Synthesis, characterization, electronic and gas-sensing properties towards H2 and CO of transparent, large-area, low-layer graphene.

Low-layered, transparent graphene is accessible by a chemical vapor deposition (CVD) technique on a Ni-catalyst layer, which is deposited on a <100> silicon substrate. The number of graphene layers on the substrate is controlled by the grain boundaries in the Ni-catalyst layer and can be studied by micro Raman analysis. Electrical studies showed a sheet resistance (R(sheet)) of approximately 1435 Ω per □, a contact resistance (R(c)) of about 127 Ω, and a specific contact resistance (R(sc)) of approximately 2.8×10(-4) â€…Ω cm(2) for the CVD graphene samples. Transistor output characteristics for the graphene sample demonstrated linear current/voltage behavior. A current versus voltage (I(ds)-V(ds)) plot clearly indicates a p-conducting characteristic of the synthesized graphene. Gas-sensor measurements revealed a high sensor activity of the low-layer graphene material towards H(2) and CO. At 300 °C, a sensor response of approximately 29 towards low H(2) concentrations (1 vol %) was observed, which is by a factor of four higher than recently reported.

In situ and operando spectroscopy for assessing mechanisms of gas sensing.

The mechanistic description of gas sensing on inorganic, organic, and polymeric materials is of great scientific and technological interest. The understanding of surface and bulk reactions responsible for gas-sensing effects will lead to increased selectivity and sensitivity in the chemical determination of gases and thus to the development of better sensors. In recent years, spectroscopic tools have been developed to follow the physicochemical processes taking place in an active sensing element in real time and under operating conditions. Thus, the monitoring of the processes in "living" gas sensors is no longer an unsolvable problem. This Review gives an overview of in situ and operando spectroscopic techniques for the study of gas-sensing mechanisms on solid-state sensors.

Interplay between O2 and SnO2: oxygen ionosorption and spectroscopic evidence for adsorbed oxygen.

Tin dioxide is the most commonly used material in commercial gas sensors based on semiconducting metal oxides. Despite intensive efforts, the mechanism responsible for gas-sensing effects on SnO(2) is not fully understood. The key step is the understanding of the electronic response of SnO(2) in the presence of background oxygen. For a long time, oxygen interaction with SnO(2) has been treated within the framework of the "ionosorption theory". The adsorbed oxygen species have been regarded as free oxygen ions electrostatically stabilized on the surface (with no local chemical bond formation). A contradiction, however, arises when connecting this scenario to spectroscopic findings. Despite trying for a long time, there has not been any convincing spectroscopic evidence for "ionosorbed" oxygen species. Neither superoxide ions O(2)(-), nor charged atomic oxygen O,(-) nor peroxide ions O(2)(2-) have been observed on SnO(2) under the real working conditions of sensors. Moreover, several findings show that the superoxide ion does not undergo transformations into charged atomic oxygen at the surface, and represents a dead-end form of low-temperature oxygen adsorption on reduced metal oxide.

Multisensor system for characterization of packaging emissions: prediction of total solvent amount and odor scores.

This work shows a fast and economic screening of packaging materials for food using a multisensor system. The multisensor system comprises a sampling system (in most cases a headspace sampler), a sensor array, and operation and evaluation electronics. The added value of the inclusion in the sampling system of a separation unit (e.g., chromatographic column) was proved for two different cases. The first is the elimination of a major interfering gas (e.g., water vapor); this was achieved with a short packed polar column that separated water vapor and organic solvents into two peaks. The second case is the extension of the correlation capability to human sensory panels. This was made possible by the use of a long capillary column that separates the high-concentration solvent components, which might not have a strong odorous effect, from the trace odorous ones. The latter are thus detected due to the high sensitivity of the sensor array.

Ambient pressure synthesis of corundum-type IN2O3.

This communication reports the formation of the high-pressure modification of indium (III) oxide (so-called corundum-type or hexagonal In2O3) under ambient pressure. Corundum-type In2O3 was obtained by precipitation from the solution of indium nitrate in methanol by adding concentrated ammonia solution and subsequent calcination of the obtained precipitate at 250-500 degrees C. The role of the impurities and the additives in the stabilization of corundum-type In2O3 is discussed.