Energy-level alignment and work function shifts for thiol-bound monolayers of conjugated molecules self-assembled on Ag, Cu, Au, and Pt

Zangmeister, Christopher D.; Picraux, Laura B.; Zee, Roger D. van; Yao, Yuxing; Tour, James M.

doi:10.1016/j.cplett.2007.06.012

Cited by 48 publications

(54 citation statements)

References 20 publications

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“…[56,79,187] Translating this observation to the SAM-induced work-function modification via Equation (7) yields the equally intriguing result that, despite the considerable difference in F of the pristine metal surfaces, the work functions of the SAM-covered surfaces are nearly identical. [56,79,187] These peculiarities regarding level alignment and DF are in agreement with experimental [38,40,232] and independent theoretical results. [85] …”

Section: Impact Of the Substrate Metalsupporting

confidence: 89%

Modeling the Electronic Properties of π‐Conjugated Self‐Assembled Monolayers

2010

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The modification of electrode surfaces by depositing self-assembled monolayers (SAMs) provides the possibility for controlled adjustment of various key parameters in organic and molecular electronic devices. Most important among them are the work function of the electrode and the relative alignment of its Fermi level with the conducting states in the SAM itself and with those in a subsequently deposited organic semiconductor. For the efficient application of such interface modifications it is crucial to reach a proper understanding of the relation between the chemical structure of a molecule, its molecular electronic characteristics, and the properties of the SAM formed by such molecules. Over the past years, quantum-mechanical calculations have proven to be a valuable tool for reaching a fundamental understanding of the relevant structure-property relations. Here, we provide a review over the field and report on recent progress in the modeling of the interfacial electronic properties of pi-conjugated SAMs. In addition to the insight that can be gained from simple electrostatic considerations, we focus on the quantum-mechanical description of the roles played by substituents, molecular backbones, chemical anchoring groups, and the packing density of molecules on the surface. Furthermore, we explicitly address the energy-level alignment at the interface between a prototypical organic semiconductor and a SAM-covered metal electrode and describe an approach suitable for extending the metallic character of the substrate onto the monolayer.

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Section: Impact Of the Substrate Metalsupporting

confidence: 89%

Modeling the Electronic Properties of π‐Conjugated Self‐Assembled Monolayers

2010

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“…[ 15 ] These results clearly indicate that metals such as Ag, Cu, and Pt merit in-depth investigation aimed at the use as S/D, exploiting their well-known ability to host thiolate monolayers. [ 16 ] We additionally note that SAMs can signifi cantly raise the chemical and thermal stability of metal surfaces by forming a robust barrier against oxidation, sulfi dation, or other corrosion. [17][18][19] In bottom-contact organic fi eld-effect transistors (OFETs), the functionalization of source/drain electrodes leads to a tailored surface chemistry for fi lm growth and controlled interface energetics for charge injection.…”

Section: −3mentioning

confidence: 99%

Decoupling the Effects of Self‐Assembled Monolayers on Gold, Silver, and Copper Organic Transistor Contacts

Kim

Hlaing

Hong

et al. 2014

Adv Materials Inter

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In bottom‐contact organic field‐effect transistors (OFETs), the functionalization of source/drain electrodes leads to a tailored surface chemistry for film growth and controlled interface energetics for charge injection. This report describes a comprehensive investigation into separating and correlating the energetic and morphological effects of a self‐assembled monolayers (SAMs) treatment on Au, Ag, and Cu electrodes. Fluorinated 5,11‐bis(triethylsilylethynyl) anthradithiophene (diF‐TES‐ADT) and pentafluorobenzenethiol (PFBT) are employed as a soluble small‐molecule semiconductor and a SAM material, respectively. Upon SAM modification, the Cu electrode devices benefit from a particularly dramatic performance improvement, closely approaching the performance of OFETs with PFBT‐Au and PFBT‐Ag. Ultraviolet photoemission spectroscopy, polarized optical microscopy, grazing‐incidence wide‐angle X‐ray scattering elucidate the metal work function change and templated crystal growth with high crystallinity resulting from SAMs. The transmission‐line method separates the channel and contact properties from the measured OFET current–voltage data, which conclusively describes the impact of the SAMs on charge injection and transport behavior.

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“…[1][2][3][4] In order to improve charge injection, several surface treatments have been reported. [5][6][7][8][9][10][11][12][13] One of the most attractive and promising ways is to modify the metal electrodes using selfassembled monolayers (SAMs). [8][9][10][11][12] Here, the SAM is sandwiched between the metal electrode and the active organic material and, thus, allows the effective work function of the electrode to be changed.…”

Section: Introductionmentioning

confidence: 99%

“…This enables control of the charge-injection barriers between the electrode Fermi level (E F ) and the frontier electronic states in the organic semiconductor. [9] However, it also introduces an additional tunneling resistance that is determined by the alignment of the electronic states within the SAM relative to E F . The latter also plays a decisive role in molecular electronics, where the SAM itself becomes the active component of the device.…”

Section: Introductionmentioning

confidence: 99%

Electronic Structure of Self‐Assembled Monolayers on Au(111) Surfaces: The Impact of Backbone Polarizability

Wang

Rangger

Romaner

et al. 2009

Adv Funct Materials

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Modifying metal electrodes with self‐assembled monolayers (SAMs) has promising applications in organic and molecular electronics. The two key electronic parameters are the modification of the electrode work function because of SAM adsorption and the alignment of the SAM conducting states relative to the metal Fermi level. Through a comprehensive density‐functional‐theory study on a series of organic thiols self‐assembled on Au(111), relationships between the electronic structure of the individual molecules (especially the backbone polarizability and its response to donor/acceptor substitutions) and the properties of the corresponding SAMs are described. The molecular backbone is found to significantly impacts the level alignment; for molecules with small ionization potentials, even Fermi‐level pinning is observed. Nevertheless, independent of the backbone, polar head‐group substitutions have no effect on the level alignment. For the work‐function modification, the larger molecular dipole moments achieved when attaching donor/acceptor substituents to more polarizable backbones are largely compensated by increased depolarization in the SAMs. The main impact of the backbone on the work‐function modification thus arises from its influence on the molecular orientation on the surface. This study provides a solid theoretical basis for the fundamental understanding of SAMs and significantly advances the understanding of structure–property relationships needed for the future development of functional organic interfaces.

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Energy-level alignment and work function shifts for thiol-bound monolayers of conjugated molecules self-assembled on Ag, Cu, Au, and Pt

Cited by 48 publications

References 20 publications

Modeling the Electronic Properties of π‐Conjugated Self‐Assembled Monolayers

Modeling the Electronic Properties of π‐Conjugated Self‐Assembled Monolayers

Decoupling the Effects of Self‐Assembled Monolayers on Gold, Silver, and Copper Organic Transistor Contacts

Electronic Structure of Self‐Assembled Monolayers on Au(111) Surfaces: The Impact of Backbone Polarizability

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