Grundlagen der Festkörperphysik

Weißmantel, Christian; Hamann, C.

doi:10.1007/978-3-642-67115-9

Cited by 69 publications

(14 citation statements)

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“…18 It has been shown that, in the case of thin-film OFETs, this so called ''access resistance'' has a strong influence on the extracted field-effect mobility (m FE ) and the device performance depending on the thickness of the active layer material. 22 The choice of the most suitable metal depends on the nature of the OSC. 17 Another important aspect that determines the contact resistance is the choice of the metal contact.…”

Section: Introductionmentioning

confidence: 99%

Organic metal engineering for enhanced field-effect transistor performance

Pfattner

Rovira

Mas‐Torrent

2015

Phys. Chem. Chem. Phys.

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A key device component in organic field-effect transistors (OFETs) is the organic semiconductor/metal interface since it has to ensure efficient charge injection. Traditionally, inorganic metals have been employed in these devices using conventional lithographic fabrication techniques. Metals with low or high work-functions have been selected depending on the type of semiconductor measured and, in some cases, the metal has been covered with molecular self-assembled monolayers to tune the work function, improve the molecular order at the interface and reduce the contact resistance. However, in the last few years, some approaches have been focused on utilizing organic metals in these devices, which have been fabricated by means of both evaporation and solution-processed techniques. Higher device performances have often been observed, which have been attributed to a range of factors, such as a more favourable organic/organic interface, a better matching of energy levels or/and to a reduction of the contact resistance. Further, in contrast to their inorganic counterparts, organic metals allow their chemical modification and thus the tuning of the Fermi level. In this perspective paper, an overview of the recent work devoted to the fabrication of OFETs with organic metals as electrodes will be carried out. It will be shown that in these devices not only is the matching of the HOMO or LUMO of the semiconductor with the metal work-function important, but other aspects such as the interface morphology can also play a critical role. Also, recent approaches in which the use of organic charge transfer salts as buffer layers at the metal contacts or on the dielectric or as doping agents of the organic semiconductors that have been used to improve the device performance will be briefly described.

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Section: Introductionmentioning

confidence: 99%

Organic metal engineering for enhanced field-effect transistor performance

Pfattner

Rovira

Mas‐Torrent

2015

Phys. Chem. Chem. Phys.

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“…The only appropriate Ansatz appears to be injection‐limited transport, known to prevail for high injection barriers between the Fermi level of the contact and the transport levels of the semiconductor. Thermionic emission, an injection process based on thermal activation, is known to be effective in systems exhibiting hopping transport, such as polymers or amorphous molecular layers commonly used in organic light‐emitting diodes (OLEDs) . This regime is rarely reported in molecular thin‐film devices, essentially because its observation requires molecular building blocks that are: i) long enough for charge transport being not exclusively governed by tunneling, and ii) stable enough to withstand a sufficient range of temperatures and bias voltages.…”

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confidence: 99%

Ultrarobust Thin‐Film Devices from Self‐Assembled Metal–Terpyridine Oligomers

et al. 2016

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or inorganic [ 13,18 ] interlayers have been introduced to protect ultrathin molecular layers from invasive, vapor deposited contacts. These approaches represent a promising pathway toward robust molecular/polymer circuits; however they require an additional organic/inorganic layer that inevitably masks the intrinsic electrical response of the molecules under investigation. A possible solution has been proposed by McCreery and co-workers, involving molecular layers that are sandwiched between carbon and copper electrodes forming stable and highly reproducible molecular junctions. [ 19 ] Remarkably, these large area junctions show high yields, endurance, and temperature stability, even though the requirement of using pyrolytic carbon as a bottom electrode might limit their applicability.Here, we demonstrate that by integration of Fe II -terpyridine redox complex oligomers [20][21][22] into large area solid-state junctions, molecular thin-fi lm devices of outstanding mechanical and electrical robustness are realized. Notwithstanding the metallic crossbar junctions are deposited in a conventional thermal evaporation process, Fe II -terpyridine oligomers are operational over a period of more than two and a half years and resist to temperatures ranging from 150-360 K. The oligomer layers show a high electron mobility ( µ e = 0.1 cm 2 V −1 s −1 ) and, most remarkably, electrical transport follows an ideal RichardsonSchottky (RS) injection behavior, as demonstrated by means of complementary experimental and theoretical investigations.Bottom electrodes are prepared by thermal evaporation of an array of eight parallel Au electrodes (each 100 µm wide) on native silicon using a shadow mask. Subsequently, metal center oligomers (MCOs) are deposited by a stepwise sequential coordination reaction of a Fe II redox center by a conjugated 1,4-di(2;2′;6′;2″-terpyridine-4′-yl)benzene (TPT) ligand ( Figure 1 a), [ 21 ] as schematically depicted in Figure 1 b. In our work, oligomers of three different lengths have been assembled by incorporation of 15, 20, and 30 Fe II metal centers (MC), yielding MCO layers with a thickness of 15, 20, and 30 nm. This allows a detailed study of their electrical characteristics as a function of molecular length. A symmetric contact of the oligomers to both Au electrodes is established by using 4′-(4-mercaptophenyl)terpyridine (MPTP) as the fi rst and last ligands of the stepwise coordination.From density functional theory (DFT) calculations, a length of 1.55 nm is derived for the repeat unit of the MCO chain (Figure 1 a). A constant increment in fi lm thickness as a function of the coordination number is determined from AFM data (Figure 1 c), following a linear regression with a slope of ≈1.08 nm per coordination step. These data and the coordination effi ciency known for the stepwise coordination process [ 23 ]

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“…These time slots were filled ad hoc with a standby discussion on current problems in the theoretical description of ultrathin metal film optical properties. Here, the authors of the present study developed their point of view that it would be useful to adopt the mean free path theory successfully applied in solid state physics [11,12] and cluster physics [13] to the modelling of thin metal film optical constants. It is the purpose of this paper to re-examine this idea and to demonstrate experimental examples on the use of this treatment.…”

Section: Introductionmentioning

confidence: 99%

“…d [11,12]. Here, v F is the Fermi velocity, and τ b the average time between two collisions suffered by a free charge carrier in the bulk.…”

Section: Introductionmentioning

confidence: 99%

Spectrophotometric Characterization of Thin Copper and Gold Films Prepared by Electron Beam Evaporation: Thickness Dependence of the Drude Damping Parameter

et al. 2019

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Copper and gold films with thicknesses between approximately 10 and 60 nm have been prepared by electron beam evaporation and characterized by spectrophotometry from the near infrared up to the near ultraviolet spectral regions. From near normal incidence transmission and reflection spectra, dispersion of optical constants have been determined by means of spectra fits utilizing a merger of the Drude model and the beta-distributed oscillator model. All spectra could be fitted in the full spectral region with a total of seven dispersion parameters. The obtained Drude damping parameters shows a clear trend to increase with decreasing film thickness. This behavior is discussed in the context of additional non-optical characterization results and turned out to be consistent with a simple mean-free path theory.

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Grundlagen der Festkörperphysik

Cited by 69 publications

References 0 publications

Organic metal engineering for enhanced field-effect transistor performance

Organic metal engineering for enhanced field-effect transistor performance

Ultrarobust Thin‐Film Devices from Self‐Assembled Metal–Terpyridine Oligomers

Spectrophotometric Characterization of Thin Copper and Gold Films Prepared by Electron Beam Evaporation: Thickness Dependence of the Drude Damping Parameter

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