| 1. |
- Smith, Anderson D., et al.
(författare)
-
Graphene-based CO2 sensing and its cross-sensitivity with humidity
- 2017
-
Ingår i: RSC Advances. - : Royal Society of Chemistry. - 2046-2069. ; 7:36, s. 22329-22339
-
Tidskriftsartikel (refereegranskat)abstract
- We present graphene-based CO2 sensing and analyze its cross-sensitivity with humidity. In order to assess the selectivity of graphene-based gas sensing to various gases, measurements are performed in argon (Ar), nitrogen (N-2), oxygen (O-2), carbon dioxide (CO2), and air by selectively venting the desired gas from compressed gas bottles into an evacuated vacuum chamber. The sensors provide a direct electrical readout in response to changes in high concentrations, from these bottles, of CO2, O-2, nitrogen and argon, as well as changes in humidity from venting atmospheric air. From the signal response to each gas species, the relative graphene sensitivity to each gas is extracted as a relationship between the percentagechange in graphene's resistance response to changes in vacuum chamber pressure. Although there is virtually no response from O-2, N-2 and Ar, there is a sizeable cross-sensitivity between CO2 and humidity occurring at high CO2 concentrations. However, under atmospheric concentrations of CO2, this cross-sensitivity effect is negligible - allowing for the use of graphene-based humidity sensing in atmospheric environments. Finally, charge density difference calculations, computed using density functional theory (DFT) are presented in order to illustrate the bonding of CO2 and water molecules on graphene and the alterations of the graphene electronic structure due to the interactions with the substrate and the molecules.
|
|
| 2. |
- Smith, Anderson D., et al.
(författare)
-
Graphene-based CO2 sensing and its cross-sensitivity with humidity
- 2017
-
Ingår i: RSC Advances. - : Royal Society of Chemistry. - 2046-2069. ; 7:36, s. 22329-22339
-
Tidskriftsartikel (refereegranskat)abstract
- We present graphene-based CO2 sensing and analyze its cross-sensitivity with humidity. In order to assess the selectivity of graphene-based gas sensing to various gases, measurements are performed in argon (Ar), nitrogen (N2), oxygen (O2), carbon dioxide (CO2), and air by selectively venting the desired gas from compressed gas bottles into an evacuated vacuum chamber. The sensors provide a direct electrical readout in response to changes in high concentrations, from these bottles, of CO2, O2, nitrogen and argon, as well as changes in humidity from venting atmospheric air. From the signal response to each gas species, the relative graphene sensitivity to each gas is extracted as a relationship between the percentage-change in graphene's resistance response to changes in vacuum chamber pressure. Although there is virtually no response from O2, N2 and Ar, there is a sizeable cross-sensitivity between CO2 and humidity occurring at high CO2 concentrations. However, under atmospheric concentrations of CO2, this cross-sensitivity effect is negligible – allowing for the use of graphene-based humidity sensing in atmospheric environments. Finally, charge density difference calculations, computed using density functional theory (DFT) are presented in order to illustrate the bonding of CO2 and water molecules on graphene and the alterations of the graphene electronic structure due to the interactions with the substrate and the molecules.
|
|
| 3. |
- Smith, Anderson D., et al.
(författare)
-
Resistive graphene humidity sensors with rapid and direct electrical readout
- 2015
-
Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3364 .- 2040-3372. ; 7:45, s. 19099-19109
-
Tidskriftsartikel (refereegranskat)abstract
- We demonstrate humidity sensing using a change of the electrical resistance of single-layer chemical vapor deposited (CVD) graphene that is placed on top of a SiO2 layer on a Si wafer. To investigate the selectivity of the sensor towards the most common constituents in air, its signal response was characterized individually for water vapor (H2O), nitrogen (N-2), oxygen (O-2), and argon (Ar). In order to assess the humidity sensing effect for a range from 1% relative humidity (RH) to 96% RH, the devices were characterized both in a vacuum chamber and in a humidity chamber at atmospheric pressure. The measured response and recovery times of the graphene humidity sensors are on the order of several hundred milliseconds. Density functional theory simulations are employed to further investigate the sensitivity of the graphene devices towards water vapor. The interaction between the electrostatic dipole moment of the water and the impurity bands in the SiO(2)d substrate leads to electrostatic doping of the graphene layer. The proposed graphene sensor provides rapid response direct electrical readout and is compatible with back end of the line (BEOL) integration on top of CMOS-based integrated circuits.
|
|
| 4. |
- Bijelovic, Stojanka, et al.
(författare)
-
Wear-resistant magnetic thin film material based on a Ti1−xFexC1−y nanocomposite alloy
- 2010
-
Ingår i: Physical Review B Condensed Matter. - : The American Physical Society. - 0163-1829 .- 1095-3795. ; 81:1, s. 014405-
-
Tidskriftsartikel (refereegranskat)abstract
- In this study we report on the film growth and characterization of thin films deposited on amorphous quartz. The experimental studies have been complemented by first-principles density-functional theory metastable Ti-Fe-C film changes. With increasing annealing time, there is a depletion of iron close to the surface of the film, while regions enriched in iron are simultaneously formed deeper into the film. Both the magnetic ordering temperature and the saturation magnetization changes significantly upon annealing. The DFT calculations show that the critical temperature and the magnetic moment both increase with increasing Fe and C-vacancy concentration. The formation of the metastable iron-rich Ti-Fe-C compound is reflected in the strong increase in the magnetic ordering temperature. Eventually, after enough annealing time nanocrystalline -Fe starts to precipitate, the amount and size of which can be controlled by the annealing procedure; after 20 min of annealing, the experimental results indicate a nanocrystalline iron-film embedded in a wear-resistant TiC compound. This conclusion is further supported by transmission electron microscopy studies on epitaxial Ti-Fe-C films deposited on single-crystalline MgO substrates where, upon annealing, an iron film embedded in TiC is formed. Our results suggest that annealing of metastable Ti-Fe-C films can be used as an efficient way of creating a wear-resistant magnetic thin film material. approximately 50-nm-thick Ti-Fe-CDFT calculations. Upon annealing of as-prepared films, the composition of the10 min, nanocrystalline -Fe starts to precipitate, the amount and size of which can be controlled by the annealing procedure; after 20 min of annealing, the experimental results indicate a nanocrystalline iron-film embedded in a wear-resistant TiC compound. This conclusion is further supported by transmission electron microscopy studies on epitaxial Ti-Fe-C films deposited on single-crystalline MgO substrates where, upon annealing, an iron film embedded in TiC is formed. Our results suggest that annealing of metastable Ti-Fe-C films can be used as an efficient way of creating a wear-resistant magnetic thin film material.
|
|
| 5. |
- Elgammal, Karim, et al.
(författare)
-
Density functional calculations of graphene-based humidity and carbon dioxide sensors : effect of silica and sapphire substrates
- 2017
-
Ingår i: Surface Science. - : Elsevier. - 0039-6028 .- 1879-2758. ; 663, s. 23-30
-
Tidskriftsartikel (refereegranskat)abstract
- We present dispersion-corrected density functional calculations of water and carbon dioxide molecules adsorption on graphene residing on silica and sapphire substrates. The equilibrium positions and bonding distances for the molecules are determined. Water is found to prefer the hollow site in the center of the graphene hexagon, whereas carbon dioxide prefers sites bridging carbon-carbon bonds as well as sites directly on top of carbon atoms. The energy differences between different sites are however minute - typically just a few tenths of a millielectronvolt. Overall, the molecule-graphene bonding distances are found to be in the range 3.1-3.3 (A) over circle. The carbon dioxide binding energy to graphene is found to be almost twice that of the water binding energy (around 0.17 eV compared to around 0.09 eV). The present results compare well with previous calculations, where available. Using charge density differences, we also qualitatively illustrate the effect of the different substrates and molecules on the electronic structure of the graphene sheet.
|
|
| 6. |
|
|
| 7. |
- Hamawandi, Bejan, PhD, et al.
(författare)
-
Composition Tuning of Nanostructured Binary Copper Selenides through Rapid Chemical Synthesis and their Thermoelectric Property Evaluation
- 2020
-
Ingår i: Nanomaterials. - : MDPI. - 2079-4991. ; 10:5
-
Tidskriftsartikel (refereegranskat)abstract
- Reduced energy consumption and environmentally friendly, abundant constituents are gaining more attention for the synthesis of energy materials. A rapid, highly scalable, and process-temperature-sensitive solution synthesis route is demonstrated for the fabrication of thermoelectric Cu2−xSe. The process relies on readily available precursors and microwave-assisted thermolysis, which is sensitive to reaction conditions; yielding Cu1.8Se at 200 °C and Cu2Se at 250 °C within 6–8 min reaction time. Transmission electron microscopy (TEM) revealed crystalline nature of as-made particles with irregular truncated morphology, which exhibit a high phase purity as identified by X-ray powder diffraction (XRPD) analysis. Temperature-dependent transport properties were characterized via electrical conductivity, Seebeck coefficient, and thermal diffusivity measurements. Subsequent to spark plasma sintering, pure Cu1.8Se exhibited highly compacted and oriented grains that were similar in size in comparison to Cu2Se, which led to its high electrical and low thermal conductivity, reaching a very high power-factor (24 µW/K−2cm−1). Density-of-states (DOS) calculations confirm the observed trends in electronic properties of the material, where Cu-deficient phase exhibits metallic character. The TE figure of merit (ZT) was estimated for the materials, demonstrating an unprecedentedly high ZT at 875 K of 2.1 for Cu1.8Se sample, followed by 1.9 for Cu2Se. Synthetic and processing methods presented in this work enable large-scale production of TE materials and components for niche applications.
|
|
| 8. |
- Jansson, Ulf, et al.
(författare)
-
Design of carbide-based nanocomposite thin films by selective alloying
- 2011
-
Ingår i: Surface & Coatings Technology. - : Elsevier BV. - 0257-8972 .- 1879-3347. ; 206:4, s. 583-590
-
Tidskriftsartikel (refereegranskat)abstract
- This paper reviews a series of studies on alloying of sputtered TiC coatings with weak carbide-forming metals, Me, such as Al, Fe, Ni, Pt and Cu. Metastable solid solutions with Me on the Ti sites are easily obtained by magnetron sputtering at low temperatures (< 300 °C). First principles density functional theory (DFT) calculations of such carbides show that a driving force exists to remove carbon from the structure as an alternative and kinetically more favourable route compared to Me precipitation. This leads to a situation where additional control of the phase composition is given by annealing: both direct influence during film growth, as well as through subsequent annealing. Thus, alloying of the nanocomposite with weak carbide-forming metals can be used to tune many mechanical, electric and magnetic properties of a carbide-based nanocomposite film.
|
|
| 9. |
|
|
| 10. |
- Lewin, Erik, et al.
(författare)
-
Design of the Lattice Parameter of Embedded Nanoparticles
- 2010
-
Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 496:1-3, s. 95-99
-
Tidskriftsartikel (refereegranskat)abstract
- It is found that the bonding of nanoparticles in nancomposites can be influenced by interactions with a surrounding matrix phase. A model involving charge transfer between phases is presented, and supported by DFT-simulations. The model explains observations in nanocomposite nc-TiCx/a-C of additional interface states and lattice expansion of TiCx. It is suggested that this approach can be extended to other types of nanocomposites, and that it opens for new possibilities in materials design.
|
|
