Surface Texturing of n- and p-Doped c-Si Using a Novel Plasma Chemical Texturing Process

Abstract n- and p-doped c-Si (100) are textured by a SF 6 /O 2 plasma chemical etching, under conditions avoiding ion bombardment. The study of the effects of plasma parameters on morphology and on surface reflectance of textured c-Si reveals a strong impact of silicon doping on texturing characteristics. SF 6 /O 2 plasma etches anisotropically n-type c-Si creating a square-based hillock-like morphology with a surface reflectivity of 6%. Conversely, for p-type Si, a H 2 plasma pretreatment is necessary to activate silicon etching and obtain a nano-textured surface with a reflectivity of 16%

Demonstration of improved charge transfer in graphene/Au nanorods plasmonic hybrids stabilized by benzyl thiol linkers

Hybrids based on graphene decorated with plasmonic gold (Au) nanostructures are being investigated as possible materials combination to add to graphene functionalities of tunable plasmon resonance and enhanced absorption at selected wavelength in the visible-near-infrared region of the spectrum. Here, we report a solution drop-casting approach for fabricating stable hybrids based on chemical vapor deposition (CVD) graphene and Au nanorods, which are able to activate effective charge transfer from graphene. We demonstrate that CVD graphene functionalization by benzyl thiol (BZT) provides the linker to strong anchoring, via S-Au bonds, Au nanorods to graphene. Optical measurements by spectroscopic ellipsometry give evidence of the introduction of plasmon resonances at 1.85 and 2.25 eV in the Au nanorods/BZT/graphene hybrids, which enable surface enhanced Raman scattering (SERS) detection. Furthermore, an effective electron transfer from graphene to Au nanorods, resulting in an enhancement of p-type doping of graphene with a consequent decrease of its sheet resistance, is probed by Raman spectroscopy and corroborated by electrical measurements

Gallium plasmonic nanoantennas unveiling multiple kinetics of hydrogen sensing, storage, and spillover

Hydrogen is the key element to accomplish a carbon-free based economy. Here, the first evidence of plasmonic gallium (Ga) nanoantennas is provided as nanoreactors supported on sapphire (α-Al2O3) acting as direct plasmon-enhanced photocatalyst for hydrogen sensing, storage, and spillover. The role of plasmon-catalyzed electron transfer between hydrogen and plasmonic Ga nanoparticle in the activation of those processes is highlighted, as opposed to conventional refractive index-change-based sensing. This study reveals that, while temperature selectively operates those various processes, longitudinal (LO-LSPR) and transverse (TO-LSPR) localized surface plasmon resonances of supported Ga nanoparticles open selectivity of localized reaction pathways at specific sites corresponding to the electromagnetic hot-spots. Specifically, the TO-LSPR couples light into the surface dissociative adsorption of hydrogen and formation of hydrides, whereas the LO-LSPR activates heterogeneous reactions at the interface with the support, that is, hydrogen spillover into α-Al2O3 and reverse-oxygen spillover from α-Al2O3. This Ga-based plasmon-catalytic platform expands the application of supported plasmon-catalysis to hydrogen technologies, including reversible fast hydrogen sensing in a timescale of a few seconds with a limit of detection as low as 5 ppm and in a broad temperature range from room-temperature up to 600 °C while remaining stable and reusable over an extended period of time.The authors thank all of the students and colleagues in their groups who were actively involved with nanoparticles research. M.L., Y.G., and F.M. have received funding from the European Union's Horizon 2020 Research and Innovation Program under Grant Agreement No. 899598—PHEMTRONICS. F.M. acknowledges MINECO (Spanish Ministry of Economy and Competitiveness, project PGC2018-096649-B-100)

Reversible and non-volatile metal-to-insulator chemical transition in molybdenum oxide films

Significant effort is being dedicated to developing alternative materials whose optical properties can be controllably and reversibly modified. Here, we experimentally demonstrate the reversible non-volatile molybdenum oxides MoO3-to-MoO2 transition associated to a change from a metallic to a dielectric behavior through cycles of thermal annealing in air and hydrogen (H2). A full cycle is demonstrated by characterizing structurally and optically the transition using Raman spectroscopy and spectroscopic ellipsometry. The potential applicability of the metal-to-insulator transition in MoOx is benchmarked through comparison with a canonical Mott insulator VO2 in a reconfigurable reflective configuration as well as in cladded waveguide schemes.European Union’s Horizon 2020 research and innovation program (No 899598 – PHEMTRONICS

Plasmonic hot-electron reconfigurable photodetector based on phase-change material Sb2S3

Hot-carrier based photodetectors and enhanced by surface plasmons (SPs) hot-electron injection into semiconductors, are drawing significant attention. This photodetecting strategy yields to narrowband photoresponse while enabling photodetection at sub-bandgap energies of the semiconductor materials. In this work, we analyze the design of a reconfigurable photodetector based on a metal-semiconductor (MS) configuration with interdigitated dual-comb Au electrodes deposited on the semiconducting Sb2S3 phase-change material. The reconfigurability of the device relies on the changes of refractive index between the amorphous and crystalline phases of Sb2S3 that entail a modulation of the properties of the SPs generated at the dual-comb Au electrodes. An exhaustive numerical study has been realized on the Au grating parameters formed by the dual-comb electrodes, and on the SP order with the purpose of optimizing the absorption of the device, and thus, the responsivity of the photodetector. The optimized photodetector layout proposed here enables tunable narrowband photodetection from the O telecom band (λ = 1310 nm) to the C telecom band (λ = 1550 nm).Horizon 2020 Framework Programme (No 899598 – PHEMTRONICS

Polymorphic gallium for active resonance tuningin photonic nanostructures: from bulk gallium totwo-dimensional (2D) gallenene

Reconfigurable plasmonics is driving an extensive quest for active materials that can support a controllable modulation of their optical properties for dynamically tunable plasmonic structures. Here, polymorphic gallium (Ga) is demonstrated to be a very promising candidate for adaptive plasmonics and reconfigurable photonics applications. The Ga sp-metal is widely known as a liquid metal at room temperature. In addition to the many other compelling attributes of nanostructured Ga, including minimal oxidation and biocompatibility, its six phases have varying degrees of metallic character, providing a wide gamut of electrical conductivity and optical behavior tunability. Here, the dielectric function of the several Ga phases is introduced and correlated with their respective electronic structures. The key conditions for optimal optical modulation and switching for each Ga phase are evaluated. Additionally, we provide a comparison of Ga with other more common phase-change materials, showing better performance of Ga at optical frequencies. Furthermore, we first report, to the best of our knowledge, the optical properties of liquid Ga in the terahertz (THz) range showing its broad plasmonic tunability from ultraviolet to visible-infrared and down to the THz regime. Finally, we provide both computational and experimental evidence of extension of Ga polymorphism to bidimensional twodimensional (2D) gallenene, paving the way to new bidimensional reconfigurable plasmonic platforms.F.M. acknowledges MICINN (Spanish Ministry of Science and Innovation) through project PGC2018-096649-B-100

High rate deposition of thin film cadmium sulphide by pulsed direct current magnetron sputtering

CadmiumSulphide (CdS) is an important n-type semiconductor widely used as a windowlayer in thin film photovoltaics Copper IndiumSelenide, Copper IndiumGallium (di)Selenide, Copper Zinc Tin Sulphide and Cadmium Telluride (CdTe). Cadmium Sulphide has been deposited using a number of techniques but these techniques can be slow (chemical bath deposition and Radio Frequency sputtering) or the uniformity and the control of thickness can be relatively difficult (close space sublimation). In this paper we report on the development of a process using pulsed Direct Current magnetron sputtering which allows nanometre control of thin film thickness using time only. The CdS thin films deposited in this process are highly uniformand smooth. They exhibit the preferred hexagonal structure at room temperature deposition and they have excellent optical properties. Importantly, the process is highly stable despite the use of a semi-insulating magnetron target. Moreover, the process is very fast. The deposition rate using 1.5 kW of power to a 6-inch circular magnetron was measured to be greater than 8 nm/s. This makes the process suitable for industrial deployment

Layered gallium sulfide optical properties from monolayer to CVD crystalline thin films

Interest in layered van der Waals semiconductor gallium monosulfide (GaS) is growing rapidly because of its wide band gap value between those of two-dimensional transition metal dichalcogenides and of insulating layered materials such as hexagonal boron nitride. For the design of envisaged optoelectronic, photocatalytic and photonic applications of GaS, the knowledge of its dielectric function is fundamental. Here we present a combined theoretical and experimental investigation of the dielectric function of crystalline 2H-GaS from monolayer to bulk. Spectroscopic imaging ellipsometry with micron resolution measurements are corroborated by first principle calculations of the electronic structure and dielectric function. We further demonstrate and validate the applicability of the established dielectric function to the analysis of the optical response of c-axis oriented GaS layers grown by chemical vapor deposition (CVD). These optical results can guide the design of novel, to our knowledge, optoelectronic and photonic devices based on low-dimensional GaS.Horizon 2020 Framework Programme (No 899598 – PHEMTRONICS)