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Browsing by Author "Motlag, Maithilee"
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Item Laser Shock Tuning Dynamic Interlayer Coupling in Graphene–Boron Nitride Moiré Superlattices(ACS, 2019) Kumar, Prashant; Liu, Jing; Motlag, Maithilee; Tong, Lei; Hu, Yaowu; Huang, Xinyu; Bandopadhyay, Arkamita; Pati, Swapan K.; Ye, Lei; Irudayaraj, Joseph; Cheng, Gary J.; Physics, School of ScienceIn the emergence of graphene and many two-dimensional (2D) materials, the most exciting applications come from stacking them into 3D devices, promising many excellent possibilities for neoteric electronics and optoelectronics. Layers of semiconductors, insulators, and conductors can be stacked to form van der Waals heterostructures, after the weak bonds formed between the layers. However, the interlayer coupling in these heterostructures is usually hard to modulate, resulting in difficulty to realize their emerging optical or electronic properties. Especially, the relationship between interlayer distance and interlayer coupling remains to be investigated, due to the lack of effective technology. In this work, we have used laser shocking to controllably tune the interlayer distance between graphene (Gr) and boron nitride (BN) in the Gr/BN/Gr heterostructures and the strains in the 2D heterolayers, providing a simple and effective way to modify their optic and electronic properties. After lase shocking, the reduction of interlayer distance is calculated by molecular dynamics (MD) simulation. Some atoms in Gr or BN are out-of-plane as well. In Raman measurements, the G peak in the heterostructure shows a red-shifted trend after laser shocking, indicating the strong phonon coupling in the interlayer. Moreover, the larger transparency after laser shocking also verifies the stronger photon coupling in the heterostructure. To investigate the effects of the interlayer coupling of heterostructure on its out-of-plane electronic behavior, we have investigated the electronic tunneling behavior. The heterostructure after laser shock reveals a lager tunneling current and lower tunneling threshold, proving an unexpected better electrical property. From DFT calculations, laser shocking can modulate the band gap structure of graphene in Gr/BN/Gr heterostructures; therefore, the heterostructures can be implemented as a unique photonic platform to modulate the emission characters of the anchored CdSe/ZnS core–shell quantum dots. Remarkably, the effective laser shocking method is also applicable to various otherwise noninteracting 2D materials, resulting in many new phenomena, which will lead science and technology to unexplored territories.Item Molecular-Scale Nanodiamond with High-Density Color Centers Fabricated from Graphite by Laser Shocking(Elsevier, 2020-05) Motlag, Maithilee; Liu, Xingtao; Nurmalasari, Ni Putu Dewi; Jin, Shengyu; Nian, Qiong; Park, Charles; Jin, Linrui; Huang, Libai; Liu, Jing; Cheng, Gary J.; Physics, School of ScienceNanodiamonds (NDs) with nitrogen vacancy (NV) color centers have the potential for quantum information science and bioimaging due to their stable and non-classical photon emission at room temperature. Large-scale fabrication of molecular-size nanodiamonds with sufficient color centers may economically promote their application in versatile multidisciplinary fields. Here, the manufacture of molecular-size NV center-enriched nanodiamonds from graphite powder is reported. We use an ultrafast laser shocking technique to generate intense plasma, which transforms graphite to nanodiamonds under the confinement layer. Molecular dynamics simulations suggest that the high pressure of 35 GPa and the high temperature of 3,000K result in the metaphase transition of graphite to nanodiamonds within 100 ps. A high concentration of NV centers is observed at the optimal laser energy of 3.82 GW/cm2, at which point molecular-size (∼5 nm) nanodiamonds can individually host as many as 100 NV centers. Consecutive melamine annealing following ultrafast laser shocking enriches the number of NV centers >10-fold and enhances the spontaneous decay rate of the NV center by up to 5 times. Our work may enhance the feasibility of nanodiamonds for applications, including quantum information, electromagnetic sensing, bioimaging, and drug delivery.