Fan Sun

Bio: Fan Sun is an academic researcher from University of Science and Technology Beijing. The author has contributed to research in topics: Magnetic susceptibility & Intercalation (chemistry). The author has an hindex of 6, co-authored 14 publications receiving 82 citations.

Chemical Intercalations in Layered Transition Metal Chalcogenides: Syntheses, Structures, and Related Properties

Abstract: Transition metal chalcogenides (TMChs) have recently attracted a great deal of interest in the chemical and physical research fields. These compounds have a common crystal structure: they usually consist of two-dimensional or quasi-two-dimensional layers stacked along the direction perpendicular to the layers. The combination between layers is generally by van der Waals interaction or weak chemical bonding, making the layered chalcogenides potential hosts for intercalation. Alkali metals, alkaline earths, rare earths, and organic groups or compounds can be intercalated into the structure as spacing layers, resulting in a variety of new compounds and exhibiting interesting physical and chemical properties. In this review, we introduce and summarize the latest advances in chemical intercalation and the role of these spacing layers in TMChs, and their relation to relevant properties. Especially, we focus on the developments of chemical intercalation in Fe chalcogenide superconductors to understand the effect...

KFeCuTe2: a new compound to study the removal of interstitial Fe in layered tellurides

Abstract: A single crystal of a new layered telluride KFeCuTe2 has been successfully synthesized by the self-flux method, which is formed by intercalating K in the parent telluride Fe1+xCuTe2. This new compound crystallizes in the space group I4/mmm with the interstitial Fe in pristine Fe1+xCuTe2 completely removed after K intercalation. X-ray photoelectron spectroscopy (XPS) shows that after intercalation, the valence of Fe switched from a mixture of +2 and +3 to the single trivalent one. The KFeCuTe2 is a Mott semiconductor (Eg = 1.06 eV) with a larger resistivity than that of Fe1+xCuTe2 due to the absence of electron doping from interstitial Fe atoms. Most importantly, the magnetic susceptibility shows the antiferromagnetic transition in KFeCuTe2 at 60 K, instead of the spin-glass behavior in Fe1+xCuTe2, indicating the crucial role of interstitial Fe in breaking the long-range magnetic ordering. Our work provides a new compound to study the effect of interstitial Fe on the crystal and magnetic structure in layered tellurides.

Kx(C2H8N2)yFe2−zS2: synthesis, phase structure and correlation between K+ intercalation and Fe depletion

Abstract: We report a new layered FeS compound Kx(C2H8N2)yFe2−zS2 synthesized by intercalating K and C2H8N2 into tetragonal FeS via a simple sonochemical route. This new compound crystallizes in a body-centered tetragonal unit cell, with the [K(C2H8N2)] and [FeS] layers alternately stacking along the c direction. The nominal concentration of K, x, can be adjusted from 0.25 to 0.45, and the lattices a and c contract from 3.6971(9) and 20.667(5) A to 3.691(1) and 20.566(7) A, respectively. When x 0.45, K reacts with FeS directly to form K2Fe4S5 impurity. It is found that the C2H8N2 molecule has been co-intercalated in between the [FeS] layers along with K, evidenced by its content, y, having a linear dependence with x. Measurements indicate that Kx(C2H8N2)yFe2−zS2 is a semiconductor and it shows a weak ferrimagnetism below 50 K. More importantly, Fe depletion resulting from the charged K+ intercalation was revealed by composition analysis, which leads to the formation of disordered Fe vacancies in the [FeS] layers and hence hinders the enhancement of original superconductivity in the FeS parent.

Black Phosphorus Field-effect Transistors

Abstract: Two-dimensional crystals have emerged as a class of materials that may impact future electronic technologies. Experimentally identifying and characterizing new functional two-dimensional materials is challenging, but also potentially rewarding. Here, we fabricate field-effect transistors based on few-layer black phosphorus crystals with thickness down to a few nanometres. Reliable transistor performance is achieved at room temperature in samples thinner than 7.5 nm, with drain current modulation on the order of 10(5) and well-developed current saturation in the I-V characteristics. The charge-carrier mobility is found to be thickness-dependent, with the highest values up to ∼ 1,000 cm(2) V(-1) s(-1) obtained for a thickness of ∼ 10 nm. Our results demonstrate the potential of black phosphorus thin crystals as a new two-dimensional material for applications in nanoelectronic devices.

Chiral magnetic effect in ZrTe 5

Abstract: The chiral magnetic effect is the generation of electric current induced by chirality imbalance in the presence of magnetic field. It is a macroscopic manifestation of the quantum anomaly in relativistic field theory of chiral fermions (massless spin 1/2 particles with a definite projection of spin on momentum) – a dramatic phenomenon arising from a collective motion of particles and antiparticles in the Dirac sea. The recent discovery of Dirac semimetals with chiral quasi-particles opens a fascinating possibility to study this phenomenon in condensed matter experiments. Here we report on the first observation of chiral magnetic effect through the measurement of magneto-transport in zirconium pentatelluride, ZrTe₅. Our angle-resolved photoemission spectroscopy experiments show that this material’s electronic structure is consistent with a 3D Dirac semimetal. We observe a large negative magnetoresistance when magnetic field is parallel with the current. The measured quadratic field dependence of the magnetoconductance is a clear indication of the chiral magnetic effect. Furthermore, the observed phenomenon stems from the effective transmutation of Dirac semimetal into a Weyl semimetal induced by the parallel electric and magnetic fields that represent a topologically nontrivial gauge field background.

Reversed active sites boost the intrinsic activity of graphene‐like cobalt selenide for hydrogen evolution

Abstract: Optimizing the hydrogen adsorption Gibbs free energy (ΔGH ) of active sites is essential to improve the overpotential of the electrocatalytic hydrogen evolution reaction (HER). We doped graphene-like Co0.85 Se with sulfur and found that the active sites are reversed (from cationic Co sites to anionic S sites), which contributed to an enhancement in electrocatalytic HER performance. The optimal S-doped Co0.85 Se composite has an overpotential of 108 mV (at 10 mA cm-2 ) and a Tafel slope of 59 mV dec-1 , which exceeds other reported Co0.85 Se-based electrocatalysts. The doped S sites have much higher activity than the Co sites, with a hydrogen adsorption Gibbs free energy (ΔGH ) close to zero (0.067 eV), which reduces the reaction barrier for hydrogen production. This work provides inspiration for optimizing the intrinsic HER activity of other related transition metal chalcogenides.

Stable Sulfur‐Intercalated 1T′ MoS2 on Graphitic Nanoribbons as Hydrogen Evolution Electrocatalyst

Abstract: The metastable 1T′ polymorph of molybdenum disulfide (MoS2) has shown excellent catalytic activity toward the hydrogen evolution reaction (HER) in water‐splitting applications. Its basal plane exhi ...

One-pot Synthesis of 2D SnS2 Nanorods with High Energy Density and Long Term Stability for High-Performance Hybrid Supercapacitor

Abstract: Two dimensional (2D) microstructure materials have attracted considerable attention due to their short-diffusion path length and large interfacial areas for hybrid supercapacitors (HSCs) in recent years. In the typical layered metal chalcogenides family, tin sulfide (SnS2) is one of the important binary compounds explored for energy storage applications. A reasonable construction of a 2D microstructure for HSCs is proposed. The structural study revealed the nanorods-like morphology with high purity and crystallinity of the sample. The 2D SnS2 nanorods were synthesized through a controlled strategy and tested as an active electrode material for HSCs. The electrochemical properties of SnS2 nanorods were examined through different experimental measurements, including both two- and three-electrode systems. In a three-electrode system, the as-synthesized 2D SnS2 nanorods exhibit superior electrochemical properties with a specific capacitance of (270 F g−1 at 10 mVs−1, and 162.2 F g−1 at 3 A g−1) and excellent cycling stability (9% capacitance loss after 8000 repeated CV cycles), due to efficient ion transport between the electrolyte to the active electrode, and charge transport between electrode and current collector, respectively. More importantly, aqueous HSCs were assembled using 2D SnS2//rGO as positive and negative electrodes operating in a wide and stable potential window up to 1.6 V in 1 M NaOH electrolyte. Moreover, HSCs deliver a high specific capacitance of (108 F g−1 at 5 mVs−1, and 92.4 F g−1 at 1 A g−1), a high specific energy of 32.8 Wh kg−1 along with excellent electrochemical stability (93% retention after 4000 cycles) due to the morphology assisted activity and unique structure of the electrode material. Additionally, we demonstrated the single HSC cell which provided sufficient energy to turn on a red LED of 20 mW and emit light over a certain period of time opens up possible realistic applications. The results manifest that the proposed hydrothermal assisted synthesis has promising applications in producing high-performance energy storage devices.