Strength of hydrogen bonds of water depends on local environment J. Chem. Phys. 136, 144305 (2012) Modeling of an ionic liquid electrospray using molecular dynamics with constraints J. Chem. Phys. 136, 124507 (2012) Epitaxial oxide bilayer on Pt (001)
The removal of single atomic layers from multi-layer graphene using a He plasma is reported. By applying sample biases of -60 and +60 V during He plasma exposure, layer removal is found to be due to electrons instead of He ions or neutrals in the plasma. The rate of layer removal depends on exposure time, sample bias and pre-annealing treatments. Optical contrast microscopy and atomic force microscopy studies show that the removal of C atoms occurs approximately one layer at a time across the entire multi-layer sample with no observable production of large pits or reduction in lateral dimensions. Layer removal is proposed to arise from the electron-stimulated dissociation of C atoms from the basal plane. This process differs from plasma techniques that use reactive species to etch multi-layer graphene.
Individualized instruction and differentiation are fundamental concepts of the Dalcroze approach to music education. Émile Jaques-Dalcroze believed that students learn to be musical by different modalities. His three core branches, eurhythmics, rhythmic solfège, and improvisation, are intertwined with active listening, positive self-expression, and joy to create a learning environment that fuels music creativity. His followers continued his work by developing lessons, clarifying concepts, and sharing knowledge. This article offers insight to Jaques-Dalcroze’s background, a description of the three core branches, and a scaffolded lesson based on Dalcroze’s approach to student-centered music education.
Due to their unique electronic and structural properties, multi-walled carbon nanotubes (MWCNTs) have been extensively studied as candidate materials for cold-cathode electron sources [1]. Plasma-enhanced chemical vapor deposition (PECVD) is a promising method for growing well-aligned MWCNTs. We report here the use of electron microscopy techniques to study the morphology and internal structures of nanotubes synthesized by PECVD in comparison to those synthesized by a thermal CVD method.In this experiment, nanotubes were synthesized on silicon substrates coated with a 15 nm TiN barrier layer. The TiN layer prevents the diffusion and reaction of Ni catalyst with the silicon substrate, which would result in reduced CNT yield. A Ni thin film with a thickness of 10 nm was prepared by a sputtering physical vapor deposition method. After the deposition of the catalyst thin film, the substrates were heated to 725°C and exposed to 50 sccm of C 2 H 2 and 200 sccm of NH 3 gases in a CVD or PECVD chamber for approximately 10 min. During this process, the Ni thin film was first transformed into Ni nanoparticles and then served as a catalyst for the CNT growth. The introduction of C 2 H 2 provides a carbon source, while the NH 3 prevents the deposition of amorphous carbon. An FEI Sirion field emission SEM and a Tecnai F-20 field emission TEM/STEM equipped with an energy-dispersive x-ray (EDX) were used to characterize the morphology and internal structures of the synthesized nanotubes.In comparison to the thermal CVD process, the significant difference in the PECVD method is that the silicon substrate was biased by a negative potential of 630 V to form glow discharge plasma. As demonstrated in Fig. 1, nanotubes synthesized by thermal CVD were curly and randomly oriented. The CNTs formed by PECVD were well aligned in a vertical configuration as shown in Fig. 2. This suggests that the electric field in the plasma caused nanotubes to grow along the electric field direction. Another difference is the shapes of the tube tips. The nanotubes made by thermal CVD terminated with an irregular shape while the tube tips made by PECVD have a more uniform shape as indicated in the insets of Fig. 1 and Fig. 2, respectively. High resolution TEM images of typical CNTs grown by PECVD are shown in Fig. 3 and Fig. 4. Note that the Ni catalyst was located at the tip of CNTs. The tip-growth mechanism is favored because of the plasma electrostatic force making the Ni nanoparticle detached from the TiN diffusion barrier [2]. The internal structures of the PECVD tubes display bamboo-like fringes characterized by periodic curving graphitic bands normal to the tube axis. Small Ni particles are also observed inside the nanotubes, as demonstrated by the STEM image in Fig. 5. The EDX line scan results in Fig. 6 clearly demonstrate the presence of a small Ni particle inside the main body of the nanotube and a large Ni particle within the nanotube tip region.It is clear that PECVD provides a more desirable and effective method for the synthesis of vertical...
Carbon nanotube field emitters (CNTs) are considered as electron sources in vacuum microelectronic devices [l]. They can be deposited on catalytic surfaces in aligned or random fashion or mixed with media such as printable inks [2]. At present, CNTs can only be fabricated in small volumes and are very expensive.We are investigating carbon black and carbon blackisilica as alternatives to CNTs. These materials are very inexpensive and can be produced in large quantities. Initial experiments concentrated on pressing carbon black and carbon blackisilica powders into pellets and gluing them onto copper coated silicon wafers, or suspending them into isopropanol and depositing drops onto the copper coated substrates. Field emission, with extraction fields ranging from 2-10 V/pm, was obtained from these samples, with the shape of the I-V curves very similar to Fig. 6.13 in [I] for single wall CNTs. They consist of an initial Fowler-Nordheim (F-N) region, followed by a saturation region, followed by a second F-N region. Adhesion of these films to the substrate was poor and delamination occurred in many instances at elevated fields of >10 V/pm.To improve adhesion, we mixed these powders with Shipley Microposit S1818 positive photoresist and spun or sprayed the material onto copper coated silicon substrates and cured the films at 120 "C in air for 10 minutes. Prior to emission testing, the resistance of the film was checked in the vertical direction to ensure sufficient supply of electrons to the top emitter surface/vacuum interface. We also prepared some samples by mixing untreated diesel exhaust, collected at the rim of the exhaust tube of a truck, with S1818.Electron emission was obtained from all of the samples with initial turn-on fields ranging from 6 -15 V/pm. After annealing the samples in vacuum at 120 "C for 30 minutes, the turn-on fields shifted to lower values reaching, in some cases, 2 -4 V/pm. The untreated diesel exhaust emitters reached values of about 6 V/pm. Macroscopic current densities of about 3 mA/cm2 were reached (0.2 mA maximum currents collected by the 3 mm diameter anode). To compare these results with CNTs, we mixed CNTs with S1818 and prepared the films in a similar manner as the CIS1818 and CISiO2IS1818 samples. Very similar results were obtained, with the CNTIS1818 films exhibiting turn-on fields of about 3 V/pm. The shapes of the I-V curves are similar to the published CNT results [I] and to the above mentioned pressed and isopropanol drop samples. We conclude that the photoresist acts mainly as an adhesion promoter of the films to the substrates. Careful measurements of the I-V curves with increasing and decreasing fields show that the initial F-N type increase in the I-V curve is maintained, indicating that desorption of impurities does not take place. It is conjectured that the observed saturation effects are due to resonant tunneling. Figures 1-4 show SEM micrographs of some of the emitters. Figure 5 shows emission results at room temperature and Figure 6 at 120 "C.Results will also be pre...
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