Leonardo F. Hernandez

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.

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.

Composites in small and simple devices to increase mixing on detector surfaces

This work aims at three different applications for the betterment of plasma generated-composite thin films: pre-mixing, spray formation in miniaturized structures and an increase in the performance of detector surfaces. Miniaturized structures were projected, simulated with FEMLAB® 3.2 software and then constructed. Clustered films made from tetraethoxysilane (TEOS) and nonafluoro(iso)butyl ether (HFE®) precursors were deposited on silicon, acrylic and quartz substrates for different kinds of film characterization/or in the projected structures. Physical and chemical characterization guided the selection of best films previous to/after UVC exposure. The active surfaces (plasma-deposited films) in structures were modified by UVC exposure and then tested. The applications include pre-mixing of liquids and/or spray formation, best results being obtained with surface covered by derivative-HFE films, which acted as passivation layers. Preliminary results show good humidity sensing for TEOS-derivative films.

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.