Photoluminescent Silicon Clusters in Oriented Hexagonal Mesoporous Silica Film

Abstract

ExperimentalThe ET2 monomer was prepared as previously reported [23]. PolyET2 films (4±6 mm thick) were deposited on indium-tin-oxide (ITO) plates by cyclic voltammetry (from ±0.2 to 1.2 V vs. SCE), of a 4.0´10 ±3 M ET2 solution in acetonitrile with TBAF (0.1 M) as the supporting electrolyte. The doping level of the polymer was changed by varying the oxidation potential (V ox ) within the range ±0.2 to +0.8 V in chronoamperometric experiments. For each explored potential, the chronoamperometry was run until very low current values were attained. All potentials are referred to the SCE. N d was calculated from the charge flow during the chronoamperometric experiments. N d was found to vary between 6.8´10 18 and 3.4´10 20 cm ±3 in the V ox range of 0 to +0.8 V. The doping level was not evaluated for V ox < 0 V because of the high error affecting the current measurement at those potentials. Immediately after electrochemical doping, the polyET2 films were removed from the ITO substrates and spread onto glass plates for electrical characterization carried out at ambient conditions. The X-ray diffraction spectra were recorded by a Philips (PW1050/81-PW1710) powder diffractometer configured in the Bragg±Brentano geometry and equipped with a graphite monochromator in the diffracted beam. Cu Ka X-radiation was employed, and the step-scanning recording was performed in the 3±50 2y range at 0.01 2y steps and with a fixed counting time of 10 s.The conductivity and R H were measured using standard van der Pauw geometry on 10´10 mm square samples. The electrical tests were carried out by placing small tips directly onto each corner of the polymer film. The measurements were performed by applying a constant current (typically 10 mA) across a pair of tips and by evaluating the voltage drop across the other electrode pair with and without the applied magnetic field (0.85 T). A detailed description of the measurement technique is reported by Mousty et al. [24]. The conductivity was found to vary between 2´10 ±5 and 3´10 1 (W cm) ±1 in the considered range of the electrochemical dopant concentration.Since the discovery of efficient room temperature light emission from porous silicon (PS), great effort has been expended to understand structural, stability, photophysical, and optoelectronic properties of PS. The consensus is that feature sizes of silicon have to be below~1 nm to evoke the short-enough radiative lifetimes needed for optoelectronic applications. While this is a challenging length scale for fabrication methods, it is a size regime where self-assembly materials chemistry may provide solutions. Herein we report a novel and very soft chemistry preparation of 1 nm silicon clusters in free-standing oriented hexagonal mesoporous silica film, OHMSF. The film displays yellow± orange photoluminescence and nanosecond luminescence lifetimes, in contrast to milli-and microsecond lifetimes for PS and nanocrystalline silicon (nc-Si). This new way of preparing light-emitting silicon clusters in oriented mesoporous silica film is purely...

Silver Nitrate/Oligo(ethylene Oxide) Surfactant/Mesoporous Silica Nanocomposite Films and Monoliths

“…It was also shown by 29 Si MAS-NMR spectroscopy that silica polymerizations continue for more than a month. Dag et al (22) have investigated the increase of the intensity ratio of the Q 4 band to the (Q 2 + Q 3 ) bands (where Q 4 is fully polymerized SiO 4 , and Q 3 and Q 2 are originated from O 3 SiOH and O 2 Si(OH) 2 partially polymerized sides, respectively) with time over 2 months. This phenomenon was assigned to further silica polymerization over time in these types of materials (22).…”

“…• C gives nanoclusters of silicon, which emit in the visible region with nanosecond lifetimes (4). Syntheses of semiconductor nanoclusters (4)(5)(6)(7)(8), metal nanoparticles (9), and polymers (10) in the internal surfaces of inorganic mesostructures and surface modifications with different organic groups are some examples of new materials of this type in the field (11)(12)(13).…”

Synthesis of solid solutions of Cd1−xZnxS nanocrystals in the channels of mesostructured silica films

“…[2][3][4][5][6][7][8][9][10] Mesoporous materials have regular and tunable pores with large surface areas. Modifying the surface with optical, magnetic and catalytic materials will prove beneficial in various applications.…”

“…There are many methods described in the literature for modifying the surface of mesoporous materials with active materials. Chemical vapor deposition, 6 ion-exchange 7,8 impregnation, 9,10 true liquid crystalline templating (TLCT), 11,12 functionalizing the pore walls with organic groups to incorporate various nanocrystals into the pores, 13 doping mesopores with quantum dots, 14 etc. are some examples of the methods.…”

“…Using various approaches, CdS, ZnS, Zn 12x Mn x S, and Cd 12x Mn x S nanoparticles have also been synthesized in the channels of mesoporous silica. [7][8][9][10]12,[15][16][17][18] In this article, we focus on the TLCT approach that uses C n EO m non-ionic surfactants in a lyotropic liquid crystalline (LLC) mesophase as the templating agent. 11 A mixture of surfactant, acid (as a catalyst), tetramethylorthosilicate (TMOS, as silica source) and water first produces a liquid mixture that undergoes a transformation, with hydrolysis and condensation, of the silica source to form an LC mesophase and then with further polymerization a solid phase.…”