Asthma is a chronic disease characterized by recurrent
attacks
of breathlessness and wheezing, which vary in severity and frequency
from person to person. H2S is considered as the biomarker
of asthma. Here, an ultrasensitive chemiresistive H2S gas
sensor based on a γ-Bi2MoO6–CuO
heterostructure with a detection limit of 5 ppb has been fabricated.
It can distinguish asthmatic patients from healthy people roughly
by analyzing the exhaled breaths of 28 asthmatic patients and 28 healthy
people, suggesting that the sensor can be used to assist physicians
in the diagnosis of asthma. Pathologically, it is discovered by this
sensor that with the relief of asthma, the concentration of H2S in one’s exhaled breath gradually increases. This
subtle concentration variation of H2S can be accurately
detected, indicating that this sensor can be used in the asthma severity
monitoring too. Physical models have been built by first-principles
calculation to reveal the causes of the sensor’s ultrasensitivity.
The stable adsorption of H2S on the surface of CuO results
in massive charge transferring and the appearance of the defect states,
which play the major role in the ultrasensitivity of the sensor. Upon
integrating this sensor with circuits, the cheap, smart, and portable
H2S sensing device can be obtained, which can make asthmatic
patients’ access to this device easy and make the severity
monitoring of asthma convenient, especially for children and the aged.
Understanding the chemical states and electronic states of superconducting materials can help researchers to grasp their superconducting mechanisms. Then, through doping, high pressure or other methods, the Tc (Critical Temperature) can be boosted. Recently, a new layered carbide superconductor ThMo2Si2C was discovered. Its chemical states and electronic states are unknown. Here, the chemical states of ThMo2Si2C are investigated using X-ray photoelectron spectroscopy assisted with argon ion sputtering and Raman spectroscopy. The physical significance behind them is elucidated. Its electronic states are investigated by first-principles calculations. It is found that the major contribution to the total DOS (Density of States) is from Mo 4d state, which plays the dominant role in the superconductivity of ThMo2Si2C. The hybridization between Th 6d and Mo 4d is very weak. Thus, a separation of the structure into independent Mo-C-Si and Th subunits (layers) is justified from the point of view of electronic structure. A flat band along the A-M high-symmetry direction is observed near the Fermi level. The influence of the interlayer distance between Mo-C-Si units (layers) on the DOS and band structure is investigated by first-principles calculations too.
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