Reduction in size often does more than simply make things smaller. There are many properties of materials that undergo qualitative, often sudden, changes below a certain size scale. This Report first describes some of these size-dependent properties. Following this general description, recent developments in a number of selected topics in nanoscience are covered. These topics are: luminescence from Au nanoparticles; Si (and related) nanoparticle luminescence; modification of optical absorption by surface adsorption on nanoparticles; and transistors (and some other devices) based on nanotubes and nanowires.

https://www.onlinelibrary.wiley.com/doi/pdf/10.1002/adma.200790035

When Small Is Different: Some Recent Advances in Concepts and Applications of Nanoscale Phenomena

A multifunctional optical film for enhancing light extraction includes a flexible substrate, a structured layer having nanoparticles of different sizes, and a backfill layer. The structured layer effectively uses microreplicated diffractive or scattering nanostructures located near enough to the light generation region to enable extraction of an evanescent wave from an organic light emitting diode (OLED) device. The backfill layer has a material having an index of refraction different from the index of refraction of the structured layer. The backfill layer also provides a planarizing layer over the structured layer in order to conform the light extraction film to a layer of an OLED display device. The film may have additional layers added to or incorporated within it to an emissive surface in order to effect additional functionalities beyond improvement of light extraction efficiency.

Light extraction film with nanoparticle coatings

The effects of the stoichiometry of the Si-rich oxide (SRO) layer, O/Si ratio, on the structural and optical properties of SRO/SiO2 multilayer films were investigated in this work. SRO/SiO2 multilayer films with different O/Si ratios were grown by a co-sputtering technique, and Si quantum dots (QDs) were formed with post-deposition annealing. By transmission electron microscopy (TEM) and glancing incidence x-ray diffraction (GIXRD), it was found that the Si QD size decreases with increases in O/Si ratio. The photoluminescence (PL) spectrum varies with the O/Si ratio in band position, shape and intensity. In addition, it was observed that the absorption edge blue-shifts with increases in the O/Si ratio. The change in the absorption edge is consistent with strengthening quantum confinement effects in Si QDs, as indicated by TEM and GIXRD. The optical properties were also investigated by 2D photoluminescence excitation (2D-PLE) and lifetime measurements. The origin of emission and absorption is discussed based on the absorption, PL, 2D-PLE and decay time measurements.

http://www.if.pwr.edu.pl/~artur/N20-2009.pdf

Effects of Si-rich oxide layer stoichiometry on the structural and optical properties of Si QD/SiO2 multilayer films.

A new approach to obtain visible luminescence from sol–gel-derived SiOC films is proposed. In order to investigate the influence of Si and C content, Si- and C-rich SiOC films were prepared as well as stoichiometric SiOC films. High intense white luminescence is obtained where the emission color can be controlled by the experimental parameters such as the starting sol–gel-composition and the pyrolysis temperature. In stoichiometric SiOC films, low pyrolysis temperature yields UV-blue luminescence, whereas high temperatures favor green-yellow luminescence. On the contrary, in Si-rich SiOC films, intense white luminescence is obtained with a broad emission from 430 to 900 nm and an external quantum efficiency (EQE) of 11.5%. Relatively, stoichiometric SiOC films showed an EQE of 5%. Finally, C-rich SiOC films did not show noticeable luminescence due to absorption by carbon clusters.

White Luminescence from Sol–Gel‐Derived SiOC Thin Films

White light luminescence from annealed thin ZnO deposited porous silicon

The effect of carbon doping on the enhancement of visible luminescence from silicon-rich silicon oxide (SRSO), which consists of Si nanoclusters embedded inside a SiO2 matrix, is investigated. C-doped SRSO films were fabricated by electron cyclotron resonance-plasma enhanced chemical vapor deposition method using SiH4, O2, and CH4 source gases followed by a high-temperature anneal. Intense blue-white visible luminescence, visible to the naked eye under daylight conditions, was observed from the film with a nearly equal amount of C and excess Si (∼16 at. %) after an anneal at 950 °C. Furthermore luminescence could be tuned from 1.8 to 2.5 eV by controlling the C to excess Si ratio, the C content, and the anneal temperature. Taken together with the infrared absorption spectra, these results indicate that the luminescence is attributed to exciton recombination in C-incorporated Si nanoclusters.

Intense blue-white luminescence from carbon-doped silicon-rich silicon oxide

The enhancement in light extraction efficiency from a periodic micron-scale rugged surface pattern on Si quantum dot light-emitting-diode (Si-QD LED) structures was investigated, both numerically and experimentally. Micron-scale rugged surface patterns were fabricated on the top layer of the Si-QD LED to increase the extraction of light from the active layer. The optimum light extraction condition for a Si-QD LED corresponded to a pattern size/period ratio of ∼0.7. In experiments, the luminescent powers of a Si-QD LED with/without micron-scale surface patterns increase linearly with current density, and the efficiency of light extraction was enhanced by a factor of 2.8.

Enhancement of light extraction from a silicon quantum dot light-emitting diode containing a rugged surface pattern

This study presents a more improved Si-LED using micron scale rugged surface pattern. This paper reports experimental results and comparisons with other studies. The differences between experimental and theoretical results from electroluminescence of Si-QD LEDs are also reported.

/pdf/high-extraction-efficiency-si-qd-led-using-rugged-surface-2isb1gnhn4.pdf

High-extraction-efficiency Si-QD LED using rugged surface pattern

Halbleiter-leuchtdiode mit einem silizium-nano-dot und herstellungsverfahren dafür

Time-resolved PL characteristic of the nc-Si QDs in SiNx matrix grown by PECVD is studied. The measured PL lifetime of nc-Si QDs is about 0.43 ns

Kwan-Sik Cho

Papers

Intense blue-white luminescence from carbon-doped silicon-rich silicon oxide

Enhancement of light extraction from a silicon quantum dot light-emitting diode containing a rugged surface pattern

High-extraction-efficiency Si-QD LED using rugged surface pattern

Halbleiter-leuchtdiode mit einem silizium-nano-dot und herstellungsverfahren dafür

Sub-ns Dynamics of nc-Si QDs in SiNx Matrix Grown by PECVD