Focused ion beam induced deflections of freestanding thin films

Kim, Young-Rok; Chen, Peng; Aziz, Michael J.; Branton, Daniel; Vlassak, Joost J.

doi:10.1063/1.2363900

Cited by 42 publications

(38 citation statements)

References 24 publications

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“…3(a) and 3(b) are observed to deflect downwards close to the pore. We attribute this effect to biaxial compressive stresses induced in the membrane by the FIB during cavity formation; its effects have been observed in free-standing silicon nitride films by Kim et al 13 In preliminary experiments we have performed with cavities formed by reactive ion etching (RIE) rather than FIB, such deflections were not observed.…”

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confidence: 67%

Nanometer-thin solid-state nanopores by cold ion beam sculpting

Kuan

Golovchenko

2012

Applied Physics Letters

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Recent work on protein nanopores indicates that single molecule characterization (including DNA sequencing) is possible when the length of the nanopore constriction is about a nanometer. Solid-state nanopores offer advantages in stability and tunability, but a scalable method for creating nanometer-thin solid-state pores has yet to be demonstrated. Here we demonstrate that solid-state nanopores with nanometer-thin constrictions can be produced by "cold ion beam sculpting," an original method that is broadly applicable to many materials, is easily scalable, and requires only modest instrumentation. Initially, "ion beam sculpting" was used to fabricate solid-state nanopores capable of detecting single DNA molecules. 1 That original process took advantage of the surprising observation that at room temperature a low energy argon ion beam can shrink large prefabricated pores in thin silicon nitride (SiN) and oxide membranes to single digit nanometer diameters, creating an accumulated volcano-like mound of material that defines the nanopore. 2 However, the material constituency and precise internal geometry (including thickness) of pores produced by this additive process are difficult to control and are not well characterized or understood. Ion beam sculpting has been semi-quantitatively described with an adatom diffusion model in which an ion beam induced electric field near the pore causes accumulation of mobile surface adatoms created by the ion beam. 3 The distance from the pore edge X m within which adatoms are more likely to reach the pore than be annihilated by the ion beam or trapped at local surface defects is characterized by 4where l trap is the average distance between surface defects, r is the cross section for adatom annihilation by an incident ion, D is the surface diffusivity of adatoms, and F is the ion flux. At low temperatures, the surface diffusivity D can be reduced to the point that X m approaches zero and prefabricated SiN pores open instead of close under ion beam exposure. 1,4 In this work we show that in the low temperature limit, surface diffusion is almost completely suppressed and removal of material by sputtering dominates pore formation, allowing the fabrication of very thin nanopores. This cold ion beam sculpting (CIBS) method does not require preexisting pores and eliminates the "volcano phenomenon."A focused ion beam (FIB) machine (FEI Micrion, 50 keV Ga) was used to mill a bowl-shaped ($100 nm diameter) cavity on one side of a $250 nm thick free-standing silicon nitride (SiN) membrane. Then, in an ion sculpting apparatus described elsewhere 5 (Fig.

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confidence: 67%

Nanometer-thin solid-state nanopores by cold ion beam sculpting

Kuan

Golovchenko

2012

Applied Physics Letters

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“…1 B and C), due to buckling of the stiff skin formed on the areas of the PDMS exposed to FIB. FIB exposure creates a tendency for the skin to expand in the direction perpendicular to the direction of FIB irradiation if it was not constrained by the PDMS substrate, similar to the effect observed in exposing metallic surfaces to ion beam irradiation (2)(3)(4). The mismatch strain between the stiff skin and its substrate give rise to skin buckling and the formation of the wrinkle patterns (5)(6)(7)(8)(9).…”

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confidence: 94%

Wrinkled hard skins on polymers created by focused ion beam

Moon

Lee

Sun

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

202

185

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A stiff skin forms on surface areas of a flat polydimethylsiloxane (PDMS) upon exposure to focused ion beam (FIB) leading to ordered surface wrinkles. By controlling the FIB fluence and area of exposure of the PDMS, one can create a variety of patterns in the wavelengths in the micrometer to submicrometer range, from simple one-dimensional wrinkles to peculiar and complex hierarchical nested wrinkles. Examination of the chemical composition of the exposed PDMS reveals that the stiff skin resembles amorphous silica. Moreover, upon formation, the stiff skin tends to expand in the direction perpendicular to the direction of ion beam irradiation. The consequent mismatch strain between the stiff skin and the PDMS substrate buckles the skin, forming the wrinkle patterns. The induced strains in the stiff skin are estimated by measuring the surface length in the buckled state. Estimates of the thickness and stiffness of the stiffened surface layer are estimated by using the theory for buckled films on compliant substrates. The method provides an effective and inexpensive technique to create wrinkled hard skin patterns on surfaces of polymers for various applications.focused ion beam surface modification ͉ polydimethylsiloxane ͉ surface wrinkles W rinkle patterns shown in Fig. 1 are formed by exposing the surface area of a flat polydimethylsiloxane (PDMS) sheet (thickness Ϸ3 mm, Young modulus Ϸ2 MPa) (1) to a focused ion beam (FIB) of Ga ϩ ions as shown schematically in Fig. 1 A. This method can create wrinkle patterns of various widths and complexity by controlling the relative motion of the polymeric substrate and the FIB to scan selected areas as shown in Fig. 1 B-E. The wrinkles appear only on the areas of the PDMS exposed to FIB (see Fig. 1 B and C), due to buckling of the stiff skin formed on the areas of the PDMS exposed to FIB. FIB exposure creates a tendency for the skin to expand in the direction perpendicular to the direction of FIB irradiation if it was not constrained by the PDMS substrate, similar to the effect observed in exposing metallic surfaces to ion beam irradiation (2-4). The mismatch strain between the stiff skin and its substrate give rise to skin buckling and the formation of the wrinkle patterns (5-9). FIB exposure differs from UV/ozone treatment of PDMS in that the latter produces a stiff skin by increasing cross-links with relatively little strain mismatch (10, 11). The morphology of the wrinkle patterns on the surface areas of PDMS is mainly a function of ion fluence as shown in Figs. 1C and 2. Fig. 1D shows that the path of the wrinkle patterns can be selected by controlling the relative motion of the substrate and ion beam. In addition, one can create islands of buckled stiff skins on the PDMS by controlling the ion beam spot diameter and spacing (see Fig. 1E).Various morphologies shown in Fig. 2 A are created by a single mode FIB scanning with the beam current of 1 nA and the fluences indicated. When the PDMS substrate is exposed with a fluence on the order of 1 ϫ 10 13 ions per cm 2 , the...

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“…Biaxial compressive stresses are known to develop in the bombarded solid, [46][47][48][49][50][51][52] and this effect could be important in the surface dynamics. Assuming a sinusoidal modulation of a free surface under biaxial compressive stress, the tangential stress increases at the troughs ͑compres-sion͒ and decreases at the peaks ͑dilation͒ by an amount proportional to the wave number of the modulation and to the applied stress 0 in the solid.…”

Section: B Asaro-tiller Mechanismmentioning

confidence: 99%

On the stabilization of ion sputtered surfaces

2007

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The classical theory of ion beam sputtering predicts the instability of a flat surface to uniform ion irradiation at any incidence angle. We relax the assumption of the classical theory that the average surface erosion rate is determined by a Gaussian response function representing the effect of the collision cascade, and consider the surface dynamics for other physically motivated response functions. We show that although instability of flat surfaces at any beam angle results from all Gaussian and a wide class of non-Gaussian erosive response functions, there exist classes of modifications to the response that can have a dramatic effect. In contrast to the classical theory, these types of response render the flat surface linearly stable, while imperceptibly modifying the predicted sputter yield vs incidence angle. We discuss the possibility that such corrections underlie recent reports of a "window of stability" of ion-bombarded surfaces at a range of beam angles for certain ion and surface types, and describe some characteristic aspects of pattern evolution near the transition from unstable to stable dynamics. We point out that careful analysis of the transition regime may provide valuable tests for the consistency of any theory of pattern formation on ion sputtered surfaces.

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Focused ion beam induced deflections of freestanding thin films

Cited by 42 publications

References 24 publications

Nanometer-thin solid-state nanopores by cold ion beam sculpting

Nanometer-thin solid-state nanopores by cold ion beam sculpting

Wrinkled hard skins on polymers created by focused ion beam

On the stabilization of ion sputtered surfaces

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