ABSTRACT
Techniques for scaling-up the direct-current (dc) triboelectricity generation in MoS2 multilayer-based Schottky nanocontacts are vital for exploiting the nanoscale phenomenon for real-world applications of energy harvesting and sensing. Here, we show that scaling-up the dc output can be realized by using various MoS2 multilayer-based heterojunctions including metal/semiconductor (MS), metal/insulator (tens of nanometers)/semiconductor (MIS), and semiconductor/insulator (a few nanometers)/semiconductor (SIS) moving structures. It is shown that the tribo-excited energetic charge carriers can overcome the interfacial potential barrier by different mechanisms, such as thermionic emission, defect conduction, and quantum tunneling in the case of MS, MIS, and SIS moving structures. By tailoring the interface structure, it is possible to trigger electrical conduction resulting in optimized power output. We also show that the band bending in the surface-charged region of MoS2 determines the direction of the dc power output. Our experimental results show that engineering the interface structure opens up new avenues for developing next-generation semiconductor-based mechanical energy conversion with high performance.
ABSTRACT
Apatite fission-track (AFT) analysis, a widely used low-temperature thermochronology method, can provide details of the hydrocarbon generation history of source rocks for use in hydrocarbon exploration. The AFT method is based on the annealing behavior of fission tracks generated by 238U fission in apatite particles during geological history. Due to the cumbersome experimental steps and high expense, it is imperative to find an efficient and inexpensive technique to determinate the annealing degree of AFT. In this study, on the basis of the ellipsoid configuration of tracks, the track volume fraction model (TVFM) is established and the fission-track volume index is proposed. Furthermore, terahertz time domain spectroscopy (THz-TDS) is used for the first time to identify the variation of the AFT annealing degree of Durango apatite particles heated at 20, 275, 300, 325, 450, and 500 â for 10 h. The THz absorbance of the sample increases with the degree of annealing. In addition, the THz absorption index is exponentially related to annealing temperature and can be used to characterize the fission-track volume index. Terahertz time domain spectroscopy can be an ancillary technique for AFT thermochronological research. More work is urgently needed to extrapolate experimental data to geological conditions.
ABSTRACT
In this paper, terahertz time-domain spectroscopy was employed to study the properties of marine kerogen from Western Canada Basin at various temperatures. On the basis of terahertz absorption coefficients of samples, the evolution model of oil and gas generation in kerogen was established, explained, and verified by IR and principal component analysis. In addition, the molecular models of kerogen were simulated by means of the quantum chemistry. Then the vibration characteristics of functional groups in terahertz band were analyzed, and the reasons for different absorptions of kerogen at different temperatures were explained. This study will provide a reference for thermal evolution kinetics of kerogen, as well as an effective complement to the potential evaluation of oil and gas resources.
ABSTRACT
Energy demands have motivated the development of shale formations as significant unconventional reservoirs. The anisotropy of shales plays a significant role in both the mechanical behavior and engineering activities. Alternating layers presented in shales affect the propagation of waves, causing anisotropy at various frequencies. Simplifying the complicated interior structures of shales is conducive to characterize the anisotropic properties. Therefore, simulative shale core samples were designed and fabricated using additive manufacturing processes, and layer-caused dielectric anisotropy was investigated by terahertz (THz) time-domain spectroscopy. On the basis of effective medium theory, the change of the optical length caused by refraction of rays was discussed and modeled. It is believed that the refraction of rays at the interfaces is the source of THz propagation anisotropy in the multilayered structure, and the anisotropy degree is mainly influenced by the layer thickness as well as the refractive index.
ABSTRACT
The study of fluid inclusion is one of the important means to understanding the evolution of mineral crystals, and can therefore provide original information of mineral evolution. In the process of evolution, outside factors such as temperature and pressure, directly affect the number and size of inclusions, and thus are related to the properties of crystals. In this paper, terahertz time-domain spectroscopy (THz-TDS) was used to detect sodium sulfate crystals with different growth temperatures, and absorption coefficient spectra of the samples were obtained. It is suggested that the evolution of sodium sulfate could be divided into two stages, and 80°C was the turning point. X-ray diffraction (XRD) and polarizing microscopy were used to support this conclusion. The research showed that THz-TDS could characterize the evolution of mineral crystals, and it had a unique advantage in terms of crystal evolution.
ABSTRACT
The characterization of fractures is of vital importance for studies in many industries. In the present work, we used terahertz reflection measurements to identify simulated gaps of different widths that resemble fractures. The time interval between pulses (Δt) was proportional to the distance between the interfaces. In addition, fast Fourier transform (FFT) corresponding to the waveforms was also employed to distinguish the gaps. The widths in frequency were found to be inversely proportional to that of the gaps. In general, both terahertz time-domain spectroscopy (THz-TDS) and terahertz frequency-domain spectroscopy (THz-FDS) can achieve the measurement of the gaps of micro size.
ABSTRACT
Understanding the geological units of a reservoir is essential to the development and management of the resource. In this paper, drill cuttings from several depths from an oilfield were studied using terahertz time domain spectroscopy (THz-TDS). Cluster analysis (CA) and principal component analysis (PCA) were employed to classify and analyze the cuttings. The cuttings were clearly classified based on CA and PCA methods, and the results were in agreement with the lithology. Moreover, calcite and dolomite have stronger absorption of a THz pulse than any other minerals, based on an analysis of the PC1 scores. Quantitative analyses of minor minerals were also realized by building a series of linear and non-linear models between contents and PC2 scores. The results prove THz technology to be a promising means for determining reservoir lithology as well as other properties, which will be a significant supplementary method in oil fields.
