Dr. Patrick Amsalem
Profil
Forschungsthemen1
Die Energieniveau Anpassungen und elektronischen Eigenschaften schwach wechselwirkender Grenzflächen im Kontext organischer Halbleiter
Quelle ↗Förderer: DFG Eigene Stelle (Sachbeihilfe) Zeitraum: 09/2014 - 12/2017 Projektleitung: Dr. Patrick Amsalem
Mögliche Industrie-Partner10
Stand: 26.4.2026, 19:48:44 (Top-K=20, Min-Cosine=0.4)
- 82 Treffer65.5%
- Interfaces in opto-electronic thin film multilayer devicesP65.5%
- Interfaces in opto-electronic thin film multilayer devices
- 31 Treffer59.5%
- Optimierte Natrium-Feststoffbatterien mit neuen Anoden basierend auf KohlenstoffgerüststrukturenP59.5%
- Optimierte Natrium-Feststoffbatterien mit neuen Anoden basierend auf Kohlenstoffgerüststrukturen
- 69 Treffer57.6%
- EU: Hybrid Organic/Inorganic Memory Elements for Integration of Electronic and Photonic Circuitry (HYMEC)P57.6%
- EU: Hybrid Organic/Inorganic Memory Elements for Integration of Electronic and Photonic Circuitry (HYMEC)
- DYnamic control in hybrid plasmonic NAnopores: road to next generation multiplexed single MOlecule detectionP56.8%
- DYnamic control in hybrid plasmonic NAnopores: road to next generation multiplexed single MOlecule detection
- 17 Treffer55.8%
- ILB: Entwicklung eines Produktions- und Pflanzverfahrens mit rohrförmigen WurzelhüllenP55.8%
- Entwicklung eines innovativen Kulturbegründungsverfahrens für Eichen zur Verbesserung der Wurzelentwicklung durch kompostierbare WurzelhüllenP43.5%
- ILB: Entwicklung eines Produktions- und Pflanzverfahrens mit rohrförmigen Wurzelhüllen
BASF SE
PT71 Treffer55.2%- Integrated Self-Assembled SWITCHable Systems and Materials: Towards Responsive Organic Electronics – A Multi-Site Innovative Training Action (iSwitch)T55.2%
- SIB-DE_Forschung - Sodium-Ion-Battery Deutschland (SIB:DE Initiative) - Eignung der Natrium-Ionen-Technologie für die europäische Energie- und MobilitätswendeP51.8%
- Integrated Self-Assembled SWITCHable Systems and Materials: Towards Responsive Organic Electronics – A Multi-Site Innovative Training Action (iSwitch)
- 38 Treffer55.2%
- Integrated Self-Assembled SWITCHable Systems and Materials: Towards Responsive Organic Electronics – A Multi-Site Innovative Training Action (iSwitch)T55.2%
- Integrated Self-Assembled SWITCHable Systems and Materials: Towards Responsive Organic Electronics – A Multi-Site Innovative Training Action (iSwitch)
- 109 Treffer55.2%
- Integrated Self-Assembled SWITCHable Systems and Materials: Towards Responsive Organic Electronics – A Multi-Site Innovative Training Action (iSwitch)T55.2%
- EU: Bottom-Up Generation of atomicalLy Precise syntheTIc 2D MATerials for High Performance in Energy and Electronic Applications – A Multi-Site Innovative Training Action (ULTIMATE)P55.0%
- Integrated Self-Assembled SWITCHable Systems and Materials: Towards Responsive Organic Electronics – A Multi-Site Innovative Training Action (iSwitch)
- 68 Treffer55.0%
- EU: Bottom-Up Generation of atomicalLy Precise syntheTIc 2D MATerials for High Performance in Energy and Electronic Applications – A Multi-Site Innovative Training Action (ULTIMATE)P55.0%
- EU: Bottom-Up Generation of atomicalLy Precise syntheTIc 2D MATerials for High Performance in Energy and Electronic Applications – A Multi-Site Innovative Training Action (ULTIMATE)
- 74 Treffer55.0%
- EU: Bottom-Up Generation of atomicalLy Precise syntheTIc 2D MATerials for High Performance in Energy and Electronic Applications – A Multi-Site Innovative Training Action (ULTIMATE)P55.0%
- EU: Simulation in Multiscale Physical and Biological Systems (STIMULATE)P48.4%
- EU: Bottom-Up Generation of atomicalLy Precise syntheTIc 2D MATerials for High Performance in Energy and Electronic Applications – A Multi-Site Innovative Training Action (ULTIMATE)
Publikationen25
Top 25 nach Zitationen — Quelle: OpenAlex (BAAI/bge-m3 embedded für Matching).
2D Materials · 198 Zitationen · DOI
Understanding the excitonic nature of excited states in two-dimensional (2D) transition-metal dichalcogenides (TMDCs) is of key importance to make use of their optical and charge transport properties in optoelectronic applications. We contribute to this by the direct experimental determination of the exciton binding energy (Eb,exc) of monolayer MoS2 and WSe2 on two fundamentally different substrates, i.e. the insulator sapphire and the metal gold. By combining angle-resolved direct and inverse photoelectron spectroscopy we measure the electronic band gap (Eg), and by reflectance measurements the optical excitonic band gap (Eexc). The difference of these two energies is Eb,exc. The values of Eg and Eb,exc are 2.11 eV and 240 meV for MoS2 on sapphire, and 1.89 eV and 240 meV for WSe2 on sapphire. On Au Eb,exc is decreased to 90 meV and 140 meV for MoS2 and WSe2, respectively. The significant Eb,exc reduction is primarily due to a reduction of Eg resulting from enhanced screening by the metal, while Eexc is barely decreased for the metal support. Energy level diagrams determined at the K-point of the 2D TMDCs Brillouin zone show that MoS2 has more p-type character on Au as compared to sapphire, while WSe2 appears close to intrinsic on both. These results demonstrate that the impact of the dielectric environment of 2D TMDCs is more pronounced for individual charge carriers than for a correlated electron–hole pair, i.e. the exciton. A proper dielectric surrounding design for such 2D semiconductors can therefore be used to facilitate superior optoelectronic device function.
Advanced Functional Materials · 187 Zitationen · DOI
Abstract Small‐molecule photovoltaic cells using diindenoperylene (DIP) as a new donor material in combination with the fullerene C 60 as an electron acceptor are demonstrated. In addition to the successful application in planar and bulk heterojunction devices, a comprehensive analysis including structural studies, the determination of the energy level alignment and electrical transport investigations is given, stressing the correlation between growth conditions, film morphology, and device performance. Due to pronounced crystallinity and a large surface area of DIP films grown at elevated temperature, exceptionally high fill factors of almost 75% are achieved in planar heterojunction cells. Bulk heterojunctions exhibit large‐scale phase separation forming a bicontinuous network of both molecular species, which enables efficient exciton dissociation and charge carrier transport. The high ionization potential of DIP and the favorable energy level alignment with the fullerene C 60 yield large open circuit voltages close to 1 V and comparable power conversion efficiencies of about 4% in both cell architectures.
Advanced Optical Materials · 164 Zitationen · DOI
This study investigates the effect of white light illumination on the electronic and chemical properties of mixed halide perovskite (CH 3 NH 3 PbI 3− x Cl x ) thin films and CH 3 NH 3 PbI 3 single crystals using photoelectron and absorption spectroscopy. The pristine materials' surfaces are found to be n‐type because of surface band bending due to the presence of donor levels, likely consisting of reduced lead (Pb 0 ) that acts as surface traps. When illuminating the sample with white light (up to 1 sun), the valence features shifted to lower binding energy due to surface photovoltage, i.e., the bulk of the materials is much less n‐type. However, the surface photovoltage is only partially reversible and vanishes for prolonged illumination time. Concomitantly, a high concentration of metallic Pb 0 is found, which induces strong Fermi‐level pinning and quenching of the surface photovoltage. This is accompanied also by the formation of PbI 2 defects. Similar experiments on single crystals reveal the presence of a high concentration of reduced (metallic) Pb 0 at the sample surface after cleaving. The present findings indicate that the chemical and electronic properties of perovskite films are very sensitive to white light illumination. Accounting for these light‐induced material changes is important to fully understand its photophysical properties and for improving the lifetime of perovskite‐based devices.
ACS Applied Materials & Interfaces · 106 Zitationen · DOI
Substantial variations in the electronic structure and thus possibly conflicting energetics at interfaces between hybrid perovskites and charge transport layers in solar cells have been reported by the research community. In an attempt to unravel the origin of these variations and enable reliable device design, we demonstrate that donor-like surface states stemming from reduced lead (Pb<sup>0</sup>) directly impact the energy level alignment at perovskite (CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3-x</sub>Cl<sub>x</sub>) and molecular electron acceptor layer interfaces using photoelectron spectroscopy. When forming the interfaces, it is found that electron transfer from surface states to acceptor molecules occurs, leading to a strong decrease in the density of ionized surface states. As a consequence, for perovskite samples with low surface state density, the initial band bending at the pristine perovskite surface can be flattened upon interface formation. In contrast, for perovskites with a high surface state density, the Fermi level is strongly pinned at the conduction band edge, and only minor changes in surface band bending are observed upon acceptor deposition. Consequently, depending on the initial perovskite surface state density, very different interface energy level alignment situations (variations over 0.5 eV) are demonstrated and rationalized. Our findings help explain the rather dissimilar reported energy levels at interfaces with perovskites, refining our understanding of the operating principles in devices comprising this material.
Applied Physics Letters · 94 Zitationen · DOI
We have used ultraviolet and inverse photoemission spectroscopy to determine the transport gaps (Et) of C60 and diindenoperylene (DIP), and the photovoltaic gap (EPVG) of five prototypical donor/acceptor interfaces used in organic photovoltaic cells (OPVCs). The transport gap of C60 (2.5 ± 0.1) eV and DIP (2.55 ± 0.1) eV at the interface is the same as in pristine films. We find nearly the same energy loss of ca 0.5 eV for all material pairs when comparing the open circuit voltage measured for corresponding OPVCs and EPVG.
The Journal of Physical Chemistry Letters · 92 Zitationen · DOI
Photovoltaic cells based on halide perovskites, possessing remarkably high power conversion efficiencies have been reported. To push the development of such devices further, a comprehensive and reliable understanding of their electronic properties is essential but presently not available. To provide a solid foundation for understanding the electronic properties of polycrystalline thin films, we employ single-crystal band structure data from angle-resolved photoemission measurements. For two prototypical perovskites (CH3NH3PbBr3 and CH3NH3PbI3), we reveal the band dispersion in two high-symmetry directions and identify the global valence band maxima. With these benchmark data, we construct “standard” photoemission spectra from polycrystalline thin film samples and resolve challenges discussed in the literature for determining the valence band onset with high reliability. Within the framework laid out here, the consistency of relating the energy level alignment in perovskite-based photovoltaic and optoelectronic devices with their functional parameters is substantially enhanced.
Materials Horizons · 90 Zitationen · DOI
The widely established picture of polarons in molecular semiconductors is revised highlighting the role of on-site Coulomb repulsion.
Advanced Materials · 89 Zitationen · DOI
Band-bending in organic semiconductors, occurring at metal/alkali-halide cathodes in organic-electronic devices, is experimentally revealed and electrostatically modeled. Metal-to-organic charge transfer through the insulator, rather than doping of the organic by alkali-metal ions, is identified as the origin of the observed band-bending, which is in contrast to the localized interface dipole occurring without the insulating buffer layer.
Angewandte Chemie International Edition · 88 Zitationen · DOI
Triazine-based graphitic carbon nitride (TGCN) is the most recent addition to the family of graphene-type, two-dimensional, and metal-free materials. Although hailed as a promising low-band-gap semiconductor for electronic applications, so far, only its structure and optical properties have been known. Here, we combine direction-dependent electrical measurements and time-resolved optical spectroscopy to determine the macroscopic conductivity and microscopic charge-carrier mobilities in this layered material "beyond graphene". Electrical conductivity along the basal plane of TGCN is 65 times lower than through the stacked layers, as opposed to graphite. Furthermore, we develop a model for this charge-transport behavior based on observed carrier dynamics and random-walk simulations. Our combined methods provide a path towards intrinsic charge transport in a direction-dependent layered semiconductor for applications in field-effect transistors (FETs) and sensors.
Advanced Materials Interfaces · 83 Zitationen · DOI
Abstract Ultraviolet photoelectron spectroscopy (UPS) is a key technique to determine the work function (Φ) of surfaces by measuring the secondary‐electron cut‐off (SECO). However, the interpretation of SECO spectra as obtained by UPS is not straightforward for multicomponent surfaces, and it is not comprehensively understood to what extent the length scale of inhomogeneity impacts the SECO. Here, this study unravels the physics governing the energy distribution of the SECO by experimentally and theoretically determining the electrostatic landscape above surfaces with defined patterns of Φ. For such samples, the measured SECO spectra exhibit actually two cut‐offs, one representing the high Φ surface component and the other one corresponding to an area‐averaged Φ value. By combining Kelvin probe force microscopy and electrostatic modeling, it is quantitatively demonstrated that the electrostatic potential of the high Φ areas leads to an additional energy barrier for the electrons emitted from the low Φ areas. Theoretical predictions of the induced energy barrier dependence on the Φ‐pattern length scale and sample bias are further experimentally verified. These findings establish a solid base for reliable SECO interpretation of heterogeneous surfaces and improved reliability of interfacial energy‐level diagrams from UPS experiments.
Physical Review B · 80 Zitationen · DOI
Recently, Niederhausen et al. [Phys. Rev. B 86, 081411(R) (2012)] have reported on the energy level alignment of C${}_{60}$ adsorbed on a bilayer \ensuremath{\alpha}-sexithiophene (6T) film on Ag(111). The possibility of charge transfer from the metal to the C${}_{60}$ through the bilayer 6T as discussed by the authors may have a strong impact on understanding the energy level alignment (ELA) at organic-organic (O-O) heterojunctions grown on electrodes. In this paper, we aim at a comprehensive picture of the ELA at O-O interfaces on a metal. We carry out a detailed investigation of the same pair of materials on Ag(111) as employed previously, however, with varying 6T interlayer thickness. The results allow unambiguous identification of integer charge transfer towards a fraction of the C${}_{60}$ molecules as the mechanism leading to the formation of interface dipoles. Varying the 6T interlayer thickness also reveals the dependence of the observed features on the C${}_{60}$-metal distance. This dependence is quantitatively addressed by electrostatic considerations involving a metal-to-overlayer charge transfer. From this, we demonstrate the important role of dipole-dipole interaction potentials in the molecular layer and electric fields resulting from interface dipole formation for the energy level alignment. These findings provide a deeper understanding of the fundamental mechanisms that establish electronic equilibrium at molecular heterojunctions and will aid the prediction of an accurate energy level alignment at device relevant heterojunctions, e.g. in organic opto-electronic devices.
ACS Applied Materials & Interfaces · 72 Zitationen · DOI
Transition-metal phosphides (TMPs) have recently emerged as efficient and inexpensive electrocatalysts for electrochemical water splitting. The synthesis of nanostructured phosphides often involves highly reactive and hazardous phosphorous-containing compounds. Herein, we report the synthesis of nickel phosphides through thermal treatment under H2(5%)/Ar of layered nickel phenylphosphonate (NiPh) or methylphosphonate (NiMe) that act as single-source precursors. Ni12P5, Ni12P5-Ni2P, and Ni2P nanoparticles (NPs) with sizes of ca. 15–45 nm coated with a thin shell of carbonaceous material were produced. Thermogravimetric analysis coupled with mass spectrometry (TG–MS) showed that H2, H2O, P2, and —C6H5 are the main compounds formed during the transformation of the precursor under argon and no hazard phosphorous-containing compounds are created, making this a simple and relatively safe route for fabricating nanostructured TMPs. The H2 most likely reacts with the —PO3 groups of the precursor to form H2O and P2, and the latter subsequently reacts with the metal to produce the phosphide. The Ni12P5-Ni2P and Ni2P NPs efficiently catalyze the hydrogen evolution reaction (HER), with Ni2P showing the best performance and generating a current density of 10 mA cm–2 at an overpotential of 87 mV and exhibiting long-term stability. Co2P and CoP NPs were also synthesized following this method. This approach may be utilized to explore the rich metal phosphonate chemistry for fabricating phosphide-based materials for electrochemical energy conversion and storage applications.
ACS Nano · 71 Zitationen · DOI
Two-dimensional (2D) semiconductors offer a convenient platform to study 2D physics, for example, to understand doping in an atomically thin semiconductor. Here, we demonstrate the fabrication and unravel the electronic properties of a lateral doped/intrinsic heterojunction in a single-layer (SL) tungsten diselenide (WSe<sub>2</sub>), a prototype semiconducting transition metal dichalcogenide (TMD), partially covered with a molecular acceptor layer, on a graphite substrate. With combined experiments and theoretical modeling, we reveal the fundamental acceptor-induced p-doping mechanism for SL-WSe<sub>2</sub>. At the 1D border between the doped and undoped SL-WSe<sub>2</sub> regions, we observe band bending and explain it by Thomas-Fermi screening. Using atomically resolved scanning tunneling microscopy and spectroscopy, the screening length is determined to be in the few nanometer range, and we assess the carrier density of intrinsic SL-WSe<sub>2</sub>. These findings are of fundamental and technological importance for understanding and employing surface doping, for example, in designing lateral organic TMD heterostructures for future devices.
ACS Nano · 69 Zitationen · DOI
A comprehensive understanding of the energy level alignment mechanisms between two-dimensional (2D) semiconductors and electrodes is currently lacking, but it is a prerequisite for tailoring the interface electronic properties to the requirements of device applications. Here, we use angle-resolved direct and inverse photoelectron spectroscopy to unravel the key factors that determine the level alignment at interfaces between a monolayer of the prototypical 2D semiconductor MoS<sub>2</sub> and conductor, semiconductor, and insulator substrates. For substrate work function (Φ<sub>sub</sub>) values below 4.5 eV we find that Fermi level pinning occurs, involving electron transfer to native MoS<sub>2</sub> gap states below the conduction band. For Φ<sub>sub</sub> above 4.5 eV, vacuum level alignment prevails but the charge injection barriers do not strictly follow the changes of Φ<sub>sub</sub> as expected from the Schottky-Mott rule. Notably, even the trends of the injection barriers for holes and electrons are different. This is caused by the band gap renormalization of monolayer MoS<sub>2</sub> by dielectric screening, which depends on the dielectric constant (ε<sub>r</sub>) of the substrate. Based on these observations, we introduce an expanded Schottky-Mott rule that accounts for band gap renormalization by ε<sub>r</sub> -dependent screening and show that it can accurately predict charge injection barriers for monolayer MoS<sub>2</sub>. It is proposed that the formalism of the expanded Schottky-Mott rule should be universally applicable for 2D semiconductors, provided that material-specific experimental benchmark data are available.
ACS Applied Materials & Interfaces · 66 Zitationen · DOI
The tremendous success of metal-halide perovskites, especially in the field of photovoltaics, has triggered a substantial number of studies in understanding their optoelectronic properties. However, consensus regarding the electronic properties of these perovskites is lacking due to a huge scatter in the reported key parameters, such as work function (Φ) and valence band maximum (VBM) values. Here, we demonstrate that the surface photovoltage (SPV) is a key phenomenon occurring at the perovskite surfaces that feature a non-negligible density of surface states, which is more the rule than an exception for most materials under study. With ultraviolet photoelectron spectroscopy (UPS) and Kelvin probe, we evidence that even minute UV photon fluxes (500 times lower than that used in typical UPS experiments) are sufficient to induce SPV and shift the perovskite Φ and VBM by several 100 meV compared to dark. By combining UV and visible light, we establish flat band conditions (i.e., compensate the surface-state-induced surface band bending) at the surface of four important perovskites, and find that all are p-type in the bulk, despite a pronounced n-type surface character in the dark. The present findings highlight that SPV effects must be considered in all surface studies to fully understand perovskites' photophysical properties.
Communications Physics · 65 Zitationen · DOI
Abstract Tuning the Fermi level (E F ) in two-dimensional transition metal dichalcogenide (TMDC) semiconductors is crucial for optimizing their application in (opto-)electronic devices. Doping by molecular electron acceptors and donors has been suggested as a promising method to achieve E F -adjustment. Here, we demonstrate that the charge transfer (CT) mechanism between TMDC and molecular dopant depends critically on the electrical nature of the substrate as well as its electronic coupling with the TMDC. Using angle-resolved ultraviolet and X-ray photoelectron spectroscopy, we reveal three fundamentally different, substrate-dependent CT mechanisms between the molecular electron acceptor 1,3,4,5,7,8-hexafluoro-tetracyano-naphthoquinodimethane (F 6 TCNNQ) and a MoS 2 monolayer. Our results demonstrate that any substrate that acts as charge reservoir for dopant molecules can prohibit factual doping of a TMDC monolayer. On the other hand, the three different CT mechanisms can be exploited for the design of advanced heterostructures, exhibiting tailored electronic properties in (opto-)electronic devices based on two-dimensional semiconductors.
Physical Review B · 62 Zitationen · DOI
The electronic structure of cobalt-phthalocyanine (CoPc) molecules adsorbed on Ag(100) is investigated by photoemission spectroscopy. The results are compared to first-principles electronic structure calculations, based on many-body perturbation theory in the GW approximation. The photoemission data, obtained from both multilayer and monolayer films of CoPc, show that charge transfer occurs between the first molecular layer and the metal surface. Varying the photon energy, to tune the photoionization cross sections, reveals that the charge-transfer-related interface states mainly involve the Co $3d$ atomic orbitals of the Co central atom. GW calculations for the neutral CoPc molecule and its anion compare well with the experimental observations for a multilayer and a monolayer CoPc film, respectively. They confirm the major role played by the Co atom in the charge-transfer process and elucidate the complex energy rearrangement of the molecular electronic levels upon metal adsorption.
Small Methods · 61 Zitationen · DOI
Abstract A room‐temperature low‐cost TiS 2 p‐type contact material is applied for the first time as the hole‐transporting material (HTM) in perovskite solar cells, with power conversion efficiencies surpassing 13.5%. Synthesized by a simple two‐step hot‐injection method, it presents a much lower price per m 2 than octakis(4‐methoxyphenyl)‐9,9′‐spirospirobi[9H‐fluorene]‐2,2′,7,7′‐tetramine (spiro‐OMeTAD), 30 times lower in price ($0.046 for TiS 2 and $1.36 for spiro‐OMeTAD at 13.54% efficiency), standing out over most of the reported HTM alternatives.
Advanced Energy Materials · 54 Zitationen · DOI
Abstract To arrive to sustainable hydrogen‐based energy solutions, the understanding of water‐splitting catalysts plays the most crucial role. Herein, state‐of‐the‐art hypotheses are combined on electrocatalytic active metal sites toward the oxygen evolution reaction (OER) to develop a highly efficient catalyst based on Earth‐abundant cobalt and zinc oxides. The precursor catalyst Zn 0.35 Co 0.65 O is synthesized via a fast microwave‐assisted approach at low temperatures. Subsequently, it transforms in situ from the wurtzite structure to the layered γ‐Co(O)OH, while most of its zinc leaches out. This material shows outstanding catalytic performance and stability toward the OER in 1 m KOH (overpotential at 10 mA cm −2 η initial = 306 mV, η 98 h = 318 mV). By comparing the electrochemical results and ex situ analyses to today's literature, clear structure‐activity correlations are able to be identified. The findings suggest that coordinately unsaturated cobalt octahedra on the surface are indeed the active centers for the OER.
Physical Review B · 46 Zitationen · DOI
Ultraviolet photoelectron spectroscopy was used to demonstrate organic/metal-contact charge injection barrier tuning by exploiting the orientation-dependent work function \ensuremath{\phi} of a molecular acceptor [hexaazatriphenylene-hexanitrile (HATCN)] interlayer on Ag(111). The work function \ensuremath{\phi} of a flat-lying HATCN monolayer on Ag was 4.6 eV (similar to a pristine Ag electrode), whereas a layer of edge-on HATCN on Ag exhibited \ensuremath{\phi} of 5.5 eV (comparable to a pristine Au electrode). The hole-injection barriers (HIBs) between HATCN-modified electrodes and the organic semiconductors tris(8-hydroxyquinoline)aluminum (Alq${}_{3}$) and N,N${}^{\ensuremath{'}}$-bis(1-naphtyhl)-N,N${}^{\ensuremath{'}}$-diphenyl-1,1${}^{\ensuremath{'}}$-biphenyl-4.4${}^{\ensuremath{'}}$-diamine (\ensuremath{\alpha}-NPD) were reduced by more than 1 eV compared to pristine Ag and Au electrodes. Noteworthy, the HIBs determined with the flat-lying HATCN interlayer were lower than those obtained for pristine Ag substrates (\ensuremath{\phi} of both electrodes is 4.6 eV), and the HIBs with the edge-on HATCN on Ag were lower than those found for pristine Au (\ensuremath{\phi} of both electrodes ca. 5.4 eV). This shows that acceptor interlayers are beneficial for charge injection in electronic devices even when the molecularly modified electrode \ensuremath{\phi} is comparable to that of a pristine metal surface. It is argued that the molecularly modified electrodes are electronically more rigid than their pristine metal counterparts, i.e., the electron spill-out at the organic-terminated surface is less pronounced compared to Ag and Au surfaces.
Physical Review B · 45 Zitationen · DOI
Fermi-level pinning of C${}_{60}$ (sub)-monolayers on a sexithiophene (6T) bilayer grown on Ag(111) is shown to induce electron transfer from the metal to a fraction of the C${}_{60}$ molecules. The electrostatic potential resulting from the charge transfer process is responsible for a potential drop within the 6T interlayer and, more remarkably, for dipole-dipole repulsion, leading to a disproportionation into coexisting neutral and charged C${}_{60}$ molecules. We suggest that charge ordering phenomena may occur for such systems.
ACS Applied Materials & Interfaces · 42 Zitationen · DOI
Heterostructures made from metal oxide semiconductors (MOS) are fundamental for the development of high-performance gas sensors. Since their importance in real applications, a thorough understanding of the transduction mechanism is vital, whether it is related to a heterojunction or simply to the shell and core materials. A better understanding of the sensing response of heterostructured nanomaterials requires the engineering of heterojunctions with well-defined core and shell layers. Here, we introduce a series of prototypes CNT-<sub>n</sub>MOS, CNT-<sub>p</sub>MOS, CNT-<sub>p</sub>MOS-<sub><i>n</i></sub>MOS, and CNT-<sub><i>n</i></sub>MOS-<sub>p</sub>MOS hierarchical core-shell heterostructures (CSHS) permitting us to directly relate the sensing response to the MOS shell or to the p-n heterojunction. The carbon nanotubes are here used as highly conductive substrates permitting operation of the devices at relatively low temperature and are not involved in the sensing response. NiO and SnO<sub>2</sub> are selected as representative p- and n-type MOS, respectively, and the response of a set of samples is studied toward hydrogen considered as model analyte. The CNT-<sub>n,p</sub>MOS CSHS exhibit response related to the <sub>n,p</sub>MOS-shell layer. On the other hand, the CNT-<sub>p</sub>MOS-<sub>n</sub>MOS and CNT-<sub>n</sub>MOS-<sub>p</sub>MOS CSHS show sensing responses, which in certain cases are governed by the heterojunctions between <sub>n</sub>MOS and <sub>p</sub>MOS and strongly depends on the thickness of the MOS layers. Due to the fundamental nature of this study, these findings are important for the development of next generation gas sensing devices.
Physical Review B · 41 Zitationen · DOI
The geometrical, electronic, and vibrational properties of one monolayer of Zinc-phthalocyanine (ZnPc) adsorbed on Ag(110) are studied by low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), and high-resolution electron energy-loss spectroscopy (HREELS). STM and LEED revealed that the molecules lie flat on the surface, ordered in a compact arrangement with a supercell defining a coincidence mesh with the substrate lattice. By comparing the HREELS spectra of one monolayer to those of a multilayer film, in which the molecules are weakly interacting, it was found that the electronic and vibrational properties of the molecular film are sensibly perturbed at the interface. The $Q$ and $B$ bands corresponding to optical interband excitations measured for the multilayer are not detected for the monolayer film and an intense low-energy Drude-like plasmon loss in the infrared region is observed. The vibrational features are also modified: several Raman modes of the isolated molecule were found to become infrared active for the monolayer because of the lowering of the molecular symmetry induced by the interaction with the substrate. Moreover a sizeable vibrational softening was measured for the selected modes indicating a charge transfer from the substrate to the molecules. Finally the strong asymmetric line shape observed for one of the Raman modes is discussed in terms of interfacial dynamical charge transfer and electron-phonon coupling.
Scientific Reports · 40 Zitationen · DOI
We reveal the rather complex interplay of contact-induced re-orientation and interfacial electronic structure - in the presence of Fermi-level pinning - at prototypical molecular heterojunctions comprising copper phthalocyanine (H16CuPc) and its perfluorinated analogue (F16CuPc), by employing ultraviolet photoelectron and X-ray absorption spectroscopy. For both layer sequences, we find that Fermi-level (EF) pinning of the first layer on the conductive polymer substrate modifies the work function encountered by the second layer such that it also becomes EF-pinned, however, at the interface towards the first molecular layer. This results in a charge transfer accompanied by a sheet charge density at the organic/organic interface. While molecules in the bulk of the films exhibit upright orientation, contact formation at the heterojunction results in an interfacial bilayer with lying and co-facial orientation. This interfacial layer is not EF-pinned, but provides for an additional density of states at the interface that is not present in the bulk. With reliable knowledge of the organic heterojunction's electronic structure we can explain the poor performance of these in photovoltaic cells as well as their valuable function as charge generation layer in electronic devices.
Scientific Reports · 38 Zitationen · DOI
Multiple functionality of tungsten polyoxometalate (POM) has been achieved applying it as interfacial layer for solution processed high performance In<sub>2</sub>O<sub>3</sub> thin film transistors, which results in overall improvement of device performance. This approach not only reduces off-current of the device by more than two orders of magnitude, but also leads to a threshold voltage reduction, as well as significantly enhances the mobility through facilitated charge injection from the electrode to the active layer. Such a mechanism has been elucidated through morphological and spectroscopic studies.
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Identität, Organisation und Kontakt aus HU-FIS.
- Name
- Dr. Patrick Amsalem
- Titel
- Dr.
- Fakultät
- Zentralinstitut Center for the Science of Materials Berlin
- Telefon
- +49 30 2093-7534
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- 26.4.2026, 01:01:55