{"title":"HfOX monolayers (X = S, Se, Te): Atomically thin semiconductors with tailored band gaps and broadband optical response","authors":"Mohamed Barhoumi , Koussai Lazaar , Wissem Dimassi , Moncef Said","doi":"10.1016/j.susc.2025.122830","DOIUrl":null,"url":null,"abstract":"<div><div>Two-dimensional (2D) mixed-anion materials, particularly oxy-chalcogenides, offer a rich platform for tailoring electronic and optical properties through compositional engineering. In this work, we present a comprehensive first-principles investigation of hafnium-based oxy-chalcogenide monolayers (HfOX, X = S, Se, Te) using density functional theory (DFT) with generalized gradient approximation (GGA) and hybrid BLYP functionals. Structural optimizations reveal that all three monolayers adopt tetragonal lattices with a systematically increasing bond length and lattice parameters from S to Te, reflecting the chalcogen-dependent steric effects. Phonon dispersion calculations confirm their dynamic stability, while electronic structure analysis shows that HfOS and HfOSe are direct band gap semiconductors (1.08 eV and 0.97 eV, respectively), whereas HfOTe exhibits an indirect gap (0.65 eV). Charge density and electrostatic potential analyses highlight the polar covalent bonding nature and asymmetric charge distribution, which are crucial for piezoelectric and dielectric applications. Optical property calculations demonstrate strong broadband absorption across the ultraviolet to near-infrared spectrum (0.6–30 eV), with tunable peaks and high absorption coefficients (<span><math><mrow><mo>></mo><mn>7</mn><mo>.</mo><mn>3</mn><mo>×</mo><mn>1</mn><msup><mrow><mn>0</mn></mrow><mrow><mn>5</mn></mrow></msup></mrow></math></span> cm<sup>−1</sup>). Notably, HfOTe extends absorption into the infrared, while HfOS shows dominant UV activity. The refractive index and optical conductivity further reveal chalcogen-dependent trends, with static dielectric constants increasing from 1.82 (HfOS) to 2.24 (HfOTe). Our results establish HfOX monolayers as a promising class of 2D semiconductors with layer-dependent band gaps, anisotropic optical responses, and potential applications in flexible optoelectronics, photovoltaics, and nanoscale dielectric devices.</div></div>","PeriodicalId":22100,"journal":{"name":"Surface Science","volume":"762 ","pages":"Article 122830"},"PeriodicalIF":1.8000,"publicationDate":"2025-08-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Surface Science","FirstCategoryId":"92","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0039602825001372","RegionNum":4,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q3","JCRName":"CHEMISTRY, PHYSICAL","Score":null,"Total":0}
引用次数: 0
Abstract
Two-dimensional (2D) mixed-anion materials, particularly oxy-chalcogenides, offer a rich platform for tailoring electronic and optical properties through compositional engineering. In this work, we present a comprehensive first-principles investigation of hafnium-based oxy-chalcogenide monolayers (HfOX, X = S, Se, Te) using density functional theory (DFT) with generalized gradient approximation (GGA) and hybrid BLYP functionals. Structural optimizations reveal that all three monolayers adopt tetragonal lattices with a systematically increasing bond length and lattice parameters from S to Te, reflecting the chalcogen-dependent steric effects. Phonon dispersion calculations confirm their dynamic stability, while electronic structure analysis shows that HfOS and HfOSe are direct band gap semiconductors (1.08 eV and 0.97 eV, respectively), whereas HfOTe exhibits an indirect gap (0.65 eV). Charge density and electrostatic potential analyses highlight the polar covalent bonding nature and asymmetric charge distribution, which are crucial for piezoelectric and dielectric applications. Optical property calculations demonstrate strong broadband absorption across the ultraviolet to near-infrared spectrum (0.6–30 eV), with tunable peaks and high absorption coefficients ( cm−1). Notably, HfOTe extends absorption into the infrared, while HfOS shows dominant UV activity. The refractive index and optical conductivity further reveal chalcogen-dependent trends, with static dielectric constants increasing from 1.82 (HfOS) to 2.24 (HfOTe). Our results establish HfOX monolayers as a promising class of 2D semiconductors with layer-dependent band gaps, anisotropic optical responses, and potential applications in flexible optoelectronics, photovoltaics, and nanoscale dielectric devices.
期刊介绍:
Surface Science is devoted to elucidating the fundamental aspects of chemistry and physics occurring at a wide range of surfaces and interfaces and to disseminating this knowledge fast. The journal welcomes a broad spectrum of topics, including but not limited to:
• model systems (e.g. in Ultra High Vacuum) under well-controlled reactive conditions
• nanoscale science and engineering, including manipulation of matter at the atomic/molecular scale and assembly phenomena
• reactivity of surfaces as related to various applied areas including heterogeneous catalysis, chemistry at electrified interfaces, and semiconductors functionalization
• phenomena at interfaces relevant to energy storage and conversion, and fuels production and utilization
• surface reactivity for environmental protection and pollution remediation
• interactions at surfaces of soft matter, including polymers and biomaterials.
Both experimental and theoretical work, including modeling, is within the scope of the journal. Work published in Surface Science reaches a wide readership, from chemistry and physics to biology and materials science and engineering, providing an excellent forum for cross-fertilization of ideas and broad dissemination of scientific discoveries.