Supported copper oxide nanosystems were synthesized by chemical vapor deposition (CVD) on Al2O3 substrates and characterized by means of glancing incidence X-ray diffraction (GIXRD), secondary ion ...mass spectrometry (SIMS) and field emission scanning electron microscopy (FESEM). The analyses showed an evolution from polycrystalline Cu2O nanodeposits to CuO samples with an entangled quasi-1D morphology upon increasing the growth temperature from 350 to 550°C. For the first time, the sensing properties of CVD copper oxide nanosystems were probed in the detection of volatile organic compounds (VOCs; e.g. CH3COCH3, CH3CH2OH). The obtained results revealed good responses even at moderate operating temperatures, with characteristics directly dependent on the system composition and nano-organization.
We report transport measurements through a single-molecule magnet, the Mn12 derivative Mn12O12(O2C-C6H4-SAc)16(H2O)4, in a single-molecule transistor geometry. Thiol groups connect the molecule to ...gold electrodes that are fabricated by electromigration. Striking observations are regions of complete current suppression and excitations of negative differential conductance on the energy scale of the anisotropy barrier of the molecule. Transport calculations, taking into account the high-spin ground state and magnetic excitations of the molecule, reveal a blocking mechanism of the current involving nondegenerate spin multiplets.
The present work reports the synthesis and the characterization of cobalt oxide thin films obtained by chemical vapor deposition (CVD) on indium tin oxide (ITO) substrates, using a cobalt(II) ...β-diketonate as precursor. The complex is characterized by electron impact mass spectrometry (EI-MS) and thermal analysis in order to investigate its decomposition pattern. The depositions are carried out in a cold wall reactor in the temperature range 350−500 °C at different oxygen pressures, to tailor film composition from CoO to Co3O4. The crystalline nanostructure is evidenced by X-ray diffraction (XRD), while the surface and in-depth chemical composition is studied by X-ray photoelectron (XPS) and X-ray excited auger electron spectroscopy (XE-AES). Atomic force microscopy (AFM) is employed to analyze the surface morphology of the films and its dependence on the synthesis conditions. Relevant results concerning the control of composition and microstructure of Co−O thin films are presented and discussed.
Iron(II) phthalocyanine (FePc) self-assembly on Ag(110) has been studied in ultrahigh-vacuum conditions at room temperature by means of scanning tunneling microscopy (STM) and density functional ...theory (DFT) calculations. For submonolayer to monolayer coverage, FePc molecules lie parallel to the Ag(110) surface, arranged in rows running along the 001 direction. Two similar yet distinct ordered phases are formed, the c(10 × 4) and p(10 × 4) superstructures. The latter is characterized by two equivalent equilibrium configurations of the constituent FePc units, that interconvert by means of a concerted transformation wherein molecules belonging to adjacent rows collectively rotate in opposite directions around the molecular axis perpendicular to the surface. The FePc adsorption site for both superstructures and the transition mechanism between the two configurations in the p(10 × 4) phase have been inferred from high resolution STM images and rationalized by means of DFT calculations. In the case of multilayer films a (1 ± 4, 4 ∓3) phase is observed, whose stacking geometry has been revealed by STM analysis. The p(10 × 4)/c(10 × 4) → (1 ± 4, 4 ∓3) coverage-dependent transformation is analyzed by DFT calculations, and shown to be driven by the overlayer−substrate interaction. The inclusion of the dispersion contribution to this interaction is found to be essential to correctly reproduce the observed phenomenon.
The design and assembly of suitable nanosystems are key issues in the development of smaller and more efficient lithium batteries. To this regard, cobalt oxides possess very favorable properties for ...use as negative electrode materials. In this work, we describe a convenient synthesis route to cobalt oxide nanomaterials (both single- and mixed-phase CoO and Co3O4) supported on Ti. The systems are grown by chemical vapor deposition starting from an innovative second-generation molecular source, Co(hfa)2·TMEDA (hfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedionate, TMEDA = N,N,N′,N′-tetramethylethylenediamine). Controlled variations of the substrate temperature and O2 pressure in the reaction atmosphere enabled tailoring both the phase composition and the system morphology. The electrochemical properties of the obtained nanosystems were evaluated by galvanostatic measurements and impedance spectroscopy. The results showed excellent cycling performances and very high specific capacity values, offering attractive perspectives for the use of the present systems as advanced anode materials in Li-ion batteries.
The incorporation of luminescent lanthanide complexes in solid matrices with controlled structural organization is of widespread interest in materials science and has witnessed important improvements ...with the development of low-temperature
soft chemistry solution processes, such as sol–gel. In this review, after an introductory part concerning some relevant aspects of the electronic and coordination properties of lanthanides, the prominent issues related to the design and synthesis of efficient luminescent antenna complexes, and their photophysical properties are presented. We describe the basic principles of ligands design to yield systems featuring a coordination site for the metal cation with appended suitable chromophores as sensitizers (two-component approach). When properly designed, these ligands are capable of forming highly luminescent complexes (overall sensitization yield,
ϕ
se
>
0.05 in aqueous medium). The photophysical properties of these complexes together with the description of some emitting materials prepared are discussed in detail. In particular we focus the attention toward those complexes emitting in the visible region that can be used in the lighting industry (e.g. for the preparation of photo- and electro-luminescent materials) and for biological immunoassays. Subsequently, some selected results of our recent work concerning the synthesis of highly luminescent colour tunable films for applications in lighting and light conversion technologies are reported. Such materials have been obtained by combining the peculiar luminescence properties of Eu
3+ and Tb
3+ antenna complexes with optically transparent inorganic matrices. The notion is to create materials with innovative properties by integrating inorganic and organic components at nanoscale or molecular level. Due to the number of scientific publications in this field, this work is far from providing an exhaustive review on the previously performed research activities. For a more detailed discussion on these methodologies, the reader can refer to specific pertinent literature.
ZrO2 and HfO2 nanoparticles are homogeneously dispersed in SiO2 matrices (supported film and bulk powders) by copolymerization of two oxozirconium and oxohafnium clusters (M4O2(OMc)12, M = Zr, Hf; ...OMc = OC(O)–C(CH3)CH2) with (methacryloxypropyl)trimethoxysilane (MAPTMS, (CH2C(CH3)C(O)O)–(CH2)3Si(OCH3)3). After calcination (at a temperature ≥800 °C), a silica matrix with homogeneously distributed MO2 nanocrystallites is obtained. This route yields a spatially homogeneous dispersion of the metal precursors inside the silica matrix, which is maintained during calcination. The composition of the films and the powders is studied before and after calcination by using Fourier transform infrared (FTIR) analysis, X‐ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), and laser ablation inductively coupled plasma mass spectrometry (LA‐ICPMS). The local environment of the metal atoms in one of the calcined samples is investigated by using X‐ray Absorption Fine Structure (XAFS) spectroscopy. Through X‐ray diffraction (XRD) the crystallization of Hf and Zr oxides is seen at temperatures higher than those expected for the pure oxides, and transmission electron microscopy (TEM) shows the presence of well‐distributed and isolated crystalline oxide nanoparticles (5–10 nm).
A two‐step modified sol–gel procedure based on the use of a bifunctional silane, with Hf‐ and Zr‐oxoclusters as molecular building blocks, is used to prepare ternary ZrO2–HfO2–SiO2 film and bulk materials of different compositions (see figure), which are characterized by the presence of homogeneously dispersed oxide nanoclusters.
Zinc oxide nanoplatelets are successfully grown on Si(100) by CVD starting from a second‐generation ZnII precursor, Zn(hfa)2·TMEDA (Hhfa = 1,1,1,5,5,5‐hexafluoro‐2,4‐pentanedione; TMEDA = ...N,N,N′,N′‐tetramethylethylenediamine). The synthesis is performed in a nitrogen + wet oxygen atmosphere under optimized conditions, at temperatures between 250 and 500 °C. Field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), and glancing incidence X‐ray diffraction (GIXRD) analyses indicate a direct correlation between morphology and microstructure. The formation of ZnO nanoplatelets, whose characteristics depend on the deposition temperature, is proposed to result from the synergistic combination of a vapor/solid (VS) mechanism and a preferential direction‐conducting growth. The chemical composition is analyzed by means of X‐ray photoelectron and energy dispersive X‐ray spectroscopies (XPS, EDXS). Finally, the photocatalytic performances of ZnO nanoplatelets in the decomposition of the azo‐dye Orange II are investigated and compared to those of uniform ZnO coatings synthesized in the absence of water vapor. The obtained results show a higher activity in the case of nanoplatelets due to their peculiar morphology.
Zinc oxide nanoplatelets have been successfully grown on Si(100) by CVD starting from a second‐generation ZnII precursor, Zn(hfa)2·TMEDA, under a nitrogen + wet oxygen atmosphere, at temperatures between 250 and 500 °C. The photocatalytic activity of ZnO nanoplatelets in the decomposition of the azo‐dye Orange II was higher than that of a continuous layer with a compact morphology, opening intriguing perspectives for the development of functional nanodevices for environmental remediation.
Nanophasic CeO2‐based thin films were grown at low temperatures on SiO2 and Si(100) by plasma‐enhanced (PE) CVD from a CeIV β‐diketonate first generation precursor. Film depositions were carried out ...in low‐pressure Ar–O2 plasmas at temperatures between 150 °C and 300 °C. The film microstructure was investigated by glancing incidence X‐ray diffraction (GIXRD) and transmission electron microscopy (TEM), while the surface and in‐depth chemical composition was studied by X‐ray photoelectron spectroscopy (XPS), and secondary ion mass spectrometry (SIMS), respectively. Optical properties were analyzed by UV‐vis optical absorption. Nanostructured CeO2‐based films, with crystal size less than 6 nm and a controllable CeIV/CeIII ratio, were obtained at temperatures even lower than that required for precursor vaporization (170 °C). In particular, TEM analyses showed an island growth mode and different microstructural features as a function of the substrate used.
A study of the initial nucleation stages of PECVD CeO2 thin films has been conducted. Ceria films are deposited in the temperature range 150–300 °C on SiO2 and Si(100) from Ce(dpm)4 in Ar and Ar–O2 plasmas. HRTEM analyses of films deposited on Si(100) indicate homogeneously distributed 5 nm diameter spherical aggregates (see Figure). The CeIV content in the films is found to be tunable by oxygen partial pressure and substrate temperature.
Multicomponent supramolecular self-assemblies of exceptional long-range order and low defectivity are obtained if C60 and 5-(4-aminophenyl)-10,15,20-triphenylporphyrin (TPP-NH2) are assembled on ...Ag(110) by sequential evaporation in the submonolayer range of TPP-NH2 and fullerene on the substrate surface and subsequent annealing. A (±2 −3, 6 ± 3) array consisting of supramolecular stripes of a 1:1 C60/TPP-NH2 2D adduct develops at 410 K (the low temperature, LT, phase). If the LT phase is annealed at 470 K, then a 3:1 fullerene/TPP-NH2 (±3 −5, 5 ± 5) nanoporous array (the HT phase) forms, with each pore containing a single porphyrin molecule. Phase separation occurs by annealing the HT phase at 520 K. Structural models are proposed and discussed on the basis of the experimental scanning tunneling microscopy results.
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