Direct Visualization of MOF Film CVD Growth Using a Dual-Heating Zone In Situ TEM Microreactor

Despite the critical role of chemical vapor deposition (CVD) in materials preparation, real-time nanoscale visualization of its processes remains challenging, primarily because conventional single-heating-zone in situ transmission electron microscopy (TEM) reactors cannot faithfully replicate realistic precursor vaporization and deposition conditions. Here, we present the TempTwin CVD-Reactor, a dual-heating-zone gas-phase in situ TEM chip that precisely integrates independently controlled source and deposition regions. Leveraging ultrathin silicon nitride windows, this device achieves angstrom-level resolution up to 900 °C, enabling direct visualization of metal-organic framework (MOF) film growth kinetics. Our observations reveal that ZIF-8 CVD deposition on ZnO nanowires follows a Volmer-Weber island growth mode─discrete nucleation and subsequent coalescence─rather than a layer-by-layer mechanism. By quantitatively tracking shell-thickness evolution and confirming composition via energy-dispersive X-ray spectroscopy, this TempTwin CVD-Reactor enables realistic simulation of key CVD conditions for MOF growth and provides critical insights into gas-solid reaction mechanisms.