Weilin Jiang

Flexible pillared graphene-paper electrodes for high-performance electrochemical supercapacitors.

Flexible graphene paper (GP) pillared by carbon black (CB) nanoparticles using a simple vacuum filtration method is developed as a high-performance electrode material for supercapacitors. Through the introduction of CB nanoparticles as spacers, the self-restacking of graphene sheets during the filtration process is mitigated to a great extent. The pillared GP-based supercapacitors exhibit excellent electrochemical performances and cyclic stabilities compared with GP without the addition of CB nanoparticles. At a scan rate of 10 mV s(-1) , the specific capacitance of the pillared GP is 138 F g(-1) and 83.2 F g(-1) with negligible 3.85% and 4.35% capacitance degradation after 2000 cycles in aqueous and organic electrolytes, respectively. At an extremely fast scan rate of 500 mV s (-1) , the specific capacitance can reach 80 F g(-1) in aqueous electrolyte. No binder is needed for assembling the supercapacitor cells and the pillared GP itself may serve as a current collector due to its intrinsic high electrical conductivity. The pillared GP has great potential in the development of promising flexible and ultralight-weight supercapacitors for electrochemical energy storage.

The effect of compression and tension on shear-band structure and nanocrystallization in amorphous Al90Fe5Gd5: a high-resolution transmission electron microscopy study

Abstract Using both conventional and high-resolution transmission electron microscopy (HRTEM), the effect of bending at room temperature on the microstructure of amorphous Al 90 Fe 5 Gd 5 was investigated. In the compressive region, nanocrystallites formed at shear bands, along small cracks and at the fracture surface; in the tensile region, nanocrystallites were observed only at the fracture surface. Combining HRTEM with frequency filtering, low-density, nanoscale defects at shear bands were imaged. In the compressive region, both the shear bands and the undeformed matrix contain few defects. In the tensile region, there is a uniform distribution of defects within the shear bands. The preferential precipitation of nanocrystallites in the compressive region is attributed to a kinetic effect due to the uniformly distributed free volume in the shear bands. In contrast, the formation of the nanocrystallites at the fracture surfaces is likely due to adiabatic heating induced by fracture.

Rate dependence of serrated flow in a metallic glass

Plastic deformation of amorphous Al 9 0 Fe 5 Gd 5 was investigated using nanoindentation and atomic force microscopy. While serrated flow was detected only at high loading rates, shear bands were observed for all loading rates, ranging from 1 to 100 nm/s. However, the details of shear-band formation depend on the loading rate.

Damage evolution and recovery on both Si and C sublattices in Al-implanted 4H–SiC studied by Rutherford backscattering spectroscopy and nuclear reaction analysis

Damage evolution and subsequent recovery in 4H–SiC epitaxial layers irradiated with 1.1 MeV Al22+ molecular ions at 150 K to ion fluences from 1.5×1013 to 2.25×1014 Al cm−2 were studied by Rutherford backscattering spectroscopy (RBS) and 12C(d,p)13C nuclear reaction analysis (NRA) using a 0.94 MeV deuterium (D+) beam in channeling geometry. Disorder on both the Si and C sublattices was measured simultaneously from the RBS scattering and NRA reaction yields. The relative disorder on both sublattices follows a nonlinear dependence on ion fluence that is consistent with a model based on simple defect accumulation and a direct-impact, defect-stimulated process for amorphization. At low ion fluences, the relative disorder on the C sublattice is higher than that on the Si sublattice. Isochronal annealing up to 870 K revealed the existence of three distinct recovery stages at ∼350, 520, and 650 K for low to intermediate damage levels. In highly damaged samples, where a buried amorphous layer is produced, the ons...

Deformation-induced nanocrystallization in an Al-based amorphous alloy at a subambient temperature

Abstract The compressive region of amorphous Al 90 Fe 5 Gd 5 , bent at −40 °C, was investigated by transmission electron microscopy. A high density of nanocrystals is observed within shear bands. Severe plastic deformation and precipitation of nanocrystallites are observed at the fracture surface. It is argued that deformation-assisted atomic transport leads to nanocrystallization.

Effect of strain rate on the formation of nanocrystallites in an Al-based amorphous alloy during nanoindentation

The effect of deformation by nanoindentation on nanocrystallization in amorphous Al90Fe5Gd5 was investigated by transmission electron microscopy. Massive precipitation of nanocrystallites is observed within the indents. Under the quasistatic condition used, a temperature rise due to adiabatic heating is likely negligible, confirming that plastic deformation can induce crystallization without a heating effect. The nucleation of nanocrystallites is significantly affected by the strain rate.

Damage profile and ion distribution of slow heavy ions in compounds

Slow heavy ions inevitably produce a significant concentration of defects and lattice disorder in solids during their slowing-down process via ion-solid interactions. For irradiation effects research and many industrial applications, atomic defect production, ion range, and doping concentration are commonly estimated by the stopping and range of ions in matter (SRIM) code. In this study, ion-induced damage and projectile ranges of low energy Au ions in SiC are determined using complementary ion beam and microscopy techniques. Considerable errors in both disorder profile and ion range predicted by the SRIM code indicate an overestimation of the electronic stopping power, by a factor of 2 in most cases, in the energy region up to 25 keV/nucleon. Such large discrepancies are also observed for slow heavy ions, including Pt, Au, and Pb ions, in other compound materials, such as GaN, AlN, and SrTiO3. Due to the importance of these materials for advanced device and nuclear applications, better electronic stoppin...

Effects of Implantation Temperature on Damage Accumulation in Al-Implanted 4H-SiC

Damage accumulation in 4H–SiC under 1.1 MeV Al22+ irradiation is investigated as a function of dose at temperatures from 150 to 450 K. Based on Rutherford backscattering spectroscopy and nuclear reaction analysis channeling spectra, the damage accumulation on both the Si and C sublattices have been determined, and a disorder accumulation model has been fit to the data. The model fits indicate that defect-stimulated amorphization is the primary amorphization mechanism in SiC over the temperature range investigated. The temperature dependence of the cross section for defect-stimulated amorphization and the critical dose for amorphization indicate that two different dynamic recovery processes are present, which are attributed to short-range recombination and long-range migration of point defects below and above room temperature, respectively. As the irradiation temperature approaches the critical temperature for amorphization, cluster formation has an increasing effect on disorder accumulation, and ion flux ...

Selective plasmonic gas sensing: H2, NO2, and CO spectral discrimination by a single Au-CeO2 nanocomposite film.

A Au-CeO(2) nanocomposite film has been investigated as a potential sensing element for high-temperature plasmonic sensing of H(2), CO, and NO(2) in an oxygen containing environment. The CeO(2) thin film was deposited by molecular beam epitaxy (MBE), and Au was implanted into the as-grown film at an elevated temperature followed by high temperature annealing to form well-defined Au nanoclusters. The Au-CeO(2) nanocomposite film was characterized by X-ray diffraction (XRD) and Rutherford backscattering spectrometry (RBS). For the gas sensing experiments, separate exposures to varying concentrations of H(2), CO, and NO(2) were performed at a temperature of 500 °C in oxygen backgrounds of 5.0, 10, and ∼21% O(2). Changes in the localized surface plasmon resonance (LSPR) absorption peak were monitored during gas exposures and are believed to be the result of oxidation-reduction processes that fill or create oxygen vacancies in the CeO(2). This process affects the LSPR peak position either by charge exchange with the Au nanoparticles (AuNPs) or by changes in the dielectric constant surrounding the particles. Spectral multivariate analysis was used to gauge the inherent selectivity of the film between the separate analytes. From principal component analysis (PCA), unique and identifiable responses were seen for each of the analytes. Linear discriminant analysis (LDA) was also used and showed separation between analytes as well as trends in gas concentration. Results indicate that the Au-CeO(2) thin film is selective to O(2), H(2), CO, and NO(2) in separate exposures. This, combined with the observed stability over long exposure periods, shows the Au-CeO(2) film has good potential as an optical sensing element for harsh environmental conditions.

Growth and structure of epitaxial CeO2 by oxygen-plasma-assisted molecular beam epitaxy

The epitaxial growth of CeO2 films on SrTiO3(001) has been investigated over a wide range of growth parameters using oxygen-plasma-assisted molecular beam epitaxy. The lattice mismatch for CeO2 on SrTiO3(001) is 2.0% (compressive) if the film nucleates with a 45° rotation about [001] relative to the substrate (i.e., CeO2(001)‖SrTiO3(001) and CeO2[110]‖SrTiO3[100]). Pure-phase, single-crystalline epitaxial films of CeO2(001) with the above epitaxial relationship readily grew on SrTiO3(001) for substrate temperatures ranging from 550 to 700 °C. However, small amounts of (111) and (220) minority orientations also nucleated at the higher substrate temperatures. In addition, the film surface was observed to become progressively smoother with increasing substrate temperature due to more extensive island agglomeration. The highest-quality film surface grown at 700 °C is unreconstructed and oxygen terminated.