Effects of Rattling Behavior of K and Cd Atoms along Different Directions in Anisotropic KCdAs on Lattice Thermal Transport and Thermoelectric Properties

We employ advanced first principles methodology,merging self-consistent phonon theory and the Boltzmann transport equation,to comprehensively explore the thermal transport and thermoelectric properties of KCdAs.Notably,the study accounts for the impact of quartic anharmonicity on phonon group velocities in the pursuit of lattice thermal conductivity and investigates 3ph and 4ph scattering processes on phonon lifetimes.Through various methodologies,including examining atomic vibrational modes and analyzing 3ph and 4ph scattering processes,the article unveils microphysical mechanisms contributing to the lowκL within KCdAs.Key features include significant anisotropy in Cd atoms,pronounced anharmonicity in K atoms,and relative vibrations in non-equivalent As atomic layers.Cd atoms,situated between As layers,exhibit rattling modes and strong lattice anharmonicity,contributing to the observed lowκL.Remarkably flat bands near the valence band maximum translate into high PF,aligning with ultralowκL for exceptional thermoelectric performance.Under optimal temperature and carrier concentration doping,outstanding ZT values are achieved:4.25(a(b)-axis,p-type,3×10^(19)cm^(−3),500 K),0.90(c-axis,p-type,5×10^(20)cm^(−3),700 K),1.61(a(b)-axis,n-type,2×10^(18)cm^(−3),700 K),and 3.06(c-axis,n-type,9×10^(17)cm^(−3),700 K).

Vibronic effect study of ^(1)A_(2) state of H_(2)O and D_(2)O

The generalized oscillator strengths of the dipole-forbidden excitations of the ^(1)A_(2) of H_(2)O and D_(2)O were calculated with the time dependent density functional theory,by taking into account the vibronic effect.It is found that the vibronic effect converts the dipole-forbidden excitation of the ^(1)A_(2) into a dipole-allowed one,which enhances the intensities of the corresponding generalized oscillator strength in the small squared momentum transfer region.The present investigation shows that the vibronic effect of H_(2)O is slightly stronger than that of D_(2)O,which exhibits a clear isotopic effect.

Entropy of Regular Black Holes in Einstein's Gravity

We calculate the entropy of spherically symmetric regular black holes by the path-integral method in Einstein's gravity. This method provides evidence that the entropy of spherically symmetric regular black holes is proportional to a quarter of horizon area, indicating no violation of the entropy-area law.

First-principles investigation of diffusion behaviours of H isotopes:From W(110) surface into bulk and in bulk W

The diffusion behaviours of hydrogen （H）, deuterium （D）, and tritium （T） from W（110） surface into bulk and in bulk W are investigated using first-principles calculations combined with simplified models. The diffusion energy barrier is shown to be 1.87 eV from W（110） surface to the subsurface, along with a much reduced barrier of 0.06 eV for the reverse diffusion process. After H enters into the bulk, its diffusion energy barrier with quantum correction is 0.19 eV. In terms of the diffusion theory presented by Wert and Zener, the diffusion pre-exponential factor of H is calculated to be 1.57×10-7 m2.s-1, and it is quantitatively in agreement with the experimental value of 4.1×10-7 m2.s-1. Subsequently, according to mass dependence （√1/m） of H isotope effect, the diffusion pre-exponential factors of D and T are estimated to be 1.11×10-7 m2.s-1 and 0.91×10-7 m2.s-1, respectively.

Optical Properties of Pr^3＋-Doped Y2SiO5 Crystals

Optical properties of Pr^3＋ doped in Y2SiO5, including absorption spectra, emission spectra, and fluorescence decay, have been investigated with a special attention in the UV region. Broad band （270-350nm） UV fluorescence assigned to the transitions 4f5d → 4f^2 ^3Hj, ^3Fj is found. The spontaneous transition probabilities in the 4f^2 intraconfiguration are calculated by utilizing the 3udd-Ofelt theory, by which three phenomenological parameters （Ω2, Ω4, Ω6,） are obtained by fitting the absorption spectra. For the evaluation of transition probability of the interconfiguration 4f5d → 4f^2, a formula for electric dipole transition is employed. In comparison of the measured fluorescence lifetime with the calculated spontaneous radiative lifetime, the fluorescence quantum efficiency is deduced.

Effect of Bias Step on the I-V Curve in Double-Barrier AlGaAs/GaAs/AlGaAs Resonant-Tunnelling Devices

We investigate the non-equilibrium electron transport properties of double-barrier AlGaAs/GaAs/AlGaAs resonant- tunnelling devices in nonlinear bias using the time-dependent simulation technique. It is found that the bias step of the external bias voltage applied on the device has an important effect on the final current-voltage （I - V） curves. The results show that different bias step applied on the device can change the bistability, hysteresis and current plateau structure of the I - V curve. The current plateau occurs only in the case of small bias step. As the bias step increases, this plateau structure disappears.

Effects of chromium on structure and mechanical properties of vanadium:A first-principles study

Stability and diffusion of chromium （Cr） in vanadium （V）, the interaction of Cr with vacancies, and the ideal me- chanical properties of V are investigated by first-principles calculations. A single Cr atom is energetically favored in the substitution site. Vacancy plays a key role in the trapping of Cr in V. A very strong binding exists between a single Cr atom and the vacancy with a binding energy of 5.03 eV. The first-principles computational tensile test （FPCTT） shows that the ideal tensile strength is 19.1 GPa at the strain of 18% along the [100] direction for the ideal V single crystal, while it decreases to 16.4 GPa at a strain of 12% when one impurity Cr atom is introduced in a 128-atom V supercell. For shear deformation along the most preferable { 110} （111） slip system in V, we found that one substitutional Cr atom can decrease the cleavage energy （7cl） and simultaneously increase the unstable stacking fault energy （]＇us） in comparison with the ideal V case. The reduced ratio of ]＇cl/]＇us in comparison with pure V suggests that the presence of Cr can decrease the ductility of V.

Radiative Lifetimes of Doubly Ionized Terbium

Radiative lifetimes of two short-lived levels （i.e. 4f^8 （TF6）6p^1/2 （6, 1/2）11/2,13/2） in Tb Ⅲ are measured by time-resolved laser-induced fluorescence （LIE） technique with a two-step excitation process. Free Tb Ⅲ ions are produced in a laser-induced plasma. Lifetime values are evaluated with a deconvolution procedure of the timeresolved fluorescence signal with the temporal shape of second-step excitation pulse （about 1 ns）. The lifetimes of the 4f^8 （^7F6）6p^1/2 （6, 1/2）11/2 and 4f^8（^7F6）6p^1/2 （6, 1/2）13/2 levels are determined to be 1.9 （2） and 2.0 （2）ns, respectively.

Adsorptions of metal adatoms on graphene-like BC3 and their rich electronic properties： A first-principles study

Density functional calculations have been performed to investigate the adsorption of twenty two different kinds of metal adatoms on graphene-like BC3. In contrast to the graphene adsorbed with adatoms, the BC3 with adatoms shows many interesting properties.（1） The interaction between the metal adatoms and the BC3 sheet is remarkably strong. The Li, Na, K, and Ca possess the binding energies larger than the cohesive energies of their corresponding bulk metals.（2）The Li, Na, and K adatoms form approximately ideal ionic bonds with BC3, while the Be, Mg, and Ca adatoms form ionic bonds with BC3 with slight hybridization of covalent bonds. The Al, Ga, In, Sn, and all transition metal adatoms form covalent bonds with BC3.（3） For all the structures studied, there exhibit metal, half-metal, semiconducting, and spin-semiconducting behaviors. Especially, the BC3 with Co adatom shows a quantum anomalous Hall（QAH） phase with a Chern number of -1 based on local density approximation calculations.（4） For Li, Na, K, Ca, Ga, In, Sn, Ti, V, Cr,Ni, Pd, and Pt, there exists a trend that the adatom species with lower ionization potential have lower work function. Our results indicate the potential applications of functionalization of BC3 with metal adatoms.

Ab initio investigation of the mechanical properties of copper

Employing the ab initio total energy method based on the density functional theory with the generalized gradient approximation, we have systematically investigated the theoretical mechanical properties of copper （Cu）. The theoretical tensile strengths are calculated to be 25.3 GPa, 5.9 GPa, and 37.6 GPa for the fcc Cu single crystal in the [001], [110], and [111] directions, respectively. Among the three directions, the [110] direction is the weakest one due to the occurrence of structure transition at the lower strain and the weakest interaction of atoms between the （110） planes, while the [111] direction is the strongest direction because of the strongest interaction of atoms between the （111） planes. In terms of the elastic constants of Cu single crystal, we also estimate some mechanical quantities of polycrystalline Cu, including bulk modulus B, shear modulus G, Young＇s modulus Ep, and Poisson＇s ratio ~.

Energetics of carbon and nitrogen impurities and their interactions with vacancy in vanadium

We studied the energetic behaviors of interstitial and substitution carbon （C）/nitrogen （N） impurities as well as their interactions with the vacancy in vanadium by first-principles simulations. Both C and N impurities prefer the octahedral site （O-site）. N exhibits a lower formation energy than C. Due to the hybridization between vanadium-d and N/C-p, the N-p states are located at the energy from -6.00 eV to -5.00 eV, which is much deeper than that from -5.00 eV to -3.00 eV for the C-p states. Two impurities in bulk vanadium, C-C, C-N, and N-N can be paired up at the two neighboring O- sites along the （111） direction and the binding energies of the pairs are 0.227 eV, 0.162 eV, and 0.201 eV, respectively. Further, we find that both C and N do not prefer to stay at the vacancy center and its vicinity, but occupy the O-site off the vacancy in the interstitial lattice in vanadium. The possible physical mechanism is that C/N in the O-site tends to form a carbide/nitride-like structure with its neighboring vanadium atoms, leading to the formation of the strong C/N-vanadium bonding containing a covalent component.

Low lattice thermal conductivity and high figure of merit in p-type doped K3IO

Based on first-principles calculations, Boltzmann transport equation and semiclassical analysis, we conduct a detailed study on the lattice thermal conductivity κL, Seebeck coefficient S, electrical conductivity σ, power factor S2σ and dimensionless figure of merit, zT, for K3IO. It is found that K3IO exhibits relatively low lattice thermal conductivity of 0.93 W·m-1·K-1 at 300 K, which is lower than the value 1.26 W·m-1·K-1 of the classical TE material PbTe. This is due to the smaller phonon group velocity νg and smaller relaxation time τλ. The low lattice thermal conductivity can lead to excellent thermoelectric properties. Thus maximum zT of 2.87 is obtained at 700 K, and the zT = 0.41 at 300 K indicate that K3IO is a potential excellent room temperature TE material. Our research on K3IO shows that it has excellent thermoelectric properties, and it is a promising candidate for applications in fields in terms of thermoelectricity.

Development of Valence Bands of C_(60)from Submonolayer to Two and Three Dimensionality

For submonolayer amounts of C_(60)condensed on Sn substrate,the peaks derived from top two occupied molecular orbitals were broadened by 0.3eV in comparison with solid C_(60).For coverageθ<1 monolayer,the broadenings are independent of the coverage.It indicates that the delocalizations of electrons in valence bands of C_(60)are weak and the widths do not reflect the true band dispersions.

Critical Point of Ising Films with Different Growth Directions

The critical temperature Tc of a spin-1/2 Ising film of cubic structures is calculated by the variational cumulant expansion method for three directions of growth.The results from different growth directions are analysed and compared with each other.In the present model,the Tc values depend largely on the number of nearest neighbors in a monolayer for films with the same number of monolayers but grown in different directions.For sc,bcc and fee structures,the highest Tc is found along the(100),(110),and(111)direction,respectively.

Enhancement of Two-photon Absorption by Ce^(3+) Sensitization in Organic Dyes

The two-photon absorption（TPA）and TPA-induced frequency upconversion emission properties of the dyes 4-[P-（dicyanoethylamino）crystal]-N-methypyrdinium iodide and the complex of 4-[P-（dicyanoethylamino）crystal]-N-methypyrdinium iodide and Ce（NO3）3 were experimentally studied.It was found that the TPA cross section for the dye sensitized by Ce3＋ is two factors larger than that of the dye without being sensitized.A three-level system model of the dye molecules was used to analyze the enhancement of TPA by the sensitizer Ce3＋,which indicated that the sensitizer results in the increase of the transition dipole moment from the one-photon allowed excited state（1Bu）to the two-photon allowed excited state（2Ag）.

Adsorption of Oxygen on K_(x)C_(60) Studied by Photoelectron Spectroscopy

Photoemission spectra of vacuum deposited K-incorporated C_(60)-K_(x)C_(60)(x≈6),before and after exposure to oxygen,show that the interaction between oxygen and potassium forms an overlayer of 40 A K-O complex with stoichiometry near to that of potassium peroxide K_(2)O_(2) on the surface.In contrary to the oxidation of potassium film,no potassium oxide K_(2)O has been observed.

Non-ionizing energy loss calculations for modeling electron-induced degradation of Cu(In,Ga)Se_2 thin-film solar cells

The lowest energies which make Cu,In,Ga,and Se atoms composing Cu（In,Ga）Se_2（CIGS） material displaced from their lattice sites are evaluated,respectively.The non-ionizing energy loss（NIEL） for electron in CIGS material is calculated analytically using the Mott differential cross section.The relation of the introduction rate（k） of the recombination centers to NIEL is modified,then the values of k at different electron energies are calculated.Degradation modeling of CIGS thin-film solar cells irradiated with various-energy electrons is performed according to the characterization of solar cells and the recombination centers.The validity of the modeling approach is verified by comparison with the experimental data.

Investigation of Hole Distribution in Y_(1-x)Pr_(x)Ba_(2)Cu_(3)O_(7)

The electronic structure of Y_(1-x)Pr_(x)Ba_(2)Cu_(3)O_(7) is described by a tight-binding Hamiltonian in which the Pr-O hybridization and the 2p_(σ)-2p_(π) Coulomb repulsion are taken into account.The dependence of planar hole-density,localized hole-density and chemical potential of holes on Pr concentration is calculated by a coherent potential approximation.The result shows that the insensitivity of hole-density on the CuO_(3) chains with the Pr-doping is due to the 2p_(σ)-2p_(π) repulsion.Some other experimental facts can also be well interpreted.

Set-up of Total Reflection X-Ray Fluorescence Analysis Technique

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Complex-amplitude Fourier single-pixel imaging via coherent structured illumination

We propose a method of complex-amplitude Fourier single-pixel imaging(CFSI)with coherent structured illumination to acquire both the amplitude and phase of an object.In the proposed method,an object is illustrated by a series of coherent structured light fields,which are generated by a phase-only spatial light modulator,the complex Fourier spectrum of the object can be acquired sequentially by a single-pixel photodetector.Then the desired complex-amplitude image can be retrieved directly by applying an inverse Fourier transform.We experimentally implemented this CFSI with several different types of objects.The experimental results show that the proposed method provides a promising complex-amplitude imaging approach with high quality and a stable configuration.Thus,it might find broad applications in optical metrology and biomedical science.