs via a two-stage process. First, intermediate tungsten oxides are formed, and second, these oxides are non-electrochemically dissolved to form the soluble tungstate anion. This process is described, in simplified form, by the two reactions
(1) W + 6OH- &#8594; WO3(S) + 3H2O + 6e-, and
(2)&#160;WO3(S) + 2OH- &#8594; WO42- + H2O.
The etching current and the NaOH solution molarity used affect the time and voltage required to etch through the tungsten rod. Studies of these effects are presented and discussed. More importantly, the etching parameters have an effect on the geometry of the tips and, as such, on their operation in field emission mode. The geometry of the tips we produced were characterized by imaging them with a scanning electron microscope (SEM). These images can be used to estimate, for example, the tip radius. In addition, the tips were operated in field emission mode by applying a negative voltage of typically a few hundred volts to a few kilovolts to them and monitoring the resulting electron emission current. The relationship between field emission current, I, and applied bias voltage, V, can be described by the Fowler-Nordheim equation11
(3) I = AV2 e-Creff/V,
where reff is the effective radius of the tip, A is a constant, and C is the second Fowler-Nordheim constant <img alt="Equation 9" src="/files/ftp_upload/54030/54030eq9.jpg" />, in which b = 6.83 eV-3/2V/nm, <img alt="Equation 11" src="/files/ftp_upload/54030/54030eq11.jpg" /> is the work function of tungsten (<img alt="Equation 11" src="/files/ftp_upload/54030/54030eq11.jpg" /> &#8776; 4.5 eV), k is a factor that depends on geometry (k &#8776; 5), and <img alt="Equation 12" src="/files/ftp_upload/54030/54030eq15.jpg" /> is the Nordheim image correction term (<img alt="Equation 12" src="/files/ftp_upload/54030/54030eq15.jpg" /> &#8776; 1)12. Hence, the effective radius of the tip can be determined by measuring the electron current as a function of bias voltage. Specifically, it can be obtained from the slope of a so-called Fowler-Nordheim (FN) plot of ln(I/V2) vs 1/V.

<table><tbody><tr><td>Tungsten Rod 0.020&quot; x 12&quot;</td><td>ESPI Metals</td><td>&lt;a href=&quot;http://www.espimetals.com/index.php/online-catalog/467-Tungsten&quot;&gt;http://www.espimetals.com/index.php/online-catalog/467-Tungsten&amp;nbsp;&lt;/a&gt;</td><td>3N8 Purity</td></tr><tr><td>50% by weight NaOH solution</td><td>Sigma-Aldrich</td><td>415413-500ML</td><td>500 ml</td></tr><tr><td>Separatory funnel</td><td>Cole-Parmer</td><td>Item#&amp;nbsp;WU-34506-03</td><td>250 ml</td></tr><tr><td>DC Power supply</td><td>BK Precision</td><td>1672</td><td>Triple Output 0 - 32 V, 0 - 3 A DC Power Supply</td></tr><tr><td>Acetone</td><td>Cole-Parmer</td><td>Item#&amp;nbsp;WU-88000-68</td><td>500 ml</td></tr><tr><td>Data Acquisition Card</td><td>National Instruments</td><td>NI PXI-6221</td><td>16 AI, 24 DIO, 2 AO</td></tr><tr><td>Relay</td><td>Magnecraft</td><td>276 XAXH-5D</td><td>7 A, 30 V DC Reed Relay</td></tr><tr><td>6-way 6&quot; conflat flange cross</td><td>Kurt J Lesker</td><td>C6-0600</td><td></td></tr><tr><td>6&quot; to 2-3/4&quot; conflat zero length reducer flange&amp;nbsp; (x3)</td><td>Kurt J Lesker</td><td>RF600X275</td><td></td></tr><tr><td>2-3/4&quot; conflat flange SHV feedthrough</td><td>Kurt J Lesker</td><td>IFTSG041033</td><td></td></tr><tr><td>2-3/4&quot; conflat flange BNC feedthrough</td><td>Kurt J Lesker</td><td>IFTBG042033</td><td></td></tr><tr><td>2-3/4&quot; conflat flange linear feedthrough</td><td>MDC</td><td>660006, REF# BLM-275-2</td><td></td></tr><tr><td>6&quot; conflat flange blankoff</td><td>Kurt J Lesker</td><td>F0600X000N</td><td></td></tr><tr><td>6&quot; conflat flange window</td><td>Kurt J Lesker</td><td>VPZL-600</td><td></td></tr><tr><td>HV Power supply</td><td>Keithley Instruments</td><td>Keithley Model #2290-5</td><td>0 - 5 kV DC HV Power Supply</td></tr><tr><td>Picoammeter</td><td>Keithley Instruments</td><td>Keithley Model #6485</td><td></td></tr><tr><td>Faraday Cup</td><td>Beam Imaging Solutions</td><td>Model FC-1 Faraday Cup</td><td></td></tr></tbody></table>

electrochemical etching and characterization of sharp field emission points for electron impact ionization

A new variation of the drop-off method for fabricating field emission points by electrochemically etching tungsten rods in a NaOH solution is described. The results of studies in which the etching current and the molarity of the NaOH solution used in the etching process were varied are presented. The investigation of the geometry of the tips, by imaging them with a scanning electron microscope, and by operating them in field emission mode is also described. The field emission tips produced are intended to be used as an electron beam source for ion production via electron impact ionization of background gas or vapor in Penning trap mass spectrometry applications.

Study of etching parameters
During the etching process the power supply is operated in constant current mode. The voltage required to maintain this constant current increases slightly as the tungsten rod is etched away (due to the increase in resistance of the rod). The current drops almost to zero when the tip etches all the way through. A small current continues to flow due to the fact that the upper tip is st...

Watch this Scientific Journal Video about Electrochemical Etching and Characterization of Sharp Field Emission Points for Electron Impact Ionization at JoVE.com

Electrochemical Etching and Characterization of Sharp Field Emission Points for Electron Impact Ionization

A method for electrochemically etching field emission tips is presented. Etching parameters are characterized and the operation of the tips in field emission mode is investigated.

A new variation of the drop-off method for fabricating field emission points by electrochemically etching tungsten rods in a NaOH solution is described. ...

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9.5K Views.  Central Michigan University. A method for electrochemically etching field emission tips is presented. Etching parameters are characterized and the operation of the tips in field emission mode is investigated.

Video: Electrochemical Etching and Characterization of Sharp Field Emission Points for Electron Impact Ionization

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 ...

Atomically Traceable Nanostructure Fabrication

Reducing the scale of etched nanostructures below the 10 nm range eventually will require an atomic scale understanding of the entire fabrication process being used in order to maintain exquisite control over both feature size and feature density. Here, we demonstrate a method for tracking atomically resolved and controlled structures from initial template definition through final nanostructure metrology, opening up a pathway for top-down atomic control over nanofabrication. Hydrogen depassivation lithography is the first step of the nanoscale fabrication process followed by selective atomic layer deposition of up to 2.8 nm of titania to make a nanoscale etch mask. Contrast with the background is shown, indicating different mechanisms for growth on the desired patterns and on the H passivated background. The patterns are then transferred into the bulk using reactive ion etching to form 20 nm tall nanostructures with linewidths down to ~6 nm. To illustrate the limitations of this process, arrays of holes and lines are fabricated. The various nanofabrication process steps are performed at disparate locations, so process integration is discussed. Related issues are discussed including using fiducial marks for finding nanostructures on a macroscopic sample and protecting the chemically reactive patterned Si(100)-H surface against degradation due to atmospheric exposure.

We report a protocol for combining the atomic metrology of the Scanning Tunneling Microscope for surface patterning with selective Atomic Layer Deposition and Reactive Ion Etching. Using a robust process involving numerous atmospheric exposures and transport, 3D nanostructures with atomic metrology are fabricated.

Reducing the scale of etched nanostructures below the 10 nm range eventually will require an atomic scale understanding of the entire fabrication process ...

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 ...

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 ...

Atom Probe Tomography Analysis of Exsolved Mineral Phases

Element diffusion rates and temperature/pressure control a range of fundamental volcanic and metamorphic processes. Such processes are often recorded in lamellae exsolved from host mineral phases. Thus, the analysis of the orientation, size, morphology, composition and spacing of exsolution lamellae is an area of active research in the geosciences. The conventional study of these lamellae has been conducted by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and more recently with focused ion beam (FIB)-based nanotomography, yet with limited chemical information. Here, we explore the use of atom probe tomography (APT) for the nanoscale analysis of ilmenite exsolution lamellae in igneous titanomagnetite from ash deposits erupted from the active Soufri&#232;re Hills Volcano (Montserrat, British West Indies). APT allows the precise calculation of interlamellar spacings (14&#8211;29 &#177; 2 nm) and reveals smooth diffusion profiles with no sharp phase boundaries during the exchange of Fe and Ti/O between the exsolved lamellae and the host crystal. Our results suggest that this novel approach permits nanoscale measurements of lamellae composition and interlamellar spacing that may provide a means to estimate the lava dome temperatures necessary to model extrusion rates and lava dome failure, both of which play a key role in volcanic hazard mitigation efforts.

Analysis of the morphology, composition, and spacing of exsolution lamellae can provide essential information to understand geological processes related to volcanism and metamorphism. We present a novel application of APT for the characterization of such lamellae and compare this approach to the conventional use of electron microscopy and FIB-based nanotomography.

Element diffusion rates and temperature/pressure control a range of fundamental volcanic and metamorphic processes. Such processes are often recorded in ...

Environment

Electrochemical Roughening of Thin-Film Platinum Macro and Microelectrodes

This protocol demonstrates a method for electrochemical roughening of thin-film platinum electrodes without preferential dissolution at grain boundaries of the metal. Using this method, a crack free, thin-film macroelectrode surface with up to 40 times increase in active surface area was obtained. The roughening is easy to do in a standard electrochemical characterization laboratory and incudes the application of voltage pulses followed by extended application of a reductive voltage in a perchloric acid solution. The protocol includes the chemical and electrochemical preparation of both a macroscale (1.2 mm diameter) and microscale (20 &#181;m diameter) platinum disc electrode surface, roughening the electrode surface and characterizing the effects of surface roughening on electrode active surface area. This electrochemical characterization includes cyclic voltammetry and impedance spectroscopy and is demonstrated for both the macroelectrodes and the microelectrodes. Roughening increases electrode active surface area, decreases electrode impedance, increases platinum charge injection limits to those of titanium nitride electrodes of same geometry and improves substrates for adhesion of electrochemically deposited films.

This protocol demonstrates a method for electrochemical roughening of thin-film platinum electrodes without preferential dissolution at grain boundaries. The electrochemical techniques of cyclic voltammetry and impedance spectroscopy are demonstrated to characterize these electrode surfaces.

This protocol demonstrates a method for electrochemical roughening of thin-film platinum electrodes without preferential dissolution at grain boundaries ...

Chemistry

Sample Preparation and Experimental Design for In Situ Multi-Beam Transmission Electron Microscopy Irradiation Experiments

There is a need to understand materials exposed to overlapping extreme environments such as high temperature, radiation, or mechanical stress. When these stressors are combined there may be synergistic effects that enable unique microstructural evolution mechanisms to activate. Understanding of these mechanisms is necessary for the input and refinement of predictive models and critical for engineering of next generation materials. The basic physics and underlying mechanisms require advanced tools to be investigated. The in situ ion irradiation transmission electron microscope (I&#179;TEM) is designed to explore these principles.
To quantitatively probe the complex dynamic interactions in materials, careful preparation of samples and consideration of experimental design is required. Particular handling or preparation of samples can easily introduce damage or features that obfuscate the measurements. There is no one correct way to prepare a sample; however, many mistakes can be made. The most common errors and things to consider are highlighted within. The I&#179;TEM has many adjustable variables and a large potential experimental space, therefore it is best to design experiments with a specific scientific question or questions in mind.
Experiments have been performed on large number of sample geometries, material classes, and with many irradiation conditions. The following are a subset of examples that demonstrate unique in situ capabilities utilizing the I3TEM. Au nanoparticles prepared by drop casting have been used to investigate the effects of single ion strikes. Au thin films have been used in studies on the effects of multibeam irradiation on microstructure evolution. Zr films have been exposed to irradiation and mechanical tension to examine creep. Ag nanopillars were subjected to simultaneous high temperature, mechanical compression, and ion irradiation to study irradiation induced creep as well. These results impact fields including: structural materials, nuclear energy, energy storage, catalysis, and microelectronics in space environments.

Sample preparation techniques are outlined with specific considerations for in situ ion irradiation TEM experiments. Ion species, energy, and fluence are discussed with methods for how to select and compute them. Finally, procedures for conducting an experiment are described and accompanied by the representative results.

There is a need to understand materials exposed to overlapping extreme environments such as high temperature, radiation, or mechanical stress. When these ...

3D Depth Profile Reconstruction of Segregated Impurities Using Secondary Ion Mass Spectrometry

The presented protocol combines excellent detection limits (1 ppm to 1 ppb) using secondary ion mass spectrometry (SIMS) with reasonable spatial resolution (~1 &#181;m). Furthermore, it describes how to obtain realistic three-dimensional (3D) distributions of segregated impurities/dopants in solid state materials. Direct 3D depth profile reconstruction is often difficult to achieve due to SIMS-related measurement artifacts. Presented here is a method to identify and solve this challenge. Three major issues are discussed, including the i) nonuniformity of the detector being compensated by flat-field correction; ii) vacuum background contribution (parasitic oxygen counts from residual gases present in the analysis chamber) being estimated and subtracted; and iii)&#160;performance of all steps within a stable timespan of the primary ion source. Wet chemical etching is used to reveal the position and types of dislocation in a material, then the SIMS result is superimposed on images obtained via scanning electron microscopy (SEM). Thus, the position of agglomerated impurities can be related to the position of certain defects. The method is fast and does not require sophisticated sample preparation stage; however, it requires a high-quality, stable ion source, and the entire measurement must be performed quickly to avoid deterioration of the primary beam parameters.

The presented method describes how to identify and solve measurement artifacts related to secondary ion mass spectrometry as well as obtain realistic 3D distributions of impurities/dopants in solid state materials.

The presented protocol combines excellent detection limits (1 ppm to 1 ppb) using secondary ion mass spectrometry (SIMS) with reasonable spatial ...

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.

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 ...

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.

Electrochemical Etching and Characterization of Sharp Field Emission Points for Electron Impact Ionization

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