Raman Spectroscopy as an Effective Tool for Assessment of Structural Quality and Polymorphism of Gallium Oxide (GaO) Thin Films.

Raman spectroscopy, a versatile and nondestructive technique, was employed to develop a methodology for gallium oxide (GaO) phase detection and identification. This methodology combines experimental results with a comprehensive literature survey. The established Raman approach offers a powerful tool for nondestructively assessing phase purity and detecting secondary phases in GaO thin films.

Photoelectron Holographic Study for Atomic Site Occupancy for Si Dopants in Si-Doped κ-GaO(001).

We investigated atomic site occupancy for the Si dopant in Si-doped κ-GaO(001) using photoelectron spectroscopy (PES) and photoelectron holography (PEH). From PES and PEH, we found that the Si dopant had one chemical state, and three types of inequivalent Si substitutional sites (Si) were formed. The ratios for the inequivalent tetrahedral, pentahedral, and octahedral Si sites were estimated to be 55.

Structural and Photoelectronic Properties of κ-GaO Thin Films Grown on Polycrystalline Diamond Substrates.

Orthorhombic κ-GaO thin films were grown for the first time on polycrystalline diamond free-standing substrates by metal-organic vapor phase epitaxy at a temperature of 650 °C. Structural, morphological, electrical, and photoelectronic properties of the obtained heterostructures were evaluated by optical microscopy, X-ray diffraction, current-voltage measurements, and spectral photoconductivity, respectively. Results show that a very slow cooling, performed at low pressure (100 mbar) under a controlled He flow soon after the growth process, is mandatory to improve the quality of the κ-GaO epitaxial thin film, ensuring a good adhesion to the diamond substrate, an optimal morphology, and a lower density of electrically active defects.

Interfacial Properties of the SnO/κ-GaO p-n Heterojunction: A Case of Subsurface Doping Density Reduction via Thermal Treatment in κ-GaO.

The interfacial properties of a planar SnO/κ-GaO p-n heterojunction have been investigated by capacitance-voltage (-) measurements following a methodological approach that allows consideration of significant combined series resistance and parallel leakage effects. Single-frequency measurements were carried out in both series- and parallel-model measurement configurations and then compared to the dual-frequency approach, which permits us to evaluate the depletion capacitance of diode independently of leakage conductance and series resistance. It was found that in the bias region, where the dissipation factor was low enough, they give the same results and provide reliable experimental - data.

Built-in tensile strain dependence on the lateral size of monolayer MoS synthesized by liquid precursor chemical vapor deposition.

Strain engineering is an efficient tool to tune and tailor the electrical and optical properties of 2D materials. The built-in strain can be tuned during the synthesis process of a two-dimensional semiconductor, such as molybdenum disulfide, by employing different growth substrates with peculiar thermal properties. In this work, we demonstrate that the built-in strain of MoS monolayers, grown on a SiO/Si substrate by liquid precursor chemical vapor deposition, is mainly dependent on the size of the monolayer.

Electrical properties and chemiresistive response to 2,4,6 trinitrotoluene vapours of large area arrays of Ge nanowires.

We study the electrical and morphological properties of random arrays of Ge nanowires (NW) deposited on sapphire substrates. NW-based devices were fabricated with the aim of developing chemiresistive-type sensors for the detection of explosive vapours. We present the results obtained on pristine and annealed NWs and, focusing on the different phenomenology observed, we discuss the critical role played by NW-NW junctions on the electrical conduction and sensing performances.

Selection and Functionalization of Germanium Nanowires for Bio-Sensing.

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.

Detection of Nitroaromatic Explosives in Air by Amino-Functionalized Carbon Nanotubes.

Nitroaromatic explosives are the most common explosives, and their detection is important to public security, human health, and environmental protection. In particular, the detection of solid explosives through directly revealing the presence of their vapors in air would be desirable for compact and portable devices. In this study, amino-functionalized carbon nanotubes were used to produce resistive sensors to detect nitroaromatic explosives by interaction with their vapors.

A Review on Chemical Vapour Deposition of Two-Dimensional MoS Flakes.

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.

Gold nanoparticle assisted synthesis of MoS monolayers by chemical vapor deposition.

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 (MoS). In comparison with the standard method, the employment of gold nanoparticles allows us to obtain large monolayer MoS flakes, up to 20 μm in lateral size, even if they are affected by the localized overgrowth of MoS bilayer and trilayer islands.

Germanium Nanowires as Sensing Devices: Modelization of Electrical Properties.

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.

Direct growth of germanium nanowires on glass.

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.

Influence of organic promoter gradient on the MoS growth dynamics.

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 MoS.

Extra-long and taper-free germanium nanowires: use of an alternative Ge precursor for longer nanostructures.

One of the challenges in the development of germanium nanowires (Ge NWs) is to increase their length beyond the 10 μm limit without enlarging the NW diameter, i.e. minimizing the tapering.

Defect influence on in-plane photocurrent of InAs/InGaAs quantum dot array: long-term electron trapping and Coulomb screening.

Metamorphic InAs/InGaAs and InAs/InGaAs quantum dot (QD) arrays are known to be photosensitive in the telecommunication ranges at 1.3 and 1.55 μm, respectively; however, for photonic applications of these nanostructures, the effect of levels related to defects still needs in-depth investigation.

Growth of germanium nanowires with isobuthyl germane.

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.

Interband Photoconductivity of Metamorphic InAs/InGaAs Quantum Dots in the 1.3-1.55-μm Window.

Photoelectric properties of the metamorphic InAs/In GaAs quantum dot (QD) nanostructures were studied at room temperature, employing photoconductivity (PC) and photoluminescence spectroscopies, electrical measurements, and theoretical modeling. Four samples with different stoichiometry of In GaAs cladding layer have been grown: indium content x was 0.15, 0.

Bipolar Effects in Photovoltage of Metamorphic InAs/InGaAs/GaAs Quantum Dot Heterostructures: Characterization and Design Solutions for Light-Sensitive Devices.

The bipolar effect of GaAs substrate and nearby layers on photovoltage of vertical metamorphic InAs/InGaAs in comparison with pseudomorphic (conventional) InAs/GaAs quantum dot (QD) structures were studied. Both metamorphic and pseudomorphic structures were grown by molecular beam epitaxy, using bottom contacts at either the grown n -buffers or the GaAs substrate. The features related to QDs, wetting layers, and buffers have been identified in the photoelectric spectra of both the buffer-contacted structures, whereas the spectra of substrate-contacted samples showed the additional onset attributed to EL2 defect centers.

Comparative Study of Photoelectric Properties of Metamorphic InAs/InGaAs and InAs/GaAs Quantum Dot Structures.

Optical and photoelectric properties of metamorphic InAs/InGaAs and conventional pseudomorphic InAs/GaAs quantum dot (QD) structures were studied. We used two different electrical contact configurations that allowed us to have the current flow (i) only through QDs and embedding layers and (ii) through all the structure, including the GaAs substrate (wafer). Different optical transitions between states of QDs, wetting layers, GaAs or InGaAs buffers, and defect-related centers were studied by means of photovoltage (PV), photoconductivity (PC), photoluminescence (PL), and absorption spectroscopies.

All-Optical Fiber Hanbury Brown &Twiss Interferometer to study 1300 nm single photon emission of a metamorphic InAs Quantum Dot.

New optical fiber based spectroscopic tools open the possibility to develop more robust and efficient characterization experiments. Spectral filtering and light reflection have been used to produce compact and versatile fiber based optical cavities and sensors. Moreover, these technologies would be also suitable to study N-photon correlations, where high collection efficiency and frequency tunability is desirable.

β-Lactam monotherapy vs β-lactam-macrolide combination treatment in moderately severe community-acquired pneumonia: a randomized noninferiority trial.

Importance: The clinical benefit of adding a macrolide to a β-lactam for empirical treatment of moderately severe community-acquired pneumonia remains controversial.

Objective: To test noninferiority of a β-lactam alone compared with a β-lactam and macrolide combination in moderately severe community-acquired pneumonia.

Design, Setting, And Participants: Open-label, multicenter, noninferiority, randomized trial conducted from January 13, 2009, through January 31, 2013, in 580 immunocompetent adult patients hospitalized in 6 acute care hospitals in Switzerland for moderately severe community-acquired pneumonia.

Role of perceived stress in the occurrence of preterm labor and preterm birth among urban women.

Introduction: This study examined whether prenatal perceived stress levels during pregnancy were associated with preterm labor or preterm birth.

Methods: Perceived stress levels were measured at 16 weeks' gestation or less and between 20 and 24 weeks' gestation in a sample of 1069 low-income pregnant women attending Temple University prenatal care clinics. Scores were averaged to create a single measure of prenatal stress.

Two-color single-photon emission from InAs quantum dots: toward logic information management using quantum light.

In this work, we propose the use of the Hanbury-Brown and Twiss interferometric technique and a switchable two-color excitation method for evaluating the exciton and noncorrelated electron-hole dynamics associated with single photon emission from indium arsenide (InAs) self-assembled quantum dots (QDs). Using a microstate master equation model we demonstrate that our single QDs are described by nonlinear exciton dynamics. The simultaneous detection of two-color, single photon emission from InAs QDs using these nonlinear dynamics was used to design a NOT AND logic transference function.

Time resolved emission at 1.3 μm of a single InAs quantum dot by using a tunable fibre Bragg grating.

Photoluminescence and time resolved photoluminescence from single metamorphic InAs/GaAs quantum dots (QDs) emitting at 1.3 μm have been measured by means of a novel fibre-based characterization set-up. We demonstrate that the use of a wavelength tunable fibre Bragg grating filter increases the light collection efficiency by more than one order of magnitude as compared to a conventional grating monochromator.