This paper describes the rheological behavior of the liquid metal eutectic gallium‐indium (EGaIn) as it is injected into microfluidic channels to form stable microstructures of liquid metal. EGaIn is well‐ ;suited for this application because of its rheological properties at room temperature: it behaves like an elastic material until it experiences a critical surface stress, at which point it yields and flows readily. These properties allow EGaIn to fill microchannels rapidly when sufficient pressure is applied to the inlet of the channels, yet maintain structural stability within the channels once ambient pressure is restored. Experiments conducted in microfluidic channels, and in a parallel‐plate rheometer, suggest that EGaIn's behavior is dictated by the properties of its surface (predominantly gallium oxide, as determined by Auger measurement s); these two experiments both yield approximately the same number for the critical surface stress required to induce EGaIn to flow (∼0 .5 N/m). This analysis–which shows that the pressure that must be exceeded for EGaIn to flow through a microchannel is inversely proportional to the critical (i.e., smallest) dimension of the channel–is useful to guide future fabrication of microfluidic channels to mold EGaIn into functional microstructures.

Herein we describe the formation of conformal electrodes from the fluid metal eutectic, Ga-In (which we abbreviate "EGaIn" and pronounce "e-gain"; 75 % Ga, 25 % In by weight, m.p. = 15.5 8C), [1] and their use in studying charge transport across self-assembled monolayers (SAMs). Although EGaIn is a liquid at room temperature, it does not spontaneously reflow into the shape with the lowest interfacial free energy as do liquids such as Hg and H 2 O: as a result, it can be formed into metastable, nonspherical structures (e.g., cones, and filaments with diameters ! 1 mm). This behavior, along with its high electrical conductivity (3.4 10 4 S cm À1 ) [2] and its tendency to make low contact-resistance interfaces with a variety of materials, [1] makes EGaIn useful for forming electrodes for thin-film devices. [3][4][5] We discuss the convenience and precision of measurements of current density (J, Acm À2 ) versus applied voltage (V, V) through SAMs of n-alkanethiolates on template-stripped, ultraflat Ag [6] (Ag-SC n Ag-SC n H 2n+1 , n = 10, 12, 14, 16) using EGaIn.An ideal electrode for physical-organic studies of SAMs would 1) make conformal, but nondamaging, physical contacts, 2) readily form small-area (micrometer diameter) contacts, to minimize the contribution of defects in the SAM to J, 3) form without specialized equipment, and 4) be nontoxic. Point 3 is particularly important: elimination of procedures such as evaporating metals or lithographic patterning would allow a wide range of laboratories-including those without access to clean rooms-to survey relationships between structure and electrical conductivity.There are currently three general techniques for forming top contacts for large-area (i.e., more than a few molecules) electrical measurements on SAMs of organic molecules: 1) The direct deposition of metals such as Au or Ti by using electron-beam or thermal evaporation [7] ensures atomic-level contact, but results in low yields of devices [8] owing to damage to the organic monolayer by reaction with hot metal vapors, and in the formation of metal filaments that short the junctions. [9] 2) The installation of an electrically conducting polymer [10,11] between the SAM and a metallic top contact inhibits formation of metal filaments, but the instability of SAMs of alkanethiolates to the temperatures [12] required to anneal most electroactive polymers limits the broad application of this approach.3) The use of Hg allows formation of conformal contacts at room temperature, [13,14] but Hg is toxic, amalgamates with metals, [15] tends to form junctions that short, is difficult to form into small contacts, and measurements with Hg must be performed under a solvent bath.EGaIn does not flow until it experiences a critical surface stress (0.5 N m À1 ), at which point it yields (i.e., flows).[16]EGaIn 1) makes conformal, nondamaging contacts at room temperature, 2) can be molded into nonspherical shapes with micrometer-scale (or larger) dimensions, 3) is commercially available, 4) can be deposited with a pipette or s...

This paper compares the structural and electrical characteristics of self-assembled monolayers (SAMs) of n-alkanethiolates, SCn (n = 10, 12, 14), on two types of silver substrates: one used as-deposited (AS-DEP) by an electron-beam evaporator, and one prepared using the method of template-stripping. Atomic force microscopy showed that the template-stripped (TS) silver surfaces were smoother and had larger grains than the AS-DEP surfaces, and reflectance-absorbance infrared spectroscopy showed that SAMs formed on TS substrates were more crystalline than SAMs formed on AS-DEP substrates. The range of current densities, J (A/cm2), measured through mercury-drop junctions incorporating a given SAM on AS-DEP silver was, on average, several orders of magnitude larger than the range of J measured through the same SAM on TS silver, and the AS-DEP junctions failed, on average, 3.5 times more often within five current density-voltage (J-V) scans than did TS junctions (depending on the length of the alkyl chains of the molecules in the SAM). The apparent log-normal distribution of J through the TS junctions suggests that, in these cases, it is the variability in the effective thickness of the insulating layer (the distance the electron travels between electrodes) that results in the uncertainty in J. The parameter describing the decay of current density with the thickness of the insulating layer, beta, was either 0.57 A-1 at V = +0.5 V (calculated using the log-mean of the distribution of values of J) or 0.64 A-1 (calculated using the peak of the distribution of values of J) for the TS junctions; the latter is probably the more accurate. The mechanisms of failure of the junctions, and the degree and sources of uncertainty in current density, are discussed with respect to a variety of defects that occur within Hg-drop junctions incorporating SAMs on silver.

In this contribution, for the first time, the molecular n-doping of a donor-acceptor (D-A) copolymer achieving 200-fold enhancement of electrical conductivity by rationally tailoring the side chains without changing its D-A backbone is successfully improved. Instead of the traditional alkyl side chains for poly{[N,N'-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl](NDI)-alt-5,5'-(2,2'-bithiophene)} (N2200), polar triethylene glycol type side chains is utilized and a high electrical conductivity of 0.17 S cm after doping with (4-(1,3-dimethyl-2,3-dihydro-1H-benzoimidazol-2-yl)phenyl)dimethylamine is achieved, which is the highest reported value for n-type D-A copolymers. Coarse-grained molecular dynamics simulations indicate that the polar side chains can significantly reduce the clustering of dopant molecules and favor the dispersion of the dopant in the host matrix as compared to the traditional alkyl side chains. Accordingly, intimate contact between the host and dopant molecules in the NDI-based copolymer with polar side chains facilitates molecular doping with increased doping efficiency and electrical conductivity. For the first time, a heterogeneous thermoelectric transport model for such a material is proposed, that is the percolation of charge carriers from conducting ordered regions through poorly conductive disordered regions, which provides pointers for further increase in the themoelectric properties of n-type D-A copolymers.

Herein we describe the formation of conformal electrodes from the fluid metal eutectic, Ga-In (which we abbreviate "EGaIn" and pronounce "e-gain"; 75 % Ga, 25 % In by weight, m.p. = 15.5 8C), [1] and their use in studying charge transport across self-assembled monolayers (SAMs). Although EGaIn is a liquid at room temperature, it does not spontaneously reflow into the shape with the lowest interfacial free energy as do liquids such as Hg and H 2 O: as a result, it can be formed into metastable, nonspherical structures (e.g., cones, and filaments with diameters ! 1 mm). This behavior, along with its high electrical conductivity (3.4 10 4 S cm À1 ) [2] and its tendency to make low contact-resistance interfaces with a variety of materials, [1] makes EGaIn useful for forming electrodes for thin-film devices. [3][4][5] We discuss the convenience and precision of measurements of current density (J, Acm À2 ) versus applied voltage (V, V) through SAMs of n-alkanethiolates on template-stripped, ultraflat Ag [6] (Ag-SC n Ag-SC n H 2n+1 , n = 10, 12, 14, 16) using EGaIn.An ideal electrode for physical-organic studies of SAMs would 1) make conformal, but nondamaging, physical contacts, 2) readily form small-area (micrometer diameter) contacts, to minimize the contribution of defects in the SAM to J, 3) form without specialized equipment, and 4) be nontoxic. Point 3 is particularly important: elimination of procedures such as evaporating metals or lithographic patterning would allow a wide range of laboratories-including those without access to clean rooms-to survey relationships between structure and electrical conductivity.There are currently three general techniques for forming top contacts for large-area (i.e., more than a few molecules) electrical measurements on SAMs of organic molecules: 1) The direct deposition of metals such as Au or Ti by using electron-beam or thermal evaporation [7] ensures atomic-level contact, but results in low yields of devices [8] owing to damage to the organic monolayer by reaction with hot metal vapors, and in the formation of metal filaments that short the junctions. [9] 2) The installation of an electrically conducting polymer [10,11] between the SAM and a metallic top contact inhibits formation of metal filaments, but the instability of SAMs of alkanethiolates to the temperatures [12] required to anneal most electroactive polymers limits the broad application of this approach.3) The use of Hg allows formation of conformal contacts at room temperature, [13,14] but Hg is toxic, amalgamates with metals, [15] tends to form junctions that short, is difficult to form into small contacts, and measurements with Hg must be performed under a solvent bath.EGaIn does not flow until it experiences a critical surface stress (0.5 N m À1 ), at which point it yields (i.e., flows).[16]EGaIn 1) makes conformal, nondamaging contacts at room temperature, 2) can be molded into nonspherical shapes with micrometer-scale (or larger) dimensions, 3) is commercially available, 4) can be deposited with a pipette or s...