Phonon Transmission by bcc Sandwich Layers in Fe/Co/Fe and Co/Fe/Co Systems

A calculation of the coherent and ballistic phonon transport via thin nanojunctions between bcc lattices is presented. The model system A/B/A consists of a finite number of bcc (001) atomic layers of an element B sandwiched between two bcc semi-infinite crystal lattices of another element A oriented in the same (001) plane. It is applied to the Fe/Co/Fe nanojunction and to the inverse Co/Fe/Co nanojunction. The theoretical calculations of the ballistic phonon transmission via the nanojunction are carried out using the matching method. The possible experimental measurements of this ballistic transmission in comparison with theoretical results should be a useful probe for the determination of alloying force constants across the interface between two such elements. The full bcc dynamics of this system is under study

Judging enzyme-responsive micelles by their covers : direct comparison of dendritic amphiphiles with different hydrophilic blocks

Enzymatically degradable polymeric micelles have great potential as drug delivery systems, allowing the selective release of their active cargo at the site of disease. Furthermore, enzymatic degradation of the polymeric nanocarriers facilitates clearance of the delivery system after it has completed its task. While extensive research is dedicated toward the design and study of the enzymatically degradable hydrophobic block, there is limited understanding on how the hydrophilic shell of the micelle can affect the properties of such enzymatically degradable micelles. In this work, we report a systematic head-to-head comparison of well-defined polymeric micelles with different polymeric shells and two types of enzymatically degradable hydrophobic cores. To carry out this direct comparison, we developed a highly modular approach for preparing clickable, spectrally active enzyme-responsive dendrons with adjustable degree of hydrophobicity. The dendrons were linked with three different widely used hydrophilic polymers-poly(ethylene glycol), poly(2-ethyl-2-oxazoline), and poly(acrylic acid) using the CuAAC click reaction. The high modularity and molecular precision of the synthetic methodology enabled us to easily prepare well-defined amphiphiles that differ either in their hydrophilic block composition or in their hydrophobic dendron. The micelles of the different amphiphiles were thoroughly characterized and their sizes, critical micelle concentrations, drug loading, stability, and cell internalization were compared. We found that the micelle diameter was almost solely dependent on the hydrophobicity of the dendritic hydrophobic block, whereas the enzymatic degradation rate was strongly dependent on the composition of both blocks. Drug encapsulation capacity was very sensitive to the type of the hydrophilic block, indicating that, in addition to the hydrophobic core, the micellar shell also has a significant role in drug encapsulation. Incubation of the spectrally active micelles in the presence of cells showed that the hydrophilic shell significantly affects the micellar stability, localization, cell internalization kinetics, and the cargo release mechanism. Overall, the high molecular precision and the ability of these amphiphiles to report their disassembly, even in complex biological media, allowed us to directly compare the different types of micelles, providing striking insights into how the composition of the micelle shells and cores can affect their properties and potential to serve as nanocarriers

Dynamic properties of a symmetric spin nanocontact

75.30.Ds Spin waves, 75.30.Fv Spin-density waves, 75.40.Gb Dynamic properties,

Calculation of the vibration properties of the Pd/Au (111) ordered surface alloy in its stable domain

In the present paper, a calculation is presented for the vibration properties of the ordered surface alloy alloy Au(111) − (√3×√3)R30° − Pd, which is a stable system in the temperature range of 500K to 600K. This surface alloy is formed by depositing Pd atoms onto the Au(111)surface, and annealing at higher temperatures. The matching theory is applied to calculate the surface phonons and local vibration densities of states (LDOS) for the clean Au (111) surface, and for the Au(111) − (√3×√3)R30° − Pd surface alloy. Our theoretical results for the surface phonon branches of the clean Au (111) surface compare favorably with previous ab initio results and experimental data. In contrast, there are no previous results for the vibrational LDOS for the atomic Au site in a clean Au (111) surface, or results for the surface phonons and vibration spectra for the surface alloy. The surface phonons are calculated for the clean Au (111) surface and the ordered surface alloy along three directions of high symmetry, namely, $\overline {\Gamma {\rm M}} ,{\rm{ }}\overline {{\rm{MK}}}$, and $\overline {K\Gamma }$. The phonon branches are strongly modified from the Au (111) surface to the surface alloy. In particular a remarkable change takes place for the LDOS between the clean Au (111) surface and the surface alloy, which may find its origin in the charge transfer from Au atoms to Pd atoms

Structural and vibrational properties of Cu(1 1 0)-2 × 1-Pd surface alloy

Investigations of surface alloys are important in various applications such as that of heterogeneous catalysis, where the electronic structure and geometric arrangement of the surface atoms strongly influence the reactions taking place on the surface. So, a deeper understanding of the physical and chemical phenomena associated with the creation of surface alloys appears to be essential in order to further progress in catalysis. In this paper, we present the calculation of vibrational properties of the Cu(1 1 0)-2×1-Pd surface alloy formed by depositing Pd atoms onto the Cu(1 1 0) surface substrate. The surface phonon frequencies and local vibration density of state (LDOS) are calculated with the use of the matching theory. New surface modes have been found on the Cu(1 1 0)-2×1-Pd surface alloy along the directions of high-symmetry $\overline{{\Gamma X}}$, $\overline{{XS}}$, $\overline{{SY}}$ and $\overline{Y\mathrm{\Gamma }}$ of the two-dimensional Brillouin zone, in comparison with the clean surface Cu(1 1 0). From the calculated local phonon densities of states (LDOS) we find that the layer DOS start to settle at the fourth layer, where there are only small differences with the bulk DOS spectrum

Calculation of the vibration properties of the Pd/Au (111) ordered surface alloy in its stable domain

In the present paper, a calculation is presented for the vibration properties of the ordered surface alloy alloy Au(111) − (√3×√3)R30° − Pd, which is a stable system in the temperature range of 500K to 600K. This surface alloy is formed by depositing Pd atoms onto the Au(111)surface, and annealing at higher temperatures. The matching theory is applied to calculate the surface phonons and local vibration densities of states (LDOS) for the clean Au (111) surface, and for the Au(111) − (√3×√3)R30° − Pd surface alloy. Our theoretical results for the surface phonon branches of the clean Au (111) surface compare favorably with previous ab initio results and experimental data. In contrast, there are no previous results for the vibrational LDOS for the atomic Au site in a clean Au (111) surface, or results for the surface phonons and vibration spectra for the surface alloy. The surface phonons are calculated for the clean Au (111) surface and the ordered surface alloy along three directions of high symmetry, namely, ΓΜ¯, MML:MK¯ $overline {Gamma {m M}} ,{m{ }}overline {{m{MK}}}$ , and KΓ¯ $overline {KGamma }$ . The phonon branches are strongly modified from the Au (111) surface to the surface alloy. In particular a remarkable change takes place for the LDOS between the clean Au (111) surface and the surface alloy, which may find its origin in the charge transfer from Au atoms to Pd atoms

Interference effects in phonon scattering across a double atomic well

We develop an analytical and numerical formalism to study the double atomic nanowell configuration influence on coherent transmission and reflection scattering, derived as elements of a Landauer-Büttiker type scattering matrix in quasi-one-dimensional multichannel waveguides. The state densities at neighbourhood of the defect region are investigated. The defect region consists in the presence of a double atomic nanowell occurring in thin film. One solves this problem by the matching method in the harmonic approximation. The theoretical formalism using simultaneously the Green's function and the matching method is detailed in order to describe the complete evanescent and the propagating fields. The phononic coherent conductance is also studied. Numerical calculations are presented and illustrated as function of the force constants occurring in the model. The fluctuations in the conductance spectra are related to Fano resonances due to the coherent coupling between travelling phonons and the localized vibration modes in the neighbourhood of the nanowell domain.

A vibrational dynamics of molecule chain on metallic surface

We investigate the vibration properties of adsorbed nanostructure on the infinite square crystalline surface. The surface is considered as an infinite slab of one atomic layer, and the nanostructure as an isolated diatomic molecule chain on the surface of a cubic lattice which is parallel to y-axis, and takes three different positions: top, hollow and bridge. The vibrational dynamics of the structure is considered within the harmonic approximation framework. The evanescent and propagating vibrational field of the perfect lattice is determined and discussed. The presence of the molecule chain breaks down the translation symmetry in one direction and gives rise to localized states on its neighborhood. The mathematical framework of the matching method is used to analyze the localization phenomena at the nanostructure boundaries. Typical dispersion curves for modes of energies along the inhomogeneity are given with their polarizations. The fine structure of the spectrum and its origins are clearly identifiable, which gives a new insight into the localization problem. Furthermore, the existence and nature of the localized phonons like modes associated with an isolated defect are derived, and the importance of the contribution of these modes to the spectral and states densities is exhibited clearly