Ryan C. Chiechi

Bio: Ryan C. Chiechi is an academic researcher from University of Groningen. The author has contributed to research in topics: Molecular electronics & Self-assembled monolayer. The author has an hindex of 34, co-authored 108 publications receiving 4769 citations. Previous affiliations of Ryan C. Chiechi include Harvard University & University of California, Los Angeles.

Eutectic Gallium-Indium (EGaIn) : A Liquid Metal Alloy for the Formation of Stable Structures in Microchannels at Room Temperature

Abstract: 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 measurements); 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.

Eutectic gallium-indium (EGaIn): a moldable liquid metal for electrical characterization of self-assembled monolayers.

Abstract: 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), 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 H2O: 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 4 10 Scm ) and its tendency to make low contact-resistance interfaces with a variety of materials, makes EGaIn useful for forming electrodes for thin-film devices. We discuss the convenience and precision of measurements of current density (J, Acm ) versus applied voltage (V, V) through SAMs of n-alkanethiolates on template-stripped, ultraflat Ag (Ag–SCn Ag–SCnH2n+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 ensures atomic-level contact, but results in low yields of devices owing to damage to the organic monolayer by reaction with hot metal vapors, and in the formation of metal filaments that short the junctions. 2) The installation of an electrically conducting polymer between the SAM and a metallic top contact inhibits formation of metal filaments, but the instability of SAMs of alkanethiolates to the temperatures 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, but Hg is toxic, amalgamates with metals, 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 Nm ), at which point it yields (i.e., flows). 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 syringe without high temperatures or vacuum, 5) has a low vapor pressure, and 6) is nontoxic. The work function of EGaIn (4.1–4.2 eV) is close to that of Hg (4.5 eV), but EGaIn does not alloy with many metals. It is therefore an ideal replacement for Hg, especially in devices that incorporate SAMs (which are generally formed on Au or Ag). Auger spectroscopy on samples of EGaIn in air show that its surface is principally composed of oxides of Ga (see the Supporting Information); gallium oxide is an n-type semiconductor. There is undoubtedly an adsorbed film of water on this surface, as EGaIn has a high surface free energy (ca. 630 dynescm ), as do oxides formed from similar metals. During our measurements, there were no observable changes in the average magnitude or range of J when EGaIn was allowed to sit in air for extended periods before we deposited it on the SAM, or when we performed the measurements using the same drop of EGaIn to form between three and five junctions, or while we flowed dry N2 over the sample: therefore the contribution of the surface oxide to J was probably constant for the duration of the experiments. We formed EGaIn electrodes by suspending a drop of EGaIn from a metal 26s-gauge needle affixed to a 10-mL syringe, bringing the drop into contact with the bare surface of a sacrificial film of Ag using a micromanipulator, and retracting the needle slowly (ca. 50 mms ); the EGaIn adhered to both the needle and the Ag (Figure 1). The drop of EGaIn pinched into to an hour-glass shape until it bifurcated into two structures, one attached to the syringe (a cone approximately 0.05 mL in volume) and one (which was discarded) attached to the Ag. We produced conical tips of EGaIn with diameters ranging from less than 1 mm to 100 mm; the larger the bore of the needle, and the more rapidly we [*] Dr. R. C. Chiechi, Dr. E. A. Weiss, Dr. M. D. Dickey, Prof. G. M. Whitesides Department of Chemistry and Chemical Biology Harvard University 12 Oxford St., Cambridge, MA 02138 (USA) Fax: (+1)617-495-9857 E-mail: gwhitesides@gmwgroup.harvard.edu

Influence of Defects on the Electrical Characteristics of Mercury-Drop Junctions: Self-Assembled Monolayers of n-Alkanethiolates on Rough and Smooth Silver

Abstract: 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, 35 times more often within five current density−voltage (J−V) scans than did TS junctions (depending on the length of the alkyl chains of

Enhancing Molecular n-Type Doping of Donor-Acceptor Copolymers by Tailoring Side Chains.

Abstract: 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-1 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.

Evidence for quantum interference in SAMs of arylethynylene thiolates in tunneling junctions with eutectic Ga-In (EGaIn) top-contacts.

Abstract: This paper compares the current density (J) versus applied bias (V) of self-assembled monolayers (SAMs) of three different ethynylthiophenol-functionalized anthracene derivatives of approximately the same thickness with linear-conjugation (AC), cross-conjugation (AQ), and broken-conjugation (AH) using liquid eutectic Ga-In (EGaIn) supporting a native skin (~1 nm thick) of Ga(2)O(3) as a nondamaging, conformal top-contact. This skin imparts non-Newtonian rheological properties that distinguish EGaIn from other top-contacts; however, it may also have limited the maximum values of J observed for AC. The measured values of J for AH and AQ are not significantly different (J ≈ 10(-1)A/cm(2) at V = 0.4 V). For AC, however, J is 1 (using log averages) or 2 (using Gaussian fits) orders of magnitude higher than for AH and AQ. These values are in good qualitative agreement with gDFTB calculations on single AC, AQ, and AH molecules chemisorbed between Au contacts that predict currents, I, that are 2 orders of magnitude higher for AC than for AH at 0 < |V| < 0.4 V. The calculations predict a higher value of I for AQ than for AH; however, the magnitude is highly dependent on the position of the Fermi energy, which cannot be calculated precisely. In this sense, the theoretical predictions and experimental conclusions agree that linearly conjugated AC is significantly more conductive than either cross-conjugated AQ or broken conjugate AH and that AQ and AH cannot necessarily be easily differentiated from each other. These observations are ascribed to quantum interference effects. The agreement between the theoretical predictions on single molecules and the measurements on SAMs suggest that molecule-molecule interactions do not play a significant role in the transport properties of AC, AQ, and AH.

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

Prospects of Colloidal Nanocrystals for Electronic and Optoelectronic Applications

Abstract: Nanocrystals (NCs) discussed in this Review are tiny crystals of metals, semiconductors, and magnetic material consisting of hundreds to a few thousand atoms each. Their size ranges from 2-3 to about 20 nm. What is special about this size regime that placed NCs among the hottest research topics of the last decades? The quantum mechanical coupling * To whom correspondence should be addressed. E-mail: dvtalapin@uchicago.edu. † The University of Chicago. ‡ Argonne National Lab. Chem. Rev. 2010, 110, 389–458 389

Semiconducting π-conjugated systems in field-effect transistors: a material odyssey of organic electronics.

Abstract: Since the discovery of highly conducting polyacetylene by Shirakawa, MacDiarmid, and Heeger in 1977, π-conjugated systems have attracted much attention as futuristic materials for the development and production of the next generation of electronics, that is, organic electronics. Conceptually, organic electronics are quite different from conventional inorganic solid state electronics because the structural versatility of organic semiconductors allows for the incorporation of functionality by molecular design. This versatility leads to a new era in the design of electronic devices. To date, the great number of π-conjugated semiconducting materials that have either been discovered or synthesized generate an exciting library of π-conjugated systems for use in organic electronics. 11 However, some key challenges for further advancement remain: the low mobility and stability of organic semiconductors, the lack of knowledge regarding structure property relationships for understanding the fundamental chemical aspects behind the structural design, and realization of desired properties. Organic field-effect transistors (OFETs) are a kind of device consisting of an organic semiconducting layer, a gate insulator layer, and three terminals (drain, source, and gate electrodes). OFETs are not only essential building blocks for the next generation of cheap and flexible organic circuits, but they also provide an important insight into the charge transport of πconjugated systems. Therefore, they act as strong tools for the exploration of the structure property relationships of πconjugated systems, such as parameters of field-effect mobility (μ, the drift velocity of carriers under unit electric field), current on/off ratio (the ratio of the maximum on-state current to the minimum off-state current), and threshold voltage (the minimum gate voltage that is required to turn on the transistor). 17 Since the discovery of OFETs in the 1980s, they have attracted much attention. Research onOFETs includes the discovery, design, and synthesis of π-conjugated systems for OFETs, device optimization, development of applications in radio frequency identification (RFID) tags, flexible displays, electronic papers, sensors, and so forth. It is beyond the scope of this review to cover all aspects of π-conjugated systems; hence, our focus will be on the performance analysis of π-conjugated systems in OFETs. This should make it possible to extract information regarding the fundamental merit of semiconducting π-conjugated materials and capture what is needed for newmaterials and what is the synthesis orientation of newπ-conjugated systems. In fact, for a new science with many practical applications, the field of organic electronics is progressing extremely rapidly. For example, using “organic field effect transistor” or “organic field effect transistors” as the query keywords to search the Web of Science citation database, it is possible to show the distribution of papers over recent years as shown in Figure 1A. It is very clear

Skin-like pressure and strain sensors based on transparent elastic films of carbon nanotubes

Abstract: Transparent films of carbon nanotubes can accommodate strains of up to 150% and demonstrate conductivities as high as 2,200 S cm−1 in the stretched state.

π-Conjugated Polymers for Organic Electronics and Photovoltaic Cell Applications†

Abstract: The optoelectronic properties of polymeric semiconductor materials can be utilized for the fabrication of organic electronic and photonic devices. When key structural requirements are met, these materials exhibit unique properties such as solution processability, large charge transporting capabilities, and/or broad optical absorption. In this review recent developments in the area of π-conjugated polymeric semiconductors for organic thin-film (or field-effect) transistors (OTFTs or OFETs) and bulk-heterojunction photovoltaic (or solar) cell (BHJ-OPV or OSC) applications are summarized and analyzed.