Shape anisotropy in colloidal zincblende CdSe nanoplatelets (NPLs) has a direct bearing on their optical and electronic properties. The lateral aspect ratio of NPLs provides an additional knob with which one can control their optical characteristics even at a fixed thickness. For example, one can regulate the polarized emission and assembly behaviors of NPLs by varying the lateral aspect ratio while keeping the optical transition at the energy fixed by the NPL thickness. Given the isotropic nature of the zincblende crystal structure, such control over shape anisotropy is intriguing yet not fully understood. In this study, based on combined experimental and simulation works, we systematically investigate the asymmetric lateral growth behavior of colloidal 4.5 monolayer thick (5 Cd and 4 Se layers) CdSe NPLs. Experimentally, it is found that NPLs with rectangular and square shapes have different growth directions, <100> and <110>, respectively. The cadmium acetate (Cd(ac) 2 )-to-Se precursor ratio turns out to have an important role in altering the lateral growth kinetics of NPLs, and the deficiency of Se under high Cd-to-Se precursor ratio conditions slows down the growth and changes the growth direction from <100> to <110>. First-principles calculations reveal that the observed growth behaviors can be explained in light of the irregular wedge-shaped conformations at the NPL side surfaces that expose {110} and {111} faces. Specifically, it is identified that the adsorption of Cd(ac) 2 on {110} ({111}) surfaces becomes an energetically unfavorable process in the low (high) Se coverage regime, explaining the fast <100>-direction (slow <110>-direction) growth into rectangular (square) NPLs. The presented mechanism for the lateral growth of zincblende NPLs provides an atomic-level understanding of the transition processes of NPL morphology and growth direction, with the control of unique anisotropic properties of NPLs on the line.

The splitting of quasi-Fermi levels (QFLs) represents a key concept utilized to describe finite-bias operations of semiconductor devices, but its atomic-scale characterization remains a significant challenge. Herein, the non-equilibrium QFL or electrochemical potential profiles within single-molecule junctions obtained from the newly developed first-principles multispace constrained-search density functional formalism are presented. Benchmarking the standard non-equilibrium Green's function calculation results, it is first established that algorithmically the notion of separate electrode-originated nonlocal QFLs should be maintained within the channel region during self-consistent finite-bias electronic structure calculations. For the insulating hexandithiolate junction, the QFL profiles exhibit discontinuities at the left and right electrode interfaces and across the molecule the accompanying electrostatic potential drops linearly and Landauer residual-resistivity dipoles are uniformly distributed. For the conducting hexatrienedithiolate junction, on the other hand, the electrode QFLs penetrate into the channel region and produce split QFLs. With the highest occupied molecular orbital entering the bias window and becoming a good transport channel, the split QFLs are also accompanied by the nonlinear electrostatic potential drop and asymmetric Landauer residual-resistivity dipole formation. Our findings underscore the importance of the first-principles extraction of QFLs in nanoscale junctions and point to a new direction for the computational design of next-generation electronic, optoelectronic, and electrochemical devices.