Ruiwen Shao

Piezoresistance behaviors of ultra-strained SiC nanowires

In situ electrical measurement experiments were carried out in individual SiC nanowires (NWs) subjected to tensile strain using a transmission electron microscope. Fracture strain approaching 10% was achieved for a diamond-structure SiC NW with a 〈111〉 direction. With an increase in the tensile strain, the conductance increased monotonously. The current rate of increase remained constant prior to fracture. The calculated piezoresistance coefficient of this SiC NW was −1.15 × 10−11 Pa−1, which is similar to the coefficient of the bulk material. Our results indicate that these SiC NWs can be used as pressure sensors even in very high-pressure environments.

Helical Growth of Aluminum Nitride: New Insights into Its Growth Habit from Nanostructures to Single Crystals

By understanding the growth mechanism of nanomaterials, the morphological features of nanostructures can be rationally controlled, thereby achieving the desired physical properties for specific applications. Herein, the growth habits of aluminum nitride (AlN) nanostructures and single crystals synthesized by an ultrahigh-temperature, catalyst-free, physical vapor transport process were investigated by transmission electron microscopy. The detailed structural characterizations strongly suggested that the growth of AlN nanostructures including AlN nanowires and nanohelixes follow a sequential and periodic rotation in the growth direction, which is independent of the size and shape of the material. Based on these experimental observations, an helical growth mechanism that may originate from the coeffect of the polar-surface and dislocation-driven growth is proposed, which offers a new insight into the related growth kinetics of low-dimensional AlN structures and will enable the rational design and synthesis of novel AlN nanostructures. Further, with the increase of temperature, the growth process of AlN grains followed the helical growth model.

Observation of enhanced carrier transport properties of Si ⟨100⟩-oriented whiskers under uniaxial strains

In this study, enhancements of the carrier transport properties of p-type ⟨100⟩-oriented Si whiskers are observed under uniaxial tensile and compressive strains. It has been found that over 400% enhancement of electrical conductivity is achieved under a 2% tensile strain, while a 2% compressive strain can only cause ∼80% conductivity enhancement. The enhancements are mainly attributed to the breaking of the degeneracy of the v2 and v1 valence bands induced a reduction of the hole effective mass. This study provides an important insight of how the carrier mobility variation caused by the strain impact on their transport properties.

Structure and photoluminescence properties of carbon nanotip-vertical graphene nanohybrids

We report on the effective enhancement and tuning of photoluminescence (PL) by combining vertical graphene nanoflakes (VGs) and carbon nanotips (CNTPs). The VGs are grown on the vertical CNTPs by hot filament chemical vapor deposition in the methane environment, where the CNTPs are synthesized on silicon substrates by CH4-H2-N2 plasma-enhanced hot filament chemical vapor deposition. The results of field emission scanning electron microscopy, transmission electron microscopy, micro-Raman spectroscopy, and X-ray photoelectron spectroscopy indicate that the VGs can be grown on the CNTP and silicon substrate surfaces with the orientation perpendicular to the surfaces of CNTPs and silicon substrates. The PL properties of VG, CNTP, and CNTP-VG structures are studied using a 325 nm line of He-Cd laser as the excitation source. The PL results indicate that the PL of VGs is enhanced by the CNTPs due to the increasing density of PL emitters, while the PL properties of the nanohybrid system can be tuned. Furthermore...

Direct observation of structural transitions in the phase change material Ge2Sb2Te5

Phase change memory, which is based on the reversible switching of phase change materials between amorphous and crystalline states, is one of the most promising bases of nonvolatile memory devices. However, the transition mechanism remains poorly understood. In this study, via in situ transmission electron microscopy with an externally applied DC voltage and nanosecond electrical pulses, for the first time we revealed a reversible structural evolution of Ge2Sb2Te5 thin films from an amorphous state to a single-crystal state via polycrystals as an intermediate state. This transition is different from the traditional understanding of structural changes in Ge2Sb2Te5, i.e., from an amorphous structure to a hexagonal close-packed structure via face-centered cubic as an intermediate structure. In situ observations indicate that this poly-to-single crystal structural transition is caused by coalescence of neighbouring grains induced by an electric field, in which a fast heating/cooling rate is found to be essential. Our study opens a new avenue for the realization of the multi-level operation of phase change materials.