[en] The growth morphologies of vicinal hillocks on KH₂PO₄ (101) surfaces have been investigated using atomic force microscopy. Both 2D and spiral dislocation growth hillocks are observed on the same crystal surface at supersaturations of ∼5%. Growth occurs on monomolecular 5 Angstrom steps both by step-flow and through layer-by-layer growth. The distribution of islands on the terraces demonstrate that surface diffusion is an important factor during growth. Terraces that are less than the diffusion length do not contain any islands. This, together with the length scale of the inter island spacing and the denuded zones provide an estimate of the diffusion length. In situ experiments at very low supersaturation (∼0.l%) show that growth is a discontinuous process due to step pinning. In addition, in situ images allow for the direct determination of the fundamental growth parameters α, the step edge energy, and β, the kinetic coefficient

[en] The National Ignition Facility (NIF), being constructed at Lawrence Livermore National Laboratory (LLNL), comprises 192 laser beams, Figure 1. The lasing medium is neodymium in phosphate glass with a fundamental frequency (1ω) of 1.053 microm. Sum frequency generation in a pair of conversion crystals (KDP/KD*P) produces 1.8 Mj of the third harmonic light (3ω or λ=0.35). On NIF the frequency conversion crystals are part of the Final Optics Assembly (FOA), whose two principal functions are to convert the laser light to 3ω and focus it on target. In addition, the FOA provides a vacuum window to the target chamber, smoothes the on- target irradiance profile, moves the unconverted light away from the target, and provides signals for alignment and diagnostics. The FOA has four Integrated Optics Modules (IOM), Figure 4, each of which contains two 41 cm square crystals are mounted with the full edge support to micro radian angular and micron flatness tolerances. This paper is intended to be an overview of the important factors that affect frequency conversion on NIF. Chief among these are angular errors arising from crystal growth, finishing, and mounting. The general nature of these errors and how they affect frequency conversion, and finally the importance of a frequency conversion metrology tool in assessing converter performance before opto-mechanical assemblies are installed on NIF will be discussed

[en] Emerging from the machinery of epitaxial science and chemical synthesis, is a growing emphasis on development of self-organized systems of complex molecular species. The nature of self-organization in these systems spans the continuum from simple crystallization of large molecules such as dendrimers and proteins, to assembly into large organized networks of nanometer-scale structures such as quantum dots or nanoparticles. In truth, self-organization in complex molecular systems has always been a central feature of many scientific disciplines including fields as diverse as structural biology, polymer science and geochemistry. But over the past decade, changes in those fields have often been marked by the degree to which researchers are using molecular-scale approaches to understand the hierarchy of structures and processes driven by this ordered assembly. At the same time, physical scientists have begun to use their knowledge of simple atomic and molecular systems to fabricate synthetic self-organized systems. This increasing activity in the field of self-organization is testament to the success of the physical and chemical sciences in building a detailed understanding of crystallization and epitaxy in simple atomic and molecular systems, one that is soundly rooted in thermodynamics and chemical kinetics. One of the fundamental challenges of chemistry and materials science in the coming decades is to develop a similarly well-founded physical understanding of assembly processes in complex molecular systems. Over the past five years, we have successfully used in situ atomic force microscopy (AFM) to investigate the physical controls on single crystal epitaxy from solutions for a wide range of molecular species. More recently, we have combined this method with grazing incidence X-ray diffraction and kinetic Monte Carlo modeling in order to relate morphology to surface atomic structure and processes. The purpose of this proposal was to extend this approach to assemblies of three classes of ''super molecular'' nanostructured materials. These included (1) dendrimers, (2) DNA bonded nano-particles, and (3) colloids, all of which form solution-based self-organizing systems. To this end, our goals were, first, to learn how to modify models of epitaxy in small molecule systems so that they are useful, efficient, and applicable to assembly of super-molecular species; and, second, to learn how systematic variations in the structure and bonding of the building blocks affect the surface kinetics and energetics that control the assembly process and the subsequent dynamic behavior of the assembled structures. AFM imaging provided experimental data on morphology and kinetics, while kinetic Monte Carlo (KMC) simulations related these data to molecular-scale processes and features

[en] Atomic-force microscopy measurements on KDP {101} faces are presented which show that the terrace width W on vicinal dislocation growth hillocks is nearly independent of supersaturation σ and Burgers vector b , in contradiction to simple Burton-Cabrera-Frank models. An analytical model taking into account the effect of dislocation cores on step rotation is presented which predicts a dependence of W on σ and b , in good agreement with the measurements. Using these results, we rescale macroscopic growth rate data onto a single Arrhenius curve, which gives a value of 0.33eV for the activation energy of step motion. copyright 1997 The American Physical Society

[en] The spectral characteristics of the internal (PO₄ tetrahedron) modes of fast-grown KH₂PO₄ crystals under sub-damage threshold, 10 ns, 355 nm laser irradiation have been investigated. Pump-and-probe Raman spectroscopy indicates transient changes of the intensity of the 915cm^-1, endash PO₄ internal mode. This change is attributed to a transient increase of the absorption due to generation by the 355 nm pump pulse of electronic defects in the bulk of the crystal. copyright 1998 American Institute of Physics

[en] A microscopic fluorescence imaging system is used to detect optically active centers located inside a transparent dielectric crystal. Defect centers in the bulk of KH₂PO ₄ crystals are imaged based on their near-infrared emission following photoexcitation. The spatial resolution of the system is 1 μm in the image plane and 25 μm in depth. The experimental results indicate the presence of a large number of optically active defect clusters in different KH₂PO ₄ crystals, whereas the concentration of these clusters depends on the crystal sector and growth method. copyright 1999 Optical Society of America

[en] We report results of x-ray topographic and optical measurements on KH₂PO₄ crystals grown at rates of 5 to 30mm/day. We show that optical distortion in these crystals is caused primarily by 3 sources: dislocations, differences in composition between adjacent growth sectors of the crystal, and differences in composition between adjacent sectors of vicinal growth hillocks within a single growth sector of the crystal. We find that the compositional heterogeneities cause spatial variations in the refractive index and induced distortion of the transmitted wave front while large groups of dislocations are responsible for strain induced birefringence which leads to beam depolarization

[en] In situ atomic force microscopy has been used to investigate step dynamics and surface evolution during the growth of single crystals of canavalin, a protein with a well known structure. Growth occurs by step flow on complex dislocation hillocks, and involves the formation and incorporation of small, mobile molecular clusters. Defects in the form of hollow channels are observed and persist over growth times of several days. The results are used to establish a physical picture of the growth mechanism, and estimate the values of the free energy of the step edge, α, and the kinetic coefficient, β

[en] We report the results of in situ and ex situ atomic force microscopy investigations of hillock structure and step dynamics on the {100} face of KDP, as well as the effects of Fe³⁺ ions on the generation and motion of both elementary and macrosteps. We compare these results to those obtained previously on the {101} face. We show that, in contrast to the {101} face, dislocation sources on the {100} face do not exhibit dislocation cores, even for large Burgers vectors. Thus, for simple dislocation sources, the measured hillock slope depends on the Burgers vector and varies linearly with supersaturation. We show that while growth hillocks on the {101} faces are characterized by elementary steps that exhibit step homogenization, even in highly purified growth solutions, KDP {100} faces exhibit a tendency towards step bunching. We trace the evolution of this bunching with distance from the dislocation source and compare it to theoretical models of impurity-induced bunching. We also trace the evolution of step dynamics with supersaturation on the {100} face. We show that well above the dead zone, elementary steps and macrosteps are straight and elementary steps move more rapidly than macrosteps. As the supersaturation is decreased, impurity pinning begins to slow elementary step motion and the macrosteps begin to move faster than the elementary steps. In the region just above the dead zone, elementary steps are highly ramified and do not move while macrosteps continue to advance, sweeping up the elementary steps at the leading edge and leaving them behind at the trailing edge. Thus, in this region, growth occurs exclusively by the propagation of macrosteps. Finally, within the dead zone, both elementary and macrosteps cease to advance