Copper Vacancies Research Articles

Point-defect engineering of nanoporous CuBi2O4 photocathode via rapid thermal processing for enhanced photoelectrochemical activity

Engineering point defects such as metal and oxygen vacancies play a crucial role in manipulating the electrical, optical, and catalytic properties of oxide semiconductors for solar water splitting. Herein, we synthesized nanoporous CuBi2O4 (np-CBO) photocathodes and engineered their surface point defects via rapid thermal processing (RTP) in controlled atmospheres (O2, N2, and vacuum). We found that the O2-RTP treatment of np-CBO increased the charge carrier density effectively without hampering the nanoporous morphology, which was attributed to the formation of copper vacancies (VCu). Further analyses revealed that the amounts of oxygen vacancies (Vo) and Cu1+ were reduced simultaneously, and the relative electrochemical active surface area increased after the O2-RTP treatment. Notably, the point defects (VCu, Cu1+, and Vo) regulated np-CBO achieved a superb water-splitting photocurrent density of −1.81 mA cm−2 under simulated sunlight illumination, which is attributed to the enhanced charge transport and transfer properties resulting from the regulated surface point defects. Finally, the reversibility of the formation of the point defects was checked by sequential RTP treatments (O2-N2-O2-N2), demonstrating the strong dependence of photocurrent response on the RTP cycles. Conclusively, the surface point defect engineering via RTP treatment in a controlled atmosphere is a rapid and facile strategy to promote charge transport and transfer properties of photoelectrodes for efficient solar water-splitting.

Synthesis of hollow Cu@Cu3−xP core-shell nanostructure as dual-functional catalyst with copper vacancy for enhancing chemical reduction and photocatalytic performance

As an important family of semiconductors, transition metal phosphides could act as effective catalysts in the treatment of organic pollutants. Herein, a novel hollow core–shell Cu@Cu3−xP catalyst with copper vacancies, possessing excellent properties of photocatalytic and catalytic reduction for organic pollutants, was prepared by the vapor deposition method. 4-Nitrophenol (4NP) (50 μM, 3 mL) could be degraded within 2 min under the action of catalyst (0.06 mg), and the reduction rate was approached to 99.8%. Meanwhile, this catalyst displayed prominently increased Rhodamine B (RhB) photo-oxidation performance, about 1.7 and 16 times more than the bare Cu3P and Cu under optimal conditions (5% Cu@Cu3−xP). Such superior catalytic performance can be ascribed to the mutual contribution of Cu vacancy (convert the band structure and supply active sites) and Cu nanowire (prevent agglomeration of Cu3P nanoparticles and promote the transfer of photoelectrons) and the unique hollow core–shell architecture(the rapid separation and low recombination of photoelectron-hole). The possible pathways of 4NP reduction and RhB photo-oxidation were proposed according to the results of degradation products obtained from HPLC, LC-Q-orbitrap/MS, GC-MS, and ATR-FTIR. This study can validate the extensive application of Cu@Cu3−xP and provide a new insight for the synthesis of dual-functional catalysts containing metal defects.

Tailoring orientation of microstructure for improving thermopower factor in Mg-doped CuCrO2 thick films

This study changed the material thickness (0.5–2.7 μm) to control the orientation of microstructure for tailoring the thermopower factor of CuCr0.85Mg0.15O2 films. As a result, the (110)-preferred orientation and copper vacancies were dominant in the thicker film, which increased conductivity σ. The Seebeck coefficient S remained unchanged within the wide film thickness range despite the remarkable increment in σ. Therefore, the thermopower factor (PF = S2σ) of the CuCr0.85Mg0.15O2 films drastically increased with the increase in the film's thickness, reaching 720 μW/mK2 at 500 °C in a 2.0 μm-thick CuCr0.85Mg0.15O2 film. This value is better than that observed in the bulk materials. A detailed discussion of physical mechanisms is presented in this manuscript.

Investigations Into the Role of Native Defects on Photovoltaic and Spintronic Properties in Copper Oxide

CuO is a promising contender for photovoltaics, photodetection, photocatalysis, and spintronics in theory, but experimental success in terms of device performance has been limited. We used experimental and theoretical techniques to examine the fascinating optoelectronic and spintronic features of a p-type semiconductor; i.e. copper oxide. Absorption spectra of CuO have revealed intriguing properties such as defect-induced strong absorption in the visible and near-infrared (NIR) regions, making it an attractive candidate for NIR and broadband detection. Additionally, due to its antiferromagnetic characteristics, CuO has potential applications in spintronics. Clearly, these applicability ranges are greatly dependent on the intrinsic material qualities and defects. To gain a better understanding of CuO band structures, defect dynamics, charge distribution, and absorption properties; ab-initio calculations were conducted in a systematic manner. Additionally, the stability of several types of defects has been investigated theoretically in Cu and O-rich environments. The literature is ambiguous about the stability of several defects in CuO, including copper vacancies, oxygen vacancies, and interstitials. Interestingly, it is discovered that V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Cu</sub> -V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">O</sub> di-vacancies and V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">O</sub> are extremely stable in O-deficient environments, whereas V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Cu</sub> is highly stable in O-rich environments. Numerous defects such as copper vacancies, oxygen vacancies, and di-vacancies all contribute significantly to the photovoltaic features such as quantum-efficiency. Furthermore, unlike pristine CuO, defect assisted CuO has a significant magnetic moment as shown by first-principle calculations, making it a suitable option for spintronics. The work will open several features of CuO for next generation devices.

Selective Defect Metal Sulfide for Localized Surface Plasmon Resonance

As a p-type semiconductor with metal vacancies in the lattice,coppersulfide Cu2-xS has been proved asan effective photocatalyst with its unique semiconducting character, non-toxic nature andexcellent optoelectronic properties. In this work, we have synthesized copper sulphide nanostructure via hydrothermal method by using cetyltrimethylammonium bromide (CTAB) as a morphology controlling agent. Due to plasmonic nature, results from copper vacancy Cu2-xS nanocrystals possess a property called localized surface plasmon resonance which makes them capable of utilizing the NIR region of solar spectrum. The aim of this study is to explore copper sulphide catalyst which is capable of absorbing NIR region of the solar spectrum. It is found that copper sulphide has significantly enhanced light absorption over the entire wavelength range (from ultra-violet to near-infrared).

Augmented photoelectrochemical water reduction: influence of copper vacancies and hole-transport layer on CuBi2O4 photocathode

Introducing Fe-doped NiOX as hole-transport layer beneath the copper vacancies induced CuBi2O4 photocathode facilitates efficient charge separation and transfer leading to remarkably enhanced photoelectrochemical performance.

Solution–processed Cu2O/ZnO/TiO2/Pt nanowire photocathode for efficient photoelectrochemical water splitting

State–of–the–art Cu2O photocathodes are mostly fabricated by means of electrodeposition and have been reported to be flooded with the copper vacancies (VCu), into which the photoexcited electrons are rapidly trapped and thereby hardly injected into the electrolyte for photoelectrochemical water splitting. To address this issue, an alternative approach consisting of simple wet chemistry combined with post–thermal treatment is employed in the present contribution to grow the Cu2O nanowires (NWs) on the Cu foil, which provides the Cu ions to fill VCu. An important result of the depletion of VCu is the space charge layer extending deep into the Cu2O NWs, wherein the photoexcited charge carriers are rectified by the surface band bending for efficient separation. The charge separation is further reinforced by using ZnO to first extract the photogenerated electrons from Cu2O, TiO2 to further glean the electrons from ZnO, and the Pt co–catalyst to facilitate their injection into the electrolyte. These materials are deposited sequentially on the Cu2O NWs by means of chemical bath deposition, which is put forward in the present contribution as a cost–effective and readily scalable alternative to the conventional atomic layer deposition technique. The synergistic effect leads to a photocurrent density of the Cu2O/ZnO/TiO2/Pt NWs of −8.2 mA cm−2, well outperforming that of the pristine Cu2O NWs by more than 2.5–fold and, moreover, being comparable to that of the electrodeposited counterparts reported in the literature.

Synthetic Ligand Selection Affects Stoichiometry, Carrier Dynamics, and Trapping in CuInSe2 Nanocrystals.

CuInSe2 nanocrystals exhibit tunable near-infrared bandgaps that bolster utility in photovoltaic applications as well as offer potential as substitutes for more toxic Cd- and Pb-based semiconductor compositions. However, they can present a variety of defect states and unusual photophysics. Here, we examine the effects of ligand composition (oleylamine, diphenylphosphine, and tributylphosphine) on carrier dynamics in these materials. Via spectroscopic measurements such as photoluminescence and transient absorption, we find that ligands present during the synthesis of CuInSe2 nanocrystals impart nonradiative electronic states which compete with radiative recombination and give rise to low photoluminescence quantum yields. We characterize the nature of these defect states (hole vs electron traps) and investigate whether they exist at the surface or interior of the nanocrystals. Carrier lifetimes are highly dependent on ligand identity where oleylamine-capped nanocrystals exhibit rapid trapping (<20 ps) followed by diphenylphosphine (<500 ps) and finally tributylphosphine (>2 ns). A majority of carrier population localizes at indium copper antisites (electrons), copper vacancies (holes), or surface traps (electrons and/or holes), all of which are nonemissive.

Al-Modified CuO/Cu2O for High-Temperature Thermochemical Energy Storage: from Reaction Performance to Modification Mechanism.

Next-generation concentrated solar power plants with high-temperature energy storage requirements stimulate the pursuit of advanced thermochemical energy storage materials. Copper oxide emerges as an attractive option with advantages of high energy density and low cost. But its easy sinterability limits its reversibility and cyclic stability performance. In this work, aluminum-doped copper oxides are synthesized and evaluated via thermogravimetric analysis. The reversibility of Cu-Al oxides reaches 99.5% in the first redox cycle and maintains 81.1% of the initial capacity after 120 cycles. The Al element can modify the CuO particle surface in the form of CuAl2O4, which separates the copper oxide particles from each other during redox cycles to avoid agglomeration and participates in the redox reaction. Through DFT analysis, the introduction of Al is found to increase the formation energy of copper vacancies in copper oxides, which helps avoid the sintering problem and thus improves the oxidation rate. This study provides a generalizable operational mechanism of element doping and can serve as a guideline for the optimization of high-performance materials in thermochemical energy storage.

Tunable structural, morphological and optical properties of undoped, Mn, Ni and Ag-doped CuInS2 thin films prepared by AACVD

The preparation of high-quality copper indium sulphide, CuInS2 photo-absorber material with tunable properties for efficient, low-cost, thin film solar cells using scalable methods remains a challenge. In order to address this, high quality off-stoichiometric undoped and Mn, Ni and Ag-doped CuInS2 (CIS) thin films have been deposited onto glass substrates by aerosol-assisted chemical vapour deposition (AACVD) using metal diethyldithiocarbamate precursors at temperatures of 350, 400 and 450 °C. Data from powder X-ray diffraction (p-XRD), Raman spectroscopy and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) suggest a correlation of morphology and composition of tetragonal phase (chalcopyrite and copper-gold-type) sulphur-deficient microcrystalline CIS thin films. For undoped thin films, near-infrared optical absorption and emission with tunable band gap between 1.32 and 1.42 eV are likely associated with donor-acceptor pairs involving deep or shallow electronic states such as sulphur vacancies (VS••), indium-copper anti-sites (InCu••) and indium interstitials (Ini•••) as donors and copper vacancies (VCu′) as acceptors. Whilst Mn-doped thin films exhibit minimal tunable properties, Ni and Ag-doped films exhibit tunable morphology, composition and near-infrared absorption for small dopant content. Though further studies are required to explore the defect chemistry, these results show the utility of AACVD in tuning structural, morphological and optical properties of undoped, Mn, Ni and Ag-doped CIS thin films.

Structural Analysis and Performance in a Dual‐Mechanism Conductive Filament Memristor

AbstractThe development of a dual‐filament model is vital for achieving better performance in next‐generation resistive random‐access memory (RRAM). In this work, the microstructure evolution and corresponding performance of a Cu/Ta2O5−x/Pt system are investigated at the atomic scale. By inducing intrinsic oxygen vacancies into tantalum oxide and applying copper as the active electrode, the RRAM device can exhibit the electrical properties of a dual‐mechanism filament. The device demonstrates a long retention time (104 s) and a large memory window of 106. By using high‐resolution transmission electron microscopy and high‐resolution X‐ray photoelectron spectroscopy, the conductive filament is found to consist of crystalline copper and oxygen vacancies. Moreover, with the growth kinetics of filaments from in situ transmission electron microscopy and curve fitting relevant to the conduction mechanism, the formation of filaments is promoted by field‐coalesced oxygen vacancies induced by the growth of copper filaments. Therefore, this work provides a unique perspective and a novel material engineering approach for tailoring RRAM devices and developing further applications in electronic technology.

Rydberg excitons in synthetic cuprous oxide Cu2O

High-lying Rydberg states of Mott-Wannier excitons are receiving considerable interest due to the possibility of adding long-range interactions to the physics of exciton-polaritons. Here, we study Rydberg excitation in bulk synthetic cuprous oxide grown by the optical float zone technique and compare the result with natural samples. X-ray characterization confirms both materials are mostly single crystal, and mid-infrared transmission spectroscopy revealed little difference between synthetic and natural material. The synthetic samples show principal quantum numbers up to $n=10$, exhibit additional absorption lines, plus enhanced spatial broadening and spatial inhomogeneity. Room temperature and cryogenic photoluminescence measurements reveal a significant excess of copper vacancies in the synthetic material. These measurements provide a route towards achieving \mbox{high-$n$} excitons in synthetic crystals, opening a route to scalable quantum devices.

Heavy-ion irradiation assisted modification of p-type transparent CuAlO2 films: Electrical, optical and thermoelectric properties

Heavy-ion (HI) irradiation is a unique approach to induce defects in semiconductor films. The ion irradiation leaves continuous columnar tracks to create various defects and reduce film density, modulating the thermoelectric properties of semiconductor films. As a p-type transparent oxide semiconductor (TOS), the as-synthesized CuAlO2 films were irradiated with different doses of Fe10+ ions at room temperature using the 320 kV High Voltage Platform, and then post-annealed to improve the microstructure and thermoelectric properties. The irradiated CuAlO2 films, with 15 × 1013 ions cm−2, can achieve an electrical conductivity of 0.14 S cm−1, which is about 200 times larger than the unirradiated counterparts. The Seebeck coefficient reaches up to 189.80 and 208.58 μV K−1 at room temperature and 600 K, respectively. Therefore, a high power factor (PF) of 9.15 μW m−1K−2 is rendered by the irradiated CuAlO2 films, whereas the unirradiated films are not detected in the given measurement range. The improved thermoelectric performance is mainly due to the increased copper vacancies in irradiated films without significantly reducing the crystallinity. The current work presents a promising strategy to improve the thermoelectric performance of semiconductor films.

Structural and electronic properties of Cu4O3 (paramelaconite): the role of native impurities

Abstract Hybrid density functional theory has been used to study the phase stability and formation of native point defects in Cu4O3. This intermediate copper oxide compound, also known as paramelaconite, was observed to be difficult to synthesize due to stabilization issues between mixed-valence Cu1+ and Cu2+ ions. The stability range of Cu4O3 was investigated and shown to be realized in an extremely narrow region of phase space, with Cu2O and CuO forming readily as competing impurity phases. The origin of p-type conductivity is confirmed to arise from specific intrinsic copper vacancies occurring on the 1+ site. Away from the outlined stability region, the dominant charge carriers become oxygen interstitials, impairing the conductivity by creating deep acceptor states in the electronic band gap region and driving the formation of alternative phases. This study further demonstrates the inadequacy of native defects as a source of n-type conductivity and complements existing experimental findings.

Cu36H10(PET)24(PPh3)6Cl2] Reveals Surface Vacancy Defects in Ligand-Stabilized Metal Nanoclusters.

Precise identification and in-depth understanding of defects in nanomaterials can aid in rationally modulating defect-induced functionalities. However, few studies have explored vacancy defects in ligand-stabilized metal nanoclusters with well-defined structures, owing to the substantial challenge of synthesizing and isolating such defective metal nanoclusters. Herein, a novel defective copper hydride nanocluster, [Cu36H10(PET)24(PPh3)6Cl2] (Cu36; PET: phenylethanethiolate; PPh3: triphenylphosphine), is successfully synthesized at the gram scale via a simple one-pot reduction method. Structural analysis reveals that Cu36 is a distorted half cubic nanocluster, evolved from the perfect Nichol's half cube. The two surface copper vacancies in Cu36 are found to be the principal imperfections, which result in some structural adjustments, including copper atom reconstruction near the vacancies as well as ligand modifications (e.g., substitution, migration, and exfoliation). Density functional theory calculations imply that the above-mentioned defects have a considerable influence on the electronic structure and properties. The modeling suggests that the formation of defective Cu36 rather than the perfect half cube is driven by the enlargement of the energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital of the nanocluster. The structural evolution induced by the surface copper atom vacancies provides atomically precise insights into the defect-induced readjustment of the local structure and introduces new avenues for understanding the chemistry of defects in nanomaterials.

Copper vacancy and C[dbnd]O bond facilitate the enhancement of oxygen reduction activity of three-dimensional flower-like Cu36NixPt45 nanospheres in microbial fuel cells

Cathodic oxygen reduction reaction (ORR) catalysts play a key role in microbial fuel cells (MFCs). Herein, the three-dimensional (3D) flower-like Cu36NixPt45 nanospheres with Cu vacancy growing on Ni(OH)2 nanosheets are rationally designed on nickel foam as the cathode material. Electron paramagnetic resonance (EPR) and positron annihilation spectroscopy (PAS) results indicate that the optimized material possesses more Cu vacancies, which is beneficial to expose more active sites for ORR kinetics. In-situ Raman proves that the CO bond could as the active species participating in electron transfer of metal active sites to facilitate the equilibrium of desorption and adsorption in ORR process. In the MFC, the maximum power density of the V–Cu36NixPt45 (1682.8 ± 40.9 mW m−2) is 2.56 times of that of the Pt/C, and the output voltage remains quite stable within 50 d of operation, also outperforms the Pt/C. This study provides a reference for preparation of efficient cation-vacancy-based ORR electrocatalytic materials.

Cu-Deficient CuInSe Quantum Dots for “Turn-On” Detection of Adenosine Triphosphate in Living Cells

Copper indium selenide (CISe) quantum dots (QDs) are a class of extremely appealing candidates for various biological applications due to their composition- and size-dependent photoluminescence and low toxicity. However, the synthesis of high-quality water-soluble CISe QDs with controlled composition in the aqueous phase is still a great challenge, which limits their biological applications. Moreover, the effects of the copper content in CISe QDs on the fluorescence and the corresponding mechanism are still subject to debate. Herein, a composition-tunable aqueous synthesis of high-quality Cu-deficient CISe QDs was presented, and the effects of the copper content on the fluorescence of CISe QDs was studied by the time-resolved fluorescence. The composition of CISe QDs could be flexibly controlled by manipulating the reaction temperature, the reaction time, and the Cu/In precursor ratio. The time-resolved fluorescence of CISe QDs with different Cu/In ratios suggested that the donor–acceptor pair (DAP) recombination was enhanced gradually with the increase of copper vacancies, resulting in the enhancement of fluorescence. However, if copper vacancies achieved an excessive concentration, the fluorescence would decrease possibly due to Auger recombination. The optimized CISe QDs with the maximum quantum yield of 10.3% were obtained with the Cu/In ratio, reaction temperature, and reaction time of 1/5, 170 °C, and 1 h, respectively. Based on the intense emission of the Cu-deficient CISe QDs, a highly sensitive “turn-on” fluorescent probe was developed for the detection of adenosine triphosphate (ATP) in living cells with a limit of detection of 56 nM. This work provides a paradigm for the aqueous-phase synthesis and applications of ternary I–III–VI QDs.

Copper vacancy activated plasmonic Cu3−xSnS4 for highly efficient photocatalytic hydrogen generation: Broad solar absorption, efficient charge separation and decreased HER overpotential

Copper vacancy activated plasmonic Cu3−xSnS4 for highly efficient photocatalytic hydrogen generation: Broad solar absorption, efficient charge separation and decreased HER overpotential

Phase Composition and Thermoelectric Properties of Materials Based on Cu2 – xSe (0.03 ≤ x ≤ 0.23)

The phase composition and thermoelectric properties of Cu2 – xSe samples with different deviations from the stoichiometric composition (x = 0.03, 0.08, 0.13, 0.18, and 0.23) are studied. Bulk thermoelectric materials based on Cu2 – xSe are synthesized by spark plasma sintering. The phase composition is studied using the X-ray diffraction method. Depending on the chemical composition, the materials based on Cu2 – xSe at room temperature can be either a single-phase material containing only the cubic β-Cu2Se phase or a two-phase material containing a mixture of monoclinic α-Cu2Se and cubic β-Cu2Se phases. It is shown that the deviation of the stoichiometric composition has a substantial effect on the electrophysical characteristics of the material. With an increase in the deviation of the stoichiometric composition, the concentration of the main charge carriers in Cu2 – xSe increases because of the formation of copper vacancies. The change in the thermal conductivity substantially contributes to the thermoelectric figure of merit of Cu2 – xSe compounds. In the investigated range of chemical compositions, the maximum values of thermoelectric figure of merit around ZT ~ 1.3 at 600°C are observed in samples with the Cu1.97Se composition.

Possibility of Doping CuGaSe2 n -Type by Hydrogen

Copper-indium-gallium-selenide (CIGS) alloys are successfully applied in thin-film solar cells. For a better use of the solar spectrum, they also offer the possibility of multijunction devices by tuning the composition in the different layers. As-grown CIGS is intrinsically p-type due to copper vacancies (${V}_{\mathrm{Cu}}$), but n-type doping is also useful for applications. While ${\mathrm{Cu}\mathrm{In}\mathrm{Se}}_{2}$ can be easily turned n-type, ${\mathrm{Cu}\mathrm{Ga}\mathrm{Se}}_{2}$ cannot, and this represents a problem, because increasing the band gap of CIGS requires a high $\mathrm{Ga}/\mathrm{In}$ ratio. Investigating the effect of hydrogen on ${\mathrm{Cu}\mathrm{Ga}\mathrm{Se}}_{2}$ by an optimized hybrid functional, we show that hydrogenation from an atomic source as, e.g., by a hydrogen plasma treatment, can turn the material n-type due to the formation of shallow donor ${V}_{\mathrm{Cu}}+2\mathrm{H}$ complexes, while ${\mathrm{H}}_{2}$ implantation, producing an internal hydrogen reservoir, can be used to produce semi-insulating material. We also show that under normal process conditions, unintentional hydrogen incorporation does not have a significant effect on ${\mathrm{Cu}\mathrm{Ga}\mathrm{Se}}_{2}$.