Surfaces

13 pages, 3559 KiB

Open AccessArticle

The Effects of Substrate Temperature on the Growth, Microstructural and Magnetic Properties of Gadolinium-Containing Films on Aluminum Nitride

by Craig A. Ekstrum, Ragavendran Venkatesan, Chito Kendrick, Moshe Einav, Paramasivam Sivaprakash, Jeyanthinath Mayandi, Sonachalam Arumugam and Joshua M. Pearce

Surfaces 2022, 5(2), 321-333; https://doi.org/10.3390/surfaces5020024 - 9 Jun 2022

Cited by 1 | Viewed by 2602

Abstract

To facilitate future novel devices incorporating rare earth metal films and III-V semiconductors on Si substrates, this study investigates the mechanisms of growth via molecular beam epitaxy of gadolinium (Gd) on aluminum nitride (AlN) by determining the impact of substrate temperature on microstructure. [...] Read more.

To facilitate future novel devices incorporating rare earth metal films and III-V semiconductors on Si substrates, this study investigates the mechanisms of growth via molecular beam epitaxy of gadolinium (Gd) on aluminum nitride (AlN) by determining the impact of substrate temperature on microstructure. The Gd films underwent extensive surface analysis via in situ reflective high energy electron diffraction (RHEED) and ex-situ SEM and AFM. Characterization of the surface features of rare earth metal films is important, as surface geometry has been shown to strongly impact magnetic properties. SEM and AFM imaging determined that Gd films grown on AlN (0001) from 80 °C to 400 °C transition from wetting, nodular films to island–trench growth mode to reduce in-plane lattice strain. XRD and Raman spectroscopy of the films revealed that they were primarily comprised of GdN, Gd and Gd₂O₃. The samples were also analyzed by a vibrating sample magnetometer (VSM) at room temperature. From the room temperature magnetic studies, the thick films showed superparamagnetic behavior, with samples grown between 240 °C and 270 °C showing high magnetic susceptibility. Increasing GdN (111) 2θ peak position and single-crystal growth modes correlated with increasing peak magnetization of the thin films, suggesting that lattice strain in single-crystal films was the primary driver of enhanced magnetic susceptibility. Full article

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3 pages, 214 KiB

Open AccessEditorial

Emerging Chemical Sensing Technologies: Recent Advances and Future Trends

by Anderson A. Felix and Marcelo O. Orlandi

Surfaces 2022, 5(2), 318-320; https://doi.org/10.3390/surfaces5020023 - 31 May 2022

Cited by 1 | Viewed by 1826

Abstract

Contemporary chemical sensing research is rapidly growing, leading to the development of new technologies for applications in almost all areas, including environmental monitoring, disease diagnostics and food quality control, among others [...] Full article

(This article belongs to the Special Issue Surfaces on Emerging Chemical Sensing Applications)

10 pages, 5696 KiB

Open AccessArticle

Surfactants for Electrophoretic Deposition of Polyvinylidene Fluoride–Silica Composites

by Zhengzheng Wang and Igor Zhitomirsky

Surfaces 2022, 5(2), 308-317; https://doi.org/10.3390/surfaces5020022 - 18 May 2022

Cited by 1 | Viewed by 2334

Abstract

This investigation is motivated by the numerous advantages of electrophoretic deposition (EPD) for the fabrication of polyvinylidene fluoride (PVDF) and composite coatings and the various applications of such coatings. It is demonstrated that gallic acid (GA), caffeic acid (CFA), cholic acid (CA) and [...] Read more.

This investigation is motivated by the numerous advantages of electrophoretic deposition (EPD) for the fabrication of polyvinylidene fluoride (PVDF) and composite coatings and the various applications of such coatings. It is demonstrated that gallic acid (GA), caffeic acid (CFA), cholic acid (CA) and 2,3,4 trihydroxybenzoic acid (THB) can be used as charging and dispersing agents for the EPD of PVDF. The deposition yield of PVDF increases in the following order: THB < CFA < CA < GA. Test results indicate that the chemical structure of the dispersants exerts influence on the deposition efficiency. Potentiodynamic and impedance spectroscopy studies show the corrosion protection properties of PVDF coatings. GA is used for the co-EPD of PVDF with nanosilica and micron-size silica. The silica content in the composite coatings is varied by the variation of silica content in the suspensions. The ability to use GA as a charging and dispersing agent for the co-EPD of materials of different types paves the way for the fabrication of advanced organic–inorganic composites using EPD. Full article

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18 pages, 7541 KiB

Open AccessArticle

SWOT Analysis of Electrical Discharge Coatings: A Case Study of Copper Coating on Titanium Alloy

by JagadeeswaraRao Maddu, Buschaiah Karrolla, Riyaaz Uddien Shaik and Diana-Petronela Burdhuhos-Nergis

Surfaces 2022, 5(2), 290-307; https://doi.org/10.3390/surfaces5020021 - 16 May 2022

Cited by 4 | Viewed by 6246

Abstract

The electrical discharge machine (EDM) has been one of the most widely used non-traditional machines in recent decades, primarily used for machining hard materials into various complex shapes and different sizes and, nowadays, used for surface modifications/hard coatings. In this study, the SWOT [...] Read more.

The electrical discharge machine (EDM) has been one of the most widely used non-traditional machines in recent decades, primarily used for machining hard materials into various complex shapes and different sizes and, nowadays, used for surface modifications/hard coatings. In this study, the SWOT (strengths, weaknesses, opportunities and threats) of electrical discharge coating was analyzed by conducting a case study. For the purpose of the case study, copper was deposited on the titanium alloy surface (Ti6Al4V). Three electrodes of different copper alloy materials, viz., brass, bronze and copper, were selected for coating the Ti6Al4V surface. Input parameters such as current, pulse-on, pulse-off, flushing pressure and the electrode material were optimized to develop a uniform coating. Experiments were designed according to the L18 orthogonal array, and among them, the samples that showed proper coating, as seen with the naked eye, were selected for morphological and elemental analyses by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX. Further, the output responses, viz., the material deposition rate (MDR), electrode wear rate (EWR), surface roughness (SR), elemental data (copper (Cu) and zinc (Zn)) and coating thickness (CT), were considered for the optimization of coatings. Implementing the Technique for Order Performance by Similarity to Ideal Solution, copper coating with a thickness of 20.43 µm, developed with an MDR with input parameters of 20 A current, 600 µs pulse-on, 120 µs pulse-off, 0.5 bar flushing pressure and the brass electrode, was selected as the optimum coating. The most influential parameters in this coating process were the current and pulse-on time. In this study, a SWOT table was developed to depict the strengths, weaknesses, opportunities and threats of electrical discharge coating. Full article

(This article belongs to the Special Issue Surface Engineering and Phase Transformations in Metals and Alloys)

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10 pages, 1342 KiB

Open AccessArticle

Density Functional Theory Calculations of the Effect of Oxygenated Functionals on Activated Carbon towards Cresol Adsorption

by Aola Supong, Upasana Bora Sinha and Dipak Sinha

Surfaces 2022, 5(2), 280-289; https://doi.org/10.3390/surfaces5020020 - 2 May 2022

Cited by 6 | Viewed by 2839

Abstract

The mechanism of adsorption of p-cresol over activated carbon adsorbent and the specific role of oxygen functional groups on cresol adsorption were studied using density functional theory (DFT) calculations. All the energy calculations and geometry optimization pertaining to DFT calculations were done [...] Read more.

The mechanism of adsorption of p-cresol over activated carbon adsorbent and the specific role of oxygen functional groups on cresol adsorption were studied using density functional theory (DFT) calculations. All the energy calculations and geometry optimization pertaining to DFT calculations were done using the B3LYP hybrid functional at basis set 6-31g level of theory in a dielectric medium of ε = 80 (corresponding to water). The interaction of cresol with different activated carbon models, namely pristine activated carbon, hydroxyl functionalized activated carbon, carbonyl functionalized activated carbon, and carboxyl functionalized activated carbon, were considered, and their adsorption energies corresponded to −416.47 kJ/mol, −54.73 kJ/mol, −49.99 kJ/mol, and −63.62 kJ/mol, respectively. The high adsorption energies suggested the chemisorptive nature of the cresol-activated carbon adsorption process. Among the oxygen functional groups, the carboxyl group tended to influence the adsorption process more than the hydroxyl and carbonyl groups, attributing to the formation of two types of hydrogen bonds between the carboxyl activated carbon and the cresol simultaneously. The outcomes of this study may provide valuable insights for future directions to design activated carbon with improved performance towards cresol adsorption. Full article

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15 pages, 3058 KiB

Open AccessArticle

Synthesis and Electrochemical Properties of Lignin-Derived High Surface Area Carbons

by Artur M. Suzanowicz, Youngjin Lee, Abigail Schultz, Otavio J. J. Marques, Hao Lin, Carlo U. Segre and Braja K. Mandal

Surfaces 2022, 5(2), 265-279; https://doi.org/10.3390/surfaces5020019 - 6 Apr 2022

Cited by 2 | Viewed by 3210

Abstract

Activated carbons play an essential role in developing new electrodes for renewable energy devices due to their electrochemical and physical properties. They have been the subject of much research due to their prominent surface areas, porosity, light weight, and excellent conductivity. The performance [...] Read more.

Activated carbons play an essential role in developing new electrodes for renewable energy devices due to their electrochemical and physical properties. They have been the subject of much research due to their prominent surface areas, porosity, light weight, and excellent conductivity. The performance of electric double-layer capacitors (EDLCs) is highly related to the morphology of porous carbon electrodes, where high surface area and pore size distribution are proportional to capacitance to a significant extent. In this work, we designed and synthesized several activated carbons based on lignin for both supercapacitors and Li-S batteries. Our most favorable synthesized carbon material had a very high specific surface area (1832 m²·g⁻¹) and excellent pore diameter (3.6 nm), delivering a specific capacitance of 131 F·g⁻¹ in our EDLC for the initial cycle. This translates to an energy density of the supercapacitor cell at 55.6 Wh·kg⁻¹. Using this material for Li-S cells, composited with a nickel-rich phosphide and sulfur, showed good retention of soluble lithium polysulfide intermediates by maintaining a specific capacity of 545 mA·h·g⁻¹ for more than 180 cycles at 0.2 C. Full article

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14 pages, 2978 KiB

Open AccessArticle

Temperature Effects in the Initial Stages of Heteroepitaxial Film Growth

by Tung B. T. To and Fábio D. A. Aarão Reis

Surfaces 2022, 5(2), 251-264; https://doi.org/10.3390/surfaces5020018 - 5 Apr 2022

Cited by 3 | Viewed by 2615

Abstract

Kinetic Monte Carlo simulations of a model of thin film heteroepitaxy are performed to investigate the effects of the deposition temperature in the initial growth stages. Broad ranges of the rates of surface processes are used to model materials with several activation energies [...] Read more.

Kinetic Monte Carlo simulations of a model of thin film heteroepitaxy are performed to investigate the effects of the deposition temperature in the initial growth stages. Broad ranges of the rates of surface processes are used to model materials with several activation energies and several temperature changes, in conditions of larger diffusivity on the substrate in comparison with other film layers. When films with the same coverage are compared, the roughness increases with the deposition temperature in the regimes of island growth, coalescence, and initial formation of the continuous films. Concomitantly, the position of the minimum of the autocorrelation function is displaced to larger sizes. These apparently universal trends are consequences of the formation of wider and taller islands, and are observed with or without Ehrlich-Schwöebel barriers for adatom diffusion at step edges. The roughness increase with temperature qualitatively matches the observations of recent works on the deposition of inorganic and organic materials. In thicker films, simulations with some parameter sets show the decrease of roughness with temperature. In these cases, a re-entrance of roughness may be observed in the initial formation of the continuous films. Full article

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13 pages, 3522 KiB

Open AccessArticle

4-Mercaptobenzoic Acid Adsorption on TiO₂ Anatase (101) and TiO₂ Rutile (110) Surfaces

by Claudia Lorena Compeán-González, Andrew Guy Thomas, Karen Louise Syres, Jordan Cole and Zheshen Li

Surfaces 2022, 5(2), 238-250; https://doi.org/10.3390/surfaces5020017 - 5 Apr 2022

Cited by 3 | Viewed by 2838

Abstract

The adsorption of 4-mercaptobenzoic acid (4-MBA) on anatase (101) and rutile (110) TiO₂ surfaces has been studied using synchrotron radiation photoelectron spectroscopy and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy techniques. Photoelectron spectroscopy results suggest that the 4-MBA molecule bonds to both [...] Read more.

The adsorption of 4-mercaptobenzoic acid (4-MBA) on anatase (101) and rutile (110) TiO₂ surfaces has been studied using synchrotron radiation photoelectron spectroscopy and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy techniques. Photoelectron spectroscopy results suggest that the 4-MBA molecule bonds to both TiO₂ surfaces through the carboxyl group, following deprotonation in a bidentate geometry. Carbon K-edge NEXAFS spectra show that the phenyl ring of the 4-MBA molecule is oriented at 70° ± 5° from the surface on both the rutile (110) and anatase (101) surfaces, although there are subtle differences in the electronic structure of the molecule following adsorption between the two surfaces. Full article

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10 pages, 4151 KiB

Open AccessCommunication

Chalcogen Atom-Doped Graphene and Its Performance in N₂ Activation

by Navaratnarajah Kuganathan

Surfaces 2022, 5(2), 228-237; https://doi.org/10.3390/surfaces5020016 - 1 Apr 2022

Viewed by 2158

Abstract

In this work, we studied dispersion correction, adsorption and substitution of chalcogen dopants (O, S, Se and Te) on the surface of graphene using density functional theory. The results reveal that a single oxygen atom is more preferred for adsorption onto the graphene [...] Read more.

In this work, we studied dispersion correction, adsorption and substitution of chalcogen dopants (O, S, Se and Te) on the surface of graphene using density functional theory. The results reveal that a single oxygen atom is more preferred for adsorption onto the graphene surface than the other dopants, with an adsorption energy of −0.84 eV. The preference of this dopant is evidenced by a greater charge transfer of 0.34 electrons from the graphene surface to the oxygen. The substitutional doping of oxygen is energetically more favourable than the doping of other atoms. While nitrogen activation is enhanced by the adsorption, the activation is not significant with the doping of chalcogen atoms. Full article

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Surfaces, Volume 5, Issue 2 (June 2022) – 9 articles

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