Growth of extended DNTT fibers on metal substrates by suppression of step-induced nucleation

Abstract

Defect mediated nucleation upon organic film growth is effectively suppressed by initial oxygen saturating of surface steps yielding extended and epitaxially aligned crystalline fibers, that are of interest for optoelectronic devices.

Selective saturation of step-edges as a tool to control the growth of molecular fibres

“…44,45 A possible reason for a broad distribution of fibre orientations could be the influence of surface defects such as step edges or kinks, which can cause parasitic nucleation and lead to deviant fibre growth, as shown before for the case of DNTT-fibres on Ag(111). 21 In that case, it was found that a step edge mediated growth could be efficiently suppressed by first exposing the sample to oxygen, which adsorbs preferentially at step edges 46,47 and thereby suppresses this specific nucleation. In general, steps on metal surfaces are chemically active sites that have greater binding energies of adsorbates and also show increased catalytic activity, which is used in heterogeneous surface reactions.…”

“…The present results further validate a strategy that had been introduced before to control the oriented growth of DNTT fibres on silver substrates. 21 While the present approach of using oxygen to decorate and thereby passivate surface steps is not directly applicable to the more inert gold surfaces, it requires more appropriate molecules. However, this might be achieved by using molecules such as fullerenes, 1,4diisocyanobenzene or 4,4 0 -biphenyl dicarboxylic acid, which in the case of low doses initially nucleate at steps 55,57,58 and thereby saturate them.…”

“…Across different material classes, defects are sometimes also actively used to induce a specific growth behaviour, [10][11][12][13][14][15][16][17][18][19] while in general they cause a parasitic film growth, reducing long-range epitaxial ordering and yielding rather undefined interfaces. [20][21][22][23] However, even on idealised substrate surfaces, organic adlayers in particular exhibit pronounced dewetting, which leads to distinct island or fibre formation. 24 Especially the latter attracted large interest as model systems for wave guiding applications.…”

“…By first exposing the metal substrate briefly to oxygen, a selective saturation of the active step sites was achieved, which successfully suppressed a step-mediated nucleation and the formation of parasitic fibres. 21 Here, we examine whether this strategy is also applicable to the alignment of p-4P fibres formed upon growth on Ag(111). Since on metal single crystals (monatomic) surface steps often appear curved, but are actually polylines that consist of short straight segments oriented along high symmetry directions, 35,36 we used instead Ag(111) films epitaxially grown on mica, because they reveal long and straight step edges which simplifies the analysis.…”

Engineering of Printable and Air‐Stable Silver Electrodes with High Work Function using Contact Primer Layer: From Organometallic Interphases to Sharp Interfaces

“…Step edges are known as active sites for surface reactions and nucleation processes and often lead to step decorations. [40][41][42][43] A closer analysis of the AFM images clearly reveals a larger roughness on the (111) terasses compared to clean substrates, thus indicating that the formation of organometallic complexes is not limited to step edges. In contrast, AFM images recorded after immediate thermal desorption of the non-reacted F 6 TCNNQ species indeed reveal flat terraces next to decorated step edges (see Supporting Information).…”