Tailoring photonic crystals with nanometer-scale precision using polyelectrolyte multilayers

In this paper, we describe a rapid, accurate, and convenient method for postsynthetically tuning the optical properties of colloidal photonic crystals. High quality photonic crystal films are first synthesized and then coated iteratively with layers of water-soluble polyelectrolytes. The coating process results in nanometer-scale shifts in the photonic stop band, a process which has been monitored by theoretical modeling. The results suggest a fundamentally different, reproducible layering mechanism inside the confined spaces of the colloidal crystal where polyelectrolyte multilayers are less densely packed.     

Matrix isolation laser Raman spectroscopy: a Raman and infrared spectral study including Raman polarisation data for the co-condensation reaction of Pd: Spectroscopic and structural data for the new tetra-carbonyls Pd(CO)4 AND Pt(CO)4

The chemical species formed in the co-condensation reactions of Pd and Pt atoms with CO at 4.2–10 °K are investigated for the first time using the combined techniques of matrix isolation infrared and laser Raman spectroscopy. Under these experimental conditions the spectroscopic data show that one major product is formed. The data when taken in conjunction with the depolarisation measurements for the matrix isolated species confirms the existence in the matrix of the previously unknown tetracarbonyls Pd(CO)₄ and Pt(CO)₄ both having T_d symmetry. Cotton-Kraihanzel force constants are calculated for the series M(CO)₄ where M = Ni, Pd and Pt.     

Direct synthesis using gold atoms: synthesis,infrared and ultraviolet-visible spectra and molecular orbital investigations of monoethylene gold(0), (C2H4Au

The reaction of Au atoms with ¹²C₂H₄ or ¹²C₂H₄/Ar mixtures at 8–10 K yields a single product. Using Au and ¹²C₂H₄ concentration experiments, warm-up studies and ¹³C₂H₄/Ar, ¹²C₂H₄/¹³C₂H₄/Ar isotopic substitution, coupled with infrared and UV-visible spectroscopy, the product is characterized to be monoethylene gold(0), (C₂H₄)Au, the first reported example of a zerovalent gold-olefin complex. Extended Hückel molecular orbital calculations proved to be a useful aid towards the assignment of the optical spectrum of (C₂H₄)Au. The thermal stability of (C₂H₄)Au in solid C₂H₄ at 70 K is discussed in terms of the feasibility of a macroscale, liquid nitrogen temperature, chemical synthesis. The molecular and electronic properties of the group of complexes (C₂H₄)M and M(0₂), where M = Ag or Au, are compared and discussed.     

Formation of organometallic polymer nanorods using a nanoporous alumina template and the conversion to magnetic ceramic nanorods

Polyferrocenylsilane nanorods were prepared using a porous anodic aluminium oxide template followed by chemical etching; pyrolysis was used to obtain magnetic iron oxide-containing ceramic nanorods.     

Measurement of absolute photoluminescence quantum yields using integrating spheres – Which way to go?

Two common methods for recording absolute photoluminescence quantum yields using integrating spheres are discussed. These methods are developed from a theoretical standpoint, with a discussion of the assumptions made in each and their principle differences, and practical comparisons between the two are made using a range of different materials and sample types. It is shown that despite the underlying theoretical differences both methods ultimately yield very similar experimental results. Additionally, the concept of a time‐dependent quantum yield is examined and preliminary studies along these lines are presented in the form of an investigation into the photo‐oxidation of a luminescent polymer film.     

Fabry-Perot etalons using colloidal photonic crystal mirrors

Fabry-Perot etalons have been fabricated with 3D colloidal photonic crystal mirrors. The colloid films were optimized for high reflection and low loss to provide good finesse values in the 1200-1700 nm spectral range. A cavity quality factor of 2400 and a finesse of 8 together with sharp 0.5 nm wide resonance transmission peaks are reported that attest to the relatively good optical quality of the three-dimensionally structured films and the promise of self-assembly colloidal crystal chemistry in providing novel microporous optical interferometers for potential applications such as environmental and biological sensing.     

Preparation of monodisperse silicon nanocrystals using density gradient ultracentrifugation

We report the preparation of monodisperse silicon nanocrystals (ncSi) by size-separation of polydisperse alkyl-capped ncSi using organic density gradient ultracentrifugation. The ncSi were synthesized by thermal processing of trichlorosilane-derived sol-gel glasses followed by HF etching and surface passivation with alkyl chains and were subsequently fractionated by size using a self-generating density gradient of 40 wt % 2,4,6-tribromotoluene in chlorobenzene. The isolated monodisperse fractions were characterized by photoluminescence spectroscopy and high-angle annular dark-field scanning transmission electron microscopy and determined to have polydispersity index values between 1.04 and 1.06. The ability to isolate monodisperse ncSi will allow for the quantification of the size-dependent structural, optical, electrical, and biological properties of silicon, which will undoubtedly prove useful for tailoring property-specific optoelectronic and biomedical devices.