Dynamical evolution of Ge quantum dots on Si(111): from island formation to high temperature decay

Heteroepitaxial growth is a process of profound fundamental importance as well as an avenue to realize nanostructures such as Ge/Si quantum dots (QDs), with appealing properties for applications in opto- and nanoelectronics. However, controlling the Ge/Si QD size, shape, and composition remains a major obstacle to their practical implementation. Here, Ge nanostructures on Si(111) were investigated in situ and in real-time by low energy electron microscopy (LEEM), enabling the observation of the transition from wetting layer formation to 3D island growth and decay. The island size, shape, and distribution depend strongly on the growth temperature. As the deposition temperature increases, the islands become larger and sparser, consistent with Brownian nucleation and capture dynamics. At 550 degrees C, two distinct Ge/Si nanostructures are formed with bright and dark appearances that correspond to flat, atoll-like and tall, faceted islands, respectively. During annealing, the faceted islands increase in size at the expense of the flat ones, indicating that the faceted islands are thermodynamically more stable. In contrast, triangular islands with uniform morphology are obtained from deposition at 600 degrees C, suggesting that the growth more closely follows the ideal shape. During annealing, the islands formed at 600 degrees C initially show no change in morphology and size and then rupture simultaneously, signaling a homogeneous chemical potential of the islands. These observations reveal the role of dynamics and energetics in the evolution of Ge/Si QDs, which can serve as a step towards the precise control over the Ge nanostructure size, shape, composition, and distribution on Si(111)

Beam Combination Of Multiple Vertical External Cavity Surface Emitting Lasers Via Volume Bragg Gratings

We present an experimental study on beam combining techniques with multiple vertical external cavity surface emitting lasers (VECSELs) using volume Bragg gratings (VBGs). The specially designed holographic gratings introduce frequency specific feedback for the near infrared wavelength VECSELs to achieve both spectral linewidth narrowing and beam combination effects. For coherent addition, we obtained \u3e3W output power with 8% slope efficiency in a coherent power scaling cavity scheme. In the multiplexed VBGs (MVBGs) wavelength beam combining compound cavity scheme, we measured \u3e6W combined output with nearly 100% combining efficiency. Both beam combining/power scaling schemes produced spectrally narrowed and near diffraction limited outputs. © 2014 SPIE

Mineral Metabolic Abnormalities and Mortality in Dialysis Patients

The survival rate of dialysis patients, as determined by risk factors such as hypertension, nutritional status, and chronic inflammation, is lower than that of the general population. In addition, disorders of bone mineral metabolism are independently related to mortality and morbidity associated with cardiovascular disease and fracture in dialysis patients. Hyperphosphatemia is an important risk factor of, not only secondary hyperparathyroidism, but also cardiovascular disease. On the other hand, the risk of death reportedly increases with an increase in adjusted serum calcium level, while calcium levels below the recommended target are not associated with a worsened outcome. Thus, the significance of target levels of serum calcium in dialysis patients is debatable. The consensus on determining optimal parathyroid function in dialysis patients, however, is yet to be established. Therefore, the contribution of phosphorus and calcium levels to prognosis is perhaps more significant. Elevated fibroblast growth factor 23 levels have also been shown to be associated with cardiovascular events and death. In this review, we examine the associations between mineral metabolic abnormalities including serum phosphorus, calcium, and parathyroid hormone and mortality in dialysis patients

Probing the Thermodynamics of Moiré Patterns in Molecular Self-Assembly at the Liquid-Solid Interface

Three types of moiré patterns, denoted as α-, β-, and γ-patterns, were observed in the molecular self-assembly of 1,3,5-tris(4-cyanophenyl)benzene (TCPB) on HOPG. Their relative stability was studied through thermally induced phase transitions monitored in situ by scanning tunneling microscopy. The incommensurate γ-pattern is thermodynamically more stable than the commensurate α- and β-patterns. The preference in the γ-pattern was explained by a static distortion wave, which was exclusively observed in this pattern. Through the lateral relaxation of TCPB lattice, the free energy of the γ-pattern can be reduced with respect to that of the α- and β-moiré patterns. This investigation provides insights into the thermodynamics of surface-confined supramolecular systems where the molecular lattice is incongruent with the substrate.</p