Reactive metal-organic interfaces studied with hard x-ray photoelectron spectroscopy: controlled formation of metalloporphyrin interphase layers during metal vapor deposition onto porphyrin films

Abstract

Interfaces between organic semiconductors and metallic layers are ubiquitous in organic (opto-) electronic devices and can significantly influence their functionality. Here, we studied in situ prepared metal-organic interfaces, which were obtained by vapor deposition of metals (Co, Fe) onto organic semiconductor films (2H-tetraphenylporphyrin), with hard x-ray photoelectron spectroscopy. In these systems, the interphase zones, which are formed by diffusion and reaction of the metal in the organic material, can be clearly distinguished spectroscopically from the unreacted organic bulk, since they comprise the corresponding metalloporphyrins, CoTPP and FeTPP. In order to gain control over the thickness of the interphase layers, we varied process parameters such as sample temperature and metal-atom flux during interface preparation. We found that the temperature of the organic film during metal deposition was the only parameter that significantly influenced the formation of the interphase layers: their thicknesses were typically ~0.5 nm for deposition at 90 K, compared to ~1 nm at 300 K, irrespective of metal atom flux and chemical nature of the metal atom (Fe versus Co). Notably, these values are significantly smaller than the thicknesses of other metal/ organics interphase regions reported in the literature.

Influence of Ring Contraction on the Electronic Structure of Nickel Tetrapyrrole Complexes: Corrole vs Porphyrin

“…2. To confirm the feasibility of the in situ metalation method, [33][34][35][36][37][38][39][40][41][42][43][44][45][46] we use a film of directly vapor-deposited NiOEP as a reference, because NiOEP is readily available and its stability is well established. 63 The Ni 2p XPS signal of this NiOEP layer is shown in Fig.…”

“…The limited diffusion and reaction depth of transition metal atoms in the molecular thin films ensures that only the topmost layers of the thin films are metalated. 45 The complexes are therefore electronically decoupled from the Ag surface by layers of pristine, unmetalated molecules. 46 Using XPS, UPS, NEXAFS, and DFT calculations, we show that NiOEP and NiHEDMC both exhibit a nickel(II) central atom in a low-spin d 8 electron configuration.…”

Tetrapyrroles at near-ambient pressure: porphyrins and phthalocyanines beyond the pressure gap

“…Metalation routes. Several metalation routes can be exploited at surfaces in UHV (figure 15) [28], including physical vapor deposition (PVD), self-metalation, tip manipulation, and chemical vapor deposition (CVD) [24,25,28,29,80,[84][85][86][87][88][89][90][91]. For PVD, both free-base macrocycles and single metal atoms are deposited on a supporting surface, and temperature-dependent metalation occurs, in some cases even at ambient temperature Table 1.…”

Preface: fresh perspectives on internal interfaces

“…The investigated systems cover a wide range from ultrathin bilayer structures to buried bulk interfaces. Organic semiconductors are the dominant class of materials [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20], reflecting their prominent role in modern (opto)electronic devices. Besides interfaces between two organic materials [4,6,12,[14][15][16]18], also metal/organic [2,7,11,16,17,20,21] and organic/inorganic [5,9,10,12,13] interfaces (especially with ZnO [9,10,12,13]) find much attention.…”

“…Organic semiconductors are the dominant class of materials [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20], reflecting their prominent role in modern (opto)electronic devices. Besides interfaces between two organic materials [4,6,12,[14][15][16]18], also metal/organic [2,7,11,16,17,20,21] and organic/inorganic [5,9,10,12,13] interfaces (especially with ZnO [9,10,12,13]) find much attention. Organic molecules are also studied on graphite and graphene [8,19] and are covalently attached to thin oxide films [3] or Si surfaces [5].…”