Two Distinct Stages of Structural Modification of ZIF-L MOF under Electron-Beam Irradiation

Abstract

Metal–organic frameworks (MOFs) are gaining more prominence as low-dielectric materials for applications in electronic devices and sensors using top–down electron-beam patterning. Using a combination of electron diffraction and electron energy-loss spectroscopy (EELS) in a transmission electron microscope, the details of structural modification of ZIF-L MOF under electron-beam irradiation were identified. It was found that the modification of ZIF-L under the electron beam happens in two distinct stages. In addition to the collapse of the original ZIF-L porous framework and loss of crystallinity occurring at the initial low-dose stage, it was observed that the disordered ZIF-L then undergoes a second stage of changes, where the molecular structure of the linker starts to breakdown. Further, it was observed that the degradation of the linker molecules in the second stage of the ZIF-L modification has a considerable impact on its dielectric function, shifting energies of the electronic transitions.

Observation of formation and local structures of metal-organic layers via complementary electron microscopy techniques

“…High-resolution TEM is the most powerful technique for imaging non-periodic local structures of materials 19 , 20 . Unfortunately, MOLs/MOFs are sensitive to electron beam irradiation and their crystalline structure cannot survive during typical TEM imaging 21 – 24 , with a recent report identifying two distinct stages of structural changes in MOFs under electron beam irradiation 25 . Reducing the electron beam effect while maintaining high spatial resolution is an active area of research.…”

Insights into Solid-To-Solid Transformation of MOF Amorphous Phases

“…The ligand integrity is also an important point in our case. In contrast to pyrolysis of MOFs, when the structure itself and the organics undergo thermally stimulated decomposition to carbon, thus forming MOF derivatives, − we have detected for the first time the formation of the solid amorphous nanomaterial based on intact ligands and crystalline metal or metal-oxide nanoparticles. Following the established terminology, , we are not able to designate a new amorphous solid as a glassy or an amorphous MOF.…”

“…Herein, the organic ligands remain intact, and the coordination binding between them and metal clusters is partially retained. In contrast, overcoming the decomposition temperature leads to the formation of amorphous materials − which consist of fully or partially decomposed ligands, carbon, and a wide range of nanoparticles. Herein, no structural integrity and coordination bonds are observed.…”

Mapping short-range order at the nanoscale in metal–organic framework and inorganic glass composites

“…75 Complete loss of long-range order, i.e., loss of Bragg diffraction and resultant structural collapse are typically recorded first (<100 e − Å −2 ). With increasing dose radiolysis is expected to occur in the ZIFs, 76,77 accompanied by electron beam-induced mass loss, primarily in the inorganic glass. 78 To gauge the loss of structural signal, the same area in Fig.…”