Germanium quantum dots: Optical properties and synthesis

Abstract

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 (UVNis) 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(l), 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 rz5-+L indirect transitions.

A study of the optical band gap of zinc phthalocyanine nanoparticles using UV–Vis spectroscopy and DFT function

“…Scholars focused on studying the nanoparticles derived from metals and inorganic semiconductors, due to their significant electrical and optical properties compared to bulk materials (Murray et al 1993;Braum et al 1996;Micic et al1995;Heath et al 1994).…”

Hydrogenated Ge nanocrystals: band gap evolution with increasing size

“…Moreover, in Ge, the gap direct (E 0 ≈ 0.9eV) is close to the indirect gap (E g ≈ 0.76eV). Then, it is considered that quantum confinement effects would appear more pronounced in Ge than in Si, and Ge nanocrystals would exhibit a direct-gap semiconductor nature [3]. Takeoka and coworkers [4] have observed a size dependent photoluminescence (PL) from nanostructures of indirect-gap in the nearinfrared region which is closer to the band gap of bulk Ge and which seems more compatible with the quantum confinement model.…”

Synthesis of Nanoamorphous Germanium and Its Transformation to Nanocrystalline Germanium

“…Bottom-up solution-phase synthetic chemistry methods offer better control of the size and shape of the nanoparticles, but often do not provide the good crystallinity required for many applications, and require the use of longchain ligands and surfactants to stabilize the particle surface and control growth. [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] Due to their ease of preparation, these solution-phase methods are also more accessible to many researchers and more amenable to scaling. As a result, their development is in great demand to prepare high-quality materials for detailed chemistry and physical studies, essential for their eventual integration into practical devices.…”

“…[8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] The germanium sources in these investigations are usually the germanium halides, GeX n , or organogermanes [23,24] in which the Ge center is either in the 4 + or 2 + oxidation state (e.g., GeCl 4 , GeBr 4 , GeI 2 ), and long-chain phosphines and alkenes are often used as surface protection ligands for nanoparticle stabilization. The reducing agents used in these investigations are usually the strong ones, such as LiAlH 4 , NaBH 4 , sodium, sodium naphthalide, butyllithium, and Ge Zintl salts.…”

“…The reducing agents used in these investigations are usually the strong ones, such as LiAlH 4 , NaBH 4 , sodium, sodium naphthalide, butyllithium, and Ge Zintl salts. [12][13][14][15][16][17][18][19][20][21][22][23][24] In these reactions, the strength of the reducing agent and the reduction reaction rate are related to each other, and usually these strong reducing agents react very quickly such that the reaction kinetics and nanocrystal growth rates cannot be explored and are not under fine control. Slowing these reduction steps and collecting kinetic information will be very beneficial for the synthesis of Ge nanoparticles and will gainfully contribute to the nanochemistry of these systems.…”