Knowledge about strain at the nanometre scale is essential for tailoring the mechanical and electronic properties of materials. Flaws, cracks and their local strain fields can be detrimental to the structural integrity of many solids. Conversely, the controlled straining of silicon can be used to improve the performance of electronic devices. Here, we demonstrate that infrared near-field microscopy allows direct, non-invasive mapping and a semiquantitative analysis of residual strain fields in polar semiconductor crystals with nanometre-scale resolution. Our experiments with silicon carbide crystals yield optical images of nanoindents showing strain features as small as 50 nm and the evolution of nanocracks. In addition, by imaging nanoindents in doped silicon, we provide experimental evidence for plasmon-assisted near-field imaging of free-carrier properties in nanoscale strain fields. Near-field infrared strain mapping provides possibilities for nanoscale material and device characterization, and could become a tool for nanoscale mapping of the local free-carrier mobility in strain-engineered semiconductors.

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SiC fibre reinforced copper is a potential novel heat sink material for the divertor of future fusion reactors to reinforce the zone between plasma facing material (W) and heat sink material (CuCrZr). The metal matrix composite (MMC) should be able to withstand heat loads up to 15 MW/m² at operating temperatures of up to 550°C. SCS6 fibres were coated by magnetron sputtering with a titanium interlayer and the copper matrix was deposited by electroplating. The composite was consolidated by hotisostatic pressing. The average ultimate tensile strength of composite samples with 20 % fibre reinforcement is 640 MPa and for the Young's modulus 162 GPa was determined.The Young's modulus decreases with increasing temperature and reaches 113 GPa at 550°C.Fracture area analysis after tensile tests show the failure of the SCS 6 fibres at the interface between the two outer carbon layers. Titanium as interlayer led to an improved bonding between the outer carbon coating of the SiC fibres and the copper matrix. IntroductionSiC fibre reinforced copper is a potential novel heat sink material for the divertor of future ExperimentalSCS6 fibres (Specialty Materials) were coated by magnetron sputtering with a 100 nm titanium interlayer for improved bonding and a 500-nm-thin copper layer without breaking the vacuum to protect the titanium layer against oxygen. In a next step the pure copper matrix was deposited by electroplating. In a CuSO 4 bath a 50-µm-thick Cu layer was grown on the fibres within 4 hours, resulting in a fibre volume fraction of 35 %.Uncoated and coated fibres were used for single fibre tensile tests at room temperature with a laser speckle extensometer for contact less strain measurements.Heat treatment of coated single fibres at 550°C in vacuum with a very slow heating rate (0.5 Kmin -1 ) served to reduce pores in the copper by outgassing of hydrogen. 4After heat treatment the coated single fibres for the composite were etched with an acid agent to remove surface oxide layers and subsequently packed in a Cu capsule (length 45 mm, diameter 8 mm), which was vacuum-sealed. The fibre reinforced zone had a diameter of 3.5 mm. The composite was consolidated by hot-isostatic pressing (HIP) of these capsules at 650°C and 100 MPa for 30 min. Tensile test specimens were machined out of the composite capsules. The overall sample length was 44 mm with a parallel gauge length of 12 mm (Fig. 1). The diameter within the parallel gauge length varied between 3.5 mm and 4.5 mm in order to obtain fibre volume fractions in the range of 10% to 20%. The threaded specimen ends were clamped by means of a hydraulic chuck.The clamp construction allowed to compensate for the temperature induced relaxation process in the copper threads and hence kept the clamping force at a sufficient level.The composite was tensile tested with a constant displacement rate of 1 mm/min. For high temperature tests the samples were inductively heated. A predominantly indirect heating characteristic was achieved by the combination of specimen, grips a...

We investigate SiC fibre reinforced copper as an additional layer at the highly loaded zone between plasma facing material (W) and heat sink (CuCrZr) for a fusion reactor divertor.Copper has a high thermal conductivity of 380 Wm -1 K -1 but a very low strength and creep resistance at 550°C. Therefore copper is reinforced with SiC long fibres (SCS6, Specialty Materials) having excellent high temperature strength.The fibres were galvanically coated with an 80-µm-thick copper layer as matrix. Hot isostatic pressing at 650°C was applied to form the composite material. The interfacial shear strength calculated from push-out tests was ̴ 6 MPa.Adding a 100-nm-thin titanium interlayer deposited by magnetron sputtering led to a higher adhesion of the SiC fibres in the copper matrix. Titanium reacted with the carbon surface of the fibre to TiC and formed with copper the alloy Cu 4 Ti during heat treatment and increased the interfacial shear strength to 70 MPa.