In recent years, two-dimensional materials, represented by graphene as the representative and combined by van der Waals forces between layers, have grown into a very large family. These van der Waals materials exhibit various electronic properties ranging from insulators, semiconductors, metals, and superconductors. The transition metal chalcogenides represented by molybdenum disulfide (MoS22) and tungsten disulfide (WS22), due to their suitable band structure and optical properties, have good application prospects in optoelectronic devices and other applications. The two-dimensional material heterojunction is composed of different two-dimensional materials combined by van der Waals forces. The stacking pattern between two layers is easier to control, and thus various electronic properties can be obtained. The process of photo-induced electron-hole pair spatial separation at the interface in a two-dimensional material heterojunction (abbreviated as separation process) plays an important role in many photovoltaic and photovoltaic applications. The heterojunction composed of MoS22 and WS22 is a type II heterojunction: the valence band top (VBM) of MoS22 is lower than that of WS22, and the conduction band top (CBM) of WS22 is higher than that of MoS22. Since the band gap of MoS22 is smaller than that of WS22, the electron-hole pair in MoS22 can be selectively excited experimentally. Due to the energy difference, holes excited in the MoS22 are conducted into the WS22 layer, thereby achieving electron-hole separation. Ultrafast laser experiments (F. Wang et al. Nat. Nanotechnol. 2014, 9, 682) found that this separation process can occur at ultrafast time scales of 50fs. It is generally believed that the electron-hole separation process at the interface depends on the inter-layer stacking mode and interlayer interactions of the heterojunction. However, the quantitative relationship between the interlayer stacking mode and the electron-hole separation process has not been resolved. Institute of Physics, Chinese Academy of Sciences/Beijing National Laboratory for Condensed Matter Physics (Group Preparation) SF10 Group Ph.D. students Zhang Jin and Postdoctoral Lian Chao cooperate with professors Liu Kaihui and Hong Hao of Peking University’s Institute of Physics under the guidance of researcher Meng Sheng. First-principles quantum-dynamics simulations of density functionals have investigated in detail the relationship between photo-excited electron-hole pairs in the two-dimensional heterojunctions of MoS22/WS22 and their interlayer stacking patterns (Fig. 1). They found that photo-excited electron-holes can achieve spatial separation around 150 fs for the most stable stacking mode (AB1-2H), and for other stacking modes with similar energy stability (AB2-2H and AA1). -3R) This process will be completed before 1000fs (Figure 2). Further, they found that there is no direct relationship between the separation process and the layer spacing between the two layers of MoS22/WS22 and the overall inter-layer coupling strength, but rather the coupling matrix element in the vertical direction between the two states of the hole states (M )the size of. The electron-hole separation rate (the reciprocal of the separation time) is proportional to the e index of the transition matrix element (Figure 3), indicating that the system is a strongly coupled system beyond the perturbation approximation and can be used to perform extremely fast charge separation processes. Sensitive regulation. This process determines the time response limit of future optoelectronic devices. This provides a new understanding and development basis for ultra-fast optoelectronic devices and high-efficiency photovoltaic applications in two-dimensional material heterojunctions. The related results were published in Advanced Science, 2017, DOI: 10.1002/advs.201700086. This research work was supported by the National Natural Science Foundation of China (Project Grant Nos. 11222431, 11474006, and 51522201) and the Ministry of Science and Technology (Project Grant No. 2016YFA0300903, 2012CB921403, and 2015CB921001).
A steel tape measure is necessary at home. For DIY fanciers, it can tell you how much the material you will need. For constructors, it helps to calculate the space.
The self marking DIY steel tape measure is a professional measuring tool that should be a wonderful addition to your home.
Features
1> Strong Belt Clip and a sling that can be hung for convenient storage
About Materials
The tape measure is made of ABS case covered with TPR, 65Mn steel tape. All the materials are eco-friendly, which pass ROHS and EN-71 tests.
1. Yellow case
About Custom Logo
Custom logo is available.
About Measurements of Scale
Two types of measurements
About Sizes
For Standard sizes we have tape measure in length of 3m/10ft, and in width19mm, also scale with only cm on one side
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2> Rubber case protects the inner mechanism and the tape
3> Bold black number marking in white blade for excellent contrast
Standard case color is yellow. When quantity meets 3000pcs, case colors can be customized according to pantone code.
The tape can be matt or polished, as well as nylon coated tape.
2. Transparent one
3. Yelllow case with rubber, the rubber case protects the whole construction from dirt, impact and abrasion.
4. White auto-lock
5. Yellow round case - with nylon tape
For 1-2 colors logo, we will use silk printing
For full color logo, we will print it with heat transfer printing.
And we also make normal sticker or epoxy plate logo sticker for single color or full color logo
1. cm and inch on one side, tape in yellow with black and red scales
2. cm only on one side, tape in white with black and red scales
5m/16ft*19mm or 5m*19mm, for 5m, we have a wider one ,in width of 25mm
7.5m/25ft*25mm or 7.5m*25mm
8m and 10m, in width of 25mm
We can add magnetic hook at the end of the tape
Strongly coupled ultra-fast charge transfer between van der Waals heterojunctions discovered by physics