Success in making artificial muscles that are faster and more powerful and that provide larger strokes would expand their applications. Electrochemical carbon nanotube yarn muscles are of special interest because of their relatively high energy conversion efficiencies. However, they are bipolar, meaning that they do not monotonically expand or contract over the available potential range. This limits muscle stroke and work capacity. Here, we describe unipolar stroke carbon nanotube yarn muscles in which muscle stroke changes between extreme potentials are additive and muscle stroke substantially increases with increasing potential scan rate. The normal decrease in stroke with increasing scan rate is overwhelmed by a notable increase in effective ion size. Enhanced muscle strokes, contractile work-per-cycle, contractile power densities, and energy conversion efficiencies are obtained for unipolar muscles.

Fluorine doping of a compositionally graded cathode, with an average concentration of Li[Ni0.80Co0.05Mn0.15]O2, yields a high discharge capacity of 216 mAhg–1 with unprecedented cycling stability by retaining 78% of its...

The development of high-performance p-type oxides with high hole mobility and a wide bandgap is critical for the applications of metal oxide semiconductors in vertically integrated CMOS devices [Salahuddin et al., Nat. Electron. 1, 442 (2018)]. Sn2+-based oxides such as SnO and K2Sn2O3 have recently been proposed as high-mobility p-type oxides due to their relatively low effective hole masses, which result from delocalized Sn s-orbital character at the valence band edge. Here, we introduce a promising ternary Sn-O-X compound, Ta2SnO6, which exhibits strong valence band dispersion and a large bandgap. In order to evaluate the performance of this oxide as a p-type semiconductor, we perform first-principles calculations of the phonon-limited room-temperature carrier mobilities in SnO, SnO2, and Ta2SnO6. Electron relaxation time is evaluated, accounting for the scatterings from acoustic deformation potentials and polar optical phonons (POP), within the isotropic and dispersionless approximation. At room temperature, the electron/hole mobilities in a given material (SnO, SnO2, and Ta2SnO6) are found to be limited by POP scattering. SnO2 shows high room-temperature electron mobility of 192 cm2/(V s), while SnO and Ta2SnO6 exhibit impressive hole mobilities, with the upper limit at 60 and 33 cm2/(V s), respectively. We find that carrier effective mass largely accounts for the differences in mobility between these oxides with correspondingly different POP scattering rates. The theoretically predicted intrinsic mobilities of each material will provide the upper limit to the real mobilities for their device applications. Our findings also suggest a necessity of further investigation to identify even higher mobility p-type oxides with smaller hole effective masses.

High quality AlSb bulk material on Si substrates using a monolithic self-assembled quantum dot nucleation layer