Thin Silicon Microdosimeter utilizing 3D MEMS Fabrication Technology: Charge Collection Study and its application in mixed radiation fields

New 10-μm-thick silicon microdosimeters utilizing 3-D technology have been developed and investigated in this paper. The TCAD simulations were carried out to understand the electrical properties of the microdosimeters\u27 design. A charge collection study of the devices was performed using 5.5-MeV He2+ ions which were raster scanned over the surface of the detectors and the charge collection median energy maps were obtained and the detection yield was also evaluated. The devices were tested in a 290 MeV/u carbon ion beam at the Heavy Ion Medical Accelerator in Chiba (HIMAC) in Japan. Based on the microdosimetric measurements, the quality factor and dose equivalent out of field were obtained in a mixed radiation field mimicking the radiation environment for spacecraft in deep space

Computer-aided manufacturing and focused ion beam technology enable machining of complex micro- and nano-structures

We present a novel framework for the fabrication of geometrically complex structures at the micro- and nano-scale which relies on the synergy of integrated computer-aided design and manufacturing systems (CAD/CAM) and focused ion beam (FIB) technology in a scanning electron microscope. Here we utilise industry standard G-code syntax, for the first time, to FIB machining by designing geometries with CAD, defining machining strategies and exporting G-codes with CAM and generating a coordinate list-based beam path by using a custom-built interpreter program. This allows the fabrication of complex structures from CAD models using syntax which is readily understood in the general fabrication industry. The use of G-code allows optimization of the beam path towards a reduction of beam blanking operations and tracing of contours, leading to minimized re-deposition of material. We give a detailed description of the method, use an application example to demonstrate advantages and prospects of the approach and provide the free and open-source interpreter program CAM2FIB for application of this method. We contrast and compare various existing available milling strategies and demonstrate the versatility of G-code based programming

Multifunctional Bi-Layered Tribofilm Generated on Steel Contact Interfaces under High-Temperature Melt Lubrication

The extreme state of high friction, severe wear, and oxidation invariably occur in mechanical contacts during high temperature steel processing. The application of lubricant to mitigate the aforementioned hindrances can enhance the process performance effectively. Melt lubricants are regarded as a highly promising class due to their good thermal stability and unique physical chemistry. The present study evaluates tribological responses of an alkaline metal borate on steel tribo-pair at 800 °C by ball-on-disk testing. It has been found that the borate melt significantly reduces the friction coefficient and the wear loss in accompany with providing excellent oxidation resistance. On the disk, the formation of a bilayered tribofilm dominates synergistic functionalities while the emergence of an ultrafine-grained layer considerably reinforces the interface integrity of the opposing ball. Cross-sectional examinations of the contact interfaces were carried out on both steel counterparts by FIB/STEM. STEM/HAADF-EDS reveal the formation of a boundary film featuring high concentration of B and significant depletion of O superimposed on a Na-rich film on the rubbing disk. On the opposing surface, a chemically complex film consisting of Na, Fe, O, amorphous C and [3]B which resides on nanograins of iron oxide is evidenced by STEM/EELS-EDS

3D Printing Metallised Plastics as Terahertz Reflectors

3D printing of new metallised plastics is investigated as a means to realise rapid creation of reflective optics for the terahertz regime. The suitability of three commercially available candidate materials was tested across a range of systems which span from 0.2 to 10 THz. Simple reflective planes were printed and characterised by spectroscopy and microscopy. Samples were polished which is shown to give a dramatic improvement to the reflectivity for these materials. The results indicate that metallised plastics have potential uses in low frequency rapid prototyping of reflective optics

Transmission Kikuchi diffraction versus electron back-scattering diffraction: A case study on an electron transparent cross-section of TWIP steel

The present case study compares transmission Kikuchi diffraction (TKD) with electron back-scattering diffraction (EBSD) on the same area of an electron transparent cross-section of a twinning induced plasticity steel. While TKD expectedly provides better clarity of internal defect substructures in the band contrast map, EBSD returns orientation data that approaches the quality of the TKD map. This was rationalised by Monte Carlo simulations of the electron energy spreads, which showed that due to the geometry-based compromises associated with adapting a conventional EBSD detector (which is off-axis with respect to the incident electron beam) to TKD, a broadening in the electron energy distribution of the forward-scattered electrons collected on the detector phosphor screen, is unavoidable. In this circumstance, the values of the full-widths at half-maximum of the energy distributions for TKD and EBSD are of the same order. It follows that EBSD on electron transparent cross-sections may be a viable alternative to TKD when: (i) conventional EBSD detectors are adapted to TKD and, (ii) sample microstructures comprise features whose sizes do not mandate the application of TKD

Unusual Competitive and Synergistic Effects of Graphite Nanoplates in Engine Oil on the Tribofilm Formation

To exploit the improved efficiency from formulated oil modified with graphite nanoplates (GNP), it is important to understand how GNP behave alongside conventional additives such as zinc dialkyl dithiophosphates (ZDDP). The results in this work demonstrate unusual tribological responses of engine oil due to GNP additions, which cannot be explained by the traditionally low shearing mechanism between graphene layers in GNP. A competitive and synergistic effect of GNP on tribofilm formation is proposed for this unusual friction and wear behavior. The presence of GNP modifies the tribofilm formation and spontaneously creates alternate hard and soft regions from the microscopic view of the surface. At low concentrations (≤0.05 wt%), graphene is formed by shear-assisted exfoliation of GNP and intermixed with intermediate oxide region. Due to its random orientation, graphene produces mechanical reinforcement of the tribofilm, but low shear yielding is not achieved. This gives rise to high friction but low wear conditions. At higher concentrations (\u3e0.05 wt%), GNP align with their hexagonal sheets parallel to the surface to promote low-shear sliding, but wear increases. This is due to GNP clumping together which makes them less effective at forming graphene and providing stable reinforcement of the tribofilm

Strain, stress and stress relaxation in oxidized ZrCuAl-based bulk metallic glass

© 2020 Surface engineering of Zr51.3Al8.5Cu31.3Ni4Ti4.9 bulk metallic glass (BMG) by gaseous oxidizing below the glass-transition temperature is investigated as a means to introduce compressive residual stress in the surface region. The ZrCuAl-based BMG was exposed to an extremely low oxygen partial pressure of 10−41 bar at 600 K for 60 h. The oxidizing treatment led to the formation of an internal oxidation zone, consisting of finely dispersed nano-crystalline cubic ZrO2 (c-ZrO2), metallic regions inclined with the surface and Cu-hillocks at the surface. The stresses introduced by the volume expansion associated with oxidation were evaluated from i) the lattice strains within c-ZrO2, as determined with an X-ray diffraction (XRD) based method, and ii) strain-relaxation as a response to annular focused ion beam (FIB) milling, as monitored with digital image correlation (DIC). XRD analysis yielded -1.5 GPa (compressive stress) in the nano-crystalline c-ZrO2, while the strain relaxation monitored with FIB-DIC analysis indicated compressive residual stresses of −1.4 GPa in the internal oxidation zone. The strains and stresses determined with the independent measurement methods are discussed. The quantitative macro-strains are discussed in relation to the microstructural features and stress relaxation mechanisms during evolution of the internal oxidation zone

The effect of β-phase condition on the tensile behaviour in a near-β Ti alloy produced by blended elemental powder metallurgy

In this study, a Ti-10V-3Fe-3Al alloy produced by the blended elemental powder metallurgy technique was subjected to two heat treatments at 675℃ and 625℃, resulting in lower β-phase stability and larger β-domain size in the sample heat treated at the higher temperature. The microstructural response to uniaxial tensile loading for the two conditions was investigated using a combination of optical microscopy, electron back-scattering diffraction and transmission electron microscopy. The observations indicate that a majority of deformation-induced products are formed in the vicinity of the fracture surface due to stress tri-axiality. Within this region, the 675℃ sample accommodated deformation via dominant {332}〈113〉 twinning, α″ martensite formation and limited {112}〈111〉 twinning. On the other hand, the sample with higher β-phase stability accommodated deformation via α″ martensite formation and perfect slip with reduced twinning activity. The formation of deformation-induced ωD phase between the β matrix and α″ martensite laths was also observed in the sample with lower β-phase stability. Reduction of the interfacial energy by stress relaxation is assumed to be the driving force for ωD formation

Creating thin magnetic layers at the surface of Sb2Te3 topological insulators using a low-energy chromium ion beam

The surfaces of Sb2Te3 topological insulator crystals were implanted using a 40 keV chromium ion beam. To facilitate uniform doping, the Sb2Te3 was passivated with a thin TiO2 film before the implantation step. The resulting chemical structure was studied using atomic-resolution transmission electron microscopy. A fluence of 7 × 1015 ions/cm2 at 40 keV lead to amorphization of the Sb2Te3 surface, with chromium predominantly incorporated in the amorphous layer. Heating to 200 °C caused the amorphous region to recrystallize and led to the formation of a thin chromium-rich interfacial layer. Near-edge x-ray absorption spectroscopy indicates a uniform valence state of Cr3+ throughout, with no evidence of metallic clustering. High-temperature superparamagnetic behavior was detected up to 300 K, with an increased magnetic moment below 50 K

A Liquid-Metal-Based Magnetoactive Slurry for Stimuli-Responsive Mechanically Adaptive Electrodes

Electrical communication between a biological system and outside equipment allows one to monitor and influence the state of the tissue and nervous networks. As the bridge, bioelectrodes should possess both electrical conductivity and adaptive mechanical properties matching the target soft biosystem, but this is still a big challenge. A family of liquid-metal-based magnetoactive slurries (LMMSs) formed by dispersing magnetic iron particles in a Ga-based liquid metal (LM) matrix is reported here. The mechanical properties, viscosity, and stiffness of such materials rapidly respond to the stimulus of an applied magnetic field. By varying the intensity of the magnetic field, regulation within a factor of 1000 of the Young\u27s modulus from ≈kPa to ≈MPa, and the ability to reach GPa with more dense iron particles inside the LMMS are demonstrated. With the advantage of high conductivity of the LM matrix, the functions of the LMMS are not only limited to the soft implanted electrodes or penetrating electrodes in biosystems: the electrical response based on the LMMS electrodes can also be precisely tuned by simply regulating the applied magnetic field