Chemical bonding and Born charge in 1T-HfS2

Neal, Sabine N.; Li, Shutong; Birol, Turan; Musfeldt, J. L.

doi:10.1038/s41699-021-00226-z

Cited by 16 publications

(18 citation statements)

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“…According to group theory, 1T-HfS 2 has vibrational modes with symmetries of A 1g + E g + A 2 u + E u at the Γ point. The A 1g + E g modes are Raman-active, while the A 2 u + E u modes are infrared-active [ 21 , 53 , 54 ]. The Raman spectra of the pristine, Mn-, Fe-, Co-, and Cu-doped HfS 2 crystals recorded at room temperature are shown in Figure 1 e. There are weak peaks observed at approximately 131.7 cm −1 .…”

Section: Resultsmentioning

confidence: 99%

“…The Raman spectra of the pristine, Mn-, Fe-, Co-, and Cu-doped HfS 2 crystals recorded at room temperature are shown in Figure 1 e. There are weak peaks observed at approximately 131.7 cm −1 . Neal et al considered these peaks were due to the E u (TO) mode, which resulted from the in-plane out-of-phase vibrations of the atomic planes of S and the atomic planes of Hf [ 53 ]. However, the same E u mode was found in the infrared spectra at around 166 cm −1 [ 52 ] and 155 cm −1 [ 53 ].…”

Section: Resultsmentioning

confidence: 99%

“…Neal et al considered these peaks were due to the E u (TO) mode, which resulted from the in-plane out-of-phase vibrations of the atomic planes of S and the atomic planes of Hf [ 53 ]. However, the same E u mode was found in the infrared spectra at around 166 cm −1 [ 52 ] and 155 cm −1 [ 53 ]. Therefore, the origin of these weak peaks observed at approximately 131.7 cm −1 should still be further investigated.…”

Section: Resultsmentioning

confidence: 99%

“…Therefore, the origin of these weak peaks observed at approximately 131.7 cm −1 should still be further investigated. The weak peaks observed at approximately 256.2 cm −1 were due to the E g mode, which resulted from the in-plane out-of-phase vibrations of the atomic planes of S. The intense peaks observed at approximately 335.3 cm −1 were due to the A 1 g mode, which resulted from the out-of-plane out-of-phase vibrations of the atomic planes of S [ 21 , 52 , 53 , 54 , 55 ]. The E g and A 1g peaks are the two most commonly observed signals in 1T HfS 2 crystals [ 21 , 27 , 53 , 55 , 56 , 57 , 58 , 59 , 60 ].…”

Section: Resultsmentioning

confidence: 99%

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Influence of Mn, Fe, Co, and Cu Doping on the Photoelectric Properties of 1T HfS2 Crystals

et al. 2021

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Doping plays a vital role in the application of transition-metal dichalcogenides (TMDCs) because it can increase the functionality of TMDCs by tuning their native characteristics. In this study, the influence of Mn, Fe, Co, and Cu doping on the photoelectric properties of HfS2 was investigated. Pristine, Mn-, Fe-, Co-, and Cu-doped HfS2 crystals were grown using the chemical vapor transport method. Scanning electron microscopy images showed that the crystals were layered and transmission electron microscopy, X-ray diffraction, and Raman spectroscopy measurements confirmed that the crystals were in the 1T-phase with a CdI2-like structure. The bandgap of pristine HfS2 obtained from the absorption and photoconductivity spectra was approximately 1.99 eV. As the dopant changed from Mn, Fe, and Co, to Cu, the bandgap gradually increased. The activation energies of the samples were determined using temperature-dependent current-voltage curves. After doping, the activation energy decreased, and the Co-doped HfS2 exhibited the smallest activation energy. Time-resolved photoresponse measurements showed that doping improved the response of HfS2 to light; the Co-doped HfS2 exhibited the best response. The photoresponsivity of HfS2 as a function of the laser power and bias voltage was measured. After doping, the photoresponsivity increased markedly; the Co-doped HfS2 exhibited the highest photoresponsivity. All the experimental results indicated that doping with Mn, Fe, Co, and Cu significantly improved the photoresponsive performance of HfS2, of which Co-doped HfS2 had the best performance.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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Influence of Mn, Fe, Co, and Cu Doping on the Photoelectric Properties of 1T HfS2 Crystals

et al. 2021

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“…The atomic charge is an informative quantum mechanical property of atoms in molecules [89] and crystals [98]. The results of our QTAIM calculations show that the integrated charge on each chalcogen site of the interacting WCh 2 unit responsible for the dimer is negative; the charge on each of S, Se, and Te are −0.388, −0.240, and −0.075 e for (WS 2 ) 2 , (WSe 2 ) 2 , and (WTe 2 ) 2 , respectively, with a decrease in negative charge paralleling the decrease in the electronegativity of the chalcogen.…”

Section: Charge Density Topological Properties Of (Wch 2 ) 2 Dimersmentioning

confidence: 99%

Chalcogen Bonding in the Molecular Dimers of WCh2 (Ch = S, Se, Te): On the Basic Understanding of the Local Interfacial and Interlayer Bonding Environment in 2D Layered Tungsten Dichalcogenides

Varadwaj

Marques

et al. 2022

IJMS

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Layered two-dimensional transition metal dichalcogenides and their heterostructures are of current interest, owing to the diversity of their applications in many areas of materials nanoscience and technologies. With this in mind, we have examined the three molecular dimers of the tungsten dichalcogenide series, (WCh2)2 (Ch = S, Se, Te), using density functional theory to provide insight into which interactions, and their specific characteristics, are responsible for the interfacial/interlayer region in the room temperature 2H phase of WCh2 crystals. Our calculations at various levels of theory suggested that the Te···Te chalcogen bonding in (WTe2)2 is weak, whereas the Se···Se and S···S bonding interactions in (WSe2)2 and (WS2)2, respectively, are of the van der Waals type. The presence and character of Ch···Ch chalcogen bonding interactions in the dimers of (WCh2)2 are examined with a number of theoretical approaches and discussed, including charge-density-based approaches, such as the quantum theory of atoms in molecules, interaction region indicator, independent gradient model, and reduced density gradient non-covalent index approaches. The charge-density-based topological features are shown to be concordant with the results that originate from the extrema of potential on the electrostatic surfaces of WCh2 monomers. A natural bond orbital analysis has enabled us to suggest a number of weak hyperconjugative charge transfer interactions between the interacting monomers that are responsible for the geometry of the (WCh2)2 dimers at equilibrium. In addition to other features, we demonstrate that there is no so-called van der Waals gap between the monolayers in two-dimensional layered transition metal tungsten dichalcogenides, which are gapless, and that the (WCh2)2 dimers may be prototypes for a basic understanding of the physical chemistry of the chemical bonding environments associated with the local interfacial/interlayer regions in layered 2H-WCh2 nanoscale systems.

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Mid‐ to Far‐Infrared Anisotropic Dielectric Function of HfS₂ and HfSe₂

Kowalski

Nolen

Varnavides

et al. 2022

Advanced Optical Materials

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spectral windows due to the lack of an established optical infrastructure. Spectroscopy in this range can be a difficult task, due to the lack of efficient radiation sources within the so-called "terahertz gap" that extends beyond the range where blackbody sources can provide sufficient power. Despite recent developments to create powerful radiation within this region, accessing solid-state properties at these frequencies remains challenging. [4][5][6] Passive optical components in the mid-to far-IR also suffer from undesirable dispersion due to the optic phonon resonances of the material. This dispersion is associated with high absorption losses and optical performance that is strongly frequency dependent, resulting in a non-uniform transmission intensity over the spectral band of interest. [7] Materials with suitable spectral properties exist, but they all suffer from other challenges. For example, cesium iodide (CsI) has extremely lowenergy vibrational modes outside of this spectral range giving rise to suitable transmission, [8][9][10] but it is hygroscopic and therefore must be operated under vacuum or kept within other inert atmospheres. While thin polymer coatings can be applied over CsI optics as a protective layer, these induce additional vibrational resonances,The far-infrared (far-IR) remains a relatively underexplored region of the electromagnetic spectrum extending roughly from 20 to 100 µm in free-space wavelength. Research within this range has been restricted due to a lack of optical materials that can be optimized to reduce losses and increase sensitivity, as well as by the long free-space wavelengths associated with this spectral region. Here the exceptionally broad Reststrahlen bands of two Hf-based transition metal dichalcogenides (TMDs) that can support surface phonon polaritons (SPhPs) within the mid-infrared (mid-IR) into the terahertz (THz) are reported. In this vein, the IR transmission and reflectance spectra of hafnium disulfide (HfS 2 ) and hafnium diselenide (HfSe 2 ) flakes are measured and their corresponding dielectric functions are extracted. These exceptionally broad Reststrahlen bands (HfS 2 : 165 cm −1 ; HfSe 2 : 95 cm −1 ) dramatically exceed that of the more commonly explored molybdenum-(Mo) and tungsten-(W) based TMDs (≈5-10 cm −1 ), which results from the over sevenfold increase in the Born effective charge of the Hf-containing compounds. This work therefore identifies a class of materials for nanophotonic and sensing applications in the mid-to far-IR, such as deeply sub-diffractional hyperbolic and polaritonic optical antennas, as is predicted via electromagnetic simulations using the extracted dielectric function.

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Chemical bonding and Born charge in 1T-HfS2

Cited by 16 publications

References 59 publications

Influence of Mn, Fe, Co, and Cu Doping on the Photoelectric Properties of 1T HfS2 Crystals

Influence of Mn, Fe, Co, and Cu Doping on the Photoelectric Properties of 1T HfS2 Crystals

Chalcogen Bonding in the Molecular Dimers of WCh2 (Ch = S, Se, Te): On the Basic Understanding of the Local Interfacial and Interlayer Bonding Environment in 2D Layered Tungsten Dichalcogenides

Mid‐ to Far‐Infrared Anisotropic Dielectric Function of HfS₂ and HfSe₂

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Chemical bonding and Born charge in 1T-HfS2

Cited by 16 publications

References 59 publications

Influence of Mn, Fe, Co, and Cu Doping on the Photoelectric Properties of 1T HfS2 Crystals

Influence of Mn, Fe, Co, and Cu Doping on the Photoelectric Properties of 1T HfS2 Crystals

Chalcogen Bonding in the Molecular Dimers of WCh2 (Ch = S, Se, Te): On the Basic Understanding of the Local Interfacial and Interlayer Bonding Environment in 2D Layered Tungsten Dichalcogenides

Mid‐ to Far‐Infrared Anisotropic Dielectric Function of HfS2 and HfSe2

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Mid‐ to Far‐Infrared Anisotropic Dielectric Function of HfS₂ and HfSe₂