Three different size distributions of Ge quantum dots (>~200, 110, and 60 A) have been synthesized via the ultrasonic mediated reduction of mixtures of chlorogermanes and organochlorogermanes (or organochlorosilanes) by a colloidal sodium/potassium alloy in heptane, followed by annealing in a sealed pressure vessel at 270 °C. The quantum dots are characterized by transmission electron microscopy, x-ray powder diffraction, x-ray photoemission, infrared spectroscopy, and Raman spectroscopy. Colloidal suspensions of these quantum dots were prepared and their extinction spectra are measured with ultraviolet/visible (UV/Vis) and near infrared (IR) spectroscopy, in the regime from 0.6 to 5 eV. The optical spectra are correlated with a Mie theory extinction calculation utilizing bulk optical constants. This leads to an assignment of three optical features to the E(1), E(0'), and E(2) direct band gap transitions. The E(0') transitions exhibit a strong size dependence. The near IR spectra of the largest dots is dominated by E(0) direct gap absorptions. For the smallest dots the near IR spectrum is dominated by the Gamma25-->L indirect transitions.

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Germanium quantum dots: Optical properties and synthesis

FT-IR characterization of tin dioxide gas sensor materials under working conditions

The hexameric n-butyloxotin benzoate, [n-BuSn(O)O2CC6H4NO2.2]6.3C6H6, 1, and the dimeric methyloxotin cyclohexanoate, [(MeSn(O)O2CC6H11)2MeSn(O2CC6H11)3]2, 4, were prepared by condensing the stannoic acid with the respective carboxylic acid. Reaction of n-butyltin. trichloride with the silver salt of the respective carboxylic acid gave the dimeric n-butyloxotin carboxylate compositions, [(n-BuSn(O)O2CR)2-n-BuSn(O2CR)3]2, 2 (R = Ph) and 3 (R = Me). These represent new substances and, as found by X-ray analysis, form a new structural class of organotin compounds for 2-4 having “unfolded drum” or “ladder” structures. The hexamer composition 1 exists in “drum” form. 119Sn NMR data show that the drum and ladder structures interconvert reversibly. 1 crystallizes in the rhombohedral/space group R3 with a H = 15.283 (4) A, cH, = 34.683 (9) A, and Z = 3. 2 crystallizes in the triclinic space group P1 with a = 13.657 (6) A, b = 14.104 (2) A, c = 14.559 (4) A, a = 99.14 (2)°, β = 111.73 (3)°, γ = 101.57 (3)...

Oxo carboxylate tin ladder clusters. a new structural class of organotin compounds

Preparation and properties of dimeric tetra-alkyldistannoxane derivatives: XR2SnOSnR2OH and XR2SnOSnR2OR′

The matrix isolation of vapor phase tin oxides leads to the identification of at least four distinct species: SnO, Sn2O2, Sn3O3, and Sn4O4. Infrared bands for these molecules are observed at 816.1 cm−1 (SnO), 612.6 and 523.2 cm−1 (Sn2O2), 761 cm−1 (Sn3O3), and 516.5 and 416.3 cm−1 (Sn4O4). The spectra of Sn2O2 and Sn3O3 are consistent with molecular symmetries Vh and D3h, respectively, while Sn4O4 may have either D4h or Td symmetry. With the aid of 18O substitution, and normal coordinate analyses, estimates are given for the molecular dimensions of these species. The concentration changes occurring on diffusion are investigated.

R. Okawara

Papers

Infrared spectra of some methyl derivatives of germanium and tin