Yibin Liu

Growth and humidity-dependent electrical properties of bulk-like MoS2 thin films on Si

Bulk-like molybdenum disulfide (MoS2) thin films were deposited on Si substrates using a dc magnetron sputtering technique and n-MoS2/p-Si junctions were fabricated at room temperature (RT) and 400 °C, respectively. The typical oscillating modes of E12g and A1g were shown in the Raman spectra of the as-grown MoS2 films. Atomic force microscopy illustrated that the surfaces of the films were composed of dense nanoscale grains and scanning electron microscopy revealed the existence of large quantities of pores in the surface. The current–voltage curves of the junctions showed obvious rectifying characteristics due to the energy-band bending near the interface of MoS2/Si. The fabricated junctions exhibited humidity-dependent electrical properties. Compared with the one with the MoS2 film deposited at RT, the junction fabricated at 400 °C showed much more obvious sensing properties to humid gas. In particular, the sensitivity of the device could be tuned by external electrical fields. In the forward voltage range, the currents increased significantly after the junction was exposed to humid conditions. The response increased with increasing voltage and reached a saturated value after V = 1.9 V. The sensing performance featured high sensitivity, fast response and recovery. The junction current in the reverse voltage range decreased under the humid condition. This was contrary to that in the forward voltage range. We also studied the dependence of the sensing response on humidity levels. An almost linear correlation was obtained in the measured range of humidity levels. The sensing mechanisms of the MoS2/Si heterojunction were proposed.

Self-powered photosensing characteristics of amorphous carbon/silicon heterostructures

Amorphous carbon (a-C) thin films are deposited on p-type silicon (Si) substrates using magnetron sputtering technique and the photodetector devices based on the a-C/Si heterostructures are fabricated. The photosensing characteristics of the devices are investigated. Under light irradiation, the fabricated a-C/Si device exhibits obvious photovoltaic characteristics. This enables its application as a self-powered photodetector operated at zero bias voltage. The obtained results show that the device is highly sensitive to broadband wavelength from the ultraviolet to near-infrared light, showing a high detectivity of ∼2.9 × 1013 cm Hz1/2 W−1, as well as a high responsitivity of ∼292.5 mA W−1, and a fast response speed of ∼8.3 μs. The mechanisms to the self-powered photosensing characteristics are clarified by the determination of the energy-band alignment near the interface of the a-C/Si heterostructures.

Enhanced photovoltaic characteristics of MoS2/Si hybrid solar cells by metal Pd chemical doping

MoS2/Si hybrid solar cells are fabricated and the device performances are improved via metal Pd chemical doping. Due to the incorporation of the Pd atoms in the MoS2 films, the photovoltaic characteristics of the solar cell are enhanced significantly and a 375% enhancement of the power conversion efficiency can be obtained.

Insights into the effect of surface functional groups on catalytic performance for hydrogen generation from sodium borohydride

Sodium borohydride hydrolysis to generate hydrogen has great potential for mobile and portable applications, and designing efficient catalysts for this reaction is indispensable. In this work, the effect of surface functional groups on hydrogen generation rate (HGR) is investigated using two polystyrene resin supported Pt catalysts. The first type of resin (resin-NH) contains –N(CH3)3OH and abundant –OH groups, while the other one (resin-SH) contains –SO3H and less –OH. After excluding the influences of basicity and Pt loading, it is found that the Pt/resin-NH catalyst exhibits a much higher HGR and lower activation energy compared with the Pt/resin-SH catalyst. Moreover, multiple techniques such as FT-IR, XRD, TEM and XPS are further employed to elucidate the intrinsic mechanism. Compared with the –SO3H group, the –N(CH3)3OH and –OH groups not only facilitate Pt dispersion by enhancing metal–support interaction but also improve the electronic conductivity during hydrolysis by forming electron-enriched Pt active sites.

Correction: Enhanced photovoltaic characteristics of MoS2/Si hybrid solar cells by metal Pd chemical doping

Correction for ‘Enhanced photovoltaic characteristics of MoS2/Si hybrid solar cells by metal Pd chemical doping’ by L. Z. Hao et al., RSC Adv., 2016, 6, 1346–1350.

Adsorption and separation of n/iso-pentane on zeolites: A GCMC study

Separation of branched chain hydrocarbons and straight chain hydrocarbons is very important in the isomerization process. Grand canonical ensemble Monte Carlo simulations were used to investigate the adsorption and separation of iso-pentane and n-pentane in four types of zeolites: MWW, BOG, MFI, and LTA. The computation of the pure components indicates that the adsorption capacity is affected by physical properties of zeolite, like pore size and structures, and isosteric heat. In BOG, MFI and LTA, the amount of adsorption of n-pentane is higher than iso-pentane, while the phenomenon is contrary in MWW. For a given zeolite, a stronger adsorption heat corresponds to a higher loading. In the binary mixture simulations, the separation capacity of n-and iso-pentane increases with the elevated pressure and the increasing iso-pentane composition. The adsorption mechanism and competition process have been examined. Preferential adsorption contributions prevail at low pressure, however, the size effect becomes important with the increasing pressure, and the relatively smaller n-pentane gradually competes successfully in binary adsorption. Among these zeolites, MFI has the best separation performance due to its high shape selectivity. This work helps to better understand the adsorption and separation performance of n- and iso-pentane in different zeolites and explain the relationship between zeolite structures and adsorption performance.

Effect of Si/Al ratio on tetralin adsorption on Y zeolite: a DFT study

Abstract Probing the adsorption of tetralin on zeolite is of prime scientific and industrial importance with the aim to upgrade the industrial process of tetralin cracking. In this work, the effect of Si/Al ratio ranging from 12 to 39 on tetralin adsorption property on Y zeolite is studied by DFT calculations. Tetralin adsorption on Y zeolite corresponds to a π-stacking adsorption mechanism between double bonds of aromatic ring and Brønsted acid sites. Therefore, the number of Brønsted acid sites influences the adsorption properties. Lower Si/Al ratio with more Brønsted acid sites interacting with the aromatic ring of tetralin leads to a higher adsorption energy. Furthermore, the charge and frontier molecular orbital analysis are also performed to understand the influence of Si/Al ratio on adsorption performance. Y zeolite with lower Si/Al ratio shows larger charge difference values and lower HOMO–LUMO gap, which directly manifests the stronger adsorption ability of tetralin and indicates bigger possibility of reacting.