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Title: Focused helium ion beam nanofabrication by near-surface swelling
The focused helium ion beam microscope is a versatile imaging and nanofabrication instrument enabling direct-write lithography with sub-10 nm resolution. Subsurface damage and swelling of substrates due to helium ion implantation is generally unwanted. However, these effects can also be leveraged for specific nanofabrication tasks. To explore this, we investigate focused helium ion beam induced swelling of bulk crystalline silicon and free-standing amorphous silicon nitride membranes using various irradiation strategies. We show that the creation of near-surface voids due to helium ion implantation can be used to induce surface nanostructure and create subsurface nanochannels. By tailoring the ion dose and beam energy, the size and depth of the swollen features can be controlled. Swelling heights of several hundred nanometers are demonstrated, and for the embedded nanochannels, void internal diameters down to 30 nm are shown. Potential applications include the engineering of texturized substrates and the prototyping of on-chip nanofluidic transport devices. more »« less
Hosemann, P.; Sebastiani, M.; Mughal, M. Z.; Huang, X.; Scott, A.; Balooch, M.
(, Journal of Materials Research)
null
(Ed.)
Helium implantation in surfaces is of interest for plasma-facing materials and other nuclear applications. Vanadium as both a representative bcc material and a material relevant for fusion applications is implanted using a Helium ion beam microscope, and the resulting swelling and nanomechanical properties are quantifed. These values are put in correlation to data obtained from micro-residual stress measurements using a focused ion beam-based ring-core technique. We found that the swelling measured is similar to literature values. Further, we are able to measure the surface stress caused by the implantation and fnd that it approaches the yield strength of the material at blistering doses. The simple calculations performed in the present work, along with several geometrical considerations deduced from experimental results confrm the driving force for blister formation comes from bulging resulting mainly from gas pressure buildup, rather than solely stress-induced buckling
Huang, Xi; Xie, Yujun; Balooch, Mehdi; Lubner, Sean; Hosemann, Peter
(, Journal of Applied Physics)
Microstructural changes induced by helium implantation in materials lead to volumetric swelling and mechanical property changes. How these properties are linked and establishing direct relationships can be difficult due to the underlying material’s microstructure evolution. Some materials also experience a phase change due to irradiation damage making them even more complex to analyze. Here, single crystalline Si (100) was used to establish a relationship among these parameters. The swelling height as a function of implantation fluence can equally fit a linear relationship. Solely irradiation induced defects are observed at low fluence below 5.0 × 10 16 ions/cm 2 . An abrupt amorphous and crystalline mixed layer of ∼200 nm thick within a highly damaged polycrystalline matrix is observed when implantation fluence exceeds 5.0 × 10 16 ions/cm 2 , leading to the appearance of irradiation induced swelling and hardening behavior. As the fluence increases beyond 1.0 × 10 17 ions/cm 2 , the amorphous layer expands in size and the bubble size distribution takes the form of a Gaussian distribution with a maximum size of up to 6.4 nm, which causes a further increase in the height of swelling. Furthermore, irradiation induced softening appeared due to the enlarged bubble size and amorphization.
Zhang, Cheng; Dyck, Ondrej; Garfinkel, David A.; Stanford, Michael G.; Belianinov, Alex A.; Fowlkes, Jason D.; Jesse, Stephen; Rack, Philip D.
(, Nanomaterials)
A helium gas field ion source has been demonstrated to be capable of realizing higher milling resolution relative to liquid gallium ion sources. One drawback, however, is that the helium ion mass is prohibitively low for reasonable sputtering rates of bulk materials, requiring a dosage that may lead to significant subsurface damage. Manipulation of suspended graphene is, therefore, a logical application for He+ milling. We demonstrate that competitive ion beam-induced deposition from residual carbonaceous contamination can be thermally mitigated via a pulsed laser-assisted He+ milling. By optimizing pulsed laser power density, frequency, and pulse width, we reduce the carbonaceous byproducts and mill graphene gaps down to sub 10 nm in highly complex kiragami patterns.
Planar magnesium diboride Josephson junctions are fabricated using focused helium ion beam irradiation. A single track of ion irradiation with a 30 kV He+ beam with nominal beam diameter < 0.5 nm is used to create a normal-metal barrier on a MgB2 film deposited by hybrid physical-chemical vapor deposition. Josephson coupling is observed below the critical temperature of the electrodes for a He+ doses between 8x1015/cm2 to 4x1016/cm2. Analysis of the temperature dependence of the normal resistance and critical voltage of the junctions shows highly uniform barriers with nearly ideal resistively-shunted junction behavior for higher-dose junctions, while nonequilibrium effects dominate the properties of lower-dose junctions over most of the temperature range. These results demonstrate that focused helium ion beam irradiation can produce high-quality proximity-coupled MgB2 Josephson junctions with tailorable properties, promising for use in superconducting devices and circuits.
Kumar, Deepak
(, University of Kentucky Libraries)
Radiolysis is a complex phenomenon in which molecules subjected to ionizing radiation form new chemical species. Electron-beam irradiation has proven to be a versatile approach for significantly altering materials’ properties and forms the basis for electron-beam lithography using both organic and inorganic resists. Electron-beam exposure is normally carried out under high vacuum conditions to reduce contamination and allow for unhindered interaction between the electrons and the resist material. Exposure under an ambient gas at sub-atmospheric pressures has been found to provide a distinct mechanism which can be exploited to circumvent some of the challenges associated with material processing and significantly alter or enhance material’s properties. This dissertation discusses the modifications in standard electron beam resist characteristics during gas assisted electron beam pattering. We studied the effect of water vapor pressure on positive and negative tone electron-beam patterning of poly methyl methacrylate (PMMA). For both positive and negative-tone patterning, it was found that increasing the water vapor pressure considerably improved the contrast of PMMA. As expected from electron scattering in a gas, the clearing dosage for positive tone patterning gradually increased with vapor pressure. Also, electron scattering in water vapor yielded a substantially larger clear region around the negative-tone patterns. This effect could be useful for increasing the range of the developed region around cross-linked PMMA far beyond the backscattered electron range. As a result, VP-EBL for PMMA offers a new means of tuning clearing/onset dose and contrast while enabling more control over the size of the cleared region around negative-tone patterns. We provide a novel way to simultaneously tune the emission wavelength and enhance the fluorescence intensity of fluorophores formed by irradiating polystyrene with a focused electron beam under various gaseous environments. We studied the effect of electron dose and gas pressure on the emission spectra and photon yield of irradiated polystyrene film on a variety of substrates. Up to 10x enhancement in fluorescence yield was achieved using water vapor and the peak emission wavelength tuned over a wide wavelength range. Thus, localized electron-beam synthesis of fluorophores in polystyrene can be controlled by both dose and by ambient water-vapor pressure. This technique could enable innovative approaches to photonics where fluorophores with tunable emission properties can be locally introduced by electron-beam patterning. We also studied the effect of ambient gases on contrast and resolution of PMMA on conducting and insulating substrates. E-beam exposures were conducted under vacuum conditions and 1 mbar of water vapor, helium, nitrogen and argon to study their effect on contrast and resolution of PMMA on silicon, fused silica and soda lime glass substrates. On silicon, exposure under water vapor yielded contrast values significantly higher than vacuum exposure, consistent with our previous work. However, exposure under helium yielded slightly improved contrast compared to vacuum exposure. On insulating substrates exposure under helium environment yielded contrast values significantly higher compared to vacuum exposure. The clearing dose was found to increase with the gases’ molecular weight and proton number, consistent with the increase in scattering cross-section. The improved contrast and sensitivity (dose to clear) of PMMA under helium motivated us to study the resolution under various gases. Resolution testing indicated that despite the lower clearing dose, helium still exhibited the best resolution with 25-nm half-pitch dense lines and spaces clearly resolved on soda lime glass. Thus, VP-EBL of PMMA under helium yields higher sensitivity and contrast on insulating substrates without sacrificing resolution.
Mo, Sherry, Byrne, Dana O, and Allen, Frances I. Focused helium ion beam nanofabrication by near-surface swelling. Retrieved from https://par.nsf.gov/biblio/10587936. Journal of Vacuum Science & Technology B 43.2 Web. doi:10.1116/6.0004100.
Mo, Sherry, Byrne, Dana O, & Allen, Frances I. Focused helium ion beam nanofabrication by near-surface swelling. Journal of Vacuum Science & Technology B, 43 (2). Retrieved from https://par.nsf.gov/biblio/10587936. https://doi.org/10.1116/6.0004100
Mo, Sherry, Byrne, Dana O, and Allen, Frances I.
"Focused helium ion beam nanofabrication by near-surface swelling". Journal of Vacuum Science & Technology B 43 (2). Country unknown/Code not available: AVS. https://doi.org/10.1116/6.0004100.https://par.nsf.gov/biblio/10587936.
@article{osti_10587936,
place = {Country unknown/Code not available},
title = {Focused helium ion beam nanofabrication by near-surface swelling},
url = {https://par.nsf.gov/biblio/10587936},
DOI = {10.1116/6.0004100},
abstractNote = {The focused helium ion beam microscope is a versatile imaging and nanofabrication instrument enabling direct-write lithography with sub-10 nm resolution. Subsurface damage and swelling of substrates due to helium ion implantation is generally unwanted. However, these effects can also be leveraged for specific nanofabrication tasks. To explore this, we investigate focused helium ion beam induced swelling of bulk crystalline silicon and free-standing amorphous silicon nitride membranes using various irradiation strategies. We show that the creation of near-surface voids due to helium ion implantation can be used to induce surface nanostructure and create subsurface nanochannels. By tailoring the ion dose and beam energy, the size and depth of the swollen features can be controlled. Swelling heights of several hundred nanometers are demonstrated, and for the embedded nanochannels, void internal diameters down to 30 nm are shown. Potential applications include the engineering of texturized substrates and the prototyping of on-chip nanofluidic transport devices.},
journal = {Journal of Vacuum Science & Technology B},
volume = {43},
number = {2},
publisher = {AVS},
author = {Mo, Sherry and Byrne, Dana O and Allen, Frances I},
}
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