Construction of Position-Controllable Graphene Bubbles in Liquid Nitrogen with Assistance of Low-Power Laser

Preparation and Modeling of Graphene Bubbles to Obtain Strain-Induced Pseudomagnetic Fields

It has been both theoretically predicted and experimentally demonstrated that strain can effectively modulate the electronic states of graphene sheets through the creation of a pseudomagnetic field (PMF). Pressurizing graphene sheets into bubble-like structures has been considered a viable approach for the strain engineering of PMFs. However, the bubbling technique currently faces limitations such as long manufacturing time, low durability, and challenges in precise control over the size and shape of the pressurized bubble. Here, we propose a rapid bubbling method based on an oxygen plasma chemical reaction to achieve rapid induction of out-of-plane deflections and in-plane strains in graphene sheets. We introduce a numerical scheme capable of accurately resolving the strain field and resulting PMFs within the pressurized graphene bubbles, even in cases where the bubble shape deviates from perfect spherical symmetry. The results provide not only insights into the strain engineering of PMFs in graphene but also a platform that may facilitate the exploration of the strain-mediated electronic behaviors of a variety of other 2D materials.

Polymer curing assisted formation of optically visible sub-micron blisters of multilayer graphene for local strain engineering

The local or global straining techniques are used to modulate the electronic, vibrational and optical properties of the two-dimensional (2D) materials. However, manipulating the physical properties of a 2D material under a local strain is comparatively more challenging. In this work, we demonstrate an easy and efficient polymer curing assisted technique for the formation of optically visible multilayer graphene (MLG) blisters of different shapes and sizes. The detailed spectroscopic and morphological analyses have been employed for exploring the dynamics of the confined matter inside the sub-micron blisters, which confirms that the confined matter inside the blister is liquid (water). From further analyses, we find the nonlinear elastic plate model as an acceptable model under certain limits for the mechanical analyses of the MLG blisters over the (poly)vinyl alcohol (PVA) polymer film to estimate the MLG-substrate interfacial adhesion energy and confinement pressure inside the blisters. The findings open new pathways for exploiting the technique for the formation of sub-micron blisters of the 2D materials for local strain-engineering applications, as well as the temperature-controlled release of the confined matter.

Universal shape of graphene nanobubbles on metallic substrate

Graphene nanobubbles (GNBs) are formed from matter trapped between a two-dimensional material and a substrate. Such structures exhibit a wide range of new fundamental phenomena and are promising for nanoelectronic applications. However, a central part of the synthesis methods leads to the formation of GNBs with undetermined matter composition. Moreover, none of the GNBs' synthesis methods allow one to control the type of trapped matter. In a recent paper [K. M. Zahra, PCCP, 22,7606 (2020)], the authors proposed a new approach that allows the production of GNBs on a copper substrate with pure nitrogen inside in a controlled manner. In this work, we continue this research by studying the geometry of the GNBs in detail and indirectly measuring the internal pressure, which depends on the van der Waals adhesion energy and elastic properties of the graphene membrane. In agreement with other studies, we observe that dome-shaped bubbles exhibit universal scaling law, i.e., constant height to radius ratio. However, the measured height to radius ratio differs significantly from the known results of experiments and computer simulations. This deviation is explained by applying the membrane theory and taking into account the high adhesion of the copper substrate and graphene sheet. The adhesion energy calculated based on experimental data is close to the measurements performed by other experimental techniques.

Metal-Organic Framework-Intercalated Graphene Oxide Membranes for Selective Separation of Uranium

Design and construction of a membrane that can achieve selective separation of uranium from spent fuel or seawater is a big challenge in the field of separation science. In this work, 1,3,5-benzenetricarboxylic acid (BTC) and three different nitrates (Zn/Ni/Cu) were used to prepare metal-organic frameworks (BTC-MOFs) with different pore sizes, and then, BTC-MOFs were intercalated into the interlayers of graphene oxide (GO) for preparing the composite membranes which presented selective separation of uranium with strong acid resistance. Composite membranes prepared by Zn/Ni/Cu-BTC-MOFs and GO can achieve the separation between ions of different valence states, and their permeability and selectivity depend on the membrane thickness, the acidity of driving solution, and the pore sizes of MOFs. Importantly, Cu-BTC-MOF-intercalated GO membranes can not only achieve the selective separation of Th⁴⁺ and UO₂²⁺ with a selectivity of ≈6 but also induce the ultra-high selectively separation of UO₂²⁺ and Ce³⁺ because the rejection rate of Ce³⁺ is about 100%. Moreover, the Zn-BTC-MOF-intercalated GO membrane shows an excellent selectivity of Th⁴⁺ and UO₂²⁺ with a selectivity of ≈25, and it may also achieve selective separation of uranium from seawater.