scholarly journals Spontaneous Grafting of OH-Terminated Molecules on Si−H Surfaces via Si–O–C Covalent Bonding

Surfaces ◽  
2021 ◽  
Vol 4 (1) ◽  
pp. 81-88
Author(s):  
Essam M. Dief ◽  
Anton P. Le Brun ◽  
Simone Ciampi ◽  
Nadim Darwish

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.

Author(s):  
Mariola Kądziołka-Gaweł ◽  
Maria Czaja ◽  
Mateusz Dulski ◽  
Tomasz Krzykawski ◽  
Magdalena Szubka

AbstractMössbauer, Raman, X-ray diffraction and X-ray photoelectron spectroscopies were used to examine the effects of temperature on the structure of two aluminoceladonite samples. The process of oxidation of Fe2+ to Fe3+ ions started at about 350 °C for the sample richer in Al and at 300 °C for the sample somewhat lower Al-content. Mössbauer results show that this process may be associated with dehydroxylation or even initiate it. The first stage of dehydroxylation takes place at a temperature > 350 °C when the adjacent OH groups are replaced with a single residual oxygen atom. Up to ~500 °C, Fe ions do not migrate from cis-octahedra to trans-octahedra sites, but the coordination number of polyhedra changes from six to five. This temperature can be treated as the second stage of dehydroxylation. The temperature dependence on the integral intensity ratio between bands centered at ~590 and 705 cm−1 (I590/I705) clearly reflects the temperature at which six-coordinated polyhedra are transformed into five-coordinated polyhedra. X-ray photoelectron spectra obtained in the region of the Si2p, Al2p, Fe2p, K2p and O1s core levels, highlighted a route to identify the position of Si, Al, K and Fe cations in a structure of layered silicates with temperature. All the measurements show that the sample with a higher aluminum content and a lower iron content in octahedral sites starts to undergo a structural reorganization at a relatively higher temperature than the less aluminum-rich sample does. This suggests that iron may perform an important role in the initiation of the dehydroxylation of aluminoceladonites.


2002 ◽  
Vol 16 (06n07) ◽  
pp. 1047-1051
Author(s):  
JIANPING MA ◽  
ZHIMING CHEN ◽  
GANG LU ◽  
MINGBIN YU ◽  
LIANMAO HANG ◽  
...  

Intense photoluminescence (PL) has been observed at room temperature from the polycrystalline SiC samples prepared from carbon-saturated Si melt at a temperature ranging from 1500 to 1650°C. Composition and structure of the samples have been confirmed by means of X-ray photoelectron spectroscopy, X-ray diffraction and scanning electron microscopy. PL measurements with 325 nm UV light excitation revealed that the room temperature PL spectrum of the samples consists of 3 luminescent bands, the peak energies of which are 2.38 eV, 2.77 eV and 3.06 eV, respectively. The 2.38 eV band is much stronger than the others. It is suggested that some extrinsic PL mechanisms associated with defect or interface states would be responsible to the intensive PL observed at room temperature.


2009 ◽  
Vol 1171 ◽  
Author(s):  
Marco Bonato ◽  
Kristin Vala Ragnarsdottir ◽  
Geoffrey C. Allen

AbstractTiO2 anatase nanotubes synthesised via anodic oxidation were used as adsorbent for the uptake of U and Pb from aqueous solution and the photoremoval of As(III). An X-ray photoelectron spectroscopy study of the sorbent medium surface revealed a high adsorption of U and Pb at pH 8. The adsorption of the uranyl ion was enhanced in an anoxy (N2) atmosphere, because this prevents the formation of very stable carbonyl complexes. As(III) was adsorbed on TiO2 but in the presence of O2 and UV light was oxidized to As(V). XPS analysis revealed that in the pH range 3-9 As(V) was always the major species detected at the surface of the titania photocatalyst.


Author(s):  
Ke Qu ◽  
Yuqi Bai ◽  
Miao Deng

Abstract The ever-increasing need for small and lightweight power sources for use in portable or wearable electronic devices has spurred the development of supercapacitors as a promising energy storage and conversion system. In this work, a simple, facile and easy-to-practice method has been developed to employ carbon paper (CP) as the support to coat molybdenum disulfide (MoS2) and graphene oxide (GO), followed by electrodeposition of polyaniline (PANI) to render CP/MoS2-GO-PANI. The preparation parameters, such as amounts of MoS2, GO and number of aniline electropolymerization cycles, have been optimized to render CP/MoS2-GO-PANI the best capacitive performance. The as-prepared optimal CP/MoS2-GO-PANI is characterized by X-ray powder diffraction, scanning electron microscopy, energy-dispersive spectroscopy, and X-ray photoelectron spectroscopy. The supercapacitive properties of CP/MoS2-GO-PANI as an electrode have been evaluated electrochemically via cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy testing. CP/MoS2-GO-PANI delivers a specific capacitance of 255.1 F/g at 1.0 A/g and exhibits excellent rate capability under larger current densities. Moreover, a symmetrical supercapacitor is assembled and three are connected in series to power a light-emitting diode for ~15 minutes, demonstrating the promising application potential of CP/MoS2-GO-PANI-based supercapacitor.


2016 ◽  
Vol 6 (6) ◽  
pp. 20160056 ◽  
Author(s):  
R. Pruna ◽  
F. Palacio ◽  
M. Martínez ◽  
O. Blázquez ◽  
S. Hernández ◽  
...  

Fabrication and organosilane-functionalization and characterization of nanostructured ITO electrodes are reported. Nanostructured ITO electrodes were obtained by electron beam evaporation, and a subsequent annealing treatment was selectively performed to modify their crystalline state. An increase in geometrical surface area in comparison with thin-film electrodes area was observed by atomic force microscopy, implying higher electroactive surface area for nanostructured ITO electrodes and thus higher detection levels. To investigate the increase in detectability, chemical organosilane-functionalization of nanostructured ITO electrodes was performed. The formation of 3-glycidoxypropyltrimethoxysilane (GOPTS) layers was detected by X-ray photoelectron spectroscopy. As an indirect method to confirm the presence of organosilane molecules on the ITO substrates, cyclic voltammetry and electrochemical impedance spectroscopy (EIS) were also carried out. Cyclic voltammograms of functionalized ITO electrodes presented lower reduction-oxidation peak currents compared with non-functionalized ITO electrodes. These results demonstrate the presence of the epoxysilane coating on the ITO surface. EIS showed that organosilane-functionalized electrodes present higher polarization resistance, acting as an electronic barrier for the electron transfer between the conductive solution and the ITO electrode. The results of these electrochemical measurements, together with the significant difference in the X-ray spectra between bare ITO and organosilane-functionalized ITO substrates, may point to a new exploitable oxide-based nanostructured material for biosensing applications. As a first step towards sensing, rapid functionalization of such substrates and their application to electrochemical analysis is tested in this work. Interestingly, oxide-based materials are highly integrable with the silicon chip technology, which would permit the easy adaptation of such sensors into lab-on-a-chip configurations, providing benefits such as reduced size and weight to facilitate on-chip integration, and leading to low-cost mass production of microanalysis systems.


Author(s):  
Thế Luân Nguyễn ◽  
Tiến Khoa Lê ◽  
Châu Ngọc Hoàng ◽  
Hữu Khánh Hưng Nguyễn ◽  
Thị Kiều Xuân Huỳnh

The Cu doped ZnO photocatalysts were prepared on ZnO substrate modified with copper nitrate by thermal shock method with different ratio % molar Cu : Zn = 0.3, 0.5, 1.0, 2.0 and 5.0 in order to study the impacts of copper content on the photocatalytic activity of ZnO under both UV and Vis light irradiation. The crystal structure, morphology bulk and surface were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Their photocatalytic activities were studied via time-dependent degradation of methylene blue in aqueous solution. The results exhibit that crystal structure and morphology of Cu doped ZnO photocatalysts is not modified significally than ZnO original but surface charateristicschanged greatly. The photocatalyst was doped with copper content under 2% showed formation of Cu species. These samples perform photocatalytic activity higher than ZnO. The CuNZO-0.05-500 had the highest rate constants for methylene blue degradation (kUV = 6,901 h-1, kVIS = 0,224 h-1), which are about 2.2 times and 1.3 times higher than unmodified ZnO under UV light and Vis light, respectively. However, the CuNZO-5.0-500 which had the formation of CuO phase and unchangeable ZnO's surface has photocatalytic activity similar to pure ZnO.


2019 ◽  
Vol 10 ◽  
pp. 62-70 ◽  
Author(s):  
Yong Li ◽  
Peng Yang ◽  
Bin Wang ◽  
Zhongqing Liu

Bimetallic phosphides have been attracting increasing attention due to their synergistic effect for improving the hydrogen evolution reaction as compared to monometallic phosphides. In this work, NiCoP modified hybrid electrodes were fabricated by a one-step electrodeposition process with TiO2 nanotube arrays (TNAs) as a carrier. X-ray diffraction, transmission electron microscopy, UV–vis diffuse reflection spectroscopy, X-ray photoelectron spectroscopy and scanning transmission electron microscopy/energy-dispersive X-ray spectroscopy were used to characterize the physiochemical properties of the samples. The electrochemical performance was investigated by cyclic voltammetry, linear sweep voltammetry, and electrochemical impedance spectroscopy. We show that after incorporating Co into Ni–P, the resulting Ni x Co y P/TNAs present enhanced electrocatalytic activity due to the improved electron transfer and increased electrochemically active surface area (ECSA). In 0.5 mol L−1 H2SO4 electrolyte, the Ni x Co y P/TNAs (x = 3.84, y = 0.78) demonstrated an ECSA value of 52.1 mF cm−2, which is 3.8 times that of Ni–P/TNAs (13.7 mF cm−2). In a two-electrode system with a Pt sheet as the anode, the Ni x Co y P/TNAs presented a bath voltage of 1.92 V at 100 mA cm−2, which is an improvment of 79% over that of 1.07 V at 10 mA cm−2.


CORROSION ◽  
10.5006/3234 ◽  
2019 ◽  
Vol 75 (12) ◽  
pp. 1474-1486
Author(s):  
Jéssica Cristina Costa de Castro Santana ◽  
Rejane Maria Pereira da Silva ◽  
Renato Altobelli Antunes ◽  
Sydney Ferreira Santos

The aim of the present work was to study the surface chemistry, microstructure, and local corrosion processes at the decarburized layer of the SAE 9254 automotive spring steel. The samples were austenitized at 850°C and 900°C, and oil quenched. The microstructure was investigated using confocal laser scanning microscopy and scanning electron microscopy. The surface chemistry was analyzed by x-ray photoelectron spectroscopy. Electrochemical impedance spectroscopy and potentiodynamic polarization were used to assess the global corrosion behavior of the decarburized samples. Scanning electrochemical microscopy was used to evaluate the influence of decarburization on the local corrosion activity. Microstructural characterization and x-ray photoelectron spectroscopy analysis indicate a dependence of the local electrochemical processes with the steel microconstituents and Si oxides in the decarburized layer.


2019 ◽  
Vol 26 (10) ◽  
pp. 1950080
Author(s):  
JIBO JIANG ◽  
HAOTIAN CHEN ◽  
LIYING ZHU ◽  
YAOXIN SUN ◽  
WEI QIAN ◽  
...  

Graphene oxide (GO) sheet and ultrasonic field (UF) were successfully employed to produce Ni–B/GO and UF–Ni–B/GO composite coatings on Q235 mild steel by electroless plating. The composite coatings’ structure and surface morphology were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Results showed that GO was successfully co-deposited in the Ni–B alloy. Moreover, UF–Ni–B/GO composite coatings have smoother surface and thicker cross-section than others. The microhardness and corrosion resistance of the sample coatings were determined using Vickers hardness tests, Tafel electrochemical tests and electrochemical impedance measurements (EIS) in 3.5[Formula: see text]wt.% NaCl solution to receive the effect of GO and ultrasonic. The findings indicated that UF–Ni–B/GO exhibited optimum hardness (856[Formula: see text]HV) and enhanced corrosion resistance (6.38 [Formula: see text][Formula: see text] over the Ni–B and Ni–B/GO coatings. Due to these interesting properties of the coating, it could be used as a protective material in the automotive and aerospace industries for parts of machines that were manipulated in high temperature and corrosive environments.


2019 ◽  
Vol 79 (12) ◽  
pp. 2357-2365 ◽  
Author(s):  
Huaisu Guo ◽  
Weilin Guo ◽  
Yang Liu ◽  
Xiaohua Ren

Abstract In this work, quinone-modified metal-organic framework MIL-101(Fe)(Q-MIL-101(Fe)), as a novel heterogeneous Fenton-like catalyst, was synthesized for the activation of persulfate (PS) to remove bisphenol A (BPA). The synthetic Q-MIL-101(Fe) was characterized via X-ray diffraction, scanning electron microscope, Fourier transform infrared, electrochemical impedance spectroscopy, cyclic voltammetry and X-ray photoelectron spectroscopy. As compared to the pure MIL-101(Fe), Q-MIL-101(Fe) displayed better catalytic activity and reusability. The results manifested that the Q-MIL-101(Fe) kept quinone units, which successfully promoted the redox cycling of Fe3+/Fe2+ and enhanced the removal efficiency. In addition, the reaction factors of Q-MIL-101(Fe) were studied (e.g. pH, catalyst dosage, PS concentration and temperature), showing that the optimum conditions were [catalyst] = 0.2 g/L, [BPA] = 60 mg/L, [PS] = 4 mmol/L, pH = 6.79, temperature = 25 °C. On the basis of these findings, the probable mechanism on the heterogeneous activation of PS by Q-MIL-101(Fe) was proposed.


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