Pathways to school readiness: Executive functioning predicts academic and social-emotional aspects of school readiness.

The current study specified the extent to which hot and cool aspects of executive functioning predicted academic and social-emotional indicators of school readiness. It was unique in focusing on positive aspects of social-emotional readiness, rather than problem behaviors. One hundred four 3- to 5-year-old children completed tasks measuring executive functioning, social-emotional readiness, academic readiness, and vocabulary. As expected, age predicted executive functioning components and social-emotional readiness. Moreover, working memory and inhibitory control directly predicted academic readiness, whereas delay of gratification predicted social-emotional readiness. Working memory and inhibitory control predicted delay of gratification, consistent with the notion that simpler executive functions may set the stage for more complex executive functions. Interestingly, social-emotional readiness predicted academic readiness. These findings confirm that hot and cool aspects of executive functioning are related to social-emotional and academic school readiness

Vibrational dynamics and band structure of methyl-terminated Ge(111)

A combined synthesis, experiment, and theory approach, using elastic and inelastic helium atom scattering along with ab initio density functional perturbation theory, has been used to investigate the vibrational dynamics and band structure of a recently synthesized organic-functionalized semiconductor interface. Specifically, the thermal properties and lattice dynamics of the underlying Ge(111) semiconductor crystal in the presence of a commensurate (1 × 1) methyl adlayer were defined for atomically flat methylated Ge(111) surfaces. The mean-square atomic displacements were evaluated by analysis of the thermal attenuation of the elastic He diffraction intensities using the Debye-Waller model, revealing an interface with hybrid characteristics. The methyl adlayer vibrational modes are coupled with the Ge(111) substrate, resulting in significantly softer in-plane motion relative to rigid motion in the surface normal. Inelastic helium time-of-flight measurements revealed the excitations of the Rayleigh wave across the surface Brillouin zone, and such measurements were in agreement with the dispersion curves that were produced using density functional perturbation theory. The dispersion relations for H-Ge(111) indicated that a deviation in energy and lineshape for the Rayleigh wave was present along the nearest-neighbor direction. The effects of mass loading, as determined by calculations for CD_3-Ge(111), as well as by force constants, were less significant than the hybridization between the Rayleigh wave and methyl adlayer librations. The presence of mutually similar hybridization effects for CH_3-Ge(111) and CH_3-Si(111) surfaces extends the understanding of the relationship between the vibrational dynamics and the band structure of various semiconductor surfaces that have been functionalized with organic overlayers

Hybridization of Surface Waves with Organic Adlayer Librations: A Helium Atom Scattering and Density Functional Perturbation Theory Study of Methyl-Si(111)

The interplay of the librations of a covalently bound organic adlayer with the lattice waves of an underlying semiconductor surface was characterized using helium atom scattering in conjunction with analysis by density functional perturbation teory. The Rayleigh wave dispersion relation of CH_(3)- and CD_(3)-terminated Si(111) surfaces was probed across the entire surface Brillouin zone by the use of inelastic helium atom time-of-flight experiments. The experimentally determined Rayleigh wave dispersion relations were in agreement with those predicted by density functional perturbation theory. The Rayleigh wave for the CH_(3)- and CD_(3)-terminated Si(111) surfaces exhibited a nonsinusoidal line shape, which can be attributed to the hybridization of overlayer librations with the vibrations of the underlying substrate. This combined synthetic, experimental, and theoretical effort clearly demonstrates the impact of hybridization between librations of the overlayer and the substrate lattice waves in determining the overall vibrational band structure of this complex interface

Experimental and theoretical study of rotationally inelastic diffraction of H_2(D_2) from methyl-terminated Si(111)

Fundamental details concerning the interaction between H_2 and CH_3–Si(111) have been elucidated by the combination of diffractive scattering experiments and electronic structure and scattering calculations. Rotationally inelastic diffraction (RID) of H_2 and D_2 from this model hydrocarbon-decorated semiconductor interface has been confirmed for the first time via both time-of-flight and diffraction measurements, with modest j = 0 → 2 RID intensities for H_2 compared to the strong RID features observed for D_2 over a large range of kinematic scattering conditions along two high-symmetry azimuthal directions. The Debye-Waller model was applied to the thermal attenuation of diffraction peaks, allowing for precise determination of the RID probabilities by accounting for incoherent motion of the CH_3–Si(111) surface atoms. The probabilities of rotationally inelastic diffraction of H_2 and D_2 have been quantitatively evaluated as a function of beam energy and scattering angle, and have been compared with complementary electronic structure and scattering calculations to provide insight into the interaction potential between H_2 (D_2) and hence the surface charge density distribution. Specifically, a six-dimensional potential energy surface (PES), describing the electronic structure of the H_2(D_2)/CH_3−Si(111) system, has been computed based on interpolation of density functional theory energies. Quantum and classical dynamics simulations have allowed for an assessment of the accuracy of the PES, and subsequently for identification of the features of the PES that serve as classical turning points. A close scrutiny of the PES reveals the highly anisotropic character of the interaction potential at these turning points. This combination of experiment and theory provides new and important details about the interaction of H_2 with a hybrid organic-semiconductor interface, which can be used to further investigate energy flow in technologically relevant systems

Experimental and theoretical study of rotationally inelastic diffraction of H_2(D_2) from methyl-terminated Si(111)

Fundamental details concerning the interaction between H_2 and CH_3–Si(111) have been elucidated by the combination of diffractive scattering experiments and electronic structure and scattering calculations. Rotationally inelastic diffraction (RID) of H_2 and D_2 from this model hydrocarbon-decorated semiconductor interface has been confirmed for the first time via both time-of-flight and diffraction measurements, with modest j = 0 → 2 RID intensities for H_2 compared to the strong RID features observed for D_2 over a large range of kinematic scattering conditions along two high-symmetry azimuthal directions. The Debye-Waller model was applied to the thermal attenuation of diffraction peaks, allowing for precise determination of the RID probabilities by accounting for incoherent motion of the CH_3–Si(111) surface atoms. The probabilities of rotationally inelastic diffraction of H_2 and D_2 have been quantitatively evaluated as a function of beam energy and scattering angle, and have been compared with complementary electronic structure and scattering calculations to provide insight into the interaction potential between H_2 (D_2) and hence the surface charge density distribution. Specifically, a six-dimensional potential energy surface (PES), describing the electronic structure of the H_2(D_2)/CH_3−Si(111) system, has been computed based on interpolation of density functional theory energies. Quantum and classical dynamics simulations have allowed for an assessment of the accuracy of the PES, and subsequently for identification of the features of the PES that serve as classical turning points. A close scrutiny of the PES reveals the highly anisotropic character of the interaction potential at these turning points. This combination of experiment and theory provides new and important details about the interaction of H_2 with a hybrid organic-semiconductor interface, which can be used to further investigate energy flow in technologically relevant systems

Atomic Surface Structure of CH_3-Ge(111) Characterized by Helium Atom Diffraction and Density Functional Theory

The atomic-scale surface structure of methyl-terminated germanium (111) has been characterized by using a combination of helium atom scattering and density functional theory. High-resolution helium diffraction patterns taken along both the ⟨1̅21̅⟩ and the ⟨011̅⟩ azimuthal directions reveal a hexagonal packing arrangement with a 4.00 ± 0.02 Å lattice constant, indicating a commensurate (1 × 1) methyl termination of the primitive Ge(111) surface. Taking advantage of Bragg and anti-Bragg diffraction conditions, a step height of 3.28 ± 0.02 Å at the surface has been extracted using variable de Broglie wavelength specular scattering; this measurement agrees well with bulk values from CH_3-Ge(111) electronic structure calculations reported herein. Density functional theory showed that methyl termination of the Ge(111) surface induces a mild inward relaxation of 1.66% and 0.60% from bulk values for the first and second Ge–Ge bilayer spacings, respectively. The DFT-calculated rotational activation barrier of a single methyl group about the Ge–C axis on a fixed methyl-terminated Ge(111) surface was found to be approximately 55 meV, as compared to 32 meV for a methyl group on the H-Ge(111) surface, sufficient to hinder the free rotation of the methyl groups on the Ge(111) surface at room temperature. However, accurate MD simulations demonstrate that cooperative motion of neighboring methyl groups allows a fraction of the methyl groups to fully rotate on the picosecond time scale. These experimental data in conjunction with theory provide a quantitative evaluation of the atomic-scale surface structure for this largely unexplored, yet technologically interesting, hybrid organic–semiconductor interface