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In this work we show the development and assessment of disposable, biocompatible, fully plastic microreactors, which are demonstrated to be highly efficient for performing on-chip direct PCR analyses of very diverse crude biological samples, such as human cells, whole blood, buccal scrape and hair bulbs, without requiring any purification steps before PCR analyses.

We performed thermo and piezoresistive measurements on GaN bulk samples grown with different techniques (PIMBE, MOCVD). By analysing the I(V) characteristics as a function of temperature, we found a temperature coefficient of resistance (TCR = a) of the same order of magnitude (a few percent per °C) as commercial thermistors, with a peak value of 19%/°C. The measured gauge factor is about five, a value comparable with that obtained for GaN by other groups. We also performed PC vs. temperature measurements on a MQW GaN/AlGaN finding a peak shift of about 0.4 meV/K.

We report measurements of hot-carrier photoluminescence from GaAs V-groove quantum wires. CW spectra reveal distinct one-dimensional subbands: at low excitation density recombination from laterally confined nv=1 states is dominant, which shows that carriers relax efficiently to the lowest subband; nv=2 and 3 recombination becomes pronounced at higher temperature and density, which indicates inhibited relaxation, possibly due to band filling. Time-resolved photoluminescence measurements at 10 K show a rise time of approximately 100 ps, which is due to energy relaxation. At later times the intensity of the nv=1 line shows a monotonic decay at low carrier density, but there is a nv pronounced plateau at high density that extends for approximately 200 ps. These results provide clear evidence of carrier relaxation and band filling in quantum wires.

Availability of reliable and quick methods to investigate defects and polarity in GaN films is of great interest. We have used photo-electrochemical (PEC) and hot wet etching to determine the defect density. We found the density of whiskers formed by the PEC process to be similar to the density of hexagonal pits formed by wet etching and to the dislocation density obtained by transmission electron microscopy (TEM). Hot wet etching was used also to investigate the polarity of MBE-grown GaN films together with convergent beam electron diffraction (CBED) and atomic force microscopy (AFM). We have found that hot H 3 PO 4 etches N-polarity GaN films very quickly resulting in the complete removal or a drastic change of surface morphology. On the contrary, the acid attacks only the defect sites in Ga-polar films leaving the defect-free GaN intact and the morphology unchanged. The polarity assignments, confirmed by CBED experiments, were related to the as-grown surface morphology and to the growth conditions.

In this work a new approach is introduced for surface properties control by laser texturing process. By UV laser irradiation, we are able to control the surface wettability of a chitosan polymeric film in which is introduced a chloroauric acid salt by immersion. Specifically the UV irradiation is responsible for the creation of gold nanoparticles at the irradiated surface of the polymeric film. This photolytic process allows us to localize and design accurately surface patterns and moreover to tune metallic particle size in the range of nanoscale. After the characterization of our gold textured surfaces by atomic force and scanning electron microscopies, we demonstrate the link between wettability surface properties and gold nanoparticles size. The experimental results indicate the influence of the laser intensity, the irradiation time and the polymer film thickness (by increasing the gold concentration) on the gold nanoparticle density and size.

We have fabricated amorphous hydrogenated carbon films by rf plasma enhanced chemical vapor deposition with very low ion bombardment energy. We demonstrate that the optical gap of the films can be tuned in a wide range, from 3.46 up to 4.95 eV, i.e., close to the diamond gap ~5.5 eV!, by proper control of the negative dc self-bias voltage. This behavior suggests that a dramatic reduction in the content and clustering of the sp2 sites occurs by lowering the ion bombardment energy.

We have studied the recombination mechanism of InGaAs/GaAs V-shaped quantum wire lasers under electrical injection and in high magnetic field, from well below to above lasing threshold. The emission originates from free-carrier recombination independent of temperature and injection density. No excitonic contribution is found, indicating that excitons are weakly bound in these wires due to the internal piezoelectric field causing a strong Stark effect. A quantitative analysis of the piezoelectric field is performed by measuring the screening induced blue-shift of the electroluminescence at different densities and comparing it with the piezoelectric potential calculated from the quantum wire cross-sections observed by transmission electron microscopy. (C) 1999 Elsevier Science Ltd. All rights reserved.

Polymer films embedding cadmium thiolate precursors have been irradiated with ultraviolet laser pulses resulting in the formation of cadmium sulfide crystalline nanoparticles through a macroscopically non-destructive procedure for the host matrix. Controlling the number of the incident laser pulses, the gradual increase of the size of the nanoparticles is accomplished, and consequently the progressive change of the emission characteristics of the formed nanocomposites. The X-ray diffraction and transmission electron microscopy measurements were used for the full characterization of the nanoparticles. This study compares two polymer matrices, poly(methyl methacrylate) and a cyclic olefin copolymer, and reveals the importance of each one for the emission characteristics of the formed cadmium sulfide nanocrystals. It is found that the poly(methyl methacrylate) matrix contributes to the increase of the trap states on the surface of the formed nanocrystals, causing the broadening of their emission. On the other hand the cadmium sulfide nanoparticles, grown into the cyclic olefin copolymer matrix, exhibit narrower emission spectra.

In this work, we studied the effect of some growth parameters on the polarization behavior of InAs/GaAs closely stacked quantum dot (CSQDs). In particular, we focused on the surface reconstruction time of GaAs spacer, its thickness and the number of QD layers. We found that the most effective parameter to enhance the TM/TE intensity ratio is the surface reconstruction time of the GaAs spacer before the subsequent QD deposition. By varying this parameter between 20 s and 120 s, a TM/TE ratio as high as 0.86 has been achieved. A further fine tuning of GaAs spacer thickness and QD layer number increased this ratio up to a value of 0.92 in structures containing only 3 QD layers.

In this contribution we report on an optical nonlinearity featuring colloidal seeded grown CdSe/CdS nanorods (NRs). It consists of a photoluminescence (PL) blueshift of single rod spectra with increasing laser power and a transient, power-dependent redshift of the spectra studied by time resolved PL measurement, strictly related to the multicarrier scattering occurring at high excitation density. We attribute this nonlinearity to a photo-induced screening of an internal field, originating from the piezoelectric polarization induced at the core/shell interface.

We present a novel model of the dielectric cubic corner, that is suitable for inclusion in a standard electromagnetic (EM) simulator. The model starts from a consideration of the equivalent current densities on the cube facets. It proceeds by employing a classical multipole expansion of the Green's function at the corner and introduces the novel principle of simultaneous transverse resonance diffraction (STRD) in order to determine the order of singularity. The theory is validated by numerical simulations, yielding information about the accuracy of the near field around a 90 deg. dielectric corner.

We report the excitation spectrum of a similar to 185 nm thick layer tris-(8-hydroxyquinolate)-aluminium, vapour deposited on a 100 mu m thick borosilicate microscopy cover glass, in the 1.9-2.4 eV range using a conventional cavity-ringdown spectrometer setup. The spectrum is collected at room temperature in ail open cavity. It shows abroad loss structure with a maximum around 2.1 eV and a width of similar to 0.2 eV. The spectrum is in conformity with literature phosphorescence spectra and with literature TDDFT Computed T-1

We have developed an all-polymer procedure for sub-microscale large area patterning of fused silica plates based on electron beam lithography. The procedure relies on the use of a high sensitivity resist, negative tone epoxy-based SU-8 and a conducting polymer, a doped PDOT, as the electron discharge layer. The chemically amplified resist SU-8 allows for a five-fold increase in exposure speed as compared to standard PMMA, and the PDOT layer makes it possible to avoid the time-consuming deposition of a metallic layer and its critical removal. Gratings of stripes and pillars, possibly useful for the realization of photonic devices, are demonstrated.

In this work. we show the fabrication of colloidal nanocrystals (NCs) based waveguide photonic devices by exploiting a new lithographic approach for the nano-positioning of NCs. Our approach relies on the dispersion of CdSe/ZnS core/shell NCs into a layer of electro-sensitive resist (poly-methyl methacrylate, PMMA), which is subsequently patterned by means of electron beam lithography (EBL). This localization technique has been demonstrated by detecting high-resolution photoluminescence (PL) maps on an e-beam nano-pattemed PMMA/NCs film through a confocal microscope. This technique has been exploited for the fabrication of distributed feedback (DFB) structures and distributed Bragg reflectors (DBR) suitable for the realization of in-plane waveguide lasers. A DFB structure has been obtained by patterning a periodical grating on a PMMA/NCs ridge waveguide. Two DBR have been similarly fabricated by creating quarter-wavelength thick alternated stripes of air and active blend; these structures have been exploited as front and back mirrors of an in-plane PMMA/NCs ridge cavity. In both cases, no following etching processes have been required. thus simplifying the steps needed for the fabrication of NCs based active photonic devices. (C) 2006 Elsevier B.V. All rights reserved.

The interest in research on inorganic colloidal nanoparticles has moved to more complex structures, such as anisotropically shaped particles and branched objects. Recently, schemes for the synthesis of heterostructures have also been presented. In this article we discuss the synthesis conditions for spherical and branched nanoparticles. The influence of parameters as temperature and composition of the mixture of surfactants on the shape of the growing particles is discussed. Also, an overview on different approaches for the formation of heterostructures is presented briefly. (C) 2006 Elsevier B.V. All rights reserved.

Planar nanoscopic contacts are observed to undergo early electrical breakdown. The authors show that the cause is high field emission capable of triggering electromigration. The phenomenon is well described by an empirical current-voltage law, well different from that usually found in nonflat field emitters; this is attributed to the particular geometry of the contacts. Although the mathematical form of the law is always the same, the intensity of breakdown current changes from sample to sample, ranging over several orders of magnitude; this is explained by the nanoscopic roughness of the emitting surfaces. They also show that the occurrence of breakdown may be dependent on the polarity of the applied voltage.

Microphotoluminescence studies of annealed In(x)Ga(1 − x)N(y)As(1 − y)/GaAs quantum wells fabricated by molecular beam epitaxy for optical emission in the 1.3 µm spectral range revealed several sharp peaks about 2–7 meV wide in the emission spectra. The intensity of the discrete lines decreased strongly with increasing lattice temperature and was absent in as-grown (unannealed) quantum wells. Such quantum dot-like emission lines are attributed to the recombination of excitons strongly localized at alloy fluctuations composed of In–N-rich clusters.

We study the optical properties of dithienothiophene functionalized with lateral dimesitylboryl groups and/or oxygen atoms at the central thienyl sulphur atom. The excitation energies, of these systems are computed using first-principles time-dependent density functional theory, and the results are discussed and compared with measured absorption spectra. The agreement between theoretical and experimental results is very good. It is found that the oxygen and the boron functionalization modifies the lowest unoccupied molecular orbital, and thus optical properties, in a different way. Moreover if the boron and the oxygen functionalization are combined together, the effects of the former dominate. (c) 2006 Elsevier B.V. All.rights reserved.

While ITO has proven a succesful transparent anode material for laboratory-based investigations of OLEDs, it is perhaps less suited to large-scale production. Here we show that float glass with an evaporated gold coating functions extremely well as the transparent anode for OLEDs. We discuss the production of an ultrathin conductive gold layer in terms of the roughness and surface energy of the float glass. We demonstrate large area OLEDs based on these substrates, in particular a green-emitting device using spin-coated films of Poly[(9,9-dioctylfluorenylene-2,7-diyl)-co-(1,4-diphenylene-vinylene-2-methoxy-5-{2-ethylhexyloxy}-benzene)] as the active layer, and a white-emitting device using, as the active layer, spin-coated films of Poly(9-vinylcarbazole) doped with the phosphorescent materials Iridium bis(2-(4,6-difluorophenyl)pyridinato-N,C2′)picolinate and Iridium bis(2-(2′-benzothienyl)pyridinato-N, C3′)(acetylacetonate). Atomic force microscopy was used to investigate the morphology during each stage of OLED fabrication. We show that large area OLEDs can be fabricated on such substrates, with the area limited by the deposition techniques used.

Phosphorescent materials represent an attractive route to high-efficiency organic LEDs, since their maximum theoretical quantum efficiency is 100%, compared to the 25% of fluorescent materials. We have studied the electronic structure of three phosphorescent iridium complexes, the red-emitter Iridium bis (2-(2′-benzothienyl) pyridinato-N, C3′) (acetylacetonate), the blue emitter, Iridium bis(2-(4,6- difluorophenyl) pyridinato-N,C2′) picolinate, and the green emitter Iridium tris (2-(4-totyl)pyridinato N,C2) using electron spectroscopies. The materials were evaporated in-situ onto a clean gold substrate in ulta-high vacuum. The valence band electronic structures were investigated using resonant photoemission, with the unoccupied states determined using X-ray absorption. The data suggests a hybridisation of the Ir 5d states with the π orbitals of the ligand. NEXAFS spectra are shown to be highly sensitive to the local environment.

In this paper we have tested two different procedures (the “three-step” and the “four-step” procedures) for the covalent immobilization of glutamate dehydrogenase (GDH) onto silicon supports. Atomic force microscopy (AFM), Fourier-transform infrared spectroscopy (FT-IR), fluorescence spectroscopy and an enzymatic assay were used to probe the structure and activity of the immobilized enzyme. Our results demonstrate that coupling through the “three-step” procedure does not significantly affect either the fold pattern or the activity of the enzyme, suggesting that this method could be ideally suited to the development of high quality monolayers for use in enzyme-based planar biosensors.

Synchrotron radiation photoemission and X-ray absorption spectroscopy (NEXAFS) have been used to investigate the electronic structure of evaporated films of the phosphorescent organic iridium complexes iridium tris-(2-(4-totyl)pyridinato-N,C 2 ), iridium bis(2-(4,6-difluorophenyl)pyridinato-N,C 2 )picolinate, and iridium bis(2-(2′-benzothienyl)pyridinato-N,C 3 )-(acetylacetonate) and spin coated films of these materials in a polymer host. Resonant photoemission at the Ir N 6,7 edge indicates that the Ir 5d states are hybridised with the π orbitals of the organic ligands, in agreement with recent calculations. The nitrogen K-edge NEXAFS shows the difference in the unoccupied orbitals induced by the acetylacetonate group compared to those of the pyridinate ligands. Although the valence bands of the ex situ prepared films are not accessible to photoemission, the Ir 4f core levels remain visible, and demonstrate that the polymer host serves to lower the electron injection barrier in the iridium complexes in comparison to the pure films.

A substrate is presented as an alternative to indium tin oxide as the anode material for organic light-emitting diodes. We show that float glass, the material most commonly used in window glass, with a thin transparent evaporated gold layer, provides a cheap, and readily available alternative. Bright organic light-emitting diodes emitting in the white, and near white, are demonstrated, using a spin coated blend of phosphorescent iridium complexes doped into a suitable polymer host, as the emissive layer. The emission colour of these blends is shown to be tunable from the blue to the red, dependant on the relative concentrations of the two phosphorescent molecules.

Covalent immobilization of glutamate dehydrogenase (GDH) onto activated Si/SiO 2 supports was analyzed by both atomic force microscopy (AFM) and an enzymatic assay. When the concentration of 3-aminopropyltriethoxysilane used in the first derivatization step of the silicon surface was decreased, the specific enzymatic activity also decreased, whereas the mean roughness increased. Thus, the activity of immobilized GDH is critically dependent on the conditions for surface derivatization, and is inversely correlated with surface roughness.

We report on the folding properties of the protein azurin, deposited onto SiO2 surfaces and subsequently dehydrated. The molecular films have been maintained at ambient conditions through several days, and the ageing effects have been investigated by fluorescence spectroscopy. The experimental results show a modest initial conformational rearrangement, followed by long-term stability. Interestingly, upon rehydration of the biomolecular films at the end of the investigated period (approximately one month), azurin returns to exhibit a native-like conformation. This study indicates a rather surprising resilience of proteins to ambient conditions and sheds a somewhat unexpected positive light on reliability in biomolecular electronics. (C) 2005 Elsevier B.V. All rights reserved.

We report on the fabrication of hybrid organic-inorganic vertical microcavities by using imprint lithography tools. The device consists of an organic active layer (rubrene-PMMA blend) embedded between two dielectric distributed Bragg reflectors (DBR). The active organic layer was spin coated on the first DBR, whereas a SU8 lithographic pattern was realized on the second DBR, which was used as the imprint mold. The two parts were then assembled together in an imprint process in order to create a vertical microcavity constituted by the rubrene active layer between two high-reflectivity mirrors. The effectiveness of this technology is demonstrated by the room temperature photoluminescence spectra, recorded on the fabricated microcavity, which show a sharp emission peak at the microcavity resonance wavelength.

We report a study of a series of heavy rare earth tris-8-hydroxyquinolines (REQ3s), using UV-visible absorption spectroscopy, infrared absorption spectroscopy, and photoluminescence (PL) measurements. We show that the heavy REQ3s are all chemically similar to each other and to aluminium tris-8-hydroxyquinoline, at least in terms of the ligand behavior. Characteristic rare earth 4f–4f luminescence is only observed for ErQ3 and YbQ3 due to the relatively low energy of the ligand triplet state. We show that a triplet transfer mechanism cannot be responsible for the observed Yb 4f–4f luminescence observed in YbQ3. Instead, an internal chemiluminescent process is shown to be energetically favorable. The thin film PL spectra of all the heavy REQ3s are dominated by triplet emission, except for that of ErQ3, for which transfer to the Er3+ ion represents an efficient alternative. The PL spectra of powder samples, which would be expected to consist of approximately equal amounts of both isomers, are dominated by singlet emission. This is in contrast to the results from the thin films, and suggests that the isomer which predominates in the thin films has a much higher intersystem crossing rate than the other isomer.

Modifications of the optical properties of dimethyl-dithienothiophenes due to the oxygen functionalization of the central sulfur atom are investigated. We have measured the absorption, photoluminescence ~PL! and PL excitation spectra, the PL quantum efficiencies, and the PL decay times. These experimental results are interpreted and compared with first-principles time-dependent density-functional theory calculations, which predict, for the considered systems, excitation and emission energies with an accuracy of 0.1 eV. It is found that the oxygenation strongly changes optical and photophysical properties. These effects are related to the modifications of the energetically lowest-unoccupied molecular orbital and the energetically second highest occupied one, which change the relative position of the two lowest singlet and triplet excited states.

Oligomer molecules offer a number of advantages for the study of their photo-physical properties and for the application to optoelectronic devices. We investigated the optical properties of a substituted quinquethiophene by first-principles calculations, determining the absorption and the emission energies, and compared these to the experimental data. The optical gain properties of the oligomer were exploited for the realization of a solid-state laser device exhibiting single-mode emission at 637 nm , with a full-width half-maximum of about 0.7 nm and a pump fluence threshold as low as 220 μJ / cm 2 .

This work explores the conditions to obtain the extension of the PL emission beyond 1.3 μm in InGaAs quantum dot (QD) structures growth by MOCVD. We found that, by controlling the In incorporation in the barrier embedding the QDs, the wavelength emission can be continuously tuned from 1.25 μm up to 1.4 μm at room temperature. However, the increase in the overall strain of the structures limits the possibility to increase the maximum gain in the QD active device, where an optical density as high as possible is required. By exploring the kinetics of QD surface reconstruction during the GaAs overgrowth, we are able to obtain, for the first time, emission beyond 1.3 μm from InGaAs QDs grown on GaAs matrix. The wavelength is tuned from 1.26 μm up to 1.33 μm and significant improvements in terms of line shape narrowing and room temperature efficiency are obtained. The temperature-dependent quenching of the emission efficiency is reduced down to a factor of 3, the best value ever reported for QD structures emitting at 1.3 μm .

The typical size of a single molecule is of the order of a few nanometres; for this reason metal electrodes separated by a nanometre-scale channel are required to make molecule-based electronic devices. In this work, we report on the fabrication of metallic (Cr/Au, Ti/Au or Ti/Pt) arrow-shaped electrodes on Si/SiO2 substrates, with tip separation between 100 and less than 10 nm. They can be used to implement two and three terminal molecular devices, just by connecting them by the chosen molecules and adding an Ag electrode on the back of the Si substrate. Electron beam lithography (EBL) allowed us to obtain electrodes with separation around 40 nm. In order to reduce the tip separation down to 20 nm, before the EBL process, we used a defocused e-beam to brush the poly(methylmethacrylate) (PMMA) layer for a short time (from 10 to 40 s). The smallest gap between the electrodes (less than 10 nm) was obtained with standard EBL and lift-off followed by Au electroplating deposition. The fabricated devices were inspected by plan-view scanning electron microscopy (SEM) and electrically tested by I/V measurements in the range ±2 V. Open-circuit characteristics gave very low currents (in the range −10 to 10 pA) and a resistance ≈1 T. As a typical example, we demonstrate a field effect transistor (FET) based on a deoxyguanosine derivative (a DNA base) placed between the fabricated planar electrodes by room temperature (RT) cast deposition. The FET device tested at RT and ambient pressure exhibited a maximum voltage gain as high as 0.76.

In this study we report a systematic investigation of phthalocyanine (Pc) optical properties, showing that the effect of re-absorption of fluorescence plays a critical role in the line-shape of Pc optical spectra. We demonstrate that a strong dependence of the photoluminescence parameters on the concentration of phthalocyanines solution accounts for the apparent experimental evidence of a fluorescent dimer band in the emission at high concentrations. Despite a model based on fluorescent aggregates seems to describe the photophysical behavior of the system, additional experiments, such as electronic absorption spectroscopy, and fluorescence spectroscopy in which the optical pathlength inside the solution is suitably modified, provide a correct explanation of the observed optical behavior. We demonstrate that the shapes of optical spectra are completely independent on phthalocyanine aggregation state and are due only to experimental artifacts, i.e. inner filter effects. (C) 2004 Elsevier B.V. All rights reserved.

We report singlet and triplet electronic excitations in oligomers of thiophene using a state-of-art ab-initio approach, i.e. the approximated coupled cluster singles and doubles method. This highly correlated and size-consistent method is required to correctly describe excitonic effects in such strongly confined systems. We show that this approach provides an excellent accuracy in reproducing absolute values and chain-length evolution of excitation energies as compared with recent photo-detachment photoelectron spectroscopy measurements. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We report a first-principles Time-Dependent Density-Functional Theory (TD-DFT) study of a new class of organic molecules, namely the branched Benzo[b]Thiophenes. We calculate excitation energies at different levels of theory, in order to evaluate the influence of excitonic contributions. We found a significant difference between the TD-DFT results obtained using a local or an non-local exchange-correlation energy functional: the latter is required to correctly describe intramolecular chargetransfer contributions, which we found to be present in these molecules. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A detailed analysis of the excitonic transitions of 8 InGaAsP MQWs grown by MOCVD into a InGaAsP barriers with different composition has permitted to experimentally determine the band offset for InGaAsP/InGaAsP heterostructures. We find a value of about 44% referred to the valence band, which is lower than the value reported for unstrained structure (≈ 56%) and in good agreement with the value estimated by a theoretical model specifically developed to design the structure. Additionally, we compared the values of the activation energies, obtained from the fits to exciton transition PL intensity, with the carrier confinement energy evaluated theoretically. The obtained activation energies confirms that in such heterostructures the unipolar detrapping of carriers is more efficient than the exciton escape. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In this work we have studied the role of excitons in two different low barrier metal–semiconductor–metal (MSM) GaN-based UV photodetectors at high temperature. The active material of the two MSM devices consists of bulk GaN grown by metal organic chemical vapour deposition (MOCVD), and of an AlGaN/GaN heterostructure forming a two-dimensional electron gas (2DEG) grown by molecular beam epitaxy/magnetron sputtering epitaxy (MBE/MSE) system. The response of the devices has been characterized at the wavelength of 325 nm (He–Cd laser) as a function of the temperature in the range between room temperature and 700 K. The Arrhenius plot obtained by the decay times of the photocurrent allowed us to calculate the activation energies of some trapping mechanisms responsible of the persistent photocurrent (PPC). This shows that in both device the GaN excitonic resonances provide the most important contribution to the PPC on the millisecond time scale at low temperature. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Electron beam lithography (EBL) and lift-off process have been used to fabricate two- and three-terminal nano-devices consisting of metallic (Cr/Au, Ti/Au or Ti/Pt) arrow-shaped electrodes on Si/SiO 2 , with tip separation between 100 and less than 10 nm. Standard EBL process allowed us to obtain nanotips with separation around 40 nm. In order to reduce the tip separation down to about 20 nm, before the EBL process, we used the defocused e-beam to brush the PMMA resist for a precise time (10÷40 s). A further reduction of the tip gap (less than 10 nm) is obtained by Au electroplating deposition. The nanotips were electrically characterized by current–voltage ( I – V ) measurements in the range ±2 V. In a typical I – V measurement in air of an “open-circuit” nanodevice, no significant current is observed (current range −10÷+10 pA, “open circuit” resistance≈1 TΩ) confirming the success of the technological process.

Thin films of the rare earth tris(8-hydroxyquinolines) YbQ 3 and ErQ 3 were evaporated in ultra-high vacuum, and studied by X-ray photoelectron spectroscopy (XPS). Evaporation was monitored by mass spectroscopy of the major cracking products, which have masses >200 a.m.u. and show further splitting due to wide isotope distributions. C and N 1s XPS data are very similar to those of aluminium tris(8-hydroxyquinolines), implying very similar ligand behaviour, while the O 1s binding energy was significantly higher, indicating a more ionic metal–oxygen bond. YbQ 3 was found to be completely trivalent, with no indication of the mixed valence behaviour observed in other Yb compounds.

A reproducible technique to fabricate nanojunctions by combining electron beam lithography and lift-off process is reported. Brushing the poly(methyl methacrylate) (PMMA) layer for a precise short time t with a defocused electron-beam allows the fabrication of planar nanoelectrodes with inter-electrode distances in the range 10-200 nm, by applying a lift-off process after the exposure. Nanotips fabricated by electron beam lithography (EBL) are good probes for transport experiments on single molecules and molecular layers but the nanodevices have to be carefully designed, tested and managed, in order to avoid damage of nanoelectrodes and SiO2 breakdown.

In this paper we report results obtained in the fabrication and use of novel coded diffractive nano-optics that, beyond focusing, can perform new optical functions. In particular, the intensity of light in the space beyond the optical elements can be redistributed with almost complete freedom. These novel X-ray optical elements have been tested and found to perform multi-focusing in single or multiple focal planes and beam shaping of a generic monochromatic beam into a desired continuous geometrical pattern. Already available extreme ultraviolet and X-ray sources are suitable as ideal sources for such diffractive optical elements. Their new optical functions have been tested in differential interference contrast microscopy and we suggest their use also in maskless lithography and chemical vapour deposition induced by extreme ultraviolet and X-ray radiation.

We have developed a method to quantitatively measure the absolute composition of nanometer sized capped quantum dots in semiconductor alloys. The method uses spatially resolved electron energy-loss spectroscopy in a scanning transmission electron microscope to measure compositional profiles across the center of the quantum dot and the adjacent nanometer wide wetting layer. The measurements from the wetting layer are used to derive a spatial broadening function which includes the effects of probe size, instabilities and beam spreading in the sample. This broadening function is employed to simulate compositional profiles from the quantum dots. Information on the dimensions of dots is extracted from annular dark-field images. The method is applied to In y Ga 1− y As ( y =0.5) quantum dots grown on a GaAs substrate. In this system, a simple truncated cone model is found to give an adequate description of the compositional variations across the dot. We find a substantial enrichment in In at the center of the dots, in agreement with theoretical predictions.

Inhomogeneous broadening is a long standing issue in the physics of nanostructures, in that it prevents the detailed assessment of their electronic and optical properties, and limits the performances of nanostructure based devices. Advances in scanning probe spectroscopies have recently permitted to overcome this problem, thus opening the way to a detailed understanding of the single nanostructure properties, by virtue of their unsurpassed capability to inject carriers or photons at local scale. In particular, luminescence spectroscopy and current-voltage spectroscopy following highly localized carrier injection by a scanning tunneling microscope into a single quantum dot (QD), are the methods of choice to overcome the inhomogeneous broadening effects due to size and compositional non-uniformity. In this way one can map the eigenstates of a single dot, elucidate the relationships between carrier injection, capture and recombination, investigate the dynamics of single-dot filling, the formation of excitons and charged excitons, the occurrence of dot-dot interactions leading to molecular states, and the diffusion of charges into neighboring dots in a grand ensemble.

We present the results of effective mass calculations for the optical properties of single and stacked InGaAs quantum dots (QD) in the presence of a longitudinal electric field. We have empirically included the effect of inhomogeneity in the In distribution. This effect leads to inverted electron-hole mean vertical positions (i.e. the holes lay above the electrons). We have calculated the variation of the fundamental interband transitions with the electric field, as well as the absorption spectrum, taking into account Gaussian fluctuations in the vertical and lateral dimensions.

A study of the electron-hole relaxation dynamics in metalorganic chemical vapour deposition (MOCVD)-grown InGaAs/GaAs quantum dots (QDs) emitting at 1.3 mum is presented. The photoluminescence (PL) rise and decay times are measured as functions of carrier density and temperature, showing that the electron-hole relaxation into the QD ground state occurs within a few picoseconds. We find that the emission of two longitudinal optical (LO) phonons is the dominant capture process at room temperature, whereas carrier-carrier scattering dominates the relaxation process at low temperatures and high carrier densities. Finally, the MOCVD-grown QD structures show relatively small PL quenching; the quenching is caused by thermal carrier escape from the QD ground state via absorption of two LO phonons.

We present a combined theoretical and experimental analysis to describe the interplay between polarization field, charge screening and radiative and non-radiative recombinations in GaN-based nanostructure. The theoretical analysis is obtained by coupling a self-consistent solution of Schrodinger and Poisson equations to determine the electronic states in the nanostructure with a rate equation model to account for time-dependent effects of charge re-arrangement. Experimental results are obtained for high quality GaN–AlGaN multiple quantum wells by means of both CW and time resolved photoluminescence techniques. We demonstrate that PL emission is influenced by charge accumulation in the well, and loss of carriers from the ground level induced by both radiative and non-radiative recombination processes.

In this talk I will report on nanotechnological strategies to fabricate electronic devices based on guanosines and guanosine-oligothiophenes complexes. Self assembled mono layers were produced by physisorption or chemisorption by cast deposition and slow solvent evaporation. Guanosine molecules were modified in order to promote their stable chemical anchoring onto gold or silicon surfaces. Molecular self assembled monolayers were tested by Atomic force microscopy and scanning force spectroscopy in order to check the ordering and aggregation properties of immobilized guanosines. Scanning tunneling spectroscopy in UHV were performed in order to map the electronic configuration and/or modification of guanosines and guanosine-complexes deposited onto conductive surfaces. On the base of these results both bare molecules and gold nanoparticles covered by guanosine ribbons were produced and trapped inside interdigitated electrodes and mesa junctions for I/V measurements and device formance testing.

In this paper it is reported a novel approach for the fabrication of polymeric microtubes based on the combination of semiconductor strain released thin films and Layer-by-Layer (LbL) deposition technique. The structure consisting of a LbL self-assembled polylectrolytes (PEs) film deposited onto a strained GaAs/InGaAs bilayer, was properly patterned and structured to enable the self rolling of an array of channels of different lengths. Then, the semiconductor film, acting as a sacrificial template, was selectively etched to obtain polymer microtubes. The so-realized polymeric channels were characterized in detail using Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). Additionally, such microtubes were analyzed by confocal microscopy to prove the successful incorporation of a dye molecule within the polymeric nanowalls.

Nature Communications 4: Article number: 1778 (2013); Published: 30 April 2013; Updated: 26 November 2014. In the key to Fig. 2a of this Article, the units for the control intensity were inadvertently given as mW instead of μW. The correct version of Fig. 2 appears below. Figure 2

Self-organized, vertically stacked 1-D (quantum wires) and 0-D (quantum dots) low-dimensional materials can exhibit different optical and structural properties by virtue of the different strength of coupling, which is related to the thickness of the barrier layers. In this work these properties have been investigated for InxGa1−xAs/GaAs self-organized quantum structures using photoluminescence spectroscopy and transmission electron microscopy. In the case of the wires, the reduced thickness of the barrier does not influence the structural properties but just splits the uncoupled levels into symmetric and antisymmetric levels. In the case of the quantum dots, a critical change of the structural properties has been observed; in particular, a transition of the InxGa1−xAs quantum well from fully developed and defect free quantum dots to completely incoherent islands has been found as a consequence of the reduction of the barrier layer thickness.