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The interface between a metal electrode and an organic semiconductor (OS) layer has a defining role in the properties of the resulting device. To obtain the desired performance, interlayers are introduced to modify the adhesion and growth of OS and enhance the efficiency of charge transport through the interface. However, the employed interlayers face common challenges, including a lack of electric dipoles to tune the mutual position of energy levels, being too thick for efficient electronic transport, or being prone to intermixing with subsequently deposited OS layers. Here, we show that monolayers of 1,3,5-tris(4-carboxyphenyl)benzene (BTB) with fully deprotonated carboxyl groups on silver substrates form a compact layer resistant to intermixing while capable of mediating energy-level alignment and showing a large insensitivity to substrate termination. Employing a combination of surface-sensitive techniques, i.e., low-energy electron microscopy and diffraction, X-ray photoelectron spectroscopy, and scanning tunneling microscopy, we have comprehensively characterized the compact layer and proven its robustness against mixing with the subsequently deposited organic semiconductor layer. Density functional theory calculations show that the robustness arises from a strong interaction of carboxylate groups with the Ag surface, and thus, the BTB in the first layer is energetically favored. Synchrotron radiation photoelectron spectroscopy shows that this layer displays considerable electrical dipoles that can be utilized for work function engineering and electronic alignment of molecular frontier orbitals with respect to the substrate Fermi level. Our work thus provides a widely applicable molecular interlayer and general insights necessary for engineering of charge injection layers for efficient organic electronics.

The interface between a metal electrode and an organic semiconductor (OS) layer has a defining role in the properties of the resulting device. To obtain the desired performance, interlayers are introduced to modify the adhesion and growth of OS and enhance the efficiency of charge transport through the interface. However, the employed interlayers face common challenges, including a lack of electric dipoles to tune the mutual position of energy levels, being too thick for efficient electronic transport, or being prone to intermixing with subsequently deposited OS layers. Here, we show that monolayers of 1,3,5-tris(4-carboxyphenyl)benzene (BTB) with fully deprotonated carboxyl groups on silver substrates form a compact layer resistant to intermixing while capable of mediating energy-level alignment and showing a large insensitivity to substrate termination. Employing a combination of surface-sensitive techniques, i.e., low-energy electron microscopy and diffraction, X-ray photoelectron spectroscopy, and scanning tunneling microscopy, we have comprehensively characterized the compact layer and proven its robustness against mixing with the subsequently deposited organic semiconductor layer. Density functional theory calculations show that the robustness arises from a strong interaction of carboxylate groups with the Ag surface, and thus, the BTB in the first layer is energetically favored. Synchrotron radiation photoelectron spectroscopy shows that this layer displays considerable electrical dipoles that can be utilized for work function engineering and electronic alignment of molecular frontier orbitals with respect to the substrate Fermi level. Our work thus provides a widely applicable molecular interlayer and general insights necessary for engineering of charge injection layers for efficient organic electronics.

The interface between a metal electrode and an organic semiconductor (OS) layer has a defining role in the properties of the resulting device. To obtain the desired performance, interlayers are introduced to modify the adhesion and growth of OS and enhance the efficiency of charge transport through the interface. However, the employed interlayers face common challenges, including a lack of electric dipoles to tune the mutual position of energy levels, being too thick for efficient electronic transport, or being prone to intermixing with subsequently deposited OS layers. Here, we show that monolayers of 1,3,5-tris(4-carboxyphenyl)benzene (BTB) with fully deprotonated carboxyl groups on silver substrates form a compact layer resistant to intermixing while capable of mediating energy-level alignment and showing a large insensitivity to substrate termination. Employing a combination of surface-sensitive techniques, i.e., low-energy electron microscopy and diffraction, X-ray photoelectron spectroscopy, and scanning tunneling microscopy, we have comprehensively characterized the compact layer and proven its robustness against mixing with the subsequently deposited organic semiconductor layer. Density functional theory calculations show that the robustness arises from a strong interaction of carboxylate groups with the Ag surface, and thus, the BTB in the first layer is energetically favored. Synchrotron radiation photoelectron spectroscopy shows that this layer displays considerable electrical dipoles that can be utilized for work function engineering and electronic alignment of molecular frontier orbitals with respect to the substrate Fermi level. Our work thus provides a widely applicable molecular interlayer and general insights necessary for engineering of charge injection layers for efficient organic electronics.

© 2022 The Authors. Published by Elsevier B.V. This work is supported by grant RTI2018-095303-B-C51, funded by MCIN/AEI/10.13039/501100011033 and by ‘‘ERDF A way of making Europe’’, by grant PID2020-117024GB-C43 (Ministerio de Ciencia eInnovación) and by grant S2018-NMT-4321, funded by the Regional Government of Madrid, Spain and by ‘‘ERDF A way of making Europe’’. L.M.G. acknowledges a sabbatical grant from DGAPA-UNAM., Li metal has been deposited on the surface of a Ru(0001) single crystal containing patches of monolayer-thick epitaxial graphene islands. The use of low-energy electron microscopy and diffraction allowed us to in situ monitor the process by measuring the local work function as well as to study the system in real and reciprocal space, comparing the changes taking place on the graphene with those on the bare Ru(0001) surface. It is found that Li deposition decreases the work function of the graphene islands but to a much smaller degree than of the Ru(0001) surface, as corresponds to its intercalation below the graphene overlayer. Finally, the diffusion process of Li out of the graphene islands has been monitored by photoelectron microscopy using a visible-light laser., Ministerio de Ciencia e Innovación (MICINN) / FEDER, Ministerio de Ciencia e Innovación (MICINN), Comunidad de Madrid, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

Li metal has been deposited on the surface of a Ru(0001) single crystal containing patches of monolayer-thick epitaxial graphene islands. The use of low-energy electron microscopy and diffraction allowed us to {\em in situ} monitor the process by measuring the local work function as well as to study the system in real and reciprocal space, comparing the changes taking place on the graphene with those on the bare Ru(0001) surface. It is found that Li deposition decreases the work function of the graphene islands but to a much smaller degree than of the Ru(0001) surface, as corresponds to its intercalation below the graphene overlayer. Finally, the diffusion process of Li out of the graphene islands has been monitored by photoelectron microscopy using a visible-light laser.

© 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license. Conferencia: E-MRS Spring Meeting / Symposium CC on In Situ Studies of Functional Nano Materials at Large Scale Facilities - From Model Systems to Applications (2016. Lille, Francia). This work is supported by the Spanish Ministry of Economy and Competitiveness through Projects No. MAT2015- 64110-C2-1-P, MAT2015-64110-C2-2-P and MAT2013-48009-C4-1-P. These experiments were performed at the CIRCE beamline of the ALBA Synchrotron Light Facility with the collaboration of ALBA staff., Mixed iron-cobalt oxides have been grown on a Ru(0001) single crystal substrate by reactive molecular beam epitaxy. The growth has been followed by low-energy electron microscopy and diffraction. Chemical characterization has been performed by selected area x-ray absorption spectroscopy. As previously known, iron grows into a wetting layer of FeO. In contrast, cobalt grows into three-dimensional islands of CoO, of either with a (111) –most common-or a (100) orientation. For mixed compositions, flat 2D growth is regained. Depending on temperature, either segregation into two FeCo compositions or a single phase is detected. In all cases the structure corresponds to an in-plane expanded (111)-oriented halite one. When only one phase is observed or for the Co-rich phase in the two phase film, its crystal structure is rotated by 30. relative to the Ru substrate, unlike the Co-poor phase which appears aligned with the substrate., Ministerio de Economía y Competitividad (MINECO), Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

Mixed iron-cobalt oxides have been grown on a Ru(0001) single crystal substrate by reactive molecular beam epitaxy. The growth has been followed by low-energy electron microscopy and diffraction. Chemical characterization has been performed by selected area x-ray absorption spectroscopy. As previously known, iron grows into a wetting layer of FeO. In contrast, cobalt grows into three-dimensional islands of CoO, of either with a (111) -most common- or a (100) orientation. For mixed compositions, flat 2D growth is regained. Depending on temperature, either segregation into two FeCo compositions or a single phase is detected. In all cases the structure corresponds to an in-plane expanded (111)-oriented halite one. When only one phase is observed or for the Co-rich phase in the two phase film, its crystal structure is rotated by 30¿ relative to the Ru substrate, unlike the Co-poor phase which appears aligned with the substrate.

Understanding the fundamental mechanisms that control van der Waals epitaxy of two-dimensional layered materials is necessary in order to grow large, defect-free crystals. Two-dimensional materials, such as graphene and transition-metal dichalcogenides, are a relatively new class of materials that display unique electronic and optical properties and are promising candidates for continued improvement of microelectronics, improved sensors, and many other applications, some not yet conceived. However, the growth of single-crystal two-dimensional materials is often frustrated by the fact that different in-plane rotational variants nucleate and grow. Their nucleation is a consequence of the weak interaction between the film and substrate that is characteristic of van der Waals epitaxy. It is well known that the nucleation and growth behavior of graphene islands greatly varies with the growth substrate, which is surprising given the weak interaction between the film and substrate. A unique system is graphene on Ir(111) because graphene islands have properties that depend on their in-plane orientation relative to the Ir(111) lattice. Thus, graphene on Ir(111) is a model system to investigate the fundamental factors that control the van der Waals epitaxy of graphene.Experimentally, Ir(111) presents significant advantages for investigation by low-energy electron microscopy, including the quantification of surface adatom concentrations during growth. By using low-energy electron microscopy, the real-time evolution of graphene islands on Ir(111) were investigated during growth and annealing. First, island growth characteristics are compared under identical driving forces in order to isolate the orientation-induced differences. In the temperature range of 750-900 °C, islands rotated relative to the Ir(111) lattice are more faceted than islands aligned with the substrate (R0). Further, the growth velocity of rotated islands depends not only on the C adatom supersaturation but al

Understanding the fundamental mechanisms that control van der Waals epitaxy of two-dimensional layered materials is necessary in order to grow large, defect-free crystals. Two-dimensional materials, such as graphene and transition-metal dichalcogenides, are a relatively new class of materials that display unique electronic and optical properties and are promising candidates for continued improvement of microelectronics, improved sensors, and many other applications, some not yet conceived. However, the growth of single-crystal two-dimensional materials is often frustrated by the fact that different in-plane rotational variants nucleate and grow. Their nucleation is a consequence of the weak interaction between the film and substrate that is characteristic of van der Waals epitaxy. It is well known that the nucleation and growth behavior of graphene islands greatly varies with the growth substrate, which is surprising given the weak interaction between the film and substrate. A unique system is graphene on Ir(111) because graphene islands have properties that depend on their in-plane orientation relative to the Ir(111) lattice. Thus, graphene on Ir(111) is a model system to investigate the fundamental factors that control the van der Waals epitaxy of graphene.Experimentally, Ir(111) presents significant advantages for investigation by low-energy electron microscopy, including the quantification of surface adatom concentrations during growth. By using low-energy electron microscopy, the real-time evolution of graphene islands on Ir(111) were investigated during growth and annealing. First, island growth characteristics are compared under identical driving forces in order to isolate the orientation-induced differences. In the temperature range of 750-900 °C, islands rotated relative to the Ir(111) lattice are more faceted than islands aligned with the substrate (R0). Further, the growth velocity of rotated islands depends not only on the C adatom supersaturation but al

The formation and nitridation of indium (In) droplets on Si (111)7 × 7, with regard to In droplet epitaxy growth of InN nanostructures, were studied using a spectroscopic photoemission and low energy electron microscopy, for the In coverages from 0.07 to 2.3 monolayer (ML). The results reveal that the In adatoms formed well-ordered clusters while keeping the Si (111)7 × 7 surface periodicity at 0.07 ML and a single 3×3 phase at 0.3 ML around 440-470 C. At 0.82 ML, owing to the presence of structurally defect areas beside the 7 × 7 domains, 3-D In droplets evolved concomitantly with the formation of 4 × 1-In cluster chains, accompanied by a transition in surface electric property from semiconducting to metallic. Further increasing the In to 2.3 ML led to a moderate increase in number density and an appreciable lateral growth of the droplets, as well as the multi-domain In phases. Upon nitridation with NH3 at ~ 480 C, besides the nitridation of the In droplets, the N radicals also dissociated the InSi bonds to form SiN. This caused a partial disintegration of the ordered In phase and removal of the In adatoms between the In droplets., QC 20130419

Advances in synthesis are imperative if graphene is to fulfill its scientific and technological potential. Single crystal graphene of is currently available only in the small flakes generated by mechanical exfoliation. Layers of larger size may be grown either by the thermal decomposition of SiC or by chemical vapor deposition on metals. However, as they are currently implemented, these methods yield graphene films of inferior quality. Thus the requirement for wafer-scale, high-quality graphene films remains unmet. This dissertation addresses this issue by examining graphene growth on metal surfaces. Through a survey of the fundamental underlying processes, it provides guidance for improving the quality of the resulting graphene films. Graphene was grown on Cu(100), Cu(111), and Au(111) by physical vapor deposition of elemental C. The nucleation and growth behaviors of graphene were evaluated by low-energy electron microscopy. Graphene tends to nucleate heterogeneously at surface imperfections although it also does so homogeneously on Cu(111) and Au(111). Graphene growing on Cu(100) is governed by the attachment kinetics of C at the propagating crystal front. The resulting angularly dependent growth rate sculpts individual crystals into elongated lobes. In contrast, graphene growth on both Cu(111) and Au(111) is surface diffusion limited. This yields ramified, dendritic graphene islands. Graphene films grown on Cu(100) contain significant rotational disorder. This disorder is partially attributable to the symmetry mismatch between film and substrate. The common symmetry between graphene and Cu(111) contributes to a significant reduction in disorder in films grown on this surface. Most graphene domains occupy a ~6º arc of orientations. On Au(111) the vast majority of graphene domains are locked into alignment with the substrate surface. The extraordinary extent of their orientational homogeneity is such that the resulting graphene film is a quasi-single crystal. The

Advances in synthesis are imperative if graphene is to fulfill its scientific and technological potential. Single crystal graphene of is currently available only in the small flakes generated by mechanical exfoliation. Layers of larger size may be grown either by the thermal decomposition of SiC or by chemical vapor deposition on metals. However, as they are currently implemented, these methods yield graphene films of inferior quality. Thus the requirement for wafer-scale, high-quality graphene films remains unmet. This dissertation addresses this issue by examining graphene growth on metal surfaces. Through a survey of the fundamental underlying processes, it provides guidance for improving the quality of the resulting graphene films. Graphene was grown on Cu(100), Cu(111), and Au(111) by physical vapor deposition of elemental C. The nucleation and growth behaviors of graphene were evaluated by low-energy electron microscopy. Graphene tends to nucleate heterogeneously at surface imperfections although it also does so homogeneously on Cu(111) and Au(111). Graphene growing on Cu(100) is governed by the attachment kinetics of C at the propagating crystal front. The resulting angularly dependent growth rate sculpts individual crystals into elongated lobes. In contrast, graphene growth on both Cu(111) and Au(111) is surface diffusion limited. This yields ramified, dendritic graphene islands. Graphene films grown on Cu(100) contain significant rotational disorder. This disorder is partially attributable to the symmetry mismatch between film and substrate. The common symmetry between graphene and Cu(111) contributes to a significant reduction in disorder in films grown on this surface. Most graphene domains occupy a ~6º arc of orientations. On Au(111) the vast majority of graphene domains are locked into alignment with the substrate surface. The extraordinary extent of their orientational homogeneity is such that the resulting graphene film is a quasi-single crystal. The

The kinetic regime of step motion on the Si(111) (1 x 1) surface is determined from observations of island decay with low-energy electron microscopy (LEEM). We have investigated the island decay on the tops of mounds fabricated by a photolithographic method. Prefabricated mounds serve as controllable and reproducible island sources and platforms for decay. Island area during decay exhibits the expected power-law dependence on time, with exponent, alpha, that is indicative of the kinetic regime. In order to overcome the basic problem of realizing the thermodynamic limit of island decay on an infinite terrace, the power-law decay exponent is extrapolated to vanishing island (r) - to - terrace (R) radius ratio, r/R = 0. The dependence of et upon r/R suggests that island decay kinetics is intermediate between the diffusion-limited (DL) and attachment/detachment-limited (ADL) regimes. Copyright (C) 2006 John Wiley & Sons, Ltd.

The kinetic regime of step motion on the Si(111) (1 x 1) surface is determined from observations of island decay with low-energy electron microscopy (LEEM). We have investigated the island decay on the tops of mounds fabricated by a photolithographic method. Prefabricated mounds serve as controllable and reproducible island sources and platforms for decay. Island area during decay exhibits the expected power-law dependence on time, with exponent, alpha, that is indicative of the kinetic regime. In order to overcome the basic problem of realizing the thermodynamic limit of island decay on an infinite terrace, the power-law decay exponent is extrapolated to vanishing island (r) - to - terrace (R) radius ratio, r/R = 0. The dependence of et upon r/R suggests that island decay kinetics is intermediate between the diffusion-limited (DL) and attachment/detachment-limited (ADL) regimes. Copyright (C) 2006 John Wiley & Sons, Ltd.

The kinetic regime of step motion on the Si(111) (1 x 1) surface is determined from observations of island decay with low-energy electron microscopy (LEEM). We have investigated the island decay on the tops of mounds fabricated by a photolithographic method. Prefabricated mounds serve as controllable and reproducible island sources and platforms for decay. Island area during decay exhibits the expected power-law dependence on time, with exponent, alpha, that is indicative of the kinetic regime. In order to overcome the basic problem of realizing the thermodynamic limit of island decay on an infinite terrace, the power-law decay exponent is extrapolated to vanishing island (r) - to - terrace (R) radius ratio, r/R = 0. The dependence of et upon r/R suggests that island decay kinetics is intermediate between the diffusion-limited (DL) and attachment/detachment-limited (ADL) regimes. Copyright (C) 2006 John Wiley & Sons, Ltd.