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This work aims to propose a promising locally resonating system consisting of a tensioned elastic membrane and two-arch masses attached on the membrane surface. Traditional membrane-type resonators, which usually create one obvious attenuation zone at low frequencies, might not be efficient in multi-frequency vibration suppression. The proposed structure can produce an extra clear flexural attenuation region and shift bandgap frequencies below 300 Hz. By adjusting geometric parameters (thickness, width, and location) of the arch mass, the bandgap region can be tuned. Introducing a feasible analytical model for accurately predicting the first and second initial frequencies of the bandgaps for a beam structure containing membrane-arch-mass resonators is another focus of this study. The proposed theoretical framework can be used to tune the bandgap to different target frequency ranges without knowing the actual width of the bandgap. Finite-element analysis and experiments are conducted to verify the theoretical predictions. A good agreement is seen among the theoretical, finite-element analysis, and experimental results. In addition, adjacent cells with different arch-mass distributions can generate two pairs of flexural bandgaps, increasing the practicality in engineering applications. The proposed structure might be used in low-frequency vibration isolation and filters.

Fluid-coupled Lamb waves (LWs) were proposed to facilitate the self-assembling of three-dimensional (3D) photonic crystals (PCs) in this work. Numerical models were constructed for proof-of-concept, and a fabrication set-up was developed for experimental demonstration. LWs were initially generated by a piezoelectric substrate. A couplant altered the propagating direction of these LWs to form the fluid-coupled LWs at a superstrate. The coffee-ring effect (CRE) of a suspension droplet on the superstrate was thus suppressed. The suspended nanospheres formed 3D PCs after the droplet dried out. Diversified PCs were fabricated using the developed set-up. Their transmittance spectra demonstrated the corresponding bandgap clearly. Advantages of utilizing fluid-coupled LWs for self-assembling 3D PCs include flexibility in excitation frequency, fabrication cost-effectiveness, acceptance for a passively oscillating substrate, and enlargement of sample area.

This study investigates the bandgap tunability of a metashaft with periodic shunted piezoelectric rings. An analytical model based on the Bloch theory and the transfer matrix technique is developed to predict bandgap characteristics and the transmission of torsional vibration in the proposed structure. The location and width of the bandgap can be easily tailored by altering the electric parameters of shunt circuits. Compared with other shunt assemblies, the use of the negative capacitance resonant shunt enables the creation of a lower bandgap with a relatively wide bandwidth. Bandgap frequencies have a strong dependency on the inductance and capacitance but not on resistance. Moreover, the frequency with an unbounded loss factor coincides with the one of maximum attenuation. Multiple bandgaps can be achieved by adding extra sets of shunt circuits to the metashaft. Theoretical results have been validated by comparing them with finite element results. Our findings provide feasible guidelines in the design of torsional active control systems.

This study introduces a novel framework for local resonant systems to low bandgap frequencies without greatly increasing spatial penalties in grid structures. The proposed double-spiral resonator (DSR) consists of a pair of spiral spring-like structures and a rigid plate acting as the “mass” of the oscillating system, which can serve as an effective mechanical filter. A rapid and accurate calculation based on the stiffness matrix method is proposed to precisely predict the fundamental resonant frequency of the resonator. Periodic installation of these resonators in a grid-like beam structure can lead to the formation of a new type of metastructure that possesses negative effective properties. Investigations on the bandgap characteristics of the proposed metastructure are conducted using the finite element method. It is found that a low-frequency resonant-type bandgap is present in such a structure. Changing the thickness of the central mass or the number of parasitic beam segments enables the manipulation of the bandgap location. The validity of the analytical results is evaluated via comparison with the finite element results and experimental measurements. By using multiple resonators with similar resonance frequencies, the attenuation bandwidth can be effectively broadened. The physics behind wave attenuation can be realized by introducing a negative effective mass density. The results demonstrate that the proposed structure exhibiting unique dynamic characteristics can successfully attenuate undesired structural vibrations at low frequencies. It may be concluded that this DSR can be used as an alternative to current vibration filtering systems.

Photoconduction (PC) properties in the ZnO films with the (110) nonpolar surface (a-plane) epitaxially grown by chemical vapor deposition on the LiGaO2 (010) substrates with low lattice mismatches (4.0% along the c-axis and 3.8% along the m-axis) have been studied. The structural and optical qualities of the epitaxial films have been characterized using theta-two theta and phi scans, X-ray diffraction, rocking curve, and photoluminescence measurements. The nonpolar ZnO film exhibits a near visible-blind ultraviolet photoresponse. The optimal photocurrent to dark current ratio (i.e., sensitivity) can reach 13360%. The responsivity of the a-plane ZnO photoconductor-type detector can also reach 17 AW−1, which is two to four orders of magnitude higher than those of the m-plane, a-plane, and r-plane photodiodes based on ZnO/ZnMgO quantum wells. The normalized gain at 2.9 cm2V−1 of the nonpolar film is also comparable with the optimal recorded value of the ZnO nanowires. In addition, the PC mechanism has also b...

RuO2 nanometer-sized rods with pyramidal tips have been grown on Cu-coated Si(100) substrates using metalorganic chemical vapor deposition. The geometry of these nanorods resembles an obelisk with an off-center tip. The aspect ratios of nanorod tips are between 0.55 and 0.73. The field emission properties of the RuO2 nanorods are studied and the stability of its emission current is assessed. The field emission results demonstrate that RuO2 nanorods material is an emitter of potential.

We report on the preparation and field-emission properties of vertically aligned conductive IrO2 nanorods. The unique geometrical features of IrO2 nanorods, including nanosized structure and self-assembled sharp tip, exhibit a strong effect on field enhancement (β∼40 000), which result in a low threshold field (Eth∼0.7 V/μm) defined at the beginning of emission. A low turn-on field for driving a current of 10 μA/cm2 is about 5.6 V/μm, which is comparable with the carbon nanotube, diamond, and amorphous carbon. The potential of using IrO2 nanorods as an emitter material has been demonstrated.

We report a method for fabrication of continuous, conformal, ultrathin (i.e., 15–30 nm) Cu films using a room temperature, aqueous-based, electroless deposition technique on silica and polymer planarizer surfaces. The Cu films are sufficiently homogeneous, electrically conductive, and optically transparent for use as resist discharge layers during e-beam patterning of the substrate. The grounded Cu film, deployed here as a resist underlayer, eliminates the 0.1–0.4 μm subfield stitching errors normally observed in the absence of the Cu film during resist patterning on a glass or insulating substrate. The Cu is readily removed using a nitric acid wet etch following patterning.

We report the development of an imaging layer technology for 50 kV electron-beam lithography based upon the displacement of noncovalently bound amine ligands from a siloxane host film. The patterned films were used as templates for the selective deposition of an electroless nickel film resulting in a positive tone imaging mechanism. The deposited nickel was sufficiently robust to function as an etch mask for pattern transfer by reactive ion etching. Metallized and etched patterns with linewidths to approximately 40 nm are demonstrated using an exposure dose of 500 μC/cm2.

The photoconduction (PC) properties of single-crystalline titanium dioxide (TiO2) nanorods (NRs) with anatase phase were investigated and compared. By examining the material's inherent properties, the anatase TiO2 NRs exhibit superior PC efficiency (quantitatively defined by normalized gain) which is near one order of magnitude higher than that of the rutile ones. The optimal photoconductive gain of the anatase NR device can also reach 1.6 × 107 at the light intensity of 0.02 Wm−2 and a low bias of 0.1 V. The power-dependent and time-resolved PC measurements were performed to investigate the physical mechanisms. The higher quantum efficiency and mobility product was confirmed to be responsible for the higher PC efficiency in the anatase TiO2 NRs in comparison to the rutile ones.

The electronic transport properties in individual niobium disulphide (NbS2) nanoflakes mechanically exfoliated from the bulk crystal with three rhombohedral (3R) structure grown by chemical vapor transport were investigated. It is found that the conductivity values of the single-crystalline nanoflakes are approximately two orders of magnitude lower than that of their bulk counterparts. Temperature-dependent conductivity measurements show that the 3R-NbS2 nanoflakes exhibit semiconducting transport behavior, which is also different from the metallic character in the bulk crystals. In addition, the noncontinuous conductivity variations were observed at the temperature below 180 K for both the nanoflakes and the bulks, which is attributed to the probable charge density wave transition. The photoconductivities in the semiconducting nanoflakes were also observed under the excitation at 532 nm wavelength. The probable mechanisms resulting in the different transport behaviors between the NbS2 nanostructure and bulk were discussed.

The photoconduction (PC) efficiencies of various single-crystalline metal oxide semiconductor nanowires (NWs) have been investigated and compared based on the materials' inherent properties. The defined PC efficiency (normalized gain) of SnO2 NWs is over one to five orders of magnitude higher than that of its highly efficient counterparts such as ZnO, TiO2, WO3, and GaN. The inherent property of the material allowed the photoconductive gain of an SnO2 single-NW photodetector to easily reach 8 × 108 at a low bias of 3.0 V and a low light intensity of 0.05 Wm−2, which is the optimal reported value so far for the single-NW photodetectors. The probable physical origins, such as charged surface state density and surface band bending, that caused the differences in PC efficiencies and carrier lifetimes are also discussed.

The normalized gains, which determines the intrinsic photoconduction (PC) efficiencies, have been defined and compared for the gallium nitride (GaN) nanowires (NWs) grown by chemical vapor deposition (CVD) and molecular beam epitaxy (MBE). By excluding the contributions of experimental parameters and under the same light intensity, the CVD-grown GaN NWs exhibit the normalized gain which is near two orders of magnitude higher than that of the MBE-ones. The temperature-dependent time-resolved photocurrent measurement further indicates that the higher photoconduction efficiency in the CVD-GaN NWs is originated from the longer carrier lifetime induced by the higher barrier height (ϕB = 160 ± 30 mV) of surface band bending. In addition, the experimentally estimated barrier height at 20 ± 2 mV for the MBE-GaN NWs, which is much lower than the theoretical value, is inferred to be resulted from the lower density of charged surface states on the non-polar side walls.

We demonstrate an on-chip silicon-based active photonic molecule (PM) structures formed by two coupled photonic quantum dots with complete photonic bandgap (PBG) light confinement. The photonic quantum dots are grown by conformal deposition of amorphous silicon nitride multilayers on patterned substrates. A fine structure of the coupled optical modes in PMs has been observed which shows similarity to the electronic bonding (BN) and antibonding (ABN) states in a molecule.

We demonstrate that Ag–Si photodiodes allow photocurrents to be modulated by changing periods of nanopatterns on Ag film. The maximum and minimum photocurrents occur in certain periods corresponding to the excitation of surface plasmon polariton and Wood’s anomaly, which can be predicted with the help of related theories. Therefore, it is feasible to design nanopatterns to satisfy special requirements.

We report on the photoconductivity study of the individual infrared-absorbing indium nitride (InN) nanowires. Temperature-dependent dark conductivity measurement indicates the semiconducting transport behavior of these InN nanowires. An enhanced photosensitivity from 0.3 to 14 is observed by lowering the temperature from 300to10K. A calculated ultrahigh photoconductive gain at around 8×107 at room temperature is obtained from the low-bandgap nitride nanowire under 808nm excitation.

The size effects on both the photoconductivity and dark conductivity have been observed in m-axial GaN nanowires grown by chemical vapor deposition (CVD). For these nanowires with diameters at 50–130 nm, the products of carrier lifetime (τ) and mobility (μ) derived from the photocurrent measurements are typically at (2–8)×10−1 cm2/V, which are over two orders of magnitude higher than the maximal reported values [τμ=(1–5)×10−4 cm2/V] for their thin film counterparts. A significant decrease of τμ value at diameter below the critical values (dcrt) at 30–40 nm is observed. Similar size dependence is also found from the dark conductivity study. The temperature-dependent measurements further indicate two different thermal activation mechanisms in GaN nanowires with sizes above and below the dcrt. These results suggest a surface-dominant transport property in GaN nanowires both in dark and under light illumination due to the presence of surface depletion and band bending. Probable reasons leading to the smaller ...

Huge photocurrent gains with a value of 10 000 detected in air and 100 000 detected in vacuum have been obtained from SnO2 nanowires. Unlike previous reports that emphasized on carrier trapping by charge oxygen molecules in metal oxide nanostructures, we point out that spatial separation of photoexcited electrons and holes due to built-in electric field induced by surface charge defects does plays a significant role especially for nanostructured materials with a large surface-to-volume ratio. The study shown here provides a useful guideline to achieve photodetectors based on nanostructured materials with high sensitivity.

An ultrahigh photocurrent gain has been found in the ultraviolet-absorbed GaN nanowires with m-directional long axis grown by chemical vapor deposition. The quantitative results have shown the gain values at 5.0×104–1.9×105 of the GaN nanowires with diameters from 40to135nm are near three orders of magnitude higher than the values of 5.2×101–1.6×102 estimated from the thin film counterparts. The intensity-dependent gain study has shown that the gain value is very sensitive to the excitation intensity following an inverse power law and no gain saturation observed in this investigated intensity range from 0.75to250W∕m2. This behavior has strongly suggested a surface-dominant rather than trap-dominant high gain mechanism in this one-dimensional nanostructure. The strong carrier localization effect induced by the surface electric field in the GaN nanowires is also discussed.

An approach was proposed to achieve Si-based three-dimensional optical microcavities, in which photons were confined by Bragg reflectors in all dimensions instead of the lateral confinement by using total internal reflection. Size-dependent photonic energy modes were observed when the lateral size is changed from 4.5to1.5μm. With decreasing lateral size the modes shift to higher energies, and the splitting between the modes increases which indicates that the three-dimensional optical microcavity looks like photonic quantum dots. The observed discrete optical eigenmodes show a quantitative agreement with numerical calculations of quantized photon states in photonic quantum dots.

Electronic structures of the nanorods of RuO2 and IrO2 metallic oxides were investigated by x-ray absorption near-edge structure (XANES) and scanning photoelectron microscopy (SPEM). O K-, Ru, and Ir L3-edge XANES results reveal that hybridization between O 2p and metal t2g orbitals is weaker in IrO2 than in RuO2. The enhancement of the tip-region SPEM intensities relative to those in the sidewall regions for both RuO2 and IrO2 nanorods is found to extend over a large energy range in contrast to those of carbon nanotubes and ZnO nanorods, which are confined to deep below and near the Fermi level, respectively.

Luminescent amorphous silicon nitride films were fabricated by plasma-enhanced chemical vapor deposition at room temperature followed by thermal oxidation at 100°C. Very bright green emissions were clearly observed with the naked eye in a bright room after the samples had been oxidized. The emission peak is located at 495nm. Fourier-transform infrared absorption spectra and results of depth profiling with x-ray photoelectron spectroscopy indicate that the introduction of oxygen is of a key role in enhancing the photoluminescence intensity of the films. Emission and excitation spectra analyses suggest that the green emission is originated from the radiative recombination in the localized states related to the Si–O bonds.

We report Raman scattering and field emission properties of rutile RuO2 nanorods obtained by metalorganic chemical vapor deposition. The RuO2 nanorods have lengths up to several micrometers and diameters in the range of 10–50 nm. The nanosize dependencies of the peak shift and the broadening of the three first-order Raman modes agree well with those calculated on the basis of the phonon confinement model. The unique geometrical features of RuO2 nanorods exhibit a strong effect on field enhancement (β∼1153), which results in a low threshold field (Eth∼4.9V∕μm) defined at the beginning of emission. The low turn-on field for driving a current of 10μA∕cm2 is about 10.3V∕μm, which is comparable with amorphous carbon film. Our results indicate that RuO2 nanorods provide an excellent alternative for field emitter due to several advantages, including nanometer structure, natural conductor, enhanced resistance to oxidation, and long-term stability.