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Keywords = in-gap band

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13 pages, 2607 KiB  
Article
Defect-Induced Modulation of Electronic and Optical Properties in Monolayer CsPb2Br5: Implications for Fiber-Optic Sensing Applications
by Meiqi An, Wenxuan Fan, Shengsheng Wei and Junqiang Wang
Photonics 2025, 12(7), 638; https://doi.org/10.3390/photonics12070638 - 24 Jun 2025
Viewed by 318
Abstract
Two−dimensional halide perovskites have emerged as promising optoelectronic materials, yet the uncontrolled defect formation during synthesis remains a critical challenge for their practical applications. In this work, we systematically investigate the structural, electronic, and optical properties of monolayer CsPb2Br5 in [...] Read more.
Two−dimensional halide perovskites have emerged as promising optoelectronic materials, yet the uncontrolled defect formation during synthesis remains a critical challenge for their practical applications. In this work, we systematically investigate the structural, electronic, and optical properties of monolayer CsPb2Br5 in two representative configurations: ds−CsPb2Br5 and ss−CsPb2Br5. By introducing four types of vacancy defects—VBr−c, VBr−b, VCs, and VPb, we analyze their structural distortions, formation energies, and their impact on band structure and optical response using first−principles calculations. Our results reveal that Br−related vacancies are energetically most favorable and induce shallow defect levels and absorption edge redshifts in the ds−CsPb2Br5 structure, while in the ss−CsPb2Br5 configuration, only VBr−b forms a defect state. VPb and VCs lead to significant sub−bandgap absorption enhancement and dielectric response due to band−edge reorganization, despite not introducing in−gap states. Notably, VBr−c exhibits distinct infrared absorption in the ss−CsPb2Br5 model without electronic trap formation. These findings underscore the critical influence of defect type and slab asymmetry on the optoelectronic behavior of CsPb2Br5, providing guidance for defect engineering in perovskite−based optoelectronic applications. Full article
(This article belongs to the Special Issue Advanced Fiber Laser Technology and Its Application)
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10 pages, 6353 KiB  
Article
Electronic Structures of Molecular Beam Epitaxially Grown SnSe2 Thin Films on 3×3-Sn Reconstructed Si(111) Surface
by Zhujuan Li, Qichao Tian, Kaili Wang, Yuyang Mu, Zhenjie Fan, Xiaodong Qiu, Qinghao Meng, Can Wang and Yi Zhang
Appl. Sci. 2025, 15(11), 6150; https://doi.org/10.3390/app15116150 - 29 May 2025
Viewed by 434
Abstract
SnSe2, as a prominent member of the post-transition metal dichalcogenides, exhibits many intriguing physical phenomena and excellent thermoelectric properties, calling for both fundamental study and potential application in two-dimensional (2D) devices. In this article, we realized the molecular beam epitaxial growth [...] Read more.
SnSe2, as a prominent member of the post-transition metal dichalcogenides, exhibits many intriguing physical phenomena and excellent thermoelectric properties, calling for both fundamental study and potential application in two-dimensional (2D) devices. In this article, we realized the molecular beam epitaxial growth of SnSe2 films on a 3×3-Sn reconstructed Si(111) surface. The analysis of reflection high-energy electron diffraction reveals the in-plane lattice orientation as SnSe2[110]//3-Sn [112]//Si [110]. In addition, the flat morphology of SnSe2 film was identified by scanning tunneling microscopy (STM), implying the relatively strong adsorption effect of 3-Sn/Si(111) substrate to the SnSe2 adsorbates. Subsequently, the interfacial charge transfer was observed by X-ray photoemission spectroscopy. Afterwards, the direct characterization of electronic structures was obtained via angle-resolved photoemission spectroscopy. In addition to proving the presence of interfacial charge transfer again, a new relatively flat in-gap band was found in monolayer and few-layer SnSe2, which disappeared in multi-layer SnSe2. The interface strain-induced partial structural phase transition of thin SnSe2 films is presumed to be the reason. Our results provide important information on the characterization and effective modulation of electronic structures of SnSe2 grown on 3-Sn/Si(111), paving the way for the further study and application of SnSe2 in 2D electronic devices. Full article
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12 pages, 5183 KiB  
Article
Nonlinear Transport through Parity–Time Symmetric Lattice Potentials
by Wei Mao and Yongping Zhang
Symmetry 2024, 16(6), 640; https://doi.org/10.3390/sym16060640 - 22 May 2024
Viewed by 860
Abstract
We study nonlinear transports of a light field through finite parity–time symmetric lattice potentials. The initial light field is trapped in a source reservoir and is released to expand toward the lattice potentials along the transverse direction due to the nonlinearity. We identify [...] Read more.
We study nonlinear transports of a light field through finite parity–time symmetric lattice potentials. The initial light field is trapped in a source reservoir and is released to expand toward the lattice potentials along the transverse direction due to the nonlinearity. We identify the transports that can be classified into in-band and in-gap transports. In the in-band transport, the light field can tunnel through the lattices into the sink reservoir, and in the in-gap transport, the light field is self-trapped inside the lattices to form a solitary wave. Full article
(This article belongs to the Special Issue Symmetry-Related Quantum Phases in Exciton-Polariton Condensates)
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16 pages, 6204 KiB  
Article
Crucial Role of Ni Point Defects and Sb Doping for Tailoring the Thermoelectric Properties of ZrNiSn Half-Heusler Alloy: An Ab Initio Study
by Eleonora Ascrizzi, Chiara Ribaldone and Silvia Casassa
Materials 2024, 17(5), 1061; https://doi.org/10.3390/ma17051061 - 25 Feb 2024
Cited by 1 | Viewed by 1596
Abstract
In the wide group of thermoelectric compounds, the half-Heusler ZrNiSn alloy is one of the most promising materials thanks to its thermal stability and narrow band gap, which open it to the possibility of mid-temperature applications. A large variety of defects and doping [...] Read more.
In the wide group of thermoelectric compounds, the half-Heusler ZrNiSn alloy is one of the most promising materials thanks to its thermal stability and narrow band gap, which open it to the possibility of mid-temperature applications. A large variety of defects and doping can be introduced in the ZrNiSn crystalline structure, thus allowing researchers to tune the electronic band structure and enhance the thermoelectric performance. Within this picture, theoretical studies of the electronic properties of perfect and defective ZrNiSn structures can help with the comprehension of the relation between the topology of defects and the thermoelectric features. In this work, a half-Heusler ZrNiSn alloy is studied using different defective models by means of an accurate Density Functional Theory supercell approach. In particular, we decided to model the most common defects related to Ni, which are certainly present in the experimental samples, i.e., interstitial and antisite Ni and a substitutional defect consisting of the replacement of Sn with Sb atoms using concentrations of 3% and 6%. First of all, a comprehensive characterization of the one-electron properties is performed in order to gain deeper insight into the relationship between structural, topological and electronic properties. Then, the effects of the modeled defects on the band structure are analyzed, with particular attention paid to the region between the valence and the conduction bands, where the defective models introduce in-gap states with respect to the perfect ZrNiSn crystal. Finally, the electronic transport properties of perfect and defective structures are computed using semi-classical approximation in the framework of the Boltzmann transport theory as implemented in the Crystal code. The dependence obtained of the Seebeck coefficient and the power factor on the temperature and the carrier concentration shows reasonable agreement with respect to the experimental counterpart, allowing possible rationalization of the effect of the modeled defects on the thermoelectric performance of the synthesized samples. As a general conclusion, defect-free ZrNiSn crystal appears to be the best candidate for thermoelectric applications when compared to interstitial and antisite Ni defective models, and substitutional defects of Sn with Sb atoms (using concentrations of 3% and 6%) do not appreciably improve electronic transport properties. Full article
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16 pages, 9602 KiB  
Perspective
Plasmonic Modification of Epitaxial Nanostructures for the Development of a Highly Efficient SERS Platform
by Ewa Dumiszewska, Aleksandra Michałowska, Libor Nozka, Dariusz Czolak and Jan Krajczewski
Crystals 2023, 13(11), 1539; https://doi.org/10.3390/cryst13111539 - 26 Oct 2023
Cited by 1 | Viewed by 1728
Abstract
Epitaxy is the process of crystallization of monocrystalline layers and nanostructures on a crystalline substrate. It allows for the crystallization of various semiconductor layers on a finite quantity of semiconductor substrates, like GaAs, InP, GaP, InGaP, GaP, and many others. The growth of [...] Read more.
Epitaxy is the process of crystallization of monocrystalline layers and nanostructures on a crystalline substrate. It allows for the crystallization of various semiconductor layers on a finite quantity of semiconductor substrates, like GaAs, InP, GaP, InGaP, GaP, and many others. The growth of epitaxial heterostructures is very complicated and requires special conditions and the precise control of the growth temperature, the pressure in the reactor, and the flow of the precursors. It is used to grow epitaxial structures in lasers, diodes, detectors, photovoltaic structures, and so on. Semiconductors themselves are not suitable materials for application in surface-enhanced Raman spectroscopy (SERS) due to poor plasmonic properties in the UV/VIS range caused by missing free electrons in the conduction band due to the existing band gap. A plasmonic material is added on top of the nanostructured pattern, allowing for the formation of mixed photon–plasmon modes called localized surface plasmon-polaritons which stand behind the SERS effect. Typically, gold and silver are used as functional plasmonic layers. Such materials could be deposited via chemical or physical process. Attention has also been devoted to other plasmonic materials, like ones based on the nitrides of metals. The SERS performance of a functional surface depends both on the response of the plasmonic material and the morphology of the underlying semiconductor epitaxial layer. In the context of SERS, epitaxial growth allows for the fabrication of substrates with well-defined 3D nanostructures and enhanced electromagnetic properties. In this work, we described the possible potential plasmonic modification, composed of various coatings such as noble metals, TiN, and others, of well-developed epitaxial nanostructures for the construction of a new type of highly active SERS platforms. This abstract also highlights the role of epitaxial growth in advancing SERS, focusing on its principles, methods, and impact. Furthermore, this work outlines the potential of epitaxial growth to push the boundaries of SERS. The ability to design substrates with tailored plasmonic properties opens avenues for ultralow concentration detection. Full article
(This article belongs to the Special Issue Epitaxial Growth of Semiconductor Materials and Devices)
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9 pages, 4734 KiB  
Article
V-Substituted ZnIn2S4: A (Visible+NIR) Light-Active Photocatalyst
by Raquel Lucena and José C. Conesa
Photochem 2021, 1(1), 1-9; https://doi.org/10.3390/photochem1010001 - 7 Jan 2021
Cited by 2 | Viewed by 2201
Abstract
ZnIn2S4 is known to be a visible light-active photocatalyst. In this work, it is shown that by substituting part of the In atoms with vanadium, the visible light range of photocatalytic activity of such material can be extended, using the [...] Read more.
ZnIn2S4 is known to be a visible light-active photocatalyst. In this work, it is shown that by substituting part of the In atoms with vanadium, the visible light range of photocatalytic activity of such material can be extended, using the so-called in-gap band scheme that has been shown to enhance photovoltaic characteristics. Characterization of this material using several techniques, complemented by DFT calculations, will support this statement. While here only the degradation of aqueous HCOOH in well-aerated conditions is discussed, the same material may be used, with an adequate sacrificial reagent, for photocatalytic H2 generation. Full article
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16 pages, 36970 KiB  
Article
Transition Metal-Hyperdoped InP Semiconductors as Efficient Solar Absorber Materials
by Gregorio García, Pablo Sánchez-Palencia, Pablo Palacios and Perla Wahnón
Nanomaterials 2020, 10(2), 283; https://doi.org/10.3390/nano10020283 - 7 Feb 2020
Cited by 12 | Viewed by 3209
Abstract
This work explores the possibility of increasing the photovoltaic efficiency of InP semiconductors through a hyperdoping process with transition metals (TM = Ti, V, Cr, Mn). To this end, we investigated the crystal structure, electronic band and optical absorption features of TM-hyperdoped InP [...] Read more.
This work explores the possibility of increasing the photovoltaic efficiency of InP semiconductors through a hyperdoping process with transition metals (TM = Ti, V, Cr, Mn). To this end, we investigated the crystal structure, electronic band and optical absorption features of TM-hyperdoped InP (TM@InP), with the formula TMxIn1-xP (x = 0.03), by using accurate ab initio electronic structure calculations. The analysis of the electronic structure shows that TM 3d-orbitals induce new states in the host semiconductor bandgap, leading to improved absorption features that cover the whole range of the sunlight spectrum. The best results are obtained for Cr@InP, which is an excellent candidate as an in-gap band (IGB) absorber material. As a result, the sunlight absorption of the material is considerably improved through new sub-bandgap transitions across the IGB. Our results provide a systematic and overall perspective about the effects of transition metal hyperdoping into the exploitation of new semiconductors as potential key materials for photovoltaic applications. Full article
(This article belongs to the Section Energy and Catalysis)
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