Hydrogen sulfide is a toxic, highly corrosive and pollutant gas, but also a key-biomarker in disease diagnosis trough breath analysis. Its detection at very low level is therefore relevant and can be achieved with chemiresistors. The present work proposes a solution consisting in a facile synthesis of CuO-loaded SnO2 hollow nanospheres deposited on interdigitated electrodes (IDEs). Synthesis, chemical and electrical character-ization, deposit process of the sensing layer and gas sensing capabilities of the sensing platform are presented. CuO loaded Sno2 sensing platforms achieved a successful sub-ppm detection at an operating temperature of 100 degrees Celsius.

This work introduces a new measurement methodology for enhancing gas detection by tuning the magnitude and polarity of back-gate voltage of a field-effect transistor (FET)-based sensor. The aim is to simultaneously strengthen the sensor response and accelerate the sensor recovery. In addition, this methodology can consume less energy compared with conventional measurements by direct current bias. To illustrate the benefits of the proposed methodology, we fabricated and characterized a polypyrrole/graphene (PPy/G) FET sensor for ammonia (NH3) detection. Our experiment, simulation and calculation results demonstrated that the redox reaction between the NH3 molecules and the PPy/G sensitive layer could be controlled by altering the polarity and the magnitude of the back-gate voltage. This proof-of-principle measurement methodology, which solves the inherent contradiction between high response and slow recovery of the chemiresistive sensor, could be extended to detect other gases, so as to improve global gas measurement systems. It opens up a new route for FET-based gas sensors in practical applications.

Since the first graphene gas sensor has been reported, functionalized graphene gas sensors have already attracted a lot of research interest due to their potential for high sensitivity, great selectivity, and fast detection of various gases. In this paper, we summarize the recent development and progression of functionalized graphene sensors for ammonia (NH3) detection at room temperature. We review graphene gas sensors functionalized by different materials, including metallic nanoparticles, metal oxides, organic molecules, and conducting polymers. The various sensing mechanism of functionalized graphene gas sensors are explained and compared. Meanwhile, some existing challenges that may hinder the sensor mass production are discussed and several related solutions are proposed. Possible opportunities and perspective applications of the graphene NH3 sensors are also presented.

This work investigates different Al2O3-based dielectric stacks for various applications, including surface passivation of solar cells and photodetectors, replacement of SiO2 gate dielectric in advanced MOSFETs. Ultra-thin Al2O3/SiO2 (3/2 nm) stacks were deposited on silicon by using different techniques. A reference sample with only a single dry-grown SiO2 layer (3 nm) was prepared for comparison purpose. The effective carrier lifetimes were measured by the contactless photoconductance decay method. The lowest surface recombination velocity was calculated to be 34 cm/s in the Al2O3/SiO2 stack. The negative fixed charge density in the stacks was extracted from C-V characteristics. Our results reveal that the effective carrier lifetimes depend on the stacks deposition techniques and conditions, and provide a guideline for optimization.

We report an ammonia (NH3) sensor in which a ultrathin polypyrrole (PPy) layer is synthesized on reduced graphene oxide (rGO) by electropolymerization. The PPy/rGO composite is characterized by scanning electron microscopy, secondary ion mass spectrometry, Raman spectroscopy, and X-ray photoelectron spectroscopy. The sensor exhibits an excellent performance in the selective sensing of NH3 at room temperature, having a high, fast, reversible and linear response. These performances are attributed to the synergistic effect of the ultrathin PPy layer and rGO. Specifically, NH3 molecules are adsorbed on the ultrathin PPy layer, electrons transfer from NH3 to the PPy layer, changing the PPy layer resistance. The ultrathin PPy layer over rGO allows NH3 molecules to pass through and react with sp2-bonded carbon atoms, also changing the rGO resistance. Moreover, the rGO sheets are not only a support material for the ultrathin PPy electropolymerization but also provide an efficient pathway for electron transfer, thereby, accelerating the sensor response and recovery. Meanwhile, the ultrathin PPy layer plays an important role in the sensor selectivity and immunity to humidity. Our research indicates that the post-step PPy electropolymerization is very promising for sensor fabrication and compatible with CMOS technology. These make it possible to design and manufacture the PPy/rGO sensors with integrated circuits onto the same Si wafer for different applications. Importantly, the fabrication method of the present sensor is easy and low cost. Therefore it is regarded as being scalable for mass production of NH3 sensors.

Graphene oxide films were formed using the ultrasonic spray coating method and studied with micro-Raman spectroscopy, atomic force microscopy, and electrical dynamic response of resistance measurements.Effect of different gases (water vapor, ethanol, acetone, ammonia, and isopropyl) on the dynamic response of resistance of the Au / graphene oxide / Au structure has been studied.The dynamic response shows that adsorption of all mentioned gases results in increase of the resistance.For ethanol, acetone and isopropyl adsorption and desorption cycles are almost identical.At the same time, in the case of water vapor and ammonia the cycle of desorption is very week, especially for the former, which attests different mechanisms of adsorption/desorption processes regarding to ethanol, acetone and isopropyl.The mechanisms of studied vapors adsorption/desorption are proposed.

Graphene oxide (GO) and reduced graphene oxide (rGO) films were formed by ultrasonic spray coating method and were studied by micro-Raman spectroscopy (mRS), current-voltage characteristics and impedance spectroscopy. Raman spectra of GO and rGO films shows two typical peaks, with maxima at ~1350 cm-1 and ~1590 cm-1 (D and G bands). One semicircle on the Nyquist curve of gold / graphene oxide / gold structure suggests the existence of homogeneous regions. Adsorption of ethanol, acetone and isopropyl vapors changes electrical conductivity of graphene oxide films in different way. The sensing mechanisms to the organic vapors are discussed.

This chapter will present a brief overview of the current sensors for VOC detection, in particular formaldehyde which has become one of the most problematic gases in indoor air. Many sensing technologies were exploited for this purpose but, in this chapter, we will focus on the impedimetric sensors. These sensors consist in a sensitive layer deposited on an insulating substrate fitted with a pair of electrodes. The detection is based on the change of conductivity of the sensitive layer due to surface interactions with the target gas provoking an electron transfer. This kind of sensor acts as a simple variable resistance and is often called chemiresistor. By principle, these sensors are simple, easy to integrate in classical electronics and cheap. Considering the nature of the sensitive coating, we can distinguish several families: metal oxide sensors, semiconductor polymer sensors or based on graphene. All 3 types of sensors will be described in this chapter.

Graphene decorated by palladium (Pd) nanoparticles has been investigated for hydrogen sensor applications. The density of Pd nanoparticles is critical for the sensor performance. We develop a new chemical method to deposit high-density, small-size and uniformly-distributed Pd nanoparticles on graphene. With this method, Pd precursors are connected to the graphene by π-π bonds without introducing additional defects in the hexagonal carbon lattice. Our method is simple, cheap, and compatible with complementary metal-oxide semiconductor (CMOS) technology. This method is used to fabricate hydrogen sensors on 3-inch silicon wafers. The sensors show high performance at room temperature. Particularly, the sensors present a shorter recovery time under light illumination. The sensing mechanism is explained and discussed. The proposed deposition method facilitates mass fabrication of the graphene sensors and allows integration with CMOS circuits for practical applications.

We report a new hybrid sensor in which an ultrathin polypyrrole (PPy) layer is deposited on the CVD-grown graphene (G) by electropolymerization. The sensor exhibits an excellent performance in the selective sensing of ammonia (NH 3 ) at room temperature, having a high, fast, and reversible response. It also shows rather good stability, reproducibility, and immunity to humidity. These performances are attributed to the synergistic effect between the PPy layer and G. Specifically, the NH 3 molecules are adsorbed on the PPy layer, electrons transfer from NH 3 to the PPy layer, changing the PPy layer resistance. Electrons can also be transferred to the G through the ultrathin PPy layer, in certain way changing the G resistance. These promote the sensor sensitivity. Moreover, the ultrathin PPy layer with porous nature plays an important role in the sensor response, selectivity, and immunity to humidity. Graphene is not only a support material for PPy electropolymerization but also provides an efficient pathway for electron transfer, thereby, accelerating the sensor response and recovery. Our research indicates that the combination of PPy and G is a very promising as a chemical sensor material. We implement a smart prototype with the present sensor in an electronic board for real-time monitoring the NH 3 concentrations. The smart prototype can be connected to a computer by a USB port for demonstrating NH 3 concentrations, transmitting the data and analyzing the sensor response curves. Our results are beneficial forward the commercial design and fabrication of sensors fulfilling the specifications of practical applications.

Objectives The aims of this study were to determine whether the administration of anti-inflammatory and antifibrotic agents affect the proliferation, viability, and expression of markers involved in the fibrotic development of the fibroblasts obtained from arthrofibrotic tissue in vitro, and to evaluate the effect of the agents on arthrofibrosis prevention in vivo. Methods Dexamethasone, diclofenac, and decorin, in different concentrations, were employed to treat fibroblasts from arthrofibrotic tissue (AFib). Cell proliferation was measured by DNA quantitation, and viability was analyzed by Live/Dead staining. The levels of procollagen type I N-terminal propeptide (PINP) and procollagen type III N-terminal propeptide (PIIINP) were evaluated with enzyme-linked immunosorbent assay (ELISA) kits. In addition, the expressions of fibrotic markers were detected by real-time polymerase chain reaction (PCR). Fibroblasts isolated from healthy tissue (Fib) served as control. Further, a rabbit model of joint contracture was used to evaluate the antifibrotic effect of the three different agents. Results Dexamethasone maintained the viability and promoted the proliferation of AFib. Diclofenac decreased the viability and inhibited the cell proliferation during the first week of cultivation. However, decorin inhibited AFib proliferation and downregulated the expressions of fibrotic markers. Additionally, decorin could improve the flexion contracture angle and inhibit the deposition of interstitial matrix components in the rabbit joint model. Conclusion Decorin decreased the expression of myofibroblast markers in AFib, inhibited the proliferation of AFib, and prevented the initial procedure of arthrofibrosis in vivo, suggesting that decorin could be a promising treatment to inhibit the development of arthrofibrosis.

Today, significant attention has been brought to the development of sensitive, specific, cheap, and reliable sensors for real-time monitoring. Molecular imprinting technology is a versatile and promising technology for practical applications in many areas, particularly chemical sensors. Here, we present a chemical sensor for detecting formaldehyde, a toxic common indoor pollutant gas. Polypyrrole-based molecularly-imprinted polymer (PPy-based MIP) is employed as the sensing recognition layer and synthesized on a titanium dioxide nanotube array (TiO2-NTA) for increasing its surface-to-volume ratio, thereby improving the sensor performance. Our sensor selectively detects formaldehyde in the parts per million (ppm) range at room temperature. It also shows a long-term stability and small fluctuation to humidity variations. These are attributed to the thin fishnet-like structure of the PPy-based MIP on the highly-ordered and vertically-aligned TiO2-NTA.

We propose an innovative, easy-to-implement approach to synthesize aligned large-area single-crystalline graphene flakes by chemical vapor deposition on copper foil. This method doubly takes advantage of residual oxygen present in the gas phase. First, by slightly oxidizing the copper surface, we induce grain boundary pinning in copper and, in consequence, the freezing of the thermal recrystallization process. Subsequent reduction of copper under hydrogen suddenly unlocks the delayed reconstruction, favoring the growth of centimeter-sized copper (111) grains through the mechanism of abnormal grain growth. Second, the oxidation of the copper surface also drastically reduces the nucleation density of graphene. This oxidation/reduction sequence leads to the synthesis of aligned millimeter-sized monolayer graphene domains in epitaxial registry with copper (111). The as-grown graphene flakes are demonstrated to be both single-crystalline and of high quality.

The formaldehyde detection is important for protecting human health and controlling environment pollution. Many metal oxide sensors have been developed for the formaldehyde detection in the last decade. The NiO sensor is considered as the most sensitive one, which is able to detect very low concentration of formaldehyde (<1 ppm). But it needs a high operating temperature. Presently, graphene has attracted much attention for sensor applications. Its high surface-to-volume ratio possesses the potential ability to detect the presence of a single interacting molecule and its high carrier mobility ensures low electrical noise and low power consumption. However, pristine graphene is chemically inert and shows weak adsorption of formaldehyde molecules. To obtain stronger adsorption ability, thereby a higher sensitivity, it is necessary to functionalize or pretreat graphene. In this study, we design a new hybrid sensor, in which graphene acts as a highly conductive network and NiO as a sensitive layer for formaldehyde. This hybrid sensor combines the advantages of both materials. Comparing to the pure graphene sensor and the usual NiO sensor, the hybrid sensor demonstrates better sensing performances, such as faster response and recovery, importantly, operating at room temperature. This sensor could be easily integrated with complementary metal oxide semiconductor (CMOS) chip in the future.

Graphene has attracted much attention for sensing applications in recent years. Its largest surface-to-volume ratio makes graphene sensors able to potentially detect a single molecule and its extremely high carrier mobility ensures low electrical noise and energy consumption. However, pristine graphene is chemically inert and weakly adsorbs gas molecules, while defective and/or doped graphene has stronger adsorption ability (high sensitivity). The high sensitivity is related to the increased number of defects or traps in graphene where the gas molecules can be readily grafted, changing the sensor resistance. Nonetheless, similar resistance changes could be induced under exposure to different gases, resulting in a lack of selectivity. Functional groups differ drastically from defects or traps since the former selectively anchor specific molecules. Here, we comparatively investigate three functionalization routes and optimize a defect-free one (2,3,5,6,-Tetrafluorohydroquinone, TFQ molecules) for the fabrication of graphene gas sensors. We use TFQ organic molecules as chemical recognition links between graphene and formaldehyde, the most common indoor pollutant gas. The sensor demonstrates a high response and a good selectivity for formaldehyde compared with interfering organic vapours. Particularly, the sensor has a strong immunity to humidity. Our results highlight that defect-free functionalization based on organic molecules not only increases the sensor’s response but also its selectivity, paving the way to the design of efficient graphene-based sensors.

This paper presents a chemical sensor based on molecularly imprinted polypyrrole for acetaldehyde detection. This molecule belongs to the family of volatile organic compounds (VOC's) and is known for its toxicity. The sensor working principle is the measurement of conductivity variations of polypyrrole films deposited on interdigitated electrodes. The molecularly imprinted polypyrrole (MIP) films are deposited on the electrodes by direct electropolymerization in a bath containing pyrrole monomer, acetonitrile as solvent and acetaldehyde as template. Non imprinted polypyrrole (NIP) films are prepared in the same conditions without template. The behaviour of both films is compared by mass adsorption measurements using a quartz crystal microbalance and impedance measurements as well. The MIP-based sensors show a rapid and reversible response to acetaldehyde in the ppm range while NIP gives an insignificant signal.

Based on micro-Raman spectroscopy (μRS) and X-ray photoelectron spectroscopy (XPS), we study the structural damage incurred in monolayer (1L) and few-layer (FL) graphene subjected to atomic-layer deposition of HfO 2 and Al 2 O 3 upon different oxygen plasma power levels. We evaluate the damage level and the influence of the HfO 2 thickness on graphene. The results indicate that in the case of Al 2 O 3 /graphene, whether 1L or FL graphene is strongly damaged under our process conditions. For the case of HfO 2 /graphene, μRS analysis clearly shows that FL graphene is less disordered than 1L graphene. In addition, the damage levels in FL graphene decrease with the number of layers. Moreover, the FL graphene damage is inversely proportional to the thickness of HfO 2 film. Particularly, the bottom layer of twisted bilayer (t-2L) has the salient features of 1L graphene. Therefore, FL graphene allows for controlling/limiting the degree of defect during the PE-ALD HfO 2 of dielectrics and could be a good starting material for building field effect transistors, sensors, touch screens and solar cells. Besides, the formation of Hf-C bonds may favor growing high-quality and uniform-coverage dielectric. HfO 2 could be a suitable high-K gate dielectric with a scaling capability down to sub-5-nm for graphene-based transistors.

We investigate the structural damage of graphene underlying dielectrics (HfO2 and Al2O3) by remote plasma-enhanced atomic layer deposition (PE-ALD). Dielectric film is grown on bilayer graphene without inducing significant damage to the bottom graphene layer. Based on Raman spectra, we demonstrate that the bottom graphene layer has the salient features of single layer graphene. During the initial half-cycle PE-ALD, the upper graphene layer reacts with the metal precursor, forming uniform nucleation islands or an active metallic carbide layer. After monolayer dielectric coverage, the bottom graphene layer has additional protection. The upper graphene layer serves as a sacrificial layer, which not only promotes the adhesion of dielectric on graphene, but also protects the lattice symmetry of the bottom graphene layer. Our results indicate that bilayer graphene allows for controlling/limiting the degree of defect during the ALD of dielectrics and could be a good starting material for building filed effect transistors and sensing devices.