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Dec 2003

Volume 10, Issue 1, pp. 1-194

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Introduction to XPS Studies of Metal and Metal-oxide Nanosystems

Lidia Armelao, Davide Barreca, Gregorio Bottaro, Silvia Gross, Alberto Gasparotto, Cinzia Maragno, Eugenio Tondello, and Andrea Zattin

Surf. Sci. Spectra 10, 137 (2003); http://dx.doi.org/10.1116/11.20050199 (6 pages) | Cited 1 time

Online Publication Date: 8 March 2005

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Metal and metal-oxide based nanosystems are intriguing candidates for a plethora of advanced applications thanks to their diversified chemico-physical properties, that can be further tailored by the use of proper synthesis procedures. Among the different preparation techniques, chemical vapor deposition (CVD), rf sputtering, and sol-gel (SG) display promising features for the design and control of nanosystem characteristics even beyond thermodynamical predictions, thanks to the soft synthetic conditions that enable nucleation to prevail over the subsequent particle agglomeration. In this context, a direct feedback between the nanosystem synthesis and characterization represents a unique tool for the optimization of the process. In particular, XPS spectroscopy plays an outstanding role for the investigation of surface and in-depth chemical composition of thin films as a function of the experimental conditions. In this article, the attention is devoted to the XPS analysis of different kinds of nanosystems, from nanostructured thin films (LaCoO3) to oxide clusters in silica matrices (HfO2 and HfO2–ZrO2 in SiO2) and metal cluster-based composites (Au/graphite, Au/TiO2, Ag/SiO2). This Introduction provides an overview of the data presented in the collected spectral data records, focusing in particular on the interest in these systems and on the most relevant results obtained by XPS investigations. © 2005 American Vacuum Society.
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61.46.-w Structure of nanoscale materials
79.60.Jv Interfaces; heterostructures; nanostructures
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
81.15.Cd Deposition by sputtering

LaCoO3 Nanosystems by a Hybrid CVD/Sol-Gel Route: An XPS Investigation

Lidia Armelao, Davide Barreca,a), Gregorio Bottaro, Alberto Gasparotto, Cinzia Maragno, and Eugenio Tondello

Surf. Sci. Spectra 10, 143 (2003); http://dx.doi.org/10.1116/11.20040303 (7 pages) | Cited 4 times

Online Publication Date: 8 March 2005

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Lanthanum cobaltite (LaCoO3) nanosystems were synthesised by an innovative combined use of the chemical vapor deposition (CVD) and sol-gel (SG) routes. In particular, a lanthanum oxyfluoride based layer was deposited by CVD on CoOx(OH)y SG substrates (xerogel). The subsequent thermal treatment in air, between 400 and 900 °C, was aimed at promoting the solid-state reaction between La-O and Co-O based layers, resulting in the complete formation of LaCoO3. The obtained samples were analyzed by glancing incidence x-ray diffraction (GIXRD), transmission electron microscopy (TEM), atomic force microscopy (AFM), secondary ion mass spectrometry (SIMS), x-ray photoelectron (XPS) and x-ray excited Auger electron (XE-AES) spectroscopies, for a detailed determination of their microstructure, chemical composition, and surface morphology. The present work focuses on the XPS and XE-AES analysis of a selected lanthanum cobaltite (LaCoO3) thin film, annealed at 700 °C for 2 h. Besides the wide scan spectrum, detailed spectra for the La 3d, Co 2p, Co LMM, O 1s, and C 1s regions and related data are presented and discussed. Both the experimental Co 2p3/2-Co 2p1/2 energy splitting and the evaluation of the Auger parameter point out to the formation of single-phase lanthanum cobaltite thin film. The presence of fluorine was never detected, indicating its elimination after thermal treatment. Moreover, carbon contamination was merely limited to the outermost sample layers. © 2005 American Vacuum Society.
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81.05.Bx Metals, semimetals, and alloys
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

HfO2-doped Silica Thin Films by XPS

Lidia Armelao, Silvia Gross, Andrea Zattin, and Eugenio Tondello

Surf. Sci. Spectra 10, 150 (2003); http://dx.doi.org/10.1116/11.20040403 (7 pages) | Cited 3 times

Online Publication Date: 8 March 2005

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The development of molecularly homogeneous multicomponent oxide based glasses is a key concern in many fields of materials chemistry. Oxide nanoparticles covalently embedded in dielectric matrices represent a class of nanocomposite systems endowed with outstanding optical, mechanical, electronic, and thermal properties. In this study, silica thin films embedding HfO2 were prepared by dip-coating on silica glass via a modified sol-gel processing. This powerful synthetic method, mainly based on the hydrolysis and condensation of metal alkoxides, provides a reliable route to oxide materials which can be processed into a variety of different forms (thin films, powders, monoliths, etc.). The novel synthetic route here presented is based on the copolymerization of the organically modified oxohafnium clusters (Hf4O2(OMc)12 with OMc = OC(O)–C(CH3)=CH2)) with (methacryloxymethyl)triethoxysilane (MAMTES). The crystalline clusters, which are the precursors for the corresponding metal oxide (MO2) were prepared via the sol-gel route by reaction of hafnium butoxide with methacrylic acid. The copolymerization of the cluster with previously prehydrolysed methacrylate-functionalized siloxane, allows the anchoring of the oxocluster to the forming silica network. Thin films were prepared starting from a THF (tetrahydrofurane) solution with molar ratios Hf4O2(OMc)12:MAMTES of 1:44 and a MAMTES:THF molar ratio of 1:5, which was stirred at room temperature for 8 h. After deposition, the film was annealed 3 h at 800 °C in air to promote the decomposition of the hafnium oxocluster to give the corresponding HfO2. The obtained HfO2-SiO2 film resulted transparent and homogeneous. The composition of the film was investigated by secondary ionization mass spectrometry (SIMS) and x-ray photoelectron spectroscopy (XPS), which were used also to investigate the in-depth distribution. The depth profiles evidenced a very homogenous distribution of hafnium within the whole silica film and a sharp film-substrate interface. TEM micrographs revealed the formation of isolated nanocrystalline particles, thus ruling out the formation of a HfO2–SiO2 mixture. Concerning the herewith reported XPS analyses, the main XPS core-levels were analyzed for the sample annealed 3 h at 800 °C. The formation of hafnium oxide was evidenced. Furthermore, a very homogeneous distribution of the guest oxide in the host matrix was evidenced, in agreement with SIMS data. © 2005 American Vacuum Society.
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82.45.Mp Thin layers, films, monolayers, membranes
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
82.70.Gg Gels and sols

HfO2–ZrO2 Doped Silica Thin Films by XPS

Lidia Armelao, Silvia Gross, Eugenio Tondello, and Andrea Zattin

Surf. Sci. Spectra 10, 157 (2003); http://dx.doi.org/10.1116/11.20040402 (7 pages) | Cited 1 time

Online Publication Date: 8 March 2005

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Silica thin films embedding ZrO2 and HfO2 were prepared by spin-coating on silica glass via a modified sol-gel processing. The novel synthetic route is based on the co-polymerization of two organically modified oxozirconium and oxohafnium clusters (M4O2(OMc)12 with M = Zr, Hf and OMc = OC(O)–C(CH3)=CH2)) with (methacryloxypropyl)trimethoxysilane (MAPTMS). The crystalline clusters, which are the precursors for the corresponding metal oxides (MO2) were prepared via the sol-gel route by reacting zirconium or hafnium butoxide with methacrylic acid. The copolymerization of the cluster with previously prehydrolyzed methacrylate-functionalized siloxane, allows the anchoring of the oxoclusters to the forming silica network. Thin films were prepared starting from a THF (tetrahydrofurane) solution with molar ratios Hf4O2(OMc)12: Zr4O2(OMc)12:MAPTMS of 1:1:88. After deposition, the films were annealed 3 h at 800 °C in air to promote the decomposition of the hafnium and zirconium oxoclusters to give the corresponding HfO2 and ZrO2 oxides. The obtained HfO2–ZrO2–SiO2 films resulted transparent, homogeneous and displayed a very good adhesion to the substrate. The composition of the films was investigated by secondary ionization mass spectrometry (SIMS) and x-ray photoelectron spectroscopy (XPS). The depth profiles evidenced a very homogenous distribution of both zirconium or hafnium species within the whole silica films and sharp film-substrate interfaces. As far as XPS analyses are concerned, the main XPS core-levels were analyzed for the annealed sample and the formation of hafnium and zirconium oxides was evidenced. © 2005 American Vacuum Society.
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82.45.Mp Thin layers, films, monolayers, membranes
81.05.Pj Glass-based composites, vitroceramics

Au Nanoparticles Supported on HOPG: An XPS Characterization

Davide Barrecaa), Gregorio Bottaro, Alberto Gasparotto, Elisabetta Pierangelo, and Eugenio Tondello

Surf. Sci. Spectra 10, 164 (2003); http://dx.doi.org/10.1116/11.20040401 (6 pages)

Online Publication Date: 8 March 2005

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Gold nanoparticles were deposited on HOPG by rf sputtering in Ar plasmas. All experiments were carried out at a substrate temperature as low as 60 °C, in order to minimize the contribution of thermal effects with respect to plasma-dependent phenomena. The system structure and composition were studied by x-ray photoelectron spectroscopy (XPS) and glancing incidence x-ray diffraction (GIXRD). This work is dedicated to the XPS characterization of a representative Au/HOPG sample (rf power = 5 W, total pressure = 0.38 mbar, deposition time = 10 min). Detailed scans for the C 1s, O 1s, N 1s, and Au 4f peaks are presented and discussed. The obtained results pointed out to the presence of metallic gold on HOPG. In particular, high-resolution Au 4f spectra evidenced the presence of a core-level shift, typical of nano-sized gold particles. © 2005 American Vacuum Society.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods

Study of Ag/SiO2 Nanosystems by XPS

Lidia Armelao, Davide Barreca, Gregorio Bottaro, Alberto Gasparotto, Cinzia Maragno, and Eugenio Tondello

Surf. Sci. Spectra 10, 170 (2003); http://dx.doi.org/10.1116/11.20040901 (12 pages)

Online Publication Date: 8 March 2005

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Silica-supported silver nanocomposites were synthesized by rf sputtering of Ag from Ar plasmas. Depositions were performed on amorphous silica substrates at temperatures as low as 60 °C. As a general rule, a careful choice of the synthesis conditions allowed the obtainment of Ag/SiO2 nanosystems with well-tailored chemico-physical properties. In fact, a proper combination of the applied rf power and total pressure resulted in a fine tailoring of the nanosystem structure and morphology, enabling the preparation of both cluster/island-like systems or continuous thin films. A detailed characterization of the obtained specimens was attained by the combined use of several analytical techniques. While laser reflection interferometry (LRI) was employed for an in situ real-time investigation of growth dynamics, glancing-incidence x-ray diffraction (GIXRD), and transmission electron microscopy (TEM) provided useful information on the system nanostructure. Furthermore, x-ray photoelectron spectroscopy (XPS), UV-Vis spectroscopy, and atomic force microscopy (AFM) were used to investigate the chemical composition, optical properties, and surface morphology, respectively. This work has been focused on the XPS characterization of two representative Ag/SiO2 specimens. In particular, detailed scans for the Ag 3d, Ag MVV, Si 2s, O 1s, and C 1s regions and related data for a silver thin film on silica and a discontinuous Ag/SiO2 specimen are presented and discussed. © 2005 American Vacuum Society.
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81.16.Be Chemical synthesis methods
81.05.Zx New materials: theory, design, and fabrication
79.60.Jv Interfaces; heterostructures; nanostructures
81.15.Cd Deposition by sputtering
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