Improving Passivation Process of Si Nanocrystals Embedded in SiO 2 UsingMetal Ion Implantation

We studied the photoluminescence (PL) of Si nanocrystals (Si-NCs) embedded in SiO2 obtained by ion implantation atMeV energy. e Si-NCs are formed at high depth (1-2 μμm) inside the SiO2 achieving a robust and better protected system. Aer metal ion implantation (Ag or Au), and a subsequent thermal annealing at 600C under hydrogen-containing atmosphere, the PL signal exhibits a noticeable increase. e ion metal implantation was done at energies such that its distribution inside the silica does not overlap with the previously implanted Si ion . Under proper annealing Ag or Au nanoparticles (NPs) could be nucleated, and the PL signal from Si-NCs could increase due to plasmonic interactions. However, the ion-metal-implantation-induced damage can enhance the amount of hydrogen, or nitrogen, that diffuses into the SiO2 matrix. As a result, the surface defects on Si-NCs can be better passivated, and consequently, the PL of the system is intensi�ed. We have selected different atmospheres (air, H2/N2 and Ar) to study the relevance of these annealing gases on the �nal PL from Si-NCs aer metal ion implantation. Studies of PL and time-resolved PL indicate that passivation process of surface defects on Si-NCs is more effective when it is assisted by ion metal implantation.


Introduction
A common process used to obtain silicon nanocrystals (Si-NCs) involves ion implantation of Si ions into silica matrix followed by thermal annealing.Precipitation of excess Si in SiO 2 typically requires temperatures in the range 1000-1100 ∘ C for 1 h and produces Si-NCs with diameters between 3 to 7 nm [1,2].Si-NCs exhibit a strong room temperature photoluminescence (PL) as a direct consequence of their small size, but nonradiative surface defects, as P b defect, compete with radiative process [3][4][5][6].SiO 2 is an appropriate matrix for Si-NCs since it can passivate some dangling bonds that can cause nonradiative transitions.However, a better control of surface defects on Si-NCs is valuable for light-emitting applications [3,6,7].Annealing in molecular hydrogen can reduce the high concentration of surface defects, and then luminescence intensity from Si-NCs signi�catively increases [2][3][4][5][6][7][8].It has been reported that a sample containing Si-NCs and passivated at 510 ∘ C in molecular hydrogen can increase its photoluminescence signal by a factor of seven [4].
Si ion implantation is typically done at energies in the range of 35-400 KeV so the formed nanocrystals are inside the silica matrix but near its surface at a distance not exceeding 1 m [1-4, 6, 8-11].So molecular hydrogen can diffuse until the region where the Si-NCs were formed and P b defects can be passivated.e closer to the Si-NCs surface are the better passivation process will be, but at the expense of greater protection and robustness of the sample.Other gases as O 2 and N 2 have been used to passivated P b defects on Si-NCs.However, annealing in N 2 has been shown to have a negligible effect on luminescence properties of Si-NCs [8,9].Annealing in N 2 at temperature in the range 750 ∘ C to 1100 ∘ C can contribute to the passivation of the Si-NCs surface and consequently the PL intensity increases [9].But at nitrogen high concentration there is a size reduction of Si-NCs by oxynitridation at their surface.As a consequence, the PL spectra could be blue shied, and if the size is strongly reduced the PL intensity can decrease [9].Another process used to reduce the surface defects concentration on Si-NCs is known as alneal [4].In this method, before annealing in forming gas (5% H 2 in N 2 ), an Al thin �lm (100 nm) is grown onto the surface of the substrate containing the Si-NCs.Atomic hydrogen can be generated within the oxide layer and it easily saturate the dangling bonds.is method has been showed to result in a more efficient passivation process and consequently in an increase of the PL signal by a factor of two, compared to a sample annealed in molecular hydrogen [4].e passivation process appears to have a limit; that is, the PL intensity from Si-NCs does not increase further, even when the sample is annealed for more than 1 h, and up to 16 h in forming gas, at annealing temperatures ranging between 300 to 600 ∘ C [4,6,8].is limit could be understood considering that there are a �nite number of Si-NCs and also a �nite number of surface defects on them.In addition to this, even though the silica matrix protects the system of Si-NCs from environment effects, it is a barrier to overcome in order to saturate the dangling bonds in the Si-NCs surface.is fact imposes a limit to the PL signal enhancement.
In this work, we synthesize a system of Si-NCs embedded in Silica by ion implantation at 1.5 MeV.At this energy, the Si-NCs are formed in a depth region inside the silica matrix.SRIM simulation shows that the Si ion implantation distribution in silica has a maximum in 1.7 m, in the range of 1-2 m under the silica surface.is deep Si ion implantation allows to obtain a more robust sample well protected from external damage and environmental contamination.A device with these properties is a good candidate for optoelectronics applications.However, the amount of hydrogen which can diffuse into the silica matrix of these samples is more limited than the samples obtained by the traditional ion implantation.In this case, the Si-NCs are at a depth greater than 1 m, so the matrix barrier imposed to the hydrogen diffusion is higher.Once the Si-NCs are synthesized by ion implantation at MeV energy, in order to overcome that barrier, the silica matrix is again irradiated with Ag ions (or Au ions).is ion irradiation is carried out at energies which make, both, metal and Si ions distributions, very close to each other but without overlapping.is slight separation between the two distributions of the implanted ions is very important to preserve the PL emission from Si-NCs.It has been observed that ion metal implantation could quench the PL from Si-NCs [12,13].On the other hand, the PL signal from Si-NCs can be enhanced by the localized plasmon interaction induced by the nucleation of metal nanoparticles under controlled annealing [14,15].en, the enhancement of the PL emission from the integrated system studied in this work could have two contributions.One of them could take place as a result of the ion-metal-implantation induced damage that could increase the amount of hydrogen that diffuses into the silica matrix.e other could be the presence of metal NPs formed inside the silica matrix that may result in a plasmonic interaction between Si-NCs and metal nanoparticles, increasing even more the �nal photoluminescence of the system.

Experiment
(A) Si-NCs Preparation.Silica glass plates (20 × 20 × 1 mm) were implanted at room temperature with 1.5 MeV Si +2 ions at �uence of 2.5 × 10 17 ions/cm 2 , using the 3 MV Tandem accelerator (NEC 9SDH-2 Pelletron) facility at the Instituto de Física of the Universidad Nacional Autónoma de México (IFUNAM).Aer implantation, we explored two methods of nucleation and growth of Si nanocrystals.One sample was thermally annealed in a reducing atmosphere (RA) consisting of 50% N 2 and 50% H 2 at 1100 ∘ C for 1 h (Method A), in order to nucleate the Si NCs from the supersaturated solution.A similar method was used by Wilkinson and Elliman [8] but in a system with Si ions implanted at 100 keV.A second piece was annealed in Ar gas at 1100 ∘ C for 1 h and then passivated at 510 ∘ C in RA for 1 h (Method B). e last method is commonly used in other works but in samples implanted with Si ions at low energy (35-200 KeV) [1,4,6,[8][9][10]16].In the following, samples prepared by method A or B will be labeled sample A or sample B, respectively.On the other hand, a twosample set was prepared according to method A, one of them was annealed again for 1 h (sample A1) and the other for 2 h (sample A2), in RA at 1100 ∘ C in order to compare the effect of annealing for more than 1 h (see Table 1).
(B) Silica Matrix with Si-NCs Implanted with Ag Ion.Once the Si-NCs have been formed inside the matrix (by Method A), the sample was cut into pieces.One of the pieces was implanted at room temperature with Ag +2 ions at energy of 1 MeV and a �uence of 6 × 10 16 ions/cm 2 .Aer the Ag implantation, the samples were again thermally annealed in RA at 600 ∘ C for 1 h (Sample A(Ag)).At this temperature, Ag nanoparticles (Ag-NPs) were formed.e Ag-NPs produced in this way have an average diameter of 6 nm [17].At the end of this process, we obtained two kinds of samples, one having only Si NCs embedded (Sample A), and a second one with Si NCs and Ag NPs embedded into the silica matrix (Sample A(Ag)).
Monte Carlo simulations were performed with the SRIM program to determine the Gaussian depth distribution of the implanted ions: the atoms of the implanted Ag were distributed in the range of 110-830 nm, with its maximum at 480 nm, while for Si the atoms were in the range of 300-2200 nm, with its maximum at 1700 nm.
T 2: Resume of the process to obtain the samples studied in this work.Si, Ag, and Au implantations were done at 1.5, 1.0, and 1.9 MeV, respectively.

Sample Implantation
Steps thermal treatment ermal treatment Au 1 1100 ∘ C for 1 h in Air * e samples with metal ion implantation were previously prepared as a sample A or A2 (see Table 1) as indicated in the �rst letter and number in its label.
In order to compare the effect of the Ag-NPs and the annealing environment, over the �nal PL intensity of the integrated system, the sample A2 with Si-NCs in SiO 2 was implanted with Ag +2 ions at the same conditions explained previously.e sample was cut into two pieces and was thermally annealed at 600 ∘ C for 1 h but one of them in RA (Sample A2(Ag)-1) and the other in Ar gas (Sample A2(Ag)-2, see Table 2).
(C) Silica Matrix with Si-NCs Implanted with Au Ion.Another sample set containing Si-NCs prepared by method A, as explained before, was implanted with Au +2 ions at energy of 1.9 MeV and a �uence of 6 × 10 16 ions/cm 2 .e sample was cut into small pieces.One of these samples was heated in RA at 600 ∘ C for 1 h (Sample A(Au)-1).Other two pieces were also heated at 1100 ∘ C, one in RA (Sample A(Au)-2) and the other in air (Sample A(Au)-3).Au nanoparticles (Au-NPs) may be formed in the sample only by heating at 1100 ∘ C in air.e Au-implanted ions were distributed in the range 160-820 nm with its maximum at 502 nm, according to the SRIM simulation.
e ion range of the Ag and Au implantations was corroborated by means of Rutherford backscattering spectrometry (RBS) using a 2 MeV He + beam.We use the RUMP code to calculate the concentration pro�le of the implanted ions.
Table 2 shows a resume of the samples studied in this work.
(D) PL, Time-Resolved PL, and Optical Absorption.Photoluminescence (PL) measurements were performed at room temperature at excitation wavelengths of 250, 355, and 420 nm using ps pulses, at a frequency repetition rate of 10 Hz, from a combined laser system PL2143A + PG401/SH by EKSPLA, at the Nonlinear Optics Laboratory of IFU-NAM.In this range of excitation wavelengths, all the Si-NCs of the sample may absorb light and then contribute to the PL signal, which was collected by a 1000 microns optical �ber and detected by an Ocean Optics USB2000+ spectrometer.Some PL spectra were obtained using 250 nm as excitation wavelength to see a possible PL from defects produced in the silica matrix aer ion implantation [18][19][20].Photoluminescence measurements versus excitation pump pulse �uence were carried out at 355 nm and 420 nm.For each of these excitation wavelengths, neutral optical densities were used to control the incident irradiance over the samples.e peak signal of the PL spectrum was acquired every 1 s over a total integration time of 3 min, for each of the excitation pump pulse �uences.All the measurements were performed by keeping the illumination area over the sample constant, using a mechanical aperture.e time-resolved PL was measured with excitation wavelength of 355 nm.e emerging PL was resolved with an Acton Series SP2300 monochromator and detected with a Hamamatsu H10721-20 photomultiplier module, connected to a digital oscilloscope where the microsecond PL signal could be visualized over a few hundred s.Emission decay lifetimes were extracted by the least-square �tting of a stretched exponential.e PL decay was investigated at a wavelength set around peak intensity of PL spectrum.e optical absorption of all the samples was measured by means of a Varian Cary 5000 UV-VIS spectrophotometer.

Results and Discussion
Figure 1(a) shows a broad PL emission, which is a characteristic emission from Si-NCs, and is observed for both preparation methods to produce our samples.It is important to point out that there is no signal from silica defects.We can also observe that the sample annealed in Ar gas (black dashed curve) increases its PL emission aer reannealing in RA (blue dotted curve, method B), but this increment remains signi�cantly smaller than the observed for the sample annealed in RA at 1100 ∘ C (red solid curve, method A). ese results could be explained considering that, aer Si ion implantation, the silica matrix is damaged so that, when the sample is annealed at 1100 ∘ C in RA, the hydrogen and nitrogen can enhance its diffusion into the matrix, and the nonradiative surface defects on Si-NCs are eliminated.On the other hand, when the sample is annealed in Ar gas at 1100 ∘ C, Si-NCs are formed, but the radiation damage is annealed, then the hydrogen diffusion into the silica matrix decreases.So when the sample is annealed at 510 ∘ C in RA the hydrogen diffusion is smaller than in a damaged matrix.erefore, a sample annealed at 1100 ∘ C in RA has a more efficient passivation than a sample annealed in Ar gas (and then in RA at 510 ∘ C), and consequently its PL emission is higher.Hence, even though the method B appears to be more complex since it is a two-step process, it cannot overcome the PL intensity obtained by the method A, which is simpler and more effective, as we clearly see in the results showed in Figure 1(a).In the following, we will only use the method A to prepare Si-NCs inside a silica matrix and will study other ways to improve its PL intensity.
A sample prepared by method A, and then annealed for 1 h in reducing atmosphere at 1100 ∘ C (sample A1), can increase even more its PL (about 30%).Furthermore, its peak value is red shied as we can see in Figure 1(b) (green dotted curve).e red solid curve (sample A) is shown for comparison.ese results have been observed before in samples annealed in RA for more than 1 h [8].More annealing time at high temperature allows that more hydrogen or nitrogen can F 1: (a) PL emission of samples is annealed at 1100 ∘ C for 1 h in reducing atmosphere (red solid curve), and in Ar gas (black dashed curve), and then is annealed at 510 ∘ C in reducing atmosphere (blue dotted curve).(b) PL from a sample is annealed at 1100 ∘ C in reducing atmosphere for 1 h (red solid curve) and then for 1 h (green dotted curve) and 2 h (blue dashed curve).e excitation wavelength was 250 nm.
diffuse into the matrix.Consequently, more surface defects on Si-NCs are passivated, and their PL signal is higher.But if we continue heating in RA at 1100 ∘ for 2 h this sample, A, the PL shows a decrease as shown in Figure 1(b) (blue dashed curve).Also its PL red shi is greater and suggests that the average size of the luminescence Si-NCs has increased.e PL intensity from Si-NCs is size dependent; that is, the largest the nanocrystals are the lower their PL efficiency will be [21,22].is effect can explain the decrease in the PL signal when the sample is annealed for more than 2 h at 1100 ∘ C.Moreover, once the silica matrix has been restored, the diffusion of hydrogen or nitrogen can decrease, and a depassivation process begins to be dominant.As a consequence of hydrogen desorption, a signi�cant number of surface defects on Si-NCs could reappear.us, PL intensity from the system of Si-NCs could decrease even more [6].
Figure 2(a) shows that the PL from a sample with Si-NCs (synthesized by method A), aer Ag ion implantation at 1 MeV, is then annealed at 600 ∘ C in RA for 1 h.Similar results are showed in Figure 2(b) but now by using Au ion implantation at 1.9 MeV, and heating at 600 ∘ C in RA for 1 h.e inset (a1) and (b1) shows the ion range of the implanted materials for the sample implanted with Ag ions and Au ions, respectively.For the implantation with Ag the PL signal has increased almost 4 times (red solid curve) compared to a reference sample (black dashed curve).e PL peak is also blue shied (∼10 nm).e inset (a2) in Figure 2 shows the Ag nanoparticle absorption band in the sample A(Ag).Similar results can be obtained if Au ions are implanted in a sample that contains Si-NCs, as we can see in Figure 2(b).However, the inset b2 shows that there are not any Au NPs formed in the sample since the characteristic plasmon band is not present.
e Ag-implanted ions can form Ag-NPs under a heating treatment at 600 ∘ C in RA.So the presence of these NPs could produce a plasmonic interaction of some Ag NPs close to some Si-NCs.In order to check this hypothesis we have prepared similar sample with Ag NPs but now nucleated under Ar atmosphere.Hence, additional passivation of surface defects on Si-NCs could not take place.In Figure 3(a) we can see the PL signal from a sample implanted with Ag ions and annealed at 600 ∘ C in Ar gas (sample A2(Ag)-2).A second sample, also implanted with Ag ions, was annealed in RA (sample A2(Ag)-1), as we have done before.In both samples Ag NPs are formed as the inset in Figure 3(a) shows.e sample annealed in Ar gas does not show a signi�cant increase in its PL, while the sample annealed in RA shows the same increment that presented the sample A(Ag).From these results we can deduce that Ag NPs formed into the sample do not have signi�cant plasmonic effect over the PL signal from Si NCs.
Figure 3(b) shows the PL of a sample implanted with Au ions, as explained previously, but annealed in RA at 1100 ∘ C for 1 h (sample A(Au)-2).ough the sample A(Au)-2 has Au NPs, as the absorption band shows, the PL from this sample increases but remains smaller than the sample annealed at 600 ∘ C in AR during 1 hr (sample(Au)-1), where there are not any Au NPs formed.erefore, we can conclude that the presence of metal nanoparticles in these systems has not any appreciable plasmonic effect over the PL emission of Si-NCs.
In order to get more insight about the origin of the PL enhancement from Si-NCs in the samples with Ag (or Au) ion implantation, studies of PL intensity in function of excitation photon �uence and time resolved photoluminescence were carried out.e saturation curve allows to obtain .e inset (b1) shows a SRIM simulation of the Au (blue circles) and Si (pink squares) implanted material at 1.9 and 1.5 MeV, respectively.e inset (b2) shows the absorption spectra for the sample with Au implantation (sample A(Au)-1).e bar graph in (a1) and (b1) is the concentration pro�le of the implanted ions calculated from R�S measures.e ion �uencies obtained are 5. 75 × 10 16 atoms/cm 2 and 6.03 × 10 16 atoms/cm 2 for the sample with Ag and Au, respectively.In both cases, the excitation wavelength was 355 nm.F 3: (a) PL emission spectra from samples with Si-NCs and 1 MeV Ag ion implantation, annealed in reducing atmosphere (red solid curve) and Ar atmosphere (blue dotted curve).e black dashed curve is the spectra of the reference sample (only Si-NCs).e excitation wavelength was 355 nm.e inset shows the absorption spectra of the sample with Ag ion implantation aer thermal annealing, (b) PL emission from samples with Si-NCs in SiO 2 (black dashed curve) and then with Au ion implantation is annealed in reducing atmosphere at 1100 ∘ C (blue dotted curve) or 600 ∘ C (red solid curve).e inset shows the absorption spectra of the sample with Au implantation aer thermal annealing.the ampli�cation factor of the PL near the saturated pumppower regime in the sample containing Ag NPs (or Au-NPs) where, as we shall see, the PL intensity is limited by the quantum efficiency of the emitters and the total numbers of them.Typical PL emission saturation curves in function of the photon �uence are shown in Figures 4(a) and 5(a) for samples with Ag or Au NPs, respectively.For the sample with Ag, we use 420 nm as excitation wavelength, that is, near the absorption band of Ag-NPs.e emission of Si-NCs is saturated at high photon �uence excitation.�y using a two levels model [23-25�, the experimental data can be �tted with the theoretical curve given by the �tting equation: where  is the total number of Si-NCs that can be excited by the incident beam,  is their PL quantum efficiency, and  exc is the Si-NCs excitation cross section.From this equation, it can be seen that for large �uencies (Φ tending to in�nitum), the saturation level is given by , that is, by the total number of excitable NCs times their PL quantum efficiency.
In the low pump-power regime, we can observe a slight difference between the samples with Ag and Au NPs.e ampli�cation factor obtained at low pump-power in Figure 4(a), for the sample with Ag implantation, is greater than at high �uence.is is re�ected by the  exc value obtained by �tting the experimental data, which is greater in the sample with Ag-NPs than that in the sample without them.On the other hand, Figure 5(a) shows the PL saturation curve of the sample with Au-implanted ions (sample A(Au)-1).is shows that both samples, one with Au-implanted ions and the other without them, have a similar  exc .In consequence, the PL ampli�cation factor is similar in both pump-powers regimes.e same results are observed in (sample A(Au)-2), not shown here.e differences observed at low pump-power regime could be explained considering that the layer containing Ag NPs re�ects a fraction of the laser excitation light.ese laser re�ections could increase the effective pump-power over the Si-NCs.To avoid these effects it is convenient to obtain the ampli�cation factor (Δ em ) of PL near the saturated pump power regime as the quotient between the PL intensity of a sample with metal ion implantation ( SiNCs−MIons ), and one without it ( SiNCs ).e factors Δ em−Ag Ions ∼ 3.7 and Δ em−Au Ions ∼ 2.1 in the pumppower-saturated regimen could be obtained from the results in Figures 4(a) and 5(a).
Figures 4(b) and 5(b) show the values of PL lifetime decay ( PL =   +   ) from sample A, A(Ag), and A(Au)-1 taken for a set of emission wavelengths.e insets in these �gures show a typical nonexponential decay curve of Si-NCs [26,27].For all emission wavelengths the stretching parameter was between 0.6 and 0.7.e increment of luminescence lifetime observed in samples A(Ag) and A(Au)-1 can only be explained if we assume that Si-NCs nonradiative recombination rate has diminished as have been observed in other works [3][4][5][6]8].is means that the nonradiative lifetime has increased.
e nonradiative state defect can be eliminated using hydrogen, nitrogen, or oxygen to passivate surface defects on Si-NCs, such as the dangling bonds defects known as P b centers [1, 3-6, 8, 9].e P b centers produce a fast nonradiative trap that can be passivated by hydrogen.Moreover, it has been shown that one P b center is sufficient to quench the luminescence of silicon nanocrystals [4][5][6]28].en, when the sample A(Ag) is annealed at 600 ∘ C in RA, many silicon nanocrystals could reduce the nonradiative decay channels and, consequently, increase their PL quantum efficiency.Other nanocrystals could be activated to emit light such that the number N of nanocrystals which are able to emit increases.From PL lifetime measurements, we can estimate the increment in the PL quantum efficiency (Δ) using its de�nition in terms of radiative and nonradiative lifetime  =  PL /  .Taking into account that we have not any evidence of plasmonics effects as a result of the presence of Ag (or Au) nanoparticles in the sample, we can assume that the radiative decay rate does not change, that is, Δ  ∼ 1, for the samples with metal ion implantation.en, we can obtain the change in PL quantum efficiency as Δ M Ions =  PL(SiNCs−M Ions) / PL(SiNCs) , that is, as the quotient between the measured  PL for samples with metal ion implantation and the measured for its reference, that is, without metal ion implantation.e increments in the PL quantum efficiency are Δ Ag Ions ∼ 2 at 710 nm emission wavelength and Δ Au Ions ∼ 1.4 at 720 nm emission wavelength, as we can obtain from the results of Figures 4(b) and 5(b), respectively.en the PL quantum efficiency of the systems has an increment about 100% and 40% aer Ag or Au ion implantation, respectively.e increment of the number of Si-NCs optically active can be obtained considering that at high excitation �uence, that is, near the saturated pump-power regime, the PL intensity only depends on the PL quantum efficiency and the total number of Si-NCs optically active.en it follows that Here, Δ M Ions =  SiNCs−M Ions / SiNCs is the increment in the number of Si-NCs optically active.According to the expression previously mentioned, the number of Si-NCs optically active has an increment about 85% in the sample with Ag ion implantation (Δ Ag Ions ∼ 1.85) and about 54% in the sample with Au ion implantation (Δ Au Ions ∼ 1.54).e differences observed in the sample containing Ag with respect to the sample containing Au could be explained by the difficulties to measure the Si implantation real �uence in SiO 2 .us, probably, the sample A(Ag) has a greater Si implantation �uence than sample A(Au)-1.at slight dissimilarity could produce a greater number of Si-NCs in sample A(Ag) than in sample A(Au)-1.Consequently, the total number of surface defects in each sample could be different.Higher number of Si-NCs means a greater total number of surface defects P b to be passivated.So the sample with a higher number of Si-NCs, that is, higher Si real �uence, will have the possibility to increase its PL efficiency even more than a sample with a lower number of them.

Conclusions
We have synthesized a system of Si-NCs embedded in silica at high depth inside the matrix (1-2 m).We observed that the annealing of the Si-ion-implanted silica in RA at 1100 ∘ C for 1 h is the best method to obtain a system of Si-NCs with high PL intensity.In addition, thermal annealing for more than one hour in reducing atmosphere can increase the PL signal during the �rst hour with about 30%.However, more than two hours under these annealing conditions produce a decrease in the PL signal, and the spectra are shied toward the infrared.On the other hand, we have found a method to amplify the PL signal from a sample containing Si-NCs by means of ion metal implantation (Ag or Au) and a second annealing treatment in RA at 600 ∘ C. is method produces a fourfold PL signal enhancement for the case of using Ag ions (or twofold PL signal enhancement using Au ions).is PL enhancement is far greater than we can obtain by a second thermal annealing (at 1100 ∘ C or 600 ∘ C, for more than 1 h in RA) without metal ion implantation.e ion-metalimplantation-induced damage can increase the amount of hydrogen, or nitrogen, which diffuses into the silica matrix.As a consequence, we achieve a better passivation of the Si-NCs system.is passivation process, assisted by metal ion implantation, increases the PL quantum efficiency and the number of Si-NCs optically active of the system.ough Si-NCs are embedded at high depth under the silica surface, the ion metal implantation process, together with proper thermal annealing, proves to be an efficient way to passivate surface defects on it.As a result, we have a robust and efficiently passivated system of Si-NCs.is system is better protected from external damage and contamination and could be used for application in light emitter silicon based for optoelectronic devices.

F 2 :
(a) Typical PL emission from a sample containing Si-NCs (sample A) and Si-NCs and Ag NPs (sample A(Ag)).e inset (a1) shows a SRIM simulation of the Ag (blue circles) and Si (pink squares) implanted materials at 1 and 1.5 MeV, respectively.e inset (a2) shows the absorption spectra for the sample with Ag NPs (sample A(Ag)), (b) PL emission from a sample containing Si-NCs (sample A) and Si-NCs and Au NPs (sample A(Au)-1)

F 4 :
(a) PL saturation curve for a sample with Si-NCs embedded in silica (blue circles) and with Si-NCs and Ag NPs (red squares), (b) lifetime PL for a set of emission wavelengths.e insets show a typical PL decay curve for sample A (upper le) and sample A(Ag) (lower right).

F 5 :
(a) PL saturation curve for a sample with Si-NCs embedded in silica (blue circles) and with Si-NCs and Au NPs (red squares), (b) lifetime PL for a set of emission wavelength.e insets shows a typical PL decay curve for sample A (upper le) and sample A(Au) 1 (lower right).