Conference Agenda

The 200 meV band gap difference between wurtzite (WZ) and zinc blende (ZB) GaN and InGaN opens the possibility of realizing homoepitaxial WZ/ZB heterostructures for light emitting devices in the visible and UV wavelength range. However, the realization of such devices requires a controlled conversion at the monolayer scale from WZ to ZB and vice-versa, which has not been achieved to date. In this work, we demonstrate that plasma-assisted MBE grown GaN nanowires (NWs) are offering a new paradigm to control WZ/ZB selection, in particular when grown in the mononuclear growth regime.

In the case of catalyst-grown NWs, the formation of ZB and WZ sections is achieved by controlling the size and the wetting angle of the catalyst droplet. This approach does not hold in the case of GaN NWs, which are grown catalyst-free in plasma-assisted MBE. However, we found that by taking advantage of the mononuclear growth regime of GaN NWs, it is possible to kinetically control the crystallographic variant and to realize ZB insertions of controlled thickness in WZ GaN NWs.

The substrates consist of in-plane organized, MOCVD-grown GaN pedestals [1]. After introduction in the MBE chamber, a ZB GaN section was grown at low temperature and high Ga/N flux ratio. In these conditions, a ZB nucleus of a new layer on top of the GaN pedestal is more stable than its WZ counterpart [2]. Following this nucleation event, the layer is next rapidly completed, before repetition of this process after an incubation time. Once completed the ZB section, growth was interrupted while temperature was increased and Ga/N flux ratio reduced, to switch to conditions favorable to growth of a WZ upper GaN section. The samples were characterized by hyperspectral cathodoluminescence and photoluminescence spectroscopy. These results assess the kinetically controlled crystallographic WZ/ZB phase selection in NWs, opening the path to the realization of full homoepitaxial, carrier confining heterostructures.

[1] C. Guérin et al, ACS Appl. Nano Mater. 2024, 7, 20301−20307 https://doi.org/10.1021/acsanm.4c03276

[2] Hang Zang et al, Phys. Rev. B 107, 165308 (2023), DOI: 10.1103/PhysRevB.107.165308

The synthesis of α-Fe2O3 nanowires with tensile strained structure has aroused the interest of researchers due to the enhancement of the physical properties advantageous for different applications such as photocatalysis or water splitting. In this work, a synthesis method based on the Joule-Heating effect has been used to synthesize a high density of α-Fe2O3 nanowires grown along the edges of the ribbon used as precursor. The morphology, composition and anisotropic nanostructure growth has been analysed by diverse electron microscopy and spectroscopy techniques, indicating that the nanostructures possess high crystalline quality. The role played by the induced current on the growth mechanisms and the characteristic strain-induced superstructure achieved are discussed. The fast and energy-saving synthesis method employed in this work, along with the potential scalability, reveals a great advantage as compared to conventional thermal oxidation routes making it highly attractive.

Hybrid semiconductor nanowire architectures are promising building blocks for next-generation optoelectronic devices due to their flexible integration, high surface-to-volume ratio, and quantum confinement effects. However, their performance is highly sensitive to clusters, secondary phases, and local structural variations, making it essential to perform a correlative investigation of their elemental composition, structural order, and optical response. While electron microscopies are commonly employed, recent advances in synchrotron-based techniques—offering increased brightness, rapid acquisition, and superior spatial resolution—enable unprecedented insights into these systems.

Here, we apply X-ray nanoprobes at the European Synchrotron Radiation Facility (ESRF) beamlines ID01 and ID16B for spatially resolved nano-analysis of wide-bandgap oxide semiconductor systems, specifically Zn2GeO4/SnxGe1-xO2 and β-Ga2O3/SnO2. By combining X-ray fluorescence (XRF), scanning X-ray diffraction microscopy (SXDM), X-ray absorption near-edge structure (XANES), and X-ray excited optical luminescence (XEOL), we correlate chemical composition, structural order, and optical properties with nanometer resolution. This multi-technique approach establishes a robust methodology for characterizing complex nanostructures and provides valuable insights for the design of advanced optoelectronic devices.

Resistive Joule heating is a fast, simple, low-cost and effective method to obtain micro- and nanostructured metal oxides, such as MoO3. Its growth mechanism is based on the electromigration processes that takes place due to the electric current flowing through the material, promoting ion diffusion associated with the thermal gradient in the wire, a characteristic process of the Joule heating. The growth of layered α-MoO3 microplates on the surface of Mo wires during Joule heating has been studied by applying an external electric field to the current carrying wire. The rapid formation of the structures is further enhanced by the external field, leading to a near instantaneous formation of MoO3 plates. Additionally, other MoO3 nanostructures have been found to grow by a thermally assisted electric-field-driven process from the Mo wire on the electrodes. To gain deeper insight into the synthesis of MoO3 by this resistive heating method, a macroscale Multiphysics approach is presented, simulating the effects of high electric currents passing through Mo wire.

This work explores the influence of bismuth incorpora-tion into the GaAs capping layer (CL) on the structural and compositional properties of InAs quantum dots (QDs). To accommodate the distinct growth tempera-tures of InAs QDs (510 °C) and GaAsBi layers (370 °C), three Time Temperature Routes (TTRs) involving growth interruptions were implemented. Two of these routes exhibited defective regions characterized by bismuth-depleted nanotracks within the GaAsBi layer, associated with the surface segregation of Bi-rich droplets. Remark-ably, one specific TTR led to the formation of embedded icosahedral-like nanoparticles (NPs) at the initial inter-face, accompanied by elongated trails. Structural and compositional analyses revealed that these NPs com-prise three distinct phases: rhombohedral Bi, elemental Ga, and a previously unreported In₄Bi intermetallic phase. The long particle trajectories and low growth temperatures suggest that the NPs stayed liquid during growth, solidifying only upon cooling. This reveals a new method for integrating non-noble metal plasmonic NPs into buried semiconductor structures.

Nanomaterials and nanocomposites are revolutionizing science and industry by offering unique properties that surpass those of conventional materials. Their applications range from electronics and medicine to energy and aerospace, driving key advances in sustainability, energy storage and smart materials, and paving the way to a new era of technological innovation. However, high production cost and low production rate hinder in numerous cases their industrial implementation. In this work, a graphene-nanoparticles nanocomposite synthesis method via plasmas at atmospheric pressure is presented. This approach enables the production of different nanocomposites based on graphene, such as the graphene-TiO2 nanocomposite reported in this work, yielding a material of high quality and purity. The process is simple, environmentally friendly, economical and scalable, thus providing an opportunity for the implementation of this and other graphene-based nanocomposites into novel applications.