Yilin Sun

Role of oxygen vacancies in tuning magnetic properties of Co-doped SnO2 insulating films

A series of films deposited under different oxygen partial pressures and annealed under different atmospheres were prepared to investigate the role of oxygen vacancies in tuning magnetic properties of Co-doped SnO2 films. The inclusive Co in SnO2 is in the 2+ state and substitutes for the Sn4+ site. Intrinsic room temperature ferromagnetism is observed in all films, which is not carrier mediated, but coexists with the dielectric behavior. A maximum magnetic moment of 2.37 μB∕Co is achieved by vacuum annealing due to the increase and diffusion of oxygen vacancies rather than the improvement of crystallinity of the film, and the magnetic moment decreases considerably after air annealing or increasing the oxygen partial pressure during deposition. The changes of oxygen vacancy concentration and distribution are indirectly demonstrated by the relative shifts of Co 2p3∕2 peaks in XPS spectra. The band gap of Co-doped SnO2 film is larger than that of pure SnO2 film, suggesting the influence of inclusive Co on t...

A Solution‐Processed High‐Performance Phototransistor based on a Perovskite Composite with Chemically Modified Graphenes

Phototransistors with a structure of a nitrogen-doped graphene quantum dots (NGQDs)-perovskite composite layer and a mildly reduced graphene oxide (mrGO) layer are fabricated through a solution-processing method. This hybrid phototransistor exhibits broad detection range (from 365 to 940 nm), high photoresponsivity (1.92 × 104 A W-1 ), and rapid response to light on-off (≈10 ms). NGQDs offer an effective and fast path for electron transfer from the perovskite to the mrGO, resulting in the improvement of photocurrent and photoswitching characteristics. The high photoresponsivity can also be ascribed to a photogating effect in the device. In addition, the phototransistor shows good stability with poly(methyl methacrylate) encapsulation, and can maintain 85% of its initial performance for 20 d in ambient air.

MoS 2 Field-Effect Transistors With Lead Zirconate-Titanate Ferroelectric Gating

We report back gate field-effect transistors (FETs) with few-layered MoS2 nanosheet controlled by lead-zirconate-titanate (PZT) ferroelectric gating. The MoS2 transistors with PZT gating (MoS2-PZT FETs) exhibit reproducible hysteresis and nonvolatile memory behaviors with high stability, which can be attributed to the polarization screening from interface adsorbates and charge dynamic trapping/detrapping into the interface defect states. The ON/OFF states ratios and memory windows have little change with the channel scaling from 2

Freestanding transparent metallic network based ultrathin, foldable and designable supercapacitors

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Enhancement in magnetic properties of magnesium substituted bismuth ferrite nanoparticles

to 200 nm, revealing the channel scaling has not obvious influence on MoS2-PZT FET properties, which suggests MoS2-PZT FET a promising candidate for future non-volatile memory applications.

Lateral multilayer/monolayer MoS 2 heterojunction for high performance photodetector applications

Fully integrated ultrathin, transparent and foldable energy storage devices are essential for the development of smart wearable electronics, yet typical supercapacitor electrodes are substrate-supported which limits their thickness, transparency and mechanical properties. Employing freestanding transparent electrodes with no substrate support could bring ultrathin, foldable and designable supercapacitors closer to reality. Herein, we report a freestanding, ultrathin ( 84% transmittance) and foldable metallic network electrode, loaded with MnO2 by electrochemical deposition, as a supercapacitor electrode. The freestanding metallic network electrode is fabricated via a simple and low-cost laser direct-writing micro-patterning technique followed by a selective electrodeposition process, where the metallic network patterns, network periods, metal thickness and also the electrode film patterns can be designed for different applications. The obtained freestanding MnO2@Ni network electrode delivers an outstanding areal capacitance of 80.7 mF cm−2 and long-term performance stability (96.3% after 10 000 cycles). Moreover, the symmetric solid-state supercapacitors employing the freestanding MnO2@Ni network electrode not only show high areal capacitance as well as high optical transparency (>80% transmittance), but also can be tailored, attached, folded, rolled up, and crumpled into any object or various shapes with only slight performance degradation. The advent of such freestanding transparent metallic network electrodes may open up a new avenue for realizing fully integrated ultrathin, foldable and designable supercapacitors towards self-powered wearable electronics.

HfO2 dielectric thickness dependence of electrical properties in graphene field effect transistors with double conductance minima

We report a potential way to effectively improve the magnetic properties of BiFeO3 (BFO) nanoparticles through Mg2+ ion substitution at the Fe-sites of BFO lattice. The high purity and structural changes induced by Mg doping are confirmed by X-ray powder diffractometer and Raman spectra. Enhanced magnetic properties are observed in Mg substituted samples, which simultaneously exhibit ferromagnetic and superparamagnetic properties at room temperature. A physical model is proposed to support the observed ferromagnetism of Mg doped samples, and the superparamagnetic properties are revealed by the temperature dependent magnetization measurements. The improved magnetic properties and soft nature obtained by Mg doping in BFO nanoparticles demonstrate the possibility of BFO nanoparticles to practical applications.

Adjustable hydrazine modulation of single-wall carbon nanotube network field effect transistors from p-type to n-type

Inspired by the unique, thickness-dependent energy band structure of 2D materials, we study the electronic and optical properties of the photodetector based on the as-exfoliated lateral multilayer/monolayer MoS2 heterojunction. Good gate-tunable current-rectifying characteristics are observed with a rectification ratio of 103 at Vgs = 10 V, which may offer an evidence on the existence of the heterojunction. Upon illumination from ultraviolet to visible light, the multilayer/monolayer MoS2 heterojunction shows outstanding photodetective performance, with a photoresponsivity of 103 A/W, a photosensitivity of 1.7 × 105 and a detectivity of 7 × 1010 Jones at 470 nm light illumination. Abnormal photoresponse under positive gate voltage is observed and analyzed, which indicates the important role of the heterojunction in the photocurrent generation process. We believe that these results contribute to a better understanding on the fundamental physics of band alignment for multilayer/monolayer MoS2 heterojunction and provide us a feasible solution for novel electronic and optoelectronic devices.

Poly (ethylene imine)-modulated transport behaviors of graphene field effect transistors with double Dirac points

We investigate the electrical properties in back-gated graphene field effect transistors (GFETs) with SiO2 dielectric and different thickness of high-k HfO2 dielectric. The results show that transform characteristic (Ids–Vgs) curves of GFETs are uniquely W-shaped with two charge neutrality point (left and right) in both SiO2 and HfO2 dielectric (SiO2-GFETs and HfO2-GFETs). The gate voltage reduces drastically in HfO2-GFETs compared with that in SiO2-GFETs, and it becomes much smaller with the decline of HfO2 thickness. The left charge neutrality point in Id–Vg curves of all HfO2-GFETs is negative, compared to the positive ones in SiO2-GFETs, which means that there exists n-doping in graphene with HfO2 as bottom dielectric. We speculate that this n-doping comes from the HfO2 layer, which brings fixed charged impurities in close proximity to graphene. The carrier mobility is also researched, demonstrating a decreasing trend of hole mobility in HfO2-GFETs contrast to that in SiO2-GFETs. In a series of HfO2-G...

Controllable Hysteresis and Threshold Voltage of Single-Walled Carbon Nano-tube Transistors with Ferroelectric Polymer Top-Gate Insulators.

Single-wall carbon nanotube (SWCNT) network field effect transistors (FETs), which show decent p-type electronic properties, have been fabricated. The use of hydrazine as an aqueous solution and a strong n-type dopant for the SWCNTs is demonstrated in this paper. The electrical properties are obviously tuned by hydrazine treatment at different concentrations on the surface of the SWCNT network FETs. The transport behavior of SWCNTs can be modulated from p-type to n-type, demonstrating the controllable and adjustable doping effect of hydrazine. With a higher concentration of hydrazine, more electrons can be transferred from the hydrazine molecules to the SWCNT network films, thus resulting in a change of threshold voltage, carrier mobility and on-current. By cleaning the device, the hydrazine doping effects vanish, which indicates that the doping effects of hydrazine are reversible. Through x-ray photoelectron spectroscopy (XPS) characterization, the doping effects of hydrazine have also been studied.