N-type Semiconductivity Research Articles

Electronic behavior of native oxide films on Ti and TiN during 90-day immersion in electrolytes with different pH levels

This work presents the electronic behavior of Ti and TiN thin films when exposed to electrolytes with pH levels of 2, 7 and 13 for 90 days. Staircase potentio-electrochemical impedance spectroscopy tests were performed on the 100-nm Ti and TiN monolithic films, and Mott–Schottky analysis of these tests was used to determine the films’ semiconductive behavior and changes in the donor/acceptor density. In addition, the flat-band potential of each film’s surface oxide was also characterized. No attempt was made to control oxide formation, and therefore, these tests reflected the native surfaces of these films. While the TiN films exhibited n-type semiconductivity in all electrolytes, the Ti films only showed n-type behavior in the acidic (pH = 2) and neutral (pH = 7) electrolytes. The semiconductivity of the Ti films transitioned to p-type during exposure to the basic electrolyte (pH = 13) after reaching 60 days. Furthermore, there was a significant increase in the donor densities for both Ti and TiN films when immersed in the basic electrolyte relative to the acidic and neutral electrolytes.

The effect of nickel on corrosion behaviour of high-strength low alloy steel rebar in simulated concrete pore solution

The effect of nickel on the corrosion behaviour of high-strength low alloy steel reinforcement was investigated by electrochemical measurement techniques, X-ray photoelectron spectroscopy, and auger electron spectroscopy. The results demonstrate that 3 wt% of nickel addition reduced the corrosion rate to 17 nA/cm2 compared to 730 nA/cm2 of carbon steel in the contaminated concrete condition. The enhancement of corrosion resistance for nickel-bearing steel was attributed to the formation of protective oxide film. The oxide film exhibited n-type semiconductivity in which oxygen vacancy was the main defect. The involvement of nickel in the formation process of oxide film changed its structure and composition. Nickel was enriched in the oxide film, simultaneously decreasing the defects density and the whole thickness of oxide film, and together with the increase of the Fe2+/Fe3+ ratio and the inner barrier oxide film thickness. The protective inner barrier layer of oxide film on the nickel-bearing steel can strongly inhibited the corrosive attack.

Growth Kinetics and Characterization of Chromia Scales Formed on Ni–30Cr Alloy in Impure Argon at 700 °C

The oxidation of a Ni–30Cr alloy at 700 °C in impure argon was studied in order to provide new elements of understanding on chromia scale growth in low oxygen partial pressure atmosphere (10−5 atm). Oxidation tests were carried out during 30 min to 50 h in a thermogravimetric analysis system using a symmetrical balance with in situ monitoring of the oxygen partial pressure. The oxidation kinetics were determined as parabolic with an estimated stationary parabolic constant value of 10−15 cm2 s−1, after a transient stage of about 3 h. The oxide scale was identified as a pure chromia layer by TEM and XPS characterisations. After 50 h at 700 °C, the scale thickness estimated by TEM cross section observation was about 100 nm. A slightly thicker and more porous oxide scale was observed above the alloy’s grain boundaries. The metal/oxide interface also exhibited a deeper recession towards the substrate above the alloy’s grain boundaries. The orientation of chromia grains was determined by TKD (transmission Kikuchi diffraction). A strong preference was noted for the orientation perpendicular to the surface, along the direction of the corundum structure. Finally, the type of semiconduction was determined for the scales formed after 7 h and 50 h of oxidation. For the shorter oxidation time, the chromia scale exhibited an n-type semiconduction, whereas for the longer exposure, both n-type and insulating semiconduction were identified.

Synthesis, physical and photoelectrochemical characterizations of Sr0.5Nb3O8·1.7H2O: application to the Rhodamine B oxidation under solar light

The layered niobate Sr0.5Nb3O8·1.7H2O is synthesized by soft chemistry in aqueous electrolyte via Sr2+ → H+ exchange between strontium nitrate and niobic acid HNb3O8·H2O. The material is identified by X-ray diffraction using Rietveld refinement, thermal analysis (TG/DSC) and optical measurements. The semiconducting and photoelectrochemical properties are investigated for the first time. The band gap of Sr0.5Nb3O8·1.7H2O is evaluated at 3.67 eV, and the transition is directly allowed due to the charge transfer O2−: 2p → Nb5+: 4d. The thermal variation of the electrical conductivity shows that 4d electrons are localized and the data are fitted by a small-polaron hopping model: σ = σo exp {− 0.13 eV/kT}. The capacitance measurement done in the ionic electrolyte (Na2SO4, 10−2 M) indicates n-type semiconductivity with a flat band potential of − 0.09 VSCE. The conduction band, made up of Nb5+: 4d orbital, is located at − 0.22 VSCE. As application, Rhodamine B (RhB) is oxidized by photocatalysis on Sr0.5Nb3O8·1.7H2O through O2· radicals; 56% of the initial concentration (10 mg L−1) is eliminated after 3 h under solar light (90 mW cm−2), and the Rh B oxidation follows a first-order kinetic with a rate constant of 0.246 h−1.

Electrochemical atomic layer deposition of cadmium telluride for Pt decoration: Application as novel photoelectrocatalyst for hydrogen evolution reaction

Metal-chalcogenide nanomaterials, as compared to their wide bandgap counterparts, are particularly attractive photoelectrocatalytic materials for the conversion of solar energy into chemical energy under visible-light irradiation. In this study, the thin layer of CdTe was deposited on the surface of Au/ITO electrode using electrochemical atomic layer deposition. Deposition process was performed through the alternate under potential deposition of the Te and Cd elements with a monolayer at a time, respectively. The images of scaning electron microscopy (SEM) indicated that nanoparticles of CdTe well dispersed on Au/ITO with an average particle size about 15 nm. The results of energy dispersive analysis by X-rays (EDAX) confirmed the off-stoichiometric CdTe layer, which lead to Cd-rich CdTe because of tellurium vacancies in the deposition potential. The resulting Cd-rich CdTe/Au/ITO electrode was used for preparation of Pt/CdTe/Au/ITO by redox replacement reaction between Pt2+ and Cd excess in CdTe layer to form 1.76 wt% of Pt element which uniformly distributed on the surface of CdTe/Au/ITO. Chronoamperometric tests in sodium sulfide solution exhibited that the Cd-rich CdTe layer had n-type semiconductivity whereas the Pt/CdTe layer showed p-type semiconductivity. The Pt/CdTe/Au/ITO electrode showed higher photoelectrocatalytic activity for the HER as compared to a commercial Pt/C on Au/ITO. The onset potential for HER is almost similar and the overpotential at −10 mA cm−2 is 160 mV more positive on Pt/CdTe/Au/ITO under light illumination with respect to Pt/C/Au/ITO. The long-term stability tests under illumination in acidic solution revealed that Cd-rich CdTe and Pt/CdTe layeres have extremely high stablity for HER compared to Pt/C. The higher photocatalytic activity on Pt/CdTe/Au/ITO electrode for HER is attributed predominantly to the synergistic effect of Pt, which not only serves as co-catalysts for promoting electron transfer to the electrocatalyst-electrolyte interface, but also accelerates the HER.

Passivity of martensitic stainless steel in borate buffer solution: Influence of sulfide ion

Upon performing electrochemical measurements, XPS and TEM characterizations, the influence of sulfide on the passive behavior of Super 13Cr martensitic stainless steel was deciphered. Mechanism interpretation is performed by optimizing the Point Defect Model based upon the impedance data. It is revealed that the passive film display n-type semiconductivity, and the donor density dropped with increasing concentration of sulfide ion. Sulfide ion can induce a current peak at −250 mVSCE (Epeak). The addition of Na2S generates a continuous outer layer which is comprised of Cr(OH)3, FeS2 and FeS at potential lower than Epeak, and Cr(OH)3 at potential higher than Epeak. This result leads to the thinner barrier layer and lower charge transfer resistance, implying a weaker protection of the substrate by the passive film.

Mg-RE Alloy Anode Materials for Mg-Air Battery Application

Commercial purity Mg, Mg-RE alloys ZE10A (UNS M11600), and EV31A (UNS M12310) were evaluated in the as-received condition for potential application as anode for Mg-air battery. Anodic and cathodic polarization studies were performed in 0.6 M of NaCl, 0.5 M of NaNO3 and 0.1 M of Na2SO4. Hydrogen evolved during anodic polarization was measured at different current densities. Electrochemical impedance spectroscopy was carried out at open circuit conditions, and galvanostatic conditions. The results showed that commercial purity magnesium had higher corrosion resistance than the Mg-RE alloy specimens in all the electrolytes tested. All the specimens showed negative difference effect (NDE) where the rate of hydrogen evolution increased with increased anodic polarization. The NDE was more pronounced on ZE10A than on other materials. The results suggest that EV31A could be a potential anode material for Mg-air battery due to its better discharge capabilities. The surface layer formed on the Mg specimen showed predominantly a p-type semiconductivity with a charge carrier density in the order of 1021 cm−3. The Mg-RE alloys showed a dual layered surface layer with bottom n-type and top p-type characters. The p-type behavior could be associated with the formation cation vacancies due to dissolution of Mg from its lattice site, and the n-type semiconductivity could be attributed to segregation of trivalent rare earth cations at the metal/oxide interface. The enhanced NDE behavior of the Mg-RE alloys could also be attributed to the surface enrichment of Zr, and presence of MgxREy type secondary phases.

Passive film on 2205 duplex stainless steel studied by photo-electrochemistry and ARXPS methods

The passive film formed on 2205 duplex stainless steel in pH 8.59 borate buffer solutions was studied by photo-electrochemical techniques and Mott-Schottky analysis. The passive film displays both n-type and p-type semiconductor character in different potential regions of the passive state. The band gap energy of barrier layer of the passive film was 2.4∼2.75 eV. Additionally, the composition of passive film was analyzed by AR-XPS; at -400∼100 mVSCE and above 600 mVSCE Fe2O3, Fe3O4, FeOOH and CrO3 dominate the passive film, showing n-type semi-conductivity; while at 100∼600 mVSCE the passive film comprises FeO, Cr2O3 and Cr(OH)3, exhibiting p-type semi-conductivity.

VUV-Assisted Photochemical Sol-Gel Processing of Metal Oxide Thin Films

Metal oxides such as TiO2, ZnO, SnO2 are useful in many of energy devices because of their high chemical stability, n-type semiconductivity and photoelectrochemical properties. Various methods of solution processing of their thin films are known, such as chemical bath deposition, electrodeposition and sol-gel reactions. Typically, high temperatures need to be applied for crystallization to achieve good properties. The need of high temperature however limits the choice of substrates to heat-resistant materials. Also, crystallization often results in pinholes and cracks to damage the performance of devices. We have developed an alternative sol-gel method to obtain ultra-smooth thin films of various metal oxides at room temperature, by employing photochemical decomposition of coated precursor by vacuum ultraviolet (VUV) light irradiation. The method is compatible with conductive plastic film substrates, so that multiple applications in thin film devices such as transparent conductive layer, light emitter, buffer layer in solar cells and thin-film encapsulation (TFE) as an example shown in Fig. 1 can be envisioned. Figure 1

Thermoelectric Properties of CoAsSb: An Experimental and Theoretical Study

Polycrystalline samples of CoAsSb were prepared by annealing a stoichiometric mixture of the elements at 1073 K for 2 weeks. Synchrotron powder X-ray diffraction refinement indicated that CoAsSb adopts arsenopyrite-type structure with space group P21/c. Sb vacancies were observed by both elemental and structural analysis, which indicate CoAsSb0.883 composition. CoAsSb was thermally stable up to 1073 K without structure change but decomposed at 1168 K. Thermoelectric properties were measured from 300 to 1000 K on a dense pellet. Electrical resistivity measurements revealed that CoAsSb is a narrow-band-gap semiconductor. The negative Seebeck coefficient indicated that CoAsSb is an n-type semiconductor, with the maximum value of −132 μV/K at 450 K. The overall thermal conductivity is between 2.9 and 6.0 W/(m K) in the temperature range 300–1000 K, and the maximum value of figure of merit, zT, reaches 0.13 at 750 K. First-principles calculations of the electrical resistivity and Seebeck coefficient confirmed n-type semiconductivity, with a calculated maximum Seebeck coefficient of −87 μV/K between 900 and 1000 K. The difference between experimental and calculated Seebeck coefficient was attributed to the Sb vacancies in the structure. The calculated electronic thermal conductivity is close to the experimental total thermal conductivity, and the estimated theoretical zT based solely on electronic thermal conductivity agrees with experimental values in the high temperature range, above 800 K. The effects of Sb vacancies on the electronic and transport properties are discussed.

Active CdS/rGO photocatalyst by a high temperature gas-solid reaction for hydrogen production by splitting of water

rGO supported CdS photocatalysts has been prepared by a two steps method, i.e. impregnation of GO/rGO with CdSO4 followed by a high temperature reaction with H2S gas. Activity of this catalyst was superior to a catalyst of same composition prepared by commonly reported hydrothermal technique. Detailed microstructure studies were carried out using FTIR, PL, DRS, XRD, TEM, SAED, TPO and XPS. A much greater chemical interaction at the interface of CdS and rGO and also a higher absorption of visible light were observed in the reported catalyst. It has been concluded that the high temperature reaction with H2S has imparted n-type semiconductivity to CdS which with p-type rGO and synergy of chemical interaction at the interface has resulted into formation of a p-n hetrojunction. The formation of hetrojunction and high electron mobility of rGO has given a superior activity due to an efficient charge separation to the catalyst prepared by the technique reported in this paper.

Threshold Chloride Concentrations and Passivity Breakdown of Rebar Steel in Real Concrete Solution at Different pH Conditions with the Addition of Glycerol

Addition of glycerol as a viscosity modifier in concrete is proposed to decrease the permeability of corrosion-inducing ions such as chloride and sulfate. In addition to controlling the permeability of concrete, glycerol could perform as an inhibitor of corrosion of rebar steel. Cyclic polarization studies were carried out on metallographically polished rebar steel specimens in actual concrete solutions at two different pH conditions (pH 12.5 and 9.0) and different chloride concentrations. The threshold concentration of chloride for passivity breakdown at pH 12.5 was greater than 50 × 10−3 mol/L in the absence of glycerol addition. The threshold increased to 81 × 10−3 mol/L upon addition of 2 wt% glycerol. The threshold chloride concentration for passivity breakdown in pH 9.0 cement solution was 0.2 × 10−3 mol/L without glycerol addition. No beneficial effect of glycerol was observed in the low pH condition. However, glycerol enhanced the passivation kinetics of the rebar steel in saturated cement solution, but did not affect the electronic properties of the passive layer. The passive layers exhibited n-type semiconductivity with a charge carrier density in the range of 2–7.5 × 1020 cm−3. Polarization of the specimens to potentials is higher than oxygen evolution potential, resulted in transition top-type semiconducting character due to an accumulation of holes. This phenomenon could be related to the passivity breakdown.

Threshold Chloride Concentration for Passivity Breakdown of Mg–Zn–Gd–Nd–Zr Alloy (EV31A) in Basic Solution

Mg–Zn–Gd–Nd–Zr alloy (EV31A) is a heat-treatable magnesium (Mg) cast alloy that can be used up to 200 °C for automobile and aerospace applications. This alloy has excellent mechanical properties (ultimate tensile strength: 280 MPa at room temperature, and ~230 MPa at 200 °C) and improved corrosion resistance. Electrochemical corrosion studies were conducted on this alloy under different heat treatment conditions in 0.1 M NaOH solution with the addition of 0–1000 ppm of chloride. The alloy showed excellent passivity in the 0.1 M NaOH solution. The passive potential range typically extended to more than 1.2 VAg/AgCl. The transpassive potential was observed to be dependent on heat treatment condition of the alloy. More than 80 ppm of chloride was required to induce passivity breakdown in any heat treatment condition. Peak aging at 200 °C for 16 h imparted better resistance for localized corrosion than other heat-treated conditions. The alloy in the as-received condition showed the highest passivation kinetics due to its smaller grain size that possibly increased the diffusion of reactive elements to form protective oxide. The passive film of the EV31A alloy showed n-type semiconductivity with a charge carrier density of ~2 × 1021 cm−3 with no chloride addition. The charge carrier density increased with chloride addition in the electrolyte which could be correlated with the susceptibility to localized corrosion.

Passivation Behavior and Surface Chemistry of 2507 Super Duplex Stainless Steel in Acidified Artificial Seawater Containing Thiosulfate

In this work, passivation behavior and surface chemistry of 2507 super duplex stainless steel (SDSS) in acidified artificial seawater (ASW) containing different concentrations of thiosulfate are investigated using electrochemical techniques, X-ray photoelectron spectroscopy and the Point Defect Model. The 2507 SDSS is resistant to thiosulfate-induced pitting corrosion in the acidified ASW with a {[Cl−] + [SO42−]}: [S2O32−] ratio ranging from 59 to 5900, while the film dissolution rate is enhanced, resulting in a higher passive current density and lower polarization resistance. The passive film exhibits n-type semiconductivity in the acidified ASW and is independent of the thiosulfate levels. The donor density shows little change while the point defect diffusivity increases with increasing thiosulfate concentration. No elemental sulfur and sulfur-containing compounds can be detected on the well-passivated surface of 2507 SDSS, but increasing thiosulfate concentration results in the depletion of Cr2O3, enrichment of oxidized Fe, and thinning of the passive film. The influence of thiosulfate on the film composition depends on the passive states. Thiosulfate promotes the formation of Fe(II) in the prepassive region and accelerates the transformation of Cr(III) to Cr(VI) in the transpassive region.

Synthesis of Gallium Nitride Photocatalysts By Reaction of Solution Synthesized Gallium Oxide and Solid Nitrogen Sources

Solar energy-driven water splitting is receiving considerable interest in hydrogen production as a renewable energy source. Various semiconductor materials for the photodecomposition of water have been investigated for solar energy conversion such as TiO2, TaON and BiVO4. GaN, GaN : ZnO and GaN : InN solid solution are also considered as the photoelectrochemically active material for solar energy-driven water splitting. And its band gap can be controlled by the composition of these solid solutions. We have reported a new technique to synthesize low cost GaN powder under moderate condition, Li3N or LiNH2 were used as a high reactive solid nitrogen source to improve the reaction rate and lowering the reaction temperature. A high yield and high purity GaN with wurtzite structure was synthesized [1, 2]. In this report we studied the method to synthesize GaN powders by the reaction of solution synthesized Ga2O3 powder with solid nitrogen sources. In previous reports commercially available Ga2O3 powder was used. When commercial Ga2O3 powder was used, by the inhomogeneous size, the reaction occurred partially and the yields became small. So the gallium oxide powder with homogeneous size was synthesized by the use of solution process. The photoelectrochemical properties of particulate electrode with synthesized GaN powder were also investigated. The GaCl3 was dissolved in 2-buthyl alcohol under stirring. Then the purified water was added gradually to the Ga containing solution to get the white precipitate. XRD analysis demonstrate that the synthesized powder is Ga2O3. The crucible with starting materials, Ga2O3 and Li3N were put into a sealed stainless steel reaction vessel and it was set vertically in an electric furnace. Then it was heated at 550 – 700°C, 2 hours in N2 atmosphere. After the reaction, the products were washed by alcoholic HCl solution and distilled water. Crystalline wurtzite GaN powder with several hundred nanometer size was successfully synthesized. The reaction yield for the GaN synthesis with solution processed Ga2O3 is higher than that with commercial Ga2O3 powder. Anodic photocurrent was clearly observed for the paste electrodes with GaN and this observation indicates that the GaN synthesized in this study shows n-type semiconductivity. GaN : InN solid solution was also successfully synthesized by the reaction with GaCl3, InCl3 and LiNH2. Photo-electrochemical properties of its paste electrode was also studied. References T. Zhang, A. Mabuchi, T. Sugiura, H. Minoura, Trans. Mater. Res. Soc. Jpn., 33(4), 1277-1280 (2008).T. Zhang, A. Kouyama, M. Miura and T. Sugiura, Trans. Mater. Res. Soc. Jpn., 36(3), 513-516 (2011).

An Azulene-Fused Tetracene Diimide with a Small HOMO-LUMO Gap.

A newly prepared tetraazulene-fused tetracene diimide (TA-fused TDI) showed absorption in the near-IR region owing to the effective extension of the π-conjugated system as well as a large two-photon absorption cross-section (σ(2) =2140 GM) at 950 nm. Four reversible reduction processes and n-type semiconductivity were also confirmed as attractive electronic properties of this compound.

Recent progress in 2D or 3D N-doped graphene synthesis and the characterizations, properties, and modulations of N species

Nitrogen (N)-doped graphene (N-substituted or nitrogenated graphene) (NG) has become a new class of graphene material due to its modified properties such as the tunable work function, n-type semiconductivity, increasing biocompatibility, and, in particular, the synergistic function with various functional materials. However, the preparation of NG by a simple and effective method is still lacking. The modification of NG mainly depends on the N species and the N content. Thus, we focus on the recent progress in preparing methods of 2D NG and the respective key modulating parameters to modulate the N species and the N content. Furthermore, many effective charactering techniques are covered to accurately analyze the properties of N species, and the distribution and topography of N atoms. Also, we review the effect of N species on graphene, especially, the optical and electronic properties. Since constructing 3D structure is considered a promising strategy to prevent the restacking of 2D NG, the summary for preparing 3D NG is made on the basis of methodology of 2D NG. In a word, this review provides a reference for preparing 2D or 3D NG, modulating and characterizing N species, which are greatly contributed to the NG application.

ChemInform Abstract: H‐Bonding Directed Programmed Supramolecular Assembly of Naphthalene‐Diimide (NDI) Derivatives

AbstractReview: 113 refs.

H-bonding directed programmed supramolecular assembly of naphthalene-diimide (NDI) derivatives.

In this review we have collated various supramolecular designs, all surrounding H-bonding among well-known functional groups (peptides, nucleic acids, amides, ureas, carboxylic acids, pyridine-hydroxyls, urethanes, imides and others), to dictate self-assembly of naphthalenediimide (NDI) π-systems (both small molecules and polymeric building blocks) that exhibit several exciting features including strong propensity for π-π interactions, π-acidity, excellent n-type semiconductivity, CT-complexation, ion-π interactions, ring-substitution dependent redox properties and photophysical properties. This article reveals that H-bonding can indeed serve as a very powerful and versatile tool to programmed self-assembly of a single or multiple dye system producing a wide range of tailored soft materials, including fibrillar gels, chromonic mesophases, foldamers, nanotubes, vesicles, reverse micelles and polymersomes, both in water and organic medium with distinct photophysical properties, charge transport properties, conductivity properties and functional group displays that are highly relevant in the fields of biology and organic electronics.

Enhanced Performance of β-Bi2O3 by In-Situ Photo-Conversion to Bi2O3-BiO2-x Composite Photoanode for Solar Water Splitting

Ordered nanoporous bismuth oxide layer consisting of metastable β-Bi2O3 phase that showed n-type semiconductivity was synthesized by a simple electrochemical anodization of bismuth substrate. When the anodic nanoporous β-Bi2O3 samples were tested as photoanodes for solar water splitting application in 0.5 M Na2SO4 (pH:5.8), and 1 M KOH (pH:13.7), the photocurrent decayed continuously with time from an initial value of 0.95 mA/cm2 under 1-sun illumination at a bias potential of 1.5 VRHE. Accumulation of photo generated holes at the photoanode/ electrolyte was attributed to the photocurrent decay. Addition of methanol as sacrificial hole scavenger was not found to be effective for the bismuth oxide photoanodes. When hydrogen peroxide was added to the 0.5 M Na2SO4 electrolyte, the photocurrent density increased to ∼4 mA/cm2 and was stable for more than 1 h of illumination of AM1.5 global light at 1.5 VRHE. Addition of hydrogen peroxide to the 1 M KOH solution showed a gradual increase in the photocurrent density for the first 300 seconds of light illumination to a maximum value of ∼10 mA/cm2 at 0.65 VRHE and then it decreased continuously. The high photocurrent density of nanoporous β-Bi2O3 in 1 M KOH + 0.3 M H2O2 was be attributed to the presence of photo-converted Bi2O4-x phase which harvested more light in the visible wavelengths.