This paper compares rates of charge transport across self-assembled monolayers (SAMs) of n-alkanethiolates having odd and even numbers of carbon atoms (n odd and n even ) using junctions with the structure M TS /SAM//Ga 2 O 3 /EGaIn (M = Au or Ag). Measurements of current density, J(V), across SAMs of n-alkanethiolates on Au TS and Ag TS demonstrated a statistically significant odd−even effect on Au TS , but not on Ag TS , that could be detected using this technique. Statistical analysis showed the values of tunneling current density across SAMs of n-alkanethiolates on Au TS with n odd and n even belonging to two separate sets, and while there is a significant difference between the values of injection current density, J 0 , for these two series (log|J 0Au,even | = 4.0 ± 0.3 and log|J 0Au,odd | = 4.5 ± 0.3), the values of tunneling decay constant, β, for n odd and n even alkyl chains are indistinguishable (β Au,even = 0.73 ± 0.02 Å ). A comparison of electrical characteristics across junctions of n-alkanethiolate SAMs on gold and silver electrodes yields indistinguishable values of β and J 0 and indicates that a change that substantially alters the tilt angle of the alkyl chain (and, therefore, the thickness of the SAM) has no influence on the injection current density across SAMs of n-alkanethiolates.

We present new flexible, transparent, and conductive coatings composed of an annealed silver nanowire network embedded in a polyurethane optical adhesive. These coatings can be applied to rigid glass substrates as well as to flexible polyethylene terephthalate (PET) plastic and elastomeric polydimethylsiloxane (PDMS) substrates to produce highly flexible transparent conductive electrodes. The coatings are as conductive and transparent as indium tin oxide (ITO) films on glass, but they remain conductive at high bending strains and are more durable to marring and scratching than ITO. Coatings on PDMS withstand up to 76% tensile strain and 250 bending cycles of 15% strain with a negligible increase in electrical resistance. Since the silver nanowire network is embedded at the surface of the optical adhesive, these coatings also provide a smooth surface (root mean squared surface roughness<10 nm), making them suitable as transparent conducting electrodes in flexible light-emitting electrochemical cells. These devices continue to emit light even while being bent to radii as low as 1.5 mm and perform as well as unstrained devices after 20 bending cycles of 25% tensile strain.

We report the fabrication and characterization of new self-assembled monolayers (SAMs) formed from dihexadecyldithiophosphinic acid [(C(16))(2)DTPA] molecules on gold substrates. In these SAMs, the ability of the (C(16))(2)DTPA headgroup to chelate to the gold surface depends on the morphology of the gold substrate. Gold substrates fabricated by electron-beam evaporation (As-Dep gold) consist of ∼50-nm grains separated by deep grain boundaries (∼10 nm). These grain boundaries inhibit the chelation of (C(16))(2)DTPA adsorbates to the surface, producing SAMs in which there is a mixture of monodentate and bidentate adsorbates. In contrast, gold substrates produced by template stripping (TS gold) consist of larger grains (∼200-500 nm) with shallower grain boundaries (<2 nm). On these substrates, the low density of shallow grain boundaries allows (C(16))(2)DTPA molecules to chelate to the surface, producing SAMs in which all molecules are bidentate. The content of bidentate adsorbates in (C(16))(2)DTPA SAMs formed on As-Dep and TS gold substrates strongly affects the SAM properties: Alkyl chain organization, wettability, frictional response, barrier properties, thickness, and thermal stability all depend on whether a SAM has been formed on As-Dep or TS gold. This study demonstrates that substrate morphology has an important influence on the structure of SAMs formed from these chelating adsorbates.

We report the formation and characterization of self-assembled monolayers (SAMs) based on dialkyldithiophosphinic acid adsorbates {[CH(3)(CH(2))(n)](2)P(S)SH (n = 5, 9, 11, 13, 15)} on gold substrates. SAMs were characterized using X-ray photoelectron spectroscopy, reflection-absorption infrared spectroscopy, contact angle measurements, and electrochemical impedance spectroscopy. Data show that there is a roughly 60:40 mixture of bidentate and monodentate adsorbates in each of these SAMs. The presence of monodentate adsorbates is due to the numerous and deep grain boundaries of the underlying gold substrate, which disrupt chelation. Comparing the characterization data of dialkyldithiophosphinic acid SAMs with those of analogous n-alkanethiolate SAMs shows that both SAMs follow a similar trend: The alkyl chains become increasingly organized and crystalline with increasing alkyl chain length. The alkyl groups of dialkyldithiophosphinic acid SAMs, however, are generally less densely packed than those of n-alkanethiolate SAMs. For short alkyl chains (hexyl, decyl, and dodecyl), the significantly lower packing densities cause the alkyl chains to be liquid-like and disorganized. Long-chain dialkyldithiophosphinic acid SAMs are only slightly less crystalline than analogous n-alkanethiolate SAMs.

The demand for materials and devices with dimensions on the nanometer scale continues to increase. To meet this demand, high-throughput, cost-effective methods for depositing nanoscale thin films are needed. In the past few years, atmospheric pressure spatial atomic layer deposition (AP-SALD) has emerged as a potential nanomanufacturing method that is scalable, open air, and operates at modest temperatures that are compatible with flexible substrates. In this Perspective, we compare AP-SALD to other high-throughput techniques for depositing nanometer-scale thin films, including gravure printing, screen printing, knife-over-edge coating, slot-die coating, inkjet printing, spray deposition, as well as high-throughput sputtering and evaporation. Although AP-SALD does not provide the same patterning capabilities as some of these printing techniques, it offers multiple advantages: it produces continuous, conformal coatings with few defects; it requires minimal thermal treatment of the deposited materials; it provides atomic scale thickness control; it facilitates tuning of material properties; and no vacuum chamber is required, which simplifies maintenance requirements and minimizes the operating cost. Areas for further development are identified, which will allow these advantages to be leveraged: new precursors need to be developed to enable deposition of a wider variety of materials, precursor recycling should be examined, and AP-SALD systems that are high-throughput (roll-to-roll coating speeds of tens or hundreds of meters per minute) and low-maintenance need to be further developed and tested.