Synthesis and Study of Aluminum Hexamolybdenocobaltate(III) and Hexamolybdenochromate(III)

Aluminum hexamolybdenocobaltate and hexamolybdenochromate of the Al[MMo₆O₁₈(OH)₆] · 16H₂O composition, where M = Co(III) or Cr(III), were synthesized for the first time. X-ray diffraction study shows that the crystals of the compounds are triclinic; space group P1, Z = 1, and _calcd = 2.665 and 2.611 g/cm³, respectively. The compounds were studied by IR spectroscopy and thermogravimetry.     

Silicon nanocrystals as photo- and sono-sensitizers for biomedical applications

Silicon nanocrystals (nc-Si) with sizes of about 2÷5 nm prepared from porous Si act as photosensitizers of the singlet oxygen generation revealed by direct detection of the luminescence at 0.98 eV (1270 nm). In vitro experiments show a suppression of the cancer cell proliferation because of the effect of photo-excited nc-Si. Aqueous suspensions of nc-Si formed by mechanical grinding (milling) of crystalline and porous Si exhibit properties of efficient sonosensitizers. A destruction of cancer cells under ultrasound irradiation in the presence of nc-Si is observed in vitro. Possible applications of nc-Si as photo- and sono-sensitizers for cancer therapy are discussed.     

Optical properties of serum albumin water solutions,containing mesoporous silicon particles

The interaction of molecules of bovine serum albumin (BSA) with silicon nanoparticles (SiNPs) was studied in water solutions of them at different pH values. The data of photon correlation spectroscopy and IR spectroscopy of studied solutions indicate the absence of interaction between BSA and SiNPs in the pH range 3–7, which is attested to by the experimentally obtained character of the pH dependence of the translational diffusion coefficient D _t and by the absence of hydrogen bonds between the protein carbonyl groups and the OH groups on the surface of mesoporous silicon nanoparticles. The obtained data may play a leading role in further in vivo application of silicon nanoparticles.     

Coherent anti-Stokes Raman scattering in silicon nanowire ensembles

In this letter, we, for the first time, report on coherent anti-Stokes Raman scattering (CARS) spectroscopy of an ensemble of silicon nanowires (SiNWs) formed by wet chemical etching of crystalline silicon with a mask of silver nanoparticles. The fabricated SiNWs have diameter ranged from 30 to 200 nm and demonstrate both visible and infrared photolumine cence (PL) and spontaneous Raman signal, with their intensities depending on presence of silver nanoparticles in SiNWs. The efficiency of CARS in SiNW ensembles is found to be significantly higher than that in crystalline silicon. The results of CARS and PL measurements are explained in terms of resonant excitation of the electron states attributed to silicon nanoparticles.     

Study of birefringence in porous silicon layers by IR Fourier spectroscopy

Birefringence in porous silicon layers prepared with different etching currents on a (110) substrate is studied by IR Fourier spectroscopy. The spectra exhibit beats in the intensity of transmitted and reflected radiation due to the summation of the intensities of the ordinary and extraordinary waves interfering in the porous layer. An analysis of the spectra shows the layers to exhibit properties of a negative uniaxial crystal with the optical axis lying in the layer plane. The difference between the refractive indices of the ordinary and extraordinary waves for a layer with a porosity of 80% reaches 18%. The experimental data are in agreement with the calculations based on the effective-medium approximation, which takes into account the anisotropy of silicon nanocrystal arrangement in a porous layer.     

X-Ray Diffraction Analysis of Aluminum Hexamolybdenocobaltate(III) and Hexamolybdenocromate(III)

Isostructural crystals of aluminum hexamolybdenocobaltate(III) and hexamolybdenocromate(III) Al[MMo₆O₁₈(OH)₆] · 16H₂O (M = Co(III) and Cr(III)) were studied using X-ray diffraction analysis. These compounds crystallize in the triclinic system: space group P , Z = 1, (calcd) = 2.665 and 2.611 g/cm³, respectively. The unit cell parameters were determined: for aluminum hexamolybdenocobaltate(III), a = 6.796(1) Å, b= 11.248(2) Å, c = 11.568(2) Å; = 101.36(2)°, = 96.95(2)°, = 102.23(2)°; for aluminum hexamolybdenocromate(III), a = 6.838(1) Å, b = 11.312(2) Å, c = 11.605(2) Å; = 101.29(3)°, = 97.13(3)°, = 102.15(3)°.     

Interaction of nitrogen dioxide molecules with the surface of silicon nanocrystals in porous silicon layers

The methods of infrared absorption spectroscopy and electron paramagnetic resonance are used for studying the effect of adsorption of NO₂ molecules, which are strong acceptors of electrons, on the electronic and optical properties of silicon nanocrystals in mesoporous silicon layers. It is found that the concentration of free charge carriers (holes) in silicon nanocrystals, which exhibits a nonmonotonic dependence on the NO₂ pressure, sharply increases in the presence of these molecules. At the same time, a monotonic increase in the concentration of dangling silicon bonds (P_b1 centers) is observed. A microscopic model proposed for explaining this effect presumes the formation of donor-acceptor pairs P ₊ ^b1 -(NO₂)^? on the surface of nanocrystals, which ensure an increase in the hole concentration in nanocrystals, as well as P_b1 centers, which are hole-trapping centers. The proposed model successfully explains a substantial increase in photoconductivity (by two or three orders of magnitude) in the layers of porous silicon in the presence of NO₂ molecules; the increment in the concentration of free charge carriers is detected within an order of magnitude of this quantity. The results can be used in designing electronic and luminescence devices based on silicon nanocrystals.     

Silicon nanocrystals as photosensitizers of active oxygen for biomedical applications

Silicon nanocrystals dispersed in water have been used to photosensitize the generation of active oxygen. The photosensitizing efficiency has been estimated through the quenching of the exciton photoluminescence of silicon nanocrystals. Experiments have revealed a strong (up to 80%) decrease in the number of cancer mouse fibroblast cells when they come into contact with photoexcited silicon nanocrystals. The obtained results show that the use of silicon nanocrystals for biomedical applications, in particular, for photodynamic therapy of cancer, is feasible.     

Chemical modification of a porous silicon surface induced by nitrogen dioxide adsorption

The effect of gaseous and liquid nitrogen dioxide on the composition and electronic properties of porous silicon (PS) is investigated by means of optical spectroscopy and electron paramagnetic resonance. It is detected that the interaction process is weak and strong forms of chemisorption on the PS surface, and the process may be regarded as an actual chemical reaction between PS and NO(2). It is found that NO(2) adsorption consists in forming different surface nitrogen-containing molecular groups and dangling bonds of Si atoms (P(b)-centers) as well as in oxidizing and hydrating the PS surface. Also observed are the formation of ionic complexes of P(b)-centers with NO(2) molecules and the generation of free charge carriers (holes) in the volume of silicon nanocrystals forming PS.