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Radiation pressure is used to push gold nanorods on multilayer graphene and create hybrid active surfaces for surface-enhanced Raman spectroscopy (SERS) in liquid. As a proof of concept, ultrasensitive detection of bovine serum albumin is shown and the aggregation kinetics is studied as a function of the irradiation time. We compare the results on graphene with experiments on glass and gold surfaces. Optical aggregation on graphene occurs on time scales of 20 min, ca. 3.5 times slower than on glass. No stable aggregation is obtained on gold. We attribute the differences to the destabilization effect of the standing wave produced on the metallic substrates, due to their higher reflectivity, and to the reduced thermophoretic effects, related to the higher heat dissipation. Despite the slowdown of the aggregation kinetics, the usage of graphene as substrate offers manifold benefits: an almost negligible fluorescence background when using near-infrared light (785 nm), the absence of thermal absorption as well as the possibility to easily functionalize the surface to enhance the affinity with the analytes. Our results enlarge the spectrum of materials that can be used for optical aggregation and SERS detection of biomolecules, highlighting the importance of controlling the physical properties of the surfaces. Graphic abstract: [Figure not available: see fulltext.]

Due to its exceptional physical properties, synthetic diamond is an ideal material for the realization of UV and X-ray detectors to be used for the characterization of laser-generated plasmas. Diamond detectors are able to operate at high temperatures and in the presence of high fluxes of ionizing radiation, where traditional silicon-based detectors usually fail. In this paper, we report on Raman and electro-optical characterization of a structure consisting of intrinsic diamond/boron-doped diamond homoepitaxially grown by chemical vapor deposition onto a commercial high pressure high temperature Ib-type diamond substrate using a 1% CH4/H2 gas mixture. A metal–insulator–semiconductor (MIS) diode was obtained by thermally evaporating an aluminum contact on the growth surface of the intrinsic layer. The detection capability of this device operating in transverse configuration was measured in the deep UV spectral range. The device sensitivity has been estimated at different biasing voltages and at two wavele...

The crucial role of precursor gas (PG) and of catalyst support (CS) in the growth of multi-walled C nanotubes (MWCNTs) by iron-catalysed chemical vapour deposition (CVD) is evidenced. This is accomplished by comparing structural and morphological properties of MWCNTs synthesised by the use of different PGs (ethane and isobutane) and CSs (silica and alumina). The results of analyses, carried out on catalysts and C deposits by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy (RS), thermo-gravimetry (TG) and X-ray diffraction (XRD), demonstrate that Al2O3-supported catalysts are more efficient than SiO2-supported ones in decomposing hydrocarbons. The use of i-C4H10 as PG allows reducing Fe-encapsulation and improving yield (YC) and selectivity, so as the large-scale production (YC > 900 wt.%) of high-quality nanotubes can be operated even at moderate reaction temperature (600 °C) after proper calibration of Fe-load (29 wt.%) and catalyst reduction temperature (500 °C).

Multiwalled carbon nanotubes (MWCNTs) were synthesised by chemical vapour deposition (CVD) in a C 2 H 6 +H 2 atmosphere over 20%Fe/SiO 2 catalysts. The influence of synthesis temperature, flow-rate and flow ratio of the reactant gases, the amount of catalyst employed and the catalyst reduction temperature on the abundance and crystalline perfection of product was analysed by scanning electron microscopy, high-resolution transmission electron microscopy and Raman spectroscopy. The changes in yield and crystalline perfection, as monitored by Raman G' band relative intensity, were correlated with the variations of synthesis temperature, the diverse catalyst surface area and H 2 /C supply ratio attained by varying growth conditions. In the range examined, the lowering of catalyst reduction-temperature turns out to be beneficial for both yield and crystalline perfection of the MWCNTs. All the other growth parameters produce opposite effects so the best compromise has to be sought.

This work shows that a set of quality indicators (QI), able to reliably monitor the basic characteristics of carbon nanotubes (CNT) grown by of Fe-catalysed chemical vapour deposition (CVD), can be derived from Raman spectroscopy (RS) measurements. Multi-walled nanotubes, prepared at 750 °C in C2H6+H2 mixture over 20%Fe/SiO2 catalyst, are demonstratively considered. By quantitatively analysing the spectra measured in the 100-3100 cm−1 range, information is obtained on level of defectiveness and degree of smoothness of C deposits, as well as, on relative amount of Fe-nanoparticles incorporated. The effect of the growth atmosphere composition on the quality of synthesis products is investigated. Indications provided by RS are confirmed by the results of scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) analyses. Raman QI agreeably correlate with the average growth rate of the carbonaceous species.

This work reports on the development and characterization of bi-dimensional deep-UV sensor arrays based on synthetic diamond to address the requirements of space-born astrophysical experiments. The material was synthesized at the University of Rome “Tor Vergata” where both heteroepitaxial polycrystalline diamond films and homoepitaxial single-crystal diamonds are grown using a tubular MWCVD reactor. The quality of chemical vapour deposited diamond was characterized by cathodoluminescence, photoluminescence, Raman spectroscopy and thermally stimulated currents. Then, suitable samples were selected and used to fabricate photoconductive single-pixel and 2D array devices by evaporating metal contacts on the growth surface. The electro-optical characterization of the devices was carried out in a wide spectral region, ranging from 120 to 2400 nm. A deuterium lamp and a 0.5 m vacuum monochromator were used to measure the detector responsivity under continuous monochromatic irradiation in the 120–250 nm spectral range, while an optical parametric oscillator tunable laser producing 5 ns pulses was used as light source from 210 up to 2400 nm. Time response, signal-to-noise ratio, responsivity and visible rejection factor were evaluated and the results are hereafter summarized.

Polycrystalline (pCVD) and single crystal (scCVD) diamond films grown from Chemical Vapour Deposition (CVD), if sufficiently pure at Raman analysis, are very good materials for beam or flux monitors inside accelerators or nuclear reactors. This is because they are very hard to damage in high radiation fields and very resistant to high temperatures. Films of pCVD diamond are, however, not so good as spectroscopy detectors due to inhomogeneities induced by their growth in grains with the consequent presence of grain boundaries which worsen their energy resolution. The latter can be significantly improved by growing scCVD diamond films onto HPHT synthetic diamond substrates. We have shown that it is possible to measure the density of defects inside diamond specimens using as probes suitable penetrating nuclear radiations. With the preliminary results reported here we'll show that, bombarding CVD diamond films grown at Roma 'Tor Vergata' with energetic protons and 4 He, Li-6 and C-12 ions produced in the accelerators of Catania laboratories, the pulse height defects are higher than those in silicon detectors and likewise well described by a power law in the deposited energy. Furthermore, we'll show that pulse heights for the same particles seem to depend on the duration of the measurement, thus exhibiting a sort of depolarization of the insulator when exposed to the electric voltage which makes it a particle detector. (c) 2006 Elsevier B.V. All rights reserved.

Date of Conference: 14–18 October 2012 Conference name: Frontiers in Optics 2012 We demonstrate a novel mechanism for optical tweezing, where a trapped particle dynamically alters an external cavity quality factor, reduceing the average intensity and photodamage, even employing low-numerical aperture lenses and wide fields-of-view. © OSA 2012.

A rapid method to detect the addition of reconstituted mandarin oils to natural mandarin essential oils is suggested. The method is based on the ratio of the two enantiomers of limonene determined by GC using an on-line coupling of non-chiral and chiral capillary columns. The ratio of (−)-limonene and (+)-limonene in the genuine mandarin oils was 2.2 to 97.8, while in reconstituted oils the same ratio was 13.4 to 86.6. Addition of reconstituted oils increases the ratio of (--) to (+)-limonene in genuine oils enabling the detection of additions of even 5% of reconstituted oils to genuine mandarin oils.

Raman amplification was demonstrated in the early 1970s, but the invention of erbium-doped fiber amplifiers (EDFA) overshadowed the interest in it. Today, Raman scattering has again become a competitive approach for optical amplification because it is only restricted by the pump wavelength and Raman active modes of the gain medium. Puresilica and germanium-doped silica fibres, currently utilized as Raman gain media in telecommunications, have quite low Raman gain coefficients and a limited usable spectral bandwidth of approx. 5 THz. Therefore, the investigation of materials possessing both large Raman gain coefficients and broader spectral bandwidth than fused silica is becoming necessary to satisfy the increasing telecommunications demands.

In this work, the characteristics of the edge emission of a homoepitaxial diamond sample grown by chemical vapor deposition (CVD) are reported. Photoluminescence has been excited at 220 nm by using a tunable optical parametric oscillator laser, giving ∼5 ns wide laser pulses. The temperature of the sample has been decreased from room temperature down to 30 K. Free exciton emission and its phonon replicas have been observed at all the temperatures explored. Excitonic lifetime shows a nonmonotonic dependence on the sample temperature. Luminescence at low temperatures from electron-hole drops at approximately 5.18 eV has been observed for the first time in CVD diamond.

Catalytic activity of iron based catalysts in the production of multi-walled carbon nanotubes (MWCNTs) has been investigated. The effect of the carbon source (ethane or isobutane), catalyst support (Al2O3 or SiO2), iron loading, catalyst reduction temperature and reaction temperature on yield and quality of carbon products has been examined. The structural and morphological properties of catalyst and carbon products obtained have been analyzed by means of scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy (RS), thermogravimetric analysis (TGA) and X-ray powder diffraction (XRD). The iron-based catalysts supported on alumina seem to be efficient systems for the production of carbon nanotubes from chemical vapor deposition (CVD) of isobutane with very interesting yields. The opportune calibration of reaction parameters, such as iron loading and reaction temperature, can in fact drive the synthesis toward the formation of high quality CNTs.

Three-layer structures consisting of intrinsic/B-doped homoepitaxial CVD diamond grown onto commercial HPHT Ib substrates have been studied by means of Raman spectroscopy and photoluminescence (PL). The intrinsic layers have been deposited, at fixed methane to hydrogen ratio (1%), by systematically changing the substrate temperature (620-820 °C). Raman measurements point out the excellent crystalline quality and phase purity of the samples. Moreover, flat PL spectra in a wide energy range (1.7 eV-2.7 eV) indicate also their great purity. As the free-exciton recombination can be used to further probe the quality of synthetic diamond, measurements of free-exciton emission at room temperature have been also performed. The excitation was produced by a 5 ns pulsed tunable laser irradiation. The results have been compared with the detection characteristics of simple alpha-particle detector prototypes based on the analyzed samples. A clear correlation between excitonic emission and detector sensitivity is demonstrated. On the basis of these results, low methane concentrations (approx. 1% CH4/H2) in the deposition gas mixture and intermediate substrate temperatures (approx. 720 °C-770 °C) have been identified as the best working conditions of our growth reactor.

Multi-walled carbon nanotubes (MWCNTs) are prepared by chemical vapor deposition (CVD) in C2H6 + H2 mixture over 20%Fe/SiO2 catalysts. The effects, in terms of yield and selectivity of the growth process, of the changes in composition (H2 at 0–75%) and flow-rate (100–150 sccm) of gas-mixture, catalyst reduction-temperature (400 °C and 650 °C), temperature (750–850 °C) and duration (0.5−6 h) of the synthesis-reaction are investigated. Although yield to C deposits improves by increasing gas flow-rate, temperature or duration of the synthesis-reaction, and by diminishing H2 volume fraction in growth atmosphere, it never exceeds 90% due to the heavy catalyst encapsulation. Moreover, the results of morphological and structural analyses show that a loss of selectivity towards nanotubes and a deterioration of CNT crystalline quality generally accompany the yield enhancement. This suggests the unsuitability of the ethane decomposition over silica-supported Fe-catalysts to the large-scale production of CNTs. Nevertheless, the nanotubes attained might be profitably used in all applications exploiting the magnetic properties originating from the encapsulated iron. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In this work, a Raman and photoluminescence (PL) study of synthetic diamond films grown by hot filament chemical vapor deposition (CVD) on WC-Co is presented. The changes in the Raman spectrum induced by the different pretreatments of the substrate and/or different growth parameters of the films are discussed. In particular, the spectra of the films grown at 740 degrees C substrate temperature, 36 mbar pressure and 1.7% methane content in the CH4-H-2 gas mixture and after different substrate pretreatments show all the features commonly observed in nanocrystalline diamond films, overlapped with a large PL background. A significant level of compressive stress is qualitatively deduced by the shift of the diamond Raman peaks. The different pretreatments of the substrates seem to have no influence on the quality of the diamond films. On the contrary, in samples grown at 700 degrees C substrate temperature, 10 mbar pressure and 1% methane content in the CH4-H-2 gas mixture, the contribution of the non-diamond carbon phases to the Raman spectrum substantially decreases, even though the diamond Raman peak remains shifted and broad. Impurities in the films have been identified by means of low-temperature PL measurements. Wand Si-related optical centers have been clearly observed, together with a band at approximately 1.967 eV probably connected to a nitrogen-related defect center. Copyright (C) 2008 John Wiley & Sons, Ltd.

We performed experiments on the synthesis of carbon nanotubes (CNTs) by iron-catalyzed chemical vapor deposition (CVD) in C 2 H 6 + H 2 atmosphere. We varied flow-rates of reactant gases (ethane: 30–120 sccm, hydrogen: 0–120 sccm), as well as their ratio, in order to study the evolution of the growth kinetics. We used scanning electron microscopy, high-resolution transmission electron microscopy and Raman spectroscopy to investigate the morphologies, dimensions and crystalline structure of the samples. Our results demonstrate the crucial role played by H 2 in the enhancement of C diffusion-rate and in the consequent development of ordered and smooth graphene layers. A faster growth-rate is achieved by the increase of C 2 H 6 flow-rate. However, if H 2 flow-rate is not adequately enhanced, the improvement is only apparent. The excess of C supplied gives rise to deposition of amorphous carbon onto the CNT walls, and to the co-production of different nanostructures. A substantial agreement is found with results reported for CVD growth of CNTs by the use of different catalysts, reactants and gas-flowing setups.

The achievement of high yields seems to be one of the most pressing demands for large-scale production of carbon nanotubes (CNT). In this work, a demonstration is given in which in the synthesis of CNT by chemical vapour deposition (CVD) higher yields are attained at the expense of crystalline quality and purity of CNT, thus suggesting that an accurate balance of competing factors is necessary for the optimisation of the preparation process. This is accomplished by comparatively discussing the results of morphologic and structural analysis carried out on multi-walled C nanotubes (MWCNT), prepared at 750 °C by CVD in C2H6–H2 mixture over 20% Fe/SiO2 catalyst, in order to clarify the role of the gas mixture composition on the issue of CNT synthesis. The results of Raman analysis, scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) observations are correlated with yield variations and understood in the light of current assessments on CNT growth. Higher ethane/hydrogen flow ratios result in enhanced carbon deposit with amorphous-phase inclusions. Among the values investigated, a dilution of ethane in hydrogen at 50% may represent the best compromise between yield and quality of reaction products.

The results of the quantitative Raman analysis, performed on multi-walled carbon nanotubes produced by iron-catalysed chemical vapour deposition, are utilised for deriving a scaling law for the growth parameters. A semi-empirical approach, already successfully applied to different materials and growth techniques, is utilised and demonstration is given that the reaction outcome, in terms of yield to C deposits and crystalline perfection of nanotubes attained, analytically depends on the growth parameters through a single dimensionless combination of them. Copyright © 2007 John Wiley & Sons, Ltd.

In this work, it is shown that some Raman-active modes may be detected, below 500cm−1, in the spectrum of nanotubes synthesized by iron catalyzed chemical vapor deposition. By comparatively discussing results of Raman, high-resolution transmission electron microscopy, and thermogravimetric analyses, demonstration is given that these spectral features originate from scattering by nanoparticles of iron catalyst encapsulated within the tubes under nonstationary growth regime. Their intensity progressively weakens with increasing carbon supply rate until bands disappear as stationary conditions are reached.

The photoresponse of high quality single crystal diamond films homoepitaxially grown by Chemical Vapor Deposition (CVD) onto low cost diamond substrates has been studied. The time evolution electrical response to the excitation by 5 ns laser pulses at 215 nm closely reproduces the laser pulse shape. The single crystal diamond response is therefore much faster than the laser pulse duration. The output signal is also very stable and reproducible, without significant priming or memory effects. Single crystal diamond films can therefore be grown by CVD having enough high quality to be used as photodetectors. However, a minor slow component shows up in the charge-integrated sample response. A systematic speed up of this slow component when increasing the detector temperature from − 25 °C to + 50 °C demonstrates its thermally activated origin. The slow component is therefore attributed to detrapping effects from shallow trapping centres. A model of the charge transport mechanism in the presence of trapping–detrapping centres can be developed and the results can be compared to the experimental ones. The activation energy of the shallow defects is accordingly determined as E a = 0.4 eV.

In this work, we report on the structural characterization of homoepitaxial Microwave Plasma Enhanced CVD diamond grown onto Ib diamond substrates by varying systematically the methane to hydrogen ratio in the gas mixture (1–7% CH 4 ). X-ray diffraction, Raman spectroscopy and photoluminescence (PL) have been used to characterize the diamond samples. Raman measurements pointed out the excellent crystalline quality and phase purity of the specimens. PL measurements in the 1.7–2.7 eV energy range have shown completely flat spectra, excluding the presence of nitrogen-related optical centers. Such results show that the homoepitaxial CVD diamond can be grown, at moderate microwave power (720 W), and at growth rates not too low (∼ 1 μm/h) preserving a good quality. Moreover, the homoepitaxial crystals exhibited a strong free-exciton recombination radiation at room temperature even at the highest methane concentration used (7%). Preliminary measurements of the lifetime of the free exciton at room temperature have been also performed. The excitation was produced by a 5 ns pulsed laser irradiation at energies above the diamond band gap. The results have been compared with the structural properties of the samples and correlated with the growth conditions.

In this paper, we report on the characterization of homoepitaxial CVD diamond grown onto HPHT Ib diamond substrates by varying systematically the methane to hydrogen ratio in the deposition gas mixture (1–7%) and the microwave power (520–720 W). Growth rates up to approximately 2.2 μm/h have been achieved. X-ray diffraction, Raman spectroscopy and photoluminescence (PL) have been used to characterize the diamond samples. Raman measurements point out an excellent crystalline quality and phase purity of the homoepitaxial specimens even at the highest CH 4 concentration used. Completely flat PL spectra registered in a wide energy range (1.7–2.7 eV) exclude impurity contamination of the diamond samples. Such results show that homoepitaxial CVD diamond can be grown, at moderate microwave power and with moderate growth rate, preserving a good crystalline quality.

Synthetic diamond has been proven as an important material for advanced electronic applications, such as those encountered in high energy physics and astrophysics. In fact, diamond transparency to visible light, its high carrier mobility, high breakdown field and strong resistance to chemical attack and radiation damage have suggested the potential application of this material for ‘solar-blind’ UV detectors which have to operate in extreme environments. To avoid the possible problems connected with the presence of grain boundaries in polycrystalline diamond films, a great effort has been devoted to the optimization of the growth process leading to high-quality single-crystal diamond on diamond substrates (homoepitaxy). In this view, characterization studies play a crucial role, because they provide the feedback for the optimization of the deposition process, in order to obtain the best quality material. In this work, a characterization study of homoepitaxial diamond grown by chemical vapor deposition (CVD) on synthetic diamond substrates is presented. The samples have been deposited in a CVD tubular reactor using a CH 4 –H 2 gas mixture (1–7%) at approximately 560 °C substrate temperature. The growth rate ranged between 0.9 μm/h and 2.2 μm/h, microwave powers between 520 W and 720 W. The crystalline quality of the diamond layer has been studied by means of Raman spectroscopy. Photoluminescence has been used to study the nature and the distribution of impurities, having energy levels in the diamond band gap, which influence negatively the electronic quality of the material. The results have been compared with electro-optical characterization of UV detectors for astrophysics based on the analyzed diamond samples. The growth parameters which guarantees both high material quality and optimal device response have been determined.

We use laser beams with radial and azimuthal polarization to optically trap carbon nanotubes. We measure force constants and trap parameters as a function of power showing improved axial trapping efficiency with respect to linearly polarized beams. The analysis of the thermal fluctuations highlights a significant change in the optical trapping potential when using cylindrical vector beams. This enables the use of polarization states to shape optical traps according to the particle geometry, as well as paving the way to nanoprobe-based photonic force microscopy with increased performance compared to a standard linearly polarized configuration. (C) 2012 Optical Society of America