What Is Driving the Growth of Inorganic Glass in Smart Materials and Opto-Electronic Devices?

Inorganic glass is a transparent functional material and one of the few materials that keeps leading innovation. In the last decades, inorganic glass was integrated into opto-electronic devices such as optical fibers, semiconductors, solar cells, transparent photovoltaic devices, or photonic crystals and in smart materials applications such as environmental, pharmaceutical, and medical sensors, reinforcing its influence as an essential material and providing potential growth opportunities for the market. Moreover, inorganic glass is the only material that is 100% recyclable and can incorporate other industrial offscourings and/or residues to be used as raw materials. Over time, inorganic glass experienced an extensive range of fabrication techniques, from traditional melting-quenching (with an immense diversity of protocols) to chemical vapor deposition (CVD), physical vapor deposition (PVD), and wet chemistry routes as sol-gel and solvothermal processes. Additive manufacturing (AM) was recently added to the list. Bulks (3D), thin/thick films (2D), flexible glass (2D), powders (2D), fibers (1D), and nanoparticles (NPs) (0D) are examples of possible inorganic glass architectures able to integrate smart materials and opto-electronic devices, leading to added-value products in a wide range of markets. In this review, selected examples of inorganic glasses in areas such as: (i) magnetic glass materials, (ii) solar cells and transparent photovoltaic devices, (iii) photonic crystal, and (iv) smart materials are presented and discussed.

Two-dimensional arrays of vertically packed spin-valves with picoTesla sensitivity at room temperature.

A new device architecture using giant magnetoresistive sensors demonstrates the capability to detect very low magnetic fields on the pT range. A combination of vertically packed spin-valve sensors with two-dimensional in-plane arrays, connected in series and in parallel, delivers a final detection level of 360 pT/[Formula: see text] at 10 Hz at room temperature. The device design is supported by an analytical model developed for a vertically packed spin-valve system, which takes into account all magnetic couplings present. Optimization concerning the spacer thickness and sensor physical dimensions depending on the number of pilled up spin-valves is necessary. To push the limits of detection, arrays of a large number of sensing elements (up to 440,000) are patterned with a geometry that improves sensitivity and in a configuration that reduces the resistance, leading to a lower noise level. The final device performance with pT detectivity is demonstrated in an un-shielded environment suitable for detection of bio-signals.

3D Magnetic Field Reconstruction Methodology Based on a Scanning Magnetoresistive Probe.

The present work provides a detailed description on quantitative 3D magnetic field reconstruction using a scanning magnetoresistance microscopy setup incorporating a 19.5 μm × 2.5 μm magnetoresistive sensor. Therefore, making use of a rotation stage, 11 nm thick ferromagnetic CoFe elements with 20 μm × 5 μm planar size were measured along different sensor axes and converted into cartesian coordinate magnetic field components by use of the analytical coordinate transform equations. The reconstruction steps were followed and validated by numerical simulations based on a field averaging model caused by a non-negligible sensor volume. Detailed in-plane magnetic component reconstruction with ability to reconstruct sub-micrometer features is achieved. A discussion on the limiting factors for optimal resolution is presented.

A Magnetoresistive Tactile Sensor for Harsh Environment Applications.

A magnetoresistive tactile sensor is reported, which is capable of working in high temperatures up to 140 °C. Hair-like bioinspired structures, known as cilia, made out of permanent magnetic nanocomposite material on top of spin-valve giant magnetoresistive (GMR) sensors are used for tactile sensing at high temperatures. The magnetic nanocomposite, consisting of iron nanowires incorporated into the polymer polydimethylsiloxane (PDMS), is very flexible, biocompatible, has high remanence, and is also resilient to antagonistic sensing ambient. When the cilia come in contact with a surface, they deflect in compliance with the surface topology. This yields a change of the GMR sensor signal, enabling the detection of extremely fine features. The spin-valve is covered with a passivation layer, which enables adequate performance in spite of harsh environmental conditions, as demonstrated in this paper for high temperature.

Magnetoresistive nanosensors: controlling magnetism at the nanoscale.

The ability to detect the magnetic fields that surround us has promoted vast technological advances in sensing techniques. Among those, magnetoresistive sensors display an unpaired spatial resolution. Here, we successfully control the linear range of nanometric sensors using an interfacial exchange bias sensing layer coupling. An effective matching of material properties and sensor geometry improves the nanosensor performance, with top sensitivities of 3.7% mT(-1). The experimental results are well supported by 3D micromagnetic and magneto-transport simulations.

Ultra-Compact 100 × 100 µm² Footprint Hybrid Device with Spin-Valve Nanosensors.

Magnetic field mapping with micrometric spatial resolution and high sensitivity is a challenging application, and the technological solutions are usually based on large area devices integrating discrete magnetic flux guide elements. In this work we demonstrate a high performance hybrid device with improved field sensitivity levels and small footprint, consisting of a ultra-compact 2D design where nanometric spin valve sensors are inserted within the gap of thin-film magnetic flux concentrators. Pole-sensor distances down to 400 nm are demonstrated using nanofabrication techniques combined with an optimized liftoff process. These 100 × 100 µm2 pixel sensors can be integrated in modular devices for surface mapping without moving parts.

Ordered arrays of tilted silicon nanobelts with enhanced solar hydrogen evolution performance.

Well-ordered tilted silicon nanobelt arrays have been fabricated over a large area (≥2.5 cm(2)) by metal assisted chemical etching of pre-patterned silicon, which demonstrated markedly enhanced solar hydrogen evolution performance, compared with planar silicon of the same type and previously reported silicon nanowires prepared in a similar way.

A versatile synthesis method of dendrites-free segmented nanowires with a precise size control.

We report an innovative strategy to obtain cylindrical nanowires combining well established and low-cost bottom-up methods such as template-assisted nanowires synthesis and electrodeposition process. This approach allows the growth of single-layer or multi-segmented nanowires with precise control over their length (from few nanometers to several micrometers). The employed techniques give rise to branched pores at the bottom of the templates and consequently dendrites at the end of the nanowires. With our method, these undesired features are easily removed from the nanowires by a selective chemical etching. This is crucial for magnetic characterizations where such non-homogeneous branches may introduce undesired features into the final magnetic response. The obtained structures show extremely narrow distributions in diameter and length, improved robustness and high-yield, making this versatile approach strongly compatible with large scale production at an industrial level. Finally, we show the possibility to tune accurately the size of the nanostructures and consequently provide an easy control over the magnetic properties of these nanostructures.

pH sensitive silica nanotubes as rationally designed vehicles for NSAIDs delivery.

A novel pH-sensitive drug delivery system based on functionalized silica nanotubes was developed for the incorporation of non-steroidal anti-inflammatory drugs (NSAIDs), aimed at a tailored drug release in acidic conditions characteristic of inflamed tissues. Silica nanotubes (SNTs) were synthesized by a nanoporous alumina template assisted sol-gel method. Inner surfaces were physically and chemically modified to improve both the functionalization and subsequent incorporation of the drug. Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and transmission electron microscopy (TEM) were used to characterize the designed nanocarriers and their functionalization. To achieve the highest degree of functionalization, three types of aminosilanes were tested and calcination conditions were optimized. APTES was shown to be the most effective aminosilane regarding the functionalization of the SNTs' inner surface and an adequate calcination temperature (220°C) was found to attain mechanical stability without compromising functionalization efficiency. Finally, the incorporation of naproxen into the nanotubes was accessed by fluorescence measurements and drug release studies were performed, revealing that the electrostatic linkage ensures effective release of the drug in the acidic pH typical of inflamed cells, while maintaining the SNT-drug conjugates stable at the typical bloodstream pH.