OH-related Defects Research Articles

Effect of arsenate and phosphate substitution on hydroxyl group in libethenite Cu2PO4OH - olivenite Cu2AsO4OH solid solution series

Libethenite and olivenite have been regarded as intriguing photocatalysts because of their singular structures. Copper hydroxy-phosphates and -arsenates exhibit distinctive properties: they incorporate bridging hydroxyl (OH) groups shared by neighboring copper atoms. In materials employed for photoelectrochemical applications, the significance of surface OH groups and OH-related defects frequently varies and is contingent upon the specific material system and the reaction under consideration. Hydroxyl groups can enhance photocatalytic performance by generating OH radicals or serving as crucial agents in catalytic reactions. Therefore, the presence of an OH group within the crystal structure of the material can give rise to potentially interesting behaviors. Seven compounds within the solid solution series of libethenite Cu2PO4OH and olivenite Cu2AsO4OH with stoichiometric ratio (Cu2(Px,As1- xO4)OH, x = 0, 0.1, 0.3, 0.5, 0.7, 0.9, 1 were synthesized at 70 °C via aqueous solutions, and their properties were examined using X-ray diffraction (XRD), Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS), Fourier-transform infrared spectroscopy (FTIR) and Raman spectroscopy. The effect of substituting (PO4)3– ions with (AsO4)3– ions on the alteration of the lattice parameters and spectral characteristics was elucidated by analyzing the correlation between the chemical composition and X-Ray diffraction peak positions. The substitution process leads to modifications in the unit cell parameters and volume. These isomorphic substitutions can be also discerned through alterations in the infrared and Raman spectra, which exhibit variations in the position and intensity of the bands corresponding to phosphates, arsenates, and hydroxyl ions. The incorporation of As into the solid solution resulted in altered bond lengths and geometries, which is consistent with the symmetry transition from orthorhombic libethenite to monoclinic olivenite. The variations in the unit cell parameters and the shifts in the peak position exhibited non-linear trends, and a discernible step was observed between the Cu2(P0·3As0.7)O4OH and Cu2(P0·5As0.5)O4OH intermediate phases. The findings of this study will prove beneficial in evaluating the feasibility of the libethenite-olivenite isometric series as a photocatalysts.

Plasma-enhanced atomic layer deposited HfO2 films using a novel heteroleptic cyclopentadienyl-based Hf precursor

Plasma-enhanced atomic layer deposition of HfO2 films using a novel (η5:η1- Cp(CH2)2NMe)Hf(NEtMe)2 (MAP-Hf01) precursor and Ar/O2 plasma as a co-reactant was studied. Saturated atomic layer deposition with nearly constant growth per cycle of 0.65 Å/cycle was observed and the O/Hf ratio was similar to that of bulk HfO2 at deposition temperatures ranging from 200 °C to 400 °C. With increasing HfO2 deposition temperature, the crystallinity and density of the HfO2 film also increased; however, the concentration of OH-related defects and surface roughness showed the opposite tendency. Notably, HfO2 film deposited at 400 °C exhibited the lowest level of hafnium suboxide (HfOx) and the highest crystallinity in monoclinic phase. The high-quality HfO2 films produced over a well-defined ALD window demonstrate that MAP-Hf01 is a promising candidate for deposition of HfO2 in advanced microelectronics.

Extremely Stable Dual Gate Coplanar Amorphous InGaZnO Thin Film Transistor With Split Active Layer by N2O Annealing

We report the effect of N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O post-fabrication annealing (PFA) on the electrical stability of dual gate, active split amorphous indium gallium zinc oxide (a-IGZO) thin-film transistor (TFT). Optimized N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O PFA at 360 °C for 3 h results in threshold voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TH</sub> ) close to zero and an increase in the on-current almost 2 times than as-fabricated TFT. N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O annealed TFT exhibited robust V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TH</sub> stability under positive bias temperature stress at 60 °C and negative bias illumination stress, exhibiting ΔV <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TH</sub> of 0.1 V ,and0.1 V, respectively, whereas as-fabricated TFT showed large ΔV <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TH</sub> of ~ 10 V and -3 V. The X-ray photoelectron spectroscopy depth profile reveals the origin of such improvement as the increasing metal-oxide bonds and the reduction in oxygen vacancy/ OH related defects.

Intrinsic luminescence centers in γ- and θ-alumina nanoparticles

In this study, we investigate the photoluminescence (PL) properties of γ and θ-alumina nanoparticles synthesized by the chemical wet method followed by annealing. The obtained experimental results indicate the presence of some favorable near ultraviolet (NUV)-orange luminescent centers for usage in various luminescence applications, such as oxygen vacancies (F, , , and F2 centers), OH related defects, cation interstitial centers, and some new luminescence bands attributed to trapped-hole centers or donor–acceptor centers. The energy states of each defect are discussed in detail. The defects mentioned could alter the electronic structure by producing some energy states in the band gap that result in the optical absorption in the middle ultraviolet (MUV) region. Spectra show that photoionazation of F and F2 centers plays a crucial role in providing either free electrons for the conduction band, or the photoconversions of aggregated oxygen vacancies into each other, or mobile electrons for electrons-holes recombination process by the Shockley–Read–Hall (SRH) mechanism.

Morphology and photodegradation performance of Ag3PO4 prepared by (NH4)3PO4, (NH4)2HPO4 and NH4H2PO4

Ag3PO4 was prepared by a facile precipitation process using three types of phosphate salts ((NH4)3PO4, (NH4)2HPO4, and NH4H2PO4) as a precipitant. The XRD, SEM and XPS results revealed that the pH of phosphate salt effectively controlled the shape and size of as-prepared Ag3PO4 samples through affecting the existing species and release rate of PO43- ions in solution. The cauliflower-like spheres Ag3PO4 synthesized by (NH4)3PO4 exhibited best photocatalytic activity towards Congo red degradation under visible light irradiation, as was primarily attributed to its smaller size and less OH-related defects compared with Ag3PO4 prepared from (NH4)2HPO4, and NH4H2PO4. In addition, this Ag3PO4 photocatalyst could degrade Rhodamine B, Malachite Green and Methylene blue, but was not much active for the degradation of Surpho Rhodamine B. More importantly, the dye decolorization efficiency was poorly correlated with the dye mineralization efficiency, which was evidenced by the removal of total organic carbon. The recyclability and stability of the photocatalysts were also evaluated by cycle test experiments using Ag3PO4 prepared by (NH4)3PO4.

Tuning the luminescence and UV photosensing properties of ZnO nanorods by strategic aqueous chemical growth

Surface-adsorbed species play an important role in the photophysical properties of one-dimensional (1D) ZnO providing a scope to comprehend the change in these properties with growth techniques as well as parameters. We have shown an unprecedented change in the photoluminescence properties of aqueous chemically grown (ACG) ZnO nanorods (NRs) by positioning the substrate at different precursor column heights by exploiting a simple phenomenon of different amounts of dissolved O2 along the depth of a precursor solution with its surface exposed to air. As anticipated, the NRs grown at the bottom of the reaction vessel show more OH-related defects and/or adsorbed O2 than those grown nearer to the liquid–air interface, resulting in better crystalline quality, ultraviolet (UV)/visible (Vis) photoluminescence intensity and UV photocurrent properties in the latter. Therefore, one can easily tune the photophysical properties of similar 1D oxide NRs simply by varying the substrate position in a columnar reaction vessel used in aqueous chemical growth.

Al2O3/GeOx gate stack on germanium substrate fabricated by in situ cycling ozone oxidation method

Al2O3/GeOx/Ge gate stack fabricated by an in situ cycling ozone oxidation (COO) method in the atomic layer deposition (ALD) system at low temperature is systematically investigated. Excellent electrical characteristics such as minimum interface trap density as low as 1.9 × 1011 cm−2 eV−1 have been obtained by COO treatment. The impact of COO treatment against the band alignment of Al2O3 with respect to Ge is studied by x-ray photoelectron spectroscopy (XPS) and spectroscopic ellipsometry (SE). Based on both XPS and SE studies, the origin of gate leakage in the ALD-Al2O3 is attributed to the sub-gap states, which may be correlated to the OH-related groups in Al2O3 network. It is demonstrated that the COO method is effective in repairing the OH-related defects in high-k dielectrics as well as forming superior high-k/Ge interface for high performance Ge MOS devices.

Role of graphene on the surface chemical reactions of BiPO4–rGO with low OH-related defects

Graphene has been widely introduced into photocatalysis to enhance photocatalytic performance due to its unique physical and chemical properties. However, the effect of graphene on the surface chemical reactions of photocatalysis has not been clearly researched, which is important for photocatalysis because photocatalytic reactions ultimately occur on the catalyst surface. Herein, a two-step solution-phase reaction has been designed to synthesize quasi-core-shell structured BiPO4-rGO cuboids and the role of graphene on the surface chemical reactions was investigated in detail. It was found that the introduced graphene modified the process and the mechanism of the surface chemical reactions. The change mainly originates from the interaction between graphene and the adsorbed O2 molecule. Due to the electron transfer from graphene to adsorbed O2, graphene could tune the interfacial charge transport and efficiently activate molecular oxygen to form O2˙(-) anions as the major oxidation species instead of ˙OH. In addition, the two-step synthesis approach could efficiently suppress the formation of OH-related defects in the lattice. As a result, the BiPO4-rGO composite exhibited superior photocatalytic activity to BiPO4 and P25, about 4.3 times that of BiPO4 and 6.9 times that of P25.

Influence of OH-related defects on the performances of BiPO4 photocatalyst for the degradation of rhodamine B

BiPO4 photocatalysts with different concentration of OH-related defects were synthesized for various hydrothermal time. The influence of the OH groups on photocatalytic activity, mineralization and degradation process of RhB was discussed in detail excluding other factors such as BET surface area and nanostructures. The defects in the lattice were observed to noticeably decrease the photocatalytic activity by forming defect levels and recombination centers. These defect levels would limit the transfer of the carriers to produce hydroxyl and super oxide radicals. Furthermore, the deethylation intermediates like N,N,N0-triethyl rhodamine and N,N0-diethyl rhodamine were found to accumulate in the solution when large quantities of OH-related defects were in the BiPO4 lattice. While the cleavage of the whole chromophore occurred when small quantities of OH-related defects were in the BiPO4 lattice. The reduction of super oxide radicals influenced by the existence of defects was demonstrated to be good for deethylation process and thus resulted in a decrease of the mineralization degree.

Espectroscopia infravermelha à baixa temperatura em quartzos e ametistas com altas concentrações de OH e H2O

O objetivo desse trabalho foi caracterizar os defeitos pontuais relacionados aos grupos OH e H2O em quartzos e ametistas, crescidos em cavidades do tipo geodo em basalto da Formação Serra Geral (RS), usando a espectroscopia infravermelha (IV) a -175°C. Em um dos cristais, os espectros foram realizados separadamente nos setores de crescimento r{10&lt;IMG SRC="/img/revistas/rem/v62n3/a050i01.gif" ALIGN="absmiddle"&gt;1} e z{01&lt;IMG SRC="/img/revistas/rem/v62n3/a050i01.gif" ALIGN="absmiddle"&gt;1}. Na faixa entre 3800 e 3000 cm-1, os espectros apresentaram várias bandas de absorção superpostas a uma intensa banda larga. As bandas atribuídas ao defeito [H4O4]0 foram observadas independentemente da coloração dos cristais, enquanto que as bandas atribuídas ao centro [AlO4/H]0 ocorreram nos quartzos translúcido e levemente amarelado (citrino). Além da intensidade da banda larga, os espectros desses cristais se caracterizaram pela existência da banda a 3595 cm-1. Ao contrário do reportado por outros autores, verificou-se que a concentração de OH e H2O e a coloração violeta da ametista são maiores nos setores z do que nos setores r. Essa inversão foi discutida em função da não uniformidade das condições de crescimento, confirmada pelo tamanho das faces romboédricas do cristal. Concluiu-se que a intensidade da coloração da ametista não é afetada pelas altas concentrações de defeitos OH e H2O.

OH-related defects in LiNbO 3:Mg,M (M = Nd, Cr, Ti, Mn) crystals

In addition to the 3539 cm −1 OH − stretching vibration related to Mg 2+OH − complexes, OH − bands at 3522 and 3506 cm −1 were found in MgNd and MgCr doubly doped LiNbO 3 crystals, respectively. These bands, polarized perpendicular to the c-axis, are interpreted as an OH − vibration in an M 3+OH −Mg 2+ association. In this complex the OH − ion is assumed to be located between the M 3+ and Mg 2+ ions which occupy Nb 5+ and Li + sites, respectively. In Mg 2+Ti 4+ and Mg 2+Mn 2+ codoped LiNbO 3, no OH − band corresponding to that kind of complex was observed. The absorption strength of the OH − ions involved in the M 3+OH −Mg 2+ association is about 6 × 10 −20cm 2 ion −1.

The effects of irradiation and electrolysis on the thermal conductivity of synthetic quartz

The low-temperature thermal conductivity of Premium Q and Electronic Grade synthetic a-quartz has been measured. Substitutional aluminum is the primary active impurity in Premium Q quartz. Irradiation at room temperature of the unswept Premium Q sample caused a dip in the thermal conductivity near 4 K. This dip can be described by a simple resonant phonon scattering relaxation time with a resonant frequency of 2.75×1012 rad/sec. A room-temperature irradiation of unswept quartz produces both [Ale+]0 and Al-OH centers either of which might cause a resonant phonon scattering. After the premium Q sample was electrolyzed (swept) in hydrogen to remove the alkalis and the [Ale+]0 center and to produce the Al-OH center, the resonant scattering was slightly enhanced. Consequently, the Al-OH center rather than the [Ale+]0 center must be responsible for this scattering. The Electonic Grade sample which has additional OH related defects showed a strongly suppressed thermal conductivity.