On red-shift of UV photoluminescence with decreasing size of silicon nanoparticles embedded in SiO2 matrix grown by pulsed laser deposition

doi:10.1016/j.jlumin.2014.04.032

Journal of Luminescence

Volume 154, October 2014, Pages 178-184

https://doi.org/10.1016/j.jlumin.2014.04.032 Get rights and content

Highlights

•
Ensembles of Si nanoparticles of mean sizes 1–5 nm and capped with SiO₂ were grown using pulsed laser deposition.
•
Photoluminescence emission was observed in UV–visible range from the grown ensembles of Si nanoparticles.
•
Redshift in the UV PL peak with decreasing size of Si nanoparticles was observed.
•
Origin of UV PL peak is attributed to direct band transition at the Г point of Si band structure.

Abstract

Ensembles of silicon nanoparticles (Si-nps) embedded in SiO₂ matrix were grown by alternate ablation of Si and SiO₂ targets using KrF excimer laser based pulsed laser deposition (PLD). The sizes of Si-nps (mean size ranging from 1–5 nm) were controlled by varying the ablation time of silicon target. Transmission electron microscopy (TEM) along with selected area electron diffraction (SAED) and Raman spectroscopy were used to confirm the growth of silicon nanoparticles, its size variation with growth time and the crystalline quality of the grown nanoparticles. TEM analysis showed that mean size and size distribution of Si-nps increased with increase in the ablation time of Si target. Intense peaks ~521 cm⁻¹ in Raman analysis showed reasonably good crystalline quality of grown Si-nps. We observed asymmetric broadening of phonon line shapes which also redshift with decreasing size of Si-nps. Photoluminescence (PL) from these samples, obtained at room temperature, was broad band and consisted of three bands in UV and visible range. The intensity of PL band in UV spectral range (peak ~3.2 eV) was strong compared to visible range bands (peaks ~2.95 eV and ~2.55 eV). We observed a small red-shift (~0.07 eV) of peak position of UV range PL with the decrease in the mean sizes of Si-nps, while there was no appreciable size dependent shift of PL peak positions for other bands in the visible range. The width of UV PL band was also found to increase with decrease of Si-nps mean sizes. Based on the above observations of size dependent redshift of UV range PL band together with the PL lifetimes and PL excitation spectroscopy, the origin of UV PL band is attributed to the direct band transition at the Г point of Si band structure. Visible range bands were ascribed as defect related transitions. The weak intensities of PL bands ~2.95 eV and ~2.55 eV suggested that Si nanoparticles grown by PLD were efficiently capped or passivated by SiO₂ with low density of surface/interface related defects.

Introduction

Silicon is the mainstay semiconductor of contemporary microelectronic industry and now a days nanoscale silicon became an active area of research because of its potential for photonics [1], [2] and other applications [3]. For photonic applications, the research on nanoscale silicon is driven by the motivation to integrate optical and electronic functionalities in silicon. Observation of room temperature photoluminescence (PL) from Si nanostructures [4] initiated this research area and since then PL properties of silicon nanoparticles (Si-nps) grown under different experimental conditions have been extensively studied [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21]. The PL emission spectra from Si-nps have been observed over different spectral ranges which almost cover the entire UV–visible and also sometimes the near infrared spectral range. Major factors attributed to influence the efficiency and the spectral ranges of PL emissions were particle size, size distribution, particle density and most importantly the surface/interface properties [9], [10], [11], [12], [13]. Therefore, based on the growth conditions and post-growth treatments like oxidation, annealing, etc. the dominance of the above mentioned factors ultimately decide the spectral range of PL emission. Possible mechanisms or origins of PL over different spectral ranges have also been discussed together with suitable theoretical models which include quantum confinement related direct or indirect band transitions, surface/interface defects, matrix effects, etc. [14], [15], [16], [17], [18], [19], [20], [21]. Although these studies have been carried out by many groups the origin of photoluminescence from Si nanoparticles is still a matter of debate, particularly PL emission in the UV spectral range [22], [23], [24], [25].

For practical applications of Si-nps in photonics and bio-imaging, UV range light emission or laser source from Si-nps is highly desirable. Therefore, the growth conditions of nanoparticles should be such that one can enhance UV light emission by subduing light emission in other wavelength ranges (which could be due to defects or otherwise) because, upon excitation, these sources of emission at other wavelengths provide additional de-excitation routes (radiative and non-radiative both) which reduces the efficiency of UV light emission. Capping Si-nps surface with a suitable wide band gap matrix is one good approach. Capping passivates the surface dangling bonds responsible for surface defect related emissions. It also provides isolation from the reactive environment and stability against aging effects. Pulsed laser deposition (PLD) has been considered as a suitable growth method amongst various other methods for the growth of Si-nps. Optimized PLD process parameters provide not only the control over the size of nanoparticles during the growth but in-situ growth of capping material as well [17], [22], [26]. Besides this the crystalline quality of the nanoparticles can also be improved with the post-annealing treatments at high temperatures [17].

In this work, we made an attempt to grow Si-nps with minimum surface defects by capping it with wide band gap SiO₂ matrix. For the growth of Si-nps and SiO₂ matrix we used KrF excimer laser based PLD. Nanoparticles size, size distribution and crystalline nature of Si-nps were confirmed using TEM, selected area electron diffraction (SAED) and Raman spectroscopy. We observed PL emissions from the ensemble of Si-nps in UV range and a small redshift of PL peak position with the decrease in the mean size of Si-nps. The low energy visible range PL emission bands were also observed but of low intensity compared to UV range PL. Based on the observations of size dependent anomalous red-shift of UV PL band together with PL lifetimes and PL excitation spectroscopy, we attribute the origin of UV range PL band as due to direct band recombination. These studies showed that using PLD, along with post annealing treatments, one not only can grow crystalline quality Si-nps but also achieve efficient capping of Si-nps with SiO₂ matrix. This has led to reduced defect related visible range PL emission and observation of UV range PL from Si-nps. To the best of our knowledge there are no reports on UV PL ~3.2 eV from the core of the Si nanoparticles (and also redshift of PL peak with size decrease) in PLD based growth of Si-nps.

Section snippets

Experimental details

A KrF excimer laser (Coherent Compex Pro 205) operating at 10 Hz, 20 ns and 248 nm at a fluence of ~2 J/cm² was utilized for pulsed laser deposition (PLD) process. A single crystal silicon wafer and sintered SiO₂ pellet were used as ablation targets to grow Si-nps and the buffer/capping layers, respectively. Single crystal sapphire plates were used as the deposition substrates. Target to substrate distance was kept constant i.e. 4 cm. Deposition chamber was initially evacuated to a base pressure of

Results and discussion

Fig. 1(a) shows the TEM micrographs of single layer of Si-nps grown with increasing duration of silicon ablation. The ensembles of Si-nps observed through these micrographs were free of chunks and nanoparticles and were nearly spherical in shape. It is also observed that, with increasing deposition time the nanoparticles׳ size also grows with enhanced dispersion. At certain locations, preferably for longer deposition time, the particles are seen coalesced in these micrographs. Fig. 1(b) shows

Conclusion

We have grown ensembles of Si-nps embedded in SiO₂ matrix using KrF excimer laser based pulsed laser deposition. We characterized the mean size (varying from 1–5 nm), size distribution and crystalline quality of Si-nps using TEM and Raman spectroscopy. Room temperature UV–vis PL was observed from Si-nps. In strongly confined Si-nps having size ≤4.8 nm the origin of dominant UV PL (peak ~3.2 eV) is attributed to direct band recombination from quantum confined Si-nps. Characteristic features of UV

References (55)

H. Föll et al.
Mater. Sci. Eng. R
(2002)
D.P. Singh et al.
Int. J. Nanosci.
(2005)
S. Takeoka et al.
Phys. Rev. B
(2000)
M.V. Rama Krishna et al.
J. Chem. Phys.
(1992)
N.A. Hill et al.
Phys. Rev. Lett.
(1995)
C. Delerue et al.
Phys. Rev. B
(1993)
S. Yang et al.
J. Phys. Chem. C
(2011)
A.P. Detty et al.
J. Nano-Electron. Phys.
(2011)
A.P. Detty et al.
J. Nanosci. Lett.
(2013)
I.H. Campbell et al.
Solid State Commun.
(1986)
V. Svrcek et al.
J. Appl. Phys.
(2008)
V. Svrcek et al.
Appl. Phys. Lett.
(2006)
M.H. Nayfeh et al.
Appl. Phys. Lett.
(2001)
R.J. Walters et al.
Nat. Mater.
(2005)
D.J. Lockwood et al.
Silicon photonics

H. Takagi et al.

Appl. Phys. Lett.

(1990)

L.T. Canham

Appl. Phys. Lett.

(1990)

P.D.J. Calcott et al.

J. Phys: Condens. Matter

(1993)

A.G. Cullis et al.

J. Appl. Phys.

(1997)

D. Babic et al.

Superlattices Microstruct

(1997)

M.H. Nayfeh et al.

Appl. Phys. Lett.

(2001)

Amir Saar

J. Nanophoton

(2009)

V. Narayanan et al.

Phys. Lett. B

(2003)

A. Romanyuk et al.

J. Lumin.

(2010)

J.H. Warner et al.

J. Phys. Chem. B

(2005)

M.V. Wolkin et al.

Phys. Rev. Lett.

(1999)

L.N. Dinh et al.

Phys. Rev. B

(1996)

E.G. Barbagiovanni et al.

J. Appl. Phys.

(2012)

J.P. Wilcoxon et al.

Phys. Rev. B

(1999)

X.Y. Chen et al.

J. Appl. Phys.

(2003)

N. Suzuki et al.

Appl. Phys. Lett.

(2000)

K. Watanabe et al.

Appl. Surf. Sci.

(2002)

I. Bineva et al.

J. Lumin.

(2007)

G. Sahu et al.

J. Phys. Codens. Mater.

(2010)

B. Rezgui et al.

J. Lumin.

(2009)

X.X. Wang et al.

Phys. Rev. B

(2005)

T. Schmidt et al.

Phys. Rev. B

(2012)

L.M. Kukreja et al.

Int. J. Nanosci.

(2011)

167

(2011)

Cited by (20)

The effect of precursor concentration on the crystallinity synchronization of synthesized copper nanoparticles
2023, Journal of Crystal Growth
Highly crystalline copper nanoparticles are formed with Chemical Reduction Method (CRM) by the application of an effective capping agent and changing the precursor concentration. In this study, copper sulphate pentahydrate is used as a precursor which is reduced by ascorbic acid. The synthesized nanoparticles are designated as P, Q and R. These are systematically characterized by X-ray Diffraction (XRD), UV–Visible Spectroscopy (UV), Differential Scanning Calorimetry (DSC), Thermo-gravimetric Analysis (TGA), Transmission Electron Microscope (TEM) coupled with Energy Dispersive X-ray Spectroscopy (EDS). XRD ensured that the crystalline phase gradually changes from 79% to 96% with the change in precursor concentration from 0.08 M to 0.10 M. UV analysis shows that due to the high conductivity of copper nanoparticles might have caused the redshift at 630–634 nm. TGA show the energy of activation (E_a) of P is 22.90 KJ/mol which is more reactive than Q and R. An excellent arrangement in XRD and TEM confirms the average particle size near about 40 nm, with consists of crystal plane (1 1 1), (2 0 0) and (2 2 0). SAED confirmed the particles are elongated with the miller indices of the synthesized nanomaterials on (1 1 1), (2 0 0) and (2 2 0) planes. The EDS confirmed the purity of nanomaterials up to 86%. The adopted process may be employed to synthesize and synchronize the crystallinity of other metal nanoparticles.
Visible light sensitive Au–TiO<inf>2</inf> nanocomposites formed by effective attachment of Au with TiO<inf>2</inf> nanoparticles using liquid-phase pulsed-laser ablation
2023, Optical Materials
Liquid-phase pulsed-laser ablation was utilized to grow visible-light-sensitive Au–TiO₂ nanocomposites. We performed the nanosecond pulsed-laser ablation of a Ti target in aqueous solution of HAuCl₄ of different concentrations varying from 0 mM to 0.24 mM. Structural characterization studies using transmission electron microscopy (TEM) and X ray diffraction (XRD) analyses confirmed formation of the nanoparticles of TiO₂ and Au–TiO₂ in respective solutions. In Au–TiO₂ samples, nanocomposites formation by efficient attachment between Au and TiO₂ nanoparticles was confirmed by absorption and X-ray photoelectron spectroscopy (XPS) analyses. Optical absorption analysis revealed that with the attachment of Au, there is a red shift in the onset of the absorption band of TiO₂ from the ultraviolet to visible range. This red shift is found to increase from 3.5 to 2.7 eV with respect to the increase in the amount of Au present in Au–TiO₂ nanocomposites. While detailed XPS analysis suggested that when the amount of Au attached with TiO₂ increased, the number density of oxygen vacancy or Ti³⁺ states increased. Therefore the attachment of Au nanoparticles and oxygen vacancy or Ti³⁺ states generations in TiO₂ were found to be responsible for the large red shift in the onset of the TiO₂ absorption band. Consequently our study showed that single step liquid phase laser ablation method and its subsequent nonequilibrium growth conditions are useful in synthesizing Au and TiO₂ nanoparticles simultaneously and also in providing efficient attachment between Au and TiO₂ which is responsible for visible range sensitization of Au-TiO₂ nanocomposites .
The role of sodium dodecyl sulfate mediated hydrothermal synthesis of MoS<inf>2</inf> nanosheets for photocatalytic dye degradation and dye-sensitized solar cell application
2022, Chemosphere
The novel properties and exciting behavior of two-dimensional nanosheet-based materials have piqued the interest of research all over the world. In this study, bulk molybdenum disulfide (bulk MoS₂) and sodium dodecyl sulfate-mediated molybdenum disulfide nanosheets (MoS₂-SDS NS) were synthesized via a facile sonication and hydrothermal process. The findings from the characterization revealed that the addition of sodium dodecyl sulfate (SDS) surfactant reduces the crystal phase and changes the structural morphology of bulk MoS₂. Furthermore, the photocatalytic and photovoltaic performance of bulk MoS₂ and MoS₂-SDS NS were also investigated. The results show that by using methylene blue dye, the photocatalytic efficiency increased from 56.30% to 91.84% at 150 min under UV–Visible light irradiation, and the photo-conversion efficiency (PEC (%)) of the dye-sensitized solar cell increased from 1.47% to 3.81% for bulk MoS₂ and MoS₂-SDS NS, respectively. Finally, we discussed in-depth the effect of SDS surfactants on MoS₂, which can improve their photovoltaic and photocatalytic performance.
Gas-assisted exfoliation montmorillonite into mono-layered nanosheets for the removal of olefins from aromatics
2021, Fuel
To date, the scalable exfoliation of the resource-rich montmorillonite (MMT) into high-quality few-layered nanosheets still remains a grand challenge. Herein, a simple, nontoxic, and efficient strategy is proposed to exfoliate layered MMT into mono-layered MMT nanosheets (MMTNS) via thermal expansion gas-assisted exfoliation method. The essence of this method is that the high temperature expands the interlayer distance while weakens the van der Waals force between interlayer of bulk MMT and then the liquid nitrogen (L-N₂) penetrated the interlayers can be quickly vaporized to exfoliate the MMT. With a high mass yield of 18–20%, the prepared MMTNS has a thickness around 1.9 nm and a reasonable aspect ratio (lateral dimension of 0.5 µm-3 µm). Meanwhile, no impurities were introduced during the whole procedure. Additionally, the exfoliated MMTNS with high specific surface area (402 m² g⁻¹) and more exposed acid sites is further applied for the removal of trace olefins from aromatics, the result shows higher olefin conversion (76.97%) than its parent bulk phase (50.66%). The possible reaction mechanism of removing olefins from aromatics was further proposed and investigated by gas chromatography-mass spectrometry (GC–MS).
Effects of oxidants on the in-situ polymerization of aniline to form Cu<inf>2</inf>O/ZnO/PANI composite photocatalyst
2020, Materials Today: Proceedings
Oxidants are known to play a key role in regulating the structure and physical properties of polyaniline (PANI) during synthesis, by just changing or altering the redox potential of the oxidants the morphologies, and dimensions of nanostructures PANIs can be managed effectively. This study aimed to determine the efficacy of both single and some composite oxidants on the synthesis of PANI on a binary composite to form a ternary composite. Cu₂O/ZnO/PANI (CZP) composite photocatalyst was produced from Cu₂O/ZnO through in-situ polymerization of aniline with ammonium persulfate (APS), ammonium persulfate/potassium dichromate (APS/K₂Cr₂O₇), and ammonium persulfate/potassium permanganate (APS/KMnO₄) oxidants using 0.1 mL aniline monomer to see the effects of different oxidants on the composite. APS/KMnO₄ was found to be the best oxidant after testing the photocatalytic activities and physicochemical properties of all the synthesized composites. CZP-APS/KMnO₄ was found to have the best photocatalytic degradation performance followed by CZP-APS, with CZP-APS/K₂Cr₂O₇ having the least activity. Likewise, analysis of the rate constant reaffirms the best activity of CZP-APS/KMnO₄, even though all the reactions followed pseudo-first order but the rate constant of CZP-APS/KMnO₄ (0.10 min⁻¹) is much higher than the rate constant of CZP-APS (0.08 min⁻¹) and that of CZP-APS/K₂Cr₂O₇ (0.03 min⁻¹).
Silicon and silicon-germanium nanoparticles obtained by Pulsed Laser Deposition
2019, Applied Surface Science
Citation Excerpt :
In our case, we focus on the possibility of converting UV photons into visible or infrared light. This conversion is known as “red-shift” or “down-shift” photoluminescence [3,6,7]. The photoluminescence behaviour directly depends on the nanoparticle structures [3,7–11], meaning that controlling size and density of the particles allow to tune their optical properties.
Semiconductor nanoparticles are of great interest in the area of microelectronics and can also be used in many optoelectrical devices as for example optical converters for photovoltaic applications.
Silicon (Si) and silicon-germanium (SiGe) quantum dots can be used as high-energy photon converters, known as “red-shift” photoluminescence (PL) in solar cells in order to improve their efficiency. We report on the possibility to produce SiGe nanoparticles by Pulsed Laser Deposition (PLD) on silicon dioxide substrates. We keep the focus on the control of morphological properties of nanoparticles considering various deposition parameters like temperature, fluence and the amount of deposited material. Si_0.5Ge_0.5 controlled ratio is obtained by optimizing the amount of matter ablated successively from Si and Ge pure targets. Rutherford Backscattering Spectroscopy (RBS) is used to confirm the stoichiometry of the deposited structures. Morphological characterization is performed by Atomic Force Microscopy (AFM), determining average diameter, height and density of the nanoparticles. In order to confirm the crystalline character of the deposited particles, Raman analyses have been performed, helping in determining the optimal deposition temperature. PLD allows to condense a very small and controlled amount of material during the deposition process, permitting this way the growth of nanostructures in a 10 nm range. With these dimensions, SiGe quantum dots are subject to have a photoluminescent (PL) behaviour. However, no photoluminescence is observed on the deposited nanoparticles.

View all citing articles on Scopus

View full text

On red-shift of UV photoluminescence with decreasing size of silicon nanoparticles embedded in SiO2 matrix grown by pulsed laser deposition

Highlights

Abstract

Introduction

Section snippets

Experimental details

Results and discussion

Conclusion

Mater. Sci. Eng. R

Int. J. Nanosci.

Phys. Rev. B

J. Chem. Phys.

Phys. Rev. Lett.

Phys. Rev. B

J. Phys. Chem. C

J. Nano-Electron. Phys.

J. Nanosci. Lett.

Solid State Commun.

J. Appl. Phys.

Appl. Phys. Lett.

Appl. Phys. Lett.

Nat. Mater.

Silicon photonics

Appl. Phys. Lett.

Appl. Phys. Lett.

J. Phys: Condens. Matter

J. Appl. Phys.

Superlattices Microstruct

Appl. Phys. Lett.

J. Nanophoton

Phys. Lett. B

J. Lumin.

J. Phys. Chem. B

Phys. Rev. Lett.

Phys. Rev. B

J. Appl. Phys.

Phys. Rev. B

J. Appl. Phys.

Appl. Phys. Lett.

Appl. Surf. Sci.

J. Lumin.

J. Phys. Codens. Mater.

J. Lumin.

Phys. Rev. B

Phys. Rev. B

Int. J. Nanosci.

167

On red-shift of UV photoluminescence with decreasing size of silicon nanoparticles embedded in SiO₂ matrix grown by pulsed laser deposition