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Summary

Abstract

Introduction

Protocol

Representative Results

Discussion

Acknowledgements

Materials

References

Engineering

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

Published: July 12th, 2016

DOI:

10.3791/54030

1Department of Physics, 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.

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.

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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1. Electrochemical Etching

  1. Experimental set-up
    1. 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 et.......

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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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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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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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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
NaOH salt Cole-Parmer Item # WU-88404-71 100 g
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

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