Electric Field Induced Schottky to Ohmic Contact Transition in Fe₃GeTe₂/TMDs Contacts

Although the two-dimensional transition metal dichalcogenides (TMDs) present excellent electrical properties, the contact resistance at the interface of metal/TMDs limits the device performance. Herein, we use 2D metallic Fe3GeTe2 (FGT) as an electrode in contact with TMDs semiconductors MX2 (M = Mo, W; X = S, Se, Te) and investigate the contact properties of FGT/MX2 based on density functional theory calculations. We demonstrated that FGT/MX2 presents n-type Schottky contacts, and their n-type Schottky barrier heights are lower than that of the most common bulk metal contacts with MX2, suggesting that FGT can be used as an efficient metallic electrode for MX2. The transitions from n-type Schottky contact to p-type Schottky contact and from Schottky contact to Ohmic contact can be achieved in FGT/MX2 under the electric field. This work not only illustrates an effective method to modulate the contact types and Schottky barrier heights of FGT/MX2 contacts but also provides a route for designing the nanodevices based on FGT/MX2 electrical contacts

New Insights into Electrochemical Lithiation/Delithiation Mechanism of α‑MoO₃ Nanobelt by in Situ Transmission Electron Microscopy

The α-MoO3 nanobelt has great potential for application as anode of lithium ion batteries (LIBs) because of its high capacity and unique one-dimensional layer structure. However, its fundmental electrochemical failure mechanism during first lithiation/delithiation process is still unclear. Here, we constructed an electrochemical setup within α-MoO3 nanobelt anode inside a transmission electron microscope to observe in situ the mircostructure evolution during cycles. Upon first lithiation, the α-MoO3 nanobelt converted into numerous Mo nanograins within the Li2O matrix, with an obvious size expansion. Interestingly, α-MoO3 nanobelt was found to undergo a two-stage delithiation process. Mo nanograins were first transformed into crystalline Li1.66Mo0.66O2 along with the disappearance of Li2O and size shrink, followed by the conversion to amorphous Li2MoO3. This irreversible phase conversion should be responsible for the large capacity loss in first cycle. In addition, a fully reversile phase conversion between crystalline Mo and amorphous Li2MoO3 was revealed accompanying the formation and disapperance of the Li2O layer during the subsequent cycles. Our experiments provide direct evidence to deeply understand the distinctive electrochemical lithiation/delithiation behaviors of α-MoO3 nanobelt, shedding light onto the development of α-MoO3 anode for LIBs

Fluorine-Ion-Mediated Electrodeposition of Rhombus-Like ZnFOH Nanorod Arrays: An Intermediate Route to Novel ZnO Nanoarchitectures

Novel rhombus-like ZnO nanorod (NR) arrays were achieved via a facile two-step synthesis strategy based on first a low-temperature aqueous electrodeposition of vertically aligned rhombic ZnFOH NR arrays in the presence of fluoride and second a pyrolysis of ZnFOH intermediate into ZnO with the same morphology. The fluorine-ion-mediated electrodeposition mechanism of ZnFOH was confirmed for the first time, and the proposed formation process that the rhombus-like ZnO NRs characterized by mesoporous structure derived from the electrodeposited ZnFOH intermediate was corroborated by systematic structural characterization of the as-prepared products. A dye-sensitized solar cell (DSSC) based on the rhombus-like ZnO NR arrays with a larger surface roughness factor was assembled, and a higher conversion efficiency of 0.69% was attained in comparison to 0.47% of the DSSC based on the hexagon-like ZnO NR arrays electrodeposited in the absence of fluoride. Further, we demonstrate that the unique two-step synthesis strategy also possessed the capability of constructing complex nanoarchitectures with 1D rhombus-like ZnO NRs as the building blocks

New Insights into Electrochemical Lithiation/Delithiation Mechanism of α‑MoO₃ Nanobelt by in Situ Transmission Electron Microscopy

The α-MoO3 nanobelt has great potential for application as anode of lithium ion batteries (LIBs) because of its high capacity and unique one-dimensional layer structure. However, its fundmental electrochemical failure mechanism during first lithiation/delithiation process is still unclear. Here, we constructed an electrochemical setup within α-MoO3 nanobelt anode inside a transmission electron microscope to observe in situ the mircostructure evolution during cycles. Upon first lithiation, the α-MoO3 nanobelt converted into numerous Mo nanograins within the Li2O matrix, with an obvious size expansion. Interestingly, α-MoO3 nanobelt was found to undergo a two-stage delithiation process. Mo nanograins were first transformed into crystalline Li1.66Mo0.66O2 along with the disappearance of Li2O and size shrink, followed by the conversion to amorphous Li2MoO3. This irreversible phase conversion should be responsible for the large capacity loss in first cycle. In addition, a fully reversile phase conversion between crystalline Mo and amorphous Li2MoO3 was revealed accompanying the formation and disapperance of the Li2O layer during the subsequent cycles. Our experiments provide direct evidence to deeply understand the distinctive electrochemical lithiation/delithiation behaviors of α-MoO3 nanobelt, shedding light onto the development of α-MoO3 anode for LIBs

Ultralow Contact Resistance and Efficient Ohmic Contacts in MoGe₂P₄–Metal Contacts

The MoGe2P4 monolayer, an emerging semiconductor with high carrier mobility, can be proposed as a promising channel material in field effect transistors (FETs). The contact resistance between MoGe2P4 and the metal electrode will limit the performance of a realistic FET. Using density functional theory (DFT) calculations, we explore the contact properties of a MoGe2P4 monolayer with six bulk metal electrodes (In, Ag, Au, Cu, Pd, and Pt). It is demonstrated that the Ohmic contacts are formed in all MoGe2P4–metal contacts due to the strong interfacial interactions, suggesting the high carrier injection efficiency. In addition, the MoGe2P4–Cu, −Pd, and −Pt contacts present 100% tunneling probability due to the absence of the tunneling barrier width. The tunneling probabilities of the MGP–In, MGP–Ag, and MGP–Au contacts are exceptionally higher than those of most other 2D semiconductors. Moreover, the tunneling-specific resistivity of all MoGe2P4–metal contacts is relatively low, indicating an ultralow contact resistance and excellent performance. These findings provide a useful guideline to design high-performance MoGe2P4-based electronic devices

Semiconductor to Metal to Half-Metal Transition in Pt-Embedded Zigzag Graphene Nanoribbons

The electronic and magnetic properties of Pt-embedded zigzag graphene nanoribbons (Pt–ZGNRs) are investigated using density-functional theory calculations. It is found that Pt–ZGNRs exhibit a semiconductor–metal–half-metal transition as the position of Pt substitutional impurities in the ribbon changes from the center to edge sites. This behavior can be attributed to the interaction between Pt impurities and edge states of ZGNRs, which governs the electron occupation of the edge states. The transition always occurs independent of ribbon width. However, Pt impurity concentration is important for obtaining this transition. Our results demonstrate that Pt–ZGNRs can be used as versatile electronic devices

Tunable Schottky Barrier and Efficient Ohmic Contacts in MSi₂N₄ (M = Mo, W)/2D Metal Contacts

Monolayer MSi2N4 (M = Mo, W) has been fabricated and proposed as a promising channel material for field-effect transistors (FETs) due to the high electron/hole mobility. However, the barrier between the metal electrode and MSi2N4 will affect device performance. Hence, it is desirable to reduce the barrier for achieving high-performance electrical devices. Here, using density functional theory (DFT) calculations, we systematically investigate the electrical properties of the van der Waals (vdW) contacts formed between MSi2N4 and two-dimensional (2D) metals (XY2, X = Nb, Ta, Y = S, Se, Te). It is found that the contact types and Schottky barrier height (SBH) of MSi2N4/XY2 can be effectively tuned by selecting 2D metals with different work functions (WFs). Specifically, n- and p-type Schottky contacts and Ohmic contacts can be achieved in MSi2N4/XY2. Among them, MoSi2N4/H-NbS2, WSi2N4/H-XS2, and WSi2N4/H-NbSe2 present Ohmic contacts due to the high WF of 2D metals. Notably, the pinning factors of MSi2N4/XY2 are obviously larger than those of the other 2D semiconductor/metal contacts, indicating that the Fermi-level pinning (FLP) effect is weak in MSi2N4/XY2. Therefore, vdW stack engineering can strongly weaken the FLP effect, making the Schottky barrier tunable in MSi2N4/XY2 by choosing 2D metals with different WFs. The results provide important insights into the selection of appropriate electrodes and valuable guidance for the development of MSi2N4-based 2D electronic devices with high performance

New Insights into Electrochemical Lithiation/Delithiation Mechanism of α‑MoO₃ Nanobelt by in Situ Transmission Electron Microscopy

The α-MoO₃ nanobelt has great potential for application as anode of lithium ion batteries (LIBs) because of its high capacity and unique one-dimensional layer structure. However, its fundmental electrochemical failure mechanism during first lithiation/delithiation process is still unclear. Here, we constructed an electrochemical setup within α-MoO₃ nanobelt anode inside a transmission electron microscope to observe in situ the mircostructure evolution during cycles. Upon first lithiation, the α-MoO₃ nanobelt converted into numerous Mo nanograins within the Li₂O matrix, with an obvious size expansion. Interestingly, α-MoO₃ nanobelt was found to undergo a two-stage delithiation process. Mo nanograins were first transformed into crystalline Li_1.66Mo_0.66O₂ along with the disappearance of Li₂O and size shrink, followed by the conversion to amorphous Li₂MoO₃. This irreversible phase conversion should be responsible for the large capacity loss in first cycle. In addition, a fully reversile phase conversion between crystalline Mo and amorphous Li₂MoO₃ was revealed accompanying the formation and disapperance of the Li₂O layer during the subsequent cycles. Our experiments provide direct evidence to deeply understand the distinctive electrochemical lithiation/delithiation behaviors of α-MoO₃ nanobelt, shedding light onto the development of α-MoO₃ anode for LIBs

Enhanced Thermal Stability of Gold and Silver Nanorods by Thin Surface Layers

Using in situ transmission electron microscopy, we find that a carbon shell governs the morphological transitions of gold and silver nanorods upon heating. Encapsulated Ag nanorods show a surprising nonuniform sublimation behavior starting from one side and leaving behind the shell. Uncovered gold nanorods transform their shape to spheres well below the bulk melting temperature through surface diffusion, which is prevented by a thin carbon shell

Synthesis of Dumbbell-Shaped Manganese Oxide Nanocrystals

Dumbbell-like homogeneous MnO nanocrystals are obtained for the first time via the pyrolysis of manganese formate in trioctylamine/oleic acid media and the orientation aggregation mechanism is proposed for this 1D growth route