Atom-surface interactions are becoming an integral part of the field of atom optics. Here the role of van der Waals atom-surface interactions in atom wave diffraction and interferometry are investigated. In particular, it is shown that van der Waals interactions influence the intensity and phase of atomic diffraction patterns obtained from material gratings. As a result the atomic diffraction patterns are utilized to make an accurate determination of the interaction strength and verify the spatial variation of the atom-surface potential. A theory for describing the modified atom wave diffraction patterns is developed through an analogy with optical waves. An atom interferometer is used to directly measure the de Broglie wave phase shift induced by atom-surface interactions. More specifically, the phases of the zeroth, first, and second diffraction orders are measured. A proposal for using electromagnetic fields to modify the van der Waals interaction is put forth. Several of the important experimental components for observing such an effect are also demonstrated.

The potential of filling carbon nanotubes in polymers has been widely acknowledged for composites with exceptional new properties owing to the high strength of carbon nanotubes. In the thesis, by employing Materials Studio 4.0 software, the buckling behaviour and vibration of polyethylene and carbon nanotube matrix composites are first discussed using molecular mechanics simulations. The research is aimed to acquire a high strength design of PE-CNT matrix with proper PE/CNT ratio as well as discovering the dynamic characteristics of the PE-CNT composites. Investigation results show that as the number of PE chains increases, the buckling strain and the resonance frequency will decrease. Van der Waals forces are collected to explain the relation of the PE chains to the buckling strain and the resonance frequency of the composites.

The potential of filling carbon nanotubes in polymers has been widely acknowledged for composites with exceptional new properties owing to the high strength of carbon nanotubes. In the thesis, by employing Materials Studio 4.0 software, the buckling behaviour and vibration of polyethylene and carbon nanotube matrix composites are first discussed using molecular mechanics simulations. The research is aimed to acquire a high strength design of PE-CNT matrix with proper PE/CNT ratio as well as discovering the dynamic characteristics of the PE-CNT composites. Investigation results show that as the number of PE chains increases, the buckling strain and the resonance frequency will decrease. Van der Waals forces are collected to explain the relation of the PE chains to the buckling strain and the resonance frequency of the composites.

The effect of large size ratios of solute to solvent on the critical properties and phase behaviour of binary mixtures of spherical particles is investigated using an "augmented van der Waals" equation of state. The equation used is essentially a van der Waals equation with an improved hard sphere repulsive term. Molecular dynamics and constant-pressure Monte Carlo simulations of binary mixtures of hard spheres with different diameter ratios and mole fractions are undertaken to check the adequacy of the hard sphere equation. Good agreement is found, even for systems with large differences in size. Furthermore, many of the hard sphere mixtures exhibited a transition from a fluid to a solid phase at high densities. Phase boundaries are calculated for model mixtures comprising spheres of different sizes between which there are long-ranged attractive forces. Particular attention is paid to the case in which the ratio of sizes is infinite. The systems show a wide variety of behaviour that includes liquid-liquid and gas-gas immiscibility, and the formation of negative azeotropes. Calculations investigating the effect of different attractive interactions between the small and large spheres show that as the magnitude of this interaction is increased, liquid-liquid immiscibility becomes the dominant feature of the phase diagram at moderate temperatures. The extent of liquid-liquid coexistence is greatest at large size differences. These model systems are shown to reproduce some of the behaviour of aqueous solutions of surfactants if it is assumed that the large spheres are models of the micelles and the small spheres models of the solvent molecules. The properties of binary lattice mixtures of bifunctional molecules whose ends are chosen to mimic surfactant and solvent molecules are also briefly investigated, to determine the effect of the asymmetric surfactant molecule on the phase separation. Closed-loops emerge in the phase diagrams as the surfactant character of one of the species is increased.

This thesis describes the commissioning and development of a pulsed supersonic nozzle, Fourier-transform microwave spectrometer and its application to the study of several weakly bound van der Waals complexes. A pulsed supersonic expansion, Fourier-transform microwave spectrometer based on the Flygare design with a number of modifications has been constructed with an operating range of 6-18 GHz. A homodyne detection circuit mixing signals to modulus values between dc and 1 MHz is used, requiring two measurements to determine absolute transition frequencies. Transition frequencies are measured from the power spectrum by determining the first derivative zero crossing point in a least squares fitting procedure. Semiautomation of many of the spectrometer operations has been achieved allowing unattended data collection over scans of up to 300 MHz. The microwave spectrum of Ar₂-OCS and Ar₂-OC³⁴S has been observed and analysed using conventional Watson S reduction hamiltonian parameters. Effective structural parameters are derived and used in a harmonic force field analysis, based on the centrifugal distortion constants, to compare the trimer interations with a model based on the sum of dimer interactions. A series of complexes containing the nitrogen molecule undergoing tunnelling motions have been studied. Hyperfine matrix elements for the first order nuclear quadrupole interaction are derived for the coupled identical nuclei case appropriate to the rapid tunnelling motions observed. The microwave spectrum of N₂-OCS is described. Tunnelling and nuclear spin statistical effects for two symmetry states are observed arising from the interchange of nitrogen nuclei. Rotational and quadrupole constants are derived; an accidental near degeneracy of two rotational levels allows the off-diagonal quadrupole coupling constant to be determined from second order effects. A tunnelling hamiltonian fitting the quadrupole coupling constants to an angular potential has been used to calculate the tunnelling frequency and barrier to N₂ rotation. The microwave spectrum of N₂-O₃ and a preliminary spectrum of N₂-SO₃ have been observed. Rotation-inversion motions of the O₃ and SO₂ moieties must be considered in addition to the N₂ tunnelling to fit the spectrum. Tunnelling frequencies for the O₃/SO₂ and geared motions with the N₂ are derived as well as structural parameters. Modifications for production of refractory molecules and complexes by laser ablation have been made. A modified nozzle employing rods of material is used with the ablation process taking place in the nozzle throat. Modifications to obtain an expansion along the axis of the microwave cavity employ a hemispherical Fabry-Perot cavity configuration. The system has been tested on a number of diatomic molecules including PbS and CuCl.

The microwave spectrum of the open-shell van der Waals complex NO-HF has been recorded in the region 6-20GHz using a pulsed nozzle Fourier transform microwave spectrometer. This is the first observation of the microwave spectrum of a open-shell van der Waals complex between two molecules. The spectrum exhibits a rich hyperfine structure with the observation of intermolecular hyperfine interactions in an isolated system providing a sensitive probe of electron transfer in the complex. The spectrum consists of four fine structure transitions 5/2(e)-3/2(e), 3/2(e)-1/2(e), 5/2(f)-3/2(f), 3/2(f)-1/2(f) which have been fitted to a semi-rigid Hamiltonian developed to include the effects of the orbital and spin angular momenta of the unpaired electron on NO. A new treatment to account for the intermolecular hyperfine interaction was developed. The structure of the complex has been determined and is significantly bent with an angle of between 37 degrees and 49 degrees between the NO internuclear axis and the a-axis of the complex. The Renner-Teller parameter, epsilon 2, is very large and negative having the value of -10 449.32(4)GHz indicating that configuration with the unpaired electron in the plane of the complex is more stable. The analysis of the hyperfine interactions of the hydrogen and fluorine nuclei uses two constants for each nucleus, one for the spatial relationship between the magnetic moments of the unpaired electron and the nuclear magnetic moment and a Fermi-contact term. The Fermi-contact term for hydrogen is the first strong evidence of intermolecular charge transfer in an isolated van der Waals molecule.

The P22 c2 repressor protein (P22R) binds to DNA sequence-specifically and helps direct the temperate lambdoid bacteriophage P22 to the lysogenic developmental pathway. To gain insight into its DNA binding mechanism, we solved the 1.6 Å x-ray structure of the N-terminal domain (NTD) of P22R in a complex with a DNA fragment containing the synthetic operator sequence [d(ATTTAAGATATCTTAAAT)]2 This operator has an A-T at position 9L and T-A at position 9R and is termed DNA9T. Van der Waals interactions between protein and DNA appear to confer sequence-specificity. The structure of the P22R NTD – NA9T complex suggests that sequence-specificity arises substantially from interaction of a valine with a complementary binding cleft on the major groove surface of DNA9T. The cleft is formed by four methyl groups on sequential base pairs of 5' TTAA 3'. The valine cleft is intrinsic to the DNA sequence and does not arise from protein-induced DNA conformational change. Protein-DNA hydrogen bonding plays a secondary role in specificity.

Dissertation (Ph.D.)--Auburn University, / Abstract. Vita. Includes bibliographic references.

Techn. Universiẗat, Diss., 2003--Darmstadt.

The isolation of single layer graphene in 2004 by Geim and Novoselov introduced a method that researchers could extend to other van der Waals materials. Interesting and new properties arise when we reduce a crystal to two dimensions where they are often different from their bulk counterpart. Due to the van der Waals bonding between layers, these single sheets of crystal can be combined and stacked with diferent sheets to create novel materials. With the goal to study the interesting physics associated to these stacks, the focus of this work is on the fabrication and characterization of van der Waals heterostructures. In this work, we first present a brief history of 2D materials, the fabrication of heterostructures, and the various tools used to characterize these materials. We then give a description of the custom-built instrument that was used to assemble various 2D heterostructures followed by the findings associated with the optimization of the cleanliness of the stack's interface and surface. Finally, we discuss the results related to the twisting of adjacent layers of stacked MoS2 and its relation to the interlayer coupling between said layers.