Direct co-deposition of mono-sized nanoparticles during sputtering

Thermally Stable Nanotwins: New Heights for Cu Mechanics

“…The codeposition of less than 1 vol% of 4 nm tungsten nanoparticles in copper facilitates nanotwin formation, and stabilizes the microstructure against coarsening up to at least 400 °C, hence retaining ≈90% initial hardness after annealing (≈3 GPa). This momentous improvement over coarse-grained and nanocrystalline alternatives corroborates our preliminary results on nc-Cu [11] and holds promise for applications in microelectronics and electric motors, as it is achieved with only a 9% rise in electrical resistance. At 400 °C, a hot hardness of 0.77 GPa is achieved with W nanoparticles: these are reasoned to resist detwinning processes.…”

“…Although nanotwins in pure Cu provide some degree of stability, [9] the extent is debated, recently being correlated to initial texture. [9b] Broadly speaking, literature and the present study concur that neither pure nc-Cu [11,32] nor nt-Cu [10] is stable at 400 °C (Figure 3). Here, hardness decreases by a factor of two after only 200 °C (Figure 2B): nt-Cu grains often coarsen to a twin-free (100) texture in thin films.…”

“…It is evident that the dominant contribution to strength is through grain size refinement-as Hazzledine commented, [29] and expanded in, [30] particle diameter should drop below 0.8 nm for the Orowan mechanism to outpace the strength benefit of Zener pinningdecreased grain sizes. In fact, as we calculated on nc-Cu with W NP, [11] the grain size stabilized by standard Zener pinning is 81 and 166 nm for W NP at 0.84 and 0.41 vol%, respectively. The refinement of nanotwins here far exceeds simple Zener pinning.…”

“…W nanoparticle formation is due to the increased Ar process gas inside the aggregation zone ahead of the sputtered W target, as well as the intermittent contamination of the aggregation volume with air. The latter is a necessary addition to the previous work [11] to deposit films with uniform tungsten content along thick cross-sections (> 1 μm here); without this, nucleation efficiency decreases significantly in under 1 h. Further details are given in Supporting Information S10. It is thought the increased nucleation efficiency after contamination is related to oxidation or nitridation of sputtered W atoms or the W target surface, onto which molecules the metallic nanoparticles can nucleate heterogeneously with greater ease.…”

Mapping pure plastic strains against locally applied stress: Revealing toughening plasticity

“…Further application of nanoscale resolution combined elastic and total strain mapping to in situ TEM deformation studies is similarly envisaged to further increase spatial resolution. Hence, not only dislocation-mediated plastic deformation but also diffusion-controlled creep at grain boundaries and in the bulk of nanocrystalline grains, or amorphous shear-banding, could be measured during loading by DIC of appropriately sized nanoparticle surface markers ( 38 , 39 ). The corresponding maps of elastic strains evolving during loading could again be measured by pointwise collection of diffraction patterns according to one of several existing techniques ( 11 , 12 , 40 ).…”