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Surfaces, Volume 4, Issue 1 (March 2021) – 11 articles

Cover Story (view full-size image): The development of non-invasive diagnostics that employ chemoresistive gas sensors to detect disease biomarkers in human breath has been a hot research topic in materials science. This growing interest is largely due to the synergic effects between the sensor performance and semiconducting metal-oxide-sensing layer. Thus, the manufacturing of high-performance gas sensor devices is directly related to the surface engineering of the selected semiconducting metal-oxide-employing advanced synthesis methods. In this study, we report the acetone-biomarker-sensing performance of well-faceted h-MoO3 microrods synthesized by an ultrafast microwave-assisted hydrothermal route. View this paper.
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Article
Noncontact and Full-Field Measurement of Residual and Thermal Stress in Film/Substrate Structures
Surfaces 2021, 4(1), 89-96; https://0-doi-org.brum.beds.ac.uk/10.3390/surfaces4010011 - 19 Mar 2021
Viewed by 434
Abstract
Residual stress and thermal stress of a film/substrate system are determined based on the curvature measurement with a 3D digital image correlation method (DIC) and calculation of the thin-film stresses by the extension of Stoney’s formula. A Ni film electroplated on a H62Cu [...] Read more.
Residual stress and thermal stress of a film/substrate system are determined based on the curvature measurement with a 3D digital image correlation method (DIC) and calculation of the thin-film stresses by the extension of Stoney’s formula. A Ni film electroplated on a H62Cu plate is used to verify the proposed method. The full fields of nonuniform thin-film stresses are obtained in a room temperature to high-temperature environment of 200 °C, which can be potentially extended to higher temperatures. These results provide a fundamental approach to understanding thin-film stresses and a feasible measurement method for high temperature. Full article
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Article
Spontaneous Grafting of OH-Terminated Molecules on Si−H Surfaces via Si–O–C Covalent Bonding
Surfaces 2021, 4(1), 81-88; https://0-doi-org.brum.beds.ac.uk/10.3390/surfaces4010010 - 05 Mar 2021
Viewed by 584
Abstract
The surface functionalization of oxide-free hydrogen-terminated silicon (Si−H) enables predictably tuning its electronic properties, by incorporating tailored functionality for applications such as photovoltaics, biosensing and molecular electronics devices. Most of the available chemical functionalization approaches require an external radical initiator, such as UV [...] Read more.
The surface functionalization of oxide-free hydrogen-terminated silicon (Si−H) enables predictably tuning its electronic properties, by incorporating tailored functionality for applications such as photovoltaics, biosensing and molecular electronics devices. Most of the available chemical functionalization approaches require an external radical initiator, such as UV light, heat or chemical reagents. Here, we report forming organic monolayers on Si–H surfaces using molecules comprising terminal alcohol (–OH) groups. Self-assembled monolayer (SAM) formation is spontaneous, requires no external stimuli–and yields Si–O–C covalently bound monolayers. The SAMs were characterized by X-ray photoelectron spectroscopy (XPS) to determine the chemical bonding, by X-ray reflectometry (XRR) to determine the monolayers thicknesses on the surface and by atomic force microscopy (AFM) to probe surface topography and surface roughness. The redox activity and the electrochemical properties of the SAMs were studied using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The availability and the ease of incorporating OH groups in organic molecules, makes this spontaneous grafting as a reliable method to attach molecules to Si surfaces in applications ranging from sensing to molecular electronics where incorporating radical initiator setups is not accessible. Full article
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Article
Fluoropolymer Film Formation by Electron Activated Vacuum Deposition
Surfaces 2021, 4(1), 66-80; https://0-doi-org.brum.beds.ac.uk/10.3390/surfaces4010009 - 22 Feb 2021
Viewed by 618
Abstract
Polytetrafluoroethylene (PTFE), polyhexafluoropropylene (PHFP) and polychlorotrifluoroethylene (PCTFE) were heated to their decomposition temperature in a high vacuum. The emitted fragments passed an electron cloud, condensed on a substrate and formed fluoropolymer film. Growth rate of PTFE and PHFP films increased up to a [...] Read more.
Polytetrafluoroethylene (PTFE), polyhexafluoropropylene (PHFP) and polychlorotrifluoroethylene (PCTFE) were heated to their decomposition temperature in a high vacuum. The emitted fragments passed an electron cloud, condensed on a substrate and formed fluoropolymer film. Growth rate of PTFE and PHFP films increased up to a factor five in the presence of the electron cloud. Mass spectrometry revealed changes in the mass spectra of fragments generated by thermal decomposition only and formed under electron activation. The observed changes were different for each fluoropolymer. Infrared spectroscopy (IRS) showed that the structure of the films was close to the structure of the bulk polymers. Atomic force microscopy (AFM) has revealed different morphologies of PTFE, PHFP and PCTFE films, suggesting a Volmer–Weber growth mechanism for PTFE and PHFP but a Frank-van der Merwe one for PCTFE. All films were smooth at nanoscale and transparent from ultraviolet to near-infrared region. Additional radio frequency (RF) plasma ignited in the emitted fragments at a low pressure increased mechanical characteristics of the films without losing their optical transparency and smoothness. Full article
(This article belongs to the Special Issue Thin Films at Surfaces)
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Article
The Cerium/Boron Insertion Impact in Anatase Nano-Structures on the Photo-Electrochemical and Photocatalytic Response
Surfaces 2021, 4(1), 54-65; https://0-doi-org.brum.beds.ac.uk/10.3390/surfaces4010008 - 15 Feb 2021
Viewed by 566
Abstract
Boron- and cerium-doped titania (Anatase) were prepared via sol-gel method. Phase composition and morphology were assessed by X-ray diffraction (XRD), scanning electronic microscopy (SEM), BET, diffuse reflectance spectra (DRS), and XPS. Photo-electrochemistry of these materials, deposited onto fluorine-doped SnO2 (FTO), was investigated [...] Read more.
Boron- and cerium-doped titania (Anatase) were prepared via sol-gel method. Phase composition and morphology were assessed by X-ray diffraction (XRD), scanning electronic microscopy (SEM), BET, diffuse reflectance spectra (DRS), and XPS. Photo-electrochemistry of these materials, deposited onto fluorine-doped SnO2 (FTO), was investigated in acid and acid-containing methanol. The boron-doped sample showed the best opto-electronic properties among the investigated samples. On the other hand, the cerium-doped titania samples annihilate to a certain extent the titania surface states, however, photogenerated charge separation was limited, and certainly associated to surface Ce3+/Ce4+ species. The substitutional effect of boron ions for O sites and interstitial sites was confirmed by XRD and XPS analyses. Full article
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Article
Synthesis and Adsorption Behavior of Microporous Iron-Doped Sodium Zirconosilicate with the Structure of Elpidite
Surfaces 2021, 4(1), 41-53; https://0-doi-org.brum.beds.ac.uk/10.3390/surfaces4010007 - 10 Feb 2021
Viewed by 560
Abstract
Decontamination of water from radionuclides contaminants is a key priority in environmental cleanup and requires intensive effort to be cleared. In this paper, a microporous iron-doped zeolite-like sodium zirconosilicate ([email protected]) was designed through hydrothermal synthesis with various Si/Zr ratios of 5, 10, and [...] Read more.
Decontamination of water from radionuclides contaminants is a key priority in environmental cleanup and requires intensive effort to be cleared. In this paper, a microporous iron-doped zeolite-like sodium zirconosilicate ([email protected]) was designed through hydrothermal synthesis with various Si/Zr ratios of 5, 10, and 20, respectively. The synthesized materials of [email protected] materials were well characterized by various techniques such as XRD, SEM, TEM, and N2 adsorption–desorption measurements. Furthermore, the [email protected] and [email protected] samples had a crystalline structure related to the Zr–O–Si bond, unlike the [email protected] which had an overall amorphous structure. The fabricated [email protected] nanocomposite showed a superb capability to remove cesium ions from ultra-dilute concentrations, and the maximum adsorption capacity was 21.5 mg g–1 at natural pH values through an ion exchange mechanism. The results of cesium ions adsorption were found to follow the pseudo-first-order kinetics and the Langmuir isotherm model. The microporous iron-doped sodium zirconosilicate is described as an adsorbent candidate for the removal of ultra-traces concentrations of Cs(I) ions. Full article
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Editorial
Acknowledgment to Reviewers of Surfaces in 2020
Surfaces 2021, 4(1), 39-40; https://0-doi-org.brum.beds.ac.uk/10.3390/surfaces4010006 - 31 Jan 2021
Viewed by 568
Abstract
Peer review is the driving force of journal development, and reviewers are gatekeepers who ensure that Surfaces maintains its standards for the high quality of its published papers [...] Full article
Article
Adsorption of 4,4″-Diamino-p-Terphenyl on Cu(001): A First-Principles Study
Surfaces 2021, 4(1), 31-38; https://0-doi-org.brum.beds.ac.uk/10.3390/surfaces4010005 - 22 Jan 2021
Viewed by 718
Abstract
Single-molecular devices show remarkable potential for applications in downscale electronic devices. The adsorption behavior of a molecule on a metal surface is of great importance from both fundamental and technological points of view. Herein, based on first-principles calculations, the adsorption of a 4,4″-diamino-p-terphenyl [...] Read more.
Single-molecular devices show remarkable potential for applications in downscale electronic devices. The adsorption behavior of a molecule on a metal surface is of great importance from both fundamental and technological points of view. Herein, based on first-principles calculations, the adsorption of a 4,4″-diamino-p-terphenyl (DAT) molecule on a Cu(001) surface has been systematically explored. The most stable configuration is the DAT molecule lying flat with a rotation angle of 13° relative to the [100] surface direction. It was found that the adsorption sites of benzene rings and nitrogen atoms in the DAT molecule have important influences on the stability of the adsorption configuration. Electron density differences analysis shows that the electrons accumulate at the DAT-Cu(001) interface. The density of states projected on a DAT molecule of DAT/Cu(001) exhibits a metallic character, while the freestanding ones are semiconducting, indicating a strong interaction between the DAT molecule and the Cu(001) surface in the most stable adsorption configuration. These results provide useful information for tuning the properties and functions of DAT molecules, and may offer useful insights for other organic molecule/surface systems. Full article
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Article
Analysis of Resonant Soft X-ray Reflectivity of Anisotropic Layered Materials
Surfaces 2021, 4(1), 18-30; https://0-doi-org.brum.beds.ac.uk/10.3390/surfaces4010004 - 11 Jan 2021
Viewed by 521
Abstract
We present here a method for the quantitative prediction of the spectroscopic specular reflectivity line-shape in anisotropic layered media. The method is based on a 4 × 4 matrix formalism and on the simulation from the first principles (through density functional theory—DFT) of [...] Read more.
We present here a method for the quantitative prediction of the spectroscopic specular reflectivity line-shape in anisotropic layered media. The method is based on a 4 × 4 matrix formalism and on the simulation from the first principles (through density functional theory—DFT) of the anisotropic absorption cross-section. The approach was used to simulate the reflectivity at the oxygen K-edge of a 3,4,9,10-perylene-tetracarboxylic dianhydride (PTCDA) thin film on Au(111). The effect of film thickness, orientation of the molecules, and grazing incidence angle were considered. The simulation results were compared to the experiment, permitting us to derive information on the film geometry, thickness, and morphology, as well as the electronic structure. Full article
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Editorial
Surfaces—Our First 100 Papers
Surfaces 2021, 4(1), 17; https://0-doi-org.brum.beds.ac.uk/10.3390/surfaces4010003 - 28 Dec 2020
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Article
Ultrafast Growth of h-MoO3 Microrods and Its Acetone Sensing Performance
Surfaces 2021, 4(1), 9-16; https://0-doi-org.brum.beds.ac.uk/10.3390/surfaces4010002 - 26 Dec 2020
Cited by 1 | Viewed by 664
Abstract
Hexagonal molybdenum trioxide (h-MoO3) was synthesized by microwave-assisted hydrothermal method, allowing an ultrafast growth of unidimensional microrods with well-faceted morphology. The crystalline structure of this metastable phase was confirmed by X-ray diffraction (XRD) and Raman spectroscopy. Scanning electron microscopy (SEM) showed [...] Read more.
Hexagonal molybdenum trioxide (h-MoO3) was synthesized by microwave-assisted hydrothermal method, allowing an ultrafast growth of unidimensional microrods with well-faceted morphology. The crystalline structure of this metastable phase was confirmed by X-ray diffraction (XRD) and Raman spectroscopy. Scanning electron microscopy (SEM) showed that hexagonal microrods can be obtained in one minute with well-defined exposed facets and the fine control of morphology. Sensing tests of the acetone biomarker revealed that the h-MoO3 microrods exhibit, at low ppm level, good sensor signal, fast response/recovery times, selectivity to different interferent gases, and a lower detection limit of 400 ppb. Full article
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Communication
Strain Induced Phase Transition of WS2 by Local Dewetting of Au/Mica Film upon Annealing
Surfaces 2021, 4(1), 1-8; https://0-doi-org.brum.beds.ac.uk/10.3390/surfaces4010001 - 22 Dec 2020
Viewed by 829
Abstract
Here, we present a proof-of-concept experiment where phase engineering at the nanoscale of 2D transition metal dichalcogenides (TMDC) flakes (from semiconducting 2H phase to metallic 1T phase) can be achieved by thermal annealing of a TMDC/Au/mica system. The local dewetting of Au particles [...] Read more.
Here, we present a proof-of-concept experiment where phase engineering at the nanoscale of 2D transition metal dichalcogenides (TMDC) flakes (from semiconducting 2H phase to metallic 1T phase) can be achieved by thermal annealing of a TMDC/Au/mica system. The local dewetting of Au particles and resulting tensile strain produced on the TMDC flakes, strongly bound to the Au surface through effective S-Au bonds, can induce a local structural phase transition. An important role is also played by the defects induced by the thermal annealing: when vacancies are present, the threshold strain needed to trigger the phase transition is significantly reduced. Scanning photoelectron microscopy (SPEM) was revealed to be the perfect tool to monitor the described phenomena. Full article
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