Gold-coated Silicon Research Articles

Gas-specific adsorption capability of titanium dioxide and MXene nanocomposite thin films prepared by ultrasonic spray printing using inks oxidized at room temperature

The development of two-dimensional (2D) layered MXene materials has opened new possibilities for gas adsorption applications due to their high specific surface area, tunable surface chemistry, and excellent selectivity towards specific gases. These materials exhibit tremendous potential in adsorption-based gas separation and detection, particularly due to their strong interactions with target gas molecules, making them highly effective in gas removal and detection applications. However, currently available methods for synthesizing these oxidized nanocomposite inks are limited by the typically high temperatures involved. The present work addresses this issue by developing titanium dioxide and MXene (TiO2/Ti3C2 MXene) nanocomposite inks, where TiO2 nanoparticles are formed between the layers of the Ti3C2 MXene via oxidation in solution state under extended exposure in an oxygen rich atmosphere at room temperature. As a proof of concept, gas adsorption studies are conducted by applying the TiO2/Ti3C2 MXene nanocomposite inks onto gold-coated silicon wafers via an ultrasonic spray printing method. The gas adsorption results demonstrate that the TiO2/Ti3C2 MXene nanocomposites possess excellent adsorption selectivity toward methane and butane among alkane gases, and can achieve maximum adsorption capacities of 8.62 and 18.8 cm3/g, respectively. The results of ultrasonic spray printing quality tests conducted for different numbers of printed layers using the proposed TiO2/Ti3C2 MXene nanocomposite ink demonstrate that the film thickness can be regulated by controlling the number of printed layers, and the average thin film thickness remains only 0.313 μm for 10 printed layers. Meanwhile, the average roughness of the films resides between 0.130 μm (3 layers) and 0.220 μm (8 layers), which is uniformly and less than the average roughness of 0.225 μm measured for the original gold-plated silicon wafer. Hence, by employing facile ink-based printing techniques, such as ultrasonic spray printing, thin films with controlled thickness can be fabricated, thereby laying the foundation for their practical applications in environmental monitoring and industrial gas separation.

Double Gold/Nitrogen Nanosecond-Laser-Doping of Gold-Coated Silicon Wafer Surfaces in Liquid Nitrogen

A novel double-impurity doping process for silicon (Si) surfaces was developed, utilizing nanosecond-laser melting of an 11 nm thick gold (Au) top film and a Si wafer substrate in a laser plasma-activated liquid nitrogen (LN) environment. Scanning electron microscopy revealed a fluence- and exposure-independent surface micro-spike topography, while energy-dispersive X-ray spectroscopy identified minor Au (~0.05 at. %) and major N (~1–2 at. %) dopants localized within a 0.5 μm thick surface layer and the slight surface post-oxidation of the micro-relief (oxygen (O), ~1.5–2.5 at. %). X-ray photoelectron spectroscopy was used to identify the bound surface (SiNx) and bulk doping chemical states of the introduced nitrogen (~10 at. %) and the metallic (<0.01 at. %) and cluster (<0.1 at. %) forms of the gold dopant, and it was used to evaluate their depth distributions, which were strongly affected by the competition between gold dopants due to their marginal local concentrations and the other more abundant dopants (N, O). In this study, 532 nm Raman microspectroscopy indicated a slight reduction in the crystalline order revealed in the second-order Si phonon band; the tensile stresses or nanoscale dimensions of the resolidified Si nano-crystallites envisioned by the main Si optical–phonon peak; a negligible a-Si abundance; and a low-wavenumber peak of the Si3N4 structure. In contrast, Fourier transform infrared (FT-IR) reflectance and transmittance studies exhibited only broad structureless absorption bands in the range of 600–5500 cm−1 related to dopant absorption and light trapping in the surface micro-relief. The room-temperature electrical characteristics of the laser double-doped Si layer—a high carrier mobility of 1050 cm2/Vs and background carrier sheet concentration of ~2 × 1010 cm−2 (bulk concentration ~1014–1015 cm−3)—are superior to previously reported parameters of similar nitrogen-implanted/annealed Si samples. This novel facile double-element laser-doping procedure paves the way to local maskless on-demand introductions of multiple intra-gap intermediate donor and acceptor bands in Si, providing related multi-wavelength IR photoconductivity for optoelectronic applications.

Purcell-Induced Bright Single Photon Emitters in Hexagonal Boron Nitride.

Single photon emitters (SPEs) in hexagonal boron nitride (hBN) are elementary building blocks for room-temperature on-chip quantum photonic technologies. However, fundamental challenges, such as slow radiative decay and nondeterministic placement of the emitters, limit their full potential. Here, we demonstrate large-area arrays of plasmonic nanoresonators (PNRs) for Purcell-induced room-temperature SPEs by engineering emitter-cavity coupling and enhancing radiative emission. Gold-coated silicon pillars with an alumina spacer enable a 10-fold local-field enhancement in the emission band of native hBN defects. We observe bright SPEs with an average saturated emission rate surpassing 5 million counts per second, an average lifetime of <0.5 ns, and 29% yield. Density functional theory reveals the beneficial role of an alumina spacer between hBN and gold, mitigating the electronic broadening of emission from defects proximal to the metal. Our results offer arrays of bright, heterogeneously integrated single-photon sources, paving the way for robust and scalable quantum information systems.

Multi-wavelength and broadband plasmonic switching with V-shaped plasmonic nanostructures on a VO2 coated plasmonic substrate

In this paper, periodic arrays of identical V-shaped gold nanostructures and variable V-shaped gold nanostructures are designed on top of a gold-coated silicon dioxide (SiO2) substrate with a thin spacer layer of vanadium dioxide (VO2) to realize multi-wavelength and broadband plasmonic switches, respectively. The periodic array of identical V-shaped nanostructures (IVNSs) with small inter-particle separation leads to coupled interactions of the elementary plasmons of a V-shaped nanostructure (VNS), resulting in a hybridized plasmon response with two longitudinal plasmonic modes in the reflectance spectra of the proposed switches when the incident light is polarized in the x-direction. The x-direction is oriented along the axis that joins the V-junctions of all VNSs in one unit cell of the periodic array. On exposure to temperature, electric field, or optical stimulus, the VO2 layer transforms from its monoclinic semiconducting state to its rutile metallic state, leading to an overall change in the reflectance spectra obtained from the proposed nanostructures and resulting in an efficient multi-wavelength switching action. Finite difference time domain modelling is employed to demonstrate that an extinction ratio (ER) >12 dB at two wavelengths can be achieved by employing the proposed switches based on periodic arrays of IVNSs. Further, plasmonic switches based on variable V-shaped nanostructures—i.e. multiple VNSs with variable arm lengths in one unit cell of a periodic array—are proposed for broadband switching. In the broadband operation mode, we report an ER >5 dB over an operational wavelength range >1400 nm in the near-IR spectral range spanning over all optical communication bands, i.e. the O, E, S, C, L and U bands. Further, it is also demonstrated that the wavelength of operation for these switches can be tuned by varying the geometrical parameters of the proposed switches. These switches have the potential to be employed in communication networks where ultrasmall and ultrafast switches with multi-wavelength operation or switching over a wide operational bandwidth are inevitably required.

Tunable Terahertz Filters Based on Gold-Coated Silicon Plates With Corrugations

Tunable Terahertz Filters Based on Gold-Coated Silicon Plates With Corrugations

Field emission from two-dimensional (2D) CdSSe flake flowers structure grown on gold coated silicon substrate: An efficient cold cathode.

Field emission finds a vital space in numerous scientific and technological applications, including high-resolution imaging at micro- and nano-scales, conducting high-energy physics experiments, molecule ionization in spectroscopy, and electronic uses. A continuous effort exists to develop new materials for enhanced field emission applications. In the present work, two-dimensional (2D) well-aligned CdSSe flake flowers (CdSSe-FFs) were successfully grown on gold-coated silicon substrate utilizing a simple and affordable chemical bath deposition approach at ambient temperature. The time-dependent growth mechanism from nanoparticles to FFs was observed at optimized parameters such as concentration of precursors, pH (~11), deposition time, and solution temperature. The crystalline nature of CdSSe-FFs is confirmed by high-resolution transmission electron microscopy (HRTEM) results, and selected area electron diffraction (SAED) observations reveal a hexagonal crystal structure. Additionally, the CdSSe-FFs thickness was confirmed by TEM analysis and found to be ~20-30 nm. The optical, photoelectric, and field emission (FE) characteristics are thoroughly explored which shows significant enhancement due to the formation of heterojunction between the gold-coated silicon substrate and CdSSe-FFs. The UV-visible absorption spectra of CdSSe-FFs show enhanced absorption at 700 nm, corresponding to the energy band gap (Eg) of 1.77 eV. The CdSSe-FFs exhibited field emission and photosensitive field emission (PSFE) characteristics. In FE study CdSSe-FFs shows an increase in current density of 387.2 μ A cm-2 in an applied field of 4.1 V m-1 which is 4.08 fold as compared to without light illumination (95.1 μ A cm-2). Furthermore, it shows excellent emission current stability at the preset value of 1.5 μA over 3 h with a deviation of the current density of less than 5% respectively. RESEARCH HIGHLIGHTS: Novel CdSSe flake flowers were grown on Au-coated Si substrate by a cost-effective chemical bath deposition route. The growth mechanism of CdSSe flake flowers is studied in detail. Field emission and Photoluminescence study of CdSSe flake flowers is characterized. CdSSe flake flowers with nanoflakes sharp edges exhibited enhanced field emission properties.

Electrochemical Aptamer-Based Biosensor Developed to Monitor PCA3 and PSA Released by Prostate Cancer Cells

1. Introduction Detection of prostate cancer (PCa) in the early stage of the disease is fundamental for the prevention of metastases and for the initiation of treatment, which may bring greater chance of patient cured; so several research groups have sought the manufacture of a simple and non-invasive methodology [1]. The early diagnosis relies on prostate specific antigen (PSA) serum test, even if it showed clear limits [2]. Recently, prostate cancer gene 3 (PCA3), a non-coding mRNA which is overexpressed in tumor cells when compared with noncancerous prostate tissue [3]. Here, we report a new method for detection of prostate cancer-specific antigen 3 (PCA3) and prostate specific antigen (PSA) released by cancer cells using an aptasensor. Electrochemical impedance spectroscopy (EIS), SEM and EDS were used to evaluate biosensor surface. 2. Experimental Part The aptamers were modified through Biosearch Technologies at 5′-terminus in C6-disulfide linker to have it bond to the gold electrode; and at 3′-end in methylene blue (MB) (as redox probe) to perform the electrochemical analysis, which was followed by the HPLC purification process to remove truncated-synthesis products and to enrich the purity of the aptamer sequences. Aptamer immobilization was done by incubation of 1 μM thiolated aptamer on the top of the gold-coated silicon electrode overnight, in the dark, at 4°C. Subsequently, the electrodes were washed with PBS and a backfilling consisted of 3 mM of MCH aqueous solution for 30 minutes was done to displace the nonspecifically adsorbed aptamer molecules and to passivate the electrode surface [26]. Finally, the electrodes were once more rinsed with PBS to remove MCH excesses. The electrochemical characterization was done in a potentiostat μAutolabIII (Metrohn, NL), using a three-electrode system, which consisted of Ag/AgCl (3M KCl), as reference electrode; Pt wire, as a counter electrode; and gold-coated silicon wafer, as a working electrode. The prostate cell lines used were normal human prostate cells (RWPE-1; ATCC® CRL-11™), androgen-sensitive human prostate cancer cells (LNCaP; ATCC® CRL-1740™), and androgen-independent human prostate cancer cells (PC-3; ATCC® CRL-1435™). The three lineages were chosen to better understand PCA3 and PSA production patterns by different cell types. 3. Results and Discussion The gold-coated silicon wafe electrode was analyzed by SEM and EDS, which acts as working electrode and substrate to anchor the thiolated aptamer on the surface. By using square wave voltammetry, the present aptasensor was able of monitoring the PCA3 and PSA released from prostate cells (normal and cancerous). The PSA and PCA3 detection limits were 1 ng/mL and 9.2 ng/mL, respectively, at linear range up to 150 ng/mL, and it was also able to detect both biomarker even in presence of several interfering compounds (UA, AA, BSA and MUC1). In addition, the herein developed aptasensor was able to verify, at accurate and robust response, the patterns of the PCA3 and PSA released by different cell lines (RWPE-1, LNCaP and PC3). The detection of PSA and PCA3 by aptasensor agree with the cell lineage type, the LNCaP is an androgen-dependent lineage. In this way, an overexpressed both biomarkres was release was verified [49,50] and it can be compared to early-stage patients. On the other hand, the PC3 cells PSA and PCA3 releasing was nearly background signal, demonstrating almost absent production of studied targets, the PC3 lineage is androgen-independent which can be compared to advanced-disease patients. Funding This work has been supported by a grant from FAPESP-Brazil, CNPq and Capes.

Piezoelectric 1D MEMS scanning micromirror fabricated with bulk PZT laminated on stainless steel plate

In this research, a piezoelectric metal scanning micromirror with a large reflective surface area is presented. Unlike conventional scanning micromirrors fabricated with single-crystal silicon, stainless steel plate is used as the structural layer material. Two distinct device models, varying in cantilever and connector geometry, were conceptualized and experimentally assessed. These fabricated devices utilized the strain induced in bulk PZT (lead zirconate titanate) plates affixed to the cantilevers on opposing sides of the reflective surface. A 5 mm-diameter gold-coated silicon mirror plate served as the reflective surface. We evaluated the performance of two bulk PZT plates, PZT-5H and PZT-8. Our experimental results reveal that model #1, driven by PZT-5H with a sinusoidal input voltage of 200 Vpp, achieved a maximum optical scan angle of 26°, while model #2 exhibited a more substantial maximum scan angle of 44°. The average resonant frequency of the PZT-5H samples was 1264 Hz for model #1 and 995 Hz for model #2. These findings underscore the viability of stainless steel plates as a robust structural layer for piezoelectric scanning micromirrors. The proposed design holds potential for integration into a 3D LiDAR system when combined with an additional slow vertical scanner.

Gold-coated porous silicon as a SERS substrate for near-infrared excitation: Off- and on-resonant conditions

Porous silicon, being one of the most popular SERS-active substrates, was in this work utilized for near-infrared 1064 nm excitation which minimizes the radiation-induced degradation of molecules. The production of porous silicon photonic crystals and deposition of gold nanoparticles, as the two possible methods for quenching the crystal silicon band-gap photoluminescence, were thoroughly discussed. For the off-resonant laser excitation conditions, gold nanoparticles were grown on porous silicon by the immersion plating procedure. For the on-resonant conditions, gold nanorods with the appropriate aspect ratio were synthesized by a seed-mediated protocol and deposited on the porous silicon surface. The capability of these metal-dielectric substrates toward SERS enhancement was evaluated using crystal violet dye and the advantages and drawbacks of both methods were addressed in detail. The obtained detection limits for the crystal violet dye were in the range between 10−7 and 10−8 M. So far, gold-coated porous silicon SERS-active substrates for near-infrared 1064 nm excitation have not been reported, both for the off- and on-resonant regimes.

Solid chip-based detection of trace morphine in solutions via portable surface-enhanced Raman spectroscopy

The accurate, sensitive and portable detection of morphine is important to handle judicial cases, but remains to be a great challenge. In this work, a flexible route is presented for the accurate identification and efficient detection of trace morphine in solutions based on surface-enhanced Raman spectroscopy (SERS) and a solid substrate/chip. A gold-coated jagged silicon nanoarray (Au-JSiNA) is designed and prepared via Si-based polystyrene colloidal template-reactive ion etching and sputtering deposition of Au. Such Au-JSiNA has three-dimensional nanostructure with good structural uniformity, high SERS activity and hydrophobic surface. Adopting this Au-JSiNA as SERS chip, trace morphine in solutions could be detected and identified in both dropping and soaking ways, and the limit of detection is below 10-4 mg/mL. Importantly, such chip is especially suitable for the detection of trace morphine in aqueous solutions and even domestic sewage. The good SERS performance is attributed to the high-density nanotips and nanogaps on this chip as well as its hydrophobic surface. Additionally, the appropriate surface modification of this Au-JSiNA chip with 3-mercapto-1-propanol or 3-mercaptopropionic acid/1-(3-dimethylaminopropyl)-3-ethylcarbodiimide can further increase its SERS performances to morphine. This work provides a facile route and practical solid chip for SERS detection of trace morphine in solutions, which is significant to develop the portable and reliable instruments for on-site analysis of drugs in solutions.

Comparative evaluation of filtration and imaging properties of analytical filters for microplastic capture and analysis

Pollution by microplastics (MPs) is a growing problem that is now well-recognized, as concerning levels of MPs have been found in drinking water, food, and even human tissues. Given the evolving understanding of their toxicological effects on human health, MPs are an area of concern requiring further study. Consequently, there is a need for greater understanding of the performance characteristics of common MP analytical methods and where possible, for standardizing methods and reporting practices. Here, we report our work comparing filtration and imaging properties of five analytical filters suitable for MP capture and analysis. We compared track-etched polycarbonate with (PCTEG) and without gold coating (PCTE), polytetrafluoroethylene (PTFE), porous silicon (PSi), and gold-coated microslit silicon nitride membranes (MSSN-Au). Four of the filter types had a nominal 1.0 μm cut-off, except for PCTEG which had a 0.8 nominal cut-off. We examined the ultrastructure of each membrane type by electron microscopy to understand how their physical properties influence filtration and imaging performance. We compared clean water filtration rates and timed volume passage for each filter in comparison to its porosity and working surface area. We further compared optical microscopy imaging properties for each filter with model MP samples in both bright-field and fluorescent modes with accompanying Nile Red staining. In terms of absolute and surface area-normalized flow rates, our measurements ranked the filters in order of MSSN-Au > PTFE > PCTE > PCTEG > PSi. Similarly, we found MSSN-Au filters compared favorably in terms of optical microscopy performance. Collectively, these data will aid practitioners when choosing analytical filters for MP surveillance and testing.

Synthesis of Optoelectronic Nanostructures on Silicon and Gold-Coated Silicon via High-Intensity Laser Pulses at Varied Pulse Durations

This work defines the generation of nanostructures on silicon and gold-coated silicon substrates by tuning the pulse duration of our proposed method: ultra-short laser pulses for in situ nanostructure generation (ULPING) under ambient conditions. The method is a single-step novel method which is efficient in synthesizing nanostructures on the substrates. We observed a higher nanofiber generation at a shorter pulse duration using Scanning Electron Microscopy (SEM) imaging. Silicon oxide formation was confirmed by Energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) analysis and a band gap of 8.19 eV was achieved for the Si + Au sample, which was determined by the Reflection Electron Energy Loss Spectroscopy (REELS) spectra. A high valence band offset of 4.93 eV was measured for the silicon-based samples for the Si/SiO2 interface. The addition of gold nanoparticles decreased the band gap and we observed a blue shift in optical conductivity for samples with nanofibers using optical spectroscopy.

Tribotronic control of an ionic boundary layer in operando extends the limits of lubrication

The effect of electric potential on the lubrication of a non-halogenated phosphonium orthoborate ionic liquid used as an additive in a biodegradable oil was studied. An in-house tribotronic system was built around an instrument designed to measure lubricant film thickness between a rolling steel ball and a rotating silica-coated glass disc. The application of an electric field between the steel ball and a set of customized counter-electrodes clearly induced changes in the thickness of the lubricant film: a marked decrease at negative potentials and an increase at positive potentials. Complementary neutron reflectivity studies demonstrated the intrinsic electroresponsivity of the adsorbate: this was performed on a gold-coated silicon block and made possible in the same lubricant system by deuterating the oil. The results indicate that the anions, acting as anchors for the adsorbed film on the steel surface, are instrumental in the formation of thick and robust lubricating ionic boundary films. The application of a high positive potential, outside the electrochemical window, resulted in an enormous boost to film thickness, implicating the formation of ionic multi-layers and demonstrating the plausibility of remote control of failing contacts in inaccessible machinery, such as offshore wind and wave power installations.

Nano-g accelerometer with differential Fabry–Pérot interferometer for low-frequency noise suppression

This paper introduces a nano-g level optical accelerometer based on a differential Fabry–Pérot interferometer(DFPI) for low-frequency (less than 1 Hz) noise suppression. The accelerometer has its proof-mass supported by two metal spring beams and has a natural frequency of 40 Hz. The DFPI structure is composed of two fiber end-faces and two reflectors made by gold-coated silicon chips attached on each side of the proof-mass. It is both theoretically analyzed and calculated that the differential structure can suppress noises caused by laser source, optical components and temperature, therefore improves the signal to noise ratio of the accelerometer. Experimental results show that the DFPI accelerometer has a noise floor of 4 ng/Hz at 3 Hz to 10 Hz, with a displacement noise floor of 0.62 pm/Hz, a measurement range of 0.88 mg and a sensitivity of 1699.7 V/g. The DFPI mechanism improves the noise performance at 0.1 Hz from 100 ng/Hz by a single FPI to 24 ng/Hz by DFPI, and improves the bias instability from 49 ng to 17 ng. The proposed DFPI accelerometer has the potential applications on seismic acceleration measurement for mineral exploration and active vibration isolation.

ZnO Nanowire-Based Piezoelectric Nanogenerator Device Performance Tests

Over the past two decades, the quick development of wireless sensor networks has required the sensor nodes being self-powered. Pushed by this goal, in this work, we demonstrated a ZnO nanowire-array-based piezoelectric nanogenerator (NG) prototype, which can convert mechanical energy into electricity. High-quality single crystalline ZnO nanowires, having an aspect ratio of about 15, grown on gold-coated silicon substrate, were obtained by using a low-cost and low-temperature hydrothermal method. The NG-device fabrication process has been presented in detail, and the NG’s performance has been tested in both compression and vibration modes. Peak power of 1.71 µW was observed across an optimal load resistance of 5 MΩ for the ZnO nanowires-based NG, with an effective area of 0.7 cm2, which was excited in compression mode, at 9 Hz, corresponding to ~38.47 mW/cm3 volume-normalized power output. The measured voltage between the top and bottom electrodes was 5.6 V. In vibration mode, at 500 Hz, the same device showed a potential of 1.4 V peak-to-peak value and an instantaneous power of 0.04 μW, corresponding to an output power density of ~0.9 mW/cm3.

Thermal release tape-assisted semiconductor membrane transfer process for hybrid photonic devices embedding quantum emitters

The ability to combine different materials enables a combination of complementary properties and device engineering that cannot be found or exploited within a single material system. In the realm of quantum nanophotonics, one might want to increase device functionality by, for instance, combining efficient classical and quantum light emission available in III–V semiconductors, low-loss light propagation accessible in silicon-based materials, fast electro-optical properties of lithium niobate, and broadband reflectors and/or buried metallic contacts for local electric field application or electrical injection of emitters. However, combining different materials on a single wafer is challenging and may result in low reproducibility and/or low yield. For instance, direct epitaxial growth requires crystal lattice matching for producing of defect-free films, and wafer bonding requires considerable and costly process development for high bond strength and yield. We propose a transfer printing technique based on the removal of arrays of free-standing membranes and their deposition onto a host material using a thermal release adhesive tape-assisted process. This approach is versatile, in that it poses limited restrictions on the transferred and host materials. In particular, we transfer 190 nm-thick GaAs membranes that contain InAs quantum dots and which have dimensions up to about 260 μm × 80 μm onto a gold-coated silicon substrate. We show that the presence of a back reflector combined with the etching of micropillars significantly increases the extraction efficiency of quantum light from a single quantum dot line, reaching photon fluxes exceeding 8 × 105 photons per second. This flux is four times higher than the highest count rates measured from emitters outside the pillars on the same chip. Given its versatility and ease of processing, this technique provides a path to realising hybrid quantum nanophotonic devices that combine virtually any material in which free-standing membranes can be made onto any host substrate, without specific compatibility issues and/or requirements.

Scanning force sensing at micrometer distances from a conductive surface with nanospheres in an optical lattice.

The center-of-mass motion of optically trapped dielectric nanoparticles in a vacuum is extremely well decoupled from its environment, making a powerful tool for measurements of feeble subattonewton forces. We demonstrate a method to trap and maneuver nanoparticles in an optical standing wave potential formed by retroreflecting a laser beam from a metallic mirror surface. We can reliably position a ∼170nm diameter silica nanoparticle at distances of a few hundred nanometers to tens of micrometers from the surface of a gold-coated silicon mirror by transferring it from a single-beam tweezer trap into the standing wave potential. We can further measure forces experienced by the particle while scanning the two-dimensional space parallel to the mirror surface, and we find no significant excess force noise in the vicinity of the surface. This method may enable three-dimensional scanning force sensing near surfaces using optically trapped nanoparticles, promising for high-sensitivity scanning force microscopy, tests of the Casimir effect, and tests of the gravitational inverse square law at micrometer scales.

SALDI-MS and SERS Multimodal Imaging: One Nanostructured Substrate to Rule Them Both.

Imaging techniques based on mass spectrometry or spectroscopy methods inform in situ about the chemical composition of biological tissues or organisms, but they are sometimes limited by their specificity, sensitivity, or spatial resolution. Multimodal imaging addresses these limitations by combining several imaging modalities; however, measuring the same sample with the same preparation using multiple imaging techniques is still uncommon due to the incompatibility between substrates, sample preparation protocols, and data formats. We present a multimodal imaging approach that employs a gold-coated nanostructured silicon substrate to couple surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) and surface-enhanced Raman spectroscopy (SERS). Our approach integrates both imaging modalities by using the same substrate, sample preparation, and data analysis software on the same sample, allowing the coregistration of both images. We transferred molecules from clean fingertips and fingertips covered with plasticine modeling clay onto our nanostructure and analyzed their chemical composition and distribution by SALDI-MS and SERS. Multimodal analysis located the traces of plasticine on fingermarks and provided chemical information on the composition of the clay. Our multimodal approach effectively combines the advantages of mass spectrometry and vibrational spectroscopy with the signal enhancing abilities of our nanostructured substrate.

Surface-enhanced Raman scattering with gold-coated silicon nanopillars arrays: The influence of size and spatial order

Nanopillars have been extensively explored as promising substrates for surface-enhanced Raman scattering (SERS) owing to their high sensitivity and excellent reproducibility. Most of the researches have been focused on the fabrication methods of nanopillars, and the dependences of SERS effects on geometrical size and spatial order are rarely investigated. In this work, SERS properties of nanopillars with different sizes (115–185 nm) and spatial orders (square and rhombus orders) have been studied. The work has shown that the nanopillars not only have high enhancement capability and high signal reproducibility, but also the enhancement is insensitive to the size and spatial orders. The measured enhancement factors (EFs) are 2.3–4.0 × 106 and signal reproducibility (relative standard deviation, RSD) are ∼ 5.2%–6.9%, which are among the best of the similar SERS substrates reported. The variation of SERS intensity was as low as approximately 4.8% with the variation of pillar size from 115, 135, 145, to 160 nm. The insensitiveness and high reproducibility have been ascribed to the combined excitation of localized surface plasmon resonance (LSPR) and propagating surface plasmons (SPPs) of the nanopillars. Optical properties of the nanopillars are studied both experimentally and numerically to understand the physics behind the SERS performance.

Gold-coated silicon nanoripples achieved via picosecond laser ablation for surface enhanced Raman scattering studies

We report the results from ablation studies of polished single crystalline Si targets (of resistivity 1–10 Ohm-cm) submerged in acetone by employing the focused Airy pattern of the p-polarized laser pulses of duration ∼ 2 ps. The Airy pattern was obtained by inserting a circular aperture with hard edge before the focusing convex lens. The ablation was performed on the Si substrate at diverse scanning speeds of the motorized stage (25–600 μm/sec) with a fixed pulse energy (∼50 μJ) resulting in high/low spatial frequency laser induced periodic surface structures (HSFLIPSS/ LSFLIPSS). These are believed to be the outcome of varied electric fields and the varied pulse numbers at different scan speeds. The effective number of pulses estimated on the Si target demonstrated the surface structures with different grating periods. At lower and higher number of pulses HSFLIPSS were obtained. At an intermediate number of pulses, LSFLIPSS were observed. Further, the obtained HSFLIPSS (with grating periods ∼111 nm, 114 nm) were gold coated (25 nm) with magnetron dc sputtering technique and subsequently employed them for surface enhanced Raman scattering (SERS) studies of explosive molecules 5-amino, 3-nitro, 1,3,5-nitrozole (ANTA) at a very low concentration of 100 nM. SERS imaging of ANTA from the mentioned HSFLIPSS illustrated the uniformity in SERS signatures with an intensity variation below 10% at different locations of the SERS active platform.