Search

X-ray photoresponse of κ-Ga2O3 is investigated for the first time. Results show that κ-Ga2O3 is a versatile material for the development of high-performance direct X-ray detectors.

In this paper, we investigate the use of dielectrophoresis to align germanium nanowire arrays to realize nanowire-based diodes and their subsequent use for bio-sensing. After establishing that dielectrophoresis is a controllable and repeatable fabrication method to create devices from germanium nanowires, we use the optimum process conditions to form a series of diodes. These are subsequently functionalized with an aptamer, which is able to bind specifically to the spike protein of SARS-Cov2 and investigated as a potential sensor. We observe a linear increase in the source to drain current as the concentration of spike protein is increased from 100 fM/L to 1 nM/L.

The metal nanoparticle size and shape impact the plasmonic enhancement of Raman and photoluminescence (PL) spectra of monolayer and few-layer MoS2 decorated with them. The plasmonic enhancement is investigated for Ag nanotriangles (NTs or nanoprisms) of different sizes in comparison to Ag nanospheres (NSs) at room temperature. After the decoration with Ag NTs, the intensity of both Raman modes of MoS2 increases up to 6.8 times. The u-PL spectra of bare MoS2 show the presence of the A and B exciton bands as well as of a weak trion component. After covering the flakes with 50 nm Ag NTs, the highest integrated PL enhancement factors are 2.9 and 2.1 under 532 and 405 nm excitations, respectively. The revealed shape effect is that Ag NTs provide much stronger Raman and exciton emission enhancement than Ag NSs, which is due to the generation of plasmonic hot spots near the sharp edges and tips of NTs. Another mechanism of enhancement is the plasmonic coupling between the neighboring Ag NTs that causes the generation of hot spots in the gap between NTs. The revealed size effect is a decrease of Raman and PL enhancement with an increase in size of Ag NTs or NSs, which is due to an increase in radiative damping of plasmon oscillation occurring with an increase in nanoparticle size. The important feature is a strong enhancement of the A-trion component after decorating MoS2 with Ag nanoparticles. The phenomenon may be explained by the surface-plasmon-mediated generation of hot electrons in Ag nanostructures, which then inject to MoS2 flakes. This work gives new fundamental insights into the physical mechanisms of light-matter coupling in hybrid twodimensional (2D) semiconductor/plasmonic nanoparticle structures, which are highly promising for next-generation optoelectronic and nanophotonic devices.

This paper presents the synthesis and functionalization of carbon nanotubes (CNTs) with amino groups to prepare sensors for detecting explosives, in particular nitroaromatic explosives such as TNT. CNTs have been rown by aerosol-chemical vapor deposition (A-CVD) technique and analyzed by SEM, TEM Raman and IR spectroscopy methods. Very smooth and long CNTs with good electrical conductive properties have been obtained. Two steps of functionalization process have been performed, oxidation and amidation. Infrared absorption and elemental analysis confirmed the successful functionalization of the CNTs. 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the Fabrication, Properties and Applications of Nano-Materials and Nano-Devices.

Chemical vapor deposition has been demonstrated to be the most efficient, versatile and reliable technique for the synthesis of monolayers of transition metal dichalcogenides. The use of organic promoters during the growth process was a turning point in order to increase the monolayer lateral size or to obtain complete coverage of the growth substrate. In this work we clarify the influence of the promoter gradient on the growth dynamics of MoS2. In particular, we place a sacrificial substrate covered with a promoter (a low sublimation-temperature perylene-based compound) downstream with respect to the growth substrate in order to maximize its gradient on the growth substrate through upstream diffusion. We demonstrate that the morphology and the number of layers of MoS2 are drastically affected by the distance of the growth substrate from the promoter sacrificial substrate. The farthermost area from the promoter substrate presents micrometric MoS2 triangular monolayers and large low hierarchy dendritic multi-layer structures. On the contrary the closest area reveals an almost continuous polycrystalline MoS2 monolayer, with bilayer terraces, with a lateral dimension up to hundreds of micrometers.

The term early-onset dementia (EOD) encompasses several forms of neurodegenerative diseases characterized by symptom onset before 65 years and leading to severe impact on subjects already in working activities, as well as on their family and caregivers. Despite the increasing incidence, the etiology is still unknown, with possible association of environmental factors, although the evidence is still scarce. In this review, we aimed to assess how several environmental and lifestyle factors may be associated with the onset of this disease.We conducted a literature search in PubMed and EMBASE databases up to May 6, 2022, to retrieve epidemiological studies evaluating the effect of environmental and lifestyle factors on EOD risk.We eventually included 22 studies, ten with cohort and twelve with case-control design. Traumatic injury, especially on the head/brain, some cardiovascular diseases such as atrial fibrillation and stroke, metabolic diseases including diabetes and hypercholesterolemia, and alcohol consumption have been identified as potential risk factors for EOD. Conversely, playing leisure activities including sports (without trauma), higher educational attainment and higher adherence to Mediterranean DASH-Intervention for Neurodegenerative Delay (MIND) diet appeared to be protective for EOD.The literature on environmental risk factors for EOD has been considerably growing in recent years. Overall, it supports an association between some environmental and lifestyle factors with disease risk. However, additional high-quality research is required to confirm these relations and its causal nature (www.actabiomedica.it).

Two-dimensional (2D) MoS2 possesses unique optical and electrical properties and has many practical applications in nano-optoelectronics. Raman spectroscopy allows readily identify monolayer of MoS2, but the unambiguous determination of the number of layers in a few-layer structure remains a challenging task. In this work, the modification of frequencies of the most intense bands arising from in-plane and out-of-plane vibrations in the spectra of mono- and few-layer MoS2 crystals is studied experimentally, using the Raman scattering technique, and systematically analyzed theoretically, considering the influence of the interlayer interaction as well as the anharmonic interactions within the layer. A good agreement between experimental spectra and theoretical simulations is demonstrated, which allows to estimate the thickness of few-layer MoS2 and also determine parameters of the interlayer and anharmonic interactions. Possible effects of Fermi resonance in 2D MoS2 and the corresponding frequency shift of fundamental modes are considered. The proposed theoretical approach can be used to analyze Raman spectra, estimate the interlayer interaction, anharmonism, and the number of layers for other 2D layered materials.

Two-dimensional (2D) materials such as graphene, transition metal dichalcogenides, and boron nitride have recently emerged as promising candidates for novel applications in sensing and for new electronic and photonic devices. Their exceptional mechanical, electronic, optical, and transport properties show peculiar differences from those of their bulk counterparts and may allow for future radical innovation breakthroughs in different applications. Control and reproducibility of synthesis are two essential, key factors required to drive the development of 2D materials, because their industrial application is directly linked to the development of a high-throughput and reliable technique to obtain 2D layers of different materials on large area substrates. Among various methods, chemical vapour deposition is considered an excellent candidate for this goal thanks to its simplicity, widespread use, and compatibility with other processes used to deposit other semiconductors. In this review, we explore the chemical vapour deposition of MoS2, considered one of the most promising and successful transition metal dichalcogenides. We summarize the basics of the synthesis procedure, discussing in depth: (i) the different substrates used for its deposition, (ii) precursors (solid, liquid, gaseous) available, and (iii) different types of promoters that favour the growth of two-dimensional layers. We also present a comprehensive analysis of the status of the research on the growth mechanisms of the flakes.

In this paper, we model the electrical properties of germanium nanowires with a particular focus on physical mechanisms of electrical molecular sensing. We use the Tibercad software to solve the drift-diffusion equations in 3D and we validate the model against experimental data, considering a p-doped nanowire with surface traps. We simulate three different types of interactions: (1) Passivation of surface traps, (2) Additional surface charges, (3) Charge transfer from molecules to nanowires. By analyzing simulated I–V characteristics, we observe that: (i) the largest change in current occurs with negative charges on the surfaces, (ii) charge transfer provides relevant current changes only for very high values of additional doping, (iii) for certain values of additional n-doping ambipolar currents could be obtained. The results of these simulations highlight the complexity of the molecular sensing mechanism in nanowires, that depends not only on the NW parameters but also on the properties of the molecules. We expect that these findings will be valuable to extend the knowledge of molecular sensing by germanium nanowires, a fundamental step to develop novel sensors based on these nanostructures.

MoS2 two-dimensional quantum dots (2D-QDs) are one of the novel 2D materials. In this work, MoS2 2D-QDs were grown on SiO2/Si by chemical vapor deposition and their exciton and trion photoluminescence were studied in comparison to MoS2 flakes. The 2D-QDs have a round-like shape with the average lateral size of 40 nm and tri-layer structure. Both the structures show two photoluminescence bands associated to A and B excitons, but the reduction of lateral dimension in 2D-QDs causes a recognized emission blueshift attributed to the quantum confinement. At the same time, the A exciton band of 2D-QDs is asymmetric, being overlapped with the trion band. We supposed that nano-dimensioned lateral sizes create quantum confinement conditions when all the excited electrons are also weakly localized in the plane of 2D-QD and much more effectively bind with holes as an additional electron of trion. It should be emphasized that 2D-QD has emission efficiency 6 times higher compared to that from the flake, that also can be explained by the charge carrier localization. These new findings offer potential applications of 2D-QDs in nano-devices operating at room temperatures involving multicolor engineering and efficient modulation of optical properties by controlling the QD lateral sizes and thickness.

The good control of the n-type doping is a key issue for the fabrication of efficient devices based on e-Ga2O3 epilayers. In this work we studied the possibility of doping the e-Ga2O3 thin films, epitaxially grown on c-oriented sapphire by metal-organic chemical vapor deposition, by means of a post-deposition treatment. For the first time, the n-type doping was achieved by depositing a tin-rich SnO2 film on top of the e-Ga2O3 layer and keeping this bi-layer system for 4 h at a temperature of 600 °C in an evacuated furnace. The diffusion of Sn atoms into the e-Ga2O3 film is evidenced by time-of-flight secondary-ion mass spectrometry depth profiles. Room-temperature resistivity of the order of 1 Ω•cm is obtained and the electrical characterization revealed a conduction mechanism based on variable range hopping, according to the Mott's model.

The use of metal nanoparticles is an established paradigm for the synthesis of semiconducting one-dimensional nanostructures. In this work we study their effect on the synthesis of two-dimensional semiconducting materials, by using gold nanoparticles for chemical vapor deposition growth of two-dimensional molybdenum disulfide (MoS2). In comparison with the standard method, the employment of gold nanoparticles allows us to obtain large monolayer MoS2 flakes, up to 20 μm in lateral size, even if they are affected by the localized overgrowth of MoS2 bilayer and trilayer islands. Important modifications of the optical and electronic properties of MoS2 triangular domains are reported, where the photoluminescence intensity of the A exciton is strongly quenched and a shift to a positive threshold voltage in back-gated field effect transistors is observed. These results indicate that the use of gold nanoparticles influences the flake growth and properties, indicating a method for possible localized synthesis of two-dimensional materials, improving the lateral size of monolayers and modifying their properties.

Producción Científica, Cathodoluminescence (CL) investigations are performed on nominally undoped and Si-doped ε-Ga2O3 samples grown by metal-organic vapor phase epitaxy on (0001)-Al2O3 substrates, using different carrier gases. All films exhibit a broad low-temperature CL emission extending over the photon energy range 2–3.4 eV. Emission deconvolution suggests that four narrower bands centered at about 2.4, 2.75, 3.0 and 3.15 eV may well account for the broad band. While the position of these peaks results independent of the growth conditions, significant intensity differences are observed. A general reduction of the broad emission is evidenced as the Si concentration increases. No band-to-band recombination is observed. Temperature dependence of the CL signal shows a trend consistent with radiative transitions from the CB to deep acceptor states, probably of intrinsic nature., Junta de Castilla y León (project VA283P18)

The exact COVID-19 severity is still not well defined and it is hotly debated due to the a few methodological issues such as the uncertainties about the spread of the SARS-CoV-2 infection.We investigated COVID-19 case-fatality rate and infection-fatality rate in 2020 in Italy, a country severely affected by the pandemic, basing our assessment on publicly available data, and calculating such measures during the first and second waves.We found that province-specific crude case-fatality rate in the first wave (February-July 2020) had a median value of 12.0%. Data about infection-fatality rate was more difficult to compute, due to large underestimation of SARS-CoV-2 infection during the first wave when asymptomatic individuals were very rarely tested. However, when using as a reference population-based seroprevalence data for anti-SARS-CoV-2 antibodies collected in May-July 2020, we computed an infection-fatality rate of 2.2%. During the second wave (Sep-Dec 2020), when SARS-CoV-2 testing was greatly increased and extended to many asymptomatic individuals, we could only compute a 'hybrid' case/infection-fatality rate with a value of 2.2%, similar to the infection-fatality rate of the first wave.Overall, this study allowed to assess the COVID-19 case- and infection-fatality rates in Italy before of variant spread and vaccine availability, confirming their high values compared with other airborne infections like influenza. Our findings for Italy were similar to those characterizing other Western European countries.

The good control of the n-type doping is a key issue for the fabrication of efficient devices based on e-Ga2O3 epilayers. In this work we studied the possibility of doping the e-Ga2O3 thin films, epitaxially grown on c-oriented sapphire by metal-organic chemical vapor deposition, by means of a post-deposition treatment. For the first time, the n-type doping was achieved by depositing a tin-rich SnO2 film on top of the e-Ga2O3 layer and keeping this bi-layer system for 4 hours at a temperature of 600 °C in an evacuated furnace. The diffusion of Sn atoms into thee-Ga2O3 film is evidenced by time-of-flight secondary-ion mass spectrometry depth profiles. Room-temperature resistivity of the order of 1 Ω cm is obtained and the electrical characterization revealed a conduction mechanism based on variable range hopping, according to the Mott’s model.

Germanium nanowires were grown using gold colloids on germanium and silicon substrates, (0 0 1) and (1 1 1) oriented. The presence of Si oxide on the surface inhibits the epitaxial growth of the nanowires, resulting in the presence of randomly oriented nanostructures. Different etching procedures of Si oxide are discussed and evaluated, with the goal to obtain epitaxial nanowires aligned with the substrate crystallographic directions. Germanium oxide may be thermally etched during the growth procedure, so that on Ge substrates the nanowires are generally well aligned without any wet-etch. We also study the effect of sonication of the nanowires, to minimize the damage to the nanostructures when they are dropcasted to a carrier substrate for further studies.

Two-dimensional semiconductors, in particular transition metal dichalcogenides and related heterostructures, have gained increasing interest as they constitute potential new building blocks for the next generation of electronic and optoelectronic applications. In this work, we develop a novel nondestructive and noncontact technique for mapping the absorption properties of 2D materials, by taking advantage of the underlying substrate cathodoluminescence emission. We map the quantitative absorption of MoS2 and MoSe2 monolayers, obtained on sapphire and oxidized silicon, with nanoscale resolution. We extend our technique to the characterization of the absorption properties of MoS2/MoSe2 van der Waals heterostructures. We demonstrate that interlayer excitonic phenomena enhance the absorption in the UV range. Our technique also highlights the presence of defects such as grain boundaries and ad-layers. We provide measurements on the absorption of grain boundaries in monolayer MoS2 at different merging angles. We observe a higher absorption yield of randomly oriented monolayers with respect to 60° rotated monolayers. This work opens up a new possibility for characterizing the functional properties two dimensional semiconductors at the nanoscale.

Heterostructures made of GaN and epsilon-Ga2O3 epitaxial layers may be very interesting because they could exploit the high electron mobility of GaN combined with the ferroelectric character of epsilon-Ga2O3. We have explored the possibility of using epsilon-Ga2O3 templates, deposited by metalorganic chemical vapor deposition on sapphire substrates, in order to reduce the lattice mismatch of GaN with sapphire. Considering that epsilon-Ga2O3 is metastable and undergoes a first phase transition at around 700 °C, the GaN layers were deposited at two different temperatures (690°C, 1050 °C). Preliminary electrical and SIMS investigations have enced the diffusion of oxygen from the epsilon-Ga2O3 to the GaN epitaxial layer, which results in an n-type conductivity and a sheet resistance as low as 70 Ohm/sq in a 1 ?m thick GaN layer. The rocking curve of the 2 GaN layers grown epsilon-Ga2O3/sapphire at standard high temperature (1050ºC) indicates a crystal quality worse than for GaN deposited directly on sapphire. In parallel, we studied the nucleation of epsilon-Ga2O3 on GaN templates. We evidenced that epsilon-Ga2O3 nucleates in 3D islands on the surface of GaN grown on on-axis sapphire, with coalescence taking place as the layer grows thicker. The use of off-cut sapphire substrates, instead, permits to inhibit islands formation, resulting in a smoother layer. The possibility of obtaining uniform and very thin epsilon-Ga2O3 layers on GaN layers opens interesting possibilities for the development of novel high electron mobility transistors (HEMT).

The mid-infrared optical spectrum hosts a variety of promising photonic applications. Herein we simulate and experimentally demonstrate reflectance enhancement of MIR light using graphene-coated silicon carbide nanowires on silicon, showing promise for on-chip MIR nanophotonics.

In this Letter, we report, to the best of our knowledge, the first demonstration of high-quality integrated microdisk resonators (MDRs) on a 3C-silicon carbide-on-insulator (SiCOI) platform, working over a wide bandwidth from visible to near-infrared wavelengths. We show record-high quality factors for 3C-silicon carbide (SiC) MDRs of 242,000, 112,000, and 83,000 at the wavelengths of 1550 nm, 770 nm, and 650 nm, respectively, based on high-quality 3C-SiC films with the surface roughness as low as 1.4 Å, achieved by sample-transfer bonding, and precise chemical-mechanical polishing of the SiC film, to remove growth defects. Our study of 3C-SiC films grown on Si using transmission electron microscopy shows that even considerably higher-quality single-crystalline SiCOI can be achieved by flipping and thinning down an ultra-thick ( ∼ 5 − 10 µ m ) 3C-SiC film grown on Si. The SiCOI platform can be used to realize ultra-wideband high-quality SiC devices that are desirable for applications in nonlinear and quantum photonics.

We report a detailed characterization of Ge NWs directly grown on glass by a MOVPE system, showing how different growth parameters can affect the final outcome and comparing NWs grown on a monocrystalline Ge(111) substrate with NWs grown on amorphous glass. Our experimental results indicate that the choice of the substrate does not affect any of the relevant morphological, crystallographic or electrical properties of Ge NWs. Lengths are in the 20-30 micrometer range with minimal tapering, while growth rates are very similar to to NWs grown on Ge(111); TEM and Raman characterization show a very good crystallinity of measured nanostructures. We have also analyzed the growth process on glass and we were able to reach a conclusion on the specific growth mechanism for Ge NWs on amorphous substrates. Our findings demonstrate that glass is a valid option as cheap substrate for the mass production of these nanostructures.

[object Object]Two-dimensional transition metal dichalcogenides are gaining increasing interest due to their promising optical properties. In particular, molybdenum disulfide (MoS2) which displays a band-gap change from indirect at 1.29 eV for bulk materials to direct at 1.8 eV for the material monolayer. This particular effect can lead to a strong light interaction which can pave the way for a new approach to the next generation of visible light emitting devices. In this work we show the nanoscale variation of light emission properties by tip-enhanced photoluminescence microscopy and spectroscopy in the MoS2 monolayer, grown by chemical vapour deposition. The variations of the light emission properties are due to different effects depending on the shape of the MoS2 single layer, for instance, a different concentration of point defect in an irregularly shaped flake and the presence of a nanoscale terrace in a triangular monolayer. Simultaneously, atomic force microscopy reveals indeed the presence of a nanometric terrace, composed of an additional layer of MoS2, and tip-enhanced PL intensity imaging shows a localized intensity decrease.

Few-layer MoS2 flakes were synthesized on silica nanowires by using a standard chemical vapor deposition (CVD) process using Mo and S powders. The flakes on the silica nanowires were analyzed by transmission electron microscopy (TEM), confirming their few-layer nature, and their chemical composition was confirmed by X-ray microanalysis.

The thermal stability of e-Ga 2 O 3 polymorph was studied by complementary methods. Epitaxial films of e-Ga 2 O 3 grown on c-oriented sapphire were annealed at temperatures in the range 700–1000 °C and then investigated by X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM). In addition, Differential Scanning Calorimetry (DSC) up to 1100 °C was carried out on fragments of pure e-Ga 2 O 3 taken from a very thick layer. The results clearly indicate that e-Ga 2 O 3 initiates modifying its crystallographic structure above 650 °C, as demonstrated by a mild endothermic bent of the DSC curves. However, the effective transition to β-phase occurs quite suddenly at 880–920 °C, depending of the DSC heating rate. XRD and TEM results confirm this evidence. TEM investigation in particular shows that after annealing at 1000 °C and rapid cooling the film is completely made of β-Ga 2 O 3 grains, most of them with orientation (310) respect to the sapphire substrate. However, if the cooling rate is substantially reduced, the converted β-Ga 2 O 3 layer assumes the standard orientation (−201) parallel to (00.1) of the Al 2 O 3 substrate. Based on the results of this study we conclude that e-Ga 2 O 3 may conveniently be used for device fabrication, exploiting its higher crystallographic symmetry and better matching to sapphire. However, all fabrication steps must be carried out at temperatures below 700 °C.

A comprehensive study by high-resolution transmission electron microscopy (TEM) and X-ray diffraction (XRD) was carried out on Ga2O3 epilayers grown at low temperature (650 °C) by vapor phase epitaxy in order to investigate the real structure at the nanoscale. Initial XRD measurements showed that the films were of the so-called e phase; i.e. they exhibited hexagonal P63mc space group symmetry, characterized by disordered and partial occupation of the Ga sites. This work clarifies the crystal structure of Ga2O3 layers deposited at low temperature at the nanoscale: TEM investigation demonstrates that the Ga atoms and vacancies are not randomly distributed, but actually possess ordering, with (110)-twinned domains of 5–10 nm size. Each domain has orthorhombic structure with Pna21 space group symmetry, referred to as κ-Ga2O3. Further XRD analysis carried out on thicker samples (9–10 μm) confirmed this finding and provided refined structural parameters. The six (110)-type twinned ordered domains together – if the domain size falls below the actual resolution of the probing techniques – can be misinterpreted as the disordered structure with its P63mc space group symmetry usually referred to as e-Ga2O3 in the current literature. The crystal structure of these Ga2O3 layers consists of an ABAC oxygen close-packed stacking, where Ga atoms occupy octahedral and tetrahedral sites in between, forming two types of polyhedral layers parallel to (001). The edge-sharing octahedra and the corner-sharing tetrahedra form zig-zag ribbons along the [100] direction. Anti-phase boundaries are common inside the domains. The polar character of the structure is confirmed, in agreement with the characteristics of the Pna21 space group and previous observations.

Semiconducting nanolayers of transition metal dichalcogenide such as MoS2 have been proposed as promising channel materials for future nanoelectronic and optoelectronic applications. One of the advantages of 2D materials comes from quantum confinement, enabling the indirect-to-direct bandgap transition as a function of the film thickness and strong photoluminescence in singlelayer form. In this stud y, we show the variation of photoluminescence and structural properties of few-layers MoS2. The flakes are grown on SiO2/Si by chemical vapor deposition using S and Mo powders. 2D material is characterized by electron and atomic force microscopies and temperature-dependent photoluminescence and Raman micro-spectroscopies. Atomic force microscopy reveals the presence of MoS2 monolayers, which are investigated by spectroscopy to compare the properties of different flakes. The PL spectrum of the flakes shows two broad bands associated to the A0, derived from an exciton, and A-, derived from a trion consists of an exciton combined with another electron, and B exciton. The light emission at room temperature is found to depend on the thickness and shape of MoS2 layers. For instance, photoluminescence close to the periphery of the flake is decreased compared to that in the center, which can be connected to a different concentration of defects. The nonradiative recombination can be related with the defect trapping and electron relaxation through the defect levels within bandgap. At the same time, the trion band is mostly decreased. In temperaturedependent measurements, the major trend is that the photoluminescence redshifts and intensity dramatically decreases from 82 to 200K. This can be attributed to the thermally activated nonradiative recombination with the increase of electron-phonon interaction. Heating from 200K to room temperature causes an increase of the photoluminescence intensity, which may be due to defect activation at higher temperatures. We can assume the presence of different mechanisms that concurrently influence the photoluminescence intensity.

We demonstrate the feasibility of the use of isobutyl germane, a novel germanium source, for the vapor-liquid-solid growth of germanium nanowires (NWs) on Si (111) substrates, using a thin gold layer as catalyst. The density and the diameter of the NWs were controlled by varying the Au layer thickness and the isobutyl germane flow. The NWs grow along (111) directions and show perfect crystallinity and lengths from several hundreds of nm to 3-4 μm. The use of isobutyl germane gives a considerable technological advantage in the growth of germanium NWs since it is a safer and more manageable germanium source and it allows to grow Ge NWs in a standard vapor phase epitaxy system at 400 °C.

Functionalised nanostructures are a viable approach to realise detectors with high sensitivity and very limited weight and electrical consumption, thanks to their high surface/volume ratio.Germanium nanowires (NWs) are proposed here as a fundamental building block of a sensor to detect traces of explosives molecules (in particular TNT), down to a detection limit of ~1x10- 6 ppt.In this communication we will report on the growth, structural and electrical characterization of these nanostructures. The first experiments on chemical functionalization tailored to bind the aromatic ring of TNT to the nanostructure will be presented. Germanium NWs were grown by Vapor Phase Epitaxy using iso buthyl germanium as a novel Ge source, at temperatures ranging from 340 to 460°C on (001) and (111) silicon and germanium substrates. Gold nanoparticles of different size (20-80 nm) were used as catalyst. The optimization of the growth procedure resulted in Ge NWs to 20 m in length. Details of the growth process and the growth conditions will be discussed, with particular emphasis on the control of the length of the NWs and their tapering. Different NW density and orientations are obtained, depending on the precursor flow and on the substrate orientation. The NW crystalline structure was observed by Transmission Electron Microscopy (TEM), evidencing their high structural quality. The NWs were detached from the substrates with ultrasonication and dispersed on a carrier substrate with Au interdigitated electrodes. Single NWs were observed with Scanning Electron Microscopy (SEM) and contacted to Au electrodes with Pt deposited by Focused Ion Beam (FIB). Pt contacts were deposited with 50 pA and 30 kV ion beam current and acceleration voltage,respectively, at each ends of the NW. Linear I-V characteristics showed the ohmic nature of Pt-NW contacts. From RT resistance measurements, using two-terminal configuration, we obtained NW electrical resistivity values in the 0.05 - 0.5 ohm cm range. We propose the unctionalization of the NWs surface with long chain alkanethiols terminating with an amino group, in order to provide the explosives recognition elements. Besides providing passivation of the NWs surface, the electronrich amino groups will bind the electron-deficient explosive molecules of TNT through chargetransfer donor-acceptor interactions, thus causing sharp changes in the conductance of the electrical-sensing anoelements.

The paper reports on the fabrication and characterization of flexural resonators designed for resonant strain sensing and manufactured using 2 $\mu \text{m}$ thick monocrystalline 3C-SiC layers grown on Silicon-On-Insulator substrates. The resonators are designed with Double-Ended-Tuning Fork geometry and actuated electrostatically using lateral electrodes fixed on the sides of the resonator tines, through coupling gaps with average width of 1.03 $\mu \text{m}$ . They show excellent performance in vacuum environment with Q-factor around 30,000 and 18 dB high resonance peaks measured in open loop with DC bias voltage of 20 V. The closed-loop operation of the resonators with an external transimpedance amplifier feedback circuit is demonstrated and the stability of the resulting MEMS oscillator is analyzed using a microcontroller-based digital readout to measure its oscillation frequency. The results of the Allan deviation tests on the MEMS oscillator indicate a relative frequency stability better than 10−7 on a measurement time of 280 ms. The results of strain sensitivity experiments in vacuum performed after adhesive attachment of the resonator chip on Al are also reported, indicating a sensitivity of 41.7 Hz/ $\mu \varepsilon $ and a resolution of about 0.82 $\text{n}\varepsilon $ for the same measurement time. [2019-0183]

Growth of gallium oxide thin films was carried out by Metalorganic Chemical Vapor Deposition (MOCVD) at different temperatures. Pure e-phase epilayers of Ga 2 O 3 , with good morphology and structural properties, were obtained, for the first time with this technique, on sapphire at the temperature of 650 °C. XRD analysis performed by high-resolution diffractometry confirmed the good crystallographic quality of the grown layers. At temperatures higher than 700 °C the usual stable β-Ga 2 O 3 phase was obtained. The e-films were successfully deposited also on (0001)-oriented GaN and (111)- and (001)-oriented 3C–SiC templates, provided that the appropriate temperature was chosen. This indicates that the temperature, rather than substrate structure, is the growth parameter which decides what phase actually forms. The growth proceeds via coalescence of hexagonal islands and is favored when a substrate with an in-plane hexagonal arrangement of the atoms is employed. By applying Atomic Layer Deposition (ALD), epitaxial growth of the e-phase was achieved at lower temperature, while the overall uniformity resulted improved, even on large sapphire substrates.

We will review recent demonstrations of single photon emission in different silicon carbide (SiC) polytypes, in both bulk and nano-structured form. Due to well established doping, and micro- and nanofabrication procedures deep defects photoluminescence (PL) can be electrically excited and incorporated in SiC nanomaterials. Finally we will report on preliminary results to incorporate near infrared defects in SiC nanoparticles.

Molybdenum disulfide (MoS2) is one of the most interesting 2D materials. However, while monolayer MoS2 is well-explored, the few-layer flakes, also promising for flexible device and nano-optoelectronics application, remain less investigated. We study the variation of exciton and trion photoluminescence (PL) and structural properties of few-layer MoS2 grown on SiO2/Si by chemical vapor deposition. Scanning electron and atomic force microscopies show that most of the flakes have a triangular shape. The µ-PL spectra of the flakes show two broad bands associated to the A exciton overlapped by trion and B exciton. The light emission at room temperature redshifts when the number of layers increases, controlled by µ-Raman spectroscopy. In the temperature-dependent measurements from 80 to 290 K, the PL redshifts according to bandgap narrowing, while the intensity decreases due to the thermally activated nonradiative recombination related to the increase of the electron-phonon interaction. Exciton and trion bands are deconvoluted and their behaviors with temperature are studied by fitting the PL data with modelling equations. This allows to evaluate the spin-orbit splitting, quenching activation energy, trion effective size and other important parameters. These new findings are useful for the potential applications of few-layer MoS2 in nano-optoelectronics involving external modulation of optical properties.

[object Object]We demonstrate an integrated mid-infrared 3C-S?C metasurface with relatively sharp transmission peaks associated with phonon-mediated magnetic polariton resonance. We further show the possibility of developing reconfigurable metasurfaces using such architectures by integrating a thin layer of phase-change material, Ge2Sb2Te5, on top of the SiC layer.

Electrical and optical properties of undoped single-phase epsilon-Ga2O3 epitaxial films prepared by MOCVD are reported. It is shown that this still unexplored polymorph of gallium oxide possesses wide bandgap and very high dark resistivity, thus allowing the design and fabrication of solar-blind UV photodetectors. Simple cost-effective photoresistors, fabricated by direct deposition of the epilayers on c-oriented sapphire substrates, exhibited good performance. The physical properties and the photoresponse of epsilon-Ga2O3 make this material very interesting in view of novel applications. (C) 2017 Elsevier B.V. All rights reserved.

The influence of growth conditions on structural properties is reported for core-shell SiC/SiO2 nanowires grown on silicon substrates by a chemical vapour deposition (CVD) technique. Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) studies show a correlation between the growth temperature and the nanowire structure and highlight the possibility to control the inner core diameter by varying the precursor concentration. The nanowire covering of the substrate was considerably enhanced and homogenized using drop casting surfactant-aided deposition of catalysts on an H-terminated silicon 100 surface.