T. van Dillen

Alternative Explanation of Stiffening in Cross-Linked Semiflexible Networks

Strain stiffening of filamentous protein networks is explored by means of a finite strain analysis of a two-dimensional network model of cross-linked semiflexible filaments. The results show that stiffening is caused by nonaffine network rearrangements that govern a transition from a bending-dominated response at small strains to a stretching-dominated response at large strains. Filament undulations, which are key in the existing explanation of stiffening, merely postpone the transition.

Colloidal Ellipsoids with Continuously Variable Shape

tBuMA block was 84 800 in PMMA-b-PtBuMA with polydispersity of 1.18. All the homopolymers used in this study were obtained from Aldrich Chemical Company, Inc., and (except for HEMA) were precipitated twice from methylene chloride into methanol for purification. For the purification of HEMA, precipitation from methanol with hexane/methylene chloride (1:1) was carried out twice. Film Preparation: 0.2 g of polymer was dissolved in 10 mL toluene and poured into an aluminum petri dish with a diameter of 5 cm. The solution was dried in ambient conditions overnight, then dried on a hotplate at 50 C for 1 day, and finally dried completely in a vacuum oven at 100 C for 2 days. The thickness of the films was about 100 lm. TEM: The films were embedded in visible-light curable resin, D-800 (JEOL DATUM Co. Ltd.), and were cured by irradiating with the light from a xenon lamp source through a UV cut filter at 100 mW/cm 2 for 5 min. The films were microtomed to give a thickness of 50 nm at room temperature. The Carl Zeiss EM 902 was operated at an accelerating voltage of 80 kV, and the images were recorded using the Imaging Plates system, FDL5000 (Fuji Photo Films Co. Ltd.). The number-average diameter of the clusters was calculated with image processing software: Ultimage Pro 2.6 (Graftek France). More than 200 particles were counted and individual diameters were assigned to those circles with equivalent area. UV-vis Absorption Spectroscopy: Measurements were carried out on a Shimadzu UV-2500PC. The 50 lm films prepared by solvent casting as mentioned above were used.

Ion beam-induced anisotropic plastic deformation at 300 keV

Contrary to earlier predictions, ion irradiation at energies as low as 300 keV causes dramatic anisotropic plastic deformation of silica glass. Spherical colloidal silica particles with diameters of 125, 305, and 1030 nm were irradiated with Xe ions at energies in the range 0.3–4.0 MeV at temperatures between 85 and 380 K. Irradiation-induced anisotropic plastic deformation changes the colloid shape from spherical into oblate ellipsoidal at a rate that strongly increases with ion energy. At a fixed fluence, the transverse diameter increases with electronic energy loss. Even at an energy as low as 300 keV large particle anisotropy was found (size aspect ratio of 1.43 at 1×1015 cm−2). The transverse plastic strain gradually decreases with increasing irradiation temperature: it decreases by a factor 4.5 between 85 and 380 K. The data are in agreement with a viscoelastic thermal spike model for anisotropic deformation.

Origin of MeV ion irradiation-induced stress changes in SiO2

The 4 MeV Xe ion irradiation of a thin thermally grown SiO2 film on a Si substrate leads to four different effects in which each manifests itself by a characteristic change in the mechanical stress state of the film: densification, ascribed to a beam-induced structural change in the silica network; stress relaxation by radiation-enhanced plastic flow; anisotropic expansion and stress generation; and transient stress relaxation ascribed to the annealing of point defects. Using sensitive wafer-curvature measurements, in situ measurements of the in-plane mechanical stress were made during and after ion irradiation at various temperatures in the range from 95 to 575 K, in order to study the magnitude of these effects, the mechanism behind them, as well as their interplay. It is found that the structural transformation leads to a state with an equilibrium density that is 1.7%–3.2% higher than the initial state, depending on the irradiation temperature. Due to the constraint imposed by the substrate, this trans...

Energy-dependent anisotropic deformation of colloidal silica particles under MeV Au irradiation

Spherical silica colloids with a diameter of 1.0 μm, made by wet chemical synthesis, were irradiated with 2–16 MeV Au ions at fluences in the range (2–11)×1014 cm−2. The irradiation induces an anisotropic plastic deformation turning the spherical colloids into ellipsoidal oblates. After 16 MeV Au irradiation to a fluence of 11×1014 cm−2, a size aspect ratio of 5.0 was achieved. The size polydispersity (∼3%) remains unaffected by the irradiation. The transverse diameter increases exponentially with ion fluence. By performing measurements as a function of ion energy at a fixed fluence, it is concluded that the transverse diameter increases linearly with the average electronic energy loss above a threshold value of ∼0.6 keV/nm. Nonellipsoidal colloids are observed in the case where the projected ion range is smaller than the colloid diameter. The data provide strong support for the thermal spike model of anisotropic deformation.

Anisotropic deformation of colloidal particles under MeV ion irradiation

Abstract Spherical silica colloids with a diameter of 1.0 μm , made by wet chemical synthesis, were irradiated with 2–16 MeV Au ions at fluences ranging from 2×10 14 to 11 ×10 14 cm −2 . The irradiation induces an anisotropic plastic deformation turning the spherical colloids into ellipsoidal oblates. After 16 MeV Au irradiation to a fluence of 11×10 14 cm −2 a size-aspect ratio of 4.7 is achieved. The size polydispersity (∼3%) remains unaffected by the irradiation. The transverse diameter increases with the electronic energy loss above a threshold value of ∼0.6 keV/nm. Non-ellipsoidal colloids are observed in the case that the projected ion range is smaller than the colloid diameter. The deformation effect is also observed for micro-crystalline ZnS and amorphous TiO2 colloids, as well as ZnS/SiO2 core/shell particles. No deformation is observed for crystalline Al2O3 and Ag particles. The data provide strong support for the thermal spike model of anisotropic deformation.

Ion beam-induced anisotropic plastic deformation of silicon microstructures

Amorphous silicon micropillars show anisotropic plastic shape changes upon irradiation with 30 MeV Cu ions. The transverse plastic strain rate is (2.5±0.2)×10−17 cm2/ion at 77 K, which is about one order of magnitude less than that of silica glass. In contrast, crystalline silicon pillars, irradiated under the same conditions, do not exhibit anisotropic deformation. A viscoelastic and free volume model is used to qualitatively describe the data. By irradiating partially amorphous structures a variety of silicon microshapes can be fabricated.

Colloidal assemblies modified by ion irradiation

Abstract Spherical SiO2 and ZnS colloidal particles show a dramatic anisotropic plastic deformation under 4 MeV Xe ion irradiation, that changes their shape into oblate ellipsoidal, with an aspect ratio that can be precisely controlled by the ion fluence. The 290 nm and 1.1 μm diameter colloids were deposited on a Si substrate and irradiated at 90 K, using fluences in the range 3×10 13 –8×10 14 cm −2 . The transverse particle diameter shows a linear increase with ion fluence, while the longitudinal diameter shrinks; the particle volume remains constant. Size aspect ratios up to 3.1 are achieved. Applications of the ion beam deformation technique are shown in studies of liquid crystalline colloidal ordering, self-assembled two-dimensional colloidal lithographic masks for thin-film deposition, and in tuning the optical properties of three-dimensional colloidal crystals.

Stress map for ion irradiation: Depth-resolved dynamic competition between radiation-induced viscoelastic phenomena in SiO2

The dynamic competition between structural transformation, Newtonian viscous flow, and anisotropic strain generation during ion irradiation of SiO2, leads to strongly depth-dependent evolution of the mechanical stress, ranging between compressive and tensile. From independent in situ stress measurements during irradiation, generic expressions are derived of the nuclear stopping dependence of both the structural transformation rate and the radiation-induced viscosity. Using these data we introduce and demonstrate the concept of a “stress map” that predicts the depth-resolved saturation stress in SiO2 for any irradiation up to several MeV.

Activation energy spectra for annealing of ion irradiation induced defects in silica glasses

Abstract In situ stress measurements were performed on alkali-borosilicate glass samples during and after 2 MeV Xe ion irradiation at several temperatures between 95 and 580 K. After switching off the ion beam, stress changes are observed that are related to the annealing of ion beam generated defects. The activation energy spectra for defect annealing are obtained from the data at each irradiation temperature. Defects are observed in the energy range from 0.26 to 1.85 eV. At each temperature the spectrum increases monotonously with activation energy. At each energy the defect density per unit energy is smaller at higher temperatures. This behavior can be explained using a binary collision model. The data are contrasted against the results obtained for 4 MeV Xe ion irradiation of thermally grown SiO2 films, which can be explained using a thermal spike model. Measurements of the radiation induced viscosity support these ideas.