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A sequential of concepts developed in last decade has enabled a resolution to multiple anomalies of water ice and its low-dimensionality, particularly. Developed concepts include the coupled hydrogen bond oscillator pair, segmental specific heat, three-body coupling potentials, quasisolidity, and supersolidity. Resolved anomalies include ice buoyancy, ice slipperiness, water skin toughness, supercooling and superheating at the nanoscale, etc. Evidence shows consistently that molecular undercoordination shortens the HO bond and stiffens its phonon while undercoordination does the OH nonbond contrastingly associated with strong lone pair polarization, which endows the low-dimensional water ice with supersolidity. The supersolid phase is hydrophobic, less dense, viscoelastic, thermally more diffusive and stable, having longer electron and phonon lifetime. The equal number of lone pairs and protons reserves the configuration and orientation of the coupled hydrogen bond bonds and restricts molecular rotation and proton hopping, which entitles water the simplest, ordered, tetrahedrally-coordinated, fluctuating molecular crystal covered with a supersolid skin. The hydrogen bond segmental cooperativity and specific-heat disparity form the soul dictating the extraordinary adaptivity, reactivity, recoverability, sensitivity of water ice when subjecting to physical perturbation. It is recommended that the premise of hydrogen bonding and electronic dynamics would deepen the insight into the core physics and chemistry of water ice., 11.7 k words, 13 figures,115 refs. Chinese Physics B 2020

In this study, a new technique of transmitting electric energy wirelessly to piezoelectric components is explored. An electromagnetic wave is used to drive a piezoelectric plate, which is made of a lead zirconate titanate (PZT) ceramic material. The piezoelectric plate is poled along thickness direction. The proposed technique is based on the principle of coupling of an electromagnetic wave and mechanical resonance. When an electric field generated by AC voltage penetrates the piezoelectric plate, an attenuated voltage is obtained across the output electrodes of the piezoelectric plate. The power received by the electrical load connected to the output electrodes reaches maximum, when frequency of the electric field is close to the mechanical resonance frequencies of the piezoelectric plate. In the design, for the generation of electric field, an AC voltage with tunable frequency is connected to two brass electrodes mounted on a plastic plate with a tunable separation. The piezoelectric plate is inserted parallel at the center of the gap between the two brass electrodes. From the experiment it has been seen that the output power achieved by the piezoelectric plate depends upon various factors like the vibration mode, electrode pattern and electrical load of the piezoelectric component, and the electric field. At the resonance frequency, a maximum output power of 5.65 mW has been achieved by the piezoelectric plate operating in the thickness vibration mode, with input voltage of 150 Vrms and 4 mm gap thickness. The output power at resonance of the piezoelectric plate, operating in the thickness vibration mode, is significantly higher than that of the plate operating in the other modes like width and longitudinal vibrations.

It is intriguing that a solid containing ~101 atoms of Ga or IV-A elements (C, Si, Ge, Sn, and Pb) melts at temperatures that are higher than the melting point of the corresponding bulk solid (Tm,b) though the Tm of a solid in the 100–2 nm size range drops universally with the sample size. Consistent insight into the phenomenon of Tm oscillation (suppression followed by elevation as the solid size is reduced from bulk to subnanometre size) over the whole range of sizes remains a scientific challenge. Here we show that the Tm oscillation arises from the joint effect of bond order loss and its consequence on bond strength gain of small clusters in particular for Ga and atoms of the IV-A elements.

An analytical solution is presented showing that the dielectric susceptibility of a nanosolid depends functionally on the crystal binding that determines the bandgap and hence the essential processes of electron polarization, and on the electron–phonon coupling, that is often overlooked in theory considerations. The derived solution covers all the measured values of bandgap expansion that are beyond the reach of available approaches. Consistency between predictions and impedance measurements evidences the impact of atomic coordination-number imperfection on the dielectric performance of nanometric semiconductors and the validity of the given solution.

Partial altervalent/aliovalent chemical substitutions for Mg or B have been attempted to modify the Fermi-level density-of-states and to alter the lattice parameters, thus varying the superconducting transition temperature (T c ) of MgB 2 . However, different from Cu oxide superconductors in which replacement of La by Y in La 2 CuO 4 forms YBa 2 Cu 3 O 7 - δ and raises T c from 35 to 93 K, most of the substitutions in MgB 2 studied to date depress T c , and at higher replacements completely suppress the superconductivity of MgB 2 . Such diminution and loss of superconductivity in MgB 2 arise from the subtle interplay between the competing/cooperating effects of the electronic and lattice structural variations, which are induced by the different charge and atomic radii of the substituents. In this work, we experimentally separate lattice structural effects from electronic contributions to superconductivity by exploiting the nanosize dependence of the lattice structure to modify the structural parameters without resorting to chemical doping. It is found that the superconductivity of MgB 2 is extremely sensitive to lattice parameter variation, such that contraction of the Mg-Mg bond dramatically depresses T c and eventually results in the loss of superconductivity as the average coordination of Mg to B falls from 12 to 8 for nano-crystalline MgB 2 of 2.5 nm in diameter.

In this work, effects of varying mechanical deformations on the relationship between mesotexture and current percolation in (Bi, Pb)2Sr2Ca2Cu3O10+x (Bi2223) tapes are investigated. Electron backscattered diffraction analysis demonstrates that the mesotexture distribution characteristics influence critical current density (Jc) as results of the processing variations. The disorientation angle distribution dependence of Jc is also discussed using current percolation theory. The results show that improving the mesotexture distribution in central region of Bi2223 tapes through optimization of the mechanical deformation processing can significantly increase Jc.

A bond-order–bond-length–bond-strength (bond-OLS) correlation mechanism is presented for consistent insight into the origin of the shape-and-size dependence of a nanosolid, aiming to provide guidelines for designing nanomaterials with desired functions. It is proposed that the coordination number imperfection of an atom at a surface causes the remaining bonds of the lower-coordinated surface atom to relax spontaneously; as such, the bond energy rises (in absolute value). The bond energy rise contributes not only to the cohesive energy (ECoh) of the surface atom but also to the energy density in the relaxed region. ECoh relates to thermodynamic properties such as self-assembly, phase transition and thermal stability of a nanosolid. The binding energy density rise is responsible for the changes of the system Hamiltonian and related properties, such as the bandgap, core-level shift, phonon frequency and the dielectrics of a nanosolid of which the surface curvature and the portion of surface atoms vary with particle size. The bond-OLS premise, involving no assumptions or freely adjustable parameters, has led to consistency between predictions and experimental observations of a number of outstanding properties of nanosolids.

Based on the recent bond-order-bond-length-bond-strength correlation mechanism (Sun C Q, Chen T P, Tay B K, Li S, Huang H, Zhang Y B, Pan L K, Lau S P and Sun X W 2001 J. Phys. D: Appl. Phys. 34 3470) and the criterion of thermal-vibration-exchange-interaction energy equilibrium, an atomistic model has been developed for the Curie temperature (TC) suppression of ferromagnetic nanosolids. At TC, the atomic thermal vibration energy (EV) overcomes the atomic cohesive energy (Ecoh), which triggers the order-disorder transition of the spin-spin exchange interaction. Besides, the coordination-number (CN) imperfection at a surface enhances the strength of the bonds of the surface atoms. The CN reduction and bond-strength enhancement modifies the surface atomic Ecoh from that of an atom inside the bulk. As such, the critical EV for an atom at a free surface will be different from the bulk value and, hence, the TC of a nanosolid will change with the portion of surface atoms. Matching between predictions and experimental observations on the TC suppression of Fe, Ni and Co nanofilms evidences the validity of the current premise, in which no assumptions or freely adjustable parameters are involved.

Ramped-current and ramped-voltage current–voltage (I–V) measurements were carried out to investigate the conduction in ultrathin SiO2 films after breakdown, and all the I–V characteristics were plotted on a log–log scale to examine the power law behavior. In most cases, the conduction was stable, and the two measurements yielded identical I–V characteristics. However, in some cases, two phenomena exhibiting instability, i.e., the current switching and voltage switching between two well-defined states, were observed in the ramped-voltage and ramped-current measurements, respectively. For both the stable conduction with a single conduction state and the unstable conduction which involved different states, a linear relationship was observed in the log–log scale I–V characteristics for each state, indicating that each state followed a power law. The conduction instability is explained by a model based on the percolation concept.

With the miniaturization of a solid, quantum and interface effects become increasingly important. As a result, the band structure of a nanometric semiconductor changes: the band gap expands, the core level shifts, the bandwidth revises, and the sublevel separation within a band increases. Unfortunately, such a thorough change goes beyond the scope of currently available models such as the ‘quantum confinement’ theory. A consistent understanding of the factors dominating the band-structure change is highly desirable. Here we present a new approach for the size-induced unusual change by adding the effect of surface-coordination deficiency-induced bond contraction to the convention of an extended solid of which the Hamiltonian contains the intraatomic trapping interaction and the interatomic binding interaction. Agreement between modelling predictions and the observed size dependency in the photoluminescence of Si oxides and some nanometric III–V and II–VI semiconductors, and in the core-level shift of Cu–O nanosolids has been reached. Results indicate that the spontaneous contraction of chemical bonds at a surface and the rise in the surface-to-volume ratio with reducing particle size are responsible for the unusual change of the band structure of a nanosolid.

Snapback behaviour, with well-defined conduction states involved, has been observed in the ramped-current current-voltage (I-V) characteristics of ultra-thin silicon dioxide films after the occurrence of hard breakdown. The comparison of the snapback behaviour with the switching behaviour observed in the ramped-voltage measurement shows that the two behaviours are similar, suggesting that they can be explained by the same mechanism. The I-V relationship of each conduction state involved in either the snapback or the switching behaviours was found to follow a power law. These observations are consistent with the percolation model, and they can be easily explained in terms of the on/off of conductive percolation paths due to detrapping/trapping or neutral trap generation at certain SiO2 lattice sites (strategic positions) during the measurements.

Deeper insight is presented into the origin of the dielectric suppression and its effect on the photoabsorption of nanometric semiconductors. Consistency between modelling predictions and experimental observations reveals that the dielectric suppression originates from the enhancement of the crystal field due to surface bond contraction and the rise of the surface-to-volume ratio with decreasing particle size. The suppression of the dielectric function will lead to a blue shift in photoabsorption edges, which may find application in microelectronic and photonic devices of nanometre scales.

This work reports that the optimum diamond grain size can be controlled by adjusting the flow rate of Ar/H2 in the reaction chamber through orthogonal optimization. The dielectric properties of the diamond films were investigated using an RCL (resistance-capacitance-inductance) meter. It was found that (i) the dominating factors in controlling the grain size are in the following order: Ar/H2 gas ratio, gas total pressure, plasma power and substrate temperature; (ii) increasing the Ar gas fraction reduces the grain size of synthetic diamond films; and (iii) reducing the grain size lowers the dielectric constant. The grain size effect on the dielectric behaviour can be explained by the change of the crystal field caused by surface bond contraction of the nanosized particles.

Measurements using TGA, SEM, Raman spectroscopy and XRD reveal that diamond oxidizes at around 750 K through oxygen impinging into the densely packed {111} planes throughout the course of the reaction. It is also found that diamond graphitizes under vacuum at about 1100 K without orientation preference, which also occurs under an Ar inert gas environment. The intriguing oxidation behaviour of diamond indicates that oxidation occurs with selectivity of the bonding environment. It is explained that the diamond {111} plane is more favourable than the {220} surface for the oxide tetrahedron formation, and that the oxide bond formation produces loosely bonded dipoles on the surface that are eroded away during the process of oxidation.

The sintered rhombohedral PbTi0.1 Zr0.9 O3 (PZT) ceramics with doped CeO2 were prepared and investigated by means of XRD, SEM, EDX, and dielectric property measurement. It is found that a 0.4% CeO2 doping has two major effects on the growth dynamics and electric properties of the PZT materials. First, the grain size, morphology flatness and growth rate are enhanced by four to eight times. Second, the Curie temperature of the PZT is lowered by about 40 °C as compared to the undoped PZT samples. It is also found that the cerium is richer at the grain boundaries and precipitates in a glass-like phase that fills the gap between grain boundary. A possible mechanism for the driving force is discussed.

The grain size effect of lead zirconate titanate PbZr1-x Tix O3 (PZT, x 0.6) caused by surface bond contraction has been investigated by using the Landau-Ginsburg-Devonshire (LGD) phenomenological theory. It has been shown that, due to the surface bond contraction, both the Curie temperature and the spontaneous polarization of tetragonal PZT decrease with decreasing grain size. These effects become more significant when the grain size is in the nanometre range. A dielectric anomaly appears with decreasing grain size, which corresponds to a size dependent phase transformation. The ferroelectric critical size below which a loss of ferroelectricity will happen is estimated from the results obtained.

The frequency of photoluminescence is determined by the gap between the conduction and valence band. The width of the band gap depends on the crystal field and the chemical reaction, because the crystal field defines the band structure and the reaction repopulates with valence electrons. It is derived that the surface bond contraction and the rise in surface-to-volume ratio enhance the crystal field and determine the trend of frequency change, while oxidation enhances this behaviour by adding a constant.

A modelling approximation regarding the behaviour of electrons on metal surfaces with chemisorbed oxygen is presented. It is suggested that, as consequences of O - metal surface bonding, ionization, polarization and removal of metal atoms cause the non-uniformity in the surface potential barrier (SPB). The inelastic potential is formulated by using a Fermi-type spatial decay and the work function that depends on the occupied density of state. This formulation takes into account that, at energies below the plasma excitation energy, electron excitation dominates and that the electron excitation occurs in the electron-occupied space with any energy greater than the work function. The present modelling method is an improvement in that (i) the elastic potential, the spatial decay and the energy dependence of the inelastic potential are associated with the electron distribution, ; (ii) all the SPB parameters are functionalized as dependents of the origin of the image plane, , or the boundary of the region occupied by electrons; (iii) the spatial localization and the variation in energy state are taken into account; and (iv) the single-variable parameterized SPB simplifies the very-low-energy electron diffraction calculations and ensures the uniqueness of the solutions. This method allows us to optimize crystal structures by uniquely comparing the shapes of the geometry-dependent curves that exhibit joint features of topography and spectroscopy revealed by STM/STS.

The observed lattice contraction of nanoparticles is attributed to both the surface bond that contracts with coordination number reduction of surface atoms, and the surface-to-volume ratio that increases with decreasing particle size. Surface bond contraction varies with materials and crystalline orientations while the surface-to-volume ratio depends on particle shape and size.

The effects of external stress on Bi2Te3 nano-films have been investigated by first-principles calculation, including stability, electronic structure, crystal structure, and bond order. It is found that the critical thickness of nano-film is sensitive to the stress in Bi2Te3 nano-film while the band gap is near constant. The critical thickness decreases under tensile stress, whereas it increases under compressive stress. The band gap and band order of Bi2Te3 film has been affected collectively by the surface and internal crystal structures, the contraction ratio between surface bond length of nano-film and the corresponding bond length of bulk decides the band order of Bi2Te3 film.

An anti reflective layer for Si photodetectors working at various wavelengths is designed based on a SiO2 film containing Si nanocrystals (nc-Si). It is shown that with a proper amount of nc-Si distributed in the oxide and at the right thickness of the film, a single layer of nc-Si/SiO2 film can serve as a perfect anti reflection coating with very low or insignificant light loss. For example, for a 110 nm layer with an nc-Si volume fraction of 34%, the reflectance and the transmittance at the wavelength of 850 nm can reach 0.008 and 99.99%, respectively.

It has long been a puzzle regarding the atomistic origin of the thermally driven elastic softening of a solid specimen since the pioneering works of Anderson in 1966 and Watchman in 1961. Here we present an analytical solution developed from the perspective of the local bond average. It is shown that the thermally driven elastic softening of crystals can be directly related to the geometric and energetic response of the representative bonds or their average of the given specimen to the temperature variation. Reproduction of the experimental results of Ag, Au, MgO, Mg2SO4, Al2O3, KCl, Si, Ge and diamond crystals has been realized giving rise to information on the mean atomic cohesive energy without involving any hypothetical parameters used in classical thermodynamics or in continuum mechanics.

We report a theoretical method to obtain the single-bond energy derivative from temperature-dependent Young's modulus and surface tension based on the extension of the recently developed bond-order-length-strength correlation mechanism to the temperature domain. Reproducing simultaneously the measured physical quantities of the Si specimen could reveal the information on the Si-Si single-bond energy. It is shown that the single-bond energy and the response of the stimulus of temperature change can be connected to the bulk properties. Analytical solutions also provide a consistent understanding of the interdependence of these quantities and their commonly atomistic origin as arising from thermally driven bond expansion and bond weakening, which is beyond the scope of conventional approaches.