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15 pages, 3390 KB

Open AccessArticle

Surface Termination and Morphology of Single Crystal AlN by Ex Situ Chemical Treatment and In Situ MOCVD Process

by Yinghao Chen, Jun Zhang, Genhao Liang, Hongyi Yi, Lei Wang, Hao Ying and Lishan Zhao

Micromachines 2026, 17(2), 242; https://doi.org/10.3390/mi17020242 - 13 Feb 2026

Viewed by 706

To achieve an atomically clean surface of single-crystal aluminum nitride (AlN) substrates, this study systematically evaluated the effects of each step in ex situ wet chemical cleaning (solvent, piranha solution, HF, HCl) and in situ hydrogen annealing. X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) analyses revealed that while the combination of solvent and piranha solution exposed step morphology, its effectiveness in removing organic contaminants was limited. HF cleaning efficiently removed the oxide layer but introduced fluorine residues, whereas HCl cleaning left no chlorine residues but exhibited lower efficiency in oxide removal. In situ hydrogen annealing significantly reduced carbon and oxygen contamination, albeit accompanied by a transformation of the surface morphology from step to island mode. By modulating the low V/III ratio during low-temperature metal–organic chemical vapor deposition (MOCVD) growth, a controlled transition from 3D island growth to 2D step-flow growth was achieved. This research provides a basis for optimizing AlN substrate surface treatment, offering important insights for advancing nitride-based optoelectronic and power devices. Full article

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13 pages, 3691 KB

Open AccessArticle

Theoretical Study of 3d VIII Atom-Decorated γ-Graphyne for Adsorbing and Detecting Heptafluoroisobutyronitrile

by Ziang Zheng, Renchu Zhao, Dachang Chen, Qing Miao, Ke Liu and Beibei Xiao

Chemosensors 2023, 11(7), 411; https://doi.org/10.3390/chemosensors11070411 - 21 Jul 2023

Cited by 11 | Viewed by 2026

Abstract

Recently, Heptafluoroisobutyronitrile (C₄F₇N) has received widespread attention in replacing one of the most greenhouse-insulating gas, SF₆. However, gas leakage is incredibly harmful to the health of operational personnel and the security of industry production, and developing C₄F₇N detection technology is of great necessity. In this work, the adsorption properties, as well as the sensing performance of C₄F₇N on 3d VIII atom-decorated γ-graphyne (γ-GY), were theoretically discussed. The adsorption structures, adsorption energies, electron transfer, adsorption distance, electron distribution, and electronic properties were compared. The results show that the introduction of Fe and Co atom enhance the chemisorption of C₄F₇N, and the adsorption of C₄F₇N brings the maximum electron redistribution of Fe/γ-GY among three TM/γ-GY. Only the adsorption on Fe/γ-GY leads to the vanishing of the magnetic moment and creates a band gap. For three different modifications of γ-GY, the chemical interactions are highly related to the overlapping of transition metal 3d and N 2p orbitals in the density of states. The adsorption on Co/γ-GY causes the maximum change in work function from 5.06 eV to 5.26 eV. In addition, based on the band structure, work function, and desorption properties, the sensing properties of 3d VIII atom-decorated γ-GY were evaluated in order to promote the experimental exploration and development of high-performance C₄F₇N gas sensors. Full article

(This article belongs to the Special Issue Advanced Methods and Chemosensor Devices for Eco-Friendly Power Equipment Fault Detection)

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14 pages, 5424 KB

Open AccessArticle

Embedding Group VIII Elements into a 2D Rigid pc-C₃N₂ Monolayer to Achieve Single-Atom Catalysts with Excellent OER Activity: A DFT Theoretical Study

by Qingxian Wang, E Yang, Ran Liu, Mingyue Lv, Wei Zhang, Guangtao Yu and Wei Chen

Molecules 2023, 28(1), 254; https://doi.org/10.3390/molecules28010254 - 28 Dec 2022

Cited by 13 | Viewed by 3264

Abstract

Under DFT calculations, a systematic investigation is carried out to explore the structures and oxygen evolution reaction (OER) catalytic activities of a series of 2D single-atom catalyst (SAC) systems, which are constructed by doping the transition metal (TM) atoms in group VIII into the cavities of rigid phthalocyanine carbide (pc-C₃N₂). We can find that when Co, Rh, Ir and Ru atoms are doped in the small or large cavities of a pc-C₃N₂ monolayer, they can be used as high-activity centers of OER. All these four new TM@C₃N₂ nanostructures can exhibit very low overpotential values in the range of 0.33~0.48 V, even smaller than the state-of-the-art IrO₂ (0.56 V), which indicates considerably high OER catalytic activity. In particular, the Rh@C₃N₂ system can show the best OER performance, given that doped Rh atoms can uniformly serve as high-OER-active centers, regardless of the size of cavity. In addition, a detailed mechanism analysis was carried out. It is found that in these doped pc-C₃N₂ systems, the number of outer electrons, the periodic number of doped TM atoms and the size of the embedded cavity can be considered the key factors affecting the OER catalytic activity, and excellent OER catalytic performance can be achieved through their effective cooperation. These fascinating findings can be advantageous for realizing low-cost and high-performance SAC catalysts for OER in the near future. Full article

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8 pages, 295 KB

Open AccessArticle

Radiative Properties of Rb-Isoelectronic Technetium (Tc VII), Ruthenium (Ru VIII) and Rhodium (Rh IX) Ions for Astrophysical Applications

by Jyoti, Mandeep Kaur and Bindiya Arora

Atoms 2022, 10(4), 138; https://doi.org/10.3390/atoms10040138 - 11 Nov 2022

Viewed by 2025

Abstract

In this work, we present high-accuracy spectroscopic properties, such as line strengths, transition probabilities and oscillator strengths for allowed transitions among

n D_{3 / 2, 5 / 2}, n^{'} S_{1 / 2}

and [...] Read more.

In this work, we present high-accuracy spectroscopic properties, such as line strengths, transition probabilities and oscillator strengths for allowed transitions among

n D_{3 / 2, 5 / 2}, n^{'} S_{1 / 2}

and

n^{'} P_{1 / 2, 3 / 2} (n = 4, n^{'} = 5, 6)

states of Rb-isoelectronic Tc (Tc VII), Ru (Ru VIII) and Rh (Rh IX) ions for their applications in the analysis of astrophysical phenomena occurring inside celestial bodies containing Tc, Ru and Rh ions. Due to the scarcity of computational data of atomic properties of these transitions, as well as considerable discrepancies within the literature about these ions, the precise determination of these properties is necessary. For this purpose, we have implemented relativistic many-body perturbation theory (RMBPT) for evaluation of the wave functions of the considered states. For better accuracy, we have accounted for electron interactions through random phase approximation, Brückner orbitals and structural radiations of wave functions in our RMBPT method for further precise evaluation of electric dipole amplitudes. Combining these values of the observed wavelengths, the above transition properties and radiative lifetimes, a number of excited states of Tc VII, Ru VIII and Rh IX ions have been calculated. For further validation of our work, we have compared our results with the data already available in the literature. Full article

(This article belongs to the Special Issue 20th International Conference on the Physics of Highly Charged Ions)

37 pages, 23480 KB

Open AccessEditor’s ChoiceReview

Engineering 2D Materials for Photocatalytic Water-Splitting from a Theoretical Perspective

by Mukesh Jakhar, Ashok Kumar, Pradeep K. Ahluwalia, Kumar Tankeshwar and Ravindra Pandey

Materials 2022, 15(6), 2221; https://doi.org/10.3390/ma15062221 - 17 Mar 2022

Cited by 90 | Viewed by 8270

Abstract

Splitting of water with the help of photocatalysts has gained a strong interest in the scientific community for producing clean energy, thus requiring novel semiconductor materials to achieve high-yield hydrogen production. The emergence of 2D nanoscale materials with remarkable electronic and optical properties has received much attention in this field. Owing to the recent developments in high-end computation and advanced electronic structure theories, first principles studies offer powerful tools to screen photocatalytic systems reliably and efficiently. This review is organized to highlight the essential properties of 2D photocatalysts and the recent advances in the theoretical engineering of 2D materials for the improvement in photocatalytic overall water-splitting. The advancement in the strategies including (i) single-atom catalysts, (ii) defect engineering, (iii) strain engineering, (iv) Janus structures, (v) type-II heterostructures (vi) Z-scheme heterostructures (vii) multilayer configurations (viii) edge-modification in nanoribbons and (ix) the effect of pH in overall water-splitting are summarized to improve the existing problems for a photocatalytic catalytic reaction such as overcoming large overpotential to trigger the water-splitting reactions without using cocatalysts. This review could serve as a bridge between theoretical and experimental research on next-generation 2D photocatalysts. Full article

(This article belongs to the Special Issue Electronic Structure Theory of Low Dimensional Materials)

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10 pages, 9354 KB

Open AccessArticle

Effect of Flux Rate Variation at Fixed V/III Ratio on Semi-Polar (11

\bar{2}

2) GaN: Crystal Quality and Surface Morphology Study

by Chong Seng Ooi, Ahmad Shuhaimi, Gary Tan, Omar Al-Zuhairi and Wan Haliza Abd Majid

Crystals 2022, 12(2), 247; https://doi.org/10.3390/cryst12020247 - 11 Feb 2022

Cited by 3 | Viewed by 2726

Abstract

We report on the crystal improvement of semi-polar (11

\bar{2}

2) gallium nitride epitaxy layer on m-plane (10

\bar{1}

0) sapphire substrate by changing the flux rate at a fixed V/III ratio. The high-resolution X-ray diffraction (HR-XRD) analysis showed that lower [...] Read more.

We report on the crystal improvement of semi-polar (11

\bar{2}

2) gallium nitride epitaxy layer on m-plane (10

\bar{1}

0) sapphire substrate by changing the flux rate at a fixed V/III ratio. The high-resolution X-ray diffraction (HR-XRD) analysis showed that lower flux rate enhanced the crystal quality of GaN epitaxy with the lowest FWHM values of 394 and 1173 arc seconds at [

\bar{11}

23] and [1

\bar{1}

00] planes, respectively. In addition, Raman spectroscopy showed that flux rate did not affect the stress state of the GaN crystal. However, atomic force microscopy (AFM) micrograph depicted an anomalous trend where the lowest flux rate produces roughest surface with RMS roughness of 40.41 nm. Further analysis of AFM results on the undulation period length along [

\bar{11}

23] and [1

\bar{1}

00] directions is carried out. It shows that as the growth rate decreases, the average undulation period along [

\bar{11}

23] and [1

\bar{1}

00] directions increases from 2.59 µm and 1.90 µm to 3.52 µm and 3.52 µm, respectively. The mechanism for the surface roughening at the lower flux rate is then explained by using the adatom surface diffusion relation

L ~ \sqrt{D τ}

. Full article

(This article belongs to the Special Issue GaN-Based Materials and Devices)

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21 pages, 894 KB

Open AccessArticle

Detailed Analysis of Configuration Interaction and Calculation of Radiative Transition Rates in Seven Times Ionized Tungsten (W VIII)

by Jérôme Deprince and Pascal Quinet

Atoms 2015, 3(3), 299-319; https://doi.org/10.3390/atoms3030299 - 30 Jun 2015

Cited by 9 | Viewed by 4842

Abstract

A new set of oscillator strengths and transition probabilities for EUV spectral lines of seven times ionized tungsten (W VIII) is reported in the present paper. These results have been obtained using the pseudo-relativistic Hartree-Fock (HFR) method combined with a semi-empirical optimization of the radial parameters minimizing the discrepancies between computed energy levels and available experimental data. The final physical model considered in the calculations has been chosen further to a detailed investigation of the configuration interaction in this atomic system characterized by complex configurations of the type 4f¹⁴5s²5p⁵, 4f¹⁴5s²5p⁴nl, 4f¹⁴5s5p⁶, 4f¹³5s²5p⁶, 4f¹³5s²5p⁵nl and 4f¹²5s²5p⁶nl (nl = 5d, 6s). Full article

(This article belongs to the Special Issue Atomic Data for Tungsten)

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