MODs vs. NPs: Vying for the Future of Printed Electronics

This Minireview compares two distinct ink types, namely metal‐organic decomposition (MOD) and nanoparticle (NP) formulations, for use in the printing of some of the most conductive elements: silver, copper and aluminium. Printing of highly conductive features has found purpose across a broad array of electronics and as processing times and temperatures reduce, the avenues of application expand to low‐cost flexible substrates, materials for wearable devices and beyond. Printing techniques such as screen, aerosol jet and inkjet printing are scalable, solution‐based processes that historically have employed NP formulations to achieve low resistivity coatings printed at high resolution. Since the turn of the century, the rise in MOD inks has vastly extended the range of potentially applicable compounds that can be printed, whilst simultaneously addressing shelf life and sintering issues. A brief introduction to the field and requirements of an ink will be presented followed by a detailed discussion of a wide array of synthetic routes to both MOD and NP inks. Unindustrialized materials will be discussed, with the challenges and outlook considered for the market leaders: silver and copper, in comparison with the emerging field of aluminium inks

Aerosol assisted chemical vapour deposition of transparent conductive aluminum-doped zinc oxide thin films from a zinc triflate precursor

The use of zinc triflate (trifluoromethanesulfonate), [Zn(OTf)2] as a precursor in the aerosol assisted chemical vapour deposition of zinc oxide thin films is described. Aluminum doped zinc oxide (AZO) thin films are also shown to be deposited when aluminum acetylacetonate [Al(acac)3] was introduced into the precursor solution, illustrating the versatility of this system. Film characterization techniques include glancing angle X-ray powder diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and optical and electrical measurements. AZO films with an Al content of 7 at.% were found to have favourable transparent conducting oxide properties with simultaneous high transparency (> 80%) in the visible light region and a low electrical resistivity (1.96 × 10− 3 Ω cm)

Synthesis of Trimeric Organozinc Compounds and their Subsequent Reaction with Oxygen

A conventional solution-based route to a cyclic trimeric organozinc compound [{Zn(Et)(β-diketonate)}3] (β-diketonate=OC(OMe)CHC(Me)O, 1) is described, with 1 structurally characterized for the first time. The ligand selection of bidentate β-diketonates is shown to be key to isolating a cyclic trimer. Additional reaction of β-diketonates with diethyl zinc were spectroscopically characterized as compounds of the type [{Zn(Et)(β-diketonate)}n] (β-diketonate=OC(Me)CHC(Me)O, 2, OC(OtBu)CHC(Me)O, 3). Further studies have shown that selective oxidation of these species produces cubanes of the general formula [{Zn(OC(R)CHC(Me)O)2Zn(Et)OEt}2] (R=OMe, 4; Me, 5; OtBu, 6), allowing a high oxygen content whilst remaining structurally suitable for use as precursors. The successful deposition of thin films of zinc oxide through aerosol-assisted chemical vapor deposition (AACVD), using a novel precursor, is described and fully characterized

Aerosol-Assisted Chemical-Vapour Deposition of Zinc Oxide from Single-Source beta-Iminoesterate Precursors

Single-source zinc β-iminoesterate precursors have been used for the first time in the aerosol-assisted chemical-vapour deposition (AACVD) of ZnO thin films. Depositions at 450 °C on silica-coated glass substrates produced strongly adherent films with excellent coverage of the substrate. The zinc β-iminoesterates [Zn(L1)2] (1) and [Zn(L2)2] (2) were synthesised by the reaction between ZnEt2 and 2 equiv. of a synthesised β-iminoester ligand CH3C[NHCH(CH3)2]CHC(O)OCH2CH3 (L1) and CH3C(NHCH3)CHC(O)OCH2CH3 (L2). The synthesised complexes were isolated and characterised by 1H and 13C NMR spectroscopy, mass spectrometry and thermal gravitational analysis (TGA). The structures of the compounds were determined by single-crystal X-ray diffraction. The ZnO films deposited from 1 and 2 were analyzed by glancing-angle X-ray powder diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and their optical properties determined by UV/Vis/NIR transmission spectroscopy. These results reveal that the organic ligand attached to the N moiety of the zinc complex has a significant effect on the level of carbon incorporated into the deposited thin film. Upon annealing, highly transparent hexagonal wurtzite ZnO thin films were produced

Synthesis, solution dynamics and chemical vapour deposition of heteroleptic zinc complexes via ethyl and amide zinc thioureides

Ethyl and amide zinc thioureides [L^{1}ZnEt]_{2} (1), [L^{1*}ZnEt]_{2} (2) and [L^{1}Zn(N(SiMe_{3})_{2})]_{2} (3) have been synthesised from the equimolar reaction of thiourea ligands (HL^{1} = iPrN(H)CSNMe2 and HL^{1*} = PhN(H)CSNMe_{2}) with diethyl zinc and zinc bis[bis(trimethylsilyl)amide] respectively. New routes towards heteroleptic complexes have been investigated through reactions of 1, 2 and 3 with β-ketoiminates (HL^{2} = [(Me)CN(H){iPr}–CHC(Me)[double bond, length as m-dash]O]), bulky aryl substituted β-diiminates (HL3 = [(Me)CN(H){Dipp}–CHC(Me)[double bond, length as m-dash]N{Dipp}] (Dipp = diisopropylphenyl) and HL3* = [(Me)CN(H){Dep}–CHC(Me)[double bond, length as m-dash]N{Dep}] (Dep = diethylphenyl)) and donor-functionalised alcohols (HL^{4} = Et_{2}N(CH_{2})_{3}OH and HL4* = Me_{2}N(CH_{2}){3}_OH) and have led to the formation of the heteroleptic complexes [L^{1*}ZnL^{3*}] (5), [L^{1}ZnL^{4}]_{2} (6), [L^{1}ZnL^{4*}]_{2} (7), [L^{1*}ZnL^{4}] (8) and [L^{1*}ZnL^{4*}] (9). All complexes have been characterised by {1}^H and 1{3}^C NMR, elemental analysis, and the X-ray structures of HL^{1*}, 1, 2, 6 and 7 have been determined via single crystal X-ray diffraction. Variable temperature 1H, COSY and NOESY NMR experiments investigating the dynamic behaviour of 5, 6 and 7 have shown these molecules to be fluxional. On the basis of solution state fluxionality and thermogravimetric analysis (TGA), alkoxyzinc thioureides 6 and 7 were investigated as single-source precursors for the deposition of the ternary material zinc oxysulfide, Zn(O,S), a buffer layer used in thin film photovoltaic devices. The aerosol-assisted chemical vapour deposition (AACVD) reaction of 7 at 400 °C led to the deposition of the heterodichalcogenide material Zn(O,S), which was confirmed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray analysis (EDX), with optical properties investigated using UV/vis spectroscopy, and surface morphology and film thickness examined using scanning electron microscopy (SEM)

Aerosol-Assisted Chemical Vapour Deposition of Transparent Zinc Gallate Films

Aerosol-assisted chemical vapour deposition (AACVD) reactions of GaMe3, ZnEt2 and the donor-functionalised alcohol HOCH2CH2OMe (6 equiv.) in toluene resulted in the deposition of amorphous transparent zinc gallate (ZnGa2O4) films at a range of temperatures (350–550 °C). The zinc–gallium oxide films were analyzed by scanning electron microscopy, X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray analysis, glancing-angle X-ray powder diffraction (XRD) and optical studies. The optimum growth temperature was found to be 450 °C, which produced transparent films with excellent coverage of the substrate. XPS confirmed the presence of zinc, gallium and oxygen in the films. Annealing these films at 1000 °C resulted in crystalline films and glancing-angle powder XRD showed that a zinc gallate spinel framework with a lattice parameter of a=8.336(5) Å was adopted

Synthetic tethered silver nanoparticles on reduced graphene oxide for alkaline oxygen reduction catalysis

There is currently an enormous drive to move away from the use of Pt group metals in catalysis, particularly for fuel cells, because of their increasing rarity and cost. Simultaneously, there have been advances in the application of graphene supported nanoparticular catalysts. However, these Pt-free, graphene supported catalysts can be complex to produce, show poor catalytic activity and degrade quickly due to particle agglomeration or isolation. Herein, we report a one-pot synthesis of silver nanoparticles (NPs) tethered to a reduced graphene oxide (rGO) template via organic linkages. This is one of the few silver precursor formations that have been combined with graphene oxide (GO) to simultaneously establish linkage binding sites, reduce GO and yield tethered nanoparticles. These materials are shown to efficiently catalyze the oxygen reduction reaction in alkaline environments, with aminoethanol linkages to 21.55 ± 2.88 nm Ag particles exhibiting the highest catalytic activity via the four-electron pathway. This method, therefore, offers a straightforward route to produce effective catalysts from inexpensive precursors, which could be developed further for significant industrial application

Metal β-diketoiminate precursor use in aerosol assisted chemical vapour deposition of gallium- and aluminium-doped zinc oxide

Aerosol assisted chemical vapour deposition (AACVD) has been used to deposit thin films of ZnO from the single-source precursor [Zn(OC(Me)CHC(Me)N( i Pr)) 2 ] (1) affording highly transparent ( > 80%) and conductive films (sheet resistance ∼70 KΩ/sq). Extension of this AACVD method whereby related precursors of the type, [R 2 M(OC(Me)CHC(Me)N( i Pr))] (R = Et, M = Al (2); R = Me, M = Ga (3)), isolated as oils, were added to the precursor solution allowed for the deposition of aluminium- and gallium-doped ZnO (AZO and GZO) films, respectively. Complexes 1–3 were characterised by elemental analysis, NMR and mass spectrometry. Films were deposited in under 30 min at 400 °C, from CH 2 Cl 2 /toluene solutions with a N 2 carrier gas. Herein we report the bulk resistivity, ρ, of AZO (0.252 Ω cm) and GZO (0.756 Ω cm) films deposited from this novel approach. All the films transparency exceeded 80% in the visible, X-ray diffraction (XRD) showed all films to crystallise in the wurtzite phase whilst X-ray photoemission spectroscopy (XPS) confirmed the presence of the Al and Ga dopants in the films, and highlighted the low C-contamination ( < 5%) this route offers. Investigation of a mechanism analogous to the Kirkendall effect confirmed that heating of GZO films at 1000 °C produced the spinel structure GaZn 2 O 4

Synthesis and Characterisation of Various Diester and Triester Adducts of TiCl4

Titanium(IV) chloride and the triester glycerol tribenzoate (gtb) were reacted under moisture-free conditions in order to investigate the use of triester-containing oils in the purification of TiCl4 in industrial processes. This resulted in the isolation of a chloro-bridged dimeric complex containing four titanium centres [{(TiCl4)2(gtb)}2] (1). Further novel coordination compounds of TiCl4 and the diesters; diisopropyl malonate, dibenzyl malonate and diethyl succinate were synthesised by direct reaction under moisture-free conditions, yielding [TiCl4{CH2(COOiPr)2}] (2), [TiCl4{CH2(COOCH2Ph)2}] (3) and [TiCl4{C2H4(COOEt)2}] (4) respectively. The structures of compounds 1–4 were determined by single-crystal X-ray diffraction. All structures assumed an octahedral geometry consisting of the titanium bound to four chloride ligands and the diester molecule acting as a bidentate ligand, through its two carbonyl oxygen atoms. Exposure of the isopropyl malonate reaction to trace amounts of water during synthesis resulted in the formation of an oxo-bridged dimeric structure [Ti2(μ-O)Cl3{CH2(COOiPr)2}2] (2b), the structure of which was also obtained via single-crystal X-ray diffraction