We propose a mode of dynamic scanning probe microscopy based on parametric resonance for highly sensitive nanoscale imaging and force spectroscopy. In this mode the microcantilever probe is excited by means of a closed-loop electronic circuit that modulates the microcantilever stiffness at a frequency close to twice its natural resonance frequency. Under ambient conditions this parametric pumping leads to self-sustained oscillations in a narrow frequency bandwidth thereby resulting in exquisitely sharp, controllable, and non-Lorentzian resonance peaks. We discuss and demonstrate the potential of imaging and force spectroscopy using this mode.

In this work, we report experimental data on the evolution of the resistance with applied voltage in nonsuspended single-walled carbon nanotubes (SWNTs) of lengths ranging from 100 nm up to 6 microm. At low bias, the differential resistance as a function of length is well described by a linear fitting. At high biases, this magnitude first saturates and then decreases for nanotubes longer than 1 microm. We also present Monte Carlo numerical simulations for the one-dimensional Boltzmann's equation, describing how the electrons propagate along the tube and how they interact with acoustic and optical phonons. Our theoretical results show a remarkable agreement with the experimental differential resistance, allowing us to give a detailed description of the electron distribution function and the chemical potential along the nanotube. Finally, we present experimental results on the transition from Anderson localization at low bias to high diffusive regime at high bias in defected SWNTs. This result is combined with those of defect-free SWNTs to present a general landscape of the electronic transport in carbon nanotubes.

We report on the mechanical properties of few-layer black phosphorus (BP) nanosheets, in high vacuum and as a function of time of exposure to atmospheric conditions [1]. BP flakes with thicknesses ranging from 4 to 30 nm suspended over circular holes are characterized by nanoindentations using an atomic force microscope tip. From measurements in high vacuum an elastic modulus of 46±10 GPa and breaking strength of 2.4±1 GPa are estimated. Both magnitudes are independent of the thickness of the flakes. Our results show that the exposure to air has substantial influence in the mechanical response of flakes thinner than 6 nm but small effects on thicker flakes. Figure 2. Indentation curves and E3D of BP drumheads in high vacuum. (a) Force versus indentation (F(δ)) curves (coloured lines) performed in HV in five BP drumheads with different thickness (4.5, 7.5, 13.3, 17 and 29 nm) and their cubic polynomial fit to Eq. (1) (thin black lines). (b) Histogram of the E3D values obtained from the cubic polynomial fit of F(δ) curves performed in 39 BP drumheads, following the first method described in the main text. The fit of the data of the histogram to a normal distribution yields E3D= 41±15 GPa. (c) Elastic constant versus t 3 /R 2 measured for 29 BP drumheads, and their linear fit to the Expression [2] (red solid line). This method yields E3D= 52±6 GPa.