Spin Selectivity in Chiral Hybrid Cobalt Halide Films with Ultrasmooth Surface

Abstract

Introducing chirality into low‐dimensional hybrid organic–inorganic halides (HOIHs) creates brand‐new opportunities for HOIHs in spintronics and spin‐related optoelectronics owing to chirality‐induced spin selectivity (CISS). However, preparing smooth films of low‐dimensional HOIHs with small roughness is still a great challenge due to the hybrid and complex crystal structure, which severely inhibits their applications in spintronic devices. Exploring new lead‐free chiral HOIHs with both efficient spin selectivity and excellent film quality is urgently desired. Here, cobalt‐based chiral metal halide crystals (R/S‐NEA)2CoCl4 constructed by 0D [CoCl4] tetrahedrons and 1‐(1‐naphtyl)ethylamine (NEA) are synthesized. The orderly configuration of NEA molecules stabilized by noncovalent CH···π interaction endows (NEA)2CoCl4 with good film‐forming ability. (NEA)2CoCl4 films exhibit strong chiroptical activity (gCD ≈ 0.05) and significant spin‐polarized transport (CISS efficiency up to 90%). Furthermore, ultrasmooth films (roughness ∼ 0.3 nm) with enhanced crystallinity can be achieved by incorporating tiny amount tris(8‐oxoquinoline)aluminum that has analogous conjugated structure to NEA. The realization of highly efficient spin selectivity and sub‐nanometer roughness in lead‐free chiral halides can boost the practical process of low‐dimensional HOIHs in spintronics and other fields.

Chiral Induced Spin Selectivity

“…Experiments show that heterogeneity or structural disorder can decrease the CISS response, or even result in a null response, as shown in ref 23, and must be considered when interpreting experiments. Indeed, some of the largest reported spin polarizations are for comparatively rigid well-defined constructs not susceptible to the same types of disorder found in organic molecule self-assemblies, e.g., metal−organic frameworks (>99%), 204 bulk crystals (>70%), 205 metal halides (>90%), 170,175 and perovskites (>90%). 168,172,173 Further evidence corroborating this idea is shown for metal oxides in which films fabricated through electrodeposition techniques, possessing ill-defined crystallinity, exhibit worse polarizations (ca.…”

“…Similar findings have since been reported in hybrid organic–inorganic perovskites and metal halides with other compositions as well (see Table ). In related work, researchers have incorporated achiral additives into the chiral matrix in order to improve the film crystallinity, yet retain their spin-filtering power. , For instance, Lee et al showed that the addition of urea to (R-/S-MBA) 2 PbI 4 perovskites causes structural changes to the perovskite host, which can enhance the chiroptical response and ensuing spin polarization measured by mc-AFM . The spin-filtered currents in these materials can persist over thicknesses of hundreds of nanometers, and it is hypothesized to arise from multiple tunneling processes through the chiral organic molecules occupying the space between the layered octahedral perovskite sheets …”

Chiral-induced spin selectivity in biomolecules, hybrid organic–inorganic perovskites and inorganic materials: a comprehensive review on recent progress

“…In 2022, chiral metal halide crystals of (R,S-NEA) 2 CoCl 4 were successfully prepared, in which the stable CH-p interaction enables strong film forming ability. 171 Fig. 20 I-V curves of (a) (R-MBA) 2 SnI 4 and (b) (S-MBA) 2 SnI 4 films obtained by magnetic conductive probe AFM at room temperature.…”

“…In 2022, chiral metal halide crystals of ( R , S -NEA) 2 CoCl 4 were successfully prepared, in which the stable CH–π interaction enables strong film forming ability. 171 The CISS efficiency is up to 90%. By adding a tiny amount of Alq3 to NEA, an ultrasmooth film with a roughness of 0.3 nm can be obtained.…”

Selective Potassium Deposition Enables Dendrite‐Resistant Anodes for Ultrastable Potassium‐Metal Batteries

“…[1][2][3][4] Alkali-metal batteries are well suited for such energy storage systems because of their high energy density. [5][6][7][8] Among battery metal anodes (e.g., alkali metals Li, Na, and K, or others, such as Ca, Mg, Zn, Al, etc. ), the potassium-metal anodes (PMAs) are the most competitive due to potassium's low cost and low redox potential (−2.93 V vs standard hydrogen electrode).…”