Sample method for formation of nanometer scale holes in membranes Page: 2 of 10
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scale holes with diameters below 10 nm has further been reported by several groups who
used swift heavy ion track etching , or ion beam sculpting with keV argon ions [1, 8].
In this letter, we describe a simple method for nano-hole formation based on monitored
closing of 100 nm scale holes by electron beam deposition of thin films. For our
experiments at the National Center for Electron Microscopy at LBNL we used an FEI
dual beam FIB, a system combining a focused ion beam with an SEM column.
Samples in our study were membranes of low stress silicon nitride with a
thickness of 200 nm on silicon frames. Membranes were coated with 5 nm of a gold
palladium alloy to prevent charging during exposure to charged particle beams. A 30
keV Ga+ beam with an intensity of 1 pA in spot with a diameter of 10 nm was used to
drill holes into the membranes. Initial hole diameters ranged from about 50 to 200 nm.
The base pressure in the FIB vacuum chamber was 3x10-6 torr. For hole closing with
hydro-carbon films (also known as contamination resist ), an electron beam (5 keV, 1
nA, nominal spot size 2 nm) was rastered over the area with the initial hole pattern at a
magnification of 150,000 to 350,000 at a rate of 5 scans per second. After an exposure
interval of 30 s to one minute, the sample area was imaged with a slower, higher contrast
scan, and the process was repeated. In Figure 1, we show a sequence of images of three
holes taken immediately following FIB drilling (a) and after several minutes of electron
beam exposure (b and c). Under these conditions, the rate of hole closing was linear with
a slope of 0.3 nm/s (Figure 2). The chemical composition of the deposited material can
be elucidated through a comparision of SEM and ransmission electron microscope
images of closed holes. In Figure 3, we show a pattern of closed holes in SEM (a) and
TEM (b) images. In SEM, contrast was obtained by detection of backscattered electrons,
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Schenkel, T.; Stach, E.A.; Radmilovic, V.; Park, S.-J. & Persaud, A. Sample method for formation of nanometer scale holes in membranes, article, February 24, 2003; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc782311/m1/2/: accessed October 22, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.