Depth-Resolved Microspectroscopy of Porous Silicon Multilayers

AbstractWe have measured micro-photoluminescence (PL) and micro-Raman spectra on the cross section of porous silicon multilayers to sample different layer depths. We find noticeable differences in the spectra of layers with different porosity, as expected from the quantum confinement of electrons and phonons in silicon nanocrystals with different average sizes. The PL emission band gets stronger, blue shifts, and narrows at the high porosity layers. The average size can be estimated from the shift. The Raman phonon band at 520 cm−1 weakens and broadens asymmetrically towards the low energy side. The line shape can be related quantitatively with the average size by the phonon confinement model. To get a good agreement with the model we add a band at around 480 cm−1, which has been attributed to amorphous silicon. We also have to leave as free parameters the bulk silicon phonon frequency and its line width, which depend on temperature and stress. We reduced laser power to eliminate heating effects. Then we use the change of frequency with depth to monitor the stress. At the interface with the substrate we find a compressive stress in excess of 10 kbar, which agrees with the reported lattice mismatch. Finally, average sizes are larger than those estimated from PL.

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Photoluminescence in Porous Silicon: Evidence for the Quantum Confinement Model

MRS Proceedings ◽

10.1557/proc-256-111 ◽

1991 ◽

Vol 256 ◽

Cited By ~ 4

Author(s):

David L. Naylor ◽

Sung B. Lee ◽

John C. Pincenti ◽

Brett E. Bouma

Keyword(s):

Porous Silicon ◽

Hydrofluoric Acid ◽

Quantum Wire ◽

Quantum Confinement ◽

Electrochemical Etching ◽

Photoluminescence Spectra ◽

Peak Wavelength ◽

Effects Of Temperature ◽

Good Agreement ◽

Confinement Model

ABSTRACTPhotoluminescence spectra have been measured in porous silicon following electrochemical etching in dilute hydrofluoric acid (HF). The effects of HF concentration during etching on the efficiency and peak wavelength of photoluminescence have been investigated. The effects of temperature between 25°C and 200°C on PL spectra have been recorded. Photoluminescence lifetimes as a function of wavelength have been studied following ultrashort UV photoexcitation. A number of lifetime components in the decay are observed the longest in good agreement over the wavelength range of 500 to 600 nm with a silicon quantum wire model. At longer wavelengths a departure from lifetimes of the wire model is observed and two hypotheses for the discrepancy are presented.

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

Journal of Metastable and Nanocrystalline Materials ◽

10.4028/www.scientific.net/jmnm.23.43 ◽

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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Comparative Optical Studies of Chemically Synthesized Silicon Nanocrystals

MRS Proceedings ◽

10.1557/proc-452-177 ◽

1996 ◽

Vol 452 ◽

Cited By ~ 5

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.

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Quantum Confinement Effects on the Dielectric Constant of Porous Silicon

MRS Proceedings ◽

10.1557/proc-283-437 ◽

1992 ◽

Vol 283 ◽

Cited By ~ 24

Author(s):

R. Tsu ◽

L. Ioriatti ◽

J. F. Harvey ◽

H. Shen ◽

R. A. Lux

Keyword(s):

Dielectric Constant ◽

Porous Silicon ◽

Size Effects ◽

Quantum Confinement ◽

Electrochemical Etching ◽

Index Of Refraction ◽

Quantum Size Effects ◽

Quantum Size ◽

Quantum Confinement Effects ◽

Shallow Impurities

ABSTRACTThe reduction of the dielectric constant due to quantum confinement is studied both experimentally and theoretically. Angle resolved ellipsometry measurements with Ar- and He-Ne-lasers give values for the index of refraction far below what can be accounted for from porosity alone. A modified Penn model to include quantum size effects has been used to calculate the reduction in the static dielectric constant (ε) with extreme confinement. Since the binding energy of shallow impurities depends inversely on ε2, the drastic decrease in the carrier concentration as a result of the decrease in ε leads to a self-limiting process for the electrochemical etching of porous silicon.

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Comparison of Small-Angle Neutron Scattering of δ' Precipitation in an Al–Li Alloy at a High-Flux Reactor and at a Pulsed-Neutron Source

Journal of Applied Crystallography ◽

10.1107/s0021889897001751 ◽

1997 ◽

Vol 30 (5) ◽

pp. 602-606 ◽

Cited By ~ 2

Author(s):

G. Albertini ◽

F. Carsughi ◽

R. Coppola ◽

R. K. Heenan ◽

M. Stefanon

Keyword(s):

Neutron Scattering ◽

Small Angle ◽

Small Angle Neutron Scattering ◽

Size Distribution Function ◽

Data Sets ◽

Flux Reactor ◽

Average Size ◽

Pulsed Neutron ◽

Pulsed Neutron Source ◽

Good Agreement

Two different small-angle neutron scattering (SANS) facilities, the D11 camera at the Institut Laue–Langevin (ILL, Grenoble, France) and the LOQ time-of-flight diffractometer at the Rutherford Appleton Laboratory (RAL, Didcot, Oxon, England), were used in the investigations of δ′-Al3Li precipitation at 463 K in Al–Li 3% alloy. The results obtained from the steady-state reactor and from the pulsed source by using two different data-acquisition techniques and two different procedures for data analysis are compared. The SANS curves for the same set of samples investigated using the two different instruments are in good agreement within the experimental uncertainties. A check was also made on the metallurgically relevant quantities, namely the average size and the size-distribution function of the δ′ precipitates at the various stages of the ageing process, obtained from the two sets of SANS curves by applying the same numerical method. Good agreement was found between the results from the two data sets.

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Influence of the Dispersion of the Size of the Si Nanocrystals on their Emission Spectra

MRS Proceedings ◽

10.1557/proc-358-193 ◽

1994 ◽

Vol 358 ◽

Cited By ~ 6

Author(s):

J. B. Khurgin ◽

E. W. Forsythe ◽

S. I. Kim ◽

B. S. Sywe ◽

B. A. Khan ◽

...

Keyword(s):

Systematic Study ◽

Quantum Confinement ◽

Emission Spectra ◽

Emission Peak ◽

Nanocrystal Size ◽

Pl Spectra ◽

Si Nanocrystals ◽

Average Size ◽

Size Dispersion ◽

Confinement Model

ABSTRACTA systematic study of the PL spectra of Si quantum nanocrystals in the SiO2 matrix has been performed. The results have been fitted to a quantum-confinement model that includes the nanocrystal size dispersion rather than a specific size of the nanocrystal. This serves as a strong confirmation of the confinement-induced nature of the PL. It has been shown that if the dispersion is taken into account, the position of the emission peak as well as the PL width can always be correlated with the average size of the nanocrystal.

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Recombination, multiplication, and transfer of electron-hole pairs in silicon nanocrystals: Effects of quantum confinement, doping, and surface chemistry

Journal of Luminescence ◽

10.1016/j.jlumin.2021.117904 ◽

2021 ◽

Vol 233 ◽

pp. 117904

Author(s):

N.V. Derbenyova ◽

A.A. Konakov ◽

V.A. Burdov

Keyword(s):

Surface Chemistry ◽

Quantum Confinement ◽

Silicon Nanocrystals ◽

Electron Hole

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Some Limitations in Applying Classical EHD Film Thickness Formulas to a High-Speed Bearing

Journal of Lubrication Technology ◽

10.1115/1.3251650 ◽

1981 ◽

Vol 103 (2) ◽

pp. 295-301 ◽

Cited By ~ 11

Author(s):

J. J. Coy ◽

E. V. Zaretsky

Keyword(s):

Film Thickness ◽

High Speed ◽

Heating Effects ◽

Theoretical Predictions ◽

Traction Fluid ◽

Shear Heating ◽

Thickness Measurements ◽

Inner Race ◽

Maximum Stresses ◽

Good Agreement

Elastohydrodynamic film thickness was measured for a 20-mm ball bearing using the capacitance technique. The bearing was thrust loaded to 90, 448, and 778 N (20, 100, and 175 lb). The corresponding maximum stresses on the inner race were 1.28, 2.09, and 2.45 GPa (185,000, 303,000, and 356,000 psi). Test speeds ranged from 400 to 14,000 rpm. Film thickness measurements were taken with four different lubricants: (a) synthetic paraffinic, (b) synthetic paraffinic with additives, (c) neopentylpolyol (tetra) ester meeting MIL-L-23699A specifications, and (d) synthetic cycloaliphatic hydrocarbon traction fluid. The test bearing was mist lubricated. Test temperatures were 300, 338, and 393 K. The measured results were compared to theoretical predictions using the formulae of Grubin, Archard and Cowking, Dowson and Higginson, and Hamrock and Dowson. There was good agreement with theory at low dimensionless speed, but the film was much smaller than theory predicts at higher speeds. This was due to kinematic starvation and inlet shear heating effects. Comparisons with Chiu’s theory on starvation and Cheng’s theory on inlet shear heating were made.

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