Comparative Optical Studies of Chemically Synthesized Silicon Nanocrystals

1996 ◽  
Vol 452 ◽  
Author(s):  
Gildardo R. Delgado ◽  
Howard W.H. Lee ◽  
Susan M. Kauzlarich ◽  
Richard A. Bley
Keyword(s):  
Porous Silicon ◽  
Silicon Nanocrystals ◽  
Surface Passivation ◽  
Theoretical Calculations ◽  
Dominant Role ◽  
Blue Emission ◽  
Surface States ◽  
Si Nanocrystals ◽  
Optical And Electronic Properties ◽  
Passivation Layers

AbstractWe studied the optical and electronic properties of silicon nanocrystals derived from two distinct fabrication procedures. One technique uses a controlled chemical reaction. In the other case, silicon nanocrystals are produced by ultrasonic fracturing of porous silicon layers. We report on the photoluminescence, photoluminescence excitation, and absorption spectroscopy of various size distributions derived from these techniques. We compare the different optical properties of silicon nanocrystals made this way and contrast them with that observed in porous silicon. Our results emphasize the dominant role of surface states in these systems as manifested by the different surface passivation layers present in these different fabrication techniques. Experimental absorption measurements are compared to theoretical calculations with good agreement. Our results provide compelling evidence for quantum confinement in both types of Si nanocrystals. Our results also indicate that the blue emission from very small Si nanocrystals corresponds to the bandedge emission, while the red emission arises from traps.

Modification of Visible Light Emission from Silicon Nanocrystals as a Function of Size, Electronic Structure, and Surface Passivation

1998 ◽  
Vol 536 ◽  
Author(s):  
M.V. Wolkin ◽  
J. Jorne ◽  
P.M. Fauchet ◽  
G. Allan ◽  
C. Delerue
Keyword(s):  
Porous Silicon ◽  
Silicon Nanocrystals ◽  
Surface Passivation ◽  
Light Emission ◽  
Electrochemical Etching ◽  
Theoretical Calculations ◽  
Surface Oxidation ◽  
Stain Etching ◽  
Visible Light Emission ◽  
Effect Of Surface

AbstractThe effect of surface passivation and crystallite size on the photoluminescence of porous silicon is reported. Oxygen-free porous silicon samples with medium to ultra high porosities have been prepared by using electrochemical etching followed by photoassisted stain etching. As long as the samples were hydrogen-passivated the PL could be tuned from the red (750nm) to the blue (400nm) by increasing the porosity. We show that when surface oxidation occurred, the photoluminescence was red-shifted. For sizes smaller than 2.8nm, the red shift can be as large as 1eV but for larger sizes no shift has been observed. Comparing the experimental results with theoretical calculations, we suggest that the decrease in PL energy upon exposure to oxygen is related to recombination involving an electron or an exciton trapped in Si=O double bonds. This result clarifies the recombination mechanisms in porous silicon.

The Oxidation Behavior of Silicon Nanocrystals in the Submonolayer Region

1997 ◽  
Vol 486 ◽  
Author(s):  
J. Diener ◽  
M. Ben-Chorin ◽  
D. I. Kovalev ◽  
G. Polisski ◽  
F. Koch
Keyword(s):  
Fourier Transform ◽  
Infrared Spectroscopy ◽  
Porous Silicon ◽  
Silicon Nanocrystals ◽  
Oxidation Behavior ◽  
Surface Oxidation ◽  
Square Root ◽  
Mesoporous Silicon ◽  
Si Nanocrystals ◽  
Evolution Of Oxygen

AbstractFourier transform infrared spectroscopy is used to determine the time evolution of oxygen incorporation onto the surface of silicon nanocrystals. Oxygen concentrations up to one monolayer are investigated. The temporal progress of surface oxidation of Si nanocrystals in porous silicon shows a linear dependence on the square root of the oxidation time. This is similar to the oxidation of bulk Si and mesoporous silicon.

Influence of the Surfaces Characteristics on the Luminescent Property of Porous Silicon

2014 ◽  
Vol 1052 ◽  
pp. 181-187
Author(s):  
Yan Li Ding ◽  
Yue Zhao ◽  
Yue Feng ◽  
Xiao Yan Liang ◽  
Lin Jun Wang ◽  
...  
Keyword(s):  
Raman Spectroscopy ◽  
Porous Silicon ◽  
Luminescent Property ◽  
Blue Emission ◽  
Surface States ◽  
Green Emission ◽  
Decay Measurement ◽  
Photoconductivity Decay

Photoluminescence of porous silicon (PS) prepared by different etched time was studied. The photoluminescence might originate from the recombination of carriers and surface states, which was proved by FTIR, Raman spectroscopy and SEM. Furthermore, the hydrogen-related groups on the PS surface could eliminate the surface states for the blue emission, but the quantities of surface states for the green emission were depended on the uncovered area on the PS surface. Moreover, the shape of photoconductivity curve was depended on the quantities of the surface states, which also was related to the uncovered area on the PS surface. In addition, the results of the microwave-detected photoconductivity decay measurement indicated thatthe defects on the PS surface increased with the increase of the etched time, which would be related to the increase of the depth of pores.

Grains of Porous Silicon Embedded in SiO2:Studies of Optical Gain and Electroluminescence

2004 ◽  
Vol 99-100 ◽  
pp. 31-36 ◽  
Author(s):  
K. Dohnalová ◽  
K. Luterová ◽  
J. Valenta ◽  
Jiří Buršík ◽  
M. Procházka ◽  
...  
Keyword(s):  
Porous Silicon ◽  
Silicon Nanocrystals ◽  
Visible Region ◽  
Optical Gain ◽  
Intrinsic Property ◽  
Stimulated Emission ◽  
Silicon Nanostructures ◽  
Porous Si ◽  
Si Nanocrystals ◽  
Excitation Spot

Recent reports on experimental observation of optical gain in silicon nanostructures in the visible region, performed at several laboratories all over the world, have triggered an extraordinary surge of interest in silicon lasing. However, attempts aimed at reproducing the red stimulated emission from „standard“silicon nanocrystals (sized 3-5 nm) at some other laboratories either failed, or. did not come to definite conclusions. Therefore, more detailed measurements of optical gain in a wider variety of samples containing Si nanocrystals are required in order to unravel whether or not the observation of optical gain is an intrinsic property of Si nanocrystals. We have performed a detailed study of optical gain in layers of densely packed Si nanocrystals in SiO2, prepared on the basis of porous Si, using the variable-stripe-length (VSL) method in combination with the shifted-excitation-spot (SES) method. In selected samples we have observed a distinct difference in behaviour between VSL and SES curves, indicating the occurrence of positive optical gain of ~ 24 cm-1. Preliminary reports on transport and electroluminescence measurements in thin films of SiO2 doped with porous silicon grains, prepared by spin-coating technique, are also discussed.

Improved Optoelectronic Characteristics of Nanocrystalline Porous Silicon by High-Pressure Water Vapor Annealing

2004 ◽  
Vol 832 ◽  
Author(s):  
Bernard Gelloz ◽  
Akira Kojima ◽  
Nobuyoshi Koshida
Keyword(s):  
High Pressure ◽  
Porous Silicon ◽  
Surface Passivation ◽  
High Surface ◽  
Peak Wavelength ◽  
Si Nanocrystals ◽  
Vapor Annealing ◽  
Pressure Water ◽  
Annealing Pressure ◽  
Very High

ABSTRACTA high-pressure H2O vapor annealing technique has been applied to nanocrystalline porous silicon (PS). The effects on the photoluminescence (PL) are reported here for PS samples of different initial porosities, in different conditions of the annealing pressure. A drastic enhancement of the PL intensity has been achieved, while both the emission band and the peak wavelength remain almost unchanged. The best results have been obtained with an initial PS porosity of about 68 %. The resulting layers consist of Si nanocrystals embedded into an SiO2tissue. The high external quantum efficiency obtained in treated PS (23%) may be attributed mainly to a very high surface passivation by high quality oxide and an enhancement in the localization of photoexcited carriers.

Enhancement in Efficiency and Stability of Oxide-Free Blue Emission from Porous Silicon by Surface Passivation

1998 ◽  
Vol 536 ◽  
Author(s):  
H. Mizuno ◽  
N. Koshida
Keyword(s):  
Porous Silicon ◽  
Surface Chemistry ◽  
Surface Passivation ◽  
Blue Emission ◽  
Hydrogen Gas ◽  
Surface Oxide ◽  
Visible Emission ◽  
Pl Spectra ◽  
Illumination Method

AbstractThe establishment of tuning techniques of visible emission from porous silicon (PS) is very important from both physical and technological viewpoints. As previously reported that the photoluminescence (PL) spectra of PS can continuously be controlled from red to blue simply by postanodization illumination method without any growth of the surface oxide. Details of this oxide-free blue emission have been studied in terms of the PL decay dynamics and surface chemistry. We report here that post-preparation exposure of PS to hydrogen gas is very useful for improvement in efficiency and stability of blue PL. Based on this technique, it has become possible to get blue electroluminescence even at low bias voltages.

Surface States and Band Gap Correlation in Silicon Nanoclusters

2015 ◽  
Vol 1107 ◽  
pp. 308-313
Author(s):  
Sib Krishna Ghoshal ◽  
M.R. Sahar ◽  
R. Arifin ◽  
M.S. Rohani ◽  
K. Hamzah
Keyword(s):  
Band Gap ◽  
Surface Passivation ◽  
Light Emission ◽  
Radiative Lifetime ◽  
Surface States ◽  
Optical Gain ◽  
Visible Luminescence ◽  
Optical And Electronic Properties ◽  
Effect Of Oxygen

Tuning the visible emission of Si nanomaterials by modifying their size and shape is one of the key issue in optoelectronics. The observed optical gain in Si-nanoclusters (NCs) has given further impulse to nanosilicon research. We develop a phenomenological model by combining the effects of surface passivation, exciton states and quantum confinement (QC). The size and passivation dependent band gap, oscillator strength, radiative lifetime and photoluminescence (PL) intensity for NCs with diameter ranging from 1.0 to 6.0 nm are presented. By controlling a set of fitting parameters, it is possible to tune the optical band gap, PL peak and intensity. In case of pure clusters, the band gap is found to decrease with increasing NC size. Furthermore, the band gap increases on passivating the surface of the cluster with hydrogen and oxygen respectively in which the effect of oxygen is more robust. Both QC and surface passivation in addition to exciton effects determine the optical and electronic properties of silicon NCs. Visible luminescence is due to radiative recombination of electrons and holes in the quantum-confined NCs. The role of surface states on the band gap as well as on the HOMO-LUMO states is also examined and a correlation is established. Our results are in conformity with other observations. The model can be extended to study the light emission from other nanostructures and may contribute towards the development of Si based optoelectronics.

Luminescence from Silicon and Germanium Nanowires: A Phenomenological Model

2014 ◽  
Vol 895 ◽  
pp. 424-428
Author(s):  
Sib Krishna Ghoshal ◽  
M.R. Sahar ◽  
Ramli Arifin ◽  
M. Supar Rohani ◽  
Khaidzirh Hamzah
Keyword(s):  
Phenomenological Model ◽  
Quantum Confinement ◽  
Room Temperature ◽  
Surface Passivation ◽  
Surface States ◽  
Exciton Energy ◽  
Germanium Nanowires ◽  
Optical And Electronic Properties ◽  
Silicon And Germanium ◽  
Room Temperature Luminescence

The room temperature luminescence intensity as a function of the size and the voltage of silicon (Si) and germanium (Ge) nanowires (NWs) having 5 to 30 atoms per wire with diameter ranging from 1.2 nm to 3.5 nm are investigated. The effects of exciton energy states, localized surface states and the quantum confinement are integrated in our phenomenological model to derive an analytical expression for the photoluminescence (PL) and electroluminescence (EL) intensity. By controlling a set of fitting parameters in the model, one can tune the EL and PL peak and intensity. Our results show that both quantum confinement and surface passivation in addition to exciton effects determine the optical and electronic properties of Si and Ge NWs. We observed that the EL and PL intensities occurs at the same energy, however the EL intensity has sharp Gaussian sub peaks and red shifted compared to the PL intensity.

scholarly journals Development of an improved two-sphere integration technique for quantifying black carbon concentrations in the atmosphere and seasonal snow

2020 ◽  
Vol 13 (1) ◽  
pp. 39-52 ◽  
Author(s):  
Xin Wang ◽  
Xueying Zhang ◽  
Wenjing Di
Keyword(s):  
Black Carbon ◽  
Light Absorption ◽  
Optical Method ◽  
Theoretical Calculations ◽  
Dominant Role ◽  
Northern China ◽  
Least Squares Regression ◽  
Seasonal Snow ◽  
Empirical Procedure ◽  
Total Light

Abstract. An improved two-sphere integration (TSI) technique has been developed to quantify black carbon (BC) concentrations in the atmosphere and seasonal snow. The major advantage of this system is that it combines two distinct integrated spheres to reduce the scattering effect due to light-absorbing particles and thus provides accurate determinations of total light absorption from BC collected on Nuclepore filters. The TSI technique can be calibrated using a series of 15 filter samples of standard fullerene soot. This technique quantifies the mass of BC by separating the spectrally resolved total light absorption into BC and non-BC fractions. To assess the accuracy of the improved system, an empirical procedure for measuring BC concentrations with a two-step thermal–optical method is also applied. Laboratory results indicate that the BC concentrations determined using the TSI technique and theoretical calculations are well correlated (R2=0.99), whereas the thermal–optical method underestimates BC concentrations by 35 %–45 % compared to that measured by the TSI technique. Assessments of the two methods for atmospheric and snow samples revealed excellent agreement, with least-squares regression lines with slopes of 1.72 (r2=0.67) and 0.84 (r2=0.93), respectively. However, the TSI technique is more accurate in quantifications of BC concentrations in both the atmosphere and seasonal snow, with an overall lower uncertainty. Using the improved TSI technique, we find that light absorption at a wavelength of 550 nm due to BC plays a dominant role relative to non-BC light absorption in both the atmosphere (62.76 %–91.84 % of total light absorption) and seasonal snow (43.11 %–88.56 %) over northern China.

Laser Induced Etching for Generation of Si Nanocrystals and Spectroscopic Investigation of Morphology

2005 ◽  
Vol 23 ◽  
pp. 43-46
Author(s):  
H.S. Mavi ◽  
S. Rath ◽  
Arun Shukla
Keyword(s):  
Quantum Confinement ◽  
Silicon Nanocrystals ◽  
Laser Wavelength ◽  
Interconnected Network ◽  
Substrate Type ◽  
Argon Ion Laser ◽  
Si Nanocrystals ◽  
Ion Laser ◽  
Laser Induced Etching ◽  
Argon Ion

Laser-induced etching of silicon is used to generate silicon nanocrystals. The pore structure depends on the substrate type and etching laser wavelength. Porous silicon (PS) samples prepared by Nd:YAG laser (1.16 eV) etching of n-type substrate showed a fairly uniform and highly interconnected network of nearly circular pores separated by thin columnar boundaries, while no circular pits were produced by argon- ion laser (2.41 eV) etching under similar conditions. The size and size distribution of the nanocrystals are investigated by Raman and photoluminescence spectroscopies and analyzed within the framework of quantum confinement models.

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