InGaN Nanowires Research Articles

Binary Iron-Manganese Cocatalyst for Simultaneous Activation of C-C and C-O Bonds to Maximally Utilize Lignin for Syngas Generation over InGaN.

Solar-powered lignin reforming offers a carbon-neutral route for syngas production. This study explores a dual non-precious iron-manganese cocatalyst to simultaneously activate both C-C and C-O bonds for maximizing the utilization of various substituents of native lignin to yield syngas. By assembling with InGaN nanowires on a Si wafer, the as-designed dual FeMn cocatalyst affords a measurable syngas evolution rate of 42.4 mol·gcat-1·h-1 from native lignin in distilled water with a high selectivity of 93% and tunable H2/CO ratios under concentrated light, leading to a considerable light-to-fuel efficiency of 11.8%. The high FeMn atom efficiency arising from the 1-dimensional nanostructure of InGaN enables the achievement of a high turnover frequency (TOF) of 220896 mol syngas per mol FeMn per hour. By correlating explorationexperiments,the critical role of the dual FeMn cocatalyst in the evolving mechanism of lignin and water toward syngas is disclosed at the atomic level. It is discovered that the synergetic iron-manganese cocatalyst supported by InGaN nanowires enables simultaneous activation of C-C and C-O bonds with comparable minimized dissociation energies.This work demonstrates a new and earth-abundant bifunctional cocatalyst for utilizing various substituents of lignin to produce syngas powered by sunlight beyond fossil fuels.

Binary Iron‐Manganese Cocatalyst for Simultaneous Activation of C‐C and C‐O Bonds to Maximally Utilize Lignin for Syngas Generation over InGaN

Solar‐powered lignin reforming offers a carbon‐neutral route for syngas production. This study explores a dual non‐precious iron‐manganese cocatalyst to simultaneously activate both C‐C and C‐O bonds for maximizing the utilization of various substituents of native lignin to yield syngas. By assembling with InGaN nanowires on a Si wafer, the as‐designed dual FeMn cocatalyst affords a measurable syngas evolution rate of 42.4 mol·gcat‐1·h‐1 from native lignin in distilled water with a high selectivity of 93% and tunable H2/CO ratios under concentrated light, leading to a considerable light‐to‐fuel efficiency of 11.8%. The high FeMn atom efficiency arising from the 1‐dimensional nanostructure of InGaN enables the achievement of a high turnover frequency (TOF) of 220896 mol syngas per mol FeMn per hour. By correlating exploration experiments, the critical role of the dual FeMn cocatalyst in the evolving mechanism of lignin and water toward syngas is disclosed at the atomic level. It is discovered that the synergetic iron‐manganese cocatalyst supported by InGaN nanowires enables simultaneous activation of C‐C and C‐O bonds with comparable minimized dissociation energies. This work demonstrates a new and earth‐abundant bifunctional cocatalyst for utilizing various substituents of lignin to produce syngas powered by sunlight beyond fossil fuels.

Green Syngas Production from Natural Lignin, Sunlight, and Water over Pt-Decorated InGaN Nanowires.

Transformation of lignin to syngas can turn waste into treasure yet remains a tremendous challenge because of its naturally evolved stubborn structure. In this work, light-driven reforming of natural lignin in water for green syngas production is explored using Pt-decorated InGaN nanowires. The spectroscopic characterizations, isotope, and model compound experiments, as well as density function theory calculation, disclose that among a variety of groups including aromatic ring, -OH, -OCH3, -C3H7 with complex chemical bonds of O-H, C-H, C-C, C-O, etc., InGaN nanowires are cooperative with Pt for preferably breaking the C-O bond of the rich O-CH3 group in lignin to liberating ⋅CH3 by photogenerated holes with a minimum dissociation energy of 2.33 eV. Syngas are subsequently yielded from the continuous evolution of ⋅CH3 and ⋅OH from photocatalytic reforming of lignin in water. Together with the superior optoelectronic attributes of Pt-decorated InGaN nanowires, the evolution rate of syngas approaches 43.4 mol ⋅ g-1 ⋅ h-1 with tunable H2/CO ratios and a remarkable turnover number (TON) of 150, 543 mol syngas per mol Pt. Notably, the architecture demonstrates a high light efficiency of 12.1 % for syngas generation under focused light without any extra thermal input. Outdoor test ascertains the viability of producing syngas with the only inputs of natural lignin, water, and sunlight, thus presenting a low-carbon route for synthesizing transportation fuels and value-added chemicals.

Green Syngas Production from Natural Lignin, Sunlight, and Water over Pt‐Decorated InGaN Nanowires

AbstractTransformation of lignin to syngas can turn waste into treasure yet remains a tremendous challenge because of its naturally evolved stubborn structure. In this work, light‐driven reforming of natural lignin in water for green syngas production is explored using Pt‐decorated InGaN nanowires. The spectroscopic characterizations, isotope, and model compound experiments, as well as density function theory calculation, disclose that among a variety of groups including aromatic ring, −OH, −OCH3, −C3H7 with complex chemical bonds of O−H, C−H, C−C, C−O, etc., InGaN nanowires are cooperative with Pt for preferably breaking the C−O bond of the rich O−CH3 group in lignin to liberating ⋅CH3 by photogenerated holes with a minimum dissociation energy of 2.33 eV. Syngas are subsequently yielded from the continuous evolution of ⋅CH3 and ⋅OH from photocatalytic reforming of lignin in water. Together with the superior optoelectronic attributes of Pt‐decorated InGaN nanowires, the evolution rate of syngas approaches 43.4 mol ⋅ g−1 ⋅ h−1 with tunable H2/CO ratios and a remarkable turnover number (TON) of 150, 543 mol syngas per mol Pt. Notably, the architecture demonstrates a high light efficiency of 12.1 % for syngas generation under focused light without any extra thermal input. Outdoor test ascertains the viability of producing syngas with the only inputs of natural lignin, water, and sunlight, thus presenting a low‐carbon route for synthesizing transportation fuels and value‐added chemicals.

Super-Nernstian potentiometric response of InN/InGaN quantum dots by fractional electron transfer

The potentiometric response of InN/InGaN quantum dots (QDs) on Si (111) is experimentally studied and modeled as a function of the In content and morphology of the InGaN layer below the QDs due to the changing N flux in stationary plasma-assisted molecular beam epitaxy. For isolated core–shell InGaN nanowires formed for N-rich growth, sub-Nernstian response with Cl− anions as the test analyte is observed. For compact columnar InGaN layers formed in a very narrow range of N flux at the N-rich to metal-rich growth transition, a maximum super-Nernstian response of 100 mV/decade is achieved, provided the In content is high. With reducing N flux and In content, low super-Nernstian response and finally sub-Nernstian response are re-established for compact planar GaN layers. The maximum super-Nernstian response and the transition to sub-Nernstian response are quantitatively modeled by the quantum partition of electrons inside and outside of the QDs and consequent fractional electron transfer in the artificial chemical reaction of the QDs with the anions.

Evidence of two-dimensional lateral quantum confinement in self-formed core–shell InGaN nanowires on Si (111) emitting in the red

The proof of strong two-dimensional lateral quantum confinement in the In-rich core of red-light emitting self-formed core–shell InGaN nanowires is given. The nanowires are directly grown on Si (111) by plasma-assisted molecular beam epitaxy. After the initial InGaN nucleation, straight nanowires with quantum-size core radius determined by x-ray diffraction, transmission electron microscopy, and energy dispersive x-ray mappings develop. Detailed comparison of the photoluminescence from the core, the In contents of the core and shell, and the core radius with theoretical modeling reveals a parabolic confinement potential with large ground state quantum confinement energies of electrons and holes. Such strong lateral quantum confinement in a vertical quantum wire active region is ideal for the performance of optoelectronic devices, in particular of our reported red InGaN light emitting diode with high brightness and color stability.

High light utilization of double-layer InxGa1−xN heterojunction nanowire array photocathodes

We propose a photocathode structure based on InxGa1−xN heterojunction nanowire array to enhance solar energy utilization efficiency. Compared with single-component InGaN nanowires, heterojunction nanowires can achieve higher effective quantum efficiency through the introduction of built-in electric field. This means that it has higher actual performance than previous studies. The maximum effective quantum efficiency of 300 nm-300 nm In0.5Ga0.5N-In0.57Ga0.43N heterojunction nanowires can reach 40.8 % when the incident light is obliquely incident at an angle of 70°. In addition, the external electric field can significantly help the heterojunction nanowires maintain higher actual performance over a longer wavelength range. This research is expected to provide theoretical support for the development and performance improvement of high-performance solar photocathode.

On the growth of InGaN nanowires by molecular-beam epitaxy: influence of the III/V flux ratio on the structural and optical properties

On the growth of InGaN nanowires by molecular-beam epitaxy: influence of the III/V flux ratio on the structural and optical properties

Peculiarities of Nucleation and Growth of InGaN Nanowires on SiC/Si Substrates by HVPE

Peculiarities of Nucleation and Growth of InGaN Nanowires on SiC/Si Substrates by HVPE

Transition from Metal-Rich to N-Rich Growth for Core–Shell InGaN Nanowires on Si (111) at the Onset of In Desorption

Transition from Metal-Rich to N-Rich Growth for Core–Shell InGaN Nanowires on Si (111) at the Onset of In Desorption

Modification of alkali metal nanoparticles for enhanced light absorption and photoemission of InGaN nanowire arrays

Due to the important role played by local surface plasmon resonance (LSPR) in the fields of photocatalysis and solar cells, this article investigates InGaN nanowire arrays adsorbed by alkali metal (Li, Na, K, Cs) nanoparticles from two perspectives of light absorption and quantum efficiency. We simulate and model the structural parameters of nanoparticles, including their shape, position and size. The results show that Na nanoparticles have the best effect on improving the photoelectric conversion performance in the visible band. Although large diameters and high density nanoparticles can bring optical gain, their own losses will also increase. The relationship between the two should be balanced in the design. InGaN nanowires modified with Na nanoparticles with diameters of 20 nm and spacings of 50 nm can achieve optimal light absorption and photoemission in the visible range. Our research will contribute to the development of efficient visible light photocathodes.

Protecting and Enhancing the Photoelectrocatalytic Performance of InGaN Nanowires toward Nitrogen Reduction to Ammonia Synthesis

Protecting and Enhancing the Photoelectrocatalytic Performance of InGaN Nanowires toward Nitrogen Reduction to Ammonia Synthesis

Structural and optical properties of composition-graded InGaN nanowires

At the moment, InGaN ternary compounds are of a great interest for the development of devices for sunlight driven water splitting. However, the synthesis of such materials is hindered by the fact that InxGa1–xN layers are susceptible to phase decomposition at x from 20 to 80%. Nanowires can be a promising solution to this problem. The purpose of our study was to analyze the structural and optical properties of InxGa1–xN nanowires with a gradient x content being inside the miscibility gap. InxGa1–xN nanowires were grown on silicon substrates using plasma-assisted molecular beam epitaxy. The structural properties of nanowires were studied using scanning and transmission electron microscopy. The chemical composition and optical properties of nanowires were analyzed using energy-dispersive microanalysis and photoluminescence spectroscopy. It was shown for the first time that the composition-graded InxGa1–xN nanowires with x from 40 to 60% can be grown using plasma-assisted molecular beam epitaxy. The grown samples exhibit photoluminescence at room temperature with a maximum at about 890 nm, which corresponds to an In content of about 62% according to the modified Vegard’s rule and the transmission electron microscopy data. The obtained results can be of practical interest for the development of devices for water splitting induced by sunlight or sources of near IR radiation

Light-driven synthesis of C2H6 from CO2 and H2O on a bimetallic AuIr composite supported on InGaN nanowires

Light-driven synthesis of C2H6 from CO2 and H2O on a bimetallic AuIr composite supported on InGaN nanowires

Tunnel Junction Engineered Photocarrier Dynamics in Epitaxial Semiconductor Nanowires for Efficient and Ultrafast Photoelectrochemical Photodetectors

Photodetection using photoelectrochemical (PEC) principles is an emerging field in photonics. In recent years, using epitaxial III-nitride nanowires as photoelectrodes, high-performance PEC-type photodetectors (PDs) have been demonstrated, making the epitaxial III-nitride nanowires a scalable, high-performance PEC-PD architecture. Despite the progress, the photodetection performance improvement mainly occurs through incorporating photocatalysts into the nanowire photoelectrodes. In this study, we show that a semiconductor tunnel junction (TJ), which can be a natural component in the epitaxy process of semiconductor nanowires, can drastically improve the photodetection performance of such nanowire-based PEC-PDs. By using a three-electrode PEC cell configuration, we clearly show that an n++-GaN/InGaN/p++-GaN TJ can lead to a factor of 9× improvement on the responsivity of the InGaN nanowire photoelectrode in the blue band due to the TJ-induced photocarrier dynamics tuning, compared to the InGaN nanowire photoelectrode without the TJ. More drastically, the TJ also improves the photoresponse speed of the nanowire photoelectrode by 2 orders of magnitude, and for the electrode with the TJ an ultrafast response time of less than 10 ms is estimated. This TJ concept can also be applied to other TJ structures for other band photodetections. This study therefore sheds new light on further improving the performance of emerging epitaxial nanowire-based PEC-PDs for a wide range of applications from sensing to information processing.

Anisotropic Two-Photon Excited Photoluminescence and Optical Constants of InGaN Nanowires

Gallium nitride (GaN) and its derivatives are important materials for optoelectronic and electronic applications, such as light-emitting diodes, solid-state lasers, optical modulators, artificial photosynthesis, etc. Controlled growth and manipulation of these materials at nanoscale dimensions and understanding their linear and nonlinear optical properties lay the foundation for developing next-generation optoelectronic and electronic devices. In this context, herein, we report on the two-photon absorption and anisotropic two-photon excited photoluminescence of InGaN (IGN) nanowires grown by molecular beam epitaxy. The IGN nanowires were imaged using a home-built two-photon photoluminescence microscope with a tunable femtosecond laser to excite over the near-IR range (690–950 nm). In addition, the polarization angle of the excitation electric field was also rotated, and the emitted photoluminescence was analyzed with a polarizer. Results showed polarized photoluminescence with a stronger signal in the direction perpendicular to the IGN nanowires’ axis. Also, we observed strong two-photon absorption above the bandgap, with several excitation spectrum peaks near 740, 790, and 870 nm. These peaks showed anisotropic response to the excitation polarization angle, which may be due to the anisotropy of the IGN nanowires’ wurtzite phase. The polarized light absorption and emission nature of IGN nanowires, as revealed in this work, may be useful for optimizing materials for future optoelectronic device applications.

Effects of geometric parameters on optical absorption characteristics of InGaN nanostructured arrays

In recent years, with the development of wide-spectrum response photodetectors, InGaN as a semiconducting material has been widely studied. The nanowire array structure has excellent trapping ability, but different structures and shapes have different absorption abilities. It is necessary to optimize the nanowire array continuously in order to obtain the highest absorption efficiency possible. Based on this background, we study the effects of the geometry and structural parameters of InGaN nanowires on the optical response properties. We define the cone ratio and fill factor, respectively, and compare the optical absorption characteristics of InGaN nanowires by using the finite difference time domain (FDTD) method. The calculation results show that the truncated nanocone arrays can enhance the light capture ability and obtain the high sensitivity of the cut-off wavelength. Its optical absorption is at least 15% higher than that of nanowires. Therefore, the research of this paper can provide a certain theoretical reference for the experiment and preparation of InGaN photocathode.

Photoluminescence Redistribution of InGaN Nanowires Induced by Plasmonic Silver Nanoparticles

Hybrid nanostructures based on InGaN nanowires with decorated plasmonic silver nanoparticles are investigated in the present study. It is shown that plasmonic nanoparticles induce the redistribution of room temperature photoluminescence between short-wavelength and long-wavelength peaks of InGaN nanowires. It is defined that short-wavelength maxima decreased by 20%, whereas the long-wavelength maxima increased by 19%. We attribute this phenomenon to the energy transfer and enhancement between the coalesced part of the NWs with 10-13% In content and the tips above with an In content of about 20-23%. A proposed Fröhlich resonance model for silver NPs surrounded by a medium with refractive index of 2.45 and spread 0.1 explains the enhancement effect, whereas the decreasing of the short-wavelength peak is associated with the diffusion of charge carriers between the coalesced part of the NWs and the tips above.

InGaN nanowire array photocathode with high electron harvesting capability

With the rise of III-V semiconductor materials, InGaN materials began to be widely concerned. Nanowire arrays have excellent light trapping ability and generate a large number of photogenerated electrons. However, the adjacent nanowires will absorb these electrons twice, so the quantum efficiency cannot perfectly measure the emission performance of the nanowire array photocathode. We introduce the collection efficiency to evaluate the photoemission performance. It is based on this background that we study the photoemission performance of InGaN nanowire array under the assistance of height, incident light Angle and applied electric field. Finite-difference time-domain (FDTD) method is used to compare the quantum efficiency and collection efficiency of InGaN nanowire. We find that when the height of the nanowire is 600 nm, the angle of incident light is 65°, and the electric field strength is 0.6V/μm, InGaN nanowire arrays have the highest collection efficiency, with the collection efficiency up to 34% and the collection ratio up to 71%. The collection efficiency is 66% higher than that without external electric field. Therefore, the research in this paper can provide a theoretical reference for the preparation and performance improvement of InGaN nanowire array photocathode.

Investigating defects in InGaN based optoelectronics: from material and device perspective

III-nitride optoelectronics have revolutionized solid-state lighting technology. However, non-radiative defects play a major bottleneck in determining the performance of InGaN-based optoelectronics devices. It becomes especially challenging when high indium is required to be incorporated to obtain emission at higher wavelength (>500 nm). In this research article, we are going to discuss our investigation on the origin of defects in InGaN-based optoelectronics devices from the material and device perspective and characterize them through various techniques. This article broadly consists of two parts. In the first part, we investigate defects in InGaN based optoelectronics from a material point of view. Here, we discuss the challenges in the growth of InGaN planar (2-dimensional) and nanowires (1-dimensional) with high indium (≥20%) incorporation using the plasma-assisted molecular beam epitaxy (PA-MBE) technique. Photoluminescence spectroscopy (PL) has been performed to characterize these grown samples to assess their optical quality. Atomic force microscopy (AFM) has been employed to characterize the surface morphology of grown InGaN layers. High-resolution transmission electron microscopy (HRTEM) and scanning electron microcopy (SEM) are also used to characterize InGaN planar and nanowire samples grown under various process conditions. In the second part, we investigate the role of defects on InGaN optoelectronics from a device point of view. Here, we discuss the fabrication of InGaN multi-quantum well-based light emitting diodes (LEDs). Temperature-dependent current versus voltage measurements are carried out to investigate the role of defects on carrier dynamics under forward and reverse bias conditions. Frequency-dependent capacitance versus voltage (CV) and conductance versus voltage (GV) techniques are employed extensively to characterize defects in fabricated InGaN LEDs.