Nanoscopic scale | EPFL Graph Search

The nanoscopic scale (or nanoscale) usually refers to structures with a length scale applicable to nanotechnology, usually cited as 1–100 nanometers (nm). A nanometer is a billionth of a meter. The nanoscopic scale is (roughly speaking) a lower bound to the mesoscopic scale for most solids. For technical purposes, the nanoscopic scale is the size at which fluctuations in the averaged properties (due to the motion and behavior of individual particles) begin to have a significant effect (often a few percent) on the behavior of a system, and must be taken into account in its analysis. The nanoscopic scale is sometimes marked as the point where the properties of a material change; above this point, the properties of a material are caused by 'bulk' or 'volume' effects, namely which atoms are present, how they are bonded, and in what ratios. Below this point, the properties of a material change, and while the type of atoms present and their relative orientations are still important, 'su

Diamond-Based Nanoscale Quantum Relaxometry for Sensing Free Radical Production in Cells

Mayeul Sylvain Chipaux, Hoda Shirzad

Diamond magnetometry makes use of fluorescent defects in diamonds to convert magnetic resonance signals into fluorescence. Because optical photons can be detected much more sensitively, this technique currently holds several sensitivity world records for room temperature magnetic measurements. It is orders of magnitude more sensitive than conventional magnetic resonance imaging (MRI) for detecting magnetic resonances. Here, the use of diamond magnetometry to detect free radical production in single living cells with nanometer resolution is experimentally demonstrated. This measuring system is first optimized and calibrated with chemicals at known concentrations. These measurements serve as benchmarks for future experiments. While conventional MRI typically has millimeter resolution, measurements are performed on individual cells to detect nitric oxide signaling at the nanoscale, within 10-20 nm from the internalized particles localized with a diffraction limited optical resolution. This level of detail is inaccessible to the state-of-the-art techniques. Nitric oxide is detected and the dynamics of its production and inhibition in the intra- and extracellular environment are followed.

WILEY-V C H VERLAG GMBH2022

Systematic investigations of uranium carbide composites oxidation from micro- to nano-scale: Application to waste disposal

Nhât-Tân Vuong

The production of radioisotope beams at the ISOLDE (Isotope Separator OnLine DEvice) facility at CERN is achieved by irradiating target materials (e.g. uranium carbides and metal foils) with protons. The materials are usually operated at temperatures above 2000°C to promote isotope release. However, materials are rapidly degraded due to sintering which results in a loss of radioisotope beam intensity. Moreover, some refractory elements are particularly difficult to extract using the conventional high temperature approach due to their low vapor pressure and high boiling point.The topic of this thesis deals with two types of target materials which were engineered to improve isotope release.The first part of this thesis concerns new micro- and nano-structured uranium carbide materials. New nanomaterials were found highly pyrophoric and not compatible with long-term storage requirements. Thus, a safe process for their conversion into oxide is investigated. However, the oxidation mechanism is not fully understood, notably the relationship between the material characteristics and its oxidation kinetics.In this thesis, characterization and thermal analysis techniques were used to study the oxidation of five different uranium carbide materials. For each material, the mechanism of the reaction was determined and the reaction rate was modeled. The model predictions were evaluated against experimental data. The influence of the materials characteristics on the oxidation kinetics was notably discussed.The reaction was found generally controlled by the diffusion of oxygen through the uranium oxide product layer. However, nanomaterials presented a shift in the rate controlling mechanism from diffusion to surface. Onset oxidation temperatures between 150°C and 280°C and activation energies between 78.9 and 128.6 kJ/mol were observed. Both values were lower for nanomaterials, which highlights the importance of materials characteristics. Other parameters such as the concentration of carbon can affect the rate of the reaction by forming an additional passivation barrier around uranium carbide.The study provided a better understanding of the oxidation properties of uranium carbides. The approach is general and can be used to investigate other actinide materials in the future. In particular, the collected data can be used to design a safe process for the conversion and disposal of target materials at ISOL facilities worldwide.The second part of this thesis dealt with the stability of graphene on metal foil target materials under irradiation. Refractory elements can be extracted from metal foils using reactive gases to form volatile molecules at room temperature. However, the gas could also react with the target material and prevent the extraction of isotopes. Protection of tantalum foils against corrosion and oxidation can be obtained using graphene coating. However, the stability of graphene under high energy proton beam irradiation was never evaluated.It was found that the coating was mainly degraded by the impact of primary protons while the contribution of secondary particles and the temperature rise induced by the interaction of the primary proton beam with the target were found negligible.The study showed that graphene is unstable under proton irradiation and cannot be used as a protection barrier against corrosion and oxidation on target materials at the fluences found in the present-day operating facilities.

EPFL2021

Metal and metaloxide nanostructures on and in plant viruses

Sinan Balci

Tobacco Mosaic Virus (TMV) is composed of 2130 identical coat protein subunits following the right-handed helix of an accompanying RNA strand to produce a 300 nm hollow cylinder with an outer diameter of 18 nm and a 4 nm wide central channel. In this work, TMV is used as a bionanotemplate for the synthesis of interesting nanomaterials. When the TMV is activated with a catalyst (Pd (II)), nickel, copper, and cobalt nanowires can be grown within the central channel of the virion. In the same way alloy nanowires (cobalt-iron) are produced inside the central channel. Due to the non-galvanic protocol, the deposition method is called electroless deposition (ELD). Apart from the deposition of metals (Ni, Co, Cu, CoFe alloy), zinc oxide, a large band gap semiconductor, is deposited on the exterior surface of the virus. The chemical compositions of the nanomaterials are revealed at the nanoscale by energy-filtering transmission electron microscopy. Various physical properties of some of the synthesized nanomaterials are measured: Electrical transport measurements on the TMV rods, contacted by gold electrodes, indicate that the TMV rods show insulating behavior at room temperature. High-resolution transmission electron microscopy images of individual nickel nanowires show the crystalline bulk phase, confined to a 3 nm wide wire, with (111) planes perpendicular to the wire axis. Cathodoluminescence measurements from individual zinc oxide rods exhibit ultraviolet emission with a photon energy of around ∼3.4 eV, which is equal to the band gap of the bulk material. Furthermore, 6 nm diameter gold nanoparticles (Au-nps) are selectively attached to the ends of the TMV particles, and they are enlarged by electroless deposition of gold. The RNA strand plays an important role in the selective attachment of the Au-nps. It is possible to print and align TMV particles on a variety of surfaces by the microcontact printing method. Several micrometer long end-to-end assembled TMV rods can be placed close to the edges within the recessed regions of polydimethysiloxane stamp structures. The reason for the selective assembly of the virions is the dewetting of the inking solvent (water) on the stamp surface. By printing, the virion pattern is transferred to solid surfaces. Alternatively, TMV particles can be selectively assembled on flat rectangular submicrometer patches with amine groups, which are generated by electron beam lithography. The experimental results show that TMV can be a model system for new bionanotemplates with huge potential in nanoscale science and possibly technology.

EPFL2006