Self-Assembly of a Jammed Black Phosphorus Nanoribbon on a Fixed Carbon Nanotube

Nanotube synthesizing from black phosphorus (BP) is still challenging in laboratory. Fabricating a BP nanotube by self-assembling of a BP nanoribbon seems promising. To estimate the feasibility of such fabrication method, this study performs numerical experiments of self-assembling a jammed BP ribbon on a fixed carbon nanotube using molecular dynamics simulation. The study is based on the following two facts: The phosphorus–phosphorus (P–P) bond is weaker than the bond of carbon–carbon (C–C) and the van der Waals interaction among nonbonding phosphorus atoms is stronger than that between phosphorus atoms and carbon atoms. The results show that when a longer BP ribbon is jammed by a shorter BP ribbon the self-assembling result depends on the relative positions of carbon nanotube (CNT) and the two BP ribbons. Only when the shorter BP ribbon is on the outside of the longer ribbon can the longer BP ribbon be wound on the CNT to form an ideal BP nanotube. The finding is helpful for practical applications of BP nanotubes in nanodevices

Spectrum of Temperature-Dependent Rotational Frequency of the Rotor in a Thermally Diven Rotary Nanomotor

By fixing of the outer tube of double-walled carbon nanotubes, a thermally driven rotary nanomotor can be obtained one or more carbon atoms at the end of the stator have an obvious inward radial deviation. Due to the asymmetry of the potential field of the stator, a collision between two tubes leads to the axial component of angular momentum that drives the rotation of the rotor. Relative sliding between the two tubes is resisted due to the roughness of the potential field of stators. Hence, the rotational frequency of the rotor has a maximal value in the balanced state. The spectrum of rotational frequency with respect to temperatures from 8 to 2000 K is presented by means of molecular dynamics simulation. The temperature interval is divided into five zones on the basis of the characteristics of the spectrum. In the robust zone, the nanomotor exhibits stationary rotation. In the controllable zone, the rotational frequency of rotor can be adjusted by varying the temperature. In particular, if a rotating rotor is cooled to an ultralow temperature, the final stable value of the rotational frequency is still very high and is slightly lower than the maximal value rather than zero; i.e., the nanomotor will theoretically never stop rotating

Over-Speeding Rotational Transmission of a Carbon Nanotube-Based Bearing

In studying the rotational transmission behavior of a carbon nanotube-based bearing (e.g., (5, 5)/(10, 10)) driven by a CNT motor (e.g., (9, 9)) at finite temperature, one can find that the rotor has different dynamic states from the motor at different environmental condition. In particular, the rotor can be in the overspeeding rotational transmission (ORT) state, in which the rotational speed of the rotor is higher than that of the motor. If we change the rotational frequency of the motor (e.g., >100 GHz) and the curved angle of the rotor, the bearing can reach the ORT state. Besides, in the ORT state, the ratio of the rotor’s rotational speed over that of the motor will be not higher than the ratio of the motor’s radius over that of the rotor. There are two major reasons that result in the bearing to the ORT state. One is that the thermal vibration of atoms between the carbon–hydrogen (C–H) end of the motor and that of the rotor has a drastic collision when the motor is in a high rotational speed. The collision causes the atoms at the end of the rotor to have a circular and axial velocity. The circular velocity leads to the rotation of the rotor and the axial velocity causes the oscillation of the rotor. Another reason is sourced from the oblique angle between the rotor and the stators due to the rotor having a curved angle. A higher oblique angle results in higher friction between the rotor and stator, and it also provides higher collision between the rotor and motor. Hence, one can adjust the transmission state of the rotor by changing not only the environmental temperature but also the rotational speed of the motor, as well as the curved angle of the rotor. The mechanism is essential in guiding a design of a rotational transmission nanodevice which transforms the rotation of the motor into other states of the rotor as output signals

Epitaxial Growth of Highly Oriented Metallic MoO₂@MoS₂ Nanorods on C‑sapphire

Molybdenum dioxide (MoO₂) has attracted many interests due to its unique properties and potential applications. Here, we report the synthesis of high quality MoO₂@MoS₂ nanorods on c-sapphire substrates through an atmospheric pressure chemical vapor deposition (APCVD) approach. Optical microscopy (OM), cross-sectional scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), and (grazing incidence) X-ray diffraction ((GI)­XRD) measurements reveal that these MoO₂ nanorods exhibit epitaxial growth behaviors on c-sapphire substrates with the orientation relationship of MoO₂(100)∥sapphire­(0001) and MoO₂ ⟨001⟩ aligned well with sapphire ⟨101̅0⟩. Raman spectroscopy/imaging, energy dispersive spectroscopy (EDS), and GIXRD results disclose that such MoO₂ nanorods are wrapped by MoS₂ (MoO₂@MoS₂). Devices based on transferred individual MoO₂@MoS₂ nanorods show a resistivity of ∼1.65 × 10^–4 Ω·cm, comfirming that such nanorods possess higher crystalline degree. Our findings will be helpful for the applications of MoO₂@MoS₂ in the fields of nanoelectronic devices