M.A. Macêdo

Yttria thin films doped with rare earth for applications in radiation detectors and thermoluminescent dosimeters

Abstract Thin films of pure and Nd doped Y 2 O 3 were prepared following a new sol–gel route on glass substrate. Sets of thin films were prepared in different oxidation and densification conditions and the effect of such conditions in the morphology, crystallization, surface aspect and thermoluminescence (TL) and radioluminescence response are analysed. The results indicates that the films are suitable for scintillating devices rather than solid state TL dosimeters.

Novel Route for the Preparation of Nanosized NiFe2O4 Powders

Nanosized NiFe2O4 powders were prepared by a novel sol-gel route. The powders calcined at 1200°C and quenched to liquid nitrogen temperature showed a mixed spinel phase, with a saturation magnetization of 49 emu/g, crystallite size of 67 nm and hyperfine magnetic field B1 = 520 kOe, B2 = 484 kOe and A = 488 kOe.

AFM and XRD characterization of silver nanoparticles films deposited on the surface of DGEBA epoxy resin by ion sputtering

In this work, silver atoms were deposited by ion sputtering on the surface of diglycidyl ether of bisphenol A (DGEBA) epoxy resin cured at 150 °C for 6 hours in air. The films of DGEBA and its precursors were characterized by Raman spectroscopy to identify the main functional groups and their relationship with the deposited silver atoms. Silver thin films of 5, 10, 15 and 20 nm were deposited on the epoxy resin at room temperature. Both the initial film of DGEBA and the subsequent silver thin film were analyzed by Atomic Force Microscopy (AFM) in the non-contact mode. Silver thin films were also analyzed using X-ray diffraction (XRD) at room temperature. The AFM results showed the formation of silver crystallites on the surface of DGEBA at very low coverage whereas XRD indicated that most of them had their main axis aligned to the normal of the surface. An increase in the coverage led to an increase in the grain size as indicated by AFM. However, XRD results indicated that the crystallite size remained almost constant while the appearance of peaks corresponding to other crystalline orientations suggests the coalescence of the original crystallites and an increase in size of the more dense planes, namely [111].

Permanent Data Storage in ZnO Thin Films by Filamentary Resistive Switching

Resistive memories are considered the most promising candidates for the next generation of non-volatile memory; however, attention has so far been limited to rewritable memory features for applications in resistive random access memories (RRAM). In this article, we provide a new insight into the applicability of resistive memories. The characteristics of non-rewritable resistive memories (NRRM) were investigated. Devices with Pt/ZnO/ITO architecture were prepared using magnetron sputtering, upon which various bipolar and unipolar resistive switching tests were performed. The results showed excellent distinction between the high resistance state (HRS) and low resistance state (LRS), with RHRS/RLRS = 5.2 × 1011 for the Pt/ZnO/ITO device with deposition time of 1 h. All samples were stable for more than 104 s, indicating that the devices have excellent applicability in NRRMs.

Mechanical properties of epoxy resin based on granite stone powder from the Sergipe fold-and-thrust belt composites

This paper studies the mechanical properties including traction, flexion, compression, and hardness characteristics of a composite made from the combination of epoxy resin and granitic stone powder from the fold-and-thrust belt located in the municipality of Nossa Senhora da Gloria, in the state of Sergipe, Brazil. Chemical and mineralogical analyses of the stone and analysis by SEM of the particle/matrix interface are performed. Two Granite types, named 53-A and 12-A, were incorporated with different mass percentages of 0%, 30% and 50%, in the polymeric matrix, DGEBA, formed by the Araldite polymer GY 279 and the curing agent Aradur 2963. The test results with 50% show a compression of 79 MPa with a maximum increase of 121% compared with the pure epoxy resin.

Nanocrystals of Zn1-xMxO (M = Co, Mn) by proteic sol-gel process

We present in this work a study on the magnetic properties of nanocrystals of Mn- or Co-doped ZnO obtained by a proteic sol-gel process. Analysis of these nanocrystals is accomplished using x-ray diffraction (XRD), the Rietveld refinement through using the General Structure Analysis System (GSAS) program, and magnetic measurements using a vibrating sample magnetometer (VSM). The samples of Zn0.9M0.1O (M = Co or Mn) possess single phase crystals with a wurtzite structure (hexagonal) and a P63mc space group. The Zn0.9Co0.1O and Zn0.9Mn0.1O samples presented, at room temperature, the behavior of a soft ferromagnetic with a coercive field (Hc) of 336 Oe and 1240 Oe, respectively, and a remanent magnetization (Mr) of 5 and 2.5 memu/g, respectively.

Production and Electrochemical Properties of LiMn2O4 Thin Films via a Proteic Sol-Gel Process

State-of-the-art lithium-ion batteries is formed of a system of LiyC/LiCoO2 multilayers [1], however the production of cathode LiCoO2 is expensive. As opposed to LiCO2, the LiMn2O4 thin film has enjoyed larger interest due to its low cost of production and low toxicity [2]. The disadvantage is that its capacity during cycles of extraction/insertion decrease for potential of 4 V. During the cycles of extraction, the cubical structure of spinel expands and contract isotropicaly. Some researchers have attributed that this problem is related to effect of solubility of the spinel electrode in the electrolyte and a reaction of deprotonation in the surface of films of kind showed in Eq. 1[3].