Surface Of Silicon Nanowires Research Articles

Femtomolar Dengue Virus Type-2 DNA Detection in Back-gated Silicon Nanowire Field-effect Transistor Biosensor

Background: Dengue is known as the most severe arboviral infection in the world spread by Aedes aegypti. However, conventional and laboratory-based enzyme-linked immunosorbent assays (ELISA) are the current approaches in detecting dengue virus (DENV), requiring skilled and well-trained personnel to operate. Therefore, the ultrasensitive and label-free technique of the Silicon Nanowire (SiNW) biosensor was chosen for rapid detection of DENV. Methods: In this study, a SiNW field-effect transistor (FET) biosensor integrated with a back-gate of the low-doped p-type Silicon-on-insulator (SOI) wafer was fabricated through conventional photolithography and Inductively Coupled Plasma – Reactive Ion Etching (ICP-RIE) for Dengue Virus type-2 (DENV-2) DNA detection. The morphological characteristics of back-gated SiNW-FET were examined using a field-emission scanning electron microscope supported by the elemental analysis via energy-dispersive X-ray spectroscopy. Results and Discussion: A complementary (target) single-stranded deoxyribonucleic acid (ssDNA) was recognized when the target DNA was hybridized with the probe DNA attached to SiNW surfaces. Based on the slope of the linear regression curve, the back-gated SiNW-FET biosensor demonstrated the sensitivity of 3.3 nAM-1 with a detection limit of 10 fM. Furthermore, the drain and back-gate voltages were also found to influence the SiNW conductance changed. Conclusion: Thus, the results obtained suggest that the back-gated SiNW-FET shows good stability in both biosensing applications and medical diagnosis throughout the conventional photolithography method.

Dps protein localization studies in nanostructured silicon matrix by scanning electron microscopy

The present work is related to the microscopic studies of the morphology of the planar and inner part of silicon nanowires arrays before and after immobilization with a natural nanomaterial, Dps protein of bacterial origin. Silicon nanowires were formed by metal-assisted wet chemical etching. To obtain the recombinant protein, Escherichia coli cells were used as excretion strain and purification were carried out using chromatography. The combination of silicon nanowires with protein molecules was carried out by layering at laboratory conditions followed by drying under air. The resulting hybrid material was studied by high-resolution scanning electron microscopy. Studies of the developed surface of the nanowires array were carried out before and after combining with the bioculture. The initial arrays of silicon wireshave a sharp boundaries in the planar part and in the depth of the array, transition layers are not observed. The diameter of the silicon nanowires is about 100 nm, the height is over a micrometer, while the distances between the nanowires are several hundred of nanometers. The pores formed in this way are available for filling with protein during the immobilization of protein.The effectiveness of using the scanning electron microscopy to study the surface morphology of the hybrid material “silicon wires – bacterial protein Dps” has been demonstrated. It is shown that the pores with an extremely developed surface can be combined with a bio-material by deposition deep into cavities. The protein molecules can easily penetrate through whole porous wires matrix array. The obtained results demonstrate the possibility of efficient immobilization of nanoscaled Dps protein molecules into an accessible and controllably developed surface of silicon nanowires.

Adsorption of urea on metal-functionalized Si nanowires for a potential uremia diagnosis: A DFT study

Uncommon concentrations of urea in the human body could be indicative of uremia, which is a symptom of kidney malfunctioning. In this paper, we investigate the effect of urea adsorption on Ag-, Au-, and Cu-decorated silicon nanowires (SiNW). We considered SiNWs grown along the [100] direction with (110) exposed surfaces and passivated with hydrogen. For the metal-decorated SiNWs, an H passivating atom on the SiNW surface is replaced by an Au, Ag, or Cu atom, which is used as adsorption site for the urea molecule. The results show that the metalized SiNWs are capable to adsorb the urea molecule, having the highest adsorption energy for the Cu case, followed by the Ag and Au cases. The adsorption of urea on the metal-decorated SiNW modifies the electronic states inside the valence and conduction bands, this hybridization confirms that the urea molecule is adsorbed by the metalized SiNW. Also, a noticeable change in the work function of the systems, provoked by the urea adsorption, could allow the detection of the molecule. These nanostructures could be used for urea capture and detection, which could lead to a potential nanosensor for the diagnosis of uremia.

Functionalization and Characterization of Silicon Nanowires for Sensing Applications: A Review.

Silicon nanowires are attractive materials from the point of view of their electrical properties or high surface-to-volume ratio, which makes them interesting for sensing applications. However, they can achieve a better performance by adjusting their surface properties with organic/inorganic compounds. This review gives an overview of the main techniques used to modify silicon nanowire surfaces as well as characterization techniques. A comparison was performed with the functionalization method developed, and some applications of modified silicon nanowires and their advantages on those non-modified are subsequently presented. In the final words, the future opportunities of functionalized silicon nanowires for chipless tag radio frequency identification (RFID) have been depicted.

Diamond-Like Carbon - Coated Silicon Nanowires as a Supercapacitor Electrode in an Aqueous LiClO4 Electrolyte

Silicon nanowires (SiNWs) were successfully coated by uniform, adherent, and homogenous films of diamond-like carbon (DLC) using electrophoretic method. The coating was performed in an organic dimethylsulfoxide (DMSO) solution at 70 °C for 60 min with an applied voltage of 150 V. The as prepared samples of SiNWs and DLC/SiNWs were characterized by a scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray (EDX), and Raman spectroscopy techniques. The SEM micrographics showed that the films were uniformly deposited on the whole of SiNWs surface and composed of compact and small spherical grains with uniform distribution. Raman spectroscopy indicates that the coating films were DLC in nature. These results were well confirmed by the EDX and XRD techniques. The electrochemical investigation including cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy, showed that the electrochemical behavior of SiNWs was clearly enhanced after coating with a DLC film. Indeed, the latter showed a specific capacitance of 400 mF/cm2at scan rate of 5 mV/s in an aqueous 0.5 M LiClO4 solution with capacitance retention of 90% after 16,000 cycles. Thus, the deposition of DLC film onto silicon nanowires (SiNWs) substrate can be considered as a simple and economical method to fabricate a high-performance electrode for supercapacitors.

Functionalized SERS substrate based on silicon nanowires for rapid detection of prostate specific antigen

Abstract Owing to its high sensitivity, surface-enhanced Raman spectroscopy (SERS) is widely used in biosensing as an efficient optical transduction technique. In this work, we report the elaboration of a novel SERS-powered aptasensing substrate for the ultra-sensitive and selective detection of prostate specific antigen (PSA). The transducing SERS substrate is formed by vertically aligned silicon nanowires (SiNWs) decorated with silver nanoparticules (AgNPs). The silver nanoparticles have two purposes : a) aptamer immobilization via thiol chemistry and b) Raman signal enhancement. The presence of PSA induces the appearance of amide bond vibration modes only if the aptamer is present on the surface of SiNWs. The platform is highly sensitive, selective and specific to PSA in a wide range of concentrations from 0.1 to 20 μg.L−1 with a detection limit of 0.1 μg.L−1, which encompasses the blood serum range of healthy subjects and ill patients. This optical biosensor shows a great stability and it is successfully validated in human blood serum samples showing very good results.

Design and Fabrication of Silicon Nanowire-Based Biosensors with Integration of Critical Factors: Toward Ultrasensitive Specific Detection of Biomolecules.

As critical factors affecting the sensing performance of silicon nanowire (SiNW) biosensors, the structure, functional interface, and detection target were analyzed and designed to improve sensing performance. For an improved understanding of the dependence of sensor structure on sensitivity, a simple theoretical analysis was proposed to predict the sensitivity of biosensors with different SiNW types, widths, and doping concentrations. Based on the theoretical analysis, a biosensor integrating optimized critical factors was designed and fabricated. Optimizations focusing on the following aspects are considered: (1) employing n-type SiNW and controlling the impurity doping concentration of SiNW at approximately 2 × 1016-6 × 1016 atoms/cm3 to obtain a suitable charge density, (2) minimizing the SiNW width to 16.0 nm to increase the surface area-to-volume ratio, (3) using a native oxide layer on SiNW as a gate insulator to transport the captured charge molecules closer to the SiNW surface, (4) modifying the SiNW surface by 2-aminoethylphosphonic acid coupling to form a high-density self-assembled monolayer for enhancing the stability bound molecules, and (5) functionalizing the SiNW with ovalbumin molecules for specifically capturing the target immunoglobulin G (IgG) molecules. The sensing performance was evaluated by detecting IgG with concentrations ranging from 6 aM to 600 nM and control experiments. The SiNW biosensor revealed ultrahigh sensitivity and specific detection of target IgG with a measured limit of detection of 6 aM. The integration of the critical SiNW biosensor factors provides a significant possibility of a rapid and ultrasensitive diagnosis of diseases at their early stages.

Formation and Magnetic Interaction of Si/MnGe Core/Shell Nanowire Arrays

We present the preparation of MnGe coated Si nanowires (NWs) using molecular beam epitaxy. Uniformly dispersed silicon NW surfaces were initially covered by Ge, and then Si/MnGe core/shell NW heterostructures were fabricated by solid phase epitaxial growth. Morphology and the magnetic properties of the Si/MnGe core/shell NWs were investigated. The results of scanning electron microscope and transmission electron microscope revealed that the shell layer of NWs was agglomerated to form clusters, which were mainly comprised of Mn5Ge3 phase. Vibrating magnetometer and X-band ferromagnetic resonance measurements indicate that the Si/MnGe core/shell NWs exhibited a slight shape anisotropy along the geometrical wire axis.

Electrical characterisation of Ag/poly(3-hexylthiophene)/silicon nanowires Schottky diode

The electrical properties of Ag/Poly(3-hexylthiophene)/Silicon nanowires heterostructure (Ag/P3HT/SiNWs) were investigated. Silicon nanowires (SiNWs) were obtained by metal-assisted chemical etching method in one-step process. P3HT polymer was deposited on SiNWs surfaces by electroless deposition method for different immersion durations (dim). The morphology of SiNWs before and after deposition of P3HT polymer has been examined by scanning electron microscope (SEM). The formation of nanowires as well as the presence of P3HT on their surfaces can be seen in SEM images. Current–voltage (I–V) measurements were carried out on Ag/P3HT/SiNWs by varying dim from 30 to 210 min. The electrical measurements on the different junctions at room temperature showed a rectifying effect. For 30 min, the ideality factor of the Schottky diode was reduced from 4 to 1,4. By using the Cheung method, the diode parameters of the different structures are determined and discussed. The different hetrostructures have been annealed at 100 °C, 200 and 300 °C. The characteristic parameters were calculated as a function of annealing temperature. The optimum temperature for these heterostructures characteristics is 100 °C. The interface states, the trapping levels and the thermal activation of the free carriers are the main factors involved in the conduction phenomenon through Ag/P3HT/SiNWs heterostructures.

Highly Efficient Silicon Nanowire Surface Passivation by Bismuth Nano-Coating for Multifunctional Bi@SiNWs Heterostructures.

A key requirement for the development of highly efficient silicon nanowires (SiNWs) for use in various kinds of cutting-edge applications is the outstanding passivation of their surfaces. In this vein, we report on a superior passivation of a SiNWs surface by bismuth nano-coating (BiNC) for the first time. A metal-assisted chemical etching technique was used to produce the SiNW arrays, while the BiNCs were anchored on the NWs through thermal evaporation. The systematic studies by Scanning Electron Microscopy (SEM), energy dispersive X-ray spectra (EDX), and Fourier Transform Infra-Red (FTIR) spectroscopies highlight the successful decoration of SiNWs by BiNC. The photoluminescence (PL) emission properties of the samples were studied in the visible and near-infrared (NIR) spectral range. Interestingly, nine-fold visible PL enhancement and NIR broadband emission were recorded for the Bi-modified SiNWs. To our best knowledge, this is the first observation of NIR luminescence from Bi-coated SiNWs (Bi@SiNWs), and thus sheds light on a new family of Bi-doped materials operating in the NIR and covering the important telecommunication wavelengths. Excellent anti-reflectance abilities of ~10% and 8% are observed for pure SiNWs and Bi@SiNWs, respectively, as compared to the Si wafer (50–90%). A large decrease in the recombination activities is also obtained from Bi@SiNWs heterostructures. The reasons behind the superior improvement of the Bi@SiNWs performance are discussed in detail. The findings demonstrate the effectiveness of Bi as a novel surface passivation coating, where Bi@SiNWs heterostructures are very promising and multifunctional for photovoltaics, optoelectronics, and telecommunications.

Liquid and solid states on-chip micro-supercapacitors using silicon nanowire-graphene nanowall-pani electrode based on microfabrication technology

Liquid and solid states on-chip micro-supercapacitors based on polyaniline (PANI) coated on graphene nanowalls which grown on silicon nanowires were reported in this work. Novel micro-fabrication technologies were investigated to create three dimension (3D) hierarchical electrodes. High aspect ratio silicon nanowires were produced by metal-assisted chemical etching (MACE). 3D hierarchical graphene nanowalls were grown on silicon nanowire surface by a microwave plasma-enhanced chemical vapor deposition (PECVD). Graphene nanowalls were subsequently coated by conductive PANI. Both of liquid and solid state micro-supercapacitors were successfully fabricated with symmetric face to face high density nanowire arrays separated by liquid and gel electrolytes, respectively. The areal energy and power density of the liquid-state on-chip micro-supercapacitor are 11.7 μWh/cm2 and 0.42 mW/cm2, respectively, while those of the solid-state on-chip micro-supercapacitor are 10.8 μWh/cm2 and 0.78 mW/cm2.

Ultra-low thermal conductivity of roughened silicon nanowires: Role of phonon-surface bond order imperfection scattering**Project supported by the National Natural Science Foundation of China (Grant No. 11874145).

The ultra-low thermal conductivity of roughened silicon nanowires (SiNWs) can not be explained by the classical phonon–surface scattering mechanism. Although there have been several efforts at developing theories of phonon–surface scattering to interpret it, but the underlying reason is still debatable. We consider that the bond order loss and correlative bond hardening on the surface of roughened SiNWs will deeply influence the thermal transport because of their ultra-high surface-to-volume ratio. By combining this mechanism with the phonon Boltzmann transport equation, we explicate that the suppression of high-frequency phonons results in the obvious reduction of thermal conductivity of roughened SiNWs. Moreover, we verify that the roughness amplitude has more remarkable influence on thermal conductivity of SiNWs than the roughness correlation length, and the surface-to-volume ratio is a nearly universal gauge for thermal conductivity of roughened SiNWs.

Bactericidal Characteristics of Bioinspired Nontoxic and Chemically Stable Disordered Silicon Nanopyramids.

Controlling bacterial growth using artificial nanostructures inspired from natural species is of immense importance in biomedical applications. In the present work, a low cost, fast processing, and scalable anisotropic wet etching technique is developed to fabricate the densely packed disordered silicon nanopyramids (SiNPs) with nanosized sharp tips. The bactericidal characteristics of SiNPs are assessed against strains implicated in nosocomial and biomaterial-related infections. Compared to the bare silicon with no antibacterial activities, SiNPs of 1.85 ± 0.28 μm height show 55 and 75% inhibition of Escherichia coli (Gram-negative) and Bacillus subtilis (Gram-positive) bacteria, whereas the silicon nanowires (SiNWs) fabricated using a metal-assisted chemical etching method show 50 and 58% inhibition of E. coli and B. subtilis. The mechanistic studies using a scanning electron microscope and live/dead bacterial cell assay reveal cell rupture and predominance of dead cells on contact with SiNPs and SiNWs, which confirms their bactericidal effects. Chemical stability and cell viability studies demonstrate the biocompatible nature of SiNP and SiNW surfaces. Owing to their capability to kill both Gram-negative and positive bacteria and minimal toxicity to murine fibroblast cells, SiNPs can be used as an antibacterial coating on medical devices to prevent nosocomial and biomaterial-related infections.

On-chip silicon shallowly etched TM0-to-TM1 mode-order converter with high conversion efficiency and low modal crosstalk

Ever-increasing capacity requirements of optical interconnects drive the emergence and fast development of mode-division-multiplexing (MDM) transmission on-chip, where efficient mode control and conversion components become indispensable. Here, we propose an on-chip silicon TM 0 - to - TM 1 mode-order converter by leveraging shallowly etched rectangular slots on the top surface of silicon nanowire. The mode conversion region consists of two rectangular slots on the same side of a silicon nanowire and a smaller one between them to realize the efficient mode-order conversion from input TM 0 to output TM 1 mode with the help of multimode interference and accumulated phase difference. By studying the etching pattern on the silicon nanowire in detail, we have achieved an on-chip TM 0 - to - TM 1 mode-order converter with a high conversion efficiency of 97.5% and low modal crosstalk < − 23 dB in a conversion length of 11.8 µm; further, the insertion loss is only 0.29 dB at the wavelength of 1.55 µm. Moreover, the device working bandwidth and fabrication tolerance are also analyzed. Note that the proposed shallowly etched slots on the silicon nanowire can also be further developed to achieve the on-chip TM 0 - to - TM 2 mode-order conversion. With these characteristics, such a device could boost the development of MDM transmission on-chip with more TM-polarized mode channels.

Highly Sensitive and Fast Detection of C-Reactive Protein and Troponin Biomarkers Using Liquidgated Single Silicon Nanowire Biosensors

ABSTRACTC-reactive protein (CRP) and cardiac troponin I (cTnI) biomolecules represent the earliest enzymes that appear in the blood when a cardiac injury occurs. Real-time and selective detection of these biomarkers is essential for the prediction and detection of cardiovascular diseases at an early stage. Here we report on the label-free specific detection of both proteins at picomolar concentrations using fabricated nanowire-based biosensors. We demonstrate a novel functionalization technique based on the attachment of dibenzocyclooctyne (DBCO)-linked troponin-specific aptamers to azide-functionalized silicon (Si) nanowire (NW) surface. Due to the fast and reliable immobilization of cTnI-specific aptamers and CRP-specific antibodies on the Si NWs, the fabricated devices can rapidly detect target biomolecules demonstrating high sensitivity. We confirm the attachment of proteins to the surface of Si NWs by atomic force microscopy (AFM). Moreover, we demonstrate that nanowire structures of different sizes enable the detection of biomarkers in a wide concentration range (from 1 pg/ml to 1 µg/ml), corresponding to CRP and cTnI elevation levels during the early stage of disease formation.

Effect of Etching Duration on the Morphological and Opto-Electrical Properties of Silicon Nanowires Obtained by Ag-Assisted Chemical Etching

Silicon nanowires (SiNWs) were obtained on p-Si (100) substrate by Ag-assisted chemical etching method in two-step process. The influence of the etching duration on the morphological, optical and electrical properties of SiNWs samples was investigated. SEM images show clearly the presence of nanowires and the existence of porous silicon structure especially for low etching duration. Fourier Transformed Infrared spectroscopy (FTIR) measurements allow identifying several particles on the SiNWs surfaces such as oxygen and hydrogen elements. The optical properties of the SiNWs layer were investigated by Photoluminescence spectroscopy (PL). A strong broad PL band was observed at room temperature for an etching time of 30 s. The PL spectra exhibit multi-band profile in the red-green region. The luminescence of SiNWs is mainly attributed to Si-oxide interface states and oxygen deficient centers. Ag/SiNWs/Si Schottky diodes were analyzed by X-ray diffraction (XRD) and studied by current - voltage (I-V) measurements. Diode parameters such as ideality factor (n), series resistance (Rs), saturation current (Is) and energy barrier (φb) were determined by analyzing the I-V characteristics. Ag/SiNWs/Si diode for an etching duration of 30 s exhibits a rectifying behavior with a factor ideality of 2.8 and a low threshold voltage of about 0.44 V in forward bias. Space charge limited current (SCLC) model is the dominant transport mechanism through Ag/SiNWs/Si diode. The trap states, on the Ag/SiNWs interface, play in important role in the conduction phenomenon through these structures.

Surface modification influenced properties of silicon nanowires grown by Ag assisted chemical etching with ECR hydrogen plasma treatment

Silicon nanowires (SiNWs) are fabricated by Ag assisted chemical etching and are treated with hydrogen plasma created by electron cyclotron resonance (ECR) plasma system at 600 watts microwave power for various time durations (0–30 min). The hydrogen plasma exposure on the surface of the SiNWs reduced the surface roughness and increased the crystalline nature. SEM analysis revealed that the diameter of the SiNWs decreased on plasma exposure. The electrical conduction measurements suggested that the hydrogen plasma exposure for 5 min on the SiNW surface enhanced the electrical conductivity when compared to as fabricated SiNW surface. The hydrophobic nature of fabricated SiNWs was transformed to hydrophilic at plasma exposure for lower time duration. On plasma exposure of NWs for 30 min the sample turned hydrophobic. Study of different properties of the SiNWs before and after plasma treatment revealed that there is pronounced effect of plasma on the nature of SiNWs.

Electro-performance of functionalized silicon nanowires by conductive polymer-coated with gold nanoparticles

In this paper, we present a novel technique to functionalize and enhance the efficiency of silicon nanowires (SiNWs) surface. SiNWs coated with a conductive polymer (polypyrrole (PPy)) prior to decoration with gold nanoparticles (AuNPs) was investigated. SiNWs and AuNPs were synthesized using metal assisted chemical etching (MACE) and Turkevich method respectively. The PPy was electrochemically polymerized on the surface of the SiNWs and visualized by scanning electron microscopy (SEM). Deposition of AuNPs on PPy/SiNWs surface was confirmed using Energy dispersive X-ray spectroscopy (EDS). Investigation of the AuNP@PPy/SiNWs composite using electrochemical impedance spectroscopy (EIS), compared to bare SiNWs and PPy/SiNWs structure, revealed significant enhancement of surface conductivity at low frequency where the charge transfer resistance decreases 80 times compared to that the bulk silicon in the end of the process and hence demonstrated effective electronic properties, primarily, the charge transfer at the semiconductor/electrolyte interface.

Chemical Vapor Deposition Growth of Silicon Nanowires with Diameter Smaller Than 5 nm.

Quantum confinement effects in silicon nanowires (SiNWs) are expected when their diameter is less than the size of the free exciton (with a Bohr radius ∼5 nm) in bulk silicon. However, their synthesis represents a considerable technological challenge. The vapor–liquid–solid (VLS) mechanism, mediated by metallic nanoclusters brought to the eutectic liquid state, is most widely used for its simplicity and control on the SiNWs size, shape, orientation, density, and surface smoothness. VLS growth is often performed within high-vacuum physical vapor deposition systems, where the eutectic composition and the pressure conditions define the minimum diameter of the final nanowire usually around 100 nm. In this article, we present and discuss the SiNWs’ growth by the VLS method in a plasma-based chemical vapor deposition system, working in the mTorr pressure range. The purpose is to demonstrate that it is possible to obtain nanostructures with sizes well beyond the observed limit by modulating the deposition parameters, like chamber pressure and plasma power, to find the proper thermodynamic conditions for nucleation. The formation of SiNWs with sub-5 nm diameter is demonstrated.

Strong photoluminescence enhancement of silicon nanowires by poly(3-hexylthiophene) deposition

Silicon nanowires (SiNWs) layer was obtained by one-step metal-assisted chemical etching method. In order to improve the optical properties of SiNWs, we deposited poly(3-hexylthiophene) (P3HT) polymer on its surface. P3HT polymer has been deposited by electroless deposition method. The formation of aligned nanowires as well as the presence of the polymer on SiNWs layer has been shown from scanning electron microscopy (SEM) analysis. Raman and Fourier Transformed Infra-Red (FTIR) spectroscopies reveal the formation of new bonds on the nanowires surface thus showing a chemical reaction between silicon and P3HT molecules. The optical properties of the elaborate samples are studied by photoluminescence spectroscopy (PL). The integrated PL intensity of SiNW–P3HT sample has been achieved enhancement of 16 orders relative to that emitted from the normal SiNWs sample. The emission domain of the nanowires is practically in the same range as that of P3HT. The PL intensity increase is due to the luminescent centers of P3HT molecules as well as the passivation of silicon nanowires surface.