Pulsed Laser Deposition and Laser-Induced Backward Transfer to Modify Polydimethylsiloxane

Polydimethylsiloxane (PDMS) is a silicone-elastomer that owes its large application in the field of stretchable electronics to its chemical and thermal stability, transparency, flexibility, non-toxicity, compatibility, and low cost. PDMS is a versatile material because it can be used both as an elastic substrate and, after functionalization, as an active material for the design of stretchable electronics. One possible route for the functionalization of PDMS, thus becoming an active material together with numerous metals and semiconductors, is the embedding of conductive nanomaterials. Presently, pulsed laser deposition (PLD) and laser-induced backward transfer (LIBT) are used to deposit carbon- based material on polydimethylsiloxane. In this study, we explore and compare the surface treatments, advantages, and disadvantages of both different employed techniques in different environments. The modification of the wettability, elasticity, morphology, composition, and optical characteristics of polydimethylsiloxane will be evaluated by surface techniques such as scanning electron microscopy, Rutherford backscattering spectrometry, and the sessile drop method.

Deuterium Retention and Release Behavior from Beryllium Co-Deposited Layers at Distinct Ar/D Ratio

Beryllium-deuterium co-deposited layers were obtained using DC magnetron sputtering technique by varying the Ar/D2 gas mixture composition (10/1; 5/1; 2/1 and 1:1) at a constant deposition rate of 0.06 nm/s, 343 K substrate temperature and 2 Pa gas pressure. The surface morphology of the layers was analyzed using Scanning Electron Microscopy and the layer crystalline structure was analyzed by X-ray diffraction. Rutherford backscattering spectrometry was employed to determine the chemical composition of the layers. D trapping states and inventory quantification were performed using thermal desorption spectroscopy. The morphology of the layers is not influenced by the Ar/D2 gas mixture composition but by the substrate type and roughness. The increase of the D2 content during the deposition leads to the deposition of Be-D amorphous layers and also reduces the layer thickness by decreasing the sputtering yield due to the poisoning of the Be target. The D retention in the layers is dominated by the D trapping in low activation binding states and the increase of D2 flow during deposition leads to a significant build-up of deuterium in these states. Increase of deuterium flow during deposition consequently leads to an increase of D retention in the beryllium layers up to 300%. The resulted Be-D layers release the majority of their D (above 99.99%) at temperatures lower than 700 K.

Uso do Método de Monte Carlo para caracterização adicional de materiais para aplicação em blindagem de fótons

As blindagens são uma parte fundamental na radioproteção. A construção de curvas de transmissão para um material utilizado como blindagem é importante para a definição da espessura necessária da blindagem. O principal objetivo deste trabalho é desenvolver um método para caracterizar novos materiais para blindagem de fótons usando a ferramenta computacional Geant4. As amostras irradiadas, denominadas Traço A, B e C, foram produzidas no Laboratório de Resistência de Materiais da UCPel. As validações experimentais de caracterização das amostras foram realizadas pelo teste da camada semirredutora (CSR), medida de kerma e medidas de Rutherford Backscattering Spectrometry (RBS), sendo os dois primeiros validados por meio de simulações. Os resultados de RBS e do imageamento mostraram a influência da granularidade dos agregados do concreto na homogeneidade e reprodutibilidade das amostras. A validação da aplicação foi feita por meio da verificação dos espectros teóricos e simulados, da geometria de radiação e caracterização do material. Os espectros teóricos e simulados foram validados por testes estatísticos, sendo considerados equivalentes. A geometria de radiação foi validada utilizando um visualizador e as ferramentas de verificação da geometria disponibilizadas pelo Geant4. Espera-se, com esses resultados, fazer medidas experimentais e criar curvas de transmissão simuladas para aplicações na radiologia diagnóstica e radioterapia.

The Effect of the Deposition Method on the Structural and Optical Properties of ZnS Thin Films

ZnS is a wide band gap material which was proposed as a possible candidate to replace CdS as a buffer layer in solar cells. However, the structural and optical properties are influenced by the deposition method. ZnS thin films were prepared using magnetron sputtering (MS), pulsed laser deposition (PLD), and a combined deposition technique that uses the same bulk target for sputtering and PLD at the same time, named MSPLD. The compositional, structural, and optical properties of the as-deposited and annealed films were inferred from Rutherford backscattering spectrometry, X-ray diffraction, X-ray reflectometry, Raman spectroscopy, and spectroscopic ellipsometry. PLD leads to the best stoichiometric transfer from target to substrate, MS makes fully amorphous films, whereas MSPLD facilitates obtaining the densest films. The study reveals that the band gap is only slightly influenced by the deposition method, or by annealing, which is encouraging for photovoltaic applications. However, sulphur vacancies contribute to lowering the bandgap and therefore should be controlled. Moreover, the results add valuable information towards the understanding of ZnS polymorphism. The combined MSPLD method offers several advantages such as an increased deposition rate and the possibility to tune the optical properties of the obtained thin films.

Radiation tolerance of nanostructured TiCrN coatings

Nanostructured TixCr1–xN coatings of various compositions 0.58 ≤ x ≤ 0.8 on the substrates made of AISI 304 stainless steel and monocrystalline silicon were formed by the method of separable vacuum-arc deposition. The elemental composition was studied by Rutherford backscattering spectrometry of helium ions. The structural-phase state and the morphology were examined by X-ray diffraction, optical and scanning electron microscopy, tribomechanical tests of the initial coatings were also carried out. The radiation tolerance of the nanostructured TixCr1–xN coatings within 0.58 ≤ x ≤ 0.8 under He+ ion irradiation with an energy of 500 keV in the fluence range of 5·1016–3·1017 ions/cm2 was studied for the first time. It was found that the TixCr1–xN coatings within 0.58 ≤ x ≤ 0.8 withstand irradiation without significant changes in the structure up to a fluence of 2·1017 ions/cm2, when a partial coating flaking (exfoliation) up to a depth of the projected range of helium ions takes place. A decrease in the average size of crystallites of coatings and the crystal lattice period reduction after radiation exposure were detected. The decrease in the microhardness of the TixCr1–xN coatings of all compositions after irradiation was found.

Effect of Silver Modification on the Photoactivity of Titania Coatings with Different Pore Structures

Nanostructured photoactive systems are promising for applications such as air and water purification, including self-cleaning coatings. In this study, mesoporous TiO2 sol-gel coatings with different pore structures were prepared and modified with silver by two methods: the “mixing” method by adding AgNO3 to the precursor sol, and the “impregnation” method by immersing the samples in AgNO3 solution (0.03 and 1 M) followed by heat treatment. Our aim was to investigate the effects that silver modification has on the functional properties (e.g., those that are important for self-cleaning coatings). Transmittance, band gap energy, refractive index, porosity and thickness values were determined from UV-Vis spectroscopy measurements. Silver content and structure of the silver modified samples were characterized by X-ray photoelectron spectroscopy, Rutherford backscattering spectrometry, High-resolution transmission electron microscopy and Energy Dispersive X-ray Spectrometry elemental mapping measurements. Wettability properties, including photoinduced wettability conversion behavior were investigated by water contact angle measurements. Photoactivity was studied under both UV and visible light with rhodamine 6G and methylene blue dye molecules, at the liquid–solid and air–solid interfaces modeling the operating conditions of self-cleaning coatings. Samples made with “impregnation” method showed better functional properties, in spite of their significantly lower silver content. The pore structure influenced the Ag content achieved by the “impregnation” method, and consequently affected their photoactivity.

Influence of Deposition Method on the Structural and Optical Properties of Ge2Sb2Te5

Ge2Sb2Te5 (GST-225) is a chalcogenide material with applications in nonvolatile memories. However, chalcogenide material properties are dependent on the deposition technique. GST-225 thin films were prepared using three deposition methods: magnetron sputtering (MS), pulsed laser deposition (PLD) and a deposition technique that combines MS and PLD, namely MSPLD. In the MSPLD technique, the same bulk target is used for sputtering but also for PLD at the same time. The structural and optical properties of the as-deposited and annealed thin films were characterized by Rutherford backscattering spectrometry, X-ray reflectometry, X-ray diffraction, Raman spectroscopy and spectroscopic ellipsometry. MS has the advantage of easily leading to fully amorphous films and to a single crystalline phase after annealing. MS also produces the highest optical contrast between the as-deposited and annealed films. PLD leads to the best stoichiometric transfer, whereas the annealed MSPLD films have the highest mass density. All the as-deposited films obtained with the three methods have a similar optical bandgap of approximately 0.7 eV, which decreases after annealing, mostly in the case of the MS sample. This study reveals that the properties of GST-225 are significantly influenced by the deposition technique, and the proper method should be selected when targeting a specific application. In particular, for electrical and optical phase change memories, MS is the best suited deposition method.