Yuezhou Wang

Planar field‐induced quantum dot transistor

We propose and demonstrate a new field‐induced quantum dot transistor that has a nanoscale dot‐gate inside the gap of a split gate. Because of the novel structure and small dot size, strong oscillations in the drain current as a function of the gate bias were observed at a temperature up to 4.2 K or with a drain bias up to 5 mV. Temperature dependent study showed that the energy gaps in the dot are as large as 4.5 meV. Simulation indicates that, in the device, quantum size effect and Coulomb effect are comparable; both contribute significantly to the energy gaps in the quantum dot.

Planar double gate quantum wire transistor

A planar double gate quantum wire transistor (QWT) is proposed and demonstrated. The transistor uses a narrow wire gate placed inside the gap of a split gate to create a single one‐dimensional (1D) quantum wire (QW). We demonstrate theoretically and experimentally that the wire gate can create a QW potential with a better confinement and therefore larger subband separations than that in other split‐gate QWTs, and that the split gate can adjust the number of electrons inside the QW while keeping the 1D QW potential almost unchanged. Furthermore, we found that, in the double gate QWT, a 1D electron channel can spatially overlap with a 2D electron channel without significant mixing.

Twisting Carbon Nanotube Ropes with the Mesoscopic Distinct Element Method: Geometry, Packing, and Nanomechanics

The geometry and internal packing of twisted ropes composed of carbon nanotubes (CNTs) are considered, and a numerical solution in the context of the mesoscopic distinct element method (MDEM) is proposed. Compared to the state of the art, MDEM accounts in a computationally tractable manner for both the deformation of the fiber and the distributed van der Waals cohesive energy between fibers. These features enable us to investigate the torsional response in a new regime where the twisted rope develops packing rearrangements and aspect-ratio-dependent geometric nonlinearities. MDEM emerges as a robust simulation method for studying twisted agglomerates comprising semiflexible nanofibers.

Ring windings from single-wall carbon nanotubes: A distinct element method study

Combining mesoscale distinct element method simulations with analytical modeling, we predict the ability of individual single-wall carbon nanotubes to form stable ring windings with multiple turns, in spite of their remarkable stiffness. The stability of these structures arises from the energy balance between the bending strain energy stored in the covalent bonds and the long-ranged van der Waals attraction along the turns. The significant energy density achieved in the ring windings made out of ultralong carbon nanotubes makes these architectures interesting for energy storage applications.

Enhancing the Elasticity of Ultrathin Single-Wall Carbon Nanotube Films with Colloidal Nanocrystals

Thin bilayers of contrasting nanomaterials are ubiquitous in solution-processed electronic devices and have potential relevance to a number of applications in flexible electronics. Motivated by recent mesoscopic simulations demonstrating synergistic mechanical interactions between thin films of single-wall carbon nanotubes (SWCNTs) and spherical nanocrystal (NC) inclusions, we use a thin-film wrinkling approach to query the compressive mechanics of hybrid nanotube/nanocrystal coatings adhered to soft polymer substrates. Our results show an almost 2-fold enhancement in the Young modulus of a sufficiently thin SWCNT film associated with the presence of a thin interpenetrating overlayer of semiconductor NCs. Mesoscopic distinct-element method simulations further support the experimental findings by showing that the additional noncovalent interfaces introduced by nanocrystals enhance the modulus of the SWCNT network and hinder network wrinkling.

Excluded Volume Approach for Ultrathin Carbon Nanotube Network Stabilization: A Mesoscopic Distinct Element Method Study

Ultrathin carbon nanotube films have gathered attention for flexible electronics applications. Unfortunately, their network structure changes significantly even under small applied strains. We perform mesoscopic distinct element method simulations and develop an atomic-scale picture of the network stress relaxation. On this basis, we put forward the concept of mesoscale design by the addition of excluded-volume interactions. We integrate silicon nanoparticles into our model and show that the nanoparticle-filled networks present superior stability and mechanical response relative to those of pure films. The approach opens new possibilities for tuning the network microstructure in a manner that is compatible with flexible electronics applications.

QUANTUM WAVE BANDSTOP FILTERS

We propose and demonstrate, based on the concept of a microwave bandstop filter, two quantum wave bandstop filter structures. Both structures employ nanoscale gates in a heterojunction transistor to induce a quantum cavity connected by two one‐dimensional wires. As the electron wavelength is changed by the gate voltage, we observed that, at certain gate voltages, the transmission of electron waves through the cavity is partially blocked and the drain current drops as large as 50%. This phenomenon is explained in terms of the destructive quantum interference between different electron wave modes in the cavity.

Observation of bias‐induced resonant tunneling peak splitting in a quantum dot

We have observed that, in zero magnetic field, a dc bias across a lateral confined quantum dot (QD) splits each resonant peak in the differential conductance versus the gate voltage measurement into two. The splitting is nearly linear with the applied bias VD. Temperature‐dependence study indicates that the corresponding energy separation between the two splitting peaks is close to eVD. A model is proposed that explains this splitting in terms of the bias‐induced shifting of energy levels in the QD and the splitting of the Fermi level. Using our model, the bias‐induced energy level shift in the QD can be calculated.

A new quantum dot transistor

Modulation doped N-AlGaAs/GaAs/InAs/GaAs/InAs/GaAs-heterostructures with InAs-quantum dots in device channel have been grown and investigated. Their photoluminescence spectra and electron transport properties both in low and high electric fields were studied. Using these structures, modulation doped FETs have been fabricated and analyzed. It was demonstrated that the quantum dot FETs present the new type of the hot electron devices, promising for high speed applications.