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A versatile nanoformulation is designed by anchoring human transferrin protein (Tf) on fluoromagnetic upconverting nanoheaters, NaGdF

Plasmonic nanostructure/semiconductor nanohybrids offer many opportunities for emerging electronic and optoelectronic device applications because of their unique geometries in the nanometer scale and material properties. However, the development of a simple and scalable synthesis of plasmonic nanostructure/semiconductor nanohybrids is still lacking. Here, we report a direct synthesis of colloidal gold nanoparticle/graphene quantum dot (Au@GQD) nanohybrids under ambient conditions using microplasmas and their application as photoabsorbers for broad band photodetectors (PDs). Due to the unique AuNP core and graphene shell nanostructures in the synthesized Au@GQD nanohybrids, the plasmonic absorption of the AuNP core extends the usable spectral range of the photodetectors. It is demonstrated that the Au@GQD-based visible light photodetector simultaneously possesses an extraordinary photoresponsivity of ∼103 A/W, ultrahigh detectivity of 1013 Jones, and fast response time in the millisecond scale (65 ms rise time and 53 ms fall time). We suggest that the synergistic effect can be attributed to the strong fluorescence quenching in Au@GQD coupled with the two-dimensional graphene layer in the device. This work provides knowledge of tailoring the optical absorption in GQDs with plasmonic AuNPs and the corresponding photophysics for broad band response in PD-related devices.

The combination of superparamagnetism and excitation independency have been packed into carbon-decorated ferrite nanodots (CDs@MNFs) for the introduction of a cost-effective and less-toxic multimodal contrast agent in fluorescence/MR imaging to replace conventional heavy metal containing Gd-DOTA. The label-free surface engineered ferrite nanodots are capable of generating twin T1 (longitudinal) and T2 (transverse) weighted magnetic resonance (MR) along with fluorescence emission. The calculated molar relaxivities and molar radiant efficiency obtained from in vitro and in vivo studies are the indication of its multimodal efficacy in medical imaging compared to the conventional contrast agents. The cellular internalization of nanodots was established by confocal microscopy and flow cytometric assay, whereas the hemolysis and cell viability assays support their appreciable toxicity. Furthermore, the surface chemistry due to the presence of -COOH was utilized to attach the anticancer agent, doxorubicin (-NH

A combined photothermal therapy (PTT) and chemotherapy (chemo) were performed in vitro on B16F10 melanoma cells and in vivo using melanoma bearing C57BL/6 mice. The 785 nm (100 mW) irradiated gold nanorods (AuNRs) were used as the PT agent, and electrostatically conjugated Doxorubicin (Dox) to a nanocarrier graphene oxide (GO) worked as the chemotherapeutic. Selection of dosage was optimized from the individual viability studies, and finally a combined therapeutic (AuNR (100 ppm), GO (125, and 250 ppm), Dox (0.0058, and 0.00058 ppm)), was delivered in vitro. PTT, followed by chemo, sequentially, resulted in10% viability, whereas simultaneous PTT with chemo resulted in a viability of ∼40% for the melanoma cells. Flow cytometry indicated optical inhomogeneity in the cells that internalized GO, and AuNR; however, the Dox amount was identical within the cells treated with or without PTT. Confocal microscopy revealed that GO+Dox was internalized, and Dox was distributed uniformly within the cells irrespective of the treatment protocol. In vivo results in melanoma bearing C57BL/6 mice resembled the in vitro data closely. The tumor growth inhibition index was highest at 0.78 for the group receiving sequential treatment, followed by 0.61 for those receiving simultaneous treatment, where the control group had a score of 0. For the sequential treatment, presoftening of the cells with PTT, followed by the chemo resulted in significantly improved toxicity of the treatment, whereas simultaneous PTT with chemo results were dominated by the Dox alone.

Composites or hybrid materials offer diverse properties not achievable in pure materials. Here we critically review the interesting and controllable fluorescence and photothermal properties of diverse hybrid materials containing up-conversion nanoparticles (UCNPs). These hybrids couple plasmons, photonic crystals, bio-surfaces, and two dimensional (2D) materials to the UCNPs, offering optical non-linearity, and enable effective photo-electro-thermal control leading to new light and heat driven applications. Among the light driven applications, coupling of UCNPs with graphene and molybdenum disulfide (MoS2) enables photodetectors with better photoresponse, and broader spectral range not accessible to individual components. Irradiated MoS2 coupled-UCNPs is a new paradigm in resistive random access memory devices. Conjugation of graphene and perovskites, with the UCNPs, have led to novel optical limiting phenomenon and better solar cells. Examples of new opportunities offered by UCNPs in heat driven applications are photothermal water desalination using solar daylight and photothermal disintegration of fat droplets in obesity treatment. Phonons, manifesting as heat, can also be utilized to enhance fluorescence and translate to high sensitivity nanothermometers. This review covers fundamentals, and applications of the new UCNP-enabled class of hybrid materials in energy harnessing, light sources and detectors, memory devices, nanothermometers, desalination, intracellular pH sensing, and cancer theranostics.

We demonstrate that the upconversion nanoparticles (UCNPs) fluoresce 50 times more on a gold (Au) coated Cicada wing. UCNPs are attractive bioimaging, and therapeutic materials as it is excited in the infrared, limited only by the low fluorescence quantum yield. Here, a plasmonic effect, coupled with an anti-reflecting (AR) Cicada wing substrate coated with Au is demonstrated to enhance the fluorescence of the UCNPs. Silica (SiO2) coated Erbium doped green emitting core-shell UCNPs (NaYF4: Yb3+, Er3+@SiO2) show conventional metal enhanced fluorescence. The AR property of the Cicada wing (R ~0.2% @ 1000 nm) contributes >6-fold enhancement as compared to flat (silicon, and quartz) substrates (R~10–30% @ 1000 nm). Upon plasmon coupling, with an optimally sputtered Au coating, an unprecedented enhancement of >50-fold for the 520, and 655 nm emission was obtained on the Au coated Cicada wings, vis-a-vis planar uncoated (silicon, and quartz) substrates. The enhancement was also confirmed by direct fluorescence imaging of the photonic substrates used. The fluorescence lifetime of the core, and the core-shell UCNPs (~300 μs) decreased by ~30–40%, and 10–30%, respectively, when placed on Au coated substrates.

Multiphoton (980 nm) absorbing lanthanide doped upconversion nanoparticles (UCNPs) are emerging as fluorophores and photothermal agents but are limited by the low quantum yield of their visible flu...

Fipronil and its metabolite fipronil sulfone, when found in some food products, such as eggs, have caused major public health concerns. In this study, we used gold nanorods (AuNRs) and graphene oxide (GO) nanocomposites to fabricate a layer-by-layer assembled three dimensional (3D) substrate for toxin detection by surface enhanced Raman scattering (SERS). The 4-layers of GO–AuNR 3D SERS substrate were optimized using rhodamine 6G. The optimized SERS substrate was used to detect fipronil and fipronil sulfone in spiked eggs. The obtained limit of detection was 10−8 M (∼4.4 ppb), which is below the maximum residue limit in Taiwan of 10 ppb. Egg samples spiked with fipronil (10−7 and 10−3 M) and fipronil sulfone (10−8 and 10−4 M) were measured and the maximum departure of the measured SERS intensity from the calibrated SERS intensity was ∼14%. Thus, a facile screening method for the detection of fipronil/fipronil sulfone in food-grade eggs by SERS is demonstrated.

Fluorescence based intracellular pH nanoprobes have been developed that overcomes the limitations imposed by shallow penetration depth of ultraviolet excitation, photostability, phototoxicity, and interference from background autofluorescence. In this study, we have constructed a Forster Resonance Energy Transfer (FRET) based pH nanoprobe using upconversion nanoparticle (UCNP) as a donor (excitation/emission @ 980/540 nm, green channel), and mOrange fluorescent protein (excitation/emission @ 548/566 nm, red channel) as acceptor. The UCNP-mOrange nanoprobe could be fluorescently imaged with 980 nm excitation, having deep penetration depth, by a fluorescence microscope on a coverslip, or uptaken in a single HeLa cell. The cellular upatake of these nanoparticles were confirmed by transmission electron microscope study. The FRET probes, with a FRET efficiency of ~20% at physiological pH of 7.0, have simultaneous self-ratiometric and ratiometric features varying linearly with local pH. The probe exhibits high accuracy, sensitivity, reversibility, and stability over a wide range of pH (3.0–8.0). The fluorescence intensity ratio from individual green, and red channels in fluorescence microscopic images could be used to estimate the pH of the intracellular compartments of HeLa cell from the pH dependent ratiometric calibration. Nigericin mediated intracellular pH (3.0, 5.0, and 7.0) could be accurately estimated from the CLSM derived FRET ratio. The pH probes demonstrate high stability and reversibility when switched between pH 3, and 8 for at least 5 cycles.

We demonstrate a gold island film (GIF) coated tattoo paper as acid free ‘green’ fabrication of transferable plasmonic patterns for surface enhanced Raman spectroscopy (SERS) based screening of food toxins. A tattoo paper, with a water soluble release layer, was optimally sputter coated with a gold pattern which can be transferred onto any real fruit surface to enable in situ molecular detection (Thiabendazole, TBZ, used here) from the surface of the fruit (orange used here). The GIF loading and morphology is simply controlled by varying the sputtering time between 1 and 8 min. The integrated plasmonic field strength, calculated by finite difference time domain simulations, peaked for the GIF obtained with 3 min of sputtering time to match the experimental results. The SERS tattoo can also be transferred to a copper foil to enable conventional ex situ molecular detection (Di 2-ethylhexyl phthalate, DEHP, used here) in commercial sports drinks. The SERS tattoo could detect 0.1 μM (0.2 ppm) of TBZ on orange in situ, and 0.0009 vol.% DEHP in sports drink ex situ. Multiplexed SERS experiments were performed to detect specific signals of TBZ, and commercial soybean oil from their combination.

We report electrostatically conjugated core- silica (SiO2) shell upconversion nanoparticle (UCNPs@SiO2), and gold nanorod (AuNR) nanocomposite (NC) combined with graphene to demonstrate > 200-fold UC fluorescence enhancement. Plasmonic AuNR and graphene, resulted in enhanced fluorescence in UCNP with a maximum for the SiO2 shell thickness of 7 nm supported by finite difference time domain simulation of electric field distribution. In addition to the conventionally reported spectroscopic evidence, the plasmon aided UC fluorescence enhancement was demonstrated by direct confocal fluorescence imaging also, which was corroborated by a ~40% decrease in fluorescence lifetime. Finally, we have fabricated a NC/graphene hybrid photodetector (PD) that showed broadband (455–980 nm) photoresponse, with photoresponsivity of ~5000 AW−1, and response times of 80–200 ms under 980 nm illumination. The multiphoton infrared (IR, ~980 nm) absorbing UCNPs also show interesting high energy (blue (B), green (G), and red (R)) photoresponse which is now conclusively attributed to one-photon absorption in the UCNPs. We report, probably for the first time, the performance of the hybrid PD under monochromatic and polychromatic illumination of B, G, R, B + G, B + R, G + R, and B + G + R, among others. The photocurrent under polychromatic conditions is dominated by the strongest monochromatic response, and does not scale with net power of the illumination. The loss in photocurrent is attributed to saturation in absorption, and photothermal heating. The fast response of the PD device has been demonstrated while detecting high frequency modulated AC remote controller signals, and attributed to the fast charge sweeping by the AuNRs.

Heavy metal, such as lead (Pb), arsenic (As), and mercury (Hg), contamination is a grave global issue that has affected public health via drinking water, paints, and a wide range of personal consumer products such as cosmetics. Here, we have used Surface enhanced Raman spectroscopy (SERS) for the novel solution phase detection of Hg2+ ions in spiked cosmetic (skin whitening) samples by using 2,5-Dimercapto-1,3,4-thiadiazole (DMcT) functionalized silver shelled iron oxide (Fe3O4@Ag-DMcT) nanoparticles (NPs). Fe3O4@Ag NPs (12 ± 4 nm) are the magneto-plasmonic SERS enhancers, and DMcT work as the Hg2+ reporter. We have optimized 2 mg/mL of Fe3O4@Ag:DMcT with 10−4 M of DMcT to be the best for SERS based Hg2+ detection in spiked samples of commercial skin whitening product. The samples mixed with the SERS probe were sealed in a capillary tube and placed on a magnet under the Raman spectroscope. A calibration curve of the variation of the 1360 cm−1 band of DMcT as a function of Hg2+ concentration was first determined using a cream, and a liquid phase randomly chosen cosmetics. Unknown samples spiked with low (10−8 M), and high (10−4 M) concentrations of Hg2+ could be successfully detected with ∼ 35 %, and 14.6 % error in measured intensities, respectively, with respect to the calibrated data. We estimate a limit of detection (LoD) for Hg2+ in real cosmetic sample as 1 nM (∼0.2 ppb).

An “all optical” methodology, including Raman and optical transmission spectroscopy, is presented to study the thermal degradation in edible oils. Oils rich in monounsaturated (MU), polyunsaturated (PU), and saturated (S) fatty acids (FA) were heated above and below their smoke point (∼230 ℃). While the intensity (I) of the identified saturated (C–C, 1440 cm−1) FA Raman marker did not change appreciably, the identified unsaturated (C=C, 1265 cm−1) FA marker decreased in these oils when heated above the smoke point. A Raman parameter, I1265/I1440, designating thermal degradation, is proposed that was found to decrease consistently for the PUFA-rich and MUFA-rich oils when heated above the smoke point, while the SFA-rich oil did not degrade at all over the whole temperature range. An optical transmission marker at 2140 nm was identified that decreased consistently with increased thermal stressing. These markers can be calibrated with the variations in the quantitative iodine value, an industrial benchmark for the degree of unsaturation, for thermally stressed oils.

Supplemental Material for Calibrated Optical Markers to Study Thermal Degradation in Edible Oils Using Raman and Optical Transmission Spectroscopy by Ho-Ying Lam, Sandip Ghosh and Surojit Chattopadhyay in Applied Spectroscopy

Graphene oxide (GO) and gold nanorods (AuNRs) have been extensively evaluated for broadband (325-980 nm) photothermal (PT) heat generation and efficiency, on substrates having contrasting thermal conductivities. Infrared thermal imaging of the PT agents under broadband irradiation showed a maximum rise of local temperature of chicken kidney tissue by 16.4, and 5.7 °C for GO and AuNR, respectively, under similar irradiation conditions. The PT conversion efficiency, derived from the cooling curves of the dynamic PT response, was found to be exceeding 60 % for GO on chicken kidney tissue under 532, 785, and 980 nm laser irradiations. The PT effect was used to enhance the dissolution rate of the kidney stone mimicking calcium oxalate crystals in the presence of hydroxyanthraquinone (AQ) solution. Mass spectrometric experiments show that the combination of AQ and GO, when irradiated with 532 nm, could chemo-photothermally dissolve calcium oxalate by at least ∼20 % more than when using AQ alone, or using a resistive way of elevating the solution temperature.

The low quantum yield of luminescence from lanthanide-doped up-conversion nanoparticles (UCNPs) has been enhanced by using an optimized ‘gold sandwich’ with a transparent top layer and a reflecting bottom layer at 980 nm excitation. Erbium (Er)-doped UCNPs, with a NaYF4:Yb,Er core, were synthesized by a thermal decomposition process and coated with silica to assist in metal-enhanced fluorescence (MEF). A bottom layer of thick coalesced gold island film, acting as a mirror, increases the optical path length of the 980 nm radiation through the UCNP layer dispersed on it. This layer enhances the UCNPs' 540 nm green emission by a factor of 5–8 compared to that in the absence of the gold reflector. A thin nanoparticle-like gold layer on top of the UCNPs, with a surface plasmon absorption around ∼550 nm, completes the sandwich, which augments the luminescence enhancement by another factor of ∼2.5, thus taking the net enhancement factor to ∼13–19 when compared to the luminescence in the absence of the gold-sandwich. The surface plasmon absorption in the top gold layer enhances the local electric field at the UCNPs to promote their radiative decay. Compared to previous reports, mostly for the solution state, the current case study is a solid state measurement.

Human osteosarcoma cells MG-63 were cultured on anodically etched titania nanotubes (TiO2 NT), with diameters ranging from 40-100 nm, to study the correlations between cell proliferation and adhesion on the 2.5 dimensional (2.5D) extracellular matrix (ECM). Unlike other reports, mostly based on mouse stem cells, and 2D cell culture, our studies indicate that the 2.5D NT promote higher proliferation and activity, but less 2D adhesion. Proliferation of the MG-63 cells was significantly higher in the NTs, the best being the 70 nm diameter sample, compared to planar titania (control). This is consistent with previous studies. However, cellular adhesion was stronger on TiO2 NT with increasing diameter, and highest on the control as obtained from shear stress measurement, paxilin imaging, and western blot measurements probing focal adhesion kinase, p130 CAS, and extracellular-regulated kinase, in addition to cell morphology imaging by fluorescence microscopy. We provide direct videography of cell migration, and cell speed data indicating faster filopodial activity on the TiO2 NT surfaces having lower adhesion. This evidence was not available previously. The NT matrices promote cells with smaller surface area, because of less 2D stretching. In contrast, on comparatively planar 2D-like surfaces uniaxial stretching of the cell body with strong anchoring of the filopodia, resulted in larger cell surface area, and demonstrated stronger adhesion. The difference in the results, with those previously published, may be generally attributed to, among others, the use of mouse stem cells (human osteosarcoma used here), and unannealed as-grown TiO2 NTs used previously (annealed ECMs used here).

Hybrid or composite nanomaterials have emerged that demonstrates superior optoelectronic performance over pure nanomaterials that lacks broadband usage, or responsivity, or both, mainly because of the limitation of the collection of photogenerated carriers. We have addressed this problem by using a composite of MoS2 and a multi-photon absorbing lanthanide doped upconversion nanoparticles (UCNPs), that emits in the visible, to make a photodetector (PD) device with ultrahigh broadband responsivity. Single flake MoS2 electrostatically conjugated with UCNPs were used to fabricate the PD device with platinum, and gold contacts. The device was irradiated with UV-to-NIR illumination, at different power density, to study its broadband photosensitivity. Photoresponsivities in excess of 100 A W-1 is easily obtained; a highest responsivity of 1254 A W-1 is reported for 980 nm at 1.0 V bias. An unprecedented normalized gain of 7.12 × 10−4 cm2 V−1, and Detectivity of 1.05 × 1015 Jones (@980 nm, 1 V) was obtained which is, to the best of our knowledge, the highest reported till date for this device class. Under vacuum conditions even higher values of these device parameters were obtained, while losing on the response speeds. The photoresponsivity in the nanocomposite followed the trend of the convoluted optical absorption of the individual components. Real application of the PD device was demonstrated using non-laser domestic appliances such as sodium vapour lamp, mobile phone flash light, and air-condition remote controller.

We present a facile surface enhanced Raman scattering (SERS) based methodology to study the thermal degradation of edible oils using a special gold sputtered SERS tattoo. The methodology is calibrated with Iodine values, which is an industrial standard. This analytical study aims to compare the safety of 7 edible oils rich in monounsaturated (MU), polyunsaturated (PU), and saturated (S) fatty acids (FA) against high temperature re-cooking as done in most restaurants, and street food joints. The changes in the SERS signal intensity (I) ratio of the saturated (@1440 cm-1), and unsaturated (@ 1265 cm−1) FA, I1265/I1440, was studied as a function of heating time, and temperature (T), around the ‘smoke point’. The SERS marker for thermal degradation, I1265/I1440, measuring the normalized unsaturated FA content in the oils decreased consistently, and significantly for the PUFA, and MUFA oils when heated above the ‘smoke point’, following the changes in the industrial standard ‘Iodine value’. Olive (MUFA), and Coconut (SFA) oil showed marginal, and no decrease, respectively, of the SERS marker over the temperature range studied. Based on the SERS marker, a parameter ζ, -the decrease of (I1265/I1440) value of the heated oil with respect to the as-purchased value, is defined that can compare the degradation of the edible oils under different thermal stressing. The Arrhenius fit of the SERS marker yielded similar activation energy of the thermal degradation to that obtained independently from Iodine value, and demonstrates the correctness of the presented methodology.

Unmodified, as-grown few layered graphene on copper substrates have been used for glucose sensing using Raman spectroscopy. Graphene with a stronger 2D band is a better Raman enhancer with significant fluorescence suppression and finer line widths of the Raman signals. The origin of the graphene enhanced Raman spectroscopy (GERS) signal of glucose is attributed to a fractional charge transfer (calculated to be 0.006 using electrochemical parameters) between glucose and graphene aided by a possible π-π interaction. Physiological concentrations of glucose (10-500 mg dl(-1)) in PBS have been used for the study. For each glucose concentration, the spectral reproducibility is within 5-25% as calculated by the relative standard deviation of several measurements. The intensity ratio of the 1122 cm(-1) peak of glucose and the 2D peak of graphene varied linearly with the glucose concentration and can be used as a calibration curve for unknown sample measurements.

A printable, surface enhanced Raman scattering (SERS) active test strip, with in situ growth of gold nanoparticles on completely untreated paper, is demonstrated to screen for bio-toxins below the maximum residue levels in the European Union, in food. The cheap disposable strip produced from as-purchased printing paper can also be used for SERS mapping of fluorescent dyes.

This article outlines state-of-the-art energy technologies, including production and storage, available to us through semiconductor nanomaterials. The nanostructure growth processes have been illustrated in detail, with emphasis on the latest developments in hierarchical and radial-composition modulated nanostructures. On the energy efficiency and generation part, light-emitting diodes, photovoltaics, photoelectrochemistry, thermoelectric, and fuel cells have been discussed. In the energy storage part, supercapacitors and lithium batteries have been discussed.

A significant improvement in the stability of high-quality GaN films, for photoelectrochemical hydrogen generation, has been demonstrated using near neutral NaCl(aq) electrolyte instead of conventional acidic HCl(aq). The experimental results conclude that the as-grown surface oxide passivates the surface from corrosion and, therefore, leads to a higher photocurrent. Our result paves the way for the future development of stable hydrogen generation with abundant sea water and high-efficiency III–V compound semiconductors.

A 3D trenched-structure metal-insulator-metal (MIM) nanocapacitor array with an ultrahigh equivalent planar capacitance (EPC) of ~300 μF cm(-2) is demonstrated. Zinc oxide (ZnO) and aluminum oxide (Al2O3) bilayer dielectric is deposited on 1 μm high biomimetic silicon nanotip (SiNT) substrate using the atomic layer deposition method. The large EPC is achieved by utilizing the large surface area of the densely packed SiNT (!5 × 10(10) cm(-2)) coated conformally with an ultrahigh dielectric constant of ZnO. The EPC value is 30 times higher than those previously reported in metal-insulator-metal or metal-insulator-semiconductor nanocapacitors using similar porosity dimensions of the support materials.

Rapid formation of radial p–n junctions on electroless-etched silicon nanowires (SiNWs) was successfully demonstrated. With a low-cost objective, a homemade nonhazardous diffusion source of high phosphor concentration annealed at a small thermal budget was used. The SiNW solar cell, with Au electrodes, has shown a power conversion efficiency of 8.41%, which is higher by 30% compared with its planar counterpart. The SiNW solar cell incorporates an inherent antireflection property, reduced diffusion length requirement, and broad-band spectral quantum efficiency. The evidence of a successful radial p–n junction formation in the NWs has been revealed through the help of a conducting atomic force microscope (AFM) scanning for the photogenerated currents on the fractured surfaces of the NWs. The demonstrated radial junction fabrication technique is believed to reduce the cost of production and promote widespread use of them.

One-dimensional semiconductor nanomaterials form the basis for new technologies as well as driving the evolution of existing ones. Although these various technologies are in different stages of development, from nucleation to pilot production, it is difficult to ignore the tremendous potential they carry, overall, for next-generation concepts. One of the several areas that have been revolutionized by one-dimensional nanostructures, and which could not have happened at a more critical time, is energy. This review outlines the impact that one-dimensional semiconductor materials are having on energy production and conversion technologies. Instead of being extensive, we provide key developments in the areas of light-emitting diodes, solar cells, photoelectrochemistry and fuel cells.

A simple growth technique capable of growing a variety of zinc oxide (ZnO) nanostructures with record growth rates of 25 μm/s is demonstrated. Visible lengths of ZnO nanowires, nanotubes, comb-like and pencil-like nanostructures could be grown by employing a focused CO2 laser-assisted heating of a sintered ZnO rod in ambient air, in few seconds. For the first time, the growth process of nanowires was videographed, in-situ, on an optical microscope. It showed that ZnO was evaporated and presumably decomposed into Zn and oxygen by laser heating, reforming ZnO nanostructures at places with suitable growth temperatures. Analysis on the representative nanowires shows a rectangular cross-section, with a [0 0 0 1] growth direction. With CO2 laser heating replacing furnace heating used conventionally, and using different reactants and forming gases, this method could be easily adopted for other semiconducting inorganic nanostructures in addition to ZnO.

Optical reflection, or in other words the loss of reflection, from a surface becomes increasingly crucial in determining the extent of the light-matter interaction. The simplest example of using an anti-reflecting (AR) surface is possibly the solar cell that incorporates an AR coating to harvest sunlight more effectively. Researchers have now found ways to mimic biological structures, such as moth eyes or cicada wings, which have been used for the AR purpose by nature herself. These nanoscopic biomimetic structures lend valuable clues in fabricating and designing gradient refractive index materials that are efficient AR structures. The reflectance from a selected sub-wavelength or gradient index structures have come down to below 1% in the visible region of the spectrum and efforts are on to achieve broader bands of such enhanced AR regime. In addition to the challenge of broader bands, the performance of AR structures is also limited by factors such as omnidirectional properties and polarization of incident light. This review presents selected state-of-the-art AR techniques, reported over the last half a century, and their guiding principles to predict a logical trend for future research in this field.

This review will give a brief introduction to the growth and characterization methods of both binary and ternary compounds, in particular those exhibiting one-dimensionality, of the family to orient the readers about the material system to be discussed. A section will deal with the size and shape selection in group III nitride nanomaterials with a stress on intriguing morphologies such as nanowires, nanotips, and nanobelts. Complex structures, such as hierarchical and core-shell structures, will be introduced. Optical, electrical, and mechanical property, such as hardness, will be discussed in a greater detail, distinguishing the bulk from the nano wherever possible. Available models of electrical conduction and photoconduction in nanomaterials and their dependence on the actual size of the objects will be presented and compared. Optical properties of ensemble and single nanostructures, wherever possible, will be addressed in detail. The section on application will focus mainly on the sensor applications,...

[*] Dr. K. H. Chen, M. H. Wu, W. C. Chen Institute of Atomic and Molecular Sciences, Academia Sinica No. 1, Sec. 4, Roosevelt Rd., Taipei 106 (Taiwan) E-mail: chenkh@pub.iams.sinica.edu.tw Dr. L. C. Chen, Dr. C. H. Chen, Dr. K. H. Chen Center for Condensed Matter Sciences, National Taiwan University No. 1, Sec. 4, Roosevelt Rd., Taipei 106 (Taiwan) E-mail: chenlc@ntu.edu.tw C. H. Lin, Prof. J. H. Lee Graduate Institute of Photonics and Optoelectronics and Department of Electrical Engineering, National Taiwan University No. 1, Sec. 4, Roosevelt Rd., Taipei 106 (Taiwan)

Nature routinely produces nanostructured surfaces with useful properties, such as the self-cleaning lotus leaf, the colour of the butterfly wing, the photoreceptor in brittlestar and the anti-reflection observed in the moth eye. Scientists and engineers have been able to mimic some of these natural structures in the laboratory and in real-world applications. Here, we report a simple aperiodic array of silicon nanotips on a 6-inch wafer with a sub-wavelength structure that can suppress the reflection of light at a range of wavelengths from the ultraviolet, through the visible part of the spectrum, to the terahertz region. Reflection is suppressed for a wide range of angles of incidence and for both s- and p-polarized light. The antireflection properties of the silicon result from changes in the refractive index caused by variations in the height of the silicon nanotips, and can be simulated with models that have been used to explain the low reflection from moth eyes. The improved anti-reflection properties of the surfaces could have applications in renewable energy and electro-optical devices for the military.

The optical properties of small radius (

Natural nanostructures in low refractive index Cicada wings demonstrate ≤ 1% reflectance over the visible spectrum. We provide design parameters for Cicada-wing-inspired nanotip arrays as efficient light harvesters over a 300-1000 nm spectrum and up to 60° angle of incidence in both low-index, such as silica and indium tin oxide, and high-index, such as silicon and germanium, photovoltaic materials. Biomimicry of the Cicada wing design, demonstrating gradient index, onto these material surfaces, either by real electron cyclotron resonance microwave plasma processing or by modeling, was carried out to achieve a target reflectance of ∼ 1%. Design parameters of spacing/wavelength and length/spacing fitted into a finite difference time domain model could simulate the experimental reflectance values observed in real silicon and germanium or in model silica and indium tin oxide nanotip arrays. A theoretical mapping of the length/spacing and spacing/wavelength space over varied refractive index materials predicts that lengths of ∼ 1.5 μm and spacings of ∼ 200 nm in high-index and lengths of ∼ 200-600 nm and spacings of ∼ 100-400 nm in low-index materials would exhibit ≤ 1% target reflectance and ∼ 99% optical absorption over the entire UV-vis region and angle of incidence up to 60°.

International audience; Nanostructured wide-bandgap semiconductors (NWS), such as III-nitrides, SiC, ZnO, TiO 2 , diamond, AlN, and BN, have attracted intensive research attention owing to prospective applications in solid-state lighting, solar cells, power electronics, sensors, spintronics, and MEMS/NEMS. These nanostructured semiconductors exhibit tremendous advantages in terms of power capability, energy conversion efficiency , optical properties, radiation strength, high temperature , and frequency operation. Although great progress has been achieved in the synthesis of the NWS materials and promising device applications have been demonstrated since the new century, much further research in the crystallinity improvement, electronic structure control, impurities doping , and devices design need to be carried out. The growth dynamics and the defect physics of NWS should be better understood to push forward their potential applications. This special issue is focused on recent research progress in wide-bandgap semiconductors materials including novel growth strategies of NWS materials, the electronic structure tailoring for functionalization, novel devices concepts, devices physics, and applications in various fields. By using first-principles calculations based on the density functional theory, D. Ma et al. investigated the defects in gallium arsenide. A deep donor level of 0.85 eV below the conduction band minimum on the gallium arsenide crystal surface was disclosed, while the lowest donor level of the defect inside the gallium arsenide bulk was 0.83 eV. The calculations also predicted that the formation energies of internal and surface defects were around 2.36 eV and 5.54 eV, respectively. They concluded that the formation of defect within the crystal was easier than that on surface. This work would assist in tailoring the electronic structures of gallium arsenide, thus favouring the development of high-performance electronic devices. Two papers on ZnO are contributed to this issue. One is on thin film ZnO and the other on 1-dimensional ZnO nanorods. L. Meng et al. report 2-dimensional electron-gas (2DEG) properties of a Zn polar ZnMgO/MgO/ZnO structure with low Mg composition layer (= 0.05) grown on a-plane (11-20) sapphire by radical-source laser molecular beam epitaxy. They observed that the insertion of a thin (1 nm) MgO layer between ZnMgO and ZnO layers in the ZnMgO/ZnO 2DEG structures resulted in an increase of the sheet density and affected the electron mobility slightly. The resultant carrier concentration was as high as 1.1 × 10 13 cm −2 and the Hall mobility was as high as 3090 cm 2 /Vs at 10 K and 332 cm 2 /Vs at RT. The authors also calculated the dependence of carrier sheet density of the 2DEG on ZnMgO

Polycrystalline diamond films are deposited on p-type Si (100) and n-type SiC (6H) substrates at the low surface deposition temperatures of 370 °C–530 °C using a microwave plasma-enhanced chemical vapor deposition system in which the surface temperature during deposition is monitored and controlled. A very high growth rate up to 1.3 μm/h on SiC substrate at 530 °C surface temperature is obtained. The room temperature in-plane thermal conductivity of the low-surface-temperature–deposited thin films is measured by a traveling wave method. The diamond films of grain sizes between 3 and 7 μm and deposited at 370 °C showed a high thermal conductivity value of ∼6.5 W/cm-K, which is much higher than the single crystal SiC thermal conductivity value at room temperature. Diamond films deposited on Si and SiC single crystals at higher temperatures showed even higher thermal conductivities of 11–17 W/cm-K. The structure and microstructure of these films are characterized by x-ray diffraction, scanning electron microscopy, and Raman spectroscopy, and are related to measured thermal conductivities.

The tip morphology in the nanoscale is discussed as a member of the one-dimensional nanostructure family. Different growth techniques used for the synthesis of the nanotips have been outlined and compared against each other including, etching, pyrolysis, physical, and chemical vapour deposition. Growth models for hollow and solid nanotips are compared and discussed in detail with a thrust on the ‘cone-helix’ model for the hollow tips and the ‘platelet stacking’ model for the solid tips. Application of the nanotips in field emission, scanning probe microscopy, sensing, anti-reflection, and nanoindentation is discussed.

Aluminum nitride (AlN) nanostructures were prepared using thermal chemical vapour deposition process. At growth temperatures of 950 °C, AlN nanotips with apex diameters of 10 nm, base diameters of ∼100 nm, and length of ∼2000 nm were obtained. Whereas when the growth temperature was 1200 °C, we obtained shorter and thicker AlN nanorods. Compelling microscopic evidences were obtained to show that stacked AlN platelets of diminishing size formed the building blocks for the nanotips. A reducing Ehrlich–Schwoebel barrier introduced into a diffusion mediated growth model explains the formation of AlN nanorods at increasing growth temperatures.

We report the simultaneous electrochemical detection of dopamine (DA), uric acid (UA) and ascorbic acid (AA) on three dimensional (3D) unmodified ‘as-grown’ epitaxial graphene nanowall arrays (EGNWs). The 3D few layer EGNWs, unlike the 2D planar graphene, offers an abundance of vertically oriented nano-graphitic-edges that exhibit fast electron-transfer kinetics and high electroactive surface area to geometrical area (EAA/GA≈134%), as evident from the Fe(CN)63−/4− redox kinetic study. The hexagonal sp2-C domains, on the basal plane of the EGNWs, facilitate efficient adsorption via spontaneous π–π interaction with the aromatic rings in DA and UA. Such affinity together with the fast electron kinetics enables simultaneous and unambiguous identification of individual AA, DA and UA from their mixture. The unique edge dominant EGNWs result in an unprecedented low limit of detection (experimental) of 0.033 nM and highest sensitivity of 476.2 µA/µM/cm2, for UA, which are orders of magnitude higher than comparable existing reports. A reaction kinetics based modeling of the edge-oriented 3D EGNW system is proposed to illustrate the superior electro-activity for bio-sensing applications.