Immersing a substrate in the precursor solution initiates heterogeneous nucleation and growth on the substrate as well as homogeneous nucleation of crystals in the solution (Fig. ). By using an ultra-dilute precursor solution (Fig. ), one can eliminate or delay homogeneous nucleation, otherwise, the nuclei from the bulk can deposit on the substrate and promote out-of-plane non-oriented growth. To understand film growth and the possibility of the influence of bulk crystals deposited from the solution, film morphology was analyzed at the early stage of growth (2-10 min). Kelvin probe force microscopy (KPFM) near the edge of Zn2(bim)4 film on HOPG revealed a distinct surface potential difference (80 mV) between the film and the substrate (Fig. and). This confirmed the presence of Zn2(bim)4 film on the substrate. At 2 min of growth, 100-200 nm sized grains appear on HOPG (Supplementary Figs. and) with a thickness of ~ 2 nm, consistent with a unit-cell-thick Zn2(bim)4 grain oriented along the c-out-of-plane direction. When the growth time was extended to 4 min, the grains merged into larger islands on the substrate (Fig. and Supplementary Fig. ) with thickness remaining ~2 nm (Fig. ). After 6 minutes, the lateral size of these islands enlarged (Fig. and Supplementary Fig. ) with the thickness increasing to ~3 nm suggesting growth to a 1.5 unit-cell thickness (Fig. ). The 1.5-unit-cell thick Zn2(bim)4 is essentially three layers of the MOF where two layers constitute a single unit cell. The grains continued to enlarge at 8 minutes (Fig. and Supplementary Fig. ), leading to a film that covered more than 80% of the substrate. At this point, the film thickness was maintained at ~3 nm (Fig. ). The islands intergrew to yield a continuous film after 10 minutes of growth (Fig. ) while the thickness increased to ~4 nm, corresponding to two unit cells (Fig. ). This demonstrates predominant in-plane grain growth (length scale ~ 1 µm) which was more than two orders of magnitude faster than the growth along the out-of-plane direction (length scale ~ 4 nm). Over time, the in-plane growth led to a continuous film while a slow out-of-plane growth resulted in extremely thin film. Analysis of grains, grown for 2-Overall, we demonstrated the growth of Zn2(bim)4 films on a substrate using an ultra-dilute precursor solution to suppress unwanted crystal nucleation. With extended growth, the grains primarily expand in-plane, forming a continuous, crystalline, and extremely thin film, with thickness gradually increasing from 2 nm to 4 nm as the grains merge and cover the whole substrate.