Amorphous Silicon Carbon Alloys Research Articles

High-performance carbon-rich amorphous silicon–carbon alloy semiconductors with low optical gaps

High-performance carbon-rich amorphous silicon–carbon alloy semiconductors with low optical gaps

Monolithically integrated optical interference and absorption filters on thin film amorphous silicon photosensors for biological detection

High selectivity of photosensors is needed for targeted biological detection. Optical interference filters are monolithically integrated with hydrogenated amorphous silicon thin film photosensors for fluorescence measurements in lab-on-chip applications using a methodology that enables customization of fluorescence detection for various applications. The design of the optical interference filters is tailored to match the requirements of each application and the filters are fabricated as nitride-oxide multilayers. The interference filters are combined with hydrogenated amorphous silicon-carbon alloys, which serve as long-pass absorption filters, depending on the spectral requirements. In this work we demonstrate the development of these filters, through simulations and design, followed by experimental fabrication and characterization of transmission spectra, and finally, integration with photosensors which are implemented in measurements to detect fluorescence in three different applications, including bacteriophage fluorescence, quantum dot and Cy3 fluorophores, and grape fluorescence for grape maturation monitoring, in a novel methodology that allows for simplification and greater portability of the measurement setup and negates the need to stack optical filters in fluorescence applications.

Fourier-Imaging Spectroscopy of Two-Dimensional Gold Nanodisk Array on Photoluminescent Layer

In this paper, we theoretically and experimentally study the reflection and photoluminescence spectra angular dependencies of the two-dimensional gold nanodisk array on top of thin luminescent layer. Hydrogenated amorphous silicon-carbon alloy was used as a luminescent material with a high refractive index in the visible spectral range. Angle-resolved optical spectra were measured by a Fourier imaging spectroscopy in p- and s-polarizations. Both transverse electric (TE) and transverse magnetic (TM) quasiguided modes are clearly seen in the reflection and photoluminescence spectra in both polarizations simultaneously.

Development of High Performance C-Rich a-SiC Semiconductors with Narrow-Optical Gap By Control of Its Phase Structure

1. Introduction For the expansion of application fields (ex. tailor-made photocatalysts and high-efficiency laser) of semiconductor, novel semiconductor materials with variable optical gaps in the range from 1.2 to 3.0 eV is necessary to be developed. The promising candidate of these semiconductor is carbon-rich amorphous silicon-carbon alloy (C-rich a-SiC).[1] The optical gaps (Eog) of C-rich a-SiC can be changed from 1.2 to 2.7 eV by changing the Si/C ratio. Hetero-junction solar cell comprising N-doped C-rich a-SiC with Eog = 2.7 eV and p-type Si have been reported to show the function of photon to electron conversion.[2] However, solar cells comprising N-doped C-rich a-SiC with Eog from 1.2 to 1.7 eV showed extremely lower conversion efficiencies. Therefore, all of these C-rich a-SiC with Eog from 1.2 to 2.7 eV may not be applied to photoelectronic devices. The objective of this study is to realize C-rich a-SiC with lower Eog (frim 1.2 to 1.7 eV) that have higher semiconductor property and are able to be applied to photoelectronic devices. a-SiC has a multiphase structure in which amorphous Si-C network (Si:C = x:1-x), sp2-hybridized carbon cluster (sp 2 clusters), and silicon-like clusters (Si-cluster) coexist. It has been reported that excess sp2 cluster worked as a recombination center of photoexcited carries. It results in the degradation of efficiencies of photon to electron conversion. In order to realize C-rich a-SiC with lower Eog and higher photon to electron conversion efficiency, the synthesis method that can enhance of ratio of C/Si in amorphous Si-C network and suppress the formation of sp 2 clusters in C-rich a-SiC is necessary to be developed. In this study, CVD synthesis using high-frequency and lower power r. f. plasma was tried to be adopted to induce two types of structural change at C-rich a-SiC. High-frequency and lower power r. f. plasma can avoid the formation of sp 2 clusters in C-rich a-SiC. It results in the semiconductor materials with lower Eog and higher photon to electron conversion efficiency.2. Experimental Nitrogen-doped C-rich a-SiC thin films were synthesized by radio frequency plasma enhanced chemical vapor deposition system (RF-PeCVD) (13.56 MHz, SAMCO Co., Ltd. Model BPD-1) using tetramethylsilane, 1,1,3,3-tetrametyldisilazane and n-hexanes as source materials. C-rich a-SiC thin films were deposited on glass plate and boron-doped silicon (100) substrate (resistivity of 2 W cm) after an in-situ sputter cleaning with argon ions. Substrate temperature was kept at 160 degree C during CVD deposition. The frequency of r.f. power supply was set at 60 MHz and r.f power were changed from 5 to 26 W. The deposition time was 80 minutes. Transmission spectra of N-doped C-rich a-SiC deposited on glass substrates were examined by UV-Vis spectrophotometer (JASCO Co., Ltd. V-670). The performance of heterojunction solar cells was investigated by current-voltage (I-V) measurement (KEYSIGHT, B2901A) with simulated AM 1.5 sunlight (ASAHI SPECTRA, HAL-320). 3. Results and Discussion Eog estimated from transmission spectra (Fig. 1) of resulting N-doped C-rich a-SiC were found to be in the range from 1.40 to 2.96 eV, as shown in Table 1. Eog was able to be controlled to lower value (1.4 eV) thorough the change of the S/C ratios in C-rich a-SiC (by changing the volume ratio of n-hexane in source materials). All hetero-junction solar cells comprising N-doped C-rich a-SiC with various Eog and p-type Si crystal were confirmed to show the function of photon-to electron conversion (Table 1). The improvement of function of photon to electron conversion at C-rich a-SiC with lower Eog (ca. 1.4 eV) might be caused by the suppression of the recombination of photo-exited electrons and holes. In Figure 1, the absorption peak of sp 2 clusters was observed at 1.1 eV and was clearly separated from the absorption peak of amorphous Si-C network (observed at 2.6 eV). The intensity decrease and peak shift to lower energy side of the absorption of sp 2 clusters in Fig. 1 indicates the decrease of the amount of sp 2 clusters and the enlargement of size of sp 2 clusters. These structural change might cause the suppression of recombination of photo-carriers. The relation between Eog and open circuit voltage of solar cell was consistent with estimated value from electronic structure of C-rich a-SiC. It was summarized that the development of C-rich a-SiC semiconductors with lower Eog (in the range from 1.4 to 1.7 eV) that are able to be applied to photo-electronic devices was successfully achieved. 4.

Enterotoxigenic Escherichia Coli Detection Using the Design of a Biosensor

The food industry and clinical analysis, among other sectors, require the development of techniques and devices that detect pathogens, while the development of implantable devices needs biocompatible materials with low degradation in biological environment to increase the lifetime of the device. Throughout this work, hydrogenated amorphous silicon-carbon alloy is proposed, obtained, characterized and incorporated into the development of a proposed interdigitated microelectrode array (PIMA) to capture the bacteria of enterotoxigenic Escherichia coli (E. coli, ETEC). a-SixC1-x:H is obtained by the technique of plasma-enhanced chemical vapor deposition (PECVD) using methane and silane as precursor gases under high hydrogen dilution and low power density in order to improve its biocompatibility. Functionally the PIMA is a transducer based on electrical impedance, namely the capture of E. coli bacteria causes changes in the electrical properties of the medium between and on the microelectrodes of the array, which are associated with changes in electrical impedance. The simulations were made with the purpose of knowing the operation that the PIMA would have under operating conditions (with bacterial environment) and of analyzing the design aspects that could affect or increase the sensitivity of the array.

P+aSixC1-x: H/i-aSi:H/n+aSi1-xGex:H graded band gap single junction solar cell with composition graded amorphous silicon carbon alloy as window layer

The work explores the conduct of composition graded amorphous silicon carbon alloy (aSixC1-x: H) as window layer on graded band gap amorphous silicon (p+aSixC1-x: H/i-aSi:H/n+aSi1-xGe x:H) solar cells, for the first time. The working principle of the proposed structure is interpreted with the aid of energy band diagram. Experimentally validated parameters were adopted for the simulation of the proposed structure. It is observed that the proposed structure is efficient in delivering conversion efficiency (η) of 15.39% at 300 K on reducing its window layer thickness to 5 nm, which is commensurate to other announced amorphous silicon solar cells. The momentous cutback in thickness of one of the active layer leads to lesser material demand and diminishes the overall manufacturing cost. Further, the effect of variation in temperature on the proposed structure has been evaluated and observed that the performance remain almost unaltered. Furthermore, the proposed solar cell structure is compared with our previous work and state of art of single junction amorphous silicon solar cell structures.

Emitting properties of a-Si:C:H films with a gold submicron grating

In this study reflection and photoluminescence spectra of a-Si:C:H thin film with gold grating on it was examined theoretically and experimentally. The hydrogenated amorphous amorphous silicon-carbon alloy films were fabricated by the PECVD technique. Arrays of gold stripes with different gold width were created by lift-off e-beam lithography. Reflection, and PL spectra has been measured by a Fourier imaging spectroscopy. The theoretical calculations are in a good agreement with experimental results. From the PL spectra it follows, that the TE polarization gives sharper and more efficient PL signal than the TM polarization, and PL efficiency almost does not depend on gold stripes widths. It was shown that only in TE modes the PL outcouples from the gratings owing to the fact that there is no plasmon’s affect in this polarization.

Electroluminescence of thin film p-i-n diodes based on a-SiC:H with integrated Ge nanoparticles

Hydrogenated amorphous substoichiometric silicon carbon alloys (a-SiC:H) with and without embedded Ge nanoparticles (NPs) have been prepared by plasma enhanced chemical vapour deposition combined with in-situ Ge evaporation and annealing on semi-transparent boron doped nano-crystalline diamond coated Ti grids. The presence of Ge NPs embedded in the amorphous phase has been confirmed by transmission electron microscopy and energy-dispersive X-ray spectroscopy analyses. Current-voltage (I–V) characteristics and near infrared electroluminescence (EL) spectra were measured to compare performance of diodes. The relatively strong EL appears in diodes with integrated Ge NPs near the direct band-gap transition of Ge at about 0.82 eV with an intensity strongly correlating with current density. However, it has also been found that Ge NPs integrated into a-SiC:H significantly deteriorates diode I–V characteristic.

Interdigitated Microelectrode Arrays Based on Non-Cytotoxic a-SixC1-x:H for E. coli Detection

Fabrication and testing of interdigitated microelectrode arrays whose structure includes non-cytotoxic hydrogenated amorphous silicon-carbon alloy (a-SixC1-x:H) as the surface to be biofunctionalized for capturing enteropathogenic Escherichia coli (E. coli, EPEC) are presented. a-SixC1-x:H films were obtained by enhanced chemical vapor deposition (PECVD). The extract method was used to assess the cytotoxicity of the films. The design of the PIMAs includes two layers of a-SixC1-x:H, one intrinsic layer deposited onto silicon dioxide (SiO2) before evaporating titanium (Ti), and one doped layer deposited onto the Ti-microelectrodes. Electrical impedance spectroscopy (EIS) was used to know the effects of the biofunctionalization layer, conductivity of the medium and any capture of bacteria by antibodies on the microelectrodes. According to the results, the high hydrogen dilution contributes to low incorporation of CHn groups improving the non cytotoxicity of the films, and the capture of bacteria on the microelectrodes improves the sensitivity. It manifests itself as a shift of the low cutoff frequency (Flow) of the impedance spectrum to the right, allowing the device to sense at frequencies lower than Flow. A percentage change in impedance of 1600% at 100 Hz was obtained after 5 minutes in contact with medium with EPEC concentration of 8.5 × 108 CFU/mL.

Amorphous Carbon-Based Semiconductor Capable of Controlling Its Optical Gap and Conductivity by Incorporating Silicon and Nitrogen Atoms

Optical gap-selective amorphous carbon (a-C) based n-type semiconductor materials were fabricated by incorporating silicon and nitrogen atoms by radio frequency plasma enhanced chemical vapor deposition method using a mixed solution of tetramethylsilane and 1,1,1,3,3,3-hexamethyldisilazane as a source material. The optical gaps can be controlled from 1.25 to 2.76 eV when Si/C ratio at amorphous Si-C network and sizes and number of sp2 clusters in multi-phase structure of the resulting carbon-rich amorphous silicon-carbon alloys (C-rich a-SiC) are varied by regulating Si atom%. The resulting Si 24 atom%-added C-rich a-SiC shows the optical gap of 1.76 eV, while Si 44 and 18 atom%-added C-rich a-SiC show 2.76 and 1.25 eV, respectively. The films show n-type conduction with the carrier density of ca. 1014 cm−3 and the carrier mobility of ca. 1 cm2V−1s−1 by doping N atoms of 1 atom%. The results of photocurrent measurement under UV exposure are verified and showed that the films have a function of photon-to-electron conversion with the quantum yield of ca. 7%, approximately one-third of the value obtained at anatase-type titanium oxide prepared by the sol-gel method.

Carbohydrate microarray for the detection of glycan-protein interactions using metal-enhanced fluorescence.

Carbohydrate arrays are potentially one of the most attractive tools to study carbohydrate-based interactions. This paper describes a new analytical platform that exploits metal-enhanced fluorescence for the sensitive and selective screening of carbohydrate-lectin interactions. The chip consists of a glass slide covered with gold nanostructures, postcoated with a thin layer of amorphous silicon-carbon alloy (a-Si0.8C0.2:H). An immobilization strategy based on the formation of a covalent bond between propargyl-terminated glycans and surface-linked azide groups was used to attach various glycans at varying surface densities onto the interface and to fabricate a carbohydrate array via efficient local "click" chemistry strategy. The specific association of the new interface with fluorescently labeled lectins was assessed by fluorescence imaging and an excellent selectivity to specific proteins was achieved. Optimization of the surface architecture and the plasmonic transducer resulted in an enhancement of the fluorescence intensity by 1 order of magnitude, when compared to the corresponding substrate devoid of gold nanostructures. The limit of detection (LOD) of such microarrays is in the picomolar range, making it a promising system for development in pharmaceutical or biomedical applications.

Optical Properties of Amorphous Silicon–Carbon Alloys (a-Si x C1-x ) Deposited by RF Co-Sputtering

Amorphous silicon–carbon alloy (a-SixC1-x) thin films have been deposited by radio frequency (RF) sputter deposition. These films were obtained, from a composite target consisting of silicon fragments regularly distributed on the surface of a pure graphite disc, for different values of silicon surface fraction RSi/C, at an RF power of 250 W. X-ray diffraction diagrams show that all the as-deposited SixC1-x thin films are amorphous. The optical properties of the a-SixC1-x films were investigated by optical transmission measurements in the ultraviolet–visible–near infrared wavelengths range. The optical band gap Eg varies, with RSi/C, from 1.4 to 1.9 eV and presents a wide maximum at an RSi/C value of about 35 %. This maximum value is attributed to amorphous silicon carbide a-SiC as confirmed by theoretical correlation between the molar fraction x and RSi/C. The refractive index n follows well the Cauchy law and the extrapolated value, at infinite wavelengths, increases from 2.1 to 2.65 as the RSi/C fraction increases.

ОПТОЭЛЕКТРОННЫЕ СВОЙСТВА ТОНКИХ ПЛЕНОК ГИДРОГЕНИЗИРОВАННОГО АМОРФНОГО КРЕМНИЯ-УГЛЕРОДА И НАНОКРИСТАЛЛИЧЕСКОГО КРЕМНИЯ

Some parameters of thin films fabricated of hydrogenated amorphous silicon–carbon alloys a-Si1 xCx:H with x = 0 and 0.5 and nanocrystalline silicon (nc-Si) and serving as a basis for developing solar cells including a Schottky barrier and p–i–n and double p–i–n heterojunctions have been considered. In double p–i–n heterojunctions, a-SiC/a-Si/nc-Si, the p-layer was made from a-SiC:H and used as a “window”, and the n-layer was made from nc-Si. The current-voltage characteristics of solar cells of each type at their illumination are studied. The highest efficiency of 11.5% was found for solar cells with the double p–i–n heterojunctions in the case where a cell 1 cm2 in area was illuminated with light of a 100-mW/cm2 intensity.

Integrated detection of intrinsic fluorophores in live microbial cells using an array of thin film amorphous silicon photodetectors

Two-dimensional fluorescence spectroscopy (2D FS) provides a non-invasive means to assess cell condition without the introduction of changes to the cell environment. The method relies on the measurement of the excitation–emission fluorescence intensity matrix of key intrinsic fluorophores, like aromatic amino acids, enzyme cofactors, and vitamins. Commonly used detection systems are complex, with multiple bandpass filters, and are hard to miniaturize. Here, an amorphous silicon photodetector array system integrated with amorphous silicon–carbon alloy filters designed to detect three key fluorophores – tryptophan (Trp), reduced nicotine adenine dinucleotide (NADH) and flavin adenine dinucleotide (FAD) – is demonstrated. These intrinsic fluorophores were detected in pure solutions and also in suspended yeast cells. The array system was used to monitor changes in intrinsic fluorophore concentration when a yeast cell solution was subject to a thermal shock stress.

Investigation of the corrosion behaviour of steel coated with amorphous silicon carbon alloys

Thin amorphous silicon (a-Si:H) and carbonated silicon (a-Si1−xCx:H) layers were deposited on stainless steel substrates using plasma-enhanced chemical vapour deposition (PECVD) in a “low-power” regime. The carbon content of the carbonated silicon (a-Si1−xCx:H) alloys was varied between 0.1 and 0.37at.%. The performance of these interfaces as effective corrosion barriers in 3% sodium chloride aqueous solutions was evaluated. Potentiodynamic polarisation curves and electrochemical impedance spectroscopy (EIS) were used next to X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) to investigate the protection efficiency of the different barriers. The a-Si:H coated showed better corrosion resistance as compared to the carbonated silicon alloys. No degradation was observed after 14days immersion of the steel substrate coated with a-Si:H in 3% sodium chloride aqueous solution, making this coating an attractive candidate as corrosion barrier.

Formation of a-Si:H and a-Si1-xCx :H nanowires by Ag-assisted electroless etching in aqueous HF/AgNO3 solution

The formation of hydrogenated amorphous silicon–carbon alloy (a-Si1-xCx:H) nanowires is studied for different carbon concentrations (0–7%) by using Ag-assisted electroless etching of the thin a-Si1-xCx:H films deposited by plasma-enhanced chemical vapour deposition from silane/methane gas mixtures. The nanowires morphologies (length, density, …), studied by scanning electron microscopy, strongly depend on the concentration of the etchant (aqueous solution of hydrofluoric acid and silver nitrate), the etching time, and the carbon concentration of the deposited layer.

Integration of thin film amorphous silicon photodetector with lab-on-chip for monitoring protein fluorescence in solution and in live microbial cells

Green fluorescent protein (GFP) and other fluorescent protein variants are widely used as powerful tools to tag and monitor complex biological processes at the cellular, tissue, and organism level. A micrometer-scale GFP detection system is demonstrated in which a p-i-n thin-film amorphous silicon light sensitive layer microfabricated on a glass substrate is integrated with an amorphous silicon carbon alloy absorption filter and an ultra-thin PDMS sheet to detect intracellular expression of GFP. GFP fluorescence was detected in aqueous solution in the nM range, and inside living cells ( Escherichia coli) expressing GFP in the 10 6 cell/mL range. The temporal evolution of the integrated fluorescence from promoter-induced GFP production was monitored in E. coli in solution over 12 h using the detection system. This microfabricated thin-film detection system can potentially be developed into an array-based sensing of GFP allowing for high-throughput and multiplexed analysis of biological and biomedical samples.

Heterogeneous immunoassays in microfluidic format using fluorescence detection with integrated amorphous silicon photodiodes

Miniaturization of immunoassays through microfluidic technology has the potential to decrease the time and the quantity of reactants required for analysis, together with the potential of achieving multiplexing and portability. A lab-on-chip system incorporating a thin-film amorphous silicon (a-Si:H) photodiode microfabricated on a glass substrate with a thin-film amorphous silicon-carbon alloy directly deposited above the photodiode and acting as a fluorescence filter is integrated with a polydimethylsiloxane-based microfluidic network for the direct detection of antibody-antigen molecular recognition reactions using fluorescence. The model immunoassay used consists of primary antibody adsorption to the microchannel walls followed by its recognition by a secondary antibody labeled with a fluorescent quantum-dot tag. The conditions for the flow-through analysis in the microfluidic format were defined and the total assay time was 30 min. Specific molecular recognition was quantitatively detected. The measurements made with the a-Si:H photodiode are consistent with that obtained with a fluorescence microscope and both show a linear dependence on the antibody concentration in the nanomolar-micromolar range.

Plasmonic properties of silver nanostructures coated with an amorphous silicon–carbon alloy and their applications for sensitive sensing of DNA hybridization

The use of an amorphous silicon-carbon alloy overcoating on silver nanostructures in a localized surface plasmon resonance (LSPR) sensing platform allows for decreasing the detection limit by an order of magnitude as compared to sensors based on gold nanostructures deposited on glass. In addition, silver based multilayer structures show a distinct plasmonic behaviour as compared to gold based nanostructures, which provides the sensor with an increased short-range sensitivity and a decreased long-range sensitivity.

Amorphous Silicon Photosensors for Detection of Intrinsic Cell Fluorophores

ABSTRACTAn amorphous silicon (a-Si:H) photoconductor array with two distinct integrated amorphous silicon carbon alloy (a-SiC:H) high pass filters is used to detect two of the cell intrinsic fluorophores. The cutoff wavelength of the filters is tuned by the carbon content in the film. The fluorophores of interest – reduced nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FAD) are indicative of the redox state of the cells. Concentrations down to 1 μM for NADH and 50 μM for FAD were detected.