Time-resolved fluorescence spectroscopy was used to explore the pathway and kinetics of energy transfer in photosynthetic membrane vesicles (chromatophores) isolated from Rhodobacter (Rba.) sphaeroides cells harvested 2, 4, 6 or 24 hours after a transition from growth in high to low level illumination. As previously observed, this light intensity transition initiates the remodeling of the photosynthetic apparatus and an increase in the number of light harvesting 2 (LH2) complexes relative to light harvesting 1 (LH1) and reaction center (RC) complexes. It has generally been thought that the increase in LH2 complexes served the purpose of increasing the overall energy transmission to the RC. However, fluorescence lifetime measurements and analysis in terms of energy transfer within LH2 and between LH2 and LH1 indicate that, during the remodeling time period measured, only a portion of the additional LH2 generated are well connected to LH1 and the reaction center. The majority of the additional LH2 fluorescence decays with a lifetime comparable to that of free, unconnected LH2 complexes. The presence of large LH2-only domains has been observed by atomic force microscopy in Rba. sphaeroides chromatophores (Bahatyrova et al., Nature, 2004, 430, 1058), providing structural support for the existence of pools of partially connected LH2 complexes. These LH2-only domains represent the light-responsive antenna complement formed after a switch in growth conditions from high to low illumination, while the remaining LH2 complexes occupy membrane regions containing mixtures of LH2 and LH1-RC core complexes. The current study utilized a multi-parameter approach to explore the fluorescence spectroscopic properties related to the remodeling process, shedding light on the structure-function relationship of the photosynthetic assembles. Possible reasons for the accumulation of these largely disconnected LH2-only pools are discussed.

A cold-wall chemical vapor deposition method for growing MoS2 that allows independent control over all deposition parameters is described. Ar carrier gas flow rate and pressure, substrate temperature, and the temperatures of the individual solid-source precursors can all be independently varied during growth onto 100-nm-thick SiO2 films on Si substrates. Individually optimizing each deposition parameter enables formation of islanded, single-layer MoS2 films with excellent run-to-run repeatability in coverage and uniformity over several square millimeter areas. Auger electron spectroscopy (AES) and Rutherford backscattering spectrometry were used to quantify the elemental composition of the films. Film morphology was analyzed using scanning electron microscopy (SEM). This analysis indicates that excess Mo deposits on the SiO2 substrate without incorporating into the stoichiometric single-layer MoS2 clusters imaged by SEM. In addition, the amount of S detected using AES is nearly identical to the amount required to form the MoS2 islands.

Indium deposition onto on-axis Si(111) substrates and those miscut by 2.5° toward [112¯] was investigated. The Si substrates were held at temperatures ranging from room temperature up to 475 °C and the In deposition rate was varied by a factor of ∼20. All depositions were performed under ultrahigh vacuum conditions onto surfaces that were cleaned in situ. For growth at 100 °C and room temperature, the In films organize into three-dimensional islands. This result suggests that In deposition onto on-axis or miscut Si(111) substrates at temperatures lower than the In melting point of 157 °C is a viable route to form In seeds for epitaxial Si or Ge nanowire growth using the vapor–liquid–solid method. The morphology of the resultant island ensembles and their formation mechanisms are discussed.

Using thermoelectric elements, we have developed a simple liquid bath chiller that is inexpensive and easy to fabricate. Typically, small experimental apparatus can be cooled using a liquid cold bath. These cold baths require continuous addition of a coolant such as dry ice or liquid N2 to maintain the desired temperature, which becomes tedious during long experiments. We demonstrate the capability of our liquid bath chiller to stably maintain a bath temperature of −28 °C for days at a time, without the need of continuous monitoring. We explore the effects of thermoelectric element capacity and configuration in addition to the temperature, composition, and flow rate of the liquid flowing through the liquid heat exchanger that transports heat away from the thermoelectric element.