A. Maçarico

Bio: A. Maçarico is an academic researcher from Instituto Superior de Engenharia de Lisboa. The author has contributed to research in topics: Microcrystalline & Amorphous solid. The author has an hindex of 10, co-authored 46 publications receiving 447 citations. Previous affiliations of A. Maçarico include University of Lisbon & Universidade Nova de Lisboa.

Particle agglomeration study in rf silane plasmas: In situ study by polarization-sensitive laser light scattering

Abstract: To determine self-consistently the time evolution of particle size and their number density in situ multi-angle polarization-sensitive laser light scattering was used. Cross-polarization intensities (incident and scattered light intensities with opposite polarization) measured at 135 degrees and ex situ transmission electronic microscopy analysis demonstrate the existence of nonspherical agglomerates during the early phase of agglomeration. Later in the particle time development both techniques reveal spherical particles again. The presence of strong cross-polarization intensities is accompanied by low-frequency instabilities detected on the scattered light intensities and plasma emission. It is found that the particle radius and particle number density during the agglomeration phase can be well described by the Brownian free molecule coagulation model. Application of this neutral particle coagulation model is justified by calculation of the particle charge whereby it is shown that particles of a few tens of nanometer can be considered as neutral under our experimental conditions. The measured particle dispersion can be well described by a Brownian free molecule coagulation model including a log-normal particle size distribution. (C) 1996 American Institute of Physics.

Study of Annealed Indium Tin Oxide-Films prepared by RF Reactive Magnetron Sputtering

Abstract: Tin doped indium oxide (ITO) films were deposited on glass substrates by rf reactive magnetron sputtering using a metallic alloy target (In-Sn, 90-10). The post-deposition annealing has been done for ITO films in air and the effect of annealing temperature on the electrical, optical and structural properties of ITO films was studied. It has been found that the increase of the annealing temperature will improve the film electrical properties. The resistivity of as deposited film is about 1.3 × 10 −1 gW ∗ cm and decreases down to 6.9 × 10 −3 Ω ∗ cm as the annealing temperature is increased up to 500 °C. In addition, the annealing will also increase the film surface roughness which can improve the efficiency of amorphous silicon solar cells by increasing the amount of light trapping.

Laser-scanned p-i-n photodiode (LSP) for image detection

Abstract: Amorphous and microcrystalline glass/ZnO:Al/p(a-Si:H)/i(a-Si:H)/n(a-Si 1 - x C x :H)/Al imagers with different n-layer resistivities were produced by plasma-enhanced chemical vapor deposition technique (PE-CVD). The transducer is a simple, large area p-i-n photodiode; an image projected onto the sensing element leads to spatially confined depletion regions that can be readout by scanning the photodiode with a low-power modulated laser beam. The essence of the scheme is the analog readout and the absence of semiconductor arrays or electrode potential manipulations to transfer the information coming from the transducer. The effect of the image intensity on the sensor output characteristics (sensitivity, linearity, blooming, resolution, and signal-to-noise ratio) are analyzed for different material composition. The results show that the responsivity and the spatial resolution are limited by the conductivity of the doped layers. An enhancement of one order of magnitude in the image intensity and on the spatial resolution is achieved with a responsivity of 0.2 mW/cm 2 by decreasing the n-layer conductivity by the same amount. In a 4 x 4 cm 2 laser-scanned photodiode (LSP) sensor, the resolution was less than 100 μm and the signal-to-noise (S/N) ratio was about 32 dB. A physical model supported by electrical simulation gives insight into the methodology used for image representation.

Highly conductive and highly transparent n-type microcrystalline silicon thin films

Abstract: The aim of this paper is to present data on the dependence of the electro-optical characteristics and structure of n-type microcrystalline silicon films on the r.f. power used during the deposition of films produced by the plasma-enhanced chemical vapour deposition technique. The interest of these films arise from the fact that they combine some electro-optical advantages of amorphous (wide optical gap) and crystalline materials (electronic behaviour), highly interesting in the production of a wide variety of optoelectronic devices such as solar cells and thin film transistors. In this paper, microcrystalline n-type films presenting simultaneously optical gaps of about 2.3 eV, dark conductivity of 6.5 S cm −1 and Hall mobility of about 0.86 cm 2 V −1 s −1 will be reported, the highest combined values for n-type microcrystalline silicon films, as far as we know.

Improved Resolution in A P-I-N Image Sensor by Changing the Structure of the Doped Layers

Abstract: An amorphous ZnO/p-i-n/Al imager that uses a small-signal scanning beam to read out the short circuit current signal is presented. An analysis of the image geometric distortion, restoration, and enhancement is performed. A simple image-processing algorithm is used to recover main features of projected images. Modifications of the transducer structure are proposed for improving the sensor performance.The effect of the doped layers and image intensity on the sensor output characteristics are analysed. Results show that a trade-off between the sensor structure and contact geometry is needed for a correct read-out. Algorithms and tools are proposed for image analysis.

Tin doped indium oxide thin films: Electrical properties

Abstract: Tin doped indium oxide (ITO) films are highly transparent in the visible region, exhibiting high reflectance in the infrared region, and having nearly metallic conductivity. Owing to this unusual combination of electrical and optical properties, this material is widely applied in optoelectronic devices. The association of these properties in a single material explains the vast domain of its applicability and the diverse production methods which have emerged. Although the different properties of tin doped indium oxide in the film form are interdependent, this article mainly focuses on the electrical aspects. Detailed description of the conduction mechanism and the main parameters that control the conductivity is presented. On account of the large varieties and differences in the fabrication techniques, the electrical properties of ITO films are discussed and compared within each technique.

Nonthermal Plasma Synthesis of Nanocrystals: Fundamental Principles, Materials, and Applications

Abstract: Nonthermal plasmas have emerged as a viable synthesis technique for nanocrystal materials. Inherently solvent and ligand-free, nonthermal plasmas offer the ability to synthesize high purity nanocrystals of materials that require high synthesis temperatures. The nonequilibrium environment in nonthermal plasmas has a number of attractive attributes: energetic surface reactions selectively heat the nanoparticles to temperatures that can strongly exceed the gas temperature; charging of nanoparticles through plasma electrons reduces or eliminates nanoparticle agglomeration; and the large difference between the chemical potentials of the gaseous growth species and the species bound to the nanoparticle surfaces facilitates nanocrystal doping. This paper reviews the state of the art in nonthermal plasma synthesis of nanocrystals. It discusses the fundamentals of nanocrystal formation in plasmas, reviews practical implementations of plasma reactors, surveys the materials that have been produced with nonthermal pla...

Poly-/metal-benzimidazole nano-composite membranes for hydrogen purification

Abstract: In this study, a novel scheme to fabricate nano-composite membrane materials containing fully dispersed nano-size zeolitic imidazolate frameworks (ZIFs) has been proposed for the first time. By mixing the as-synthesized ZIF-7 nano-particles without the traditional drying process with polybenzimidazole (PBI), the resultant membranes not only achieve an unprecedented ZIF-7 loading as high as 50 wt%, but also overcome the low permeability nature of PBI. The membranes exhibit characteristics of high transparency and mechanical flexibility, together with enhanced H2 permeability and ideal H2/CO2 permselectivity surpassing both neat PBI and ZIF-7 membranes. Advanced instrument analyses have confirmed the unique ZIF–polymer interface and elucidated the mixed matrix structure that contributes to the high ZIF loading and enhanced gas separation performance superior to the prediction from the Maxwell model. The high thermal stability, good dispersion of ZIF nanoparticles with minimal agglomeration and the attractive gas separation performance at elevated temperatures up to 180 °C indicate the practicability of this nano-composite material for hydrogen production and CO2 capture in realistic industrial applications under harsh and extreme environments.

Natural gas purification and olefin/paraffin separation using thermal cross-linkable co-polyimide/ZIF-8 mixed matrix membranes

Abstract: Using three 6FDA-based polyimides (6FDA-Durene, 6FDA-Durene/DABA (9/1), 6FDA-Durene/DABA (7/3)) and nano-size zeolitic imidazolate framework-8 (ZIF-8), we have fabricated mixed matrix membranes (MMMs) with uniform morphology comprising ZIF-8 as high as 40 wt% loading by directly mixing as-synthesized ZIF-8 suspension into the polymer solution. Permeability of all gases (CO 2 , CH 4 , C 3 H 6 , and C 3 H 8 ) increases rapidly with an increase in ZIF-8 loading. However, the addition of ZIF-8 nano-particles into the polymer matrix increases the ideal CO 2 /CH 4 selectivity of only 6.87%, while the ideal C 3 H 6 /C 3 H 8 selectivity improves 134% from 11.68 to 27.38 for the MMM made of 6FDA-Durene/DABA (9/1) and 40 wt% ZIF-8. Experimental data show that the plasticization resistance and gas pair selectivity of MMMs are strongly dependent on the amount of cross-linkable moiety and annealing temperature. MMMs made of 6FDA-Durene do not show considerable improvements on resistance against CO 2 -induced plasticization after annealing at 200–400 °C, while MMMs synthesized from cross-linkable co-polyimides (6FDA-Durene/DABA (9/1) and 6FDA-Durene/DABA (7/3)) show significant enhancements in CO 2 /CH 4 and C 3 H 6 /C 3 H 8 selectivity as well as plasticization suppression characteristics up to a CO 2 pressure of 30 atm after annealing at 400 °C due to the cross-linking reaction of the carboxyl acid (COOH) in the DABA moiety. The MMM made of 6FDA-Durene/DABA (9/1) and 40 wt% ZIF-8 possess a notable ideal C 3 H 6 /C 3 H 8 selectivity of 27.38 and a remarkable C 3 H 6 permeability of 47.3 Barrer. After thermally annealed at 400 °C, the MMM made of 6FDA-Durene/DABA (9/1) and 20 wt% ZIF-8 shows a CO 2 /CH 4 selectivity of 19.61 and an impressive CO 2 permeability 728 Barrer in mixed gas tests. The newly developed MMMs may have great potential for industrial nature gas purification and C 3 H 6 /C 3 H 8 separation.

The physics and chemistry of dusty plasmas

Abstract: An overview of the most recent experimental and modelling efforts on powder formation in reactive plasmas is given. The physics and chemistry of these dusty plasmas and their fundamental mechanisms leading to the production of nanometre-sized particles and their successive agglomeration leading to micrometre-sized particles are reviewed. The central role of particle charging and of charge fluctuations regarding the particle agglomeration is emphasised. Finally, the influence of the dust particles on the plasma parameters is described and an outlook on the most eminent problems towards the understanding of the reactive, dusty plasmas is given.