Bound states in the continuum in metal-dielectric photonic crystal with a birefringent defect

By using the difference of the band structure for the TE and TM waves in the metal-dielectric photonic crystals beyond the light cone and the birefringence of the anisotropic crystal,a one-dimensional photonic system is constructed to realize the bound states in the continuum(BICs).In addition to the BICs arising from the polarization incompatibility,the Friedrich-Wintgen BICs are also achieved when the leaking TM wave is eliminated due to the destructive interference of its ordinary and extraordinary wave components in the anisotropic crystal.A modified scheme favorable for practical application is also proposed.This scheme for BICs may help to suppress the radiation loss in the metal-dielectric photonic crystal systems.

Fabricating multifunctional polymeric nanofilm capable of resisting corrosion and activating copper surface by electrochemical and hydrolysis-condensation approach

A multifunctional polymeric nanofilm of triazinedithiolsilane monosodium salt, which can resist corrosion and activatecopper surface concurrently, was prepared by galvanostatic technique and the following hydrolysis-condensation approach.Electrochemical tests were carried out to evaluate the resistant ability of nanofilm. The changes of functional groups atop thenanofilms were monitored with Fourier transform infrared spectroscopy （FT-IR） and contact angles （CA） simultaneously. Thechemical composition and the morphology of the polymeric nanofilm were investigated by X-ray photoelectron spectroscopy （XPS）and scanning electron microscope （SEM）, respectively. The results reveal that the preferentially developed disulfide units protect thecopper during the whole preparation process, and the subsequently hydrolyzed nanofilms without/with heating shape into newinterface phases bearing the multifunctionality. This multifunctional interface （the polymeric nanofilm on copper surface） opens upthe possibilities for other OH-containing reagents to be anchored onto copper surface in demanding researches or industrialapplications.

On the role of piezoelectricity in phonon properties and thermal conductivity of GaN nanofilms

The effect of piezoelectricity on phonon properties and thermal conductivity of gallium nitride （GaN） nanofilms is theoretically investigated. The elasticity model is utilized to derive the phonon properties in spatially confined GaN nanofilms. The piezoelectric constitutive relation in GaN nanofilms is taken into account in calculating the phonon dispersion relation. The modified phonon group velocity and phonon density of state as well as the phonon thermal conductivity are also obtained due to the contribution of piezoelectricity. Theoretical results show that the piezoelectricity in GaN nanofilms can change significantly the phonon properties such as the phonon group velocity and density of states, resulting in the variation of the phonon thermal conductivity of GaN nanofilms remarkably. Moreover, the piezoelectricity of GaN can modify the dependence of thermal conductivity on the geometrical size and temperature. These results can be useful in modeling the thermal performance in the active region of GaN-based electronic devices.

Effects of surface charges on phonon properties and thermal conductivity in GaN nanofilms

Surface charges can modify the elastic modulus of nanostructure,leading to the change of the phonon and thermal properties in semiconductor nanostructure.In this work,the influence of surface charges on the phonon properties and phonon thermal conductivity of GaN nanofilm are quantitatively investigated.In the framework of continuum mechanics,the modified elastic modulus can be derived for the nanofilm with surface charges.The elastic model is presented to analyze the phonon properties such as the phonon dispersion relation,phonon group velocity,density of states of phonons in nanofilm with the surface charges.The phonon thermal conductivity of nanofilm can be obtained by considering surface charges.The simulation results demonstrate that surface charges can significantly change the phonon properties and thermal conductivity in a GaN nanofilm.Positive surface charges reduce the phonon energy and phonon group velocity but increase the density of states of phonons.The surface charges can change the size and temperature dependence of phonon thermal conductivity of GaN nanofilm.Based on these theoretical results,one can adjust the phonon properties and temperature/size dependent thermal conductivity in GaN nanofilm by changing the surface charges.

Different effects of grain boundary scattering on charge and heat transport in polycrystalline platinum and gold nanofilms

The in-plane electrical and thermal conductivities of several polycrystalline platinum and gold nanofilms with different thicknesses are measured in a temperature range between the boiling point of liquid nitrogen （77K） and room temperature by using the direct current heating method. The result shows that both the electrical and thermal conductivities of the nanofilms reduce greatly compared with their corresponding bulk values. However, the electrical conductivity drop is considerably greater than the thermal conductivity drop, which indicates that the influence of the internal grain boundary on heat transport is different from that of charge transport, hence leading to the violation of the Wiedemann-Franz law. We build an electron relaxation model based on Matthiessen＇s rule to analyse the thermal conductivity and employ the Mayadas ＆ Shatzkes theory to analyse the electrical conductivity. Moreover, a modified Wiedemann-Franz law is provided in this paper, the obtained results from which are in good agreement with the experimental data.

Preparation and Tribological Investigation of Rare Earth Nanofilm on Single-Crystal Silicon Substrate

The self-assembled silicon substrate. The resultant contact angle meter and atomic method was introduced to successfully obtain film was characterized by means of X-ray rare earth（RE） nanofilm on a single-crystal photoelectron spectroscopy （XPS）, ellipsometer, force microscopy （AFM）. The scratch experiment was performed for interfacial adhesion measurement of the RE film. The friction and wear behavior of RE nanofilm was examined on a DF-PM reciprocating friction and wear tester. The results indicate the RE nanofilm is of low coefficient of friction （COF） and high wear resistance. These desirable characteristics of RE nanofilm together with its nanometer thickness, strong bonding to the substrate and low surface energy make it a promising choice as a solid lubricant film in micro electromechanical system （MEMS） devices.

Frequency Dispersion of Love Waves in a Piezoelectric Nanofilm Bonded on a Semi-infinite Elastic Substrate

Research on the propagation of elastic waves in piezoelectric nanostructures is very limited. The frequency dispersion of Love waves in layered piezoelectric nanostructures has not yet been reported when surface effects are taken into account. Based on the surface elasticity theory, the propagation of Love waves with surface effects in a structure consisting of a nanosized piezoelectric film and a semi-infinite elastic substrate is investigated focusing on the frequency dispersion curves of different modes. The results show that under the electrically-open conditions, surface effects give rise to the dependence of Love wave dispersion on the film thickness when the thickness of the piezoelectric film reduces to nanometers. For a given wave frequency, phase velocity of Love waves in all dispersion modes exhibit obvious toward shift as the film thickness decreases or the surface parameters increase. Moreover, there may exist a cut-off frequency in the first mode dispersion below which Love waves will be evanescent in the structure due to surface effects. The cut-off frequency depends on the film thickness, the surface parameters and the bulk material properties.

Structure and dynamics of ordered water in a thick nanofilm on ionic surfaces

The structure and dynamics of water in a thick film on an ionic surface are studied by molecular dynamic simulations. We find that there is a dense monolayer of water molecules in the vicinity of the surface. Water molecules within this layer not only show an upright hydrogen-down orientation, but also an upright hydrogen-up orientation. Thus, water molecules in this layer can form hydrogen bonds with water molecules in the next layer. Therefore, the two-dimensional hydrogen bond network of the first layer is disrupted, mainly due to the 0 atoms in this layer, which are affected by the next layer and are unstable. Moreover, these water molecules exhibit delayed dynamic behavior with relatively long residence time compared with those bulk-like molecules in the other layers. Our study should be halpful to further understand the influence of water film thickness on the interfacial water at the solid-liquid interface.

Growth of brass nanofilms sputtered on organic substrate

The growth of brass nanofilms sputtered on acrylics substrate was studied through experimental investigation of the effect of sputtering voltage, target-to-substrate distance, chamber pressure and sputtering time on the content, growth rate and surface morphology of brass nanofilms. The results show that compared with original brass target, Cu content in brass nanofilms changes by no more than 6.23%(mass fraction). High sputtering voltage and short target-to-substrate distance help to improve brass nanofilm deposition rate. There exists an optimal chamber pressure where deposition rate of nanofilm reaches the maximum. The key factor affecting surface morphology is the kinetic energy of sputtering particles. Low sputtering voltage, large target-to-substrate distance and low chamber pressure are very important for the formation of the high-quality brass nanofilms. The brass films prepared under the conditions of sputtering voltage 1.6kV, target-to-substrate distance 2.5cm, chamber pressure 10Pa and sputtering time 20min, possess following characteristics: smooth and uniform surface, thickness of 41nm and Cu content of 71.0%(mass fraction).

Surface saturation control on the formation of wurtzite polytypes in zinc blende SiC nanofilms grown on Si-(100) substrates

We investigate the formations of wurtzite （WZ） SiC nano polytypes in zinc blende （ZB） SiC nanofilms hetero-grown on Si-（100） substrates via low pressure chemical vapor deposition （LPCVD） by adjusting the Si/C ratio of the introduced precursors. Through SEM, TEM, and Raman characterizations, we find that the nanofilms consist of discrete WZ SiC nano polytypes and ZB SiC polytypes composed of WZ polytypes （WZ ＋ ZB） and disordered ZB SiC polytypes, respectively, according to Si/C ratios of 0.5, 1.5, and 3. We attribute the WZ polytype formation to being due to a kinetic mechanism based on the Si/C surface saturation control.

Carrier Density and Plasma Frequency of Alummum Nanofilms

In this work, the prerequisite and mode of electromagnetic response of Al nanof ilms to electromagnetic wave field was suggested. Reflectance, transmittance in infrared region and carrier density of the films was measured. With the carrier density of the films, the dependence of their plasma frequencies on the film thickness was obtained. On the other hand, the dependence of absorptance on the frequency of electromagnetic wave field was set up by using the measured reflectance and transmittance, which provided plasma frequency-film thickness relation as well. Similarity of both plasma frequency-film thickness relations proved plasma resonance as a mode of electromagnetic response in Al nanofilms.

Peptide friction in water nanofilm on mica surface

Peptide frictions in water nanofilms of various thicknesses on a mica surface are studied via molecular dynamics simulations. We find that the forced lateral motion of the peptide exhibits stick-slip behaviour at low water coverage; in contrast, the smooth gliding motion is observed at higher water coverage. The adsorbed peptide can form direct peptide-surface hydrogen bonds as well as indirect peptide-water-surface hydrogen bonds with the substrate. We propose that the stick-slip phenomenon is attributed to the overall effects of direct and indirect hydrogen bonds formed between the surface and the peptide.

Microstructure and UV Fluorescence of Amorphous I/Au Composite Nanofilms Based on LVDCS Method

The amorphous I/Au composite nanofilms were prepared by low vacuum direct current sputtering(LVDCS) method. The optimized preparation technologies contain growth pressure, time, gaseous environment and annealing conditions. The maximum fluorescence emission(λemmax) of I/Au nanofilms was observed at wavelength of 375 nm, and the intensity of fluorescence emission peak of annealed I/Au films was smaller than that of unannealed one due to fewer amorphous Au nanoparticles, caused by annealing treatment. In the UV-Vis absorption spectra, the intensity of UV-Vis absorption peak of annealed I/Au nanofilms is larger than that of the unannealed one. This work also developed a new way to grow I/Au composite fluorescent thin films.

Influence of surface scattering on the thermal properties of spatially confined GaN nanofilm

Gallium nitride（GaN）, the notable representative of third generation semiconductors, has been widely applied to optoelectronic and microelectronic devices due to its excellent physical and chemical properties. In this paper, we investigate the surface scattering effect on the thermal properties of GaN nanofilms. The contribution of surface scattering to phonon transport is involved in solving a Boltzmann transport equation（BTE）. The confined phonon properties of GaN nanofilms are calculated based on the elastic model. The theoretical results show that the surface scattering effect can modify the cross-plane phonon thermal conductivity of GaN nanostructures completely, resulting in the significant change of size effect on the conductivity in GaN nanofilm. Compared with the quantum confinement effect, the surface scattering leads to the order-of-magnitude reduction of the cross-plane thermal conductivity in GaN nanofilm. This work could be helpful for controlling the thermal properties of Ga N nanostructures in nanoelectronic devices through surface engineering.

New Method of Thermal Energy—To Electrical Energy Conversion in Vacuum Devices with the Metal—Dielectric Nanofilm Electron Sources

New method of thermal energy—to electrical energy conversion in vacuum devices with the metal (W)—dielectric nanofilm (ZrO2) electron source is offered and studied. According to estimates and results of modeling, the energy effectiveness (χ) of the proposed method may exceed χ for the known thermionic energy conversion method to 2 - 3 orders of magnitude.

Rolling structure from bilayer nanofilm by mismatch

A continuum theoretical scheme for self-rolling nanotubes from bilayers by mismatch is obtained by considering surface elasticity,surface stress,and symmetry lowering effects.For an ultrathin nanofilm with only several nanometers in thickness,isotropic mismatch,and isotropic surface stress usually induce anisotropic rolling behavior.The isotropic Timoshenko formula should be modified anisotropically to explain the mechanical behavior of anisotropic rolling structure of nanotubes accurately.The nanofilm rolls up in tangential direction while remaining straight in cylindrical direction theoretically.Therefore,in this paper the anisotropic shape of nanotubes is taken into consideration.Along the cylindrical direction,although it maintains straight and its residual strain is uniform,the stress varies in the radial direction due to the Poisson's effect of tangential strain.The results of the current theory applied to Si-Si nanotube,InAs-GaAs nanotube,and InGaAs-Cr nanotube systems show good agreement with the experimental data.Beside the surface elasticity effect and surface stress effect,the symmetry breaking and the anisotropic rolling structure are of great importance in theoretically describing the mechanical behavior of rolling-up of nanotubes.

Molecular dynamics study on the dependence of thermal conductivity on size and strain in GaN nanofilms

The thermal conductivity of GaN nanofilm is simulated by using the molecular dynamics(MD)method to explore the influence of the nanofilm thickness and the pre-strain field under different temperatures.It is demonstrated that the thermal conductivity of GaN nanofilm increases with the increase of nanofilm thickness,while decreases with the increase of temperature.Meanwhile,the thermal conductivity of strained GaN nanofilms is weakened with increasing the tensile strain.The film thickness and environment temperature can affect the strain effect on the thermal conductivity of GaN nanofilms.In addition,the analysis of phonon properties of GaN nanofilm shows that the phonon dispersion and density of states of GaN nanofilms can be significantly modified by the film thickness and strain.The results in this work can provide the theoretical supports for regulating the thermal properties of GaN nanofilm through tailoring the geometric size and strain engineering.

Nanomechanical Properties of Amyloid Fibrils Formed in a Water Nanofilm on Mica Surface

The assessment of nanomechanical properties of a single amyloid fibril in a confined space provides important information for understanding the role of fibrils in a cell microenvironment. In this study, the structure and nanomechanical properties of different fibrils formed in water nanofilms on mica surface are carefully investigated by using the new atomic force microscopy imaging mode-peak force quantitative nanomechanics （PF-QNM）. We find that two types of fibrils with different morphologies are formed in water nanofilm on mica. The compression elasticities of these two types of fibrils are 3.9±0.9 and 2.5±0.6 GPa, respectively. The remarkable difference is possibly due to the structural discrepancy in two types of fibrils.

Controllable growth of wafer-scale PdS and PdS_(2) nanofilms via chemical vapor deposition combined with an electron beam evaporation technique

Palladium(Pd)-based sulfides have triggered extensive interest due to their unique properties and potential applications in the fields of electronics and optoelectronics.However,the synthesis of large-scale uniform PdS and PdS_(2)nanofilms(NFs)remains an enormous challenge.In this work,2-inch wafer-scale PdS and PdS_(2) NFs with excellent stability can be controllably prepared via chemical vapor deposition combined with electron beam evaporation technique.The thickness of the pre-deposited Pd film and the sulfurization temperature are critical for the precise synthesis of PdS and PdS_(2) NFs.A corresponding growth mechanism has been proposed based on our experimental results and Gibbs free energy calculations.The electrical transport properties of PdS and PdS_(2) NFs were explored by conductive atomic force microscopy.Our findings have achieved the controllable growth of PdS and PdS_(2) NFs,which may provide a pathway to facilitate PdS and PdS_(2) based applications for next-generation high performance optoelectronic devices.