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Electronic and Optical Properties of Noble Metal Oxides M(2)O (M = Cu, Ag and Au): First-principles Study


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In this work, first-principles calculations for the structural, electronic, and optical properties of noble metal oxides M(2)O (M = Cu, Ag, Au) with the cuprite structure are performed by using a plane wave pseudopotential method in the framework of density functional theory (DFT) and the generalized gradient approximation (GGA). The structural, electronic, and optical properties are investigated and discussed. For Cu(2)O and Ag(2)O, good agreement was achieved between calculated and experimental results. Within the same framework, Au(2)O is predicted to be a semiconductor. In comparison with the copper and the silver oxides, the gold oxide has less ionic bonding between Au and O, and the intra-atomic hybridization is expected to be more evident as the depletion of the Au 5d shell appears to be more profound than it is for the Cu 3d and the Ag 4d shells.
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Journal of the Korean Physical Society, Vol. 55, No. 3, September 2009, pp. 12431249
Electronic and Optical Properties of Noble Metal Oxides M2O
(M = Cu, Ag and Au): First-principles Study
Fei Pei, Song Wu, Gang Wang, Ming Xu, Song-You Wangand Liang-Yao Chen
The Key Laboratory of Advanced Photonic Materials and Devices,
Department of Optical Science and Engineering, Fudan University, Shanghai 200433, China
Yu Jia
School of Physics and Engineering, Zhengzhou University, Zhengzhou 450052, China
(Received 25 August 2008)
In this work, first-principles calculations for the structural, electronic, and optical properties of
noble metal oxides M2O (M = Cu, Ag, Au) with the cuprite structure are performed by using a
plane wave pseudopotential method in the framework of density functional theory (DFT) and the
generalized gradient approximation (GGA). The structural, electronic, and optical properties are
investigated and discussed. For Cu2O and Ag2O, good agreement was achieved between calculated
and experimental results. Within the same framework, Au2O is predicted to be a semiconductor.
In comparison with the copper and the silver oxides, the gold oxide has less ionic bonding between
Au and O, and the intra-atomic hybridization is expected to be more evident as the depletion of
the Au 5dshell appears to be more profound than it is for the Cu 3dand the Ag 4dshells.
PACS numbers: 71.15.Mb, 71.20.-b, 78.20.-e
Keywords: Noble metal oxide, First-principles calculation, Electronic, Optical properties
Cuprous oxide, Cu2O, is a p-type semiconductor with
potential applications in solar energy conversion and
catalysis [1, 2]. One of the attractive features of Cu2O
is that it has the cuprite structure with a space group
P n¯
3m, as shown in Fig. 1. Each copper atom bonds to
two oxygen atoms in an unusual linear fashion. This
type of bonding is also present in copper-oxide high-
temperature superconductors. Cu2O is, thus, exten-
sively regarded and has been studied as a meaningful
benchmark material for exploring the origin of high-
temperature superconductivity discovered in oxygen-
doped cuprate materials [3]. The interaction between
Cu+and O2based on a simple closed-shell model is
inadequate; thus, a more complex bonding mechanism
has been proposed and adopted [4,5]. The intra-atomic
hybridization of Cu 3dwith the Cu 4sor 4pstates is
regarded as crucial for explaining the low coordination
number and the stability of the crystal structure.
Isostructural Ag2O has also been widely studied for
its important roles in fast-ion-conducting glasses of the
type AgI-Ag2O-B2O3, AgI-Ag2O-V2O3, and AgI-Ag2O-
P2O5[6,7]. Knowledge of the bonding between silver and
oxygen is helpful for understanding the micro structure
of glass and the mechanism of ionic conduction [8].
Recently, a binary system like oxygen-gold has at-
tracted renewed interest because of its possible role as
an intermediary in the preparation and the operation
of supported gold nanoparticle catalysts for heteroge-
neous oxidation reactions [9–14]. Gold oxide (Au2O3)
can be synthesized under hydrothermal conditions with
Fig. 1. Ball and stick model of noble metal oxides, M2O,
with a cuprite structure. The dark and the light balls rep-
resent the noble metal atoms and the oxygen atoms, respec-
-1244- Journal of the Korean Physical Society, Vol. 55, No. 3, September 2009
pressures up to several 1000 atm, as those reported in an
extended X-ray-absorption fine-structure study [12]. A
recent experimental study has proposed that with ther-
mal treatment, heating to around 450 K, Au2O3decom-
poses in a process in which Au2O is a possible interme-
diary [15]. To our knowledge, studies on Au2O with a
cuprite structure have been limited so far. Concerning
the remarkably different reactivity of gold compared to
copper and silver [16–18], as well as the modern impor-
tant application of gold chemistry [19], a study of the
properties of Au2O, which might add to the understand-
ing of gold-based catalysts for heterogeneous oxidation
reactions, is of interest.
In this work, we present first-principles calculations
for noble metal oxides M2O (M = Cu, Ag and Au) with
the cuprite structure. The structural, electronic, and
optical properties are investigated and discussed. For
Cu2O and Ag2O, good agreement between our results
and experimental ones has been achieved to show the
validity of our calculations. Within the same framework,
Au2O is predicted to be a semiconductor. In comparison
with copper and silver oxides, the Au-O bonding is less
ionic, and the intra-atomic hybridization is expected to
be more evident in Au2O as the depletion of the Au 5d
shell appears more profound than those of the Cu 3dand
the Ag 4dshells.
The plane-wave-based density functional theory
(DFT) calculations are performed using the CASTEP
[20,21] code with the core orbitals replaced by ultrasoft
pesudopotentials [22]. The generalized gradient approxi-
mation (GGA) function of Perdew, Burke, and Ernzerhof
[23] (PBE) is used for the exchange correlation potential.
The energy cutoff is chosen as 400.0 eV. The Monkhorst-
Pack k-point sampling is set as 8 ×8×8. The initial ge-
ometry configurations are optimized by using the Broy-
den, Fletcher, Goldfarb, and Shannon minimizer [24].
The properties of M2O, including the electronic band
structures, density of states, difference electron density,
and optical properties, are calculated for the correspond-
ing optimized crystal structures. All of parameters are
tested for convergence in the calculation. The difference
electron density is defined as the difference between the
crystalline charge density and the superposition of the
atomic densities:
n(r) = n(r)nM(r)nO(r),(1)
where n(r) is the total electron density of the optimized
bulk M2O system, and nM(r) and nO(r) are, respec-
tively, the electron densities of the metal and the oxygen
atoms held at the same positions those in the bulk M2O.
The dielectric function of the material is a complex
symmetric second-order tensor that describes the linear
response of an electronic system to an applied external
electric field. The imaginary part of the dielectric tensor
is directly related to the electronic band structure of a
solid, so it can be computed from knowledge of the elec-
tronic structure. The density functional calculation is
well known to tend to underestimate the band gap. To
take this into account, one can use a scissors-operator
(or self-energy operator) approximation [25] to correct
for the limitation of the density functional calculations
of the dielectric function. This approach has been widely
and successfully used to calculate the linear and the non-
linear optical properties for many bulk semiconductors
[26–29]. In most cases, the use of the rigid-scissors ap-
proximation will shift the unoccupied states, resulting in
a calculated value in agreement with experimental ones
to within a few percent.
The optical properties of the solid materials can be de-
scribed by means of the complex dielectric function ε(ω).
The contributions to the complex dielectric function ε(ω)
mainly come from the intraband and the interband tran-
sitions. The contribution from intraband transitions is
significant for metallic materials. The interband tran-
sitions can be divided into direct and indirect transi-
tions. The direct transitions play an important role in
the process of optical response, whereas indirect transi-
tions make a small contribution as scattering of phonons
is involved. Therefore, the intraband transitions and in-
direct interband transitions are neglected in our calcula-
In the limit of linear optics in the visible-to-ultraviolet
region, the imaginary part of the dielectric function,
ε2(ω), represents the optical absorption in the crystal,
which can be calculated from the momentum matrix ele-
ments between the occupied and unoccupied wave func-
tions, and the real part, ε1(ω), is evaluated from the
imaginary part, ε2(ω), by the Kramers-Kr¨onig transfor-
mation. A Lorentzian broadening of 0.15 eV is used.
1. Crystal Structure
Results of the geometrical optimization of M2O are
listed in Table 1, along with the experimental data and
other theoretical values. The calculated lattice constant
for Cu2O is in good agreement with the experimental
result [30]. For Ag2O, the calculated value ais larger by
1.48% with respect to the experimentally measured one
[30]. The lattice constant for Au2O is 4.82 ˚
A, which is
consistent with previous calculations (4.80 ˚
A [31], 4.81
A [3]) reported using GGA-PAW method. The lattice
constant for Au2O is only negligibly larger than that for
Ag2O, which can be attributed to the comparable atomic
radii of Ag and Au.
The isotropic variation of the volume of the cubic unit
cell employed in the determination of the lattice param-
eter can be used to evaluate the bulk modulus. The
Electronic and Optical Properties of Noble Metal Oxides M2O··· – Fei Pei et al. -1245-
Table 1. Calculated lattice constants and bulk moduli for Cu2O, Ag2O, and Au2O. Available experimental data and other
calculation results are listed for comparison.
A) Bulk modulus (GPa)
This work Expt. [30] Theor. [3,31] This work Expt. [32]
Cu2O 4.27 4.27 4.31 118 112
Ag2O 4.81 4.74 4.83 74
Au2O 4.82 4.80, 4.81 97
Fig. 2. Band structures for (a) Cu2O, (b) Ag2O, and (c)
Au2O. The dashed lines are shown as Fermi levels.
calculated bulk modulus for Cu2O is 118 GPa, which is
overestimated by about 5.4% compared to the experi-
mental value of 112 GPa [32]. For Ag2O and Au2O, the
bulk moduli are 74 and 97 GPa, respectively. The lower
bulk modulus for Ag2O is related to the more ionic na-
ture of the Ag-O bond with respect to the Au-O bond.
The bond characteristic for M2O will be discussed in de-
tail in the following sections.
2. Electronic Structure
A. Band structures
The optical properties are related to the band struc-
ture and to the probabilities of interband optical transi-
tions. Therefore, it is of interest to analyze the electronic
structure in detail. The band structures for M2O are pre-
sented in Fig. 2. As shown in Figs. 2(a) and (b), Cu2O
and Ag2O are found to be semiconductors with direct
band gaps at the Γ point. The calculated band gaps for
Cu2O and Ag2O are 0.65 eV and 0.08 eV, respectively,
which are smaller than the experimental values (2.17 eV
for Cu2O [33], 1.30 eV for Ag2O [34]). This discrepancy
is due to an underestimate of the DFT, which consid-
ers only excited states in the calculation. For Au2O, the
calculation shows that the band gap opening at the Γ
Fig. 3. Total densities of states for (a) Cu2O, (b) Ag2O,
and (c) Au2O. An angle-integrated photoemission spectrum
[36] measured for Cu2O is also plotted for comparison.
point is close to zero, resulting in no overlap between the
highest valence band and the lowest conduction band.
Therefore, one can accept that Au2O may actually have
a semiconductor band structure with a larger gap due to
the well-known trend of the DFT to underestimate the
gap value. Previous DFT-GGA and GGA+U calcula-
tions [31] have suggested that Au2O is metallic as the
valence and the conduction bands are found to cross at
the zone center, but this overlap is only marginal and
may possibly be removed by correction of the conduc-
tion band level. Additionally, a notable band gap of 0.83
eV for Au2O has been identified in the calculation using
the screened-exchange local density approximation (SX-
LDA) approach [31]. Further experimental studies are
required to give a clear picture of the electronic struc-
ture of Au2O.
B. Density of states
The calculated total density of states (TDOS) and par-
tial density of states (PDOS) for M2O are plotted in
Figs. 3 and 4, respectively. The vertical line indicates
-1246- Journal of the Korean Physical Society, Vol. 55, No. 3, September 2009
Fig. 4. Partial densities of states for (a) Cu2O, (b) Ag2O, and (c) Au2O.
the Fermi level. The O 2sstates (not shown in Figs.
3 and 4) are well localized at –19.5, –17.8, and –19.2
eV in Cu2O, Ag2O, and Au2O, respectively. The va-
lence band of M2O is clearly split into two regions. The
lower region mostly likely has the O 2pfeatures whereas
the upper one is dominated by M ndstates (n= 3, 4,
5 for Cu, Ag, and Au, respectively). There are some
hybridized M dstates with M sand O 2pstates near
the Fermi level, with no practical contribution from M p
states that have a dominant weight in the bottom of the
conduction band. It is noteworthy that M s,pstates ex-
hibit non-vanishing distributions within the valence band
to have an intra-atomic hybridization of M dstates with
Ms,pstates. This hybridization has been extensively
recognized in other studies on Cu2O. A similar situation
is observed in Ag2O and Au2O, as well.
The calculated width of the valence band for Cu2O is
about 8 eV, which is in agreement with the experimental
data of 8 eV from ultraviolet photoelectron spectroscopy
[35]. The structure of the valence band is also well re-
produced in this calculation, as shown in Fig. 3(a). The
angle-resolved photoemission spectrum [36] is presented
for comparison. The plot has been displaced by about
0.6 eV to make the valence band maximum align with
the theoretical value. There is a good representation of
the features labeled A, B, C, and F in the calculated
density of states, as seen in Fig. 3(a). Features A and
B are shown to mainly have the characteristic of oxygen
atoms. In the upper region, the most prominent feature,
feature D, corresponds to the Cu 3dmaximum. While
the photoemission spectrum gives a large displacement
between features D and F (about 1.8 eV), this displace-
ment has been underestimated by approximately 0.5 eV
in this work. The discrepancy can be attributed to the
incomplete description of localized dorbitals in the GGA
calculation. Feature E is not visible in our calculation.
Table 2. Mulliken population analysis.
s(e)p(e)d(e) Total(e)
Cu 0.57 0.45 9.65 0.33
Ag 0.58 0.33 9.74 0.35
Au 0.83 0.29 9.57 0.30
However, this feature is weak in the quoted experimen-
tal spectrum and was not detected in some other angle-
resolved photoemission spectrum studies, reported by
Bruneval et al. [37].
For Ag2O, the width of the valence band is equal to 7
eV. The Ag 4dstates have an intensity peak at –3.2 eV
(at –4.0 eV according to the XPS data [34]). In the lower
region, the two O 2pmaxima are found at –6.0 and –4.6
eV, respectively. In the upper part, the contribution of
O 2pstates is larger than that found in Cu2O.
The calculated valence band structure for Au2O has a
width of 8 eV. The PDOS plots in Fig. 4(c) are consistent
with the results reported in a previous study [31].
C. Difference electron density
According to the calculated difference electron density
distributions for M2O as shown in Fig. 5, there is an
increase in the electron density at the O sites whereas a
complex redistribution of the electron charge around the
M sites has happened. The Mulliken population analysis
presented in Table 2 gives values of +0.33, +0.35, and
+0.30 for the effective charges of Cu, Ag, and Au, re-
spectively, indicating the ionic feature of the M-O bond.
Au-O is less ionic than Cu-O and Ag-O due to that Au
has a much larger electronegativity (2.54) than Cu (1.90)
Electronic and Optical Properties of Noble Metal Oxides M2O··· – Fei Pei et al. -1247-
Fig. 5. Difference electron densities in the (110) plane calculated for (a) Cu2O, (b) Ag2O, and (c) Au2O. Positive values
representing an increase in the electron density are shown as full, negative values represent a depletion of the electron density are
shown as dashed lines, and zero is shown as dotted lines. The contour lines are presented with a constant step of 6.5×105e/cell.
and Ag (1.93). However, it should be noted that the
bonding between M and O might have some covalence,
resulting in M-O bond length being smaller than the sum
of the ionic radii of M+and O2ions. The depletion of
electrons around the M sites, with the characteristics of
dorbitals, suggests that some d-orbital holes may have
been introduced on the metal ion. Positive values of the
difference electron density at the M sites can be regarded
as evidence of sdand pdintra-atomic hybridiza-
tions. An experimental study on Cu2O has confirmed
that about 0.22 electrons per atom are removed from Cu
zstates [38], while our calculation give a comparable
value of 0.35. The numbers of delectrons missing from
Ag and Au are 0.26 and 0.43, respectively. The intra-
atomic hybridization is expected to be more evident in
Au2O as the depletion of the Au 5dshell appears to
be more profound than it is in the Cu 3dand the Ag
4dshells. However, the number of M d-orbital holes is
much smaller than the charge occupying the nominally
empty M sand porbitals, implying that the ionization
is incomplete, with some electrons normally expected to
be transferred to O now occupying M sand pstates.
3. Optical Prop erties
The optical properties of M2O have been analyzed ac-
cording to the calculated dielectric functions. The scissor
operators are used to rigidly shift the conduction bands
by 1.52 eV and 1.22 eV for Cu2O and Ag2O, respectively,
according to the difference between the experimental and
the calculated band gaps. The scissor operator is not
used for Au2O because the experimental band gap value
is lacking. The real and the imaginary parts of the di-
electric functions calculated for M2O are shown in Fig.
6. The imaginary curve for Cu2O indicates that there
is negligible optical absorption in the low-energy region
up to 3 eV. Two remarkable features are identified at
4.52 and 5.46 eV. These two peaks are observed at 3.58
and 4.34 eV in the experimental data [39] and are as-
signed to band-to-band transitions. The peak positions
in our calculations are about 1 eV blue-shifted with re-
spect to the experimental data. However, the separation
between the two peaks is 0.94 eV, which is close to the
Fig. 6. Calculated dielectric functions for (a) Cu2O, (b)
Ag2O, and (c) Au2O.
experimental value of 0.76 eV. The excitonic effects ob-
served at 2.54 and 2.69 eV in the experiments are not
found in our calculations. The calculated static dielec-
tric constant ε0for Cu2O is about 6.7, which is slightly
smaller than the experimental value of 7.5 [40]. This un-
derestimate is reasonable due to the intraband and the
phonon contribution, which has not been effectively con-
sidered in the calculation. The refractive index nand the
extinction coefficient kcan be derived from the dielectric
function. For Cu2O, the refractive index nhas a value
of 2.8 at 600 nm and decreases to 2.6 as the wavelength
approaches infrared (1500 nm), close to the experimen-
tal values of 2.5 2.4 in this range [41]. The value of
extinction coefficient kwithin the visible light region is
For Ag2O, the optical absorption is also weak in the
energy region below 3.5 eV. Similarly, the imaginary part
presents a two-peak structure located at 4.58 and 5.57
eV, respectively. According to an experimental study
-1248- Journal of the Korean Physical Society, Vol. 55, No. 3, September 2009
[42], the refractive index for Ag2O is about 2.4 in the
400-to-800-nm wavelength region, as compared to the
values of 2.4 2.8 given in this work. The extinction
coefficient kis also negligible in the visible range.
We tentatively present the dielectric function for Au2O
because the electronic structure of Au2O has not been
verified by the experiment result, which will be funda-
mentally important to calculate the optical properties
with higher accuracy. Although the calculated gap value
is negligible, strong optical absorption seems to happen
in the region of photon energies above 2 eV. There are
two notable features, one located at 2.97 and the other
at 3.91 eV.
In this work, first-principles calculations for noble
metal oxides M2O (M = Cu, Ag, Au) with the cuprite
structure are performed by using a plane-wave pseudopo-
tential method in the framework of DFT and the GGA.
The atomic, electronic, and optical properties of M2O
are investigated. The structural parameters for Cu2O
and Ag2O are in good agreement with experimental re-
sults. The lattice constant for Au2O is identical with
that for Ag2O. The direct band gap structures for Cu2O
and Ag2O obtained from the calculation are consistent
with the experimental results. Au2O is expected to have
a band structure similar to that of a semiconductor with
a small gap at the Γ point, but the actual gap value may
be larger than the calculated one if the typical tendency
of DFT to underestimate values is considered. Electron
charge transfer illustrates the ionic feature of the M-O
bonding. The Au-O bond is less ionic than the Cu-O and
Ag-O bonds. The calculated difference electron densities
suggest d-orbital holes with some complex intra-atomic
hybridization between M dand M s,pstates, especially
for Au2O which has a charge depletion of the Au 5dshell
that appears to be more profound than those of the Cu
3dand the Ag 4dshells.
This work was partially supported by National Basic
Research Program of China (No. 2010CB933700) and
the STCSM project of China (Grant No. 07TC14058).
The computation was performed at the National High
Performance Computing Center at Fudan University.
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... The Ag2O compound with cuprite structure. [24], used the plane-wave-pseudopotential method as incorporated in the CASTEP code to study the structural, electronic, and optical properties of Ag 2 O with cubic cuprite structure. Jeremy P. Allen et al., [25], have described the electronic structure of Ag 2 O using various calculation methods. ...
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The primary goal of this study is to investigate the effect of different exchange-correlation functionals on the optoelectronic and elastic properties of the Ag2O chalcogenide compound. For the electronic structures and optical spectra, the Tran-Blaha modified Becke-Johnson approach combined with GGA and with GGA+U (mBJ-GGA-PBEsol and mBJ-GGA-PBEsol+U, respectively) was used. The available theoretical and experimental data for the bandgap energy were reported to determine whether there is a correlation with our results. The electronic structure revealed that our compound is a direct semiconductor at the R-symmetry point with a bandgap of 1.22 eV, which this value agrees well with the experimental values for the first time. The elastic constants were also evaluated using the IRelast package, which revealed that the compound was mechanically stable. Finally, the optical response was systematically studied, and it was found that Ag2O exhibited excellent optical efficiency.
... The exchanged Ag ions as well as the Brønsted acid site (both 1:1 with Al) were positioned closest to the Al, and bound to the neighboring O but not the Al itself. The Ag 2 O adsorption site in this work is 54,55 Ag may be distributed among two of the candidate active sites. (The Brønsted acid sites do not involve Ag.) ...
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Three potential adsorption sites within the Ag/SSZ-13 zeolite are compared for their ethylene and water adsorption capacity. Ethylene acts as a model hydrocarbon molecule in this work to stand in for vehicle exhaust, as Ag/SSZ-13 is a candidate material for trapping vehicle emissions during cold-start. Water is also present in vehicle exhaust and competes for adsorption sites with ethylene. The three active sites studied are the intended Ag ion-exchanged with an H in the zeolite framework, an H site (known as a Brønsted acid site) and Ag2O which may form as a non-zeolite adsorption site during the Ag ion-exchange synthesis. Density functional theory (DFT) calculations are conducted using the BEEF-vdw functional for up to two molecules of ethylene and/or water adsorbed per site. A microkinetic model parameterized by the DFT predicts the ethylene adsorption capacity for shifting ethylene feed gas concentrations at 100C in the presence of 6% water. Experimental observations are taken at matching conditions as microkinetic model simulations. The DFT energies and their uncertainties for each adsorption site are updated from experiments using a Bayesian statistical framework. The Ag ion and Ag2O sites adsorb more ethylene relative to the Brønsted acid site. The Ag ion and Brønsted acid sites adsorb more water relative to Ag2O.
... A band gap value of approximately 1.58 eV was determined for Ag 2 O, which agrees with the reported band gap energy of 1.50 eV[30]. The reports suggest that Ag 2 O optical band gap is formed by O 2p, and, Ag 4d states in the valence band (BV) while the conduction band (CB) consists of Ag 5s, p, and 4d states[31,32]. Moreover, the calculated band value for the Ag/Ag 2 O nanocomposites are 1.53, 1.45 and 1.40 eV for the samples S1, S2 and S3, respectively. ...
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Ag2O was synthesized by the precipitation method and it was used as support to prepare Ag/Ag2O nanocomposites using different sodium citrate volumes to control the size and amount of Ag nanoparticles. Materials were characterized by X-ray powder diffraction, diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, scanning and transmission electron microscopy and nitrogen adsorption–desorption at − 196 °C analyses, respectively. Ibuprofen was selected as a probe molecule and materials were assessed as photocatalysts under simulated visible light irradiation. The SEM and TEM analysis revealed the presence of Ag nanoparticles over Ag2O support showing a size increase as citrate volume increased. By means of DRS analysis a band gap shift was observed, suggesting the formation of metallic silver during Ag impregnation while XPS results proved the co-existence of Ag⁰ and Ag2O composites. On the other hand, the photocatalysis results revealed the formation of intermediaries during ibuprofen photodegradation. Visible light absorption by Ag nanoparticles produced superoxide anion radicals (due to surface plasmon resonance) that enhanced the formation of intermediaries. The reaction mechanism proposed involves the generation of a Ag/Ag2O heterojunction where the metal acts as an electron scavenger decreasing the recombination of the e⁻–h⁺ pair. Graphic Abstract
... Since the defect formation energy is more favorable for interstitial doping, therefore, the DOS and band structure calculations have been done on this optimized structure only. The present DFT calculations employ the GGA-PBE functional which has earlier predicted a zero bandgap for pure Ag 2 O [22]. The DOS (Fig. 5a) and the band structure (Fig. 6a) results of our calculations also underestimate and predict a zero bandgap for Ag 2 O. Fig. 5b shows the DOS for the interstitially doped Zn-doped optimized structure. ...
Semiconductor bandgap widening is a little investigated phenomenon in photocatalysis literature. The present investigation attempts the widening of the narrow bandgap of Ag2O to make it a semiconductor with more attractive properties. The synthesis of Zn doped Ag2O nanostructures followed a typical hydrothermal synthesis procedure. An increase in the lattice parameters of Ag2O with doping indicated the occupation of an interstitial position by the dopant metal ion. Density functional theory calculations also demonstrated the expansion of the Ag2O crystal lattice with the dopant at an interstitial location. The bandgap of the Ag2O increased to 1.65 eV for 5-mol percent doping. The DFT calculated density of states (DOS) plots also exhibit an increase in the bandgap of Ag2O after Zn doping. These doped Ag2O nanoparticles were useful in photocatalysis of methyl orange degradation under visible light irradiation.
... The refractive index for the Ag2O layer was set to n = 2.4 [210,211]. In Figure 88 ...
This report is concerns with optical nano-antennas in their various forms such as metallic nano-rods, cross-shaped nano-particles and apertures, periodic meta-surfaces such hole arrays and bullseye structures. Their applications in wavelength division multiplexing/demultiplexing, shaping the radiation pattern and the state of polarization of the transmitted light, refractive index based sensing, enhancement to the radiative decay rate of nearby quantum emitters and novel approach in achieving such effects are presented.
... where C sc is the space-charge capacitance (in F cm À2 ), ε is the dielectric constant of the semiconductors [35,36]; e is the electronic charge in C; N A is the carrier (hole) density in cm À3 ; ε 0 is the permittivity of free space; E fb is the flat band potential in V; k is the Boltzmann constant; and T is the temperature in K. Fig. 8a represents the Mott-Schottky plot of Cu 2 O thin films deposited at the different applied potentials at a fixed frequency region. The negative slope of the lines indicates the p-type semiconductivity for all samples. ...
2‐Hydroxy‐1‐naphthaldehyde oxime was oxidized by AgO (or Ag2O), in presence of N‐methyl morpholine N‐oxide (NMMO), to the title spiro adduct‐dimer (±)‐Spiro{naphthalene‐1 (2H),4ʹ‐(naphtho[2ʹ,1ʹ:2,3]pyrano[4,5‐c]furazan)}‐2‐one‐11ʹ‐oxide by a Diels‐Alder(D‐A) type self‐cycloaddition, through the agency of an o‐naphthoquinone nitrosomethide (o‐NQM). Moreover, 2‐hydroxy‐8‐methoxy‐1‐naphthaldehyde oxime was prepared and subjected to the same oxidation conditions. Its sterically guided result, 9‐methoxynaphtho[1,2‐d]isoxazole, was isolated, instead of the expected spiro adduct. The peri intramolecular H bonding in the oxime is considered to have a key contribution to the outcome. Geometry and energy features of the oxidant‐ and stereo‐guided selectivity of both oxidation outcomes have been explored by DFT, perturbation theory and coupled cluster calculations. The reaction free energy of the D‐A intermolecular cycloaddition is calculated at ‐82.0 kcal/mol, indicating its predominance over the intramolecular cyclization of ca. ‐37.6 kcal/mol. The cycloaddition is facilitated by NMMO through dipolar interactions and hydrogen bonding with both metal complexes and o‐NQM. The 8(peri)‐OMe substitution of the reactant oxime sterically impedes formation of the spiro adduct, instead it undergoes a more facile cyclodehydration to the isoxazole structure by ca. 4.9 kcal/mol
Foam-like binary Cu2O/Ag2O nanoheterostructures have been obtained by an electrochemical method. Their photoelectrochemical and spectral properties have been studied. The photocatalytic properties of these composites in the process of gas-phase reduction of carbon dioxide with water vapor have been studied. The formation of binary nanoheterostructures leads to an increase in methane yield and an increase in the amount of other organic products (acetaldehyde, ethylene, and ethanol) while the system is irradiated with visible light when compared to Cu2O. This effect can be explained by the formation of a nanostructured Cu2O/Ag2O binary composite with a mutually consistent energy profile.
With the worldwide industrial growth, major concern is rapid surge in water pollution. Notably, the water is contaminated by strong industrial dyes and pathogenic microorganisms. To address the issue, a simple heterostructure GO/Ag2O was synthesized in room temperature, which can serve the purpose of industrial waste management. In general, Ag2O nanostructures with absorptivity in NIR range is able to absorb 57% of solar spectrum, but our synthesized Ag2O nanowires can absorb Visible-NIR spectral range (peak ~ 850 nm) due to presence of multiple energy states, confirmed by the density of states (DOS) of Ag2O using density functional theory (DFT) analysis. Developing a nanocomposite with graphene oxide exhibited blue shifting of absorption maximum at 700 nm and improved absorptivity covering the entire solar spectrum (200-1800 nm). The DFT analysis of designed geometrical relaxed structure of GO/Ag2O approved the unique optical properties of nanocomposite. The nanocomposite degraded a very strong medical dye (Safranin-O) for 40 minutes white light exposures. In addition, our nanocomposite also showed antibacterial activity against E. coli with an MBC ~ 0.05 mg/ml. Molecular Docking analysis also established the improved interaction of an E.coli ribosomal and membrane protein with GO in nanocomposite in comparison with that of pure GO, which supports the experimental results. Fast charge transfer between Ag2O and GO increases the super oxide and hydroxide radicals in our synthesized hetero-system, which results excellent solar photocatalytic activity and ROS species to destroy the bacterial colonies.
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Silver layers were deposited on plastic web by DC magnetron sputtering using different additional oxygen inlet. Single Ag layers sputtered at an oxygen inlet below 14 sccm, which amounts to 12.3% (Ar: 100 sccm) of the whole gas flow, exhibited no noticeable change in optical properties. At 112 sccm O2 the synthesis of Ag2O is reached. At higher flow, a semi transparent coating was formed, which is assumed to be AgO. The dispersions for synthesized single AgO fit the resulting oxide layer, grown by a subsequent oxygen rich plasma process, very well. The modeling of plasma oxidation of silver showed, that the formation of the AgO phase is not the only reason for the degradation of silver containing layer stacks. Beside that agglomeration of silver takes place, intrinsic stresses (caused by the oxidation) resulting in partial delaminations and a dramatic increased roughness occurs.
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A striking feature of metal oxide chemistry is the unusual electronic and chemical behaviour of Cu(I) and Ag(I): a case in point is that detailed understanding of Cu-O bonding is essential to the theory of high-temperature copper oxide superconductors. Both cations are usually coordinated in a linear fashion to two oxygens, particularly for Cu(I). In many compounds, the Cu(I) and Ag(I) cations also adopt close-packed (and related) configurations with short metal-metal distances that are strongly suggestive of the occurrence of metal-metal bonding despite their formal nd10 configuration. Such observations have been explained by invoking the participation in bonding of electronic orbitals of higher principal quantum number-that is, (n + 1)s and (n + 1)p-accompanied by the creation of d-orbital holes on the metal ion. To test this hypothesis, we have used a recently developed method of quantitative convergent-beam electron diffraction combined with X-ray diffraction to map the charge-density distribution in the simple oxide Cu2O, the results of which we then compare with electronic-structure calculations. We are able to image directly the d holes on the copper atoms, and also demonstrate the existence of Cu-Cu bonding in this compound.
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The band structure, total and projected densities of states, and distributions of the valence and difference electron densities for copper and silver oxides are calculated in the framework of the density functional theory in the local approximation with ab initio norm-conserving pseudopotentials in the basis set of pseudoatomic orbitals. The results obtained are compared with the experimental data and calculations performed by other authors. The energy spectrum and spatial distribution of electrons in crystals are similar to each other. Metal ions are bonded to each other through charge density channels with a weakly pronounced maximum at the center of the empty tetrahedron.
FSDP measurements were performed by X-ray diffraction, neutron diffraction and elastic neutron scattering experiments for AgI–Ag2O–V2O5 and some of AgBr–Ag2O–V2O5, AgCl–Ag2O–V2O5 and AgI–AgPO3 glasses at room temperature. FSDP observed by X-ray diffraction is due to the density fluctuation of the network structure. Composition change of this FSDP profile for AgI–Ag2O–V2O5 glasses corresponds to those of the ionic conductivity and the molar volume. New FSDP was found in the high AgI region of AgI–Ag2O–V2O5 system by elastic neutron scattering. FSDP observed by neutron scattering suggests the formation of medium range order of doped AgI in highly AgI-doped glasses.
The optical spectra of Cu2O at room temperature have been interpreted in terms of band structure. The optical constants have been obtained by a Kramers-Kronig analysis of the normal incidence reflectivity spectrum for photon energies up to 25 eV. Data obtained at 35°K for energies between 2 and 6 eV are also presented.RésuméNous avons étudié le spectra optique de Cu2 O, par reflexion entre 2 et 25 eV. Les constantes optiques ont été calculeés à l'aide des formule de Kramers-Krönig. L'étude, effectuée à basse température (T = 35°K) entre 2 et 6 eV, montre la coexistence de transitions interbandes et d'excitons.
Photocatalytic decomposition of water into H2 and O2 on Cu2O under visible light irradiation is investigated; the photocatalytic water splitting on Cu2O powder proceeds without any noticeable decrease in the activity for more than 1900 h.
We present angle-resolved photoemission data along the M-Γ-M direction from a Cu2O(111) single crystal, collected at high photon energies (hν=619 and 891 eV) and T=100 K. Because of the high photon energies and effective background subtraction, our data give a clear picture of the bulk band structure. The results confirm the existence of a hybridized Cu 3d–Cu 4s state located between the two main Cu 3d and O 2p band regions. Several theoretical studies have predicted the existence of this band, but until now it has not been detected in any photoemission measurements. The experimentally derived band structure is compared to local density approximation calculations with and without the Hubbard potential U. The clear band dispersion in our experimental data has enabled us to extract a refined Hubbard U value, which makes it possible to achieve a better agreement between theoretically calculated bands and experimental data.
The novel method with the use of resistance foil strain gauges is described and employed for the determination of the isothermal volume compressibility coefficient of xAgI–(1−x)(Ag2O–P2O5) (0.05≤x≤0.5) glasses. It has been found that compressibility is dependent on pressure–time–history of the glass. The results are discussed and explained on a model assuming that high pressure causes the network to be more densely packed resulting in lower compressibility. Also, concentration of AgI in the glass affects the compressibility value. The linear dependence of compressibility vs. molar fraction of AgI has been found. The linear model of resultant compressibility of composite materials has been suggested to explain the observations.
This article describes recent technical developments that have made the total-energy pseudopotential the most powerful ab initio quantum-mechanical modeling method presently available. In addition to presenting technical details of the pseudopotential method, the article aims to heighten awareness of the capabilities of the method in order to stimulate its application to as wide a range of problems in as many scientific disciplines as possible.