Laila Abuhassan

Quenching of porous silicon photoluminescence by deposition of metal adsorbates

Various metals were deposited on luminescent porous silicon (PS) by immersion in metal ion solutions and by evaporation. The photoluminescence (PL) was quenched upon immersion in ionic solutions of Cu, Ag, and Au but not noticeably quenched in other ionic solutions. Evaporation of 100 A of Cu or 110 A of Au was not observed to quench PL. Auger electron spectroscopy performed on samples quenched and then immediately removed from solution showed a metallic concentration in the PS layer of order 10 at.%, but persisting to a depth of order 3000 A.

Ideal anodization of silicon

Silicon has been anodized such that the porous layer is passivated with a homogeneous stretching phase by incorporating H2O2 in the anodization mixture. Fourier transform infrared spectroscopy measurements show that the Si–H stretching mode oriented perpendicular to the surface at ∼2100 cm−1 dominates the spectrum with negligible contribution from the bending modes in the 600–900 cm−1 region. Material analysis using Auger electron spectroscopy shows that the samples have very little impurities, and that the luminescent layer is very thin (5–10 nm). Scanning electron microscopy shows that the surface is smoother with features smaller than those of conventional samples.

Si–N linkage in ultrabright, ultrasmall Si nanoparticles

Ultrabright ultrasmall (∼1 nm) blue luminescent Si29 nanoparticles are chlorinated by reaction with Cl2 gas. A Si–N linkage is formed by the reaction of the chlorinated particles with the functional amine group in butylamine. Fourier transform infrared spectroscopy and x-ray photospectroscopy measurements confirm the N linkage and the presence of the butyl group, while emission, excitation, and autocorrelation femtosecond optical spectroscopy show that, after the linkage formation, the particles with the ultrabright blue luminescent remain, but with a redshift of 40 nm.

Current-less anodization of intrinsic silicon powder grains: Formation of fluorescent Si nanoparticles

We examine current-less anodization of Si powder grains which are dispersed in a liquid. The grains are prepared red luminescent using a platinum catalyst from a chloroplatinic acid precursor. We also use the procedure to form dispersions of fluorescent Si nanoparticles in the size range of 3–6 nm across by subsequent sonication of the grains. The results are discussed in terms of the calculated thickness of the depletion layer in the grains due to a light metal doping and compared with recent results for the anodization of wirelike geometry.

Luminescence efficiency of silica during ion beam excitation

Abstract During ion beam implantation of silica light is produced by electronic excitation of the glass network. In order to vary the mechanisms of excitation and decay data were taken with a wide range of ions and ion energies (e.g. H + , H + 2 , He + , Ne + , N + , N + 2 and A + from 5 keV to 2.8 MeV). The results suggest that the light is generated with different luminescence efficiency in regions of electronic damage, collision damage and, in the case of nitrogen, of impurities. Additionally, exciton or electron diffusion from the implanted region generates luminescence several microns beneath the implant. The relative efficiencies in these processes are discussed. One consequence of these differences is that in measurements of the luminescence efficiency as a function of energy one observes an apparent peak in efficiency if the sequence commences at high energy. The “peak” is a function of the initial energy.

The effect of ultrathin oxides on luminescent silicon nanocrystallites

The effect of ultrathin oxides on nanocrystallites of luminescent porous silicon is studied using infrared, optical, and Auger spectroscopy. Room-temperature oxidation is performed using H2O2 immersion and UV ozone interactions, producing oxides of ∼5 and ∼10 A, respectively. The H2O2 oxidized sample is optically active, while the ozone oxidized sample is not active. UV–ozone produces a transverse optical Si–O–Si mode blueshifted by ∼90 cm−1 from bulk oxide, which H2O2 does not produce. Auger Si LVV spectra show an oxidelike signal for UV/ozone samples and a Si-like signal for H2O2 samples. We discuss this in terms of different oxidation behaviors that either preserve or break Si–Si dimers that may be responsible for the optical behavior.

Silver colloid formation in Ag+ implanted LiNbO3

Abstract Implantation of silver in LiNbO 3 produces a blue/green absorption band characteristic of silver colloids. Thermal treatments allow colloid aggregation and the absorption peak moves towards the red end of the spectrum. Peak shifts can be followed from 470 to 550 nm. The colloid size is a function of ion energy, dose, current density and implant temperature. Colloid radii ranged from 0.3 nm initially to 0.53 nm after annealing. The larger clusters are partially dissociated by subsequent ionisation and totally reduced to the 0.3 nm dimensions with second Ag + implants. Major differences are noted for implant in X, Y and Z cut samples. Some similar features are noted after Ag + implants in Al 2 O 3 .

Time-resolved measurements of the photoluminescence of Cu-quenched porous silicon

We have performed time‐resolved photoluminescence measurements in the submicrosecond to microsecond time regime on porous silicon samples under several diffusion‐based chemical treatments with copper ion solutions that produce varying crystallite surface conditions. Our results for short emission wavelengths emanating from high lying states indicate that Cu acts largely on the population process commencing from the top of the well at short relaxation time scales immediately after excitation, and to less extent on the radiating states in the microsecond regime.

Cathodoluminescence of small silicon nanoparticles under electron-beam excitation

The temperature (300–25K) behavior of visible luminescence from silicon nanoparticles in thin films under electron-beam bombardment [cathodoluminescence (CL)] is reported. Emission signals occur near 420, 450, 630, and 750nm. Unlike cathodoluminescence of fused silica or heavily oxidized porous layers, which is known to fade with cooling, the nanoparticle films are found to exhibit luminescence that variously fade away or grow with cooling. The CL bands of the film are also observed in the photoluminescence spectra under 365- and 254-nm excitations. There is an approximate coincidence of the peak energy observed for the photoluminescence and CL spectra. The temperature behavior of the cathodoluminescence points to a strong contribution from spatial quantum confinement at nanostructures.

LUMINESCENCE EXCITED IN SIO2 DURING ION-IMPLANTATION

Ion beam induced luminescence of silica has been recorded in the energy ranges 5–55 key and 0.2–2.8 MeV during excitation with H+, H2+, N+ and N2+, for samples at 77 K. The data reveal that the light is stimulated by electronic energy deposition 0 but the efficiency is a function of the damage retained in the silica. Damage retention is a function of the overlap of nuclear collision and 07 electronic excitation processes during the slowing down of the ion beam so the net effect of these competing features is to produce a maximum in the ion energy dependence of the light production for nitrogen ions (near 42 key), whereas for protons the dependence is a monotonic function of energy as it is dominated by the electronic excitation. Computer modelling of the luminescence production predicts a maximum in the energy dependence which is in agreement with the observations.