Influence of reaction parameters on the photoluminescence properties of free standing functionalized silicon nanocrystals

2010 ◽  
Vol 1260 ◽  
Author(s):  
Anoop Gupta ◽  
Hartmut Wiggers
Keyword(s):  
Optical Properties ◽  
Surface Functionalization ◽  
Silicon Nanocrystals ◽  
Organic Molecules ◽  
Surface Passivation ◽  
Light Emission ◽  
Emission Spectra ◽  
Surface Oxidation ◽  
Free Standing ◽  
The Stability

AbstractWhile silicon nanostructures acquire novel optical properties due to miniaturization, the stability of light emission is severely limited because of exciton trapping due to surface oxidation coming along with the formation of defects. Grafting of organic molecules on a hydrogen-terminated silicon surface via hydrosilylation provides a promising route to stabilize their surface against oxidation. In this communication, we report on the effect of surface passivation on the optical properties of freestanding silicon nanocrystals (Si-NCs). The surface functionalization of hydrogen-terminated Si-NCs with organic molecules was achieved via liquid phase hydrosilylation. We demonstrate that surface functionalization does not preserve the original emission of hydrogen-terminated Si-NCs. It is observed that the emission spectrum of green emitting hydrogen-terminated Si-NCs is red shifted after surface functionalization. We find that the direction of shift does not depend on the type of organic ligands and the reaction conditions, however, the amount of shift can be altered. The factors influencing the shift in the emission spectra of functionalized Si-NCs with respect to hydrogen-terminated samples are discussed.

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.

First-Principles Study of Silicon Nanocrystals: Structural and Electronic Properties, Absorption, Emission, and Doping

2008 ◽  
Vol 8 (2) ◽  
pp. 479-492 ◽  
Author(s):  
Stefano Ossicini ◽  
O. Bisi ◽  
Elena Degoli ◽  
I. Marri ◽  
Federico Iori ◽  
...  
Keyword(s):  
Optical Properties ◽  
Silicon Nanocrystals ◽  
Density Functional ◽  
Stokes Shift ◽  
Emission Spectra ◽  
Visible Range ◽  
Hydrogenated Silicon ◽  
Absorption And Emission ◽  
Co Doping ◽  
Electron Hole Pair

Total energy calculations within the Density Functional Theory have been carried out in order to investigate the structural, electronic, and optical properties of un-doped and doped silicon nano-structures of different size and different surface terminations. In particular the effects induced by the creation of an electron-hole pair on the properties of hydrogenated silicon nanoclusters as a function of dimension are discussed in detail showing the strong interplay between the structural and optical properties of the system. The distortion induced on the structure by an electronic excitation of the cluster is analyzed and considered in the evaluation of the Stokes shift between absorption and emission energies. Besides we show how many-body effects crucially modify the absorption and emission spectra of the silicon nanocrystals. Starting from the hydrogenated clusters, different Si/O bonding at the cluster surface have been considered. We found that the presence of a Si—O—Si bridge bond originates significative excitonic luminescence features in the near-visible range. Concerning the doping, we consider B and P single- and co-doped Si nanoclusters. The neutral impurities formation energies are calculated and their dependence on the impurity position within the nanocrystal is discussed. In the case of co-doping the formation energy is strongly reduced, favoring this process with respect to the single doping. Moreover the band gap and the optical threshold are clearly red-shifted with respect to that of the pure crystals showing the possibility of an impurity based engineering of the absorption and luminescence properties of Si nanocrystals.

Nonlinear Optical Properties of Silicon Nanocrystallites: Effects of Passivation

1994 ◽  
Vol 358 ◽  
Author(s):  
A.A. Seraphin ◽  
F.J. Aranda ◽  
E. Werwa ◽  
D.V.G.L.N. Rao ◽  
K.D. Kolenbrander
Keyword(s):  
Thin Films ◽  
Optical Properties ◽  
Nonlinear Optical ◽  
Surface Passivation ◽  
Light Emission ◽  
Strong Dependence ◽  
Nonlinear Optical Susceptibility ◽  
Picosecond Pulses ◽  
Silicon Nanocrystallites ◽  
Behavior Systems

ABSTRACTDegenerate four-wave mixing with picosecond pulses at 532 nm has been used to study the third-order nonlinear optical susceptibility (x(3)) for a series of passivated thin films of silicon nanocrystallites. A pulsed laser ablation supersonic expansion source of isolated silicon nanocrystallites was used to deposit thin films onto inert substrates. These films were subsequently passivated using chemical etches or oxidation steps. We observe a strong dependence of the measured x(3) as a function of the degree of passivation, indicating the fundamental importance of the surface of the nanocrystallite in enabling the nonlinear optical behavior. Systems providing more complete passivation were found to have greatly enhanced X(3) behavior when compared to poorly passivated systems. Surface passivation is also shown to be critical to the visible photoluminescence behavior of the thin films, as poorly passivated nanocrystallites exhibit very weak light emission, while well passivated systems show efficient emission. In both cases, the passivation controls the recombination pathways of excited carriers and determines the material's optical properties.

Photoluminescent Silicon Nanocrystals with Mixed Surface Functionalization for Biophotonics

2006 ◽  
Vol 958 ◽  
Author(s):  
Folarin Erogbogbo ◽  
Mark T. Swihart
Keyword(s):  
Surface Functionalization ◽  
Silicon Nanocrystals ◽  
Surface Composition ◽  
Buffer Solutions ◽  
Alkyl Groups ◽  
Residual Hydrogen ◽  
Reactive Groups ◽  
In Series ◽  
The Stability ◽  
Multiple Molecules

ABSTRACTOrange-emitting photoluminescent silicon nanocrystals have been grafted with pairs of compounds to produce a mixed monolayer on their surface. Vinyl acetic acid (VA) is used to enhance dispersibility in water by providing carboxyl termination, while alkyl groups are used to improve the stability of the photoluminescence (PL). The grafting of these molecules to the surface is enabled by an etching procedure that leaves a hydrogen terminated surface on the silicon nanocrystals. Multiple molecules can be grafted in series by taking advantage of the residual hydrogen present after initial grafting with a first compound. Multiple molecules can also be grafted in parallel by allowing them to compete for surface reactive sites and varying their concentration in solution to control the composition of the mixed surface layer. Both series and parallel grafting result in particles that have a mixture of two distinct molecules on their surface, and thereby allow control of the particle dispersibility in different solvents and the density of reactive groups for subsequent functionalization steps. Optimizing the surface composition may allow production of particles that can be reacted with proteins via carbodiimide linking chemistries while maintaining their PL and their dispersibility in water and buffer solutions. Here we focus on the parallel grafting approach.

Free-Standing 2D Silicon Nanocrystals Stabilized with Perfluorophenyl Ligands: Experiment and Ab Initio Research

2015 ◽  
Vol 233-234 ◽  
pp. 575-578 ◽  
Author(s):  
Leonid Aslanov ◽  
Igor Kudryavtsev ◽  
Valery Zakharov ◽  
Erkin Kulatov ◽  
Yurii Uspenskii
Keyword(s):  
Atomic Force Microscopy ◽  
Optical Properties ◽  
Ab Initio ◽  
Electronic Structures ◽  
Silicon Nanocrystals ◽  
Silicon Nanoparticles ◽  
Free Standing ◽  
Force Microscopy ◽  
Atomic Force ◽  
Easy Integration

Silicon (Si) is currently the basis of most of nanodevice technology, therefore ultrathin materials based on Si have the great advantage of easy integration into existing circuitry. First flat silicon nanoparticles have been obtained with perfluorophenyl (PFPh) ligand coating. The size of these particles varied from 15 to 50 nm. Their thickness evaluated with the atomic force microscopy was about 3.3 nm. Based on ab initio DFT calculations we investigate the geometries and electronic structures of free-standing PFPh-stabilized 2D silicon in order to see if such systems have promising electronic and optical properties. We also examined the effect of doping PFPh-stabilized 2D silicon by the Mn atoms.

Surface oxidation effects on the optical properties of silicon nanocrystals

2002 ◽  
Vol 65 (12) ◽  
Author(s):  
Igor Vasiliev ◽  
James R. Chelikowsky ◽  
Richard M. Martin
Keyword(s):  
Optical Properties ◽  
Silicon Nanocrystals ◽  
Surface Oxidation

Effects of different valence atoms on surface passivation of silicon carbide nanowires

2021 ◽  
pp. 2150207
Author(s):  
Wan-Duo Ma ◽  
Wei-Kai Liu ◽  
Pei Gong ◽  
Ya-Hui Jia ◽  
Ying-Ying Yang ◽  
...  
Keyword(s):  
Silicon Carbide ◽  
Optical Properties ◽  
Ultraviolet Light ◽  
Vacuum Ultraviolet ◽  
Surface Passivation ◽  
Light Region ◽  
Mechanism Of Interaction ◽  
Deep Ultraviolet ◽  
The Stability ◽  
Cl Atoms

In this paper, based on the first principles, we study the properties of silicon carbide nanowires (SiCNWs) passivated by monovalent hydrogen (H), heptavalent fluorine (F) and chlorine (Cl) atoms at the electronic level to reveal the mechanism of interaction between different valence electrons in the passivation process. The results show that the passivation can improve the inhomogeneity of the surface and internal Si–C bonds, and improve the stability of the SiCNWs structure. The structure of F-SiCNWs is the most stable. Meanwhile, passivation increases the bandgap of the SiCNWs, and the bandgap of H, F and Cl passivation SiCNWs decreases successively, this is because the potential energy of H-1s, F-2p and Cl-3p interacting with Si-3p decreases in turn. Besides, heptavalent F and Cl passivation can regulate some optical properties of the SiCNWs to the deep-ultraviolet light regions such as absorption, conductivity, refractive index and loss function. Monovalent H passivation can regulate some optical properties of the SiCNWs to the vacuum ultraviolet light region (UVD). These studies have potential application value for the development of deep-ultraviolet micro–nano devices.

scholarly journals Synthesis and Optical Properties of Thiol Functionalized CdSe/ZnS (Core/Shell) Quantum Dots by Ligand Exchange

2014 ◽  
Vol 2014 ◽  
pp. 1-14 ◽  
Author(s):  
Huaping Zhu ◽  
Michael Z. Hu ◽  
Lei Shao ◽  
Kui Yu ◽  
Reza Dabestani ◽  
...  
Keyword(s):  
Quantum Dots ◽  
Optical Properties ◽  
Ligand Exchange ◽  
Surface Passivation ◽  
Emission Spectra ◽  
Trioctylphosphine Oxide ◽  
Core Shell ◽  
Initial Surface ◽  
Cdse Core ◽  
Surface Modified

The colloidal photoluminescent quantum dots (QDs) of CdSe (core) and CdSe/ZnS (core/shell) were synthesized at different temperatures with different growth periods. Optical properties (i.e., UV/Vis spectra and photoluminescent emission spectra) of the resulting QDs were investigated. The shell-protected CdSe/ZnS QDs exhibited higher photoluminescent (PL) efficiency and stability than their corresponding CdSe core QDs. Ligand exchange with various thiol molecules was performed to replace the initial surface passivation ligands, that is, trioctylphosphine oxide (TOPO) and trioctylphosphine (TOP), and the optical properties of the surface-modified QDs were studied. The thiol ligand molecules in this study included 1,4-benzenedimethanethiol, 1,16-hexadecanedithiol, 1,11-undecanedithiol, biphenyl-4,4′-dithiol, 11-mercapto-1-undecanol, and 1,8-octanedithiol. After the thiol functionalization, the CdSe/ZnS QDs exhibited significantly enhanced PL efficiency and storage stability. Besides surface passivation effect, such enhanced performance of thiol-functionalized QDs could be due to cross-linked assembly formation of dimer/trimer clusters, in which QDs are linked by dithiol molecules. Furthermore, effects of ligand concentration, type of ligand, and heating on the thiol stabilization of QDs were also discussed.

Luminescence of Silicon Nanocrystals in SiO2: Effects of Excitation Spectrum

2003 ◽  
Vol 777 ◽  
Author(s):  
A. Hryciw ◽  
C.W. White ◽  
K.H. Chow ◽  
A. Meldrum
Keyword(s):  
Ion Implantation ◽  
Silicon Nanocrystals ◽  
Light Emission ◽  
Emission Spectra ◽  
Excitation Power ◽  
Fused Silica ◽  
Peak Emission Wavelength ◽  
Si Nanocrystals ◽  
Recombination Processes ◽  
High Pump

AbstractSilicon nanocrystals formed by ion implantation and annealing of fused silica wafers show a strong, broad photoluminescence (PL) peak centered at a wavelength between 750 and 900 nm, depending on the processing conditions. This luminescence has been extensively investigated and trial device structures based on these materials have been built. However, relatively few studies also report the optical absorption spectra. In fact, the absorbance of these specimens is quite low (usually < 10%) at wavelengths greater than 450 nm (i.e., at the pump wavelengths typically used for PL studies). This suggests that in numerous studies of Si nanocrystals produced by ion implantation, only a small fraction of the nanocrystals is responsible for the observed PL at the typical pump wavelengths. In this study, we investigated how the PL spectrum and intensity depend on the power and wavelength of the pump laser. We find that the PL intensity approaches saturation at high pump fluences, and that the peak emission wavelength is sensitive to the excitation power. These observations can be attributed to the dynamics of the excitation/recombination processes at different energies, and indicate that considerable care must be taken when comparing the emission spectra of different specimens. Our data are uniformly consistent with a mechanism of light emission involving subgap states (i.e., radiative trap sites) and are not supportive of a “pure” quantum confinement model.

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