Direct Patterning of Colloidal Nanocrystals via Thermally Activated Ligand Chemistry

Abstract

Precise patterning with microscale lateral resolution and widely tunable heights is critical for integrating colloidal nanocrystals into advanced optoelectronic and photonic platforms. However, patterning nanocrystal layers with thickness above 100 nm remains challenging for both conventional and emerging direct photopatterning methods, due to limited light penetration depths, complex mechanical and chemical incompatibilities, and others. Here, we introduce a direct patterning method based on a thermal mechanism, namely, the thermally activated ligand chemistry (or TALC) of nanocrystals. The ligand cross-linking or decomposition reactions readily occur under local thermal stimuli triggered by near-infrared lasers, affording high-resolution and nondestructive patterning of various nanocrystals under mild conditions. Patterned quantum dots fully preserve their structural and photoluminescent quantum yields. The thermal nature allows for TALC to pattern over 10 μm thick nanocrystal layers in a single step, far beyond those achievable in other direct patterning techniques, and also supports the concept of 2.5D patterning. The thermal chemistry-mediated TALC creates more possibilities in integrating nanocrystal layers in uniform arrays or complex hierarchical formats for advanced capabilities in light emission, conversion, and modulation.

A General Approach to Stabilize Nanocrystal Superlattices by Covalently Bonded Ligands

“…Under UV irradiation (254 nm), the cross-linkers (e.g., bis­(perfluorophenyl) azides, or bisPFPA) generate nitrene-based intermediates at both ends that can nonspecifically cross-link molecules containing C–H moieties via the formation of covalent (C–N) bonds (Scheme a). This chemistry has been recently applied to cross-link the native ligands (typically hydrocarbon chains containing 8–18 −CH 2 – units) of NCs for the direct photopatterning of NC layers. − Here we adopted this chemistry in the formation and stabilization of NC superlattices via separated (i) self-assembly (weak interparticle interactions) and (ii) ligand cross-linking (strong covalent bonds) processes, as shown in Scheme b. At the first stage, adding a small amount of bisPFPA cross-linkers to the NC solution does not change the surface chemistry of NCs or their spontaneous organization behavior; NCs form 2D or 3D superlattices by conventional solvent evaporation or slow destabilization approaches (Figure S1).…”

Stabilization and Coagulation of Colloidal Suspensions during Crystallization

“…When the interparticle distances (between the rod surfaces) d is short (d < a/2), eq 3 can be simplified as (5) The equation for the van der Waals attractive energy between crossed rods is 30 (6) Hamaker constant of cefradine crystal rods in water has not been reported and determined. It can be estimated by the following equation: 31,32 (7)…”

“…A colloidal suspension, the special state between ideal fluid and solid, is formed by the colloidal particles dispersed in the liquid medium (Figure ). The colloidal particles could be rearranged under artificial control, which shows great potential in fields like nanomaterials, energy, and biomedicine. − For example, similar to the way that atoms bond to form crystalline structures, colloidal nanocrystals (NCs) could be prepared by precisely controlling the interactions between particles in colloidal suspension, which has been used in photodetectors, light-emitting devices, solar cells, and other devices. , However, the instability and irregular particle motion, determined by properties and interactions of colloidal particles, limit the development of colloidal materials. , Consequently, it is urgent to establish a comprehensive theory on particle motion and stability of colloid suspension.…”

“…2−4 For example, similar to the way that atoms bond to form crystalline structures, colloidal nanocrystals (NCs) could be prepared by precisely controlling the interactions between particles in colloidal suspension, which has been used in photodetectors, light-emitting devices, solar cells, and other devices. 5,6 However, the instability and irregular particle motion, determined by properties and interactions of colloidal particles, limit the development of colloidal materials. 7,8 Consequently, it is urgent to establish a comprehensive theory on particle motion and stability of colloid suspension.…”

Photo-processing of perovskites: current research status and challenges

“…A more explorative direction for modulating the opto-electronic properties of the perovskite via photoprocessing is expected. Besides, developing diverse optoelectronic devices based on photo-processed perovskites for the applications in optics and photonics is promising 140,141 . Furthermore, the typical principles of the photo-processing techniques such as photochemical effect, photothermal effect, and laser ablation can be applicable to other NCs or quantum dots, such as CdTe, CdSe, InP, ZrO 2 , Fe 2 O 3 , Al 2 O 3 , and Au, with controlled light source and precursors 18,142−145 .…”