Light management with quantum nanostructured dots-in-host semiconductors

Insightful knowledge on quantum nanostructured materials is paramount to engineer and exploit their vast gamut of applications. Here, a formalism based on the single-band effective mass equation was developed to determine the light absorption of colloidal quantum dots (CQDs) embedded in a wider bandgap semiconductor host, employing only three parameters (dots/host potential barrier, effective mass, and QD size). It was ascertained how to tune such parameters to design the energy level structure and consequent optical response. Our findings show that the CQD size has the biggest effect on the number and energy of the confined levels, while the potential barrier causes a linear shift of their values. While smaller QDs allow wider energetic separation between levels (as desired for most quantum-based technologies), the larger dots with higher number of levels are those that exhibit the strongest absorption. Nevertheless, it was unprecedently shown that such quantum-enabled absorption coefficients can reach the levels (10⁴-10⁵cm^-1) of bulk semiconductors.

Enhanced solar photocatalysis of TiO2 nanoparticles and nanostructured thin films grown on paper

Titanium dioxide nanoparticles and nanostructured thin films were simultaneously synthesized using a microwave-assisted hydrothermal method. The synthesis formed very fine particles, appearing as nanospheres in the 11 nm size range. As for the nanostructured films, they have displayed similar structural characteristics to the nanoparticles, with thickness of 130 nm. These films covered uniformly and homogenously the Whatman paper, while maintaining its flexibility. The materials processed had their photocatalytic activity assessed from rhodamine B degradation under solar radiation (91% degradation after 40 min for the powder material and 68% after 6 h for the nanostructured thin films). Reusability experiments were also carried out, revealing superior performance concerning the Degussa P25, the most common photocatalyst used. The results of the present work can be thought as an option for the existing photocatalysts activated under solar light, namely for water purification, as it simultaneously produces enhanced photocatalytic powders and photocatalytic papers fully disposable and that can be easily recycled.

Mobile based gold nanoprobe TB diagnostics for point-of-need

Nanotechnology based diagnostics has provided improved tools for pathogen detection and sensitive and specific characterization of antibiotic resistance signatures. Tuberculosis (TB) is caused by members of the Mycobacterium tuberculosis Complex (MTBC) and, according to the World Health Organization, is one of the most serious infectious diseases in the world. Recent advances in molecular diagnostics of TB have improved both the detection time and sensitivity but they still require specialized technical personnel and cumbersome laboratory equipment. Diagnostics at point-of-need is crucial to TB control as it may provide rapid identification of pathogen together with the resistance profile of TB strains, originated from single nucleotide polymorphisms (SNPs) in different loci, allowing for a more accurate indication of the adequate therapy.Gold nanoparticles have been widely used in molecular diagnostics platforms. Here, we describe the use of gold nanoprobes (oligonucleotide functionalized gold nanoparticles) to be used in a non-cross-linking colorimetric method for the direct detection of specific DNA targets. Due to the remarkable optical properties of gold nanoparticles, this detection system provides colorimetric detection of the pathogen together with the potential of identification of several single nucleotide polymorphisms (SNPs) involved in TB resistance to antibiotics. For point-of-need use, we adapted this strategy to a low-cost mobile scheme using a paper based revelation platform and where the spectral signature is transposed to RGB data via a smartphone device. This way, identification of pathogen and characterization of resistance signatures is achieved at point-of-need.

A low cost, safe, disposable, rapid and self-sustainable paper-based platform for diagnostic testing: lab-on-paper

There is a strong interest in the use of biopolymers in the electronic and biomedical industries, mainly towards low-cost applications. The possibility of developing entirely new kinds of products based on cellulose is of current interest, in order to enhance and to add new functionalities to conventional paper-based products. We present our results towards the development of paper-based microfluidics for molecular diagnostic testing. Paper properties were evaluated and compared to nitrocellulose, the most commonly used material in lateral flow and other rapid tests. Focusing on the use of paper as a substrate for microfluidic applications, through an eco-friendly wax-printing technology, we present three main and distinct colorimetric approaches: (i) enzymatic reactions (glucose detection); (ii) immunoassays (antibodies anti-Leishmania detection); (iii) nucleic acid sequence identification (Mycobacterium tuberculosis complex detection). Colorimetric glucose quantification was achieved through enzymatic reactions performed within specific zones of the paper-based device. The colouration achieved increased with growing glucose concentration and was highly homogeneous, covering all the surface of the paper reaction zones in a 3D sensor format. These devices showed a major advantage when compared to the 2D lateral flow glucose sensors, where some carryover of the coloured products usually occurs. The detection of anti-Leishmania antibodies in canine sera was conceptually achieved using a paper-based 96-well enzyme-linked immunosorbent assay format. However, optimization is still needed for this test, regarding the efficiency of the immobilization of antigens on the cellulose fibres. The detection of Mycobacterium tuberculosis nucleic acids integrated with a non-cross-linking gold nanoprobe detection scheme was also achieved in a wax-printed 384-well paper-based microplate, by the hybridization with a species-specific probe. The obtained results with the above-mentioned proof-of-concept sensors are thus promising towards the future development of simple and cost-effective paper-based diagnostic devices.

Nanocrystalline cellulose applied simultaneously as the gate dielectric and the substrate in flexible field effect transistors

Cotton-based nanocrystalline cellulose (NCC), also known as nanopaper, one of the major sources of renewable materials, is a promising substrate and component for producing low cost fully recyclable flexible paper electronic devices and systems due to its properties (lightweight, stiffness, non-toxicity, transparency, low thermal expansion, gas impermeability and improved mechanical properties).Here, we have demonstrated for the first time a thin transparent nanopaper-based field effect transistor (FET) where NCC is simultaneously used as the substrate and as the gate dielectric layer in an 'interstrate' structure, since the device is built on both sides of the NCC films; while the active channel layer is based on oxide amorphous semiconductors, the gate electrode is based on a transparent conductive oxide.Such hybrid FETs present excellent operating characteristics such as high channel saturation mobility (>7 cm(2) V (-1) s(-1)), drain-source current on/off modulation ratio higher than 10(5), enhancement n-type operation and subthreshold gate voltage swing of 2.11 V/decade. The NCC film FET characteristics have been measured in air ambient conditions and present good stability, after two weeks of being processed, without any type of encapsulation or passivation layer. The results obtained are comparable to ones produced for conventional cellulose paper, marking this out as a promising approach for attaining high-performance disposable electronics such as paper displays, smart labels, smart packaging, RFID (radio-frequency identification) and point-of-care systems for self-analysis in bioscience applications, among others.

The influence of fibril composition and dimension on the performance of paper gated oxide transistors

Paper electronics is a topic of great interest due the possibility of having low-cost, disposable and recyclable electronic devices. The final goal is to make paper itself an active part of such devices. In this work we present new approaches in the selection of tailored paper, aiming to use it simultaneously as substrate and dielectric in oxide based paper field effect transistors (FETs). From the work performed, it was observed that the gate leakage current in paper FETs can be reduced using a dense microfiber/nanofiber cellulose paper as the dielectric. Also, the stability of these devices against changes in relative humidity is improved. On other hand, if the pH of the microfiber/nanofiber cellulose pulp is modified by the addition of HCl, the saturation mobility of the devices increases up to 16 cm(2) V(-1) s(-1), with an ION/IOFF ratio close to 10(5).

Enigmatic reticulated filaments in subsurface granite

In the last few years, geomicrobiologists have focused their researches on the nature and origin of enigmatic reticulated filaments reported in modern and fossil samples from limestone caves and basalt lava tubes. Researchers have posed questions on these filaments concerning their nature, origin, chemistry, morphology, mode of formation and growth. A tentative microbial origin has been elusive since these filaments are found as hollow tubular sheaths and could not be affiliated to any known microorganism. We describe the presence of similar structures in a 16th century granite tunnel in Porto, Northwest Portugal. The reticulated filaments we identify exhibit fine geometry surface ornamentation formed by cross-linked Mn-rich nanofibres, surrounded by a large amount of extracellular polymeric substances. Within these Mn-rich filaments we report for the first time the occurrence of microbial cells.

Oxide semiconductor thin-film transistors: a review of recent advances

Transparent electronics is today one of the most advanced topics for a wide range of device applications. The key components are wide bandgap semiconductors, where oxides of different origins play an important role, not only as passive component but also as active component, similar to what is observed in conventional semiconductors like silicon. Transparent electronics has gained special attention during the last few years and is today established as one of the most promising technologies for leading the next generation of flat panel display due to its excellent electronic performance. In this paper the recent progress in n- and p-type oxide based thin-film transistors (TFT) is reviewed, with special emphasis on solution-processed and p-type, and the major milestones already achieved with this emerging and very promising technology are summarizeed. After a short introduction where the main advantages of these semiconductors are presented, as well as the industry expectations, the beautiful history of TFTs is revisited, including the main landmarks in the last 80 years, finishing by referring to some papers that have played an important role in shaping transparent electronics. Then, an overview is presented of state of the art n-type TFTs processed by physical vapour deposition methods, and finally one of the most exciting, promising, and low cost but powerful technologies is discussed: solution-processed oxide TFTs. Moreover, a more detailed focus analysis will be given concerning p-type oxide TFTs, mainly centred on two of the most promising semiconductor candidates: copper oxide and tin oxide. The most recent data related to the production of complementary metal oxide semiconductor (CMOS) devices based on n- and p-type oxide TFT is also be presented. The last topic of this review is devoted to some emerging applications, finalizing with the main conclusions. Related work that originated at CENIMAT|I3N during the last six years is included in more detail, which has led to the fabrication of high performance n- and p-type oxide transistors as well as the fabrication of CMOS devices with and on paper.

Li(+)- and Eu(³+)-doped poly(ε-caprolactone)/siloxane biohybrid electrolytes for electrochromic devices

The sol-gel process has been successfully combined with the "mixed cation" effect to produce novel luminescent and ion conducting biohybrids composed of a diurethane cross-linked poly(ε-caprolactone) (PCL530)/siloxane hybrid network (PCL stands for the poly(ε-caprolactone) biopolymer and 530 is the average molecular weight in gmol(-1)) doped with a wide range of concentrations of lithium and europium triflates (LiCF(3)SO(3) and Eu(CF(3)SO(3))(3), respectively) (molar ratio of ca. 50:50). The hybrid samples are all semicrystalline: whereas at n = 52.6 and 27.0 (n, composition, corresponds to the number of (C(═O)(CH(2))(5)O) repeat units of PCL(530) per mixture of Li(+) and Eu(3+) ions) a minor proportion of crystalline PCL(530) chains is present, at n = 6.1, a new crystalline phase emerges. The latter electrolyte is thermally stable up to 220 °C and exhibits the highest conductivity over the entire range of temperatures studied (3.7 × 10(-7) and 1.71 × 10(-4) S cm(-1) at 20 and 102 °C, respectively). According to infrared spectroscopic data, major modifications occur in terms of hydrogen bonding interactions at this composition. The electrochemical stability domain of the biohybrid sample with n = 27 spans more than 7 V versus Li/Li(+). This sample is a room temperature white light emitter. Its emission color can be easily tuned across the Commission Internationale d'Éclairage (CIE) chromaticity diagram upon simply changing the excitation wavelength. Preliminary tests performed with a prototype electrochromic device (ECD) comprising the sample with n = 6.1 as electrolyte and WO(3) as cathodically coloring layer are extremely encouraging. The device exhibits switching time around 50 s, an optical density change of 0.15, good open circuit memory under atmospheric conditions (ca. 1 month) and high coloration efficiency (577 cm(2) C(-1) in the second cycle).

Next Generation of Thin Film Transistors Based on Zinc Oxide

We report high performance ZnO thin film transistor (ZnO-TFT) fabricated by rf magnetron sputtering at room temperature with a bottom gate configuration. The ZnO-TFT operates in the enhancement mode with a threshold voltage of 19 V, a field effect mobility of 28 cm2/Vs, a gate voltage swing of 1.39 V/decade and an on/off ratio of 3×105. The ZnO-TFT present an average optical transmission (including the glass substrate) of 80 % in the visible part of the spectrum. The combination of transparency, high field-effect mobility and room temperature processing makes the ZnO-TFT a very promising low cost optoelectronic device for the next generation of invisible and flexible electronics.

Nanostructured silicon films produced by PECVD

This paper presents the process conditions that lead to the production of nanostructured silicon films grown by plasma enhanced chemical vapour deposition close to the so-called gamma regime (powder formation), highly dense and with low density of bulk states. Thus, the powder management is one important issue to be addressed in this paper. As a general rule we observed that high quality films (low density of states and high μτ products) are obtained when films are grown under low ion bombardment at high hydrogen dilution and deposition pressure conditions, to allow the proper surface passivation and surface activation.

High Sensitivity Photochemical Sensors Based on Amorphous Silicon

Hydrogenated amoiphous silicon photochemical sensors based on Pd-MIS structures were produced by Plasma Enhanced Chemical Vapor Deposition with two different oxidized surfaces (thermal and chemical oxidation). The behaviour of dark and illuminated current-voltage characteristics in air and in the presence of a hydrogen atmosphere is explained by the changes induced by the gases in the work function of the metal, modifying the electrical properties of the interface. The photochemical sensors produced present more than 2 orders of magnitude variation on the reverse dark current when in presence of 400 ppm hydrogen to which it corresponds a decrease of 45% on the open circuit voltage.

Improvement of the ITO-P Interface in a-Si:H Solar Cells Using a Thin SiO Intermediate Layer

The use of ITO thin films on glass/ITO/p-i-n/metal amorphous silicon solar cells is reviewed. It is suggested a new application for silicon monoxide thin films on the ITO-p interface, as an intermediate layer, to minimize the ITO thin film deterioration process, during the early stage of exposure to a silane plasma rich in hydrogen. The thickness of the silicon monoxide thin films is chosen not to worsen the optical and electrical properties of the ITO thin films. The ITO-p interface is optimized (due to impurities diffusion decrease), leading to an overall improvement of the device performance

Spray-Deposited Metal Oxide Films with Various Properties for Micro- and Optoelectronic Applications: Growth and Characterization

This work reports the structure and electro-optical characteristics of different metal oxide films obtained by spray pyrolysis on heated glass substrates, aiming their application in optoelectronic devices. The results show that this technique leads to thin films with properties ranging from dielectric to degenerate semiconductors, offering the following advantages: simplicity, low cost, high productivity and the possibility of covering large areas, highly important for large area device applications.

Some studies on Molybdenum doped Indium oxide thin films rf sputtered at room temperature

Thin films of molybdenum doped indium oxide (IMO) were rf sputtered onto glass substrates at room temperature. The films were studied as a function of oxygen volume percentage (OVP) ranging 1.4 - 10.0 % in the sputtering chamber. The thickness of the films found varying between 180 and 260 nm. The X-ray diffraction pattern showed the films are polycrystalline with the peaks corresponding to (222) and (400) planes and one among them showing as a preferential orientation. It is observed that the preferred orientation changes from (222) plane to (400) as the OVP increases from 1.4 to 10.0 %. The transmittance spectra were found to be in the range of 77 to 89 %. The optical band gap calculated from the absorption coefficient of transmittance spectra was around 3.9 eV. The negative sign of Hall coefficient confirmed the films were n-type conducting. The bulk resistivity increased from 2.26 × 10−3 to 4.08 × 10−1 Ω−cm for the increase in OVP from 1.4 to 4.1 %, and thereafter increased dramatically so as the Hall coefficients were not detectable. From the AFM morphologies it is evaluated that the RMS roughness of the films ranges from 0.9 to 3.2 nm.

Role of trimethylboron to silane ratio on the properties of p-type nanocrystalline silicon thin film deposited by radio frequency plasma enhanced chemical vapour deposition

Trimethylboron (TMB) has been receiving attention as a valid alternative to diborane and methane mixtures for the deposition of p-type silicon films for applications in optoelectronic devices such as solar cells. In this paper we report on p-type hydrogenated nanocrystalline silicon carbide (nc-Si:C:H) films produced by standard 13.56 MHz plasma enhanced chemical vapour deposition technique, using TMB as gas source, under high hydrogen dilution (98%) and using high deposition pressures (3 Torr). The films obtained were characterized by spectroscopic ellipsometry (SE), Raman spectroscopy (RS), and electrical measurements to determine their optical, structural and electrical properties. We achieved conductivities as high as 8.3 (omega cm)(-1), one of the highest values of conductivity published to date using TMB with standard rf-PECVD. Spectroscopic ellipsometry modeling revealed that the films growth mechanism proceeds through a sub-surface layer mechanism that leads to the formation of nanocrystalline silicon.

Nanostructured silicon based thin film transistors processed in the plasma dark region

Nanostructured silicon (na-Si:H) thin films were fabricated using plasma enhanced chemical vapour deposition (PECVD) technique under high silane hydrogen dilution and a discharge frequency of 27 MHz, where the substrate was located in the dark region of the plasma, protected by a grounded metal grid. By not exposing the growth surface directly to the plasma we avoid the silicon growth surface to sustain a high ion bombardment leading to a less defective surface and highly compact films. The intrinsic films grown under these conditions were used to produce the channel region of thin film transistors (TFTs) with a bottom gate staggered configuration, integrating different dielectric layers. The devices produced exhibit a field effect mobility close to 1.84 cm2 V(-1) s(-1), threshold voltage around 2 V, on/off ratio above 10(7) and sub-threshold slope below 0.5 V/decade, depending on the dielectric used.

Induction of apoptosis in Jurkat cells by photoexcited psoralen derivatives: Implication of mitochondrial dysfunctions and caspases activation

The prevailing form of cell death in lymphocytes exposed to psoralen plus UVA light (PUVA), was investigated. We studied the well known drug 8-methoxypsoralen (8-MOP) and an angular derivatives: angelicin (ANG). We evaluated the induction of apoptosis in a human tumor T-cell line (Jurkat). Both compounds provoke a significant induction of apoptosis at 24h from irradiation as demonstrated by a remarkable percentage of cells Annexin-V positive. We investigated the effects of the psoralen derivatives upon UVA irradiation on the cell cycle. The flow cytometric analysis of propidium labeled cells indicates that treatment induces, in a dose dependent manner, a massive accumulation of cells, for both compounds, in G2-S phase after 24h from the irradiation. We have focused our attention on the mitochondrial functionality after irradiation in the presence of psoralen derivatives. We evaluated, by flow cytometry, (i) the mitochondrial potential (Deltapsi(mt)), (ii) the production of reactive oxygen species (ROS) and (iii) the oxidation of cardiolipin, a phospholipid restricted to the inner mitochondrial membrane. Furthermore the activation of caspases -3, -8 and -9 was also investigated. The obtained data indicated that, upon UVA irradiation, the two compounds induce a strong decrease in mitochondrial functions and activate caspase-3, -8 and -9.

Estimation of single motor unit conduction velocity from surface electromyogram signals detected with linear electrode arrays

This work addresses the problem of estimating the conduction velocity (CV) of single motor unit (MU) action potentials from surface EMG signals detected with linear electrode arrays during voluntary muscle contractions. In ideal conditions, that is without shape or scale changes of the propagating signals and with additive white Gaussian noise, the maximum likelihood (ML) is the optimum estimator of delay. Nevertheless, other methods with computational advantages can be proposed; among them, a modified version of the beamforming algorithm is presented and compared with the ML estimator. In real cases, the resolution in delay estimation in the time domain is limited because of the sampling process. Transformation to the frequency domain allows a continuous estimation. A fast, high-resolution implementation of the presented multichannel techniques in the frequency domain is proposed. This approach is affected by a negligible decrease in performance with respect to ideal interpolation. Application of the ML estimator, based on two-channel information, to ten firings of each of three MUs provides a CV estimate affected by a standard deviation of 0.5 m s(-1); the modified beamforming and ML estimators based on five channels provide a CV standard deviation of less than 0.1 m s(-1) and allow the detection of statistically significant differences between the CVs of the three MUs. CV can therefore be used for MU classification.

Noninvasive estimation of motor unit conduction velocity distribution using linear electrode arrays

Determining the conduction velocity of motor unit action potentials is one of the most important problems in surface electromyography. The estimate of one average conduction velocity value depends on a variety of uncontrollable factors. More meaningful information is obtained from the estimation of the distribution of the different delays in the myoelectric signals. A solution to the problem is the separation and characterization of the individual components propagating at different velocities. A technique, based on surface electrode array recording, is proposed to estimate motor unit conduction velocity distribution. The method consists in the identification of the single action potentials in the time scale domain (with the continuous wavelet transform) and in the estimation of their conduction velocities based on the beamforming algorithm. The performances of the technique have been evaluated using simulated and real myoelectric signals. The results demonstrate that the technique is accurate and reliable. The method may be useful for the diagnosis of neuromuscular disorders, for the monitoring of muscle fatigue and for noninvasive investigation of individual motor units.

Large Area Position Sensitive Detector Based on Amorphous Silicon Technology

We have developed a rectangular dual-axis large area Position Sensitive Detector (PSD), with 5 cm × 5 cm detection area, based on PIN hydrogenated amorphous silicon (a-Si:H) technology, produced by Plasma Enhanced Chemical Vapor Deposition (PECVD). The metal contacts are located in the four edges of the detected area, two of them located on the back side of the ITO/PIN/A1 structure and the others two located in the front side. The key factors of the detectors resolution and linearity are the thickness uniformity of the different layers, the geometry and the contacts location. Besides that, edge effects on the sensor's corner disturb the linearity of the detector. In this paper we present results concerning the linearity of the detector as well as its optoelectronic characteristics and the role of the i-layer thickness on the final sensor performances.