Roberto R. Lima

First Experiments with the IFUSP Microtron Injector

The first accelerating structures of the Sao Paulo microtron accelerator presently deliver a continuous‐wave 1.9 MeV electron beam, which can be used in atomic physics studies. An energy‐analyzed beam line with focalization magnets, irradiation chamber, movable target system and Faraday cup was built. Here, we will describe the preliminary results of two experiments. In the first one, upper limits on K‐shell ionization cross sections of Pd and Au atoms by electron impact were obtained. To this end, thin targets of these elements were irradiated with the beam impinging at 45° while the emitted Kα x‐rays were recorded with an HPGe x‐ray detector positioned at 90° with respect to the beam direction. The other experiment was the measurement of the bremsstrahlung energy spectra produced by the aforementioned targets in the same geometrical configuration but using an HPGe γ‐ray detector instead. The latter experiment enabled the determination of the electron‐beam energy as 1.909(5) MeV.

Low cost microstructures for preconcentration of polar and non-polar organic compounds

Films produced by plasma polymerization of ethyl ether and methyl or ethyl acetate show good adsorption characteristic for polar and non-polar organic compounds. These films when used in microchannels machined in a 3D-structure present some preconcentration of organic compounds. Therefore, the aim of this work is to investigate the physical-chemical preconcentration mechanisms on this structure. The test molecules used were n-hexane and 2-propanol. Quartz crystal microbalance and mass spectrometry were used to measure preconcentration. Two different procedures for reactant injection on the structure were used: a continuous flow during several minutes or a small amount injected on a single pulse and in a few seconds. The microchannels were also modified by the introduction of small ceramic particles for enhancement of the flow dispersion. It was possible to notice for all films a similar kinetic of retention. The main removal mechanism is adsorption. Although all films can provide the removal of the adsorbents molecules, the most important characteristic for the adsorption and/or retention is the surface condition. Thus, the retention of polar compound can be troubled if a non-polar compound was used previously. The most promising films for retention are ethyl ether and ethyl acetate when n-hexane and 2-propanol are used as test molecules. The results using n-hexane or 2-propanol point out the use of low-cost microchannels for preconcentration development.

Plasma polymerized acetaldehyde thin films for retention of volatile organic compounds

The aim of this work is the production and characterization of plasma polymerized acetaldehyde thin films. These films show highly polar species, are hydrophilic, organophilic and easily adsorb organic reactants with CO radicals but only allow permeation of reactants with OH radicals. The good step coverage of films deposited on aluminum trenches is useful for sensor development. Films deposited on hydrophobic substrates may result in a discontinued layer, which allows the use of preconcentration in sample pretreatment. Deposition on microchannels showed the possibility of chromatographic columns and/or retention system production to selectively detect or remove organic compounds from gas flows.

Large Surface Area of HMDS Plasma Polymerized Thin Film Used for Production of Miniaturized Structures

The aim of this work was the production of a large surface area of hexamethyldisilazane (HMDS) plasma-deposited thin films and their applicability in a miniaturized structure useful for preliminary analysis of organic mixtures. The HMDS plasma films were produced with different surface areas and morphologies, and all films adsorbed polar and non-polar organic compounds. A low cost miniaturized structure was manufactured in glass using a Milling cutter and covered with HMDS plasma films. Good agreement was observed between simulation and experimental results on those microstructures. The observed different performance between pure and mixtures of organic compound samples suggests that the proposed system is a simple setup that could be useful for rough analysis of a fuel.

A switching magnet for the IFUSP microtron

In this work we present the design of a switching magnet for the IFUSP microtron beam line. A configuration with azimuthal symmetry was adopted in order to comply with the boundary conditions of the accelerator building and to ease the machining process. The distribution and uniformity of the magnetic field are presented, as well as the project and construction of the vacuum chamber.

TEOS plasma polymerized films: Impact of clustered material in humidity measurement

This work aims to humidity and VOCs measurement using TEOS films or TEOS/HFE composites. Films, exposed or not to ultraviolet, were tested on cycles of relative humidity ranging from 25% to 85% and VOCs interference were also evaluated. TEOS films showed good reproducibility up to 85% relative humidity but quick reaction on 90%. The best detection limit was 100 ppm, using TEOS films exposed to UVC and TEOS/HFE composites show sensitivity of 4 Hz/% humidity, but interdigitated electrodes quickly saturate. VOCs were detected in the 1% w/w in air and do not interfere in the relative humidity detection.

TEOS and TEOS/HFE plasma thin films used in electrochemical measurements

TEOS and/or TEOS/HFE plasma polymerized thin films, exposed or non-exposed to ultraviolet (UVC) radiation, were obtained on gold electrodes and tested for electrochemical measurements. All films presented good performance on electrochemical measurements. The electronic signal does not change significantly after 24h on physiologic serum but thin TEOS films allow ion permeation. Thus, these films are useful as membranes to reference and measuring electrodes.

P2.9.2 Small and Simple Devices for Increase Mixing on Detector Surfaces

Due to transport phenomena, analyte adsorption on the detector surface can be hindered, which increases the detection limit. Therefore, this work aims the simulation, production and tests of a simple miniaturized structure that favors mixing on detector surfaces. The conception of the manufactured device is based on passive mixers. Mixing is improved by changing the surfaces properties of plasma deposited thin films. Hexamethyldisilazane (HMDS) and nonafluoro(iso)butyl ether (HFE) and codeposited HMDS/HFE plasma films were modified by ultraviolet (UVC) or beta radiation exposure (electron beam, 2 MeV, from 10 nA to 100 nA). Silicon, acrylics and piezoelectric quartz crystal (PQC) were used as substrates. Film characterization used profilemeter for thickness and ellipsometer for refractive index determinations; Raman, infrared (FTIR) and x-ray photoelectron (XPS) spectroscopies determined chemical composition. Optical, scanning electron (SEM) and atomic force (AFM) microscopies evaluated the film resistance toward ultraviolet light or beta radiation and cluster formation; cluster size were estimated using ImageJ software. Contact angle measurements tested hydrophobicity and the adsorption of volatile organic compounds (VOCs). Simulations of detector surfaces (based on PQC detection) and respective package used FEMLAB 3.2 software. All films are hydrophobic and adsorbent, even after exposition to ultraviolet radiation. HMDS films exposed to ultraviolet form a silicone-like structure whereas beta radiation exposure leads to carbon nodules formation. HFE films act as passive layer, even for beta radiation. Best design for surface modification has approximately a sinoidal shape.

Transition Radiation and its uses in particle accelerators

Transition Radiation (TR) is a physical process in which a uniformly moving charge emits radiation. For emission to occur, it is necessary a variation of the electromagnetic properties of the media that surrounds the particle. The main characteristics of this kind of radiation are: linearity between the radiation intensity and the generating charge, polarization and formation time. The continuous spectrum covers a wide wavelength range, including visible light (Optical Transition Radiation—OTR). These characteristics make OTR an excellent tool for beam diagnostics in particle accelerators. In this work we discuss the role OTR plays in beam instrumentation and the progress of the undergoing project of an OTR based diagnostic tool for the IFUSP Microtron. This is an innovative design since it is planned to be used to diagnose a low energy and low current electron beam.

Perfluorocompound and Hexamethyldisilazane Thin Film Composite Material Used for Surface Modification

The aim of this work was to produce, to characterize and test selective membranes based on derivatives from organic fluorinated/silicon compounds. The produced composites presented silicon and fluorinated species on the surface. The morphology of these non uniform surfaces showed big domains in the micrometer scale but a closer view reveals structures also in the nanometer range. Contact angle measurements showed a mildly hydrophobic and organophilic surface. Polymeric tapes treated with this composite showed an increase on permeation rate for the organic compounds. An acrylic device that employed this modified polymeric tape was manufactured and used for sample pretreatment during chemical analysis.