Controlled Growth, Microstructure, and Properties of Functional Si Quantum Dot Films via Plasma Chemistry and Activated Radicals

Abstract

Control of plasma and radical generation and associated energy deposition near the growing thin films are still the main challenges in materials fabrication in the plasma-assisted deposition of Si quantum dot (QD) thin film. To control and enhance the material’s performance concerning film properties and application durability, we prepare 2.6 nm sized Si QDs with a fully ordered structure and entrapped them in amorphous silicon nitride using advanced dual frequency capacitively coupled plasmas. Raman and XRD analyses consistent with the high-resolution transmission electron micrographs reveal that the QD size can be controlled and altered from ∼2.6 to 4.0 nm simply by changing the operating pressure, which affects the film’s crystallinity in a broad range from 60% to 72% and the resulting microstructure. Further, a broad visible range ∼ 1.8–3.0 eV photoluminescence, with intense intensity and narrow to broad widths, is observed from Si QDs films. It is also seen that the observed photoluminescence featured is due to the quantum confinement effect within the QD material. Data reveal that the film properties are controllable by modifying a change in the plasma properties and radical parameters. The radio frequency and ultrahigh frequency dual frequency plasmas at low operating pressures have produced a very high atomic density of H and N radicals and a very high plasma density at low electron temperature, which are critically necessary and favorable to the control of film growth, nucleation, and other film properties. It is also seen that the deposition energy plays a significant role for the resulting microstructure and the QD size. The high luminescent yields in the visible range with a PL lifetime of ∼0.75 ns and size-tunable low-temperature deposition with plasma and radical control enable these QD materials as a good candidate for light emitting applications. Additionally, a plausible mechanism is foreseen for the QD film formation.

SiO2 microstructure evolution during plasma deposition analyzed via ellipsometric porosimetry

“…A more detailed connection between plasma properties and film formation is often performed by using line intensities from optical emission spectra [10][11][12][13] that can be connected to a modeling of the emission spectra or to a global chemistry model of the plasma of interest. [14] These connections are often not conclusive since only densities of excited species are directly measured, whereas all global chemistry models require ground state densities.…”

Direct synthesis of magnetron sputtered nanostructured Cu films with desired properties via plasma chemistry for their efficient antibacterial application

“…Particularly, the energy and thermal conditions near the environment of film growth is affected by different plasma species like ions, neutrals, electrons, etc. These plasma species undergo elementary reaction processes such as adsorption, diffusion, and chemical reactions along with the growth and the development of the microstructure of the films . Among the various contributions of deposition energy fluxes, the major contribution of energy fluxes on the substrate can be due to the contribution from radiations from the excited species in the plasma .…”

“…Moreover, the processing/synthesis time is usually long in chemical‐based methods, which involve thermal treatments or sol‐aging for the removal or stabilization of the by‐products . In this sense, plasma‐based deposition could be effective and advantageous, which could bypass these limitations . However, most of these studies including the MS based depositions have utilized either a composite/an alloy film with Cu (Cu 2 O, CuO, Cu‐Ti, Cu‐C alloy, etc.)…”

The size effect to O2−–Ce4+ charge transfer emission and band gap structure of Sr2CeO4

“…With decrease in crystalline size, surface area increased. Grain surface energy was more than the energy of the internal atoms, understood as surface energy . Due to the destruction of the three‐dimensional structure, the grain surface produced excess electrons and repulsion of electrons.…”

“…Grain surface energy was more than the energy of the internal atoms, understood as surface energy. [18,21] Due to the destruction of the threedimensional structure, the grain surface produced excess electrons and repulsion of electrons. The enhanced charge repulsion was caused by the increased electron charge density on the surface, retarding diffusion of negative ions to the surface and thus leading to the reduced phosphor crystalline.…”