Covalent Functionalization of Silicon with Plasma-Grown "Fuzzy" Graphene: Robust Aqueous Photoelectrodes for CO Reduction by Molecular Catalysts.

Carbon electrodes are ideal for electrochemistry with molecular catalysts, exhibiting facile charge transfer and good stability. Yet for solar-driven catalysis with semiconductor light absorbers, stable semiconductor/carbon interfaces can be difficult to achieve, and carbon's high optical extinction means it can only be used in ultrathin layers. Here, we demonstrate a plasma-enhanced chemical vapor deposition process that achieves well-controlled deposition of out-of-plane "fuzzy" graphene (FG) on thermally oxidized Si substrates.

Photoelectrochemical Proton-Coupled Electron Transfer of TiO Thin Films on Silicon.

TiO thin films are often used as protective layers on semiconductors for applications in photovoltaics, molecule-semiconductor hybrid photoelectrodes, and more. Experiments reported here show that TiO thin films on silicon are electrochemically and photoelectrochemically reduced in buffered acetonitrile at potentials relevant to photoelectrocatalysis of CO reduction, N reduction, and H evolution. On both n-type Si and irradiated p-type Si, TiO reduction is proton-coupled with a 1e:1H stoichiometry, as demonstrated by the Nernstian dependence of the Ti on the buffer p.

Coordination of copper within a crystalline carbon nitride and its catalytic reduction of CO.

Inherently disordered structures of carbon nitrides have hindered an atomic level tunability and understanding of their catalytic reactivity. Starting from a crystalline carbon nitride, poly(triazine imide) or PTI/LiCl, the coordination of copper cations to its intralayer -triazine groups was investigated using molten salt reactions. The reaction of PTI/LiCl within CuCl or eutectic KCl/CuCl molten salt mixtures at 280 to 450 °C could be used to yield three partially disordered and ordered structures, wherein the Cu cations are found to coordinate within the intralayer cavities.

Control of ZIF-62 and aZIF-62 Film Thickness within Asymmetric Tubular Supports through Pressure and Dose Time Variation of Atomic Layer Deposition.

Thin-films of metal-organic frameworks (MOFs) have widespread potential applications, especially with the emergence of glass-forming MOFs, which remove the inherent issue of grain boundaries and allow coherent amorphous films to be produced. Herein, it is established that atomic layer deposition (ALD) of zinc oxide lends excellent control over the thickness and localization of resultant polycrystalline and glass zeolitic imidazole framework-62 (ZIF-62) thin-films within tubular α-alumina supports. Through the reduction of the chamber pressure and dose times during zinc oxide deposition, the resultant ZIF-62 films are reduced from 38 µm to 16 µm, while the presence of sporadic ZIF-62 (previously forming as far as 280 µm into the support) is prevented.

Reduced fatigue and leakage of ferroelectric TiN/HfZrO/TiN capacitors by thin alumina interlayers at the top or bottom interface.

HfZrO(HZO) thin films are promising candidates for non-volatile memory and other related applications due to their demonstrated ferroelectricity at the nanoscale and compatibility with Si processing. However, one reason that HZO has not been fully scaled into industrial applications is due to its deleterious wake-up and fatigue behavior which leads to an inconsistent remanent polarization during cycling. In this study, we explore an interfacial engineering strategy in which we insert 1 nm AlOinterlayers at either the top or bottom HZO/TiN interface of sequentially deposited metal-ferroelectric-metal capacitors.

Role of Oxygen Source on Buried Interfaces in Atomic-Layer-Deposited Ferroelectric Hafnia-Zirconia Thin Films.

Hafnia-zirconia (HfO-ZrO) solid solution thin films have emerged as viable candidates for electronic applications due to their compatibility with Si technology and demonstrated ferroelectricity at the nanoscale. The oxygen source in atomic layer deposition (ALD) plays a crucial role in determining the impurity concentration and phase composition of HfO-ZrO within metal-ferroelectric-metal devices, notably at the HfZrO /TiN interface. The interface characteristics of HZO/TiN are fabricated via sequential no-atmosphere processing (SNAP) with either HO or O-plasma to study the influence of oxygen source on buried interfaces.

Toward understanding the phase-selective growth mechanism of films and geometrically-shaped flakes of 2D MoTe.

Two-dimensional (2D) molybdenum ditelluride (MoTe) is an interesting material for fundamental study and applications, due to its ability to exist in different polymorphs of 2H, 1T, and 1T', their phase change behavior, and unique electronic properties. Although much progress has been made in the growth of high-quality flakes and films of 2H and 1T'-MoTe phases, phase-selective growth of all three phases remains a huge challenge, due to the lack of enough information on their growth mechanism. Herein, we present a novel approach to growing films and geometrical-shaped few-layer flakes of 2D 2H-, 1T-, and 1T'-MoTe by atmospheric-pressure chemical vapor deposition (APCVD) and present a thorough understanding of the phase-selective growth mechanism by employing the concept of thermodynamics and chemical kinetics involved in the growth processes.

analysis of growth rate evolution during molecular layer deposition of ultra-thin polyurea films using aliphatic and aromatic precursors.

Organic thin films formed by molecular layer deposition (MLD) are important for next-generation electronics, energy storage, photoresists, protective barriers and other applications. This study uses ellipsometry and quartz crystal microbalance to explore growth initiation and growth rate evolution during MLD of polyurea using aromatic -phenylene diisocyanate (PDIC) or aliphatic 1,6-hexamethylene diisocyanate (HDIC) combined with ethylenediamine (ED) or 1,6-hexanediamine (HD) co-reactants. During the first 10-20 cycles of growth, we show the growth rate can increase and/or decrease substantially depending on the substrate as well as the flexibility, length, and structure of the isocyanate and amine reactants used.

Stretchable and Multi-Metal-Organic Framework Fabrics Via High-Yield Rapid Sorption-Vapor Synthesis and Their Application in Chemical Warfare Agent Hydrolysis.

Protocols to create metal-organic framework (MOF)/polymer composites for separation, chemical capture, and catalytic applications currently rely on relatively slow solution-based processing to form single MOF composites. Here, we report a rapid, high-yield sorption-vapor method for direct simultaneous growth of single and multiple MOF materials onto untreated flexible and stretchable polymer fibers and films. The synthesis utilizes favorable reactant absorption into polymers coupled with rapid vapor-driven MOF crystallization to form high surface area (>250 m/g) composites, including UiO-66-NH, HKUST-1, and MOF-525 on spandex, nylon, and other fabrics.

Multimaterial Self-Aligned Nanopatterning by Simultaneous Adjacent Thin Film Deposition and Etching.

Printed component sizes in electronic circuits are approaching 10 nm, but inherent variability in feature alignment during photolithography poses a fundamental barrier for continued device scaling. Deposition-based self-aligned patterning is being introduced, but nuclei defects remain an overarching problem. This work introduces low-temperature chemically self-aligned film growth simultaneous thin film deposition and etching in adjacent regions on a nanopatterned surface.

Doubly Protective MOF-Photo-Fabrics: Facile Template-Free Synthesis of PCN-222-Textiles Enables Rapid Hydrolysis, Photo-Hydrolysis and Selective Oxidation of Multiple Chemical Warfare Agents and Simulants.

New materials and chemical knowledge for improved personal protection are among the most pressing needs in the international community. Reported attacks using chemical warfare agents (CWAs,) including organophosphate soman (GD) and thioether mustard gas (HD) are driving research in field-deployable catalytic composites for rapid toxin degradation. In this work, we report simple template-free low temperature synthesis that enables for the first time, a deployable-structured catalytic metal-organic framework/polymer textile composite "MOF-fabric" showing rapid hydrolysis and oxidation of multiple active chemical warfare agents, GD and HD, respectively, and their simulants.

The Effect of Surface Hydroxylation on MOF Formation on ALD Metal Oxides: MOF-525 on TiO/Polypropylene for Catalytic Hydrolysis of Chemical Warfare Agent Simulants.

Metal-organic framework (MOF) fibrous composites were synthesized in a variety of methods in attempt to incorporate the highly effective reactivity of MOFs into a more facile and applicable format. Recent advances have demonstrated incorporating a metal oxide nucleation surface or reactive layer promotes conformal, well-adhered MOF growth on substrates. These materials have demonstrated promising reactivity in capturing or degrading chemical warfare agents and simulants.

Air, Water Vapor, and Aerosol Transport through Textiles with Surface Functional Coatings of Metal Oxides and Metal-Organic Frameworks.

Currently, air permeable chemical/biological (CB) protective garments are based on activated carbon technology, which reduces moisture vapor transport needed for evaporative cooling and has potential to absorb and concentrate toxic materials. Researchers are exploring classes of sorbent materials that can selectively accumulate and decompose target compounds for potential to enhance protective suits and allow for novel filtration devices. Here, the metal-organic frameworks (MOFs) UiO-66-NH and HKUST-1 have been identified as such materials.

Investigation of the Corrosion Behavior of Atomic Layer Deposited Al₂O₃/TiO₂ Nanolaminate Thin Films on Copper in 0.1 M NaCl.

Fifty nanometers of Al₂O₃ and TiO₂ nanolaminate thin films deposited by atomic layer deposition (ALD) were investigated for protection of copper in 0.1 M NaCl using electrochemical techniques. Coated samples showed increases in polarization resistance over uncoated copper, up to 12 MΩ-cm² as measured by impedance spectroscopy.

Water-Stable Chemical-Protective Textiles via Euhedral Surface-Oriented 2D Cu-TCPP Metal-Organic Frameworks.

Abatement of chemical hazards using adsorptive metal-organic frameworks (MOFs) attracts substantial attention, but material stability and crystal integration into functional systems remain key challenges. Herein, water-stable, polymer fiber surface-oriented M-TCPP [M = Cu, Zn, and Co; H TCPP = 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin] 2D MOF crystals are fabricated using a facile hydroxy double salt (HDS) solid-source conversion strategy. For the first time, Cu-TCPP is formed from a solid source and confirmed to be highly adsorptive for NH and 2-chloroethyl ethyl sulfide (CEES), a blistering agent simulant, in humid (80% relative humidity (RH)) conditions.

Solvothermal Synthesis of MIL-96 and UiO-66-NH2 on Atomic Layer Deposited Metal Oxide Coatings on Fiber Mats.

Metal-organic frameworks (MOFs), which contain reactive metal clusters and organic ligands allowing for large porosities and surface areas, have proven effective in gas adsorption, separations, and catalysis. MOFs are most commonly synthesized as bulk powder, requiring additional processes to adhere them to functional devices and fabrics that risk decreasing the powder porosity and adsorption capacity. Here, we demonstrate a method of first coating fabrics with metal oxide films using atomic layer deposition (ALD).

Toxic Organophosphate Hydrolysis Using Nanofiber-Templated UiO-66-NH Metal-Organic Framework Polycrystalline Cylinders.

Metal organic frameworks (MOFs), the UiO series in particular, have attracted much attention because of the high surface area and ability to capture and decontaminate chemical warfare agents. Much work has been done on incorporating these MOFs into or onto textile materials while retaining the desirable properties of the MOF. Many different techniques have been explored to achieve this.

Time-Resolved Attenuated Total Reflectance Infrared Spectroscopy for Probing Metal-Organic Framework Thin Film Growth.

chemical measurements of solution/surface reactions during metal-organic framework (MOF) thin film growth can provide valuable information about the mechanistic and kinetic aspects of key reaction steps, and allow control over crystal quality and material properties. Here, we report a new approach to study the growth of MOF thin films in a flow cell using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). Real-time spectra recorded during continuous flow synthesis were used to investigate the mechanism and kinetics that govern the formation of (Zn, Cu) hydroxy double salts (HDSs) from ZnO thin films and the subsequent conversion of HDS to HKUST-1.

Thermally Driven Self-Limiting Atomic Layer Etching of Metallic Tungsten Using WF and O.

The semiconductor industry faces a tremendous challenge in the development of a transistor device with sub-10 nm complex features. Self-limiting atomic layer etching (ALE) is essential for enabling the manufacturing of complex transistor structures. In this study, we demonstrated a thermally driven ALE process for tungsten (W) using sequential exposures of O and WF.

Synthesis of organic aerogels with tailorable morphology and strength by controlled solvent swelling following Hansen solubility.

We introduce a generalized approach to synthesize aerogels that allows remarkable control over its mechanical properties. The Hansen solubility parameters are used to predict and regulate the swelling properties of the precursor gels and, consequently, to achieve aerogels with tailored density and mechanical properties. As a demonstration, crosslinked organogels were synthesized from cellulose esters to generate aerogels.

UiO-66-NH Metal-Organic Framework (MOF) Nucleation on TiO, ZnO, and AlO Atomic Layer Deposition-Treated Polymer Fibers: Role of Metal Oxide on MOF Growth and Catalytic Hydrolysis of Chemical Warfare Agent Simulants.

Metal-organic frameworks (MOFs) chemically bound to polymeric microfibrous textiles show promising performance for many future applications. In particular, Zr-based UiO-66-family MOF-textiles have been shown to catalytically degrade highly toxic chemical warfare agents (CWAs), where favorable MOF/polymer bonding and adhesion are attained by placing a nanoscale metal-oxide layer on the polymer fiber preceding MOF growth. To date, however, the nucleation mechanism of Zr-based MOFs on different metal oxides and how product performance is affected are not well understood.

Large-Area Nanolattice Film with Enhanced Modulus, Hardness, and Energy Dissipation.

We present an engineered nanolattice material with enhanced mechanical properties that can be broadly applied as a thin film over large areas. The nanolattice films consist of ordered, three-dimensional architecture with thin-shell tubular elements, resulting in favorable modulus-density scaling (n ~ 1.1), enhanced energy dissipation, and extremely large material recoverability for strains up to 20% under normal compressive loading.