A. Pancotti | Ufg - Academia.edu (original) (raw)

Papers by A. Pancotti

Agradeço profundamente a minha família, pela atenção dada a minha formação acadêmica e principalm... more Agradeço profundamente a minha família, pela atenção dada a minha formação acadêmica e principalmente a paciência que tiveram comigo nesses longos anos. Agradeço a minha esposa Cléria de L. T. Pancotti pela enorme paciência que teve enquanto estava realizando esse trabalho. Agradeço ao Prof. Richard Landers pela sua valiosa orientação e paciência que teve comigo nesse meu trabalho, agradeço principalmente a pessoa que é, ou seja, uma pessoa acessível e dedicada às pessoas que forma como futuro pesquisadores desse país. Agradeço ao Prof. George G. Kleiman, pela amizade, pelas discussões que tivemos e pelas aulas de Estado Sólido, aulas em que me dediquei em estudar grande parte da teoria desenvolvida aqui nesta tese. Agradeço ao Prof. Abner de Siervo pela grande ajuda que me deu nesse trabalho, pelo apoio e incentivo aos cálculos aqui apresentados. Agradeço aos companheiros do Grupo de Física de Superfície da Unicamp, os quais me ajudaram em parte deste trabalho:

We have previously identified new compounds with high in vitro efficacies against the intraerythr... more We have previously identified new compounds with high in vitro efficacies against the intraerythrocytic stages of Plasmodium falciparum (P.f.) (IC50 <10 nM), but the molecular target is unknown and preliminary results indicate that indeed multiple targets may exists.(1-4) Proteomics offers a unique tool for target identification and several proteomic approaches are available. One of the most interesting is the so called \u201cchemical proteomics\u201d, which couples affinity purification methods with mass spectrometry and therefore permits to increase selectivity and sensitivity. Several limitations can affect the results of chemical proteomics approaches. For example, it is necessary to use tag compounds that present high activity and affinity for the target protein. Moreover, considering that LC-MS analysis is a very sensitive methodology used for identification of the target protein, non-specific protein binding could cause high background noise, therefore greatly complicating...

Arquivo Brasileiro de Medicina Veterinária e Zootecnia, 2020

The elastic cartilage is composed by chondroblasts and chondrocytes, extracellular matrix and sur... more The elastic cartilage is composed by chondroblasts and chondrocytes, extracellular matrix and surrounded by perichondrium. It has a low regeneration capacity and is a challenge in surgical repair. One of obstacles in engineering a structurally sound and long-lasting tissue is selecting the most appropriate scaffold material. One of the techniques for obtaining biomaterials from animal tissues is the decellularization that decreases antigenicity. In this work, alkaline solution was used in bovine ear elastic cartilages to evaluate the decellularization and the architecture of the extracellular matrix. The cartilages were treated in alkaline solution (pH13) for 72 hours and lyophilized to be compared with untreated cartilages by histological analysis (hematoxylin-eosin, Masson's trichrome and Verhoeff slides). Areas of interest for cell counting and elastic fiber quantification were delineated, and the distribution of collagen and elastic fibers and the presence of non-fibrous pro...

$Research paper thumbnail of Surface structure characterization by X-ray photoelectron diffraction of Sn ultra-thin films deposited on Pd(111)$

Surface Science, 2019

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service... more This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Highlights  The formation of surface alloys Pd 2 Sn was characterized by XPS, LEED and XPD.  XPD results indicated the formation of a corrugated bi-dimensional Pd2Sn surface alloy.  Annealing the surface alloy at at 600 K produced a (3 3x)R30 o LEED pattern.

Revista Latino-Americana de Educação em Astronomia, 2021

Apresentamos uma proposta simplificada de determinação da Unidade Astronômica (UA) através de dad... more Apresentamos uma proposta simplificada de determinação da Unidade Astronômica (UA) através de dados experimentais obtidos pelo registro do trânsito de Mercúrio em frente ao Sol, de fácil desenvolvimento junto a estudantes da última fase da educação básica. O registro do trânsito foi realizado durante uma sessão de observação astronômica realizada em uma escola brasileira e, também, em cooperação com uma instituição internacional. Esta atividade mostrou que, apesar da pouca distância entre os dois locais de observação, em relação ao planeta Terra, o registro do trânsito de Mercúrio de 2019 permitiu determinar o valor da UA com uma boa aproximação. Os trânsitos de planetas possuem importância didático-pedagógica, podendo ser utilizados por educadores na educação formal como elemento motivador. A atividade permite conhecer e aplicar dados experimentais, desenvolver conhecimentos como construções geométricas, trigonometria, razões e proporções, as Leis de Kepler do movimento planetário,...

Physical Review Materials, 2021

Journal of Materials Science: Materials in Medicine, 2021

Nanoparticles (NPs) have a wide range of applications in various areas. For health application, c... more Nanoparticles (NPs) have a wide range of applications in various areas. For health application, cytotoxicity tests are used to ensure its efficiency and safety. In this paper, ZnFe2O4, CoFe2O4, Zn0.5Co0.5Fe2O4 NPs were synthesized, characterized and their antibacterial properties were evaluated. The Sol-Gel method was used to synthesize the NPs. Their electronic and crystallographic structures were characterized by Fourier Transform Infrared Spectroscopy Analysis (FTIR), X-ray fluorescence (XRF), X-Ray Diffraction (XRD), and Transmission Electron Microscopy (TEM). To perform the antibacterial evaluation, ferrites were dispersed through nanoemulsion to prevent the crystals from accumulating together. Then the evaluation was performed through microdilution in a 96-well plate and diffusion in agar disc in contact with 3 different strains of Staphylococcus aureus and Escherichia coli. It demonstrated that the Sol-Gel method was efficient to synthesize NPs with suitable sizes for health ...

$Research paper thumbnail of Surface structure characterization of a (√5  ×  √5)-R26.6° reconstruction of strontium titanate (001) by x-ray photoelectron diffraction$

Surface Science, 2021

ABSTRACT The surface composition of a (√5 × √5)-R26.6° (Rt5) reconstruction of a strontium tita... more ABSTRACT The surface composition of a (√5 × √5)-R26.6° (Rt5) reconstruction of a strontium titanate (001) single crystal surface was characterized by x-ray photoelectron spectroscopy (XPS), and its atomic surface structure was determined by a combination of low energy electron diffraction (LEED) and x-ray photoelectron diffraction (XPD). The comparison between experimental and theoretical XPD results involving multiple scattering calculations indicated that the analyzed Rt5 reconstruction of the SrTiO3 (001) surface has two possible terminations: 40% of SrO and 60% of TiO2.

Physical Review B, 2020

We have studied the surface structure of single-crystal, wide-gap semiconductor β-Ga 2 O 3 (010) ... more We have studied the surface structure of single-crystal, wide-gap semiconductor β-Ga 2 O 3 (010) using x-ray photoelectron diffraction (XPD), low-energy electron diffraction (LEED), and x-ray photoelectron spectroscopy (XPS). The XPS measurements show typical spectra for stoichiometric Ga 2 O 3 (010). Annealing in vacuum produced a sharp (1 × 1) LEED pattern, characteristic of the monoclinic structure. The XPD angular anisotropies were collected for the Ga 2p 3/2 and O 1s core levels. Surface interlayer relaxation up to 8% of the bulk interplanar distance and 0.11-0.14 Å rumpling are observed at the β-Ga 2 O 3 (010) surface. At the surface, the oxygen atoms shift toward the vacuum with respect to the gallium atoms. The rumpling decreases to zero and and the interplanar distance reaches the bulk value of 1.52 Å by the sixth atomic layer. The surface structure agrees with that predicted by first-principles density functional theory calculations which, in addition, suggest a significant band gap narrowing of ≈ 1 eV in the surface layer, due to surface states spatially localized on surface oxygen atoms of O II type.

Journal of Applied Physics, 2020

Ferroelectric hafnia-based thin films are promising candidates for emerging high-density embedded... more Ferroelectric hafnia-based thin films are promising candidates for emerging high-density embedded nonvolatile memory technologies, thanks to their compatibility with silicon technology and the possibility of 3D integration. The electrode-ferroelectric interface and the crystallization annealing temperature may play an important role in such memory cells. The top interface in a TiN=Hf 0:5 Zr 0:5 O 2 =TiN metal-ferroelectric-metal stack annealed at different temperatures was investigated with X-ray photoelectron spectroscopy. The uniformity and continuity of the 2 nm TiN top electrode was verified by photoemission electron microscopy and conductive atomic force microscopy. Partial oxidation of the electrode at the interface is identified. Hf is reduced near the top interface due to oxygen scavenging by the top electrode. The oxygen vacancy (V O) profile showed a maximum at the top interface (0.71%) and a sharp decrease into the film, giving rise to an internal field. Annealing at higher temperatures did not affect the V O concentration at the top interface but causes the generation of additional V O in the film, leading to a decrease of the Schottky Barrier Height for electrons. The interface chemistry and n-type film doping are believed to be at the origin of several phenomena, including wake-up, imprint, and fatigue. Our results give insights into the physical chemistry of the top interface with the accumulation of defective charges acting as electronic traps, causing a local imprint effect. This may explain the wake-up behavior as well and also can be a possible reason of the weaker endurance observed in these systems when increasing the annealing temperature.

Journal of Materials Science, 2019

Titanium alloys are promising candidates for biomedical applications, and alloys based on the Ti-... more Titanium alloys are promising candidates for biomedical applications, and alloys based on the Ti-rich side of Ti-Nb-Sn system have presented material properties deserved for orthopedic implant applications. However, to our knowledge, the structural studies related to surface of these alloys are limited. Ti-18Nb-11Sn and Ti-35Nb-4Sn alloys were synthesized, and the influence of thermochemical treatment on the bioactivity was investigated. The alloys were synthesized by arc melting furnace and then were submitted to thermochemical treatment. X-ray diffraction and scanning electron micrograph analysis showed high crystallinity and maintenance of microstructure of the both alloys before and after thermochemical treatment. The results indicated that the Ti-18Nb-11Sn alloy was not demonstrated to be bioactive, while the Ti-35Nb-4Sn alloy slightly presented bioactivity, which increased after the thermochemical treatment. Meanwhile, the Ti-18Nb-11Sn alloy presented a low hardness value, making it not compatible with biomedical applications. However, the Ti-35Nb-4Sn alloy presented an acceptable hardness value for biomedical applications. We believe that the results reported herein suggest that the Ti-35Nb-4Sn alloy may be attractive for designing biomedical devices with improved performances toward the adhesion of apatite.

$Research paper thumbnail of Ultra-thin films of In on Pd(111) characterized by X-ray photoelectron diffraction$

Thin Solid Films, 2019

Metallic surfaces involving transition metals are widely used in the preparation of catalysts. Th... more Metallic surfaces involving transition metals are widely used in the preparation of catalysts. The conversion rates and the selectivity can be improved, in many instances, by a surface alloy formed by a transition metal with a less reactive sp metal. Bimetallic systems based on PdeIn have been shown to be efficient catalysts for methanol steam reforming and nitrate reduction in water. The catalytic reaction depends on both the electronic structure and the geometric arrangement of the surface alloy atoms. In and Pd have very limited miscibility in the bulk but can form ordered surface alloys. We have investigated the growth and the surface alloy formation of an ultra-thin film of In deposited on a Pd(111) single-crystal substrate surface. The electronic structure and the surface composition have been characterized by X-ray photoelectron spectroscopy (XPS), and the atomic surface structure has been determined by a combination of low energy electron diffraction (LEED) and X-ray photoelectron diffraction (XPD). Ultra-thin films of In having approximately 1 to 5 monolayers (ML) were deposited at room temperature, and then annealed at 500 K. Pd 3d and In 3d intensities obtained by XPS indicated the Stranski-Krastanov growth mode, i.e. flat bi-dimensional overlayers in the first layer followed by three-dimensional islands. For annealed In films having 0.33 to 2.5 ML, a (x 3 3)R30°LEED pattern was observed. For a non-annealed In film having approximately 3 ML, a p(2 × 2) LEED pattern was observed, that changed to (x 3 3)R30°upon annealing at 500 K. For a slightly higher coverage, about 3.6 ML, a (1 × 1) pattern was obtained after annealing. XPS results for the annealed~3.6 ML film indicate the diffusion of In atoms into the outermost layers of the Pd(111) single-crystal. For the same In film, XPD indicated the formation of bidimensional In islands, with some bare patches of the substrate.

$Research paper thumbnail of Surface Characterization of NbO Islands Formed on Nb(100) by X-Ray Photoelectron Diffraction$

Topics in Catalysis, 2018

An ordered thin film of niobium oxide (NbO) was formed on the Nb(100) surface by heating the niob... more An ordered thin film of niobium oxide (NbO) was formed on the Nb(100) surface by heating the niobium single crystal at 1023 K for 2 min under an oxygen atmosphere. The surface composition was analyzed by X-ray photoelectron spectroscopy (XPS), and the surface structure was characterized by low energy electron diffraction (LEED) and X-ray photoelectron diffraction (XPD) generated by synchrotron radiation. Annealing at 1223 K in ultra-high vacuum yielded a reconstructed (3 × 1) LEED pattern. XPS measurements indicated that the surface comprised of metallic and oxidized niobium species. The comparison between experimental and theoretical XPD results indicated that 60% of the Nb(100) surface was covered by two-layered nanoislands of NbO, and 40% had bare patches.

CrystEngComm, 2017

A rhodium ultra-thin film was deposited on a Pd-supported α-Fe2O3 (0001) film by molecular beam e... more A rhodium ultra-thin film was deposited on a Pd-supported α-Fe2O3 (0001) film by molecular beam epitaxy (MBE). The surface atomic and electronic structures were studied using X-ray photoelectron diffraction (XPD), X-ray photoelectron spectroscopy (XPS), and low energy electron diffraction (LEED). For an oxide thin film (∼16.5 A), an ordered (√3 × √3)R30° structure was observed. The multiple scattering calculation approach combined with a genetic algorithm for surface structure optimization was used to investigate precisely the atomic structure of the oxide support as well as the Rh nanoislands or nanoparticles (NPs). Rh exhibited 3D growth on an α-Fe2O3 thin film forming NPs with a lattice constant expanded by 5.26% relative to the Rh bulk value. The coexistence of 60° rotated domains and also evidence of Fe termination at the surface of α-Fe2O3 were observed.

Topics in Catalysis, 2011

Ultra-thin films (1 and 3 monolayers) of Pd were deposited on the Au(111) surface and then charac... more Ultra-thin films (1 and 3 monolayers) of Pd were deposited on the Au(111) surface and then characterized by X-ray photoelectron spectroscopy (XPS), X-ray excited Auger spectroscopy (XAES), low-energy electron diffraction (LEED), and X-ray photoelectron diffraction (XPD). For the 1 ML Pd film annealed at 450 °C, XPS and XAES results indicated that Pd had diffused into the Au substrate. For the

Physical Review B, 2006

High dielectric constant materials, such as HfO 2 , have been extensively studied as alternatives... more High dielectric constant materials, such as HfO 2 , have been extensively studied as alternatives to SiO 2 in new generations of Si based devices. Hf silicate/silicide formation has been reported in almost all literature studies of Hf based oxides on Si, using different methods of preparation. A silicate interface resembles close to the traditional Si/ SiO 2. The silicate very likely forms a very sharp interface between the Si substrate and the metal oxide, and would be suitable for device applications. However, the thermal instability of the interfacial silicate/oxide film leads to silicidation, causing a dramatic loss of the gate oxide integrity. Despite the importance of the Hf silicide surface and interface with Si, only a few studies of this surface are present in the literature, and a structural determination of the surface has not been reported. This paper reports a study of the Hf silicide formation upon annealing by using a combination of XPS, LEED, and x-ray photoelectron diffraction ͑XPD͒ analyses. Our results clearly indicate the formation of a unique ordered Hf silicide phase ͑HfSi 2 ͒, which starts to crystallize when the annealing temperature is higher than 550°C.

$Research paper thumbnail of Photoelectron spectroscopy (XPS) and photoelectron diffraction (XPD) studies on the system hafnium silicide and hafnium oxide on Si(100)$

Materials Science in Semiconductor Processing, 2006

Continuous down-scaling of silicon based transistors results in device lengths of less than 100 n... more Continuous down-scaling of silicon based transistors results in device lengths of less than 100 nm. This requires a reduction of the gate dielectric thickness to less than 15Å which is not possible for SiO 2 due to an increasing leakage current. One of the most promising candidates for a replacement material for the gate dielectric is HfO 2 [Wilk GD, Wallace RM, Anthony JM. J Appl Phys 2001; 89:5243]. In this work we applied X-ray photoelectron spectroscopy (XPS) and photoelectron diffraction measurements in order to study the interface of hafnium oxide to Si(1 0 0). The high resolution measurements were performed with synchrotron radiation at beamlines 5 and 11 at DELTA (Dortmund). For the first time, photoelectron diffraction patterns for this system were recorded. The spectral resolution allowed to separate different spectral components. The preparation of hafnium oxide films on Si(1 0 0) was performed by evaporation of hafnium at a partial oxygen background pressure of 1 Â 10 À8 mbar. Three different spectral components were observed in the hafnium 4f photoemission signal by high resolution XPS. The photoelectron signals with binding energies shift of 3.1 and 1.2 eV with respect to signal of hafnium silicide were assigned to hafnium dioxide and hafnium silicate, respectively. The corresponding high-resolution diffraction patterns result from different local environments for each component. The experimental patterns are compared with simulations for a model structure of hafnium silicide.