Porous Silicon Nanocomposites Research Articles

Optical and Mechanical Properties of Europium-Doped Silicon Oxynitride Thin Films

Light emission from silicon-based systems has gained significant interest over the past few decades with the vision of developing an optoelectronic platform that can be integrated with the existing metal-oxide-semiconductor (MOS) technology [1]. Rare earth doping of silicon-based materials is a promising approach to fabricating efficient light emitting devices because of their excellent luminescence properties and their chemical stability [2]. Europium (Eu) ions are attractive dopants for silicon photonic applications due to their intense emission in the visible spectral region. The efficiency of such photonic devices can be influenced by the mechanical properties of the Eu-doped films. Thus, the integration of these films in photonic devices requires an understanding of their mechanical properties as well. In this work, we discuss the relationship between the photoluminescence (PL) behavior and the elasticity and hardness of Eu doped silicon oxynitride (SiON) thin films.We have fabricated thin films using an electron cyclotron resonance plasma-enhanced chemical vapor deposition system with integrated magnetron sputtering system [3] on p-type 3” Si (100) substrates. Silane (diluted in 90% argon) and nitrogen (diluted in 90% argon) were used as precursor gases, while a 99.9% pure Eu sputtering target was used as a sputtering source. Different sets of samples were fabricated by changing the sputtering power and argon flow rate to understand the effect of deposition parameters on the dopant concentration and the optical and mechanical properties. Post-deposition annealing in nitrogen and a mixture of nitrogen with hydrogen (5%) were performed over a wide range of temperatures from 600° to 1100° C. The effect of hydrogen passivation was studied as well. The atomic concentration of the constituents was identified by Rutherford backscattering spectrometry. Optical properties were investigated by variable angle spectroscopic ellipsometry (VASE) analysis. The PL spectra were obtained at room temperature with a laser diode excitation source, operating at a wavelength of 375nm. Finally, we performed nanoindentation measurements to understand the deformation behavior of SiON films with the incorporation of Eu. The indentation hardness and Young’s modulus of the films were investigated, respectively, for different Eu concentrations and different deposition parameters.Reference[1] A. Moadhen, H. Elhouichet, M. Oueslati, and M. Férid, “Photoluminescence properties of europium-doped porous silicon nanocomposites,” J. Lumin., vol. 99, no. 1, pp. 13–17, 2002, doi: 10.1016/S0022-2313(02)00322-8.[2] Z. Lin R. Huang, H. Wang, Y. Wang, Y. Zhang, Y. Gao, J. Song, C. Song, H. Li, “Dense nanosized europium silicate clusters induced light emission enhancement in Eu-doped silicon oxycarbide films,” J. Alloys Compd., vol. 694, pp. 946–951, 2017, doi: 10.1016/j.jallcom.2016.10.132.[3] J. W. Miller, Z. Khatami, J. Wojcik, J. D. B. Bradley, and P. Mascher, “Integrated ECR-PECVD and magnetron sputtering system for rare-earth-doped Si-based materials,” Surf. Coatings Technol., vol. 336, pp. 99–105, 2018, doi: 10.1016/j.surfcoat.2017.08.051.

Temperature and excitation power dependence of photoluminescence and electrical characterization of Ni‐passivated porous silicon

A porous silicon (PS) layer was obtained on p-Si (100) substrate by electrochemical anodization and Ni-porous silicon nanocomposites (Ni–PS) were elaborated by the electrodeposition method using nickel chloride aqueous solution. PS and Ni–PS samples were analyzed by X-ray diffraction (XRD). The XRD patterns revealed the presence of nickel elements in the PS matrix. The investigation by Photoluminescence spectroscopy (PL) enabled us to exam the evolutions of PL peak position, PL intensity, and full width at half maximum (FWHM) as a function of temperature and excitation power density. The modified Arrhenius formula, considering two activation energies, has been used to fit the temperature-dependent integration of PL intensities. PL investigations show that Ni ions cause changes in the recombination process of PS by the creation of new radiative centers as well as the reduction of non-radiative transitions. For Ni–PS nanocomposites, the laser power dependence of the integrated PL intensity shows that the most of transitions are free to bound or bound to bound where as the excitonic transitions are the most dominant in untreated PS. The current–voltage (I–V) characteristics of Ag/PS and Ag/Ni–PS Schottky diodes have been examined. The Cheung method was adopted to extract the parameters of the diode. Experimental results show that the values of ideality factor (n), resistance series (Rs), and barrier height (φb) are affected by the presence of nickel in the porous matrix.

Electrical Properties of Porous Silicon as a Biosensor Material

The electrical properties of porous silicon nanocomposites with various glucose solutions were studied. The current-voltage characteristics (I–V) of glucose solutions in water and tear fluid, as well as porous silicon samples of various porosities saturated with these solutions were measured. The porosity and glucose content in the pores were determined by the gravimetric method. Measurements of the I–V characteristics and photoconductivity of nanocomposites showed that their electrical conductivity appreciably depends on the glucose content in solutions .

In situ synthesis of carbon doped porous silicon nanocomposites as high-performance anodes for lithium-ion batteries

We demonstrate the in situ synthesis of carbon doped porous silicon (Si/C) nanocomposites by a simple thermal displacement process between Mg2Si and inorganic gas CO2 in one-step. Via the decomposition of Mg2Si, the reduction process occurred between Mg and CO2, leading the uniform doping of many distributed tiny carbon nanoparticles into Si. Meanwhile, the porous structure was formed after an acid treatment. When worked as anodes for lithium-ion batteries, the as-prepared s-porous Si/C nanocomposites exhibited good cycling stability and high-rate capability, which were superior to the porous Si and porous Si/C nanocomposites. It was revealed that the enhanced electrochemical properties could be ascribed to the novel porous structure and doped carbon nanoparticles that can buffer the volume expansion, as well as enhance the electronic conductivity of Si. The reaction mechanism was well investigated by studying the influence of reaction temperature and raw Mg2Si particle size on the morphology and component of the porous Si/C nanocomposites.

Porous Silicon Nanocomposites with Combined Hard and Soft Magnetic Properties

Magnetic nanostructures of two ferromagnetic metals have been combined within porous silicon, and the magnetic switching behavior of the resulting porous silicon/metal nanocomposite has been modified by varying the arrangement. The two magnetic materials are Ni and Co, whereas Co is the magnetic harder one. These “hard/soft” magnetic nanocomposites have been achieved by two different routes. On the one hand, double-sided porous silicon has been used whereas one side has been filled with Ni nanostructures and the other one with Co nanostructures. On the other hand, Ni and Co have been deposited within one porous layer alternatingly. The filling of the pores has been carried out by electrodeposition with varying the deposition parameters. In systems which offer two distinct slopes of the hysteresis curves due to the different saturation behavior of the two types of deposited metal, magnetic exchange coupling is not present. For samples which show smooth hysteresis curves exchange, coupling between the Ni and Co nanostructures seems to be present. The aim is to control especially the structure size of the soft and the hard magnetic materials and the distance between them at the nanoscale to optimize exchange coupling resulting in a maximum energy product.

Preclinical development of porous silicon nanocomposites for translational biomedical applications

Event Abstract Back to Event Preclinical development of porous silicon nanocomposites for translational biomedical applications Hélder A Santos1 1 University of Helsinki, Division of Pharmaceutical Chemistry and Technology, Finland Novel engineering technologies affords unprecedented advances toward medical research. Personalized medicine offers the opportunity to respond to the questions of identifying the right nanomaterial for a particular therapy, reaching the right therapeutic target in the body at the right time, and simultaneously providing feedback as for its efficacy and undesired collateral effects. Nanoengineered biomaterials are of great interest in the context of the drive toward personalized medicine, and may prove to be the necessary catalyst for its large-scale implementation. In this work, prominent biomaterials, such as nanoporous silicon (pSi) biomaterials are presented and discussed as potential platforms for the individualization of medical intervention; these biomaterials are promising advanced drug delivery technologies for biomedical applications[1]-[8]. It is demonstrated that the surface biofunctionalization of these biomaterials using advanced technologies, such as click-chemistry, microfluidics, etc. Examples on how these materials can be used to enhance the bioavailability of drug/peptide molecules, demonstrating their cytocompatibility, in vivo biocompatibility, intracellular targeting (Figure 1), and theranostic applications, will also be presented and demonstrated. Applications for cancer, diabetes, and cardiovascular diseases of the developed pSi nanocomposites will be discussed and elucidated Figure 1: Intracellular targeting of pSi-modified nanoparticles prepared by the microfluidics technology for cancer therapy. The recent cutting-edge advances on pSi nanomaterials is anticipated to overcome some of the therapeutic window and clinical applicability of many drug/peptide molecules and can also act as innovative theranostic platform and tool for the clinic. The emergence of pSi theranostic systems are expected to convey substantial benefits to the field of drug delivery and cancer/diabetes/cardiovascular therapies as it offers a less invasive alternative compared to the conventional therapeutic strategies and, thereby, enhancing the expectancy and quality of life of the patients. The Academy of Finland (decisions no. 252215 and 281300), the University of Helsinki Research Funds, the Biocentrum Helsinki, and the European Research Council under the European Union's Seventh Framework Programme (FP/2007–2013, grant no. 310892) are highly acknowledge for financial support.

Luminescence and fine structure correlation in ZnO permeated porous silicon nanocomposites.

Nanocomposites formed by porous silicon (PS) and zinc oxide (ZnO) have potential for applications in optoelectronic devices. However, understanding the distribution of both materials in the nanocomposite, and especially the fine structure of the synthesized ZnO crystals, is key for future device fabrication. This study focuses on the advanced characterization of a range of PS-ZnO nanocomposites by using photon- and ion-based techniques, such as X-ray absorption spectroscopy (XAS) and elastic backscattering spectroscopy (EBS), respectively. PS substrates formed by the electrochemical etching of p(+)-type Si are used as host material for the sol-gel nucleation of ZnO nanoparticles. Different properties are induced by annealing in air at temperatures ranging from 200 °C to 800 °C. Results show that wurtzite ZnO nanoparticles form only at temperatures above 200 °C, coexisting with Si quantum dots (QDs) inside a PS matrix. Increasing the annealing temperature leads to structural and distribution changes that affect the electronic and local structure of the samples changing their luminescence. Temperatures around 800 °C activate the formation of a new zinc silicate phase and transform PS into an amorphous silicon oxide (SiOx, x≈ 2) matrix with a noticeably reduced presence of Si QDs. Thus, these changes affect dramatically the emission from these nanocomposites and their potential applications.

Engineering near-infrared fluorescent styrene-terminated porous silicon nanocomposites with bovine serum albumin encapsulation for in vivo imaging.

A novel strategy to fabricate bovine serum albumin and styrene-terminated porous silicon nanocomposites with stable near-infrared fluorescence under physiological conditions was described. And these resultant nontoxic porous silicon-based nanocomposites were administrated into nude mice via subcutaneous injection, which exhibited a potential application for in vivo fluorescence imaging.

SPECTRAL INVESTIGATIONS OF NANOCOMPOSITES ON THE BASIS OF POROUS SILICON

The results of experimental studies of porous silicon nanocomposites with biological materials: powder mineral phase of bone (hydroxyapatite) and biochemical solution identical to the natural tear fluid are presented in the work. Layers of porous silicon have been obtained in the process of electrochemical etching silicon wafers. There have been studies of IR reflection spectra of samples of nanocomposites in the range 4000-550 cm-1 produced.

Regularities of formic acid oxidation in the presence of porous silicon nanocomposites with palladium

Nanocomposites demonstrating high catalytic activity in the oxidation of formic acid were obtained by depositing palladium on porous silicon support. The palladium samples on porous silicon are superior to commercial samples on carbon black in many characteristics. A decrease in the size of palladium nanoparticles favors an increase in the catalytic activity of the palladium/porous silicon nanocomposites.

Time-resolved photoluminescence study of stabilised iron–porous silicon nanocomposites

Porous silicon (PS) passivated by iron (PS/Fe) shows an intense, board and stable photoluminescence (PL) band centred at 1.77 eV. The time-resolved photoluminescence (TRPL) of PS and PS/Fe, in the range of some tenth of μs, were investigated at room temperature. Contrary to PS, the TRPL spectrum of PS/Fe exhibits a multi-band profile, attributed to the presence of iron in porous silicon matrix. Hence, the passivation of PS by iron provides the formation of two states located in the PS band gap. The PL decay line shape, in PS and PS/Fe, is well described by stretched exponential. The decay time ( τ) in PS has been found lower than that of PS/Fe which is due to the reduction of the non-radiative transitions. Such paths occur when excited carriers escape by tunnelling from less passivated nanocrystallites silicon. The analyses of the TRPL spectra as well as the decay times approve the passivation of Si nanocrystallites by iron.

Preparation of porous silicon nanocomposites with iron and cobalt and investigation of their electron structure by X-ray spectroscopy techniques

A method for the galvanic deposition of iron-group metals onto porous silicon (por-Si) substrates has been developed. The morphology and phase composition of por-Si nanocomposites containing galvanically deposited particles of Fe, Co, and their mixtures have been studied by scanning electron microscopy (SEM), ultrasoft X-ray emission spectroscopy (USXES), and X-ray absorption near-edge structure spectroscopy (XANES) techniques. It is established that iron uniformly covers the surface of porous silicon, whereas cobalt penetrates deep into pores in the form of nanoparticles. During the galvanic codeposition of both metals from a mixed solution of their salts, cobalt favors the penetration of iron in depth of the pores.

Electronic excitations induced modifications of structural and optical properties of ZnO–porous silicon nanocomposites

The influence of swift heavy ion (SHI) irradiation on structural and photoluminescence (PL) properties of ZnO nanocrystallites deposited into porous silicon (PS) templates by the sol–gel process was studied. The ZnO/PS nanocomposites were irradiated using 120 MeV Au ions at different fluences varying from 1 × 10 12 to 1 × 10 13 ions/cm 2. The intensity of the X-ray diffraction peaks is suppressed at the high fluence, without evolution of any new peak. The PL emission from PS around 700 nm is found to decrease with increase in ion fluence, while the PL emission from deep level defects of ZnO nanocrystallites is increased with ion fluence. At the highest fluence, the observation of drastic increase in PL emission due to donor/acceptor defects in the region 400–600 nm and suppressions of XRD peaks could be attributed to the defects induced structural modifications of ZnO nanocrystallites.

Electronic states and luminescence in higher fullerene/porous Si nanocrystal composites

Photoluminescence (PL) measurements have been performed on the nanocomposites of higher fullerene-coupled porous silicon (PS) nanocrystals. For the C70PS and C76(78)PS nanocomposites, the PL spectra show a pinning wavelength at approximately 565 nm and for the C84PS and C94PS nanosystems the pinning wavelength is at approximately 590 nm. The PL pinning property is closely related to the sorts of the coupled fullerenes. A band mixing model of direct and indirect gaps in a nanometer environment consisting of nc-Si core, SiO2 surface layer, and coupled fullerene has been proposed for calculation of electronic states. Good agreement is achieved between the experiments and theory.