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

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Prospects of Colloidal Nanocrystals for Electronic and Optoelectronic Applications

2.2. Materials 929 2.3. Factors Influencing Charge Mobility 931 2.3.1. Molecular Packing 931 2.3.2. Disorder 932 2.3.3. Temperature 933 2.3.4. Electric Field 934 2.3.5. Impurities 934 2.3.6. Pressure 934 2.3.7. Charge-Carrier Density 934 2.3.8. Size/molecular Weight 935 3. The Charge-Transport Parameters 935 3.1. Electronic Coupling 936 3.1.1. The Energy-Splitting-in-Dimer Method 936 3.1.2. The Orthogonality Issue 937 3.1.3. Impact of the Site Energy 937 3.1.4. Electronic Coupling in Oligoacene Derivatives 938

Charge transport in organic semiconductors.

Electron and ambipolar transport in organic field-effect transistors.

Acenes have long been the subject of intense study because of the unique electronic properties associated with their pi-bond topology. Recent reports of impressive semiconductor properties of larger homologues have reinvigorated research in this field, leading to new methods for their synthesis, functionalization, and purification, as well as for fabricating organic electronic components. Studies performed on high-purity acene single crystals revealed their intrinsic electronic properties and provide useful benchmarks for thin film device research. New approaches to add functionality were developed to improve the processability of these materials in solution. These new functionalization strategies have recently allowed the synthesis of acenes larger than pentacene, which have hitherto been largely unavailable and poorly studied, as well as investigation of their associated structure/property relationships.

The larger acenes: versatile organic semiconductors.

Field-effect transistors based on solution-processible organic semiconductors have experienced impressive improvements in both performance and reliability in recent years, and printing-based manufacturing processes for integrated transistor circuits are being developed to realize low-cost, large-area electronic products on flexible substrates. This article reviews the materials, charge-transport, and device physics of solution-processed organic field-effect transistors, focusing in particular on the physics of the active semiconductor/dielectric interface. Issues such as the relationship between microstructure and charge transport, the critical role of the gate dielectric, the influence of polaronic relaxation and disorder effects on charge transport, charge-injection mechanisms, and the current understanding of mechanisms for charge trapping are reviewed. Many interesting questions on how the molecular and electronic structures and the presence of defects at organic/organic heterointerfaces influence the device performance and stability remain to be explored.

Device Physics of Solution‐Processed Organic Field‐Effect Transistors

We describe gated four-probe measurements designed to measure contact resistance in pentacene-based organic thin-film transistors (OTFTs) The devices consisted of metal source and drain electrodes contacting a 300-A-thick pentacene film thermally deposited on Al2O3 or SiO2 dielectrics with a p-doped Si substrate serving as the gate electrode Voltage-sensing leads extending into the source-drain channel were used to monitor potentials in the pentacene film while passing current during drain voltage (VD) or gate voltage (VG) sweeps We investigated the potential profiles as a function of contact metallurgy (Pt, Au, Ag, and Ca), substrate chemistry, VG, and temperature The contact-corrected linear hole mobilities were as high as 175cm2∕Vs and the film sheet resistance and specific contact resistance were as low as 600kΩ∕◻ and 13kΩ-cm, respectively, at high gate voltages In the temperature range of 50–200K, the pentacene OTFTs displayed an activated behavior with activation energies of 15–30meV Importa

Gated four-probe measurements on pentacene thin-film transistors: Contact resistance as a function of gate voltage and temperature

Surface potentials of operating pentacene thin-film transistors (TFTs) with two different contact geometries (bottom or top) were mapped by Kelvin probe force microscopy (KFM). The surface potential distribution was used to isolate the potential drops at the source and drain contacts. These potential drops were converted to resistances by dividing by the appropriate drain current values. The bottom contact TFTs were contact limited at large gate voltages, while the top contact TFTs were not contact limited. In both geometries, the contact and the channel resistances decreased strongly with increasing (negative) gate bias but did not depend strongly on the drain bias. This study demonstrates the utility of KFM for visualizing charge transport bottlenecks in operating pentacene devices and for correlating electrical behavior with device structure by comparison of surface potential and topographic maps.

Surface potential profiling and contact resistance measurements on operating pentacene thin-film transistors by Kelvin probe force microscopy

We describe variable temperature contact resistance measurements on pentacene organic thin-film transistors via a gated four-probe technique. The transistors consist of Au source and drain electrodes contacting a pentacene film deposited on a dielectric/gate electrode assembly. Additional voltage sensing leads penetrating into the source-drain channel were used to monitor potentials in the pentacene film while passing current between the source and drain electrodes during gate voltage sweeps. Using this device structure, we investigated contact resistance as a function of film thickness (60–3000A), deposition temperature (25 or 80°C), gate voltage, electrode geometry (top or bottom contact), and temperature. Contact resistance values were approximately 2×103–7×106Ωcm, depending on film thickness. In the temperature range of 77–295K, the contact resistance displayed activated behavior with activation energies of 15–160meV. Importantly, it was observed that the activation energies for the source and drain r...

Film and contact resistance in pentacene thin-film transistors: Dependence on film thickness, electrode geometry, and correlation with hole mobility

Various embodiments concern a dual stage actuation flexure having a motor contact paddle for connecting to a terminal of a piezoelectric motor. The flexure comprises a paddle having a top side and a bottom side, the paddle comprising at least one void, each void extending through the paddle from the bottom side to the top side. The paddle further comprises a stainless steel base, a conductor comprising a layer of metal, and a dielectric layer having a first section and a second section, the first section positioned between the conductor and the stainless steel base to overlap the stainless steel base and the second section extending beyond the stainless steel base to not overlap the stainless steel base. The bottom side of the paddle is configured to connect to the terminal with electrically conductive adhesive.

Electrical contacts to motors in dual stage actuated suspensions

Insulation of components of an SMA actuation arrangement in a miniature camera A miniature camera comprises an SMA actuator arrangement including at least one SMA actuator wire arranged to effect focus, zoom or optical image stabilization. At least one component of the SMA actuator arrangement that is not the SMA actuator wire is coated with an electrically insulating layer, thereby reducing the risk of short circuiting of the drive current of the SMA actuator wire. The SMA actuator wire may not be coated at all.

Paul V. Pesavento

Papers

Gated four-probe measurements on pentacene thin-film transistors: Contact resistance as a function of gate voltage and temperature

Surface potential profiling and contact resistance measurements on operating pentacene thin-film transistors by Kelvin probe force microscopy

Film and contact resistance in pentacene thin-film transistors: Dependence on film thickness, electrode geometry, and correlation with hole mobility

Electrical contacts to motors in dual stage actuated suspensions

Insulation of components of an sma actuation arrangement in a miniature camera