MXene‐mediated Interfacial Growth of 2D‐2D Heterostructured Nanomaterials as Cathodes for Zn‐based Aqueous Batteries

2024-02-22T13:08:00+00:00February 22nd, 2024|Categories: Publications|Tags: , |

In this study, we introduce a novel approach for synthesizing two-dimensional (2D) MXene heterostructures featuring a sandwiched and cross-linked network structure. This method addresses the common issue of activity degradation in 2D nanomaterials caused by inevitable aggregation. By utilizing the distinct surface characteristics of MXene, we successfully induced the growth of various 2D nanomaterials on MXene substrates. This strategy effectively mitigates self-stacking defects and augments the exposure of surface areas. In particular, the obtained 2D-2D MXene@NiCo-layered double hydroxide (MH-NiCo) heterostructures exhibit enhanced structural stability, improved chemical reversibility, and heightened charge transfer efficiency, outperforming pure NiCo LDH. The aqueous MH-Ni4Co1//Zn@carbon cloth (MH-Ni4Co1//Zn@CC) battery demonstrates exceptional performance with a remarkable specific capacity of 0.61 mAh cm−2, maintaining 96.6% capacitance after 2300 cycles. Additionally, it achieves an energy density of 1.047 mWh cm−2 and a power density of 32.899 mW cm−2. This research not only paves the way for new design paradigms in energy-related nanomaterials but also offers invaluable insights for the application and optimization of 2D-2D heterostructures in advanced electrochemical devices.

Published in: "Angewandte Chemie International Edition".

Lateral Heterometal Junction Rectifier Fabricated by Sequential Transmetallation of Coordination Nanosheet

2024-02-20T13:08:15+00:00February 20th, 2024|Categories: Publications|Tags: |

A lateral heterojunction, fabricated by spatially confined transmetallation of a precursor zinc(II) benzenehexathiolato coordination nanosheet with Fe(II) and Cu(II) ions is reported. Structural differences between the transmetallated and the as-prepared nanosheets lead to physical and chemical differences. Band structure bending across the interface of the transmetallated nanosheets results in the observed rectifying behavior. Abstract Heterostructures of two-dimensional materials realise novel and enhanced physical phenomena, making them attractive research targets. Compared to inorganic materials, coordination nanosheets have virtually infinite combinations, leading to tunability of physical properties and are promising candidates for heterostructure fabrication. Although stacking of coordination materials into vertical heterostructures is widely reported, reports of lateral coordination material heterostructures are few. Here we show the successful fabrication of a seamless lateral heterojunction showing diode behaviour, by sequential and spatially limited immersion of a new metalladithiolene coordination nanosheet, Zn3BHT, into aqueous Cu(II) and Fe(II) solutions. Upon immersion, the Zn centres in insulating Zn3BHT are replaced by Cu or Fe ions, resulting in conductivity. The transmetallation is spatially confined, occurring only within the immersed area. We anticipate that our results will be a starting point towards exploring transmetallation of various two-dimensional materials to produce lateral heterojunctions, by providing a new and facile synthetic route.

Published in: "Angewandte Chemie International Edition".

Metavalent Bonding in 2D Chalcogenides: Structural Origin and Chemical Mechanisms

2023-11-21T13:08:12+00:00November 21st, 2023|Categories: Publications|Tags: |

An unusual set of anomalous functional properties of rocksalt crystals of Group IV chalcogenides were recently linked to a kind of bonding termed as metavalent bonding (MVB) which involves violation of the 8-N rule. Precise mechanisms of MVB and the relevance of lone pair of group IV cations are still debated. With restrictions of low dimensionality on the possible atomic coordination, 2D materials provide a rich platform for exploration of MVB. Here, we present first-principles theoretical analysis of the nature of bonding in five distinct 2D lattices of group IV chalcogenides MX (M: Sn, Pb, Ge and X: S, Se, Te), in which the natural out-of-plane expression of the lone pair versus in-plane bonding can be systematically explored.  While their honeycomb lattices respecting the 8-N rule are shown to exhibit covalent bonding, their square and orthorhombic structures exhibit MVB only in-plane, withcationic lone-pair activating the out-of-plane structural puckering that controls their relative stability. Anomalies in Born-effective charges, dielectric constants, Grüneisen parameters occur only in their in-plane behaviour, confirming MVB is confined strictly to 2D and originates from p-p orbital interactions. Our work opens up directions for chemical design of MVB based 2D materials and their heterostructures.

Published in: "Angewandte Chemie International Edition".

Synergistic Combination of Reductive Covalent Functionalization and Atomic Layer Deposition—Towards Spatially Defined Graphene‐Organic‐Inorganic Heterostructures

2023-11-15T13:08:43+00:00November 15th, 2023|Categories: Publications|Tags: , |

The unprecedented covalent three dimensionally patterned graphene heterostructures consisting of a graphene monolayer, a tailor-made organophenyl bridging layer, and three metal oxide films (ZnO, Al2O3, and CuO) were constructed. These spatially resolved and hierarchically structured nano-ensembles are generated via a 2D-functionalization-mediated atomic layer deposition growth process. Abstract Three-dimensionally (3D) well-ordered and highly integrated graphene hybrid architectures are considered to be next-generation multifunctional graphene materials but still remain elusive. Here, we report the first realization of unprecedented 3D-patterned graphene nano-ensembles composed of a graphene monolayer, a tailor-made structured organophenyl layer, and three metal oxide films, providing the first example of such a hybrid nano-architecture. These spatially resolved and hierarchically structured quinary hybrids are generated via a two-dimensional (2D)-functionalization-mediated atomic layer deposition growth process, involving an initial lateral molecular programming of the graphene lattice via lithography-assisted 2D functionalization and a subsequent stepwise molecular assembly in these regions in the z-direction. Our breakthrough lays the foundation for the construction of emerging 3D-patterned graphene heterostructures.

Published in: "Angewandte Chemie International Edition".

Surface Termination on Unstable Methylammonium‐based Perovskite Using a Steric Barrier for Improved Perovskite Solar Cells

2023-11-01T09:25:29+00:00November 1st, 2023|Categories: Publications|Tags: |

Compared to widely adopted low-dimensional/three-dimensional (LD/3D) heterostructure, functional organic cation based surface termination on perovskite can not only realize advantage of defect passivation but also prevent potential disadvantage of the heterostructure induced intercalation into 3D perovskite. However, it is still very challenging to controllably construct surface termination on organic-inorganic hybrid perovskite because the functional organic cations’ substitution reaction is easy to form LD/3D heterostructure. Here, we report using a novel benzyltrimethylammonium (BTA) functional cation with rational designed steric hindrance to effectively surface terminate onto methylammonium lead triiodide (MAPbI3) perovskite, which is composed of the most unstable MA cations. The BTA cation is difficult to form a specific 1.5-dimensional perovskite of BTA4Pb3I10 by cation substitution with MA cation, which then provides a wide processing window (around 10 minutes) for surface terminating on MAPbI3 films. Moreover, the BTAI surface terminated BTAI-MAPbI3 shows better passivation effect than BTA4Pb3I10-MAPbI3 heterojunction. Finally, BTAI surface terminated solar cell (0.085 cm2) and mini-module (11.52 cm2) obtained the efficiencies of 22.03% and 18.57%, which are among the highest efficiencies for MAPbI3 based ones.

Published in: "Angewandte Chemie International Edition".

Boosting Fe Cationic Vacancies with Graphdiyne to Enhance Exceptional Pseudocapacitive Lithium Intercalation

2023-07-06T13:08:21+00:00July 6th, 2023|Categories: Publications|Tags: , |

Modulating the electronic structure of electrode materials at atomic level is the key to controlling electrodes with outstanding rate capability. On the basis of modulating the electronic structure of materials, we proposed the design idea of graphdiyne/ferroferric oxide heterostructure (IV-GDY-FO) and controllable preparation of anode materials containing Fe Cationic vacancies. The goal is to motivate lithium-ion batteries (LIBs) toward ultra-high capacity, superior cyclic stability, and excellent rate performance. The graphdiyne is used as carriers to disperse Fe3O4 uniformly without agglomeration and induce high valence of Fe with reducing the energy in the system. The presence of Fe vacancy could regulate the charge distribution around vacancies and adjacent atoms, leading to facilitate electronic transportation, enlarge the lithium-ion diffusion, and decrease Li+ diffusion barriers, and thus displaying significant pseudocapacitive process and advantageous lithium-ion storage. The optimized electrode IV-GDY-FO reveals a capacity of 2084.1mAh g-1 at 0.1C, superior cycle stability and rate performance with a high specific capacity of 1057.4 mAh g-1 even at 10C.

Published in: "Angewandte Chemie International Edition".

High‐throughput Synthesis of Solution‐Processable van der Waals Heterostructures through Electrochemistry

2023-06-07T13:08:21+00:00June 7th, 2023|Categories: Publications|Tags: , , , , |

A general method is demonstrated for the preparation of high-quality van der Waals heterostructures in solution through an electrochemical strategy. The produced van der Waals heterostructures exhibit strong interlayer coupling, extraordinary structural integrity, large lateral dimension and good optoelectronic properties. Abstract Two-dimensional van der Waals heterostructures (2D vdWHs) have recently gained widespread attention because of their abundant and exotic properties, which open up many new possibilities for next-generation nanoelectronics. However, practical applications remain challenging due to the lack of high-throughput techniques for fabricating high-quality vdWHs. Here, we demonstrate a general electrochemical strategy to prepare solution-processable high-quality vdWHs, in which electrostatic forces drive the stacking of electrochemically exfoliated individual assemblies with intact structures and clean interfaces into vdWHs with strong interlayer interactions. Thanks to the excellent combination of strong light absorption, interfacial charge transfer, and decent charge transport properties in individual layers, thin-film photodetectors based on graphene/In2Se3 vdWHs exhibit great promise for near-infrared (NIR) photodetection, owing to a high responsivity (267 mA W−1), fast rise (72 ms) and decay (426 ms) times under NIR illumination. This approach enables various hybrid systems, including graphene/In2Se3, graphene/MoS2 and graphene/MoSe2 vdWHs, providing a broad avenue for exploring emerging electronic, photonic, and exotic quantum phenomena.

Published in: "Angewandte Chemie International Edition".

Imaging Moir’e Excited States with Photocurrent Tunneling Microscopy. (arXiv:2306.00859v1 [cond-mat.mes-hall])

2023-06-02T02:29:45+00:00June 2nd, 2023|Categories: Publications|Tags: , |

Moir’e superlattices provide a highly tunable and versatile platform to explore novel quantum phases and exotic excited states ranging from correlated insulators1-17 to moir’e excitons7-10,18. Scanning tunneling microscopy has played a key role in probing microscopic behaviors of the moir’e correlated ground states at the atomic scale1,11-15,19. Atomic-resolution imaging of quantum excited state in moir’e heterostructures, however, has been an outstanding experimental challenge. Here we develop a novel photocurrent tunneling microscopy by combining laser excitation and scanning tunneling spectroscopy (laser-STM) to directly visualize the electron and hole distribution within the photoexcited moir’e exciton in a twisted bilayer WS2 (t-WS2). We observe that the tunneling photocurrent alternates between positive and negative polarities at different locations within a single moir’e unit cell. This alternating photocurrent originates from the exotic in-plane charge-transfer (ICT) moir’e exciton in the t-WS2 that emerges from the competition between the electron-hole Coulomb interaction and the moir’e potential landscape. Our photocurrent maps are in excellent agreement with our GW-BSE calculations for excitonic states in t-WS2. The photocurrent tunneling microscopy creates new opportunities for exploring photoexcited non-equilibrium moir’e phenomena at the atomic scale.

Published in: "arXiv Material Science".

Thickness Insensitive Nanocavities for 2D Heterostructures using Photonic Molecules. (arXiv:2305.20034v1 [cond-mat.mes-hall])

2023-06-01T04:30:22+00:00June 1st, 2023|Categories: Publications|Tags: , |

Two-dimensional (2D) heterostructures integrated into nanophotonic cavities have emerged as a promising approach towards novel photonic and opto-electronic devices. However, the thickness of the 2D heterostructure has a strong influence on the resonance frequency of the hybrid cavity. For a single cavity, the resonance frequency shifts approximately linearly with the thickness. Here, we propose to use the inherent non-linearity of the mode coupling to render the cavity mode insensitive to the thickness of the 2D heterostructure. Based on the couple mode theory, we reveal that this goal can be achieved using either a homoatomic molecule with a filtered coupling or heteroatomic molecules. We perform numerical simulations to further demonstrate the robustness of the eigenfrequency in the proposed photonic molecules. Our results render nanophotonic structures insensitive to the thickness of 2D materials, thus owing appealing potential in energy- or detuning-sensitive applications such as cavity quantum electrodynamics.

Published : "arXiv Mesoscale and Nanoscale Physics".

Interplay between optical emission and magnetism in the van der Waals magnetic semiconductor CrSBr in the two-dimensional limit. (arXiv:2305.18094v1 [physics.app-ph])

2023-05-30T04:30:37+00:00May 30th, 2023|Categories: Publications|Tags: |

The Van der Waals semiconductor metamagnet CrSBr offers an ideal platform for studying the interplay between optical and magnetic properties in the two-dimensional limit. Here, we carried out an exhaustive optical characterization of this material by means of temperature and magnetic field dependent photoluminescence (PL) on flakes of different thicknesses down to the monolayer. We found a characteristic emission peak that is quenched upon switching the ferromagnetic layers from an antiparallel to a parallel configuration and exhibits a different temperature dependence from that of the peaks commonly ascribed to excitons. The contribution of this peak to the PL is boosted around 30-40 K, coinciding with the hidden order magnetic transition temperature. Our findings reveal the connection between the optical and magnetic properties via the ionization of magnetic donor vacancies. This behavior enables a useful tool for the optical reading of the magnetic states in atomically thin layers of CrSBr and shows the potential of the design of two-dimensional heterostructures with magnetic and excitonic properties.

Published : "arXiv Mesoscale and Nanoscale Physics".

From incommensurate bilayer heterostructures to Allen-Cahn: An exact thermodynamic limit. (arXiv:2305.18186v1 [math-ph])

2023-05-30T02:29:34+00:00May 30th, 2023|Categories: Publications|Tags: , |

Assuming any site-potential dependent on two-point correlations, we rigorously derive a new model for an interlayer potential for incommensurate bilayer heterostructures such as twisted bilayer graphene. We use the ergodic property of the local configuration in incommensurate bilayer heterostructures to prove convergence of an atomistic model to its thermodynamic limit without a rate for minimal conditions on the lattice displacements. We provide an explicit error control with a rate of convergence for sufficiently smooth lattice displacements. For that, we introduce the notion of Diophantine 2D rotations, a two-dimensional analogue of Diophantine numbers, and give a quantitative ergodic theorem for Diophantine 2D rotations.

Published in: "arXiv Material Science".

Excitonic interactions and mechanism for ultrafast interlayer photoexcited response in van der Waals heterostructures. (arXiv:2305.17335v1 [cond-mat.mtrl-sci])

2023-05-30T02:29:21+00:00May 30th, 2023|Categories: Publications|Tags: |

Optical dynamics in van der Waals heterobilayers is of fundamental scientific and practical interest. Based on a time-dependent adiabatic GW approach, we discover a new many-electron (excitonic) channel for converting photoexcited intralayer to interlayer excitations and the associated ultrafast optical responses in heterobilayers, which is conceptually different from the conventional single-particle picture. We find strong electron-hole interactions drive the dynamics and enhance the pump-probe optical responses by an order of magnitude with a rise time of ~300 fs in MoSe$_2$/WSe$_2$ heterobilayers, in agreement with experiment.

Published in: "arXiv Material Science".

Dual‐Functional Z‐Scheme TiO2@MoS2@C Multi‐Heterostructures for Photo‐Driving Ultra‐Fast Sodium Ion Storage

2023-05-29T13:08:25+00:00May 29th, 2023|Categories: Publications|Tags: , , |

Exploiting dual-functional photoelectrodes to harvest and store solar energy is a challenging but efficient way of achieving renewable energy utilization. Herein, TiO2@MoS2@C multi-heterostructures with photoelectric conversion and electronic transmission interfaces are designed as dual-functional photoelectrode for ultra-fast sodium ion storage. When assembled to photo sodium ion battery (photo-SIB), its capacity increases to 444.1 mAh g-1 with a high photo-conversion efficiency of 0.71% switching from dark to visible light at 2.0 A g-1. Remarkably, the photo-SIB can be recharged only by light and provide a striking capacity of 231.4 mAh g-1. Experimental and theoretical results confirm the multi-heterostructures can enhance sodium ion storage kinetics, ensure structural stability, and facilitate photo-excited carrier separation and transmission under light. This work presents a brand-new strategy to design dual-functional photoelectrodes for efficient solar harvesting and storage.

Published in: "Angewandte Chemie International Edition".

Room temperature quantum Hall effect in a gated ferroelectric-graphene heterostructure. (arXiv:2305.16825v1 [cond-mat.mes-hall])

2023-05-29T04:30:25+00:00May 29th, 2023|Categories: Publications|Tags: , , |

The quantum Hall effect is widely used for the investigation of fundamental phenomena, ranging from topological phases to composite fermions. In particular, the discovery of a room temperature resistance quantum in graphene is significant for compact resistance standards that can operate above cryogenic temperatures. However, this requires large magnetic fields that are accessible only in a few high magnetic field facilities. Here, we report on the quantum Hall effect in graphene encapsulated by the ferroelectric insulator CuInP2S6. Electrostatic gating of the graphene channel enables the Fermi energy to be tuned so that electrons in the localized states of the insulator are in equilibrium with the current-carrying, delocalized states of graphene. Due to the presence of strongly bound states in this hybrid system, a quantum Hall plateau can be achieved at room temperature in relatively modest magnetic fields. This phenomenon offers the prospect for the controlled manipulation of the quantum Hall effect at room temperature.

Published : "arXiv Mesoscale and Nanoscale Physics".

Strong magnetic proximity effect in Van der Waals heterostructures driven by direct hybridization. (arXiv:2305.16813v1 [cond-mat.mes-hall])

2023-05-29T04:30:18+00:00May 29th, 2023|Categories: Publications|Tags: , , |

We propose a new class of magnetic proximity effects based on the spin dependent hybridization between the electronic states at the Fermi energy in a non-magnetic conductor and the narrow spin split bands of a ferromagnetic insulator. Unlike conventional exchange proximity, we show this hybridization proximity effect has a very strong influence on the non-magnetic layer and can be further modulated by application of an electric field. We use DFT calculations to illustrate this effect in graphene placed next to a monolayer of CrI$_3$, a ferromagnetic insulator. We find strong hybridization of the graphene bands with the narrow conduction band of CrI$_3$ in one spin channel only. We show that our results are robust with respect to lattice mismatch and twist angle variations. Furthermore, we show that an out-of-plane electric field can be used to modulate the hybridization strength, paving the way for applications.

Published : "arXiv Mesoscale and Nanoscale Physics".

Flat bands in bilayer graphene induced by proximity with polar $h$-BN superlattices. (arXiv:2305.09749v2 [cond-mat.mes-hall] UPDATED)

2023-05-29T02:30:22+00:00May 29th, 2023|Categories: Publications|Tags: , , |

Motivated by the observation of polarization superlattices in twisted multilayers of hexagonal boron nitride ($h$-BN), we address the possibility of using these heterostructures for tailoring the properties of multilayer graphene by means of the electrostatic proximity effect. By using the combination of first-principles and large-scale tight-binding model calculations coupled via the Wannier function approach, we demonstrate the possibility of creating a sequence of well-separated flat-band manifolds in AB-stacked bilayer graphene at experimentally relevant superlattice periodicities above $sim$30 nm. Our calculations show that the details of band structures depend on the local inversion symmetry breaking and the vertical electrical polarization, which are directly related to the atomic arrangement. The results advance the atomistic characterization of graphene-based systems in a superlattice potential beyond the continuum model.

Published in: "arXiv Material Science".

Direct visualization of the charge transfer in Graphene/$alpha$-RuCl$_3$ heterostructure. (arXiv:2305.17130v1 [cond-mat.mtrl-sci])

2023-05-29T02:30:20+00:00May 29th, 2023|Categories: Publications|Tags: , , |

We investigate the electronic properties of a graphene and $alpha$-ruthenium trichloride (hereafter RuCl$_3$) heterostructure, using a combination of experimental and theoretical techniques. RuCl$_3$ is a Mott insulator and a Kitaev material, and its combination with graphene has gained increasing attention due to its potential applicability in novel electronic and optoelectronic devices. By using a combination of spatially resolved photoemission spectroscopy, low energy electron microscopy, and density functional theory (DFT) calculations we are able to provide a first direct visualization of the massive charge transfer from graphene to RuCl$_3$, which can modify the electronic properties of both materials, leading to novel electronic phenomena at their interface. The electronic band structure is compared to DFT calculations that confirm the occurrence of a Mott transition for RuCl$_3$. Finally, a measurement of spatially resolved work function allows for a direct estimate of the interface dipole between graphene and RuCl$_3$. The strong coupling between graphene and RuCl$_3$ could lead to new ways of manipulating electronic properties of two-dimensional lateral heterojunction. Understanding the electronic properties of this structure is pivotal for designing next generation low-power opto-electronics devices.

Published in: "arXiv Material Science".

Dual‐Functional Z‐Scheme TiO2@MoS2@C Multi‐Heterostructures for Photo‐Driving Ultra‐Fast Sodium Ion Storage

2023-05-28T08:36:08+00:00May 28th, 2023|Categories: Publications|Tags: , , |

Exploiting dual-functional photoelectrodes to harvest and store solar energy is a challenging but efficient way of achieving renewable energy utilization. Herein, TiO2@MoS2@C multi-heterostructures with photoelectric conversion and electronic transmission interfaces are designed as dual-functional photoelectrode for ultra-fast sodium ion storage. When assembled to photo sodium ion battery (photo-SIB), its capacity increases to 444.1 mAh g-1 with a high photo-conversion efficiency of 0.71% switching from dark to visible light at 2.0 A g-1. Remarkably, the photo-SIB can be recharged only by light and provide a striking capacity of 231.4 mAh g-1. Experimental and theoretical results confirm the multi-heterostructures can enhance sodium ion storage kinetics, ensure structural stability, and facilitate photo-excited carrier separation and transmission under light. This work presents a brand-new strategy to design dual-functional photoelectrodes for efficient solar harvesting and storage.

Published in: "Angewandte Chemie International Edition".

Spin and Charge Fluctuation Induced Pairing in ABCB Tetralayer Graphene. (arXiv:2305.14438v2 [cond-mat.supr-con] UPDATED)

2023-05-28T08:32:56+00:00May 28th, 2023|Categories: Publications|Tags: , |

Motivated by the recent experimental realization of ABCB stacked tetralayer graphene [Wirth et al., ACS Nano 16, 16617 (2022)], we study correlated phenomena in moir’e-less graphene tetralayers for realistic interaction profiles using an orbital resolved random phase approximation approach. We demonstrate that magnetic fluctuations originating from local interactions are crucial close to the van Hove singularities on the electron- and hole-doped side promoting layer selective ferrimagnetic states. Spin fluctuations around these magnetic states enhance unconventional spin-triplet, valley-singlet superconductivity with $f$-wave symmetry due to intervalley scattering. Charge fluctuations arising from long range Coulomb interactions promote doubly degenerate $p$-wave superconductivity close to the van Hove singularities. At the conduction band edge of ABCB graphene, we find that both spin and charge fluctuations drive $f$-wave superconductivity. Our analysis suggests a strong competition between superconducting states emerging from long- and short-ranged Coulomb interactions and thus stresses the importance of microscopically derived interaction profiles to make reliable predictions for the origin of superconductivity in graphene based heterostructures.

Published : "arXiv Mesoscale and Nanoscale Physics".

Bandgap manipulation of hBN by alloying with aluminum: absorption properties of hexagonal BAlN. (arXiv:2305.15810v1 [cond-mat.mtrl-sci])

2023-05-28T08:31:04+00:00May 28th, 2023|Categories: Publications|Tags: , , |

The versatile range of applications for two-dimensional (2D) materials has encouraged scientists to further engineer the properties of these materials. This is often accomplished by stacking layered materials into more complex van der Waals heterostructures. A much less popular but technologically promising approach is the alloying of 2D materials with different element compositions. In this work, we demonstrate a first step in manipulating the hBN bandgap in terms of its width and indirect/direct character of the optical transitions. We present a set of aluminum alloyed hexagonal boron nitride (hBAlN) samples that were grown by metal organic vapor phase epitaxy (MOVPE) on 2-inch sapphire substrates with different aluminum concentration. Importantly, the obtained samples revealed a sp$^2$-bonded crystal structure. Optical absorption experiments disclosed two strong peaks in the excitonic spectral range with absorption coefficient $alpha sim 10^6$ cm$^{-1}$. Their energies correspond very well with the energies of indirect and direct bandgap transitions in hBN. However, they are slightly redshifted. This observation is in agreement with predictions that alloying with Al leads to a decrease of the bandgap energy. The observation of two absorption peaks can be explained in terms of mixing electronic states in the K and M conduction band valleys, which leads to a significant enhancement of the absorption coefficient for indirect transitions.

Published in: "arXiv Material Science".

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