Pentacene ultrathin film formation on reduced and oxidized Si surfaces

Ruiz, Ricardo; Nickel, Bert; Koch, Norbert; Feldman, L. C.; Haglund, Richard F.; Kahn, Antoine; Scoles, G.

doi:10.1103/physrevb.67.125406

Cited by 211 publications

(224 citation statements)

References 26 publications

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“…Specifically, we assume that the substrate is composed of a thin amorphous layer with density ρ 1 and thickness T 1 = cτ on an amorphous, semi-infinite layer with density ρ 0 . This model is particularly suitable for amorphous substrates such as SiO 2 , but also valid for Si substrates with a thin SiO 2 native oxide 29 , and thick, thermal SiO 2 layers covered by a self-assembled monolayer 20,30 or an interfacial water layer 16,31 .…”

Section: Theory a X-ray Scatteringmentioning

confidence: 99%

Quantitative modeling ofin situx-ray reflectivity during organic molecule thin film growth

2011

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Synchrotron-based x-ray reflectivity is increasingly employed as an in situ probe of surface morphology during thin film growth, but complete interpretation of the results requires modeling the growth process. Many models have been developed and employed for this purpose, yet no detailed, comparative studies of their scope and accuracy exists in the literature. Using experimental data obtained from hyperthermal deposition of pentane and diindenoperylene (DIP) on SiO2, we compare and contrast three such models, both with each other and with detailed characterization of the surface morphology using ex-situ atomic force microscopy (AFM). These two systems each exhibit particular phenomena of broader interest: pentacene/SiO2 exhibits a rapid transition from rough to smooth growth. DIP/SiO2, under the conditions employed here, exhibits growth rate acceleration due to a different sticking probability between the substrate and film. In general, independent of which model is used, we find good agreement between the surface morphology obtained from fits to the in situx-ray data with the actual morphology at early times. This agreement deteriorates at later time, once the root-mean squared (rms) film roughness exceeds about 1 ML. A second observation is that, because layer coverages are under-determined by the evolution of a single point on the reflectivity curve, we find that the best fits to reflectivity data -corresponding to the lowest values of χ 2 ν -do not necessarily yield the best agreement between simulated and measured surface morphologies. Instead, it appears critical that the model reproduce all local extrema in the data. In addition to showing that layer morphologies can be extracted from a minimal set of data, the methodology established here provides a basis for improving models of multilayer growth by comparison to real systems.

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Section: Theory a X-ray Scatteringmentioning

confidence: 99%

Quantitative modeling ofin situx-ray reflectivity during organic molecule thin film growth

2011

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“…The nucleation starts presumably at defects or impurities, similar to the case of SiO x substrates. 24 At higher coverages, the molecules form large uniform covered areas. For example, the AFM picture for a pentacene nominal coverage of 7 Å shown in Fig.…”

Section: Structural Propertiesmentioning

confidence: 99%

Morphology and electronic properties of the pentacene on cobalt interface

Tiba

Jonge

Koopmans

et al. 2006

Journal of Applied Physics

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In this paper, we report the structural and electronic properties of pentacene thin films grown on a polycrystalline Co film using atomic force microscopy and ultraviolet photoemission spectroscopy ͑UPS͒, respectively. Investigation of this type of interface is of importance for the engineering of hybrid organometallic spintronic devices for which the use of spin polarized electrodes is a prerequisite. Uniform single crystalline areas of pentacene as large as several micrometers, with molecules arranging almost perpendicular to the substrate, were obtained. For the electronic properties at this interface, we have found an energy barrier for the hole injection of about 1 eV, in spite of the fact that the ionization potential of pentacene reported previously equals the work function of Co. A shift of the vacuum level of the same magnitude has also been observed. A comparison of the UPS spectra of the pentacene films with the gas phase spectrum directly indicates that hybridization effects are present at this interface. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2363707͔ INTRODUCTIONMolecular organic semiconductors have become a very active area of research during the past decade. The structural flexibility due to weak intermolecular bonds and the endless possibilities for chemical synthesis of new molecules give molecular systems a unique advantage over inorganic semiconductors for relatively simple fabrication of ͑opto-͒ electronic devices such as light emitting diodes for flexible or even transparent displays, transistors, solar cells, sensors, and solid state lasers. Applications into electronic devices in which the spin degree of freedom of the electron is exploited ͑spintronics͒ have recently started to be considered, motivated by the notion that organic semiconductors are materials with large spin relaxation times. [1][2][3][4][5] Spin valves with a significant magnetoresistance have been produced with Alq 3 thin films sandwiched between two ferromagnetic electrodes. 4,5 In response to the technological success of the organic semiconductors, fundamental research, with the goal of understanding the surface and interface properties of these systems, has followed. Such studies have proven to be valuable for device engineering, as well as from the fundamental viewpoint, electronic properties of interfaces between organic semiconductors and metals being still puzzling for scientists. While the electronic and structural properties of large organic molecules on noble metals and semiconducting or semimetallic substrates have been extensively studied, only a limited number of studies on more reactive substrates, such as the ferromagnetic transition metals, have been reported. 6 Such investigations are of crucial relevance to understand and control efficient spin injection from ferromagnetic electrodes into organic thin films.In the ferromagnetic transition metals, both the magnetic behavior and the reactivity originate from the high density of the d states near the Fermi level. For the structural propertie...

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“…The development of single-crystal organic field effect transistors (SCOFETs) makes it possible to explore intrinsic properties of these materials [9][10][11]. p-Type organic semiconductors such as pentacene, rubrene and derivatives of them have been investigated widely [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27]. The recently improved theoretical understandings of organic semiconductors have even addressed the design rule of organics with high hole mobilities [28][29][30][31].…”

Section: Introductionmentioning

confidence: 99%