Decoupling the effects of confinement and passivation on semiconductor quantum dots

Abstract

Semiconductor (SC) quantum dots (QDs) have recently been fabricated by both chemical and plasma techniques for specific absorption and emission of light. Their optical properties are governed by the size of the QD and the chemistry of any passivation at their surface. Here, we decouple the effects of confinement and passivation by utilising DC magnetron sputtering to fabricate SC QDs in a perfluorinated polyether oil. Very high band gaps are observed for fluorinated QDs with increasing levels of quantum confinement (from 4.2 to 4.6 eV for Si, and 2.5 to 3 eV for Ge), with a shift down to 3.4 eV for Si when oxygen is introduced to the passivation layer. In contrast, the fluorinated Si QDs display a constant UV photoluminescence (3.8 eV) irrespective of size. This ability to tune the size and passivation independently opens a new opportunity to extending the use of simple semiconductor QDs.

Inorganic Thin Film Deposition and Application on Organic Polymer Substrates

“…With the growing interest from several sectors to replace common hard substrates by lightweight and flexible ones, polymers are more frequently used as substrates in PVD processes and limit the capabilities to increase the temperature during the thin film deposition drastically. [34] Regardless of chemistry, molecular weight, and substrate type (be it a μm thick foil [46] or mm to cm thick solid polymer bulk, [41b,47] a spin-coated thin layer, [41a,48] a polymer melt, [49] in liquid phase, [50] partially reticulated elastomer, [51] or a chemically grafted polymer brush onto another substrate [52] ), the inherent properties of polymers might represent a challenge during PVD. The heat distortion and glass transition temperatures of most polymers are well below the melting point of most inorganic materials (indium and tin being the most commonly used low melting point sputtered materials with T m of around 150 and 230 C, respectively).…”

“…[91c] This intermixing between the metal and polymer phases depend on the reactivity of the metal. The deposition of sputtered particles into a polymeric liquid had been reported by Rudd et al, [50] where Si nanoparticles were sputtered into a Polyfluoropolyether (PFPE) oil. This embedding process is triggered by the wetting of the metallic particles by the polymer chains above their T g and has also been reported for very slow deposition rates.…”

“…Being able to define and control the location of nucleation points at on the surface and modify the subsequent growth of a film represents the first step toward a 'low-cost nanofabrication process". [34] Regardless of chemistry, molecular weight, and substrate type (be it a μm thick foil [46] or mm to cm thick solid polymer bulk, [41b,47] a spin-coated thin layer, [41a,48] a polymer melt, [49] in liquid phase, [50] partially reticulated elastomer, [51] or a chemically grafted polymer brush onto another substrate [52] ), the inherent properties of polymers might represent a challenge during PVD. A general summary of these complications is presented in Figure 7.…”

“…Another method to create the hybrid nanocomposites is to deposit the inorganic particles onto or into the polymeric matrix. The deposition of sputtered particles into a polymeric liquid had been reported by Rudd et al, [50] where Si nanoparticles were sputtered into a Polyfluoropolyether (PFPE) oil. Such deposition is challenging to perform for several reasons.…”

Comparison of the Optical Properties of Graphene and Alkyl-terminated Si and Ge Quantum Dots

“…the ratio between the number of incident photons and the collected photocarriers) is often not sufficient for implementation in optical devices 20 . It is possible to enhance the optical activity of Si QDs by passivating the surface with oxygen, hydrogen or carbon 21 – 23 . In particular, capping the surface with aliphatic carbon chains has been reported to have a dramatic effect on the optical properties of group IV semiconductor QDs.…”