Dr Cheng Fang

Rapid synthesis of silver nanowires (Ag NWs) with high quality and a broad processing window is challenging because of the low selectivity of the formation of multiply twinned particles at the nucleation stage for subsequent Ag NWs growth. Herein we report a systematic study of the water-involved heterogeneous nucleation of Ag NWs with high rate (less than 20min) in a simple and scalable preparation method. Using glycerol as a reducing agent and a solvent with a high boiling point, the reaction is rapidly heated to 210°C in air to synthesize Ag NWs with a very high yield in gram level. It is noted that the addition of a small dose of water plays a key role for obtaining highly pure Ag NWs in high yield, and the optimal water/glycerol ratio is 0.25%. After investigating a series of forming factors including reaction temperature and dose of catalysts, the formation kinetics and mechanism of the Ag NWs are proposed. Compared to other preparation methods, our strategy is simple and reproducible. These Ag NWs show a strong Raman enhancement effect for organic molecules on their surface.

Site-specific masking with graphene films has the potential to facilitate low-cost, high-throughput micro-patterns on silicon substrates over large areas. Here, a facile approach to using graphene as a masking agent on silicon wafers for site-specific patterning is demonstrated. Graphene sheets were deposited via a sealing-tape-exfoliation method onto hydride-terminated (Si-H) silicon substrates. Raman confocal mapping showed inhibition of oxidation of the Si wafer underlying the graphene, indicating that the graphene restricts the diffusion of oxygen onto the Si surface. The graphene coated Si substrates were then electrochemically etched in an aqueous HF/ethanol (3:1 (v/v)) anodization solution. Scanning electron microscopy showed that the graphene layer successfully restricted the etching of the Si surface, however, near the edge sites of the graphene deep etching occurred. © 2014 Springer Science+Business Media New York.

Single-molecule surface-enhanced Raman scattering (SM-SERS) utilizes localized surface plasmons in metallic nanostructures for enhanced signal detection. This work demonstrates the use of SM-SERS on an electrochemically anodized biocompatible nanoporous gold (NpAu) substrate using a bi-analyte Raman technique. It was found that the positions (so-called hot-spots) with the closest etched valley widths (w), or the smallest w/valley wall width (D) (ligaments), of the Au nanopores dominated the Raman scattering. By using an etched substrate with a w < 10 nm and a w/D < 0.2 an estimated enhancement factor of ~107 for both Nile blue and Rhodamine 6G dyes was achieved. Importantly, the bi-analyte Raman technique enabled the clear confirmation of single (or few) molecule detection on the Np/Au substrates. © the Partner Organisations 2014.

We describe the self-assembly of silver nanocubes (AgNC) into dense bowl-shaped arrays using a template made from polystyrene nanospheres (PSNS). Interestingly, we found that most AgNCs were arranged facet-to-facet. When used as substrates for surface-enhanced Raman scattering (SERS), we observed that the SERS hot spot positions were located at the corners of the cubes. This was confirmed using the formation of a self-assembled monolayer (SAM) of 1-dodecanethiol (DDT) covering the cubes' facet surface, whilst the pinholes in the DDT SAM at the corners were subsequently filled with 2-mercaptopyridine (MPy). Due to the high enhancement from the densely arranged AgNCs, single molecule detection was achieved from this SERS substrate and evidenced using the bi-analyte Raman technique. © The Royal Society of Chemistry 2013.

An approach was demonstrated to detect oligonucleotide by attaching redox probes onto its backbone. First, peptide nucleic acid (PNA) with a neutral backbone was immobilized onto a gold (Au) electrode surface as a capture. Second, when the PNA capture hybridized with a target oligonucleotide (a short DNA), an assembly of Au-PNA-DNA formed and phosphate groups were thus brought into the assembly from the DNA's backbone. The linker ion of Zr4+ exhibits a strong coordination interaction with the phosphate group and the carboxylic group. The hybridized target DNA provides the phosphate group while a derivatized redox probe of ferrocene (Fc) carboxyl acid offers the carboxylic group. Therefore, the redox probe can be attached to the phosphate group by the linker to form an assembly of Au-PNA-DNA-Zr-Fc. Its redox process was studied and the detection conditions of oligonucleotide were optimized. A limit of detection of 1.0×10-12M or ~2attomol was reached. © 2010 Elsevier B.V.

We have demonstrated for the first time that silver can be electrochemically etched to form porous structures ranging from the nano- to the microscale. Silver wires, foils and films deposited on a silicon wafer were etched in both acidic (HF) and basic (NH3) N,N-dimethylformamide (DMF) solutions. We describe a possible etching mechanism for pore formation in which the convection within the etching solution focuses the etching current, while the organic solvent component stabilizes the nascent pore walls. Finally, the fabricated porous silver was shown to act as an effective substrate for surface-enhanced Raman scattering (SERS). © 2011 Elsevier B.V. All rights reserved.

This report introduces a bleaching-independent temperature measurement method based on the analysis of the fluorescence emitted during the melting of DNA molecules with the SYBR-Green I intercalator, in a microvolume where the strong non-linearity of the signal is used to eliminate the photobleaching effect as well as to determine the heat transfer rate between a heater and the sample and the temperature non-uniformity within the sample. © 2010 The Royal Society of Chemistry.

A simple method was demonstrated to metallize silicon (Si) nanowire (NW) just by dipping it into an aqueous deposition solution for several minutes. During the metallization process, metal ions were reduced and deposited on the top of the Si NW (where surface Si was oxidized). The surface silicon oxide was simultaneously dissolved and removed by hydrogen fluoride (HF), so that the deposition reaction was sustainable and controllable. The deposited silver (Ag) nanoparticles (NPs) uniformly self-assembled along the Si NW and developed into a metal covering with the NW as its core. Not only Ag+ but also Cu2+, Pd2+, Co2+, Au3-, and Pt 4- were deposited to metallize the Si NW using the simplified metallization process. Applications of the new nanocomposite materials were also explored. When the resulting Ag NP/Si NW was tested as a surface-enhanced raman scattering (SERS) substrate, an extremely strong signal was observed and a detection limit of ~600 molecules or 200-300 Ag NPs per laser spot was reached. The significantly enhanced SERS effect appears to be associated with the close packing of the neighboring NPs that self-assemble along the highly curved NW. © 2009 American Chemical Society.

A simple approach was demonstrated to prepare a silver (Ag) nanoparticle (NP) assembly as a SERS substrate. Just by dipping a flat silicon (Si) wafer into an aqueous deposition solution of hydrogen fluoride (HF) +silver nitrate (AgNO3), a monolayer of Ag NPs was uniformly deposited onto the Si wafer surface. In order to load the to-be-detected sample onto the as-prepared SERS substrate, three methods have been individually tested, (i)by incubating the SERS substrate in the sample solution, (ii)by dropping and drying a small volume of the sample solution (1-2µl) onto the SERS substrate surface, or (iii)by directly introducing the sample into the deposition solution. The last approach was also employed to metalize a Si nanowire (NW). Due to the NW's highly curved surface, the Ag NPs self-assembled and aggregated along the NW with a close interdistance. The aggregated Ag NPs on the NW surface can also be used as a SERS substrate. The demonstrated approach holds the promise to prepare a fresh SERS substrate at the point-of-use with the sample already loaded to promptly collect the SERS signal for the field application. © 2009 IOP Publishing Ltd.

Sequence-specific DNA detection is a routine job in medical diagnostics and genetic screening. Alternative to a fluorescence readout scheme or electrophoresis approach, various kinds of rapid, low-cost, facile, and label-free methods have also been developed in last decades. Among these, direct electrical detection of DNA received increasing attention but more research is desirable. Particularly, enhancement with high discrimination must be employed to selectively amplify the responding signal. A chip-based biosensor was developed in this work to electrically detect 22-mer oligonucleotide DNA at low concentration, from 50 fM to 10 pM. First, a gold nanoparticle (NP) was capped with 3-mercaptopropionic acid through a thiol-gold bond. The derivatized carboxylic acid group showed strong complex interaction with an inorganic linker, Zr4+. As a result, Zr4+ could link several hundreds of individual gold NPs together to form an aggregate of nanoparticles (ANP), which was capable of being used as a conductive tag for the electrical detection of DNA. Second, in order to achieve the discriminative localization of ANP to bridge two comb-shaped electrodes (with height of ~50 nm and interdistance of 300-350 nm) gapped with insulative material of silicon oxide, peptide nucleic acids were covalently bonded to the silicon oxide in the gap as capture sites for DNA. After hybridization with target DNA, the charged phosphate-containing backbone of DNA was introduced into the gap. Phosphate groups also exhibited strong complex interaction with the linker of Zr 4+ and could react with the residual Zr4+ on the ANP surface. As a consequence, the conductive tags were linked to the phosphate groups and localized into the gap, which could modify the conductance between the two comb-shaped electrodes in turn. The degree of modification correlated directly to the amount of hybridized DNA and to the concentration of target DNA in sample solution. Compared with the individual NPs used as the tag, a strong enhancement from the gold ANP was obtained. © 2008 American Chemical Society.

A self-assembly method is demonstrated to link nanoparticles into nanostructure of nanochain or nanosphere. Gold nanoparticles were covered with capping molecules by forming Au-S bonds with thiol group at one terminate. Another terminating group, carboxylic acid, showed strong complex interaction with inorganic linker Zr4+ to form covalent complex bond. The different nanostructures were obtained by moving a balance between two opposite interactions, the linking interaction of Zr4+ and the electrostatic repulsive interaction of net surface charge. When the capping molecule with different chain length was used, the linked nanochain feature exhibited a tunable interdistance between the neighboring nanoparticles. © 2008 American Institute of Physics.

A technique is demonstrated to detect DNA hybridization at low concentrations, based on Surface-Enhanced Raman Scattering (SERS) using silicon nanostructures coated with gold-silver as substrate. Standard silicon process technologies were employed to fabricate the SERS substrates featuring nanogaps with a characteristic distance of 15 ± 10 nm. Target DNA was hybridized with cysteine-modified Peptide Nucleic Acids (PNA), which was previously fixed into the nanogaps as the capture sites. After hybridization, the introduced phosphate groups from the backbone of the target DNA showed strong affinity to an inorganic linker, Zr4+, so that resulting in the assembly substrate-PNA-DNA-Zr. Since PNA does not possess phosphate groups, the linker is avoided when there is no hybridization from the complimentary DNA. Subsequently, the assembly of substrate-PNA-DNA-Zr was incubated with a Raman label, Rhodamine B (RB). The carboxylic acid group in RB reacted with the linker Zr4+ allowing this Raman Label to be attached to the assembly substrate-PNA-DNA-Zr. The Raman peaks corresponding to RB were selected to detect the target DNA, with a detection limit of 1 × 10-12 M. © 2008 Elsevier B.V. All rights reserved.

Deep macropores in n-type Si have been completely filled with copper (Cu). Homogeneous metal deposition inside the deep pores was achieved by means of electroplating using a solution containing only Cu2 S O4 mixed with H2 S O4 and no additives. Initial nucleation of the Cu deposition was confined to the bottom of the pores and, by optimizing the filling conditions, uniform filling from the bottom to the top could be achieved. Macropores as deep as 150 µm with diameters in the 2 µm range could be filled with Cu, without encountering the so-called "bottleneck" effect. © 2006 The Electrochemical Society.

Deep straight macropores in n-type Si have been completely filled with copper (Cu). Homogeneous metal deposition inside the deep pores was achieved by means of electroplating using a solution containing only CuSO 4 mixed with H 2SO 4 and an optimized process that begins at the bottom of the pores. Pores as deep as 150 iµm could be filled without encountering the so-called "bottleneck" effect. Straight macropores with diameters below 100 nm and extreme aspect ratios in InP could be filled with Cu using a pulsed process. Interconnected pores extending in the available set of (111) directions in {100} GaAs and forming domains could not be filled with Cu; instead the volume occupied by the pore domain was completely filled with Cu; i.e. the porous structure was destroyed. A possible reason for this new effect will be given. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA.

Arrays of highly ordered n-type silicon nanowires (SiNW) are fabricated using complementary metal-oxide semi-conductor (CMOS) compatible technology, and their applications in biosensors are investigated. Peptide nucleic acid (PNA) capture probe-functionalized SiNW arrays show a concentration-dependent resistance change upon hybridization to complementary target DNA that is linear over a large dynamic range with a detection limit of 10 fM. As with other SiNW biosensing devices, the sensing mechanism can be understood in terms of the change in charge density at the SiNW surface after hybridization, the so-called "field effect". The SiNW array biosensor discriminates satisfactorily against mismatched target DNA. It is also able to monitor directly the DNA hybridization event in situ and in real time. The SiNW array biosensor described here is ultrasensitive, non-radioactive, and more importantly, label-free, and is of particular importance to the development of gene expression profiling tools and point-of-care applications. © 2007 American Chemical Society.

A versatile method, based on the metallization of DNA strands, is developed to prepare palladium nanoparticles on indium tin oxide (ITO) coated glass surface. Resulted palladium nanoparticles are distributed along the DNA strands and their size is controllable in the range of 10-100 nm. This is contrast to the branched palladium aggregates formed on bare ITO surface. When used as an electrochemical sensor, the nanoparticles show strong catalytic activity for the reduction of hydrogen peroxide and the oxidation of ascorbic acid, respectively. Higher catalytic activity is observed with the nanoparticles formed on double-stranded DNA (dsDNA) templates than those on single-stranded DNA (ssDNA) templates. © 2007 Elsevier B.V. All rights reserved.

While electrochemical pore etching in semiconductors has become a thriving field for research (and applications) in the past 15 years or so, little work has been done in Ge. Besides Si, Ge is the only semiconductor with a diffusion length large enough to enable the use of backside illumination, which has proved to be the decisive "trick" for the formation of excellent macropores in Si, and experiments in this vein have been conducted. However, Ge proved to behave in rather unexpected ways - the large body of pore etching knowledge obtained with Si and the III-V's was not directly applicable to Ge. While no good pores could be produced in most previous endeavours including our own, we finally succeeded in producing deep pores in n-type but also in p-type Ge of various doping levels and crystal orientations. A host of new and not yet totally understood phenomena was discovered. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA.

Nucleation and growth of electrochemically etched pores in Germanium (Ge) was investigated for n- and p-type Ge single crystals with {1 0 0}, {1 1 0}, and {1 1 1} orientations and doping concentrations of (1014-1018) cm-3. Various types of electrolytes, illumination conditions (front side, back side or none), and pre-treatments for optimizing nucleation were used. Several kinds of macropores could be obtained, mostly for the first time. In particular, pores could be obtained in p-type Ge samples. Pore geometries, morphologies, and growth peculiarities were found to be quite different from other semiconductors. Nucleation is generally difficult, the preferred growth direction is <1 0 0> or <1 1 1>, stop planes are of {1 1 0} type, and there is always a strong electropolishing component compromising pore geometry and stability. Porous membranes have been produced showing electrocapillarity effects. © 2006 Elsevier B.V. All rights reserved.

While electrochemical pore etching in semiconductors has become a thriving field for research and applications in the past 15 years or so, little work has been done in Ge. Besides Si, Ge is the only semiconductor with a minority carrier diffusion length large enough to enable the use of backside illumination, which has proved to be the decisive "trick" for the formation of excellent macropores in Si. First experiments in Ge have been performed, but Ge proved to behave in rather unexpected ways-the large body of pore etching knowledge obtained with Si and the III-V semiconductors was not directly applicable to Ge. While no good pores could be produced in most previous endeavors including our own, we finally succeeded in producing deep pores in n-type but also in p-type Ge of various doping levels and crystal orientations. In particular, it is now possible to create "good" macropores in a uniform distribution. A host of new and not yet totally understood phenomena was discovered, including pores of various kinds and crystallography. The paper will shortly outline the results obtained and relate it to what is known from other semiconductors under comparable circumstances. © 2006 Elsevier Ltd. All rights reserved.

Germanium (Ge) nanowires have been produced by electrochemical etching of single-crystalline n-type Ge {100} in a HCI-containing aqueous electrolyte. Macropores could be etched at various etching currents after an optimized procedure for homogeneous pore nucleation was used. Because of the narrow band gap of Ge (0.66 eV), the leakage current through pore walls is much higher than that, for example, in Si, leading to a constant dissolution of the pore walls. At sufficiently high current densities, it is then possible to form nanowires with diameters determined by the width of the space charge region, ranging from roughly 50 to 500 nm, and a length of several hundred micrometers. The role of the space charge region for stabilizing pore formation and in the formation of nanowires will be discussed. © 2006 American Chemical Society.

A novel electrophoresis technique, in which the separation column was replaced by a strip of Nafion membrane (5.0 cm × 0.20 mm × 0.25 mm), was developed for the separation of an amino acid mixture (glycine, asparic acid and lysine), followed by quadruple-pulse electrochemical detection. Nafion membrane contains hydrophilic pores (10-20 Å and 50-60 Å in size) acting as very narrow electrophoresis channels. The fixed-charge sites (-SO3-) on the hydrophilic pore surface provide a strong charged background. A platinum disk electrode (0.90 mm inner diameter) was employed as the detection electrode and the electrophoresis cathode was used as the quasi-reference and counter electrode for the end-column electrochemical detector, without decoupler. Under optimized conditions the mixture of amino acids could be separated at a voltage of only 90 V with a detection limit of 10-7 M, indicating that Nafion membrane electrophoresis is a potentially attractive technique for the separation of small organic molecules or ions.

The glutathione (GSH) monolayer and complex monolayer of GSH-metallic ion on polycrystalline gold electrode were studied by using K3Fe(CN)6 as the redox probe. As for the GSH monolayer, it was found that the metallic ions could open the ion-gate in the monolayer dramatically in the order La3+>Pb2+»Ba2+>Ca2+ whereas Zn2+ ion closed the ion-gate. The complexes of GSH-metallic ions were capable of self-assembling the different kind of monolayer. All the differences were related to the structural configuration of the anchored GSH molecule, which changed with the different metallic ions or pH.

On-line monitoring in photocatalytic degradation process of organic compound 4-chlorophenol (4-CP) was carried out by using cyclic voltammetry and UV-Vis spectrometry. The result showed that the degradation process undertook at least a two-route mechanism to the complete mineralization: through redox pairs of benzoquinone(BQ) and hydrobenzoquinone(HQ) and of hydroxybenzoquinone(HBQ) and hydroxy-hydrobenzoquinone(HHQ). UV-Vis spectra taken at different time showed the breakage of benzene ring and the complete mineralization. The electroanalysis was proved to be a proper technique for on-line monitoring as it could detect simultaneously both initial reactants and intermediates, and thus it is suitable for on-line monitoring and complementary for mechanism study.

A gold electrode modified with adsorbed thionine monolayer was investigated with ac impedance and cyclic voltammetry method. It was found there were some different redox properties for the adsorbed thionine depended on the different potential scanning rate. At the slower potential scanning rate (10 mV · s-1), the dimer of thionine appeared and possessed the catalytic activity for the oxidation of ascorbic acid. The underpotential deposition (UPD) and the bulk deposition of Cu2+ were also employed to investigate the monolayer of adsorbed thionine.

Monolayer films of thiols with different terminal groups (-CH3, -COOH and -NH2) were prepared on gold electrodes using a self-assembling procedure. Cyclic voltammetry was used to investigate the electron-transfer reaction of potassium ferricyanide at the thiol modified gold electrode in the presence of surfactants. It was found that surfactants show some effects on the electron-transfer reaction at the thiol modified electrode. Cationic surfactants can improve the reversibility of a redox reaction at the thiol modified gold electrodes, while anionic surfactants cause a little inhibition of electron transfer of the redox at both methyl and carboxyl terminal thiol modified gold electrodes. Surfactants can interact with thiol monolayers in different ways, changing the structure and properties of the monolayer film, and can further affect electron transfer at the modified gold electrode.

Glutathione (GSH) was prepared on a gold electrode by self-assembled procedure. Cyclic voltammetry was used to investigate the electrochemical behavior of GSH self-assembled monolayer modified on a gold electrode on the activation of surfactants in potassium ferricyanide and benzoquinone (BQ) solution. It was found that GSH monolayer showed an ion-gate behavior in the presence of cationic surfactants and the electron transfer was improved with the increase of the concentration of cationic surfactants, which results from the fact that the interaction between the monolayer and surfactant changes the conformation of GSH monolayer. Anionic surfactant showed some inhibition to electron transfer at GSH monolayer modified gold electrode.

A monolayer membrane of 2-mercaptobenzothiazole (MBT) was prepared on a gold electrode through a self-assembly procedure. The monolayer structure and the electrochemical properties were investigated by various electrochemical techniques, like cyclic voltammetry and an impedance measurement with external redox. Experiments show that MBT can form a closely packed monolayer that can be charged due to the active N atom. The amount of charge on the membrane surface varies with the solution pH, and the monolayer shows 'opening and closing' which depends on the solution pH. The electrostatic interaction of the monolayer with other ions is also related to the pH in solution. An impedance analysis shows that the heterogeneous electron-transfer rate of a fast redox like Fe(CN)6(3-/4-) decreases from 1.2 x 10-2 to 4.7 x 10-5 cm s-1 in neutral solution due to blockage of the self-assembled monolayer membrane.

Mixed dodecanethiol-glutathinone self-assembled monolayers (DDT-GSH) were prepared on a gold electrode and further derivatized to form a monolayer of cupric hexacyanoferrate (CuHCF). Electrochemical behavior of the modified electrode was investigated by cyclic voltammetry. This inorganic monolayer modified electrode is electroactive and its surface concentration is 4.2x10-10 mol cm-2. It is observed that this modified electrode shows selectivity to potassium ion and exhibits an ideal Nernstian response with a slope of 60 mV/decade to potassium ions the range from 10-2 to 1.0 mol L-1.

A novel glassy carbon electrode modified with Malachite Green was investigated. The modified electrode can be used to determine dopamine (DA) and ascorbic acid (AA). The anodic peaks for ascorbic acid and dopamine were Separated (¿E(pa) about 200 mV) at the poly(malachite green) modified electrode. Thus, DA can be determined in the presence of AA.

Cyclic voltammetry and chronoamperometry were used to study the deposition of polypyrrole on a decanethiol self-assembled monolayer modified gold electrode (PPY/SAM/Au). The voltammetric behavior of the PPY/SAM film was investigated in the presence of several different electrolytes. It is found that the SAM shows great influence on the nucleation and growth of the PPY film The reaction of the SAM and the anions causes the different voltammetric behavior of the polymerization of pyrrole on the modified electrode Chronoamperometry shows the nucleation and growth of the PPY is initially inhibited but followed by a rapid increase. The SAM also influences electrochemical behavior of PPY film. Experiments show that the SAM can greatly depress the diffusion of anions in the PPY film and minimize the background capacitance current.

Determination of omethoate by modified PQC (piezoelectric quartz crystal) sensor is described. Several modified films were studied and compared. Omethoate of 0.1-10 ppm can be determined directly and sensitively with PVC-dioctyl sebacate film modified PQC. The modified crystal has good reversibility and reproductivity. The lifetime is about 1 month.

This paper reports our recent study for the spectroelectrochemistry of hemoglobin at bare silver electrodes using a self-made long optical path UV/Visible thin-layer spectroelectrochemical cell. By this cell, the electron transfer number(n = 1. 04), the adsorbance (G = 8. 95 × 10 -14 mol/mm 2) and the formal redox potential (E 0' = 0. 14 V) of hemoglobin at bare silver electrodes were studied.

The determination of BSA (bovine serum albumin)with a silver-plate quartz crystal microbalance(QCM) was discussed. The frequency shift was proprotional to the concentrations of BSA in the range of 0. 5-50 mg/L. The reusability of the electrode was studied in detail. The 0. 2 mol/L glycine-HCl(pH = 2. 0)was selected as the washing solution.

This paper reports the development of a silicon-based microfluidic device that enables ultra fast melting curve analysis (MCA) for genomic studies (DNA) and drug discovery (proteins). The system relies on the flow of nanoliter-sized discrete phase samples through a buried silicon channel. The samples are subjected to a temperature gradient generated by two external heaters along the channel. The channel also simultaneously serves as a light guide to illuminate the droplets and guide the emitted fluorescence to the detector outside the channel. The system provides a simple melting analysis of fluorescent-labeled molecular complexes, with high multiplexing capability and throughput. The chip-based solution is attractive due to nanolitre sized samples handling, resulting in fast heat transfer thus achieving ultra fast MCA for genomic studies and drug discoveries.

A simple method was developed to metallize silicon nanowires using an elec-troless displacement deposition reaction. The resulting metal nanoparticles were self-assembled along a nanowire core to get a metal covering. The silver nanoparti-cles array aggregated along the nanowire was used as a SERS substrate. The en-hancement for SERS response was high even from a single metallized nanowire. The significantly high enhancement came from the close interdistance among the neighbouring nanoparticles aggregated along nanowire by self-assembly. © 2008 CBMS.

CMOS compatible silicon technologies are used to fabricate schematically arranged arrays of nanostructures for Surface Enhanced Raman Spectroscopy (SERS), incorporating processes like DUV photolithography, reactive ion etching and physical vapour deposition of silver and gold. The surface treatment of cuvette and tubes used to handle Rhodamine 6G (R6G) and the substrate pre-treatment procedures, being significant for concentration less than 10 -9 M, are elaborated. The Raman signal is also enhanced by the addition of sodium chloride to R6G and by optimizing the sample immersion time in the analytes. 10-10 and 10-12 M R6G with 1mM sodium chloride is detected on silver and gold terminated SERS substrates respectively. ©2007 IEEE.

Arrays of highly ordered silicon nanowires (SiNWs) are fabricated using complementary metal-oxide semiconductor (CMOS) compatible technology and their applications in biosensors are investigated. The SiNW arrays show a concentration-dependent resistance change upon hybridization to complementary target DNA. As in the case of other SiNW biosensing devices, the sensing mechanism can be understood in terms of the change in charge density at the SiNW surface after hybridization, the so called "field effect". The SiNW arrays discriminate satisfactorily against mismatched target DNA. ©2007 IEEE.

Little was known about porous Ge until recently; here some substantial progress in producing porous Ge will be reported, mostly for the first time, i) n-type Ge in aqueous solution: Pore geometries, morphologies and growth peculiarities were found to be quite different from other semiconductors, such as Si and III-V. Nucleation is generally difficult, the preferred growth direction is <100> (and <111>), major stop planes are of the {110} type, but others are also found. In addition, there is always a strong electropolishing component compromising pore geometry and stability, ii) n- and p-type Ge in organic solution: In DMSO solution, the growth direction is <111>, and the stopping planes are still mainly {110}; somewhat unexpected, because this has never been observed in Si, and because no pores have been found in other p-type semiconductors so far, with the exception of Si. Nucleation seems to be difficult too, and new domain-forming phenomena are observed. Smooth or rough pore walls can be obtained, dependent on the experimental conditions.

In this work we present a theoretical model that explains the current and voltage oscillations at the Si electrode in HF media. A simulation computer program based on this model is implemented and results are shown. Oscillations of the current and (for the first time) the voltage obtained numerically fit perfectly with experiments. The model allows to obtain more information about the system in the form of maps (accompanied by histograms) of e.g.: oxide thickness distribution, SiO2/HF and Si/SiO2 interfaces morphology, or local voltage losses. Other characteristics of the oxide like capacitance or roughness can also be obtained.