Properties Of Silicon Nanostructures Research Articles

Nonlinear heating and scattering in a single crystalline silicon nanostructure.

Silicon nanophotonics has attracted significant attention because of its unique optical properties such as efficient light confinement and low non-radiative loss. For practical applications such as all-optical switch, optical nonlinearity is a prerequisite, but the nonlinearity of silicon is intrinsically weak. Recently, we discovered a giant nonlinearity of scattering from a single silicon nanostructure by combining Mie resonance enhanced photo-thermal and thermo-optic effects. Since scattering and absorption are closely linked in Mie theory, we expect that absorption, as well as heating, of the silicon nanostructure shall exhibit similar nonlinear behaviors. In this work, we experimentally measure the temperature rise of a silicon nanoblock by in situ Raman spectroscopy, explicitly demonstrating the connection between nonlinear scattering and nonlinear heating. The results agree well with finite-element simulation based on the photo-thermo-optic effect, manifesting that the nonlinear effect is the coupled consequence of the red shift between scattering and absorption spectra. Our work not only unravels the nonlinear absorption in a silicon Mie-resonator but also offers a quantitative analytic model to better understand the complete photo-thermo-optic properties of silicon nanostructures, providing a new perspective toward practical silicon photonics applications.

Morphological, Structural, and Optical Properties of Silicon Nanostructures Formed in a Solution Containing Hydrogen Hexafluorosilicate H2(SiF6)

Photoluminescent boron-doped (100)-oriented porous silicon fabricated on a p-type silicon substrate by electrochemical etching in a solution containing fluorosilicic acid and ethanol is studied. The morphological, structural, and optical properties of silicon nanostructures obtained in solutions containing H2(SiF6) and ethanol are analyzed in comparison with the corresponding characteristics of samples formed in solutions of HF and ethanol. The morphological, structural, and optical properties were studied using scanning probe microscopy and spectrophotometry. It is shown that the porous silicon samples formed in solutions containing H2(SiF6) and ethanol have better optical properties, in particular, they exhibit more intense photoluminescence than the samples obtained in HF–ethanol solutions.

Response Surface Methodology (RSM) in Fabrication of Nanostructured Silicon

In this paper, a respond surface methodology (RSM) model has been developed using three levels Box-Benkhen experimental design (BBD) technique to study the influence of several metal-assisted chemical etching (MACE) process variables on the properties of nanostructured silicon (Si) wafer. Five process variables are examined i.e. concentrations of silver (Ag), hydrofluoric acid (HF), deposition time, H2O2 concentration and etching time as a function of etching rate. Design-Expert® software (version 7.1) is used in formulating the RSM model of five factors with 46 experiments. A regression quadratic model is developed to correlate the process variables where the most significant factors are identified and validated using analysis of variance (ANOVA). The model for etching rate is found to be significant with R2 of 0.8, where both Ag concentrations and etching time are the major influence.

Biosensors based on a method for determining the conductance matrix of multiterminal semiconductor nanostructures

A method for determining the conductance matrix is analyzed to study the properties of silicon nanostructures fabricated within Hall geometry on an n-type Si(100) surface as ultra-narrow p-type silicon quantum wells bounded by δ barriers heavily doped with boron. Within the proposed approach, the total current flowing through the multiterminal silicon nanostructure is written in the matrix form as I = G · V, where I and V are the columns of currents and voltages for each of the N terminals, G is the N × N conductance matrix uniquely describing the conductance of the structure under study, taking into account the contribution of contact-area resistances. The high sensitivity of matrix elements to changes in the state of the silicon nanostructure surface under conditions of the precipitation of sodium-acetate solution containing single-strand synthetic oligonucleotides is demonstrated. The prospects of practical application of the results obtained in developing modern biosensors based on determining the conductance matrix of multiterminal semiconductor nanostructures are discussed.

The Properties of Nanosized Silicon Prepared by Plasmochemical and Electrolytic (HCl : HF : C2H5OH ) Techniques

The structural and optical properties of nanostructured silicon obtained by plasmachemical and electrolytic techniques are presented. For electrolytic etching of silicon electrolyte the chlorine acid was added to standard HF:C2H5OH electrolyte. It was found that adding of HCl to the electrolyte slows the process of electrochemical etching thus creating conditions for efficient etching and formation of Si-O and Si-H bonds on the formed nanosilicon surface. In the present study the nanosilicon samples were obtained in ultra-high frequency plasmochemical system by means of recondensation of ultradispersed silicon powder in nitrogen flux heated to mean temperature of 3500 K. Morphology of films was found to consist of quantum nanowires of a mean diameter of 2 nm. Results indicating stability of nanosized silicon (NanoSi) under intense laser irradiation are presented. It is demonstrated that substantial increase of NanoSi photoluminescence signal can be attributed to their specific structure, as well as to the SiO2 thin film formed on the nanocrystalline surface.

UNCD electron emitters using Si nanostructure as a template

The electron field emission (EFE) properties of silicon nanostructures (SiNSs) coated with ultra-nanocrystalline diamond (UNCD) were characterized. The SiNS, comprising cauliflower-like grainy structure and nanorods, was generated by reaction of a Si substrate with an Au film at 1000 °C, and used as templates to grow UNCD. The UNCD films were deposited by microwave plasma-enhanced chemical vapour deposition (MPECVD) using methane and argon as reaction gases. The UNCD films can be grown on the SiNS with or without ultrasonication pretreatment with diamond particles. The EFE properties of the SiNS were improved by adding an UNCD film. The turn-on field ( E 0) decreased from 17.6 V/μm for the SiNS to 15.2 V/μm for the UNCD/SiNS, and the emission current density increased from 0.095 to 3.8 mA/cm 2 at an electric field of 40 V/μm. Ultrasonication pretreatments of SiNS with diamond particles varied the structure and EFE properties of the UNCD/SiNS. It is shown that the ultrasonication pretreatment degraded the field emission properties of the UNCD/SiNS in this study.

Calculation of thermodynamic and mechanical properties of silicon nanostructures using the local phonon density of states

We investigate thermodynamic and mechanical properties of silicon nanostructures at finite temperature. Thermodynamic properties for finite-temperature solid systems under isothermal conditions are characterized by the Helmholtz free energy density. The static part of the Helmholtz free energy is obtained directly from the interatomic potential, while the vibrational part is calculated by using the theory of local phonon density of states (LPDOS). The LPDOS is calculated efficiently from the on-site phonon Green's function by using a recursion technique based on a continued fraction representation. The Cauchy-Born hypothesis is employed to compute the mechanical properties. By considering ideal Si{001}, $(2\ifmmode\times\else\texttimes\fi{}1)$ reconstructed Si{001}, and monolayer-hydrogen-passivated $(2\ifmmode\times\else\texttimes\fi{}1)$ reconstructed Si{001} surfaces of a silicon nanowire, we calculate the local phonon structure and local thermodynamic and mechanical properties at finite temperature and observe that the surface effects on the local thermal and mechanical properties are localized to within one or two atomic layers of the silicon nanowire.

Stability of Emission Properties of Silicon Nanostructures

The aging process of silicon nanostructures obtained by magnetron sputtering and electrochemical etching is investigated by photoluminescence and Raman scattering methods. It is shown that oxidation of silicon crystallites takes place in both types of structures and results in appearance of additional emission bands. However the degree of oxidation in etched structures exceeds significantly this value for sputtered samples. It is found that the intensity and spectral position of the emission band caused by exciton recombination in Si crystallites do not change practically during aging in sputtered structures in contrast to etched ones. It is shown that the oxidation of silicon amorphous phase occur during aging in sputtered structures.

Properties of Silicon Nanopillar Structures

Silicon nanostructures present a new class of material systems that possess electrical and optical properties distinctly different from bulk silicon. Fabrication process for silicon nanopillars has been described earlier. Now we present optical studies of nanostructures based on silicon nanopillars. Properties of silicon nanostructures were investigated by photoluminescence (PL) and cathodoluminescence (CL) techniques. For electroluminescence (EL) measurements the pillar based device described in [A. G. Nassiopoulos et al. Appl. Phys. Lett. 69, 2267 (1996)] was used. Electroluminescent devices, based on silicon nanostructures were made after planarisation and top electrode formation. Obvious distinctions between PL and EL spectra show that the PL and EL of the pillars are caused by various luminescent centers, located in different parts of the pillars. EL originates from the top contact part of the pillars. The origin of PL is connected to the combined effect of a texturised surface and nonuniform sidewall composition of the pillars.

Informative essence of noise: New findings in the electrochemistry of silicon

The paper outlines recent advances in studies on the electrochemical dissolution of silicon made with flicker noise spectroscopy (FNS), a novel phenomenological method of studying the evolution of nonlinear dissipative systems in time, space, and energy. We analyze stochastic components of the anodic current (voltage) during the electrochemical dissolution of silicon and show that FNS provides microscopic-level information on the dissolution kinetics and mechanism. We also study the giant oscillations of voltage during the anodic polarization of silicon and show that it is a collective effect where all local sites at the corroding Si surface are working synchronously to yield an integral oscillatory response of the system. Finally, we discuss the electrical and optical properties of nanocrystalline porous silicon films and show that the FNS method gives the possibility to specify the mechanisms contributing to the electroconduction and luminescent properties of silicon nanostructures.