arXiv subjects

Chang Q. Sun

Publications and source records attributed to Chang Q. Sun.

At least 19 recordsLinked to original sources

arXiv2020

A short-range metastable defect in the double layer ice

Although the phase of water has extensively investigated whether there exists a defect distorting only locally the structure still under debate. Here we report a localized 5775 defect phase presented in the double layer ice on the Au (111) surface, which is a metastable structure with 5- and 7-membered rings compared with a perfect hexagonal one. Without altering the total number of the hydrogen bonds of the ice, the defect only introduces 0.08 Å molecular displacement and 3.27% interaction energy change outside the defected area. Such defect also exists without Au support but causes a larger lattice relaxation or smaller interaction energy change. The excessively high barrier as well as the low quantum tunneling and thermodynamic probabilities hinder the formation of the defect by post-grown isomerization from the perfect to the defected structure. This finding indicates that the defected ice is stable, and the defect can be formed during the ice growth stage.

cond-mat.mtrl-sci↗

arXiv2018

Bond relaxation, electronic and magnetic behavior of 2D metals structures Y on Li(110) surface

We investigated the bond, electronic and magnetic behavior of adsorption Yttrium atoms on Lithium (110) surface using a combination of Bond-order-length-strength(BOLS) correlation and density-functional theory(DFT). We found that adsorption Y atoms on Li(110) surfaces form two-dimensional (2D) geometric structures of hexagon, nonagon, solid hexagonal, quadrangle and triangle. The consistent with the magnetic moment are 6.66μB, 5.54μB, 0.28μB, 1.04μB, 2.81μB, respectively. In addition, this work could pave the way for design new 2D metals electronic and magnetic properties.

cond-mat.mtrl-sci↗

arXiv2018

Electronic structure and bond relaxation at Na/Ta(110) interfaces and 1D-chain and 2D-ring Ta metal structures on Na(110)

We investigated the mechanism of Na/Ta(110) and Ta/Na(110) interfaces using a combination of bond band barrier (BBB) and zone selective electron spectroscopy (ZES) correlation. We found that 7/9 ML and 8/9 ML Ta metal on a Na(110) surface form one dimensional (1D) chain and two dimensional (2D) ring structures, respectively. Moreover, we show that on Na(110), the Ta-induced Na(110) surface binding energy (BE) shifts are dominated by quantum entrapment. On the contrary, on a Ta(110) surface, the Na-induced Ta(110) surface BE shifts are dominated by polarization. Thus, the BBB and ZES strategy could potentially be used for designing 1D and 2D metals with desired structures and properties.

physics.comp-ph↗

arXiv2015

Why does pressure melt ice?

Compression shortens the O:H nonbond and lengthens the H-O bond simultaneously via O:H-O Coulomb repulsion. The energy loss of the elongated H-O bond lowers the melting point.

cond-mat.soft↗

arXiv2015

Water skin anomalies: density, elasticity, hydrophobicity, thermal stability, interface repulsivity, etc

Molecular undercoordination induced O:H-O bond relaxation and dual polarization dictates the supersolid behavior of water skins interacting with other substances such as flowing in nanochannels, dancing of water droplets, floating of insects. The BOLS-NEP notion unifies the Wenzel-Cassie-Baxter models and explains controllable transition between hydrophobicity and hydrophilicity.

cond-mat.soft↗

arXiv2015

Anomalies of water nanobubbles and nanodroplets: molecular undercoordination

Molecular undercoordination shortens and stiffens the H-O bond but lengthens and softens the O:H nonbond simultaneously associated with O 1s energy entrapment and nonbonding electron dual polarization, which dictates behavior of water and ice dominated by undercoordinated molecules, such as droplets, bubbles, defects, skins, etc.

cond-mat.soft↗

arXiv2015

Elastic Coulomb-levitation: why is ice so slippery?

The elastic, less dense, polarized, and thermally stable supersolid skin lubricates ice. Molecular undercoordination shortens the H-O bond and lengthens the O:H nonbond through O-O repulsion, which is associated with low-frequency and high-magnitude of O:H vibration and a dual O-O polarization. The softer O:H springs attached with stronger molecular dipoles provide forces levitating objects sliding on ice, like Maglev or Hovercraft.

cond-mat.soft↗

arXiv2015

Hidden force floating ice

Because of the segmental specific-heat disparity of the hydrogen bond (O:H-O) and the Coulomb repulsion between oxygen ions, cooling elongates the O:H-O bond at freezing by stretching its containing angle and shortening the H-O bond with an association of larger O:H elongation, which makes ice less dense than water, allowing it to float.

cond-mat.soft↗

arXiv2014

A Supersolid Skin Covering both Water and Ice

The mysterious nature and functionality of water and ice skins remain baffling to the community since 1859 when Farady firstly proposed liquid skin lubricating ice. Here we show the presence of supersolid phase that covers both water and ice using Raman spectroscopy measurements and quantum calculations. In the skin of two molecular layers thick, molecular undercoordination shortens the H-O bond by ~16% and lengthens the OH nonbond by ~25% through repulsion between electron pairs on adjacent O atoms, which depresses the density from 0.92 for bulk ice to 0.75 gcm-3. The O:H-O cooperative relaxation stiffens the H-O stretching phonon from 3200/3150 cm-1 to the same value of 3450 cm-1 and raises the melting temperature of both skins by up to ~310 K. Numerical derivatives on the viscosity and charge accumulation suggests that the elastic, polarized, and thermally stable supersolid phase makes the ice frictionless and water skin hydrophobic and ice like at room temperature.

cond-mat.soft↗

arXiv2013

Mass-density and Phonon-frequency Relaxation Dynamics of Under-coordinated Water Molecules

The interplay between intra-molecular H-O covalent bond contraction, due to molecular under-coordination, and inter-molecular O:H expansion, due to inter-electron pair Coulomb repulsion, has been shown to be the source of the anomalous behavior of under-coordinated water molecules in nanoclusters and in the surfaces of water. The shortening of the H-O bond raises the local density of bonding electrons, which in turn polarizes the lone pairs of electrons on oxygen. The stiffening of the H-O bond increases the magnitude of O1s binding energy shift, causes the blueshift of the H-O phonon frequencies, and furthermore, elevates the melting point of molecular clusters and ultrathin films of water, which gives rise to their ice-like behavior at room temperature. At the same time, the elongation of the entire O:H-O bond polarizes and enlarges the under-coordinated H$_2$O molecules.

physics.chem-ph↗

arXiv2013

Mass-density and Phonon-frequency Relaxation Dynamics of Water and Ice at Cooling

Coulomb repulsion between the bonding electron pair in the H-O covalent bond (denoted by "-") and the nonbonding electron pair of O (":") and the specific-heat disparity between the O:H and the H-O segments of the entire hydrogen bond (O:H-O) are shown to determine the O:H-O bond angle-length-stiffness relaxation dynamics and the density anomalies of water and ice. The bonding part with relatively lower specific-heat is more easily activated by cooling, which serves as the "master" and contracts, while forcing the "slave" with higher specific-heat to elongate (via Coulomb repulsion) by different amounts. In the liquid and solid phases, the O:H van der Waals bond serves as the master and becomes significantly shorter and stiffer while the H-O bond becomes slightly longer and softer (phonon frequency is a measure of bond stiffness), resulting in an O:H-O cooling contraction and the seemingly "regular" process of cooling densification. In the water-ice transition phase, the master and the slave swap roles, thus resulting in an O:H-O elongation and volume expansion during freezing. In ice, the O--O distance is longer than it is in water, resulting in a lower density, so that ice floats.

physics.chem-ph↗

arXiv2012

The Volume Rule in the Random Packing Ratio

The study on the relationship between the spheres and voids in packing system suggests that the edge effect at the interface between the container and the particles is an important factor lowering the packing ratio. To pack spheres in a container with high packing ratio, an optimized sphere size and an optimized sequence of sphere sizes exist for the packing of single-sized and multi-sized spheres, respectively. We suggest that the concepts of volume and contact should be clearly defined for the packing problem in specific scale.

cond-mat.stat-mech↗

arXiv2011

Hydrogen bond relaxation dynamics and the associated vibronic and volumetric anomalies of H2O upon frozen

A combination of the extended Ice Rule of Pauling, Raman spectroscopy, and molecular dynamics calculations has enabled us to clarify the bonding origin of the anomalous volume expansion, Raman phonon relaxation, and the stiffness and fragility of H2O upon frozen. We found that the initially shorter-and-stronger intramolecular "H+/p-O2-" bond follows the regular rule of cooling-contraction while the initially longer-and-weaker intermolecular "O2- : H+/p" nonbond turns to be even longer yet stiffer in the "O2- : H+/p-O2-" hydrogen-bond of H2O upon frozen, as a consequence of the polarization and Coulomb repulsion between the unevenly-bounded bonding and nonbonding electron pairs. The elongation of the nonbond and the polarization of the nonbonding lone pair are responsible, respectively, for the volume expansion and the stiffness and the fragility of ice. Findings should form important impact to the understanding of the physical anomalies of H2O under other stimuli such as pressure and confinement.

cond-mat.other↗

arXiv2011

Photoelectronic scoping of adatoms, atomic vacancies, and the outermost layer of a surface

An effective yet simple means disclosed herewith has allowed us to gain the atomistic, local, and quantitative information of bonds and electrons at sites surrounding undercoordinated atoms, complementing the scanning tunneling microscopy/spectroscopy and photoelectron spectroscopy (XPS). Examining Rh and Pt surfaces with and without adatoms and graphite surface with and without atomic vacancies, we confirmed that: i) bonds between undercoordinated atoms become shorter and stronger; ii) subjective polarization happens to the valence electrons of defects or adatoms by the densely entrapped bonding electrons, which in turn screens and splits the crystal field and hence the core band of the specimen.

cond-mat.mes-hall↗

arXiv2011

Controlling the band gap of ZnO by programmable annealing

Annealing has been extensively used to control crystal growth and physical properties of materials with unfortunately unclear mechanism and quantitative correlations. Here we present the "annealing temperature - grain size - band gap" correlation for ZnO nanocrystals with experimental evidence. Findings revealed that the annealing condition determines the critical size by equating the thermal and the cohesive energy of the undercoordinated atoms in the surface skin, which in turn induce local strain and quantum entrapment, perturbing the Hamiltonian and hence the band gap. The formulation provides a general guideline for controlling crystal growth and performance of materials, and makes predictive design and fabrication of functional nanomaterials into reality.

cond-mat.mes-hall↗

arXiv2011

Zone-resolved photoelectronic scoping of the local bonding and electronic dynamics at the graphite skin with and without atomic vacancy and the associated graphene edge states

A zone-resolved photoelectron spectroscopy (ZPS) has enabled us to gain the local and quantitative information and hence confirm our theoretical expectations on the bonding and electronic dynamics at graphite skin with and without atomic vacancy defects. The ZPS study has revealed: i) the 1s energy level of an isolated carbon atom is located at 282.57 eV, which shifts by 1.32 eV deeper upon diamond bulk formation; ii) the graphite surface bonds contract by 18% with 165% gain in energy compared with the C-C bond in the bulk diamond; the surface C 1s energy shifts 2.08 eV deeper from the 1s level of an isolated carbon atom; and iii) the defect bonds are ~26% shorter and 215% stronger with the binding energy shift of ~2.85 eV. An additional polarization peak centered at 1.28 eV below the C 1s level presents when the vacancy is formed. Associated with the scanning tunneling microscopy/spectroscopy observations and density functional theory calculations, the ZPS measurements clarify, for the first time, that the graphitic Dirac-Fermi polarons at atomic vacancy or graphene zigzag edge arise from the polarization of the unpaired dangling-bond electrons by the undercoordination-induced local densification and quantum entrapment of the bonding electrons.

cond-mat.mes-hall↗

arXiv2011

Raman spectroscopic determination of the length, strength, compressibility, Debye temperature, elasticity, and force constant of the C-C bond in graphene

From the perspective of bond relaxation and vibration, we have reconciled the Raman shifts of graphene under the stimuli of the number-of-layer, uni-axial-strain, pressure, and temperature in terms of the response of the length and strength of the representative bond of the entire specimen to the applied stimuli. Theoretical unification of the measurements clarifies that: (i) the opposite trends of Raman shifts due to number-of-layer reduction indicate that the G-peak shift is dominated by the vibration of a pair of atoms while the D- and the 2D-peak shifts involves z-neighbor of a specific atom; (ii) the tensile strain-induced phonon softening and phonon-band splitting arise from the asymmetric response of the C3v bond geometry to the C2v uni-axial bond elongation; (iii) the thermal-softening of the phonons originates from bond expansion and weakening; and (iv) the pressure- stiffening of the phonons results from bond compression and work hardening. Reproduction of the measurements has led to quantitative information about the referential frequencies from which the Raman frequencies shift, the length, energy, force constant, Debye temperature, compressibility, elastic modulus of the C-C bond in graphene, which is of instrumental importance to the understanding of the unusual behavior of graphene.

cond-mat.mes-hall↗

arXiv2008

The strongest size in the inverse Hall-Petch relationship

Incorporating the bond-order-length-strength correlation mechanism [Sun CQ, Prog Solid State Chem 35, 1 -159 (2007)] and Borns criterion for melting [J. Chem. Phys. 7, 591(1939)] into the conventional Hall-Petch relationship has turned out an analytical expression for the size and temperature dependence of the mechanical strength of nanograins, known as the inverse Hall-Petch relationship (IHPR), that has long been a topic under debate regarding the possible mechanisms. Reproduction of the measured IHPR of Ni, NiP and TiO2 nanocrystals revealed that: (i) the size induced energy densification and cohesive energy loss of nanograins originates the IHPR that could be activated in the contact mode of plastic deformation detection; (ii) the competition between the inhibition of atomic dislocations, via the surface energy density gain and the strain work hardening, and the activation for dislocations through cohesive energy loss determine the entire IHPR profile of a specimen; (iii) the presence of a soft quasisolid phase is responsible for the size-induced softening and the superplasticity as well of nanostructures; (iv) the bond nature involved and the T/Tm ratio between the temperature of operating and the temperature of melting dictate the measured strongest sizes of a given specimen.

cond-mat.mtrl-sci↗