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Elamurugu, E.a, Shanmugam Gonçalves Franco Alves Martins Fortunato P. a G. a. "The electronic transport mechanism in indium molybdenum oxide thin films RF sputtered at room temperature." EPL. 97 (2012). AbstractWebsite

Indium molybdenum oxide (IMO) thin films were radio-frequency (RF) sputtered at room temperature (RT) and studied as a function of base pressure (BP). The crystallinity of the films is decreased with the increase in BP. A maximum mobility (μ) of 49.6 cm 2 V -1 s -1 was obtained from the IMO films deposited at RT without any post-annealing treatment. The electronic behaviour of the deposited films was investigated by temperature-dependent (100-550 K) Hall measurements. Study on the scattering mechanisms based on the experimental data and theoretical models show that the ionized scattering centres are dominating. The films possess wide work function (4.91 eV) and high transmittance (> 70%) over visible and near infrared (NIR) range. The obtained results, especially the high work function and NIR transmittance, are very promising particularly in applications such as optical detectors and solar cells. Copyright © EPLA, 2012.

Martins, R., Ferreira Fortunato I. E. "Electronics with and on paper." Physica Status Solidi - Rapid Research Letters. 5 (2011): 332-335. AbstractWebsite

Today there is a strong interest in the scientific and industrial community concerning the use of biopolymers for electronic applications, driven mainly by low-cost and disposable applications. Adding to this interest, we must recognise the importance of the dream of wireless auto-sustained and low-energy-consumption electronics. This dream can be fulfilled by cellulose paper, the lightest and the cheapest known substrate material, as well as the Earth's major biopolymer and of tremendous global economic importance. Most of the paper used up to now is optimised in terms of the required mechanical and physical properties to be used as the support of inks of different origins. In the future, specific electronic heterogeneous paper sheets should be fabricated aiming to get paper fibers with required bulk and surface functionalities, proper water/vapour barrier, size and diameter/thickness of the fibrils and full paper thickness. This will be the function of components/devices to be incorporated/integrated such as thin-film transistors, complementary metal oxide semiconductor devices, passive electronic components (resistances, inductors and capacitors), memory transistors, electrochromics and thin-film paper batteries. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Gaspar, D.a, Pereira Delattre Guerin Fortunato Martins L. a A. b. "Engineered cellulose fibers as dielectric for oxide field effect transistors." Physica Status Solidi (C) Current Topics in Solid State Physics. 12 (2015): 1421-1426. AbstractWebsite

When thinking on low cost and sustainable electronic systems, paper can be considered as an interesting option to be used as substrate but also as a component of such systems. In this work we have tailored paper samples that were used simultaneously as physical support and dielectric in oxide based paper field effect transistors (FETs). It was observed that the gate leakage current in these devices depends directly from fibril's dimension and arrangement, being lower for micro/nano fibrillated cellulose paper. Moreover, extra ionic charge added to the paper during its production results in the improvement of FETs' electrical properties, with saturation mobility of 16 cm 2V -1s -1 and on/off current ratio close to 105. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Martins, R., Ferreira Águas Silva Fortunato Guimarães I. H. V. "Engineering of a-Si:H device stability by suitable design of interfaces." Solar Energy Materials and Solar Cells. 73 (2002): 39-49. AbstractWebsite

Where a-Si:H pin devices are concerned, one of the main obstacles regarding improved performance is device stability, usually attributed to adverse behaviour at various interfaces within the device. Several attempts have been made to overcome this problem, such as the use of blocking layers at the interfaces. Although these have led to some improvements in device performance, most of the problems associated with device stability remain. This is mainly due to the defects at the interfaces, since the blocking layers (silicon alloys with carbon, nitrogen or oxygen) usually have a high density of bulk states, in comparison to intrinsic a-Si:H films. In this paper, we present a method that seems to be capable of improving device stability. It consists of performing a controlled removal of oxide interlayers at the interfaces, by an appropriate etching process. This enables the production of highly smoothed interfaces, and reduces possible cross-contamination of the i-layer from the adjacent doped layers. This amounts to a new design of typical pin devices, in which thin absorber layers are placed at the p/i and i/n interfaces. Their purpose is to trap most of the impurity atoms diffused from the doped layers, after which they are removed by appropriate etching. The fabrication of the absorbers (sacrificial layers), the nature of the etching and the tailoring of the defect profile at the interfaces will be discussed, including the performance exhibited by the resulting devices. © 2002 Elsevier Science B.V. All rights reserved.

Martins, R., Ferreira Carvalho Guimarães I. N. L. "Engineering of plasma deposition systems used for producing large area a-Si:H devices." Journal of Non-Crystalline Solids. 137-138 (1991): 757-760. AbstractWebsite

One of the main problems in producing large area amorphous silicon devices concerns films uniformity. In this paper we present data concerning the role of reactor geometry and design and on the film performances as well as the problems related to mechanical mismatches in scaling up the reactor size. © 1991 Elsevier Science Publishers B.V. All rights reserved.

Martins, R., Ferreira I. "Engineering of the energy coupling in PECVD systems used to produce large area a-Si:H coatings." Vacuum. 45 (1994): 1107-1108. AbstractWebsite

This paper deals with the engineering aspects related to the rf energy coupling in Plasma Enhanced Chemical Vapour Deposition (PECVD) processes, in a diode-type unit in which an extra grid is used. The main emphasis is given in the determination of the real power delivered to the gas and comparing it with the total power losses, besides determining the best way to control the powder formed during the process. © 1994.

Fortunate, E., Gonçalves De Carvalho Pimentel Lavareda Marques Martins A. C. N. "Enhancement of the electrical properties of ITO deposited on polymeric substrates by using a ZnO buffer layer." Materials Research Society Symposium Proceedings. Vol. 814. 2004. 231-236. Abstract

In this paper we present the effect of the insertion of a non-doped nanocrystalline zinc oxide/buffer layer on the electrical, optical and structural properties of indium tin oxide produced at room temperature by radio frequency plasma enhanced reactive thermal evaporation on polymeric substrates. The electrical resistivity of the ITO films is reduced by more than two orders of magnitude (4.5×10-1 to 2.9×10-3 Ωcm). From the Hall effect measurements it is observed that the large decrease associated to the electrical resistivity, is due to the increase associated to the Hall mobility. Concerning the optical properties no effect was observed, being the transmittance in the visible and near the infra red region always higher than 80%.

Nayak, P.K., Pinto Gonçalves Martins Fortunato J. V. G. "Environmental, optical, and electrical stability study of solution-processed zinc-tin-oxide thin-film transistors." IEEE/OSA Journal of Display Technology. 7 (2011): 640-643. AbstractWebsite

In this paper, we report the environmental, optical, and gate bias stress stability of amorphous zinc-tin-oxide (ZTO) thin-film transistors (TFTs) fabricated by sol-gel spin-coating method. The ZTO TFTs showed excellent environmental and optical stability. The threshold voltage stability of ZTO TFTs was sensitive to both positive and negative gate bias stress. Maximum threshold voltage shifting of +1.9 and -3.2 V was observed under a gate bias stress of +10 and -10 V, respectively, with no significant change to subthreshold swing value. © 2006 IEEE.

b Fortunato, E.a, Figueiredo Barquinha Elamurugu Barros Goņalves Park Hwang Martins V. a P. a. "Erratum: Thin-film transistors based on p-type Cu2 O thin films produced at room temperature (Applied Physics Letters (2010) 96 (192102))." Applied Physics Letters. 96 (2010). AbstractWebsite
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Ferreira, I., Fortunato Martins E. R. "Ethanol vapour detector based in porous a-Si:H films produced by HW-CVD technique." Sensors and Actuators, B: Chemical. 100 (2004): 236-239. AbstractWebsite

In this work, we show the possibility to use undoped porous silicon (PS) thin films produced by hot wire chemical vapour deposition technique (HW-CVD) as ethanol detector. Silicon thins films produced by HW-CVD technique, under certain deposition conditions, have a porous structure [Vacuum 52 (1999) 147]. Therefore, in the presence of an alcohol, the OH group is adsorbed by the uncompensated bonds behaving as donor-like carriers leading to an increase in the current flowing through the material. This current enhancement is bias dependent in glass/ITO/i-a-Si:H/Al sensor and increases as the ethanol vapour pressure increases from 10-1mbar to atmospheric pressure. The response time of the current of the sensor and its recovery time are in the range of 10-50s at room temperature. Ethanol quantities above 50ppm can be detected. © Published by Elsevier B.V.

Topic, M., Smole Furlan Fortunato Martins F. J. E. "Examination of 1-D position sensitive detector performance through analysis of front contact heterojunction." Materials Research Society Symposium - Proceedings. Vol. 420. 1996. 171-176. Abstract

The influence of different TCOs (SnO2 and ITO) on the photoelectrical properties of 1-D position sensitive detectors based on p-i-n structures was studied. A strong cross-contamination in the p-layer and contamination in the i-layer reduce the quality of the device. Numerical analysis of TCO/p-i-n structure also revealed a strong increase in defect states at the p-layer surface which can be attributed to the reduction of TCO. ITO seems to be less appropriate for a front TCO, although the spectral response of the p-i-n structure under reverse bias is not significantly affected by the conditions at the TCO/p heterojunction.

Grimmeiss, H.a, Martins Duart R. b J. M. "Excellence in European universities." Materials Today. 7 (2004): 56-60. AbstractWebsite

The need to improve the efficiency of the European university system is discussed. It is considered possible to increase university funding by letting students pay for their education. It is suggested that European universities raise more money for research from private sources by selling services. It is found appropriate to strive for excellence at the level of specific departments or schools to begin with.

Pinto, J.V.a, Branquinho Barquinha Alves Martins Fortunato R. a P. a. "Extended-gate ISFETs based on sputtered amorphous oxides." IEEE/OSA Journal of Display Technology. 9 (2013): 729-734. AbstractWebsite

We present the results obtained with an extended-gate ISFET totally based on amorphous oxides (GIZO as the semiconductor, +{\hbox{Ta}}-{2}{\hbox{O}}-{5}{\ hbox{:SiO}}-inf2-inf as the dielectric and +{\hbox{Ta}}-{2}{\hbox{O}}-inf5-inf as the sensitive layer). A full characterization of the device was performed with constant ionic strength pH buffer solutions, revealing a sensitivity of 40 mV/pH with small hysteresis, and good linearity in the pH 4-pH 10 range buffer solutions. These results clearly show that it is possible to produce room-temperature disposable and low cost bio-sensors. © 2005-2012 IEEE.

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Prabakaran, R., Fortunato Martins Ferreira E. R. I. "Fabrication and characterization of hybrid solar cells based on copper phthalocyanine/porous silicon." Journal of Non-Crystalline Solids. 354 (2008): 2892-2896. AbstractWebsite

This work refers to the fabrication of hybrid solar cells based on porous silicon (PS) filled with copper phthalocyanine (CuPc) to form GZO/CuPc-PS/Si/Al structure. We used n-type Si since photoinduced charge transfer from CuPc to Si is observed only for n-type Si. The characteristic 100% peak at 6.8°2θ from XRD confirms that the CuPc coating on PS exists in α-CuPc polymorph. The systematic increase in FWHM of XRD peak at 69.1°2θ and red-shift of LO phonon Raman spectra indicate a progressive reduction of Si nanocrystallites size with increasing etching time and the estimated size agrees well with atomic force microscopic images. The FTIR results confirm the formation of α-CuPc polymorph and it is also corroborated well with XRD and Raman results. © 2008.

Águas, H., Marques Martins Fortunato A. R. E. "Fast and cheap method to qualitatively measure the thickness and uniformity of ZrO2 thin films." Materials Science in Semiconductor Processing. 4 (2001): 319-321. AbstractWebsite

This work presents a fast method to determine qualitatively the uniformity and the thickness of transparent or semitransparent thin films in the visible to near-infrared region. The method proposed is based on the information recorded by a colour scanner in the form of coloured regions, due to the constructive interferences caused by multibeam wavelength light sources as function of the film thickness and refractive index. The method is well applied in transparent films, where the uniformity cannot be seen by visual inspection. This paper shows that the results obtained for ZrO2 films are satisfactory enabling the application of this technique to determine the films uniformity in fast and cheap way.

c d e Fortunato, E.a b, Pereira Águas Ferreira Martins L. a H. a. "Flexible a-Si: H position-sensitive detectors." Proceedings of the IEEE. 93 (2005): 1281-1286. AbstractWebsite

Flexible and large area (5 mm × 80 mm with an active length of 70 mm) position-sensitive detectors (PSDs) deposited onto polymeric substrates (polyimide - Kapton VN) have been fabricated. The optimized structure presented is based on a heterojunction of amorphous silicon (a-Si: H)/ZnO: Al. The sensors were characterized by spectral response, photocurrent dependence as a function of light intensity, and position detection measurements. The set of data obtained on one-dimensional PSDs based on the heterojunction show excellent performances with a maximum spectral response of 0.12 A/W at 500 nm and a nonlinearity of ±10% over 70-mm length. The produced sensors present a nonlinearity higher than those ones produced on glass substrates, due to the different thermal coefficients exhibited by the polymer and the a-Si: H film. In order to prove this behavior, it was measured the defect density obtained by the constant photocurrent method on a-Si: H thin films deposited on polymeric substrates and bent with different radii of curvature. © 2005 IEEE.

Barquinha, P., Pereira Pereira Wojcik Grey Martins Fortunato S. L. P. "Flexible and Transparent WO3 Transistor with Electrical and Optical Modulation." Advanced Electronic Materials. 1 (2015). AbstractWebsite
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Fortunato, E., Ferreira Giuliani Martins I. F. R. "Flexible large area thin film position sensitive detectors." Sensors and Actuators, A: Physical. 86 (2000): 182-186. AbstractWebsite

Large area thin film position sensitive detectors based on amorphous silicon technology have been prepared on polyimide substrates using the conventional plasma-enhanced chemical vapour deposition. The sensors have been characterized by spectral response, light intensity dependence and linearity measurements in a bent state in order to evaluate the properties in real working conditions. The obtained one-dimensional (1D) position sensors with 10 mm width and 20 mm length present a non-linearity of ±1% which are comparable to the ones produced on glass substrates.

Fortunato, E., Pereira Águas Ferrira Martins L. H. I. "Flexible position sensitive photodetectors based on a-Si:H heterostructures." Sensors and Actuators, A: Physical. 116 (2004): 119-124. AbstractWebsite

This work describes the fabrication and characterization of an improved version of large area (5mm×80mm with an active length of 70mm) flexible position sensitive detectors deposited onto polymeric substrates (polyimide-Kapton® VN). The new configuration presented by the sensor is based on a heterostructure of a-Si:H/ZnO:Al. The sensors were characterized by spectral response, photocurrent dependence as a function of light intensity and position detection measurements. The set of data obtained on one-dimensional position sensitive detectors based on the heterostructure show excellent performances with a maximum spectral response of 0.12A/W at 500nm and a non-linearity of ±10% over 70mm length. The produced sensors present a non-linearity higher than those ones produced on glass substrates, due to the different thermal coefficients exhibited by the polymer and the amorphous silicon film. In order to prove this behaviour, it was measured the defect density obtained by the constant photocurrent method on amorphous silicon deposited on polymeric substrates bended with different radius of curvature. © 2004 Elsevier B.V. All rights reserved.

Martins, R., Pereira Barquinha Correia Gonçalves Ferreira Dias Fortunato L. P. N. "Floating gate memory paper transistor." Proceedings of SPIE - The International Society for Optical Engineering. Vol. 7603. 2010. Abstract

Reported herein is a nonvolatile n-type floating gate memory paper field-effect transistor, emphasizing the role of the paper structure and properties on the device performance recorded such as in the high capacitance per unit area at low frequencies (>2.5 μFcm-2) and so on the set of high charge retention times achieved (>16000 hours). The device was built via the hybrid integration of natural cellulose fibers, which act simultaneously as substrate and gate dielectric, using amorphous indium zinc and gallium indium zinc oxides respectively for the gate electrode and channel layer. This was complemented by the use of continuous patterned metal layers as source/drain electrodes. © 2010 Copyright SPIE - The International Society for Optical Engineering.

Fortunato, N.a, Jang Barquinha Nathan Martins J. b P. a. "Foreword." IEEE/OSA Journal of Display Technology. 9 (2013): 687. AbstractWebsite
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Fortunato, Elvira, Lavareda Guilherme Martins Rodrigo Soares Fernando Fernandes Luis. "From intelligent materials to smart sensors." Proceedings of SPIE - The International Society for Optical Engineering. Vol. 2779. 1996. 269-274. Abstract

A Linear array Thin Film Position Sensitive Detector (LTFPSD) based on hydrogenated amorphous silicon (a-Si:H) is proposed for the first time, taking advantage of the optical properties presented by a-Si:H devices we have developed a LTFPSD with 128 integrated elements able to be used in 3D inspections/measurements. Each element consists on a 1D LTFPSD, based on a p.i.n. diode produced in a conventional PECVD system, where the doped layers are coated with thin resistive layers to establish the required device equipotentials. By proper incorporation of the LTFPSD into an optical inspection camera it will be possible to acquire information about an object/surface, through the optical cross- section method. The main advantages of this system, when compared with the conventional CCDs, are the low complexity of hardware and software used and that the information can be continuously processed (analogue detection).

Fortunato, E., Fernandes Soares Lavareda Martins M. F. G. "From intelligent materials to smart sensors: a-Si:H position sensitive detectors." Materials Research Society Symposium - Proceedings. Vol. 420. 1996. 165-170. Abstract

This work presents the main static and dynamic performances showed by one dimensional thin film position sensitive detectors (1D TFPSD), based on a-Si:H technology, with a size of 80 mm × 5 mm. The results obtained show that the TFPSD is able to respond to light powers as low as 2μ W/cm2, presenting a detection accuracy, linearity and response frequency better than 10 μm, 2% and 2 KHz, respectively. These results are quite promising regarding the application of these sensors to a wide variety of optical inspection systems where continuous quality control is required.

Madan, A.a, Martins R. b. "From materials science to applications of amorphous, microcrystalline and nanocrystalline silicon and other semiconductors." Philosophical Magazine. 89 (2009): 2431-2434. AbstractWebsite

The special Professor Walter E. Spear commemoration issue of the Philosophical Magazine, published in October 2009, contains papers which cover the numerous relevant issues, driven by commercial applications, primarily solar energy and displays. Kocka reviews the complex microstructure of crystallites embedded in the amorphous silicon tissue, the transport mechanism is determined by the conductive grains and influenced by the passivation through H at the grain boundaries. Hugger and co-researchers report on transient photocapacitance spectroscopy and drive-level capacitance profiling as a way of elucidating the fundamental electronic properties of hydrogenated ncSi. Tawada recounts the history of a-Si:H pin heterojunction solar cells, emphasizing the role of the p-type silicon carbide layer in the improvement of the device. Schubert and colleagues focus their work on the production of flexible PV modules with many applications in the architectural arena or integrated into clothing.

Ferreira, I.a, Costa Fortunato Martins M. E. V. b. "From porous to compact films by changing the onset conditions of HW-CVD process." Thin Solid Films. 427 (2003): 225-230. AbstractWebsite

Doped a/μc-Si:H films were produced in different starting deposition conditions by the hot wire chemical vapor deposition technique. In this paper, we show that by changing the initial onset deposition conditions of the process and maintaining the overall pressure, hydrogen dilution and filament temperature, it is possible to control the compactness of the films. As the films nucleation is the key parameter to produce compact films, we show that starting the process with hydrogen and progressively introducing the process gas enhances the compactness and improve the electrical properties of the films produced. © 2002 Elsevier Science B.V. All rights reserved.