Direct production of carbon nanotubes decorated with Cu2O by thermal chemical vapor deposition on Ni catalyst electroplated on a copper substrate

Carbon nanotubes (CNTs) decorated with Cu₂O particles were grown on a Ni catalyst layer deposited on a Cu substrate by thermal chemical vapor deposition from liquid petroleum gas. Ni catalyst nanoparticles with different sizes were produced in an electroplating system at 45 °C using the corrosive effect of H₂SO₄ which was added to solution. These nanoparticles provide the nucleation sites for CNT growth avoiding the need for a buffer layer. The surface morphology of the Ni catalyst films and CNT growth over this catalyst was studied by scanning electron microscopy (SEM). High temperature surface segregation of the Cu substrate into the Ni catalyst layer and its exposition to O₂ at atmospheric environment, during the CNTs growth, lead to the production of CNTs decorated with about 6 nm Cu₂O nanoparticles. We used SEM to study the surface characteristics of Ni catalyst films and characteristic of grown CNTs. Raman spectroscopy, transmission electron microscopy (TEM), electron diffraction (EDX), X-ray diffraction, and X-ray photoelectron spectroscopy (XPS) revealed the formation of CNTs. The selected area electron diffraction pattern, EDX, and XPS studies show that these CNTs were decorated with Cu₂O nanoparticles. This way of fabrication is the easiest and lowest cost method.     

Native oxidation of ultra high purity Cu bulk and thin films

The effect of microstructure and purity on the native oxidation of Cu was studied by using angle-resolved X-ray photoelectron spectroscopy (AR-XPS) and spectroscopic ellipsometry (SE). A high quality copper film prepared by ion beam deposition under a substrate bias voltage of −50 V (IBD Cu film at V_s = −50 V) showed an oxidation resistance as high as an ultra high purity copper (UHP Cu) bulk, whereas a Cu film deposited without substrate bias voltage (IBD Cu film at V_s = 0 V) showed lower oxidation resistance. The growth of Cu₂O layer on the UHP Cu bulk and both types of the films obeyed in principle a logarithmic rate law. However, the growth of oxide layer on the IBD Cu films at V_s = 0 and −50 V deviated upward from the logarithmic rate law after the exposure time of 320 and 800 h, respectively. The deviation from the logarithmic law is due to the formation of CuO on the Cu₂O layer after a critical time.     

Growth and characterization of Y2O3 thin films

Y₂O₃ thin films were grown on silicon (1 0 0) substrates by pulsed-laser deposition at different substrate temperatures and O₂ pressures. The structure and composition of films are studied by using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The Y₂O₃ thin films deposited in vacuum strongly oriented their [1 1 1] axis of the cubic structure and the film quality depended on the substrate temperature. The magnitude of O₂ pressure obviously influences the film structure and quality. Due to the silicon diffusion and interface reaction during the deposition, yttrium silicate and SiO₂ were formed. The strong relationship between composition and growth condition was discussed.     

HREELS and LEED studies on Cu deposited on 1 × 1 reconstructed α-Fe2O3(0001) surfaces

High-resolution electron energy-loss spectroscopy (HREELS), low-energy electron diffraction, and X-ray photoelectron spectroscopy have been used to study clean 825 K-preannealed α-Fe₂O₃-1 × 1 (haematite) surfaces, an α-Fe₂O₃-(0001)-1 × 1 surface reconstructed with Fe₃O₄(111)-1 × 1 and to study Cu deposited on room-temperature surfaces of those. Three pronounced losses, at 47.5, 55.5 and 78.0 meV, of the surface phonons for the clean α-Fe₂O₃(0001) were observed. By deposition of copper, Cu---O vibrational features observed by HREELS indicate formation of a Cu(I) state for the very low coverages. Increased submonoloayer amounts of Cu result in clustering of the copper, leading for both the α-Fe₂O₃(0001)-1 × 1 and the reconstructed composite substrate surfaces to Cu(111) epitaxial growth.     

Active oxidation of Cu3Au(1 1 0) using hyperthermal O2 molecular beam

Oxidation of Cu₃Au(1 1 0) using a hyperthermal O₂ molecular beam (HOMB) was investigated by X-ray photoemission spectroscopy in conjunction with a synchrotron light source. From the incident energy dependence of the O-uptake curve, the precursor-mediated dissociative adsorption occurs, where the trapped O₂ molecule can migrate and dissociate at the lower activation-barrier sites, dominantly at thermal O₂ exposures. Dissociative adsorption of O₂ on Cu₃Au(1 1 0) is as effective at the thermal O₂ exposure as on Cu(1 1 0). On the other hand, at the incident energies of HOMB where the direct dissociative adsorption is dominant, it was determined that the dissociative adsorption of O₂ implies a higher activation barrier and therefore less reactivity due to the Au alloying in comparison with the HOMB oxidation of Cu(1 1 0). The dissociative adsorption progresses with the Cu segregation on Cu₃Au(1 1 0) similarly as on Cu₃Au(1 0 0). The growth of Cu₂O for 2 eV HOMB suggests that the diffusion of Cu atoms also contribute to the oxidation process through the open face, which makes the difference from Cu₃Au(1 0 0).     

The interface reaction of high-k La2Hf2O7/Si thin film grown by pulsed laser deposition

The La₂Hf₂O₇ films have been deposited on Si (1 0 0) substrate by using pulsed laser deposition (PLD) method. X-ray diffraction (XRD) demonstrates that the as-grown film is amorphous and crystallizes after 1000 °C annealing. The interface structure is systematically studied by Synchrotron X-ray reflectivity (XRR), Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS). Silicide, silicate and SiO_x formations from interfacial reaction are observed on the surface of the Si substrate in the as-grown film. The impact of silicide formation on the electrical properties is revealed by capacitance-voltage (C-V) measurements. By post-deposition annealing (PDA), silicide can be effectively eliminated and C-V property is obviously improved.     

Thermal decomposition of Mo(CO)6 on thin Al2O3 film: A combinatorial investigation by XPS and UPS

A thin and homogeneous alumina film was prepared by deposition and oxidation of aluminum on a refractory Re(0 0 0 1) substrate under ultrahigh vacuum conditions. X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS) and high-resolution electron-energy-loss spectroscopy (HREELS) demonstrate that the oxide film is long-range ordered, essentially stoichiometric and free from surface hydroxyl groups. The chemisorption and thermal decomposition of Mo(CO)₆ on the Al₂O₃ film were investigated by means of XPS and UPS. Mo(CO)₆ adsorbs molecularly on the oxide film at 100 K; however, thermal decomposition of the adsorbate occurs upon annealing at high temperatures. Consequently the metallic molybdenum clusters are deposited on the thin alumina film via complete decarbonylation of Mo(CO)₆.     

XPS and UPS study of Na deposition on thin film V2O5

The deposition of Na on thin film V₂O₅ has been study by using photoelectron spectroscopy. Vanadium ions are strongly reduced due to the deposition of Na. Three kinds of Na species were observed on the surface: the first is assigned to intercalated Na; the second is contributed to Na₂O₂; the third is appointed to metallic Na. The formation of Na₂O₂ leads to arise an emission line at about 10.3 eV in the valence band spectra. The metallic Na will further react with the oxides substrate and form Na₂O₂ on the surface in UHV chamber.     

“In situ” XPS study of band structures at Cu2O/TiO2 heterojunctions interface

In an attempt to investigate influence of the defects on electronic structure of Cu₂O/TiO₂ heterojunctions, thin Cu₂O layers were successively deposited on TiO₂ that has different levels of defect concentrations, and the resultant band bending and offset characteristics were studied by in situ X-ray photoelectron spectroscopy (XPS). The TiO₂ substrates with defects were prepared by Ar⁺ sputtering, followed by annealing at different temperatures in oxygen atmosphere. Presence of the defects in TiO₂ surface dramatically influences on the band bending and band offset at the interface: more defects are on TiO₂ surface, less band bending are at the interface, inducing smaller conduction band offsets. On the reduced TiO₂ surface, Cu₂O was disproportionately decomposed to form CuO and Cu.     

Photoelectron spectroscopic investigation of transformation of trifluoroacetate precursors into superconducting YBa2Cu3O7−δ films

X-ray photoelectron spectroscopy (XPS) has been used to investigate the evolution of surface chemistry of YBa₂Cu₃O_7−δ (Y123) films prepared by the metalorganic deposition (MOD) process using trifluoroacetate (TFA) precursors. Detailed XPS core-level spectra obtained from the samples quenched from various points during the calcining and firing stages have been reported for the first time and are used to identify surface species. The XPS data show evidence of formation of intermediate phases such as Y-O-F, BaF₂, and CuO during the calcining process, which are the decomposition products of yttrium, barium, and copper trifluoroacetates, respectively. The TFA precursors are completely decomposed at the end of calcination. The change of binding energies for Y 3d_5/2, Ba 3d_5/2, and O 1s during the firing process indicates that Y123 starts to form at 800 °C after 0.5 h firing. Based on the experimental results, an alternative mechanism of the chemical evolution from precursor to final film in the TFA-MOD process is proposed.     

High-performance hierarchical cypress-like CuO/Cu<Subscript>2</Subscript>O/Cu anode for lithium ion battery

Composite CuO/Cu₂O/Cu anode for lithium ion battery was designed and synthesized via facile electrodeposition and the subsequent in situ thermal oxidation in air at 300 °C for 1 h. The as-prepared composite CuO/Cu₂O/Cu anode was studied in terms of scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), galvanostatic charge/discharge, cyclic voltammetry (CV), and AC impedance. As expected, the composite CuO/Cu₂O/Cu with CuO-rich surface displayed hierarchical cypress-like morphology; furthermore, the hierarchical cypress-like CuO/Cu₂O/Cu anode also delivered satisfactory electrochemical performances. For example, the reversible discharge capacity remained at 534.1 mAh/g even after 100 cycles. The enhanced electrochemical performances were attributed to the hierarchical cypress-like porous structure and the synergistic effect among the composite active copper oxides and highly conductive Cu current collector.     

X-RAY PHOTOELECTRON SPECTROSCOPY STUDY ON ELECTROCHROMIC V2O5 THIN FILM

Nanocrystalline V₂O₅ thin films were reactively radio-frequency magnetron-sputtered under optimal deposition parameters. Their electrochemical and electrochromic characteristics were investigated by cyclic voltammetry and in-situ monochromatic transmittance measurements. Upon lithium intercalation, V₂O₅ thin films showed a double electrochromic behavior depending on the wavelength and the intercalation extent. X-ray photoelectron spectroscopy results showed that part of the V⁵⁺ in V₂O₅ was reduced to V⁴⁺ during the Li⁺ intercalation process.     

In-situ XAS study on the Cu and Ce local structural changes in a CuO-CeO2/Al2O3 catalyst under propane reduction and re-oxidation

The redox behaviour of a CuO-CeO₂/Al₂O₃ catalyst is studied under propane reduction and re-oxidation. The evolution of the local Cu and Ce structure is studied with in-situ transmission X-ray absorption spectroscopy (XAS) at the Cu K and Ce L₃ absorption edges.CuO and CeO₂ structures are present in the catalyst as such. No structural effect on the local Cu structure is observed upon heating in He up to 873 K or after pre-oxidation at 423 K.Exposure to propane at reaction temperature (600-763 K) fully reduces the Cu²⁺ cations towards metallic Cu⁰. Quick EXAFS spectra taken during reduction show a small amount of intermediate Cu¹⁺ species. Parallel to the CuO reduction, CeO₂ is also reduced in the same temperature range. About 25% of the Ce⁴⁺ reduces rapidly to Ce³⁺ in the 610-640 K temperature interval, while beyond 640 K a further slower reduction of Ce⁴⁺ to Ce³⁺ occurs. At 763 K, Ce reduction is still incomplete with 32% of Ce³⁺.Re-oxidation of Cu and Ce is fast and brings back the original oxides.The propane reduction of the CuO-CeO₂/Al₂O₃ catalyst involves both CuO and CeO₂ reduction at similar temperatures, which is ascribed to an interaction between the two compounds.     

Structure and surface characterization of ZrO2-Y2O3-Cr2O3 system

3-mol% Y₂O₃ and 0.3 to 3-mol % Cr₂O₃ co-doped ZrO₂ nanopowders were synthesized using co-precipitation technique and investigated by terms of X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. Structural analysis shows no significant impact of chromium on powders structure except of presence of small amount of m-phase. Surface analysis reveals segregation of yttrium and chromium atoms to the surface along with surface enrichment by oxygen that can be attributed to residual water. Chromium surface atoms present in three oxidation states with catalytically active Cr²⁺ sites possibly controlling m-phase appearance through lattice distortion.     

Fabrication and characterization of a Cu seed layer on a 60-nm trench-patterned SiO2 substrate by a self-assembled-monolayer (SAM) process

Continuous electroless deposition of a 10-nm thick layer of Cu was successfully performed on a SiO₂/Si substrate coated with a 3-nm Au catalytic layer. The Au catalytic layer was formed by a self-assembled monolayer (SAM) process terminated with NH₂ headgroups, upon which negatively charged Au particles were deposited via electrostatic interaction with the positively charged NH₂-SAM. The Au and NH₂-SAM layers were analyzed by X-ray photoelectron spectroscopy (XPS) and contact angle analysis. Atomic force microscopy, field emission scanning electron microscopy, and XPS revealed that the Cu layer formed by this electroless processes had good step-coverage, small grain size, and excellent adhesion to the substrate. The proposed process is a very promising method for fabrication of a conductive Cu seed layer in a 60-nm trench-pattern.     

A first principle study on the magnetic properties of Cu2O surfaces

Spin-polarized density functional theory calculations were performed to investigate the magnetism of bulk and Cu₂O surfaces. It is found that bulk Cu₂O, Cu/O-terminated Cu₂O(111) and (110) surfaces have no magnetic moment, while, the O-terminated Cu₂O(100) and polar O-terminated Cu₂O(111) surfaces have magnetism. For low index surfaces with cation and anion vacancy, we only found that the Cu vacancy on the Cu₂O(110) Cu/O-terminated surface can induce magnetism. For atomic and molecular oxygen adsorption on the low index surfaces, we found that atomic and molecular oxygen adsorption on the Cu-terminated Cu₂O(110) surface is much stronger than on the Cu/O-terminated Cu₂O(111) and Cu-terminated Cu₂O(100) surfaces. More interesting, O and O₂ adsorption on the surface of Cu/O terminated Cu₂O(111) and O₂ adsorption on the Cu-terminated Cu₂O(110) surface can induce weak ferromagnetism. In addition, we analysis origin of Cu₂O surfaces with magnetism from density of state, the surface ferromagnetism possibly due to the increased 2p–3d hybridization of surface Cu and O atoms. This is radically different from other systems previously known to exhibit point defect ferromagnetism, warranting a closer look at the phenomenon.     

Al2O3/SiO2 films prepared by electron-beam evaporation as UV antireflection coatings on 4H-SiC

Al₂O₃/SiO₂ films have been deposited as UV antireflection coatings on 4H-SiC by electron-beam evaporation and characterized by reflection spectrum, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The reflectance of the Al₂O₃/SiO₂ films is 0.33% and 10 times lower than that of a thermally grown SiO₂ single layer at 276 nm. The films are amorphous in microstructure and characterize good adhesion to 4H-SiC substrate. XPS results indicate an abrupt interface between evaporated SiO₂ and 4H-SiC substrate free of Si-suboxides. These results make the possibility for 4H-SiC based high performance UV optoelectronic devices with Al₂O₃/SiO₂ films as antireflection coatings.     

A density functional theory study on the adsorption of CO and O2 on Cu-terminated Cu2O （111） surface

The adsorptions of CO and 02 molecules individually on the stoichiometric Cu-terminatcd Cu20 （111） surface are investigated by first-principles calculations on the basis of the density functional theory. The calculated results indicate that the CO molecule preferably coordinates to the Cu2 site through its C atom with an adsorption energy of-1.69 eV, whereas the 02 molecule is most stably adsorbed in a tilt type with one O atom coordinating to the Cu2 site and the other O atom coordinating to the Cul site, and has an adsorption energy of -1.97 eV. From the analysis of density of states, it is observed that Cu 3d transfers electrons to 2π orbital of the CO molecule and the highest occupied 5σ orbital of the CO molecule transfers electrons to the substrate. The sharp band of Cu 4s is delocalized when compared to that before the CO molecule adsorption, and overlaps substantially with bands of the adsorbed CO molecule. There is a broadening of the 2π orbital of the 02 molecule because of its overlapping with the Cu 3d orbital, indicating that strong 3d-2π interactions are involved in the chemisorption of the 02 molecule on the surface.     

Crystallization and surface segregation in CuIn0.7Ga0.3Se2 thin films on Cu foils grown by pulsed laser deposition

This work reports unexpected crystallization and segregation behavior of CuIn_0.7Ga_0.3Se₂ (CIGS) thin films deposited on flexible Cu foils by pulsed laser deposition. A composite-type microstructure containing nanometer-scaled CIGS crystallites embedded in amorphous Cu-rich matrix is observed even at the high temperature of 500 °C. The findings are attributed to very fast condensation of the ablated species and random nucleation induced from the amorphous matrix. Cu-rich particulates tend to precipitate on the film surface, and their average size, shape, number density and composition exhibit a strong dependence on the substrate temperature up to 500 °C. The similar crystallization properties of the films on Cu foils and glass substrates are noticeable to the use of Cu foils for flexible solar cells.     

Cu adsorption on Pt(111) and its effects on Chemisorption: A comparison with electrochemistry

The growth modes and interaction of vapor-deposited Cu on a clean Pt(111) surface have been monitored by Auger electron spectroscopy (AES), low energy electron diffraction (LEED), and work function measurements. The LEED data indicate that below 475 K Cu grows in p(1 × 1) islands in the first monolayer with the interatomic Cu spacing the same as the Pt(111) substrate. The second monolayer of Cu grows in epitaxial, rotationally commensurate Cu(111) planes with the CuCu distance the same as bulk Cu. For substrate temperatures below ～ 475 K, the variation of work function and “cross-over beam voltage” with Cu coverage show characteristic features at one monolayer that are quite useful for calibration of θ_Cu. Above 525 K, Cu-Pt alloy formation was observed in AES and LEED data. Thermal desorption spectroscopy of H₂ and CO has demonstrated that simple site blocking of the Pt(111) surface by vapor-deposited Cu occurs linearly with chemisorption being essentially eliminated at θ_Cu = 1.0–1.15. Conclusions drawn from this work correlate very favorably with the well-known effects of under potentially deposited copper on the electrochemistry of the H₂2H⁺ couple at platinum electrodes.