We report the synthesis and characterization of graphene nanoribbons (GNRs) decorated with iron oxide (Fe3O4) nanoparticles to obtain the GNR_Fe3O4 nanocomposite and its use as a DNA sensor. Characterization results confirm the successful synthesis of a nanocomposite based on reduced GNRs and mostly Fe3O4 nanoparticles distributed randomly and homogeneously on the ribbon's surface and whose specific surface area (766 m2 g−1) is higher compared to pure GNRs (588 m2 g−1). These characteristics make this nanocomposite suitable for effective DNA immobilization and hybridization in sensor applications. Taking advantage of the latter, the electrochemical analysis demonstrated that GNR_Fe3O4-based electrodes amplify the electrochemical signal by more than one order of magnitude compared to bare carbon electrodes, and 70% more compared to pristine GNRs-based electrodes. The capability of the GNR_Fe3O4 nanocomposite as a DNA sensor was evaluated in terms of the electrochemical response by monitoring the cathodic peak in DNA immobilization and hybridization through a redox process. The electrochemical current was measured in immobilized single-stranded DNA and double-stranded DNA to be 92 and 49 μA, respectively, for GNR_Fe3O4-based electrodes; these values are indicative of an effective discrimination between the immobilization and hybridization of DNA. The present work demonstrates the viability of a DNA sensor based on the facile synthesis of GNRs decorated with Fe3O4 nanoparticles.

InN epitaxial films with cubic phase were grown by rf-plasma-assisted molecular beam epitaxy (RF-MBE) on GaAs(001) substrates employing two methods: migration-enhanced epitaxy (MEE) and conventional MBE technique. The films were synthesized at different growth temperatures ranging from 490 to 550 °C, and different In beam fluxes (BEPIn) ranging from 5.9 × 10−7 to 9.7 × 10−7 Torr. We found the optimum conditions for the nucleation of the cubic phase of the InN using a buffer composed of several thin layers, according to reflection high-energy electron diffraction (RHEED) patterns. Crystallographic analysis by high resolution X-ray diffraction (HR-XRD) and RHEED confirmed the growth of c-InN by the two methods. We achieved with the MEE method a higher crystal quality and higher cubic phase purity. The ratio of cubic to hexagonal components in InN films was estimated from the ratio of the integrated X-ray diffraction intensities of the cubic (002) and hexagonal (101¯1) planes measured by X-ray reciprocal space mapping (RSM). For MEE samples, the cubic phase of InN increases employing higher In beam fluxes and higher growth temperatures. We have obtained a cubic purity phase of 96.4% for a film grown at 510 °C by MEE.

Infrared optical studies were carried out in a group of cubic InN samples grown by gas source molecular beam epitaxy on MgO (001) substrates. Room temperature (RT) reflectance and low-temperature (LT) transmittance measurements were performed by using fast Fourier transform infrared spectrometry. Reflectance fittings allowed to establish that β-InN films have large free-carrier concentrations present (>1019 cm−3), a result that is corroborated by Hall effect measurements. Each sample explored exhibited a different optical absorption edge. The Varshni parameters that describe adequately the optical absorption edge responses with temperature are obtained for the set of samples studied. The observed temperatures changes, from LT to RT, are the lowest reported for III-V semiconductor binary compounds. The temperature coefficient of the conduction band depends on the strength of the electron–phonon interaction (e-ph-i), as well as on the thermal expansion. It has been predicted that cubic InN has one of the smallest e-ph-i of all III-V compounds, which is corroborated by these results. The variation in values of absorption edges is clearly consistent with the Burstein–Moss and band renormalization effects, produced by high free electron concentrations. It is shown that the conduction band in β-InN, analogous to wurtzite InN, follows a nonparabolic behavior.

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We report on the optical characterization of a nitrogen plasma source based on radiofrequency (RF) used to grow III-nitride materials by molecular beam epitaxy (MBE). Optical emission spectroscopy (OES) was used to study the nitrogen plasma response as a function of the RF power applied and the flow rate of molecular nitrogen. Analysis of the intensities of spectral signals assigned to atomic and molecular species and the ratio of these intensities is performed in detail. The OES results show that the plasma source studied is sensitive to the RF power applied to produce an atomic nitrogen signal, while varying the incoming flow impacts the signal of metastable nitrogen molecules; this outcome allows for the determination of conditions under which certain types of nitrogen species are favored over others. InN films were grown on AlN-buffered Si(111) substrates by MBE under different plasma operational parameters, where, according to the OES studies, atomic nitrogen or excited molecular nitrogen is favored in the plasma. In situ reflection high-energy electron diffraction, scanning electron microscopy, and x-ray diffraction techniques were employed to characterize the InN samples. It is found that the surface morphology of the InN films is highly sensitive to the plasma conditions. A transition in the growth mode from smooth compact films to coalesced islands and columnar structures is observed when the dominant reactive species is atomic nitrogen or excited molecular nitrogen. The results of the characterization are discussed and correlated with the reactive nitrogen species present in the plasma.