No abstract

Macroporous silicon substrates, with square-shaped pores, have been used to crystallize hen egg white lysozyme by the sitting drop vapor diffusion method. The X-ray diffraction technique was used to determine the tetragonal structure of the crystals. Use of an asymmetric anodization procedure to produce pore size gradients in porous structure, ranging from 400 nm to 1 μm, resulted in the formation of sub-micrometer-sized protein crystals within the macroporous structure. The presence of the crystals was observed by field emission scanning electron microscopy and confirmed by Raman and infrared spectroscopy. The present work provides experimental evidence of sub-micrometer crystal growth from pore corners and rough sides of the pore walls, attributed to the reduction of the potential energy for nucleation, in accordance with the different mathematical models developed so far.

No abstract

Morphological properties of thermochromic VO2—porous silicon based hybrids reveal the growth of well-crystalized nanometer-scale features of VO2 as compared with typical submicron granular structure obtained in thin films deposited on flat substrates. Structural characterization performed as a function of temperature via grazing incidence X-ray diffraction and micro-Raman demonstrate reversible semiconductor-metal transition of the hybrid, changing from a low-temperature monoclinic VO2(M) to a high-temperature tetragonal rutile VO2(R) crystalline structure, coupled with a decrease in phase transition temperature. Effective optical response studied in terms of red/blue shift of the reflectance spectra results in a wavelength-dependent optical switching with temperature. As compared to VO2 film over crystalline silicon substrate, the hybrid structure is found to demonstrate up to 3-fold increase in the change of reflectivity with temperature, an enlarged hysteresis loop and a wider operational window for its potential application as an optical temperature sensor. Such silicon based hybrids represent an exciting class of functional materials to display thermally triggered optical switching culminated by the characteristics of each of the constituent blocks as well as device compatibility with standard integrated circuit technology.