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.
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Method Article
Electrochemical Etching and Characterization of Sharp Field Emission Points for Electron Impact Ionization
In This Article
Summary
Abstract
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.
Introduction
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 pro....
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Protocol
1. Electrochemical Etching
- Experimental set-up
- 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.- Make a tungsten rod holder from an approximately 100 mm long 6 mm diamet....
- Apparatus
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Results
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.......
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Discussion
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.......
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Disclosures
The authors have nothing to disclose.
Acknowledgements
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.
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Materials
| Name | Company | Catalog Number | Comments |
|---|---|---|---|
| Tungsten Rod 0.020" x 12" | ESPI Metals | http://www.espimetals.com/index.php/online-catalog/467-Tungsten | 3N8 Purity |
| 50% by weight NaOH solution | Sigma-Aldrich | 415413-500ML | 500 ml |
| Separatory funnel | Cole-Parmer | Item# WU-34506-03 | 250 ml |
| DC Power supply | BK Precision | 1672 | Triple Output 0 - 32 V, 0 - 3 A DC Power Supply |
| Acetone | Cole-Parmer | Item# WU-88000-68 | 500 ml |
| Data Acquisition Card | National Instruments | NI PXI-6221 | 16 AI, 24 DIO, 2 AO |
| Relay | Magnecraft | 276 XAXH-5D | 7 A, 30 V DC Reed Relay |
| 6-way 6" conflat flange cross | Kurt J Lesker | C6-0600 | |
| 6" to 2-3/4" conflat zero length reducer flange (x3) | Kurt J Lesker | RF600X275 | |
| 2-3/4" conflat flange SHV feedthrough | Kurt J Lesker | IFTSG041033 | |
| 2-3/4" conflat flange BNC feedthrough | Kurt J Lesker | IFTBG042033 | |
| 2-3/4" conflat flange linear feedthrough | MDC | 660006, REF# BLM-275-2 | |
| 6" conflat flange blankoff | Kurt J Lesker | F0600X000N | |
| 6" conflat flange window | Kurt J Lesker | VPZL-600 | |
| HV Power supply | Keithley Instruments | Keithley Model #2290-5 | 0 - 5 kV DC HV Power Supply |
| Picoammeter | Keithley Instruments | Keithley Model #6485 | |
| Faraday Cup | Beam Imaging Solutions | Model FC-1 Faraday Cup |
References
- Muller, E. W., Bahadur, K. Field Ionization of Gases at a Metal Surface and the Resolution of the Field Ion Microscope. Phys. Rev. 102, 624(1956).
- Binnig, G., Rohrer, H. Scanning Tunneling Microscopy. Helv. Phys. Acta. 55, 726-735 (1982).
- Melmed, A. J.
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