Nanosized gas sensor elements are potentially faster, require lower power, come with a lower limit of detection, operate at lower temperatures, obviate the need for expensive catalysts, are more heat shock resistant and might even come at a lower cost than their macro-counterparts. In the last two decades, there have been important developments in two key areas that might make this promise a reality. First is the development of a variety of very good performing nanostructured metal oxide semiconductors (MOSs), the most commonly used materials for gas sensing; and second are advances in very low power loss miniaturized heater elements. Advanced nano- or micro–nanogas sensors have attracted much attention owing to a variety of possible applications. In this article, we first discuss the mechanism underlying MOS-based gas sensor devices, then we describe the advances that have been made towards MOS nanostructured materials and the progress towards low-power nano- and microheaters. Finally, we attempt to design an ideal nanogas sensor by combining the best nanomaterial strategy with the best heater implementation. In this regard, we end with a discussion of a suspended carbon nanowire-based gas sensor design and the advantages it might offer compared with other more conventional gas sensor devices.

When certain polymers are heat-treated beyond their degradation temperature in the absence of oxygen, they pass through a semi-solid phase, followed by the loss of heteroatoms and the formation of a solid carbon material composed of a three-dimensional graphenic network, known as glassy (or glass-like) carbon. The thermochemical decomposition of polymers, or generally of any organic material, is defined as pyrolysis. Glassy carbon is used in various large-scale industrial applications and has proven its versatility in miniaturized devices. In this article, micro and nano-scale glassy carbon devices manufactured by (i) pyrolysis of specialized pre-patterned polymers and (ii) direct machining or etching of glassy carbon, with their respective applications, are reviewed. The prospects of the use of glassy carbon in the next-generation devices based on the material’s history and development, distinct features compared to other elemental carbon forms, and some large-scale processes that paved the way to the state-of-the-art, are evaluated. Selected support techniques such as the methods used for surface modification, and major characterization tools are briefly discussed. Barring historical aspects, this review mainly covers the advances in glassy carbon device research from the last five years (2013–2018). The goal is to provide a common platform to carbon material scientists, micro/nanomanufacturing experts, and microsystem engineers to stimulate glassy carbon device research.

Thermochemical decomposition of organic materials under heat-treatment in the absence of oxygen, known as the pyrolysis process, is often employed to convert micro and nano patterned polymers into carbon structures, which are subsequently used as device components. Pyrolysis is performed at ≥900 °C, which entails substrate materials with a high thermal stability that excludes flexible, polymeric substrates. We use optimized laser radiation to pattern graphitic carbon structures onto commercially available polyimide (Kapton) sheets in the micrometer to millimeter scale by inducing a localized, rapid pyrolysis, for the fabrication of flexible devices. Resulting laser carbon films are electrically conductive and exhibit a high-surface area with a hierarchical porosity distribution along their cross-section. The material is obtained using various combinations of laser parameters and pyrolysis environment (oxygen-containing and inert). Extensive characterization of laser carbon is performed to understand the correlation between the material properties and laser parameters, primarily fluence and power. A photothermal carbonization mechanism based on the plume formation is proposed. Further, laser carbon is used for the fabrication of enzymatic, pH-based urea sensors using two approaches: (i) direct urease enzyme immobilization onto carbon and (ii) electrodeposition of an intermediate chitosan layer prior to urease immobilization. This flexible sensor is tested for quantitative urea detection down to 10⁻⁴ M concentrations, while a qualitative, color-indicative test is performed on a folded sensor placed inside a tube to demonstrate its compatibility with catheters. Laser carbon is suitable for a variety of other flexible electronics and sensors, can be conveniently integrated with an external circuitry, heating elements, and with other microfabrication techniques such as fluidic platforms.

Thermally induced chemical decomposition of organic materials in the absence of oxygen is defined as pyrolysis. This process has four major application areas: (i) production of carbon materials, (ii) fabrication of pre-patterned micro and nano carbon-based structures, (iii) fragmentation of complex organic molecules for analytical purposes and (iv) waste treatment. While the underlying process principles remain the same in all cases, the target products differ owing to the phase and composition of the organic precursor, heat-treatment temperature, influence of catalysts and the presence of post-pyrolysis steps during heat-treatment. Due to its fundamental nature, pyrolysis is often studied in the context of one particular application rather than as an independent operation. In this review article, an effort is made to understand each aspect of pyrolysis in a comprehensive fashion, ensuring that all state-of-the-art applications are approached from the core process parameters that influence the ensuing product. Representative publications from recent years for each application are reviewed and analyzed. Some classical scientific findings that laid the foundation of the modern-day carbon material production methods are also revisited. In addition, classification of pyrolysis, its history and nomenclature and the plausible integration of different application areas are discussed.

Fabricating electronic devices from natural, renewable resources is a common goal in engineering and materials science. In this regard, carbon is of special significance due to its biocompatibility combined with electrical conductivity and electrochemical stability. In microelectronics, however, carbon's device application is often inhibited by tedious and expensive preparation processes and a lack of control over processing and material parameters. Laser‐assisted carbonization is emerging as a tool for the precise and selective synthesis of functional carbon‐based materials for flexible device applications. In contrast to conventional carbonization via in‐furnace pyrolysis, laser‐carbonization is induced photo‐thermally and occurs on the time‐scale of milliseconds. By careful selection of the precursors and process parameters, the properties of this so‐called laser‐patterned carbon (LP‐C) such as porosity, surface polarity, functional groups, degree of graphitization, charge‐carrier structure, etc. can be tuned. In this critical review, a common perspective is generated on laser‐carbonization in the context of general carbonization strategies, fundamentals of laser‐induced materials processing, and flexible electronic applications, like electrodes for sensors, electrocatalysts, energy storage, or antennas. An attempt is made to have equal emphasis on material processing and application aspects such that this emerging technology can be optimally positioned in the broader context of carbon‐based microfabrication.