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Item type:Publication, Access status: without files , Bending of nanoporous thin films under ion radiation(Elsevier, 2019-07-11); ; ; In general, fundamental understanding of radiation resistance of high surface density nanoporous materials and nanoporous coatings is severely lacking. In this contribution ion-induced bending phenomena are studied in free-standing nanoporous Au cantilevers with thickness in the range of 100 to 200 nm. Experiments were performed in a Tescan Lyra dual beam system with Ga+ ion irradiation normal to the sample surface up to a maximum fluence of ~3 × 1019 m−2. Cantilevers bend towards the incident ion beam. It was found that the sensitivity of nanoporous Au samples to radiation-induced bending is substantially higher in comparison to the solid bulk counterparts. The process is described in terms of ion-induced coarsening of the structure top layers, which generates a volume contraction responsible for the bending moment. Therefore it is concluded that radiation-induced coarsening/sintering leads to negative swelling. Radiation-modified effective Young's modulus of the top layers was shown to influence essentially the fluence dependence of bending curvature. Model predictions agree well with our experimental findings showing that inhomogeneous radiation-induced coarsening of nanoporous structure results in bending and that nanoporous materials are less suitable for coatings in nuclear applications under the test conditions.Publicationtype: Journal Article9 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Size-dependent ion-induced densification of nanoporous gold(Elsevier, 2019-01-28); ; ; Relative density is a major factor governing the mechanical properties of (nano-)porous materials. In nanoporous gold, a correlation between relative density and the ligaments aspect ratio was recently reported as the result of a meta-study that measured hundreds of published images. The effects of ion-irradiation on nanoporous structures however are not yet well explored. We irradiated samples of nanoporous gold of two different initial characteristic lengths with 30 keV Ga + ions. The degree of densification was found to be higher for the samples with finer ligaments and to proceed by thickening of ligaments besides the reduction in length also observed in the coarser samples. The proportionality between relative density and aspect ratio in the ion irradiated samples was found to agree well with the previously reported results from specimens of various processing and coarsening routes. The present study points at ion irradiation as a tool to tune these parameters in nanoporous structures and suggests that the correlation between relative density and aspect ratio may be involved in the volume contraction observed during the formation of nanoporous samples by dealloying.Publicationtype: Journal Article15 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , On the fabrication of micro- and nano-sized objects : the role of interstitial clusters(Springer, 2018-05-01); ; ; Ion-induced bending phenomena were studied in free-standing nano-sized Al cantilevers with thicknesses in the range of 89–200 nm. The objective is to present a predictive and useful model for the fabrication of micro- and nano-sized specimens. Samples were irradiated in a Tescan Lyra dual beam system with 30 kV Ga+ ions normal to the sample surface up to a maximum fluence of ~ 2 × 1021 m−2. Irrespective of thickness, all samples bent initially away from the Ga+ beam; as irradiation proceeded, the bending direction was reversed. The Al cantilever bending behavior is discussed in terms of depth-dependent volume change due to implanted Ga atoms, radiation-induced point defects and interstitial clusters. A kinetic model is designed which is based on a set of rate equations for concentrations of vacancies, interstitial atoms, Ga atoms and clusters of interstitial atoms. The bending crossover is explained by the formation of sessile interstitial clusters in a zone beyond the Ga+ penetration range. Model predictions agree with our experimental findings.Publicationtype: Journal Article26 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , On the mechanism of ion-induced bending of nanostructures(2018-02-06); ; ; This contribution concentrates on ion-induced bending phenomena which may serve as a versatile tool to manufacture nanostructured devices. In particular bending was studied in free standing Au cantilevers. The preparation and irradiation of the cantilevers were performed using a TESCAN LYRA dual beam system. Cantilevers with thicknesses ranging between 90 and 200 nm were irradiated with 30 keV Ga ions normal to the sample surface up to a maximum fluence of ∼3 × 10 20 Ga/m 2 . The bending of the cantilevers towards the incident beam is discussed in terms of local volume change due to accumulation of radiation-induced vacancies and substitutional Ga atoms in the Ga implantation layer, as well as due to accumulation of interstitial type clusters in the region beyond the Ga penetration range. A model is proposed to explain the observations, based on a set of rate equations for concentrations of point defects, i.e. vacancies, self-interstitials and implanted Ga atoms. The influence of preexisting defects is also discussed. The work shows that an in-depth understanding the ion-beam bending can play a predictive role in a quantitative control in for the micro- and nanofabrication of small-sized products.Publicationtype: Journal Article15 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , On the optimum resolution of transmission-electron backscattered diffraction (t-EBSD)(Elsevier, 2016-01); ; ; ; The work presented aims at determining the optimum physical resolution of the transmission-electron backscattered diffraction (t-EBSD) technique. The resolution depends critically on intrinsic factors such as the density, atomic number and thickness of the specimen but also on the extrinsic experimental set-up of the electron beam voltage, specimen tilt and detector position. In the present study, the so-called physical resolution of a typical t-EBSD set-up was determined with the use of Monte Carlo simulations and confronted to experimental findings. In the case of a thin Au film of 20. nm, the best resolution obtained was 9. nm whereas for a 100. nm. Au film the best resolution was 66. nm. The precise dependence of resolution on thickness was found to vary differently depending on the specific elements involved. This means that the resolution of each specimen should be determined individually. Experimentally the median probe size of the t-EBSD for a 140. nm thick AuAg specimen was measured to be 87. nm. The first and third quartiles of the probe size measurements were found to be 60. nm and 118. nm. Simulation of this specimen resulted in a resolution of 94. nm which fits between these quartiles.Publicationtype: Journal Article12 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Formation of Nanoporous Gold Studied by Transmission Electron Backscatter Diffraction(2015-10-30); ; ; ; Transmission electron backscatter diffraction (t-EBSD) was used to investigate the effect of dealloying on the microstructure of 140-nm thin gold foils. Statistical and local comparisons of the microstructure between the nonetched and nanoporous gold foils were made. Analyses of crystallographic texture, misorientation distribution, and grain structure clearly prove that during the dealloying manufacturing process of nanoporous materials the crystallographic texture is enhanced significantly with a clear decrease of internal strain, whereas maintaining the grain structure.Publicationtype: Journal Article17 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Pressure and temperature induced electrical resistance change in nano-carbon/epoxy composites(Elsevier, 2015-04-24); ; ; ; In this study, we investigate the changes of electrical resistance of the carbon black (CB) and carbon nanotube (CNT) filled epoxy composites upon compression, swelling and temperature variation. For all samples we observe a decrease of electrical resistance under compression, while an increase of electrical resistance is found upon swelling due to water absorption. With the same volumetric change, the CB/epoxy composites have a more pronounced change of electrical resistance than the CNT/epoxy composites. The influence of temperature variations on the overall electrical resistance is somewhat more complex. At low temperatures, electrical resistance clearly decreases with increasing temperature, mainly owing to the thermal fluctuation induced tunneling conduction mechanism. At high temperatures, electrical resistance decreases much slower and may even increase due to a more prominent thermal expansion effect. The thermal expansion of the epoxy matrix leads to a decrease of tunneling conduction. Without the contribution of the thermal expansion, the sensitivity and linearity of electrical resistance change upon temperature variations is higher.Publicationtype: Journal Article60