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the structural suppression of friction is accompanied by a transition in the nature of transport from a simultaneous slipping regime reducible to an effective single-particle PT model, to a kink propagation regime characteristic of the infinite FK model.In Fig. 4, we plot the measured maximum static friction force F s , averaged over the ions in the crystal, versus the matching q. (The dissipated energy DW follows the same q dependence). As q is lowered from 1, the friction drops quickly, then slowly approaches a much reduced value at q = 0, which decreases with increasing crystal size. Notably, at q = 0 (mismatched limit) there is an almost 10-fold reduction in friction already for N = 2 ions, and a 100-fold reduction for N = 6 ions. Numerical simulations of this behavior at zero temperature (dashed lines in Fig. 4) show qualitative agreement but fail to account for the finite temperature of the ions in the experiment. For lower q values, the effective barrier separating two potential minima is reduced, and the friction becomes more sensitive to temperature (28). To take temperatureinduced friction reduction (thermolubricity) (1) into account, we perform full dynamics simulations accounting for the finite crystal temperature (28) and find good agreement with the experiment (solid lines in Fig. 4). These simulations indicate that in the limit of low q, thermolubricity and superlubricity (mismatch-induced lubricity) reduce the observed friction by similar factors in our data.Our results indicate that it may be possible to engineer nanofriction by structural control in finite-size systems. Intriguing future possibilities include the coupling to internal states of the ions (30) for the study of spin-dependent transport and friction (22) and the regime of weak periodic potentials, where quantum-mechanical tunneling may lead to new quantum phases (19, 22 Physica D 7, 240-258 (1983). 11. G. Binnig, C. F. Quate, C. Gerber, Phys. Rev. Lett. 56, 930-933 (1986). 12. C. M. Mate, G. M. McClelland, R. Erlandsson, S. Chiang, Phys.Rev. Lett. 59, 1942Lett. 59, -1945Lett. 59, (1987 M acroscopic friction and wear remain the primary modes of mechanical energy dissipation in moving mechanical assemblies such as pumps, compressors, and turbines, leading to unwanted material loss and wasted energy. It is estimated that nearly one third of the fuel used in automobiles is spent to overcome friction, while wear limits mechanical component life. Even a modest 20% reduction in friction can substantially affect cost economics in terms of energy savings and environmental benefits (1). In that context, superlubricity is desirable for various applications and therefore is an active area of research. To date, superlubricity has been primarily realized in a limited number of experiments involving atomically smooth and perfectly crystalline materials (2-5) and supported by theoretical studies (6, 7). Superlubricity has been demonstrated for highly oriented pyrolytic graphite (HOPG) surfaces (8), as well as for multiwalled carbon nanotubes (...

Ultrananocrystalline diamond (UNCD) films with up to 0.2% total nitrogen content were synthesized by a microwave plasma-enhanced chemical-vapor-deposition method using a CH4(1%)/Ar gas mixture and 1%–20% nitrogen gas added. The electrical conductivity of the nitrogen-doped UNCD films increases by five orders of magnitude (up to 143 Ω−1 cm−1) with increasing nitrogen content. Conductivity and Hall measurements made as a function of film temperature down to 4.2 K indicate that these films have the highest n-type conductivity and carrier concentration demonstrated for phase-pure diamond thin films. Grain-boundary conduction is proposed to explain the remarkable transport properties of these films.

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In this article, we report only 10 atomic layer thick, high mobility, transparent thin film transistors (TFTs) with ambipolar device characteristics fabricated on both a conventional silicon platform as well as on a flexible substrate. Monolayer graphene was used as metal electrodes, 3-4 atomic layers of h-BN were used as the gate dielectric, and finally bilayers of WSe2 were used as the semiconducting channel material for the TFTs. The field effect carrier mobility was extracted to be 45 cm(2)/(V s), which exceeds the mobility values of state of the art amorphous silicon based TFTs by ∼100 times. The active device stack of WSe2-hBN-graphene was found to be more than 88% transparent over the entire visible spectrum and the device characteristics were unaltered for in-plane mechanical strain of up to 2%. The device demonstrated remarkable temperature stability over 77-400 K. Low contact resistance value of 1.4 kΩ-μm, subthreshold slope of 90 mv/decade, current ON-OFF ratio of 10(7), and presence of both electron and hole conduction were observed in our all two-dimensional (2D) TFTs, which are extremely desirable but rarely reported characteristics of most of the organic and inorganic TFTs. To the best of our knowledge, this is the first report of all 2D transparent TFT fabricated on flexible substrate along with the highest mobility and current ON-OFF ratio.