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CF4 plasma-passivation enhanced size dependence of the blueshift in photoemission and photoabsorption, E2p-level shift, and band-gap expansion of porous silicon has been measured and analyzed numerically based on the recent “bond order-length-strength” correlation [C. Q. Sun, Phys. Rev. B 69, 045105 (2004)]. Matching predictions to the measurements conducted before and after fluorination reveals that fluorination further enhances both the crystal binding intensity that determines the band gap and core level shift and the electron-phonon coupling that contributes to the energies of photoemission and photoabsorption. This approach enables us to discriminate the effect of surface-bond contraction from the effect of surface-bond nature alteration on the unusual behavior of photons, phonons, and electrons in nanosolid Si.

Dielectric impedance measurements of porous silicon within the frequency range of 50 Hz–1.0 MHz and temperature range of 298–798 K revealed three semicircles in a Cole–Cole plot when the temperature is raised to 773 K; they are thought to correspond to contributions from the grain interior, grain boundary, and electrode/film interface, respectively. The enhancement in conductivity by heating follows an Arrhenius law with an activation energy transition from 0.07 to 0.79 eV at ∼565 K, which originates from band tail hopping that occurs around the Fermi edge. At a critical temperature, a high degree of dispersion in the real and imaginary parts of the permittivity also occurs at low frequencies. This dispersion behavior is interpreted as a combination of electron-lattice polarization associated to the band tail hopping and the crystal field weakening due to thermal expansion.

Hybrid graphene and carbon nanotube (CNT) field emitters were fabricated with electrophoretic deposition (EPD). The combination of both materials was used to improve the turn-on field for pure carbon nanotubes emitters and the reliability of pure graphene emitters deposited by the same method. The CNT was envisioned to hold down the graphene flakes, like a safety belt or Velcro, at high voltages to prevent an early short circuit at relatively low voltages. These hybrid emitters were studied for their field emission performance in relation to the EPD deposition duration. It was observed that the emitters performed better when the EPD duration was increased due to the increase in the amount and density of graphene flakes. Possible reasons for the improvement of field emission performance were suggested. The roles of graphene and CNT in these hybrid emitters were also discussed.

Large area graphene field emitters were fabricated using electrophoretic deposition. By varying the deposition time, we were able to fabricate emitters with varied field enhancement factors. The turn-on field increased when the deposition time increased, and it was observed that a monolayer of graphene flakes covered on the substrate gave the best results. The low emission turn-on field obtained from the graphene field emitters was attributed to the random orientation of graphene flakes which give protruded edges that acted as field enhancing spots. Graphene emitters produced by this method present a low cost cold cathode that can be mass produced.

Correlation between the elastic modulus (B) and the Raman shift (Δω) of TiO2 and their responses to the variation of crystal size, applied pressure, and measuring temperature have been established as a function depending on the order, length, and energy of a representative bond for the entire specimen. In addition to the derived fundamental information of the atomic cohesive energy, binding energy density, Debye temperature and nonlinear compressibility, theoretical reproduction of the observations clarified that (i) the size effect arises from the under-coordination induced cohesive energy loss and the energy density gain in the surface up to skin depth; (ii) the thermally softened B and Δω results from bond expansion and bond weakening due to vibration; and, (iii) the mechanically stiffened B and Δω results from bond compression and bond strengthening due to mechanical work hardening. With the developed premise, one can predict the changing trends of the concerned properties with derivatives of quantita...

Although the physics behind the bulk modulus, B(T,P), as a function of temperature (T) and pressure (P), has been intensively investigated, an atomic scale understanding of this attribute remains a high challenge. Here, we show that the B(T,P) for BaXO3 (X=Ti,Zr,Nb) can be established by connecting the B directly to the bond length and bond energy and their response to the applied T and P in the form of binding energy density, B[E/d3(T,P)]. Besides an estimation of the Debye temperature and single bond energy, outcomes clarified that the thermally softened B arises from bond expansion and bond weakening due to lattice vibration and the mechanically stiffened B results from bond compression and bond strengthening due to mechanical work hardening.

Although the size- and shape-induced blueshift in the photoluminescence and photoabsorption of nanostructured ZnO has been extensively investigated, the underlying mechanism remains yet unclear. Here we show that theoretical reproduction of the observed trends clarifies that the blueshift originates from the Hamiltonian perturbation due to the broken-bond-induced local strain and quantum trapping and electron-phonon coupling in the surface skin up to two atomic layers in depth while bonds in the core interior retain their bulk nature. The extent of the blue shift depends on the tunable fraction of undercoordinated atoms in the surface skin. Therefore, the quantum confinement effect is indeed more “superficial” than first thought [H. Winn, OE Mag. 8, 10 (2005)].

The thermally induced softening of the elastic and vibronic identities in crystals and their correlations have long been a puzzle. Analytical solutions have been developed, showing that the detectable elastic and vibronic properties could be related directly to the bonding parameters, such as bond length and strength, and their response to the temperature change. Reproduction of measured T-dependent Young’s modulus and Raman shift of Si, Ge, and diamond reveals that the thermally driven softening of the elasticity and the optical Raman frequency arises from bond expansion and vibration, with derived information about the atomic cohesive energy and clarification of their interdependence.

Electrosorption of ions from aqueous solutions with carbon nanotubes and nanofibers (CNTs-CNFs) composite film electrodes has been demonstrated. The large area CNTs-CNFs film was directly grown on Ni plate by low pressure and low temperature thermal chemical vapor deposition. The CNTs-CNFs electrodes have great advantages such as low cost, easy operation, long-term reproducibility, and integrity of monolithic CNTs-CNFs film and current collector. Batch-mode experiments at low voltage (0.4–2V) were conducted in a continuously recycling system to investigate the electrosorption process. Purification of water with good reproducibility was achieved because of optimal pore size distribution of CNTs-CNFs composite films.