原子层沉积(Atomic Layer Deposition,ALD)的自限制反应特征,赋予了ALD技术高度保型、均匀的薄膜沉积能力。ALD广泛应用于光伏领域。然而,实现工业规模的ALD薄膜沉积,依赖于ALD设备的设计和过程的开发。为此,我们开发了基于虚拟ALD阀门、源瓶的供气系统模型、真空腔体流体力学传递过程模型、大面积平面/维纳结构基底的薄膜沉积模型,致力于全流程的ALD过程与装备仿真设计,相关模型已在国内外高校、企业的研究级、工业级ALD机台得到了系统验证。相关ALD技术已应用于存储芯片、钙钛矿太阳能电池、气体分离膜等领域的工艺和装备开发。

Zeolitic imidazolate framework (ZIF-8) is a promising material for gas separation applications. It also serves as a prototype for numerous ZIFs, including amorphous ones, with a broader range of possible applications, including sensors, catalysis, and lithography. It consists of zinc coordinated with 2-methylimidazolate (2mIm) and has been synthesized with methods ranging from liquid-phase to solvent-free synthesis, which aim to control its crystal size and shape, film thickness and microstructure, and incorporation into nanocomposites. Depending on the synthesis method and postsynthesis treatments, ZIF-8 materials may deviate from the nominal defect-free ZIF-8 crystal structure due to defects like missing 2mIm, missing zinc, and physically adsorbed 2mIm trapped in the ZIF-8 pores, which may alter its performance and stability. Infrared (IR) spectroscopy has been used to assess the presence of defects in ZIF-8 and related materials. However, conflicting interpretations by various authors persist in the literature. Here, we systematically investigate ZIF-8 vibrational spectra by combining experimental IR spectroscopy and first-principles molecular dynamics simulations, focusing on assigning peaks and elucidating the spectroscopic signals of putative defects present in the ZIF-8 material. We attempt to resolve conflicting assignments from the literature and to provide a comprehensive understanding of the vibrational spectra of ZIF-8 and its defect-induced variations, aiming toward more precise quality control and design of ZIF-8-based materials for emerging applications.

Zeolitic imidazolate frameworks (ZIFs) are a subset of metal-organic frameworks with more than 200 characterized crystalline and amorphous networks made of divalent transition metal centres (for example, Zn2+ and Co2+) linked by imidazolate linkers. ZIF thin films have been intensively pursued, motivated by the desire to prepare membranes for selective gas and liquid separations. To achieve membranes with high throughput, as in angstrom-scale biological channels with nanometre-scale path lengths, ZIF films with the minimum possible thickness-down to just one unit cell-are highly desired. However, the state-of-the-art methods yield membranes where ZIF films have thickness exceeding 50 nm. Here we report a crystallization method from ultradilute precursor mixtures, which exploits registry with the underlying crystalline substrate, yielding (within minutes) crystalline ZIF films with thickness down to that of a single structural building unit (2 nm). The film crystallized on graphene has a rigid aperture made of a six-membered zinc imidazolate coordination ring, enabling high-permselective H2 separation performance. The method reported here will probably accelerate the development of two-dimensional metal-organic framework films for efficient membrane separation.Unit-cell-thick films of metal-organic frameworks with ordered porosity would be attractive for membrane applications as these thin systems combine large molecular flux with high selectivity. Here crystalline ZIF films are grown on a crystalline substrate with high H2/N2 gas separation performance.

The effective operation of atomiclayer deposition (ALD) feedingsystem is the premise of realizing specific ALD processes. In thepresent work, a detailed computational fluid dynamics (CFD) modelof the feeding system has been developed and validated, which accountsfor the roles of ALD valves and manifolds. A numerical simulationof the compressible fluid flow and heat/mass transfer within the feedingsystem was conducted. The dosing amounts and the spatiotemporal distributionsof the precursors can be accurately predicted using the CFD model,as validated by experimental results. Different precursors, operatingconditions, and structures of the feeding system were simulated andanalyzed to examine the operating flexibility of the feeding system.The simulation results can be adopted as the upstream boundary conditionsfor simulations of the ALD process in the reaction chamber. The substrate-scalesimulation indicates that the effect of the feeding system on thefilm deposition is highly related to the surface kinetics of ALD.The present work can serve as a guide for the development and optimizationof different ALD-based processes via proper operation and even thedesign of the feeding system.

Surface characterization is critical for understanding the processes used for preparing catalysts, sorbents, and membranes. Nonthermal plasma (NTP) is a process that achieves high reactivity at low temperatures and is used to tailor the surface properties of materials. In this work, we combine the capabilities of infrared reflection absorption spectroscopy (IRRAS) with NTP for the in situ interrogation of zeolitic imidazolate framework-8 (ZIF-8) thin films to probe modifications in the material induced by oxygen and nitrogen plasmas. The IRRAS measurements in oxygen plasma reveal etching of organic ligands with sequential removal of the methyl group and imidazole ring and with the formation of carbonyl moieties (C=O). In contrast, nitrogen plasma induces mild etching and grafting of nitrile groups (-C N). Scanning electron microscopy imaging shows that oxygen plasma, at prolonged times, significantly degrades the ZIF-8 film at the grain boundaries. Treatment of ZIF-8 membranes using mild plasma conditions yields a fivefold enhancement for H-2/N-2 and CO2/CH4 ideal selectivities and an eightfold enhancement for CO2/N-2 ideal selectivity. Additionally, the new tools described here can be used for spectroscopic in situ tracking of plasma-induced chemistry on thin films in general.

Patterning metal-organic frameworks (MOFs) at submicrometer scale is a crucial yet challenging task for their integration in miniaturized devices. Here we report an electron beam (e-beam) assisted, bottom-up approach for patterning of two MOFs, zeolitic imidazolate frameworks (ZIF), ZIF-8 and ZIF-67. A mild pretreatment of metal oxide precursors with linker vapor leads to the sensitization of the oxide surface to e-beam irradiation, effectively inhibiting subsequent conversion of the oxide to ZIFs in irradiated areas, while ZIF growth in non-irradiated areas is not affected. Well-resolved patterns with features down to the scale of 100 nm can be achieved. This developer-free, all-vapor phase technique will facilitate the incorporation of MOFs in micro- and nanofabrication processes.There is a long-standing interest in the development of patterning process for porous materials. Here, the authors report a solvent-free bottom-up approach for the patterning of zeolitic imidazolate frameworks; well-resolved patterns with features down to the scale of 100 nm can be achieved.

In the last decade, zeolitic imidazolate frameworks (ZIFs) have been studied extensively for their potential as selective separation membranes. In this review, we highlight unique structural properties of ZIFs that allow them to achieve certain important separations, like that of propylene from propane, and summarize the state of the art in ZIF thin-film deposition on porous substrates and their modification by postsynthesis treatments. We also review the reported membrane performance for representative membrane synthesis approaches and attempt to rank the synthesis methods with respect to potential for scalability. To compare the dependence of membrane performance on membrane synthesis methods and operating conditions, we map out fluxes and separation factors of selected ZIF-8 membranes for propylene/propane separation. Finally, we provide future directions considering the importance of further improvements in scalability, cost effectiveness, and stable performance under industrially relevant conditions.

ZnO deposition in porous gamma-Al2O3 via atomic layer deposition (ALD) is the critical first step for the fabrication of zeolitic imidazolate framework membranes using the ligand-induced perm-selectivation process (Science, 361 (2018), 1008-1011). A detailed computational fluid dynamics (CFD) model of the ALD reactor is developed using a finite-volume-based code and validated. It accounts for the transport processes within the feeding system and reaction chamber. The simulated precursor spatiotemporal profiles assuming no ALD reaction were used as boundary conditions in modeling diethylzinc reaction/diffusion in porous gamma-Al2O3, the predictions of which agreed with experimental electron microscopy measurements. Further simulations confirmed that the present deposition flux is much less than the upper limit of flux, below which the decoupling of reactor/substrate is an accurate assumption. The modeling approach demonstrated here allows for the design of ALD processes for thin-film membrane formation including the synthesis of metal-organic framework membranes.

Modification of the gas permeation properties of ZIF-8 membranes using electron beam irradiation is reported. 3.8 and 3.2 fold enhancements in ideal selectivity for CO2/N-2 and CO2/CH4 can be achieved with less than 1 min exposure time.

Vapor-phase treatment of ZIF-8 membranes with manganese(II) acetylacetonate (Mn(acac)(2)) allows permselectivity tuning. Propylene/propane selectivity increases from 31 to 210 after the Mn(acac)(2) treatment at 165 degrees C for 30 min, while selectivities increase from 14.6 to 242 for H-2/CH4, from 2.9 to 38 for CO2/CH4, from 2.4 to 29 for CO2/N-2, and from 2.9 to 7.5 for O-2/N-2, after Mn(acac)(2) treatment at 175 degrees C for 30 min. Stable equimolar propylene/propane mixture selectivity of 165 at ambient temperature and 4 bar equimolar feed with a propylene flux of 8.3x10(-4) mol m(-2) s(-1) is established. A control experiment excludes thermal treatment alone causing these changes. XPS analysis reveals the presence of Mn(acac)(2) on the outer surface of the vapor-treated ZIF-8 membranes while no other changes are detectable by X-ray diffraction and infrared spectroscopy.