Chemisorption Of Organic Molecules Research Articles

Modulation of Ionically Generated Space Charge Effects at Hybrid Perovskite and Oxide Interfaces via Surface Modification

AbstractInterfacial space charges significantly influence transport and recombination of charge carriers in optoelectronic devices. Due to the mixed ionic‐electronic conducting properties of halide perovskites, not only electronic effects, but also ionic interactions at their interfaces need to be considered in the analysis of space charges. Understanding of these interactions and their control is currently missing. This study elucidates the ionic effects on space charge formation at the interface between methylammonium lead iodide (MAPI) and alumina, and its modulation through surface modification using organic molecules. Embedding insulating alumina nanoparticles within MAPI films leads to enhancement of the electronic conductivity. This effect is consistent with the formation of an interfacial inversion layer in MAPI and can only be explained on the basis of ionic interactions. Such an effect is attenuated by surface modification of the oxide via the chemisorption of organic molecules. Finally, the same trend is observed in solar cells, where reducing the potential of the distributed space charges within the composite active layer improves device performance. These findings emphasize the necessity of taking into account ionic interactions to control the space charge formation at interfaces involving mixed ionic‐electronic conductors, an essential aspect in the performance optimization of halide perovskite‐based devices.

Functionalizing self-assembled monolayers to reduce interface scattering in ruthenium/dielectric for next-generation microelectronic interconnects

As the number of transistor increases in modern devices, the resistivity of metal lines increases with the downscaling of the vias dimension due to the increased in surface scattering of electrons. Herein, we evaluated the electrical performance and the adhesion strength of the Ru/SiO2 substrate upon functionalizing with benzyliminetriethoxysilane (BITES) and aminoproyltriethoxysilane (APTES) self-assembled monolayers (SAMs)s at the Ru/SiO2 interface. The covalent bonding and retention of the SAM film on the SiO2 surface were characterized via angle-resolved X-ray Photoelectron Spectroscopy (AR-XPS) and Time-of-Flight Secondary Ion Mass Spectrometry (Tof-SIMS), respectively. According to the Fuchs–Sondheimer (FS) model and scratch test, the specularity parameter and the adhesion strength of the Ru/BITES/SiO2 simultaneously improved after thermal annealing compared to the non-functionalized Ru/SiO2 substrate. The effect of different SAM’s terminal groups (amine and benzylimine) on the electron scattering behavior was investigated based on the formation of an interface dipole upon chemisorption of organic molecules on the metal film. Our results indicate that SAM with the benzylimine terminal group formed a larger positive dipole at the SAM layer of the Ru/BITES/SiO2 interface compared to the Ru/APTES/SiO2, leading to an increased in specular electron scattering events and, thus an enhanced electrical performance of the Ru/BITES/SiO2.

(Invited) Covalent Functionalization of Graphene and MoS2 : Towards Nanometer Scale Chemical Patterning

Atomically thin sheets of materials (2D materials) came to prominence in the early 2000s with the successful isolation of graphene. Since then, the interest in graphene has steadily increased thanks to its exceptional electronic, optical, mechanical and thermal properties. It also led to the isolation of other 2D materials such as black phosphorous, silicene, germanene and transition metal dichalcogenides (TMDs) such as MoS2. Due to their exceptional properties, these materials offer virtually endless opportunities for fundamental research as well as cutting edge applications.Most of these 2D materials can be stabilized by the covalent attachment of organic molecules. For instance, the chemisorption of organic units can promote the stabilization of dispersions of 2D materials in organic solvents improving their solution processability. Moreover, such chemisorption of organic molecules allows manipulation of their physicochemical properties by addition of desired functional groups in a tailor made fashion. However, controlling the spatial distribution of the covalently bound units remains a major challenge due to the highly reactive nature of the reagents used for the covalent modification process.In this talk, I will discuss the covalent modification of graphene, graphite and MoS2 using diazonium chemistry. The chemically activated decomposition of diazonium salts using mild conditions will be discussed in detail. The characterization of the modified materials using atomic force microscopy (AFM), scanning tunnelling microscopy (STM), and Raman spectroscopy will be presented. The micrometre-scale multicomponent patterning of surface-supported graphene achieved through a combination of e-beam lithography and diazonium chemistry will also be discussed. The impact of this functionalization on the surface potential will be evaluated through scanning probe microscopies. Lastly, I will also show how the chemical patterning can be extended to the lower end of the nanoscale by using physisorbed self-assembled monolayers of alkanes as sacrificial templates.

(Invited) Covalent Functionalization of Graphene and MoS2: Chemical Versus Electrochemical Routes

Atomically thin sheets of materials, the so-called two-dimensional (2D) materials arrived on the scene in early 2000s with the successful isolation of graphene as freestanding monolayer films. Graphene, a single atom thick sheet of sp2-hybridized carbon bonded in a honeycomb lattice, has exceptional electronic, optical, mechanical and thermal properties that outperform those of most of the existing materials. The research on graphene further fuelled emergence of related 2D materials such as black phosphorous, silicene, germanene and transition metal dichalcogenides (TMDs) such as MoS2. Due to their exotic properties, these materials offer virtually endless opportunities for fundamental research as well as cutting edge applications. Most of these 2D materials however exist as single layers only when supported by another solid surface or when stabilized by physisorbed or chemisorbed organic molecules. Given their layered nature, most 2D materials are extremely difficult to disperse in typical solvents. Chemisorption of organic molecules onto their basal plane allows dispersion of these materials in (organic) solvents thereby improving their solution processability. Such dispersions can be used in composite materials and as functional inks. Moreover, covalent functionalization allows modification of the intrinsic electrical, electronic and optical properties of these 2D materials. In this talk, I will discuss covalent modification graphene, graphite and MoS2 using diazonium chemistry. Two different routes for reductive decomposition of diazonium salts namely, chemical and electrochemical, will be discussed in detail. Special focus is on sub-nanometer characterization of modified materials using scanning tunneling and atomic force microscopy (STM and AFM). Initial results towards patterned covalent functionalization using physisorbed self-assembled templates will also be presented besides the discussion on the use of such surfaces as seed layers for atomic layer deposition (ALD).

Recent advances in self-assembled monolayers based biomolecular electronic devices

Self-assembled monolayers (SAMs) have aroused much interest due to their potential applications in biosensors, biomolecular electronics and nanotechnology. This has been largely attributed to their inherent ordered arrangement and controllable properties. SAMs can be formed by chemisorption of organic molecules containing groups like thiols, disulphides, amines, acids or silanes, on desired surfaces and can be used to fabricate biomolecular electronic devices. We focus on recent applications of organosulphur compounds (thiols) based SAMs to biomolecular electronic devices in the last about 3 years.

Substrate-related feature in the loss structure of contamination C 1s

It has been shown that the characteristic loss structure associated with the photoelectron peak can be separated into two components related, respectively, to extrinsic and intrinsic energy loss. The extrinsic component is related to transport of the photoelectron through the solid phase and has been well described by Tougaard. The intrinsic component is related to excitation of alternative final states in or adjacent to the photoexcited atom. Although it is difficult to discern, separately, the two contributions in the energy-loss region outside the peak, it is theoretically predicted that the extrinsic contribution has a negligible effect in the peak region. This has been confirmed by Tougaard: his background removes very little intensity under the peak and eventually leaves an asymmetric peak whose tail can be related only to 'intrinsic' processes. We have suggested that the background step 'under the peak position' as derived by the Shirley algorithm-used for background subtraction in most data systems-is related to this latter process. We have also shown that it is useful to characterize the shape of the Shirley-type background by means of a parameter κ. The intensity of the Shirley background at the peak maximum, and thus the value of K, was shown to be primarily a function of the position of the element in the Periodic Table: the transition elements have very intense backgrounds whilst elements such as carbon in organic compounds have little or no background. In compounds there is an opportunity for photoexcitation of one element to excite electrons to higher energy states in its chemical partner, and hence to show similar intrinsic losses, even when such losses are not observed in the pure element itself. We have given examples of this in the XPS spectra of oxides and intermetallic alloys. In this paper we illustrate the manner in which the 'intrinsic' background of the C 1s peak in adsorbed contamination varies with the substrate on which it is adsorbed. We believe this to arise from the fact that photoexcitation of the C 1s is able to create excited final states in the valence band of the underlying material. It is concluded that strong chemisorption of organic molecules can be recognised by reference to the shape of the intrinsic loss background.

Chemisorption of organic molecules on ZnO(11̄00) surfaces: C 5H 5N, (CH 3) 2CO, and (CH 3) 2SO

Ultraviolet photoemission studies of pyridine, acetone, and dimethyl sulfoxide adsorbed on ZnO(11̄00) show the involvement of molecular orbitals having π, π ★, and nitrogen and oxygen lone-pair character in formation of the chemisorption bond. No decomposition products from adsorption of these molecules are observed on the surface.

Chemisorption of organic molecules on single crystal surfaces of transition metals. Adlayer stoichiometry, arrangement and electronic states

XPS and UPS of alkenes and haloalkenes, chemisorbed on a clean Pt(100) surface, are reported. The dissociative chemisorption of vinyl fluoride and vinyl chloride at low coverages is modified when the clean surface is pre-treated with carbon monoxide. Arguments are presented that the activation of carbon–hydrogen bonds takes place preferentially at four-fold bridging sites on the surface. The differing patterns of sorption of ethylene on the Pt(100) and Ni(111) surfaces are discussed and some general comments provided on the importance of intra-adlayer interactions in determining some surface reactions.