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Mechanically Induced Switching of Molecular Layers
摘要： Within the field of switchable surfaces, azobenzenes are an extensively studied group of molecules, known for reversibly changing conformation upon illumination with light of different wavelengths. Relying on the ability of the molecules to change properties and structure as a response to external stimuli, they have been incorporated in various devices, such as molecular switches and motors. In contrast to the well-documented switching by light irradiation, we report the discovery of mechanically triggered switching of self-assembled azobenzene monolayers, resulting in changes of surface wettability, adhesion, and friction. This mechanically induced cis?trans isomerization is triggered either locally and selectively by AFM or macroscopically by particle impact. The process is optically reversible, enabling consecutive switching cycles. Collective switching behavior was also observed, propagating from the original point of impact in a domino-like manner. Finally, local force application facilitated nondestructive and erasable nanopatterning, the cis?trans nanolithography.
关键词： Molecular switch,self-assembled monolayers,mechanical switching,nanolithography,azobenzene
更新于2025-09-19 17:15:36
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Spectral Interrogation based SPR Sensor for Blood Glucose Detection with Improved Sensitivity and Stability
摘要： A sensor chip for specific detection of blood glucose was developed. The sensor utilized a surface-plasmon-resonance (SPR) setup on a prism based Kretschmann configuration utilizing spectral interrogation scheme. Self-assembled monolayers (SAMs) based preparation provided the chip stability due to covalent bonds and hence it can be reused for multiple times. Such a scheme can be advantageous in continuous monitoring of blood glucose, without changing the chip. Control experiments were performed without molecular recognition layer to confirm the performance of the sensor. Furthermore, the measurements were performed on blood serums and compared with that of a conventional glucometer. The present sensor has the advantages of improved sensitivity (0.14 nm/(mg/dl)) and stable response for 3 months, which are better compared to existing reports.
关键词： Blood glucose,Self assembled monolayers,Surface plasmon resonance,Biosensor
更新于2025-09-19 17:15:36
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Study of the Molecular Bending in Azobenzene Self-Assembled Monolayers Observed by Tip-Enhanced Raman Spectroscopy in Scanning Tunneling Mode
摘要： Tip-enhanced Raman Spectroscopy (TERS) is capable of amplifying the extremely weak Raman response of azobenzene self-assembled monolayers (SAMs), thus allowing for the chemical characterization of the sample surface at the nanoscale. Recently, we introduced a physical model describing the TERS intensity of azobenzene SAMs probed in a scanning tunneling mode configuration (STM-TERS), that takes into account the molecular bending induced by the high electric field inside the tunneling junction. The model predicts quite well the experimental variation in the TERS intensity of a hexil azobenzene SAM (AzoC6) on gold polycrystalline film (111) with changing the electric field in the gap between the tip and the substrate. Nevertheless, a disagreement between the model and the experiment has been observed while studying, in the same conditions, the TERS intensity of undecyl azobenzene (AzoC11) SAM formed by molecules featuring an alkyl chain nearly two times longer with respect to the previous case. In this work we extend the molecular bending model through considering an additional bending mechanism due to the mechanical interaction between the tip and the SAM, occurring when the tip-to-sample distance is shorter than the molecular length. The extended model is able to describe well the TERS intensity behavior with changing either the bias voltage or the tip-to-sample distance for both AzoC6 and AzoC11. Eventually, we determine quantitatively the difference in elastic properties of the two molecules physically accounting for the difference in the TERS intensity behavior of the two SAMs.
关键词： STM-TERS,self-assembled monolayers,SAMs,Tip-enhanced Raman Spectroscopy,TERS,molecular bending,azobenzene
更新于2025-09-19 17:13:59
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Modulating the luminance of organic light-emitting diodes via optical stimulation of a photochromic molecular monolayer at transparent oxide electrode
摘要： Self-assembled monolayers (SAMs) deposited on bottom electrodes are commonly used to tune charge carrier injection or blocking in optoelectronic devices. Beside the enhancement of device performance, the fabrication of multifunctional devices in which the output can be modulated by multiple external stimuli remains a challenging target. In this work, we report the functionalization of an indium tin oxide (ITO) electrode with a SAM of a diarylethene derivative designed for optically control the electronic properties. Following the demonstration of dense SAM formation and its photochromic activity, as a proof-of-principle, an organic light-emitting diode (OLED) embedding the light-responsive SAM-covered electrode was fabricated and characterized. Optically addressing the two-terminal device by irradiation with ultraviolet light doubles the electroluminescence. The original value can be restored reversibly by irradiation with visible light. This expanded functionality is based on the photoinduced modulation of the electronic structure of the diarylethene isomers, which impact the charge carriers’ confinement within the emissive layer. This approach could be successfully exploited in the field of opto-communication technology, for example to fabricate opto-electronic logic circuits.
关键词： photochromic,optoelectronic devices,diarylethene,Self-assembled monolayers,organic light-emitting diodes
更新于2025-09-19 17:13:59
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Self-Assembled Monolayers with Embedded Dipole Moments for Work Function Engineering of Oxide Substrates
摘要： Self-assembled monolayers (SAMs) are frequently used for work function (WF) engineering of different materials. For this, typically dipolar groups are attached to the molecule terminus at the SAM?ambient interface, which also influences its chemistry. WF engineering and interface chemistry can, however, be decoupled from one another using embedded dipolar groups, as has been demonstrated before for thiolate SAMs on metals. Herein, we extend this concept to oxide substrates. For this, a series of biphenyl-based molecules with a phosphonic acid (PA) anchoring group was synthesized, with one of the nonpolar phenyl units exchanged for a polar pyrimidine moiety, the dipole moment of which is oriented either toward (“down”) or away (“up”) to/from the PA group and, consequently, to/from the substrate. SAMs of these molecules formed on indium tin oxide (ITO), a frequently used and application-relevant oxide substrate, feature a uniform molecular configuration, dense molecular packing, and an upright molecular orientation. These SAMs exhibit pronounced electrostatic effects associated with the embedded dipolar groups, viz. shifts of the characteristic peaks in the C 1s X-ray photoelectron spectra and WF variations. The latter values were found to be 3.9, 4.85, and 4.4 eV for the up, down, and nonpolar reference SAM-engineered ITO, respectively. Consequently, these SAMs can serve as a powerful tool to monitor WF engineering effects in a variety of device assembles, decoupling these effects from the interface chemistry. The comparably low WF value for the up SAM is particularly important since it extends a rather limited variety of SAMs capable of lowering the WF of ITO.
关键词： Phosphonic acid,Self-assembled monolayers,Work function engineering,Embedded dipolar groups,Indium tin oxide,Oxide substrates
更新于2025-09-19 17:13:59
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Self-assembled monolayers of polyoxovanadates with phthalocyaninato lanthanide moieties on gold surfaces
摘要： The two first representatives of phthalocyaninato (Pc) lanthanide-ligated polyoxovanadate cages {[V12O32(Cl)](LnPc)n}n(cid:2)5 (n = 1 or 2, Ln = Yb3+) were synthesised and fully characterised. These magnetic complexes form two-dimensional self-assembled monolayers exhibiting electrical conductivity on gold substrate surfaces, as assessed by using an EGaIn tip.
关键词： gold surfaces,electrical conductivity,phthalocyaninato lanthanide,polyoxovanadates,self-assembled monolayers
更新于2025-09-16 10:30:52
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Simulated revelation of the adsorption behaviours of acetylcholinesterase on charged self-assembled monolayers
摘要： An acetylcholinesterase (AChE)-based electrochemical biosensor, as a promising alternative to detect organophosphates (OPs) and carbamate pesticides, has gained considerable attention in recent years, due to the advantages of simplicity, rapidity, reliability and low cost. The bio-activity of AChE immobilized on the surface and the direct electron transfer (DET) rate between an enzyme and an electrode directly determined the analytical performances of the AChE-based biosensor, and experimental studies have shown that the charged surfaces have a strong impact on the detectability of the AChE-based biosensor. Therefore, it is very important to reveal the behaviour of AChE in bulk solution and on charged surfaces at the molecular level. In this work, the adsorption orientation and conformation of AChE from Torpedo californica (TcAChE) on oppositely charged self-assembled monolayers (SAMs), COOH-SAM and NH2-SAM with different surface charge densities, were investigated by parallel tempering Monte Carlo (PTMC) and all-atom molecular dynamics simulations (AAMD). Simulation results show that TcAChE could spontaneously and stably adsorb on two oppositely charged surfaces by the synergy of an electric dipole and charged residue patch, and opposite orientations were observed. The active-site gorge of TcAChE is oriented toward the surface with the “end-on” orientation and the active sites are close to the surface when it is adsorbed on the positively charged surface and the tunnel cost for the substrate is lower than that on the negatively charged surface and in bulk solution, while for TcAChE adsorbed on the negatively charged surface, the active site of TcAChE is far away from the surface and the active-site gorge is oriented toward the solution with a “back-on” orientation. It suggests that the positively charged surface could provide a better microenvironment for the efficient bio-catalytic reaction and quick DET between TcAChE and the electrode surface. Moreover, the RMSD, RMSF, dipole moment, gyration radius, eccentricity and superimposed structures show that only a slight conformational change occurred on the relatively flexible structure of TcAChE during simulations, and the native conformation is well preserved after adsorption. This work helps us better comprehend the adsorption mechanism of TcAChE on charged surfaces and might provide some guidelines for the development of new TcAChE-based amperometric biosensors for the detection of organophosphorus pesticides.
关键词： electrochemical biosensor,carbamate pesticides,molecular dynamics simulations,conformation,organophosphates,acetylcholinesterase,self-assembled monolayers,adsorption orientation
更新于2025-09-16 10:30:52
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Interfacial Engineering through Chloride-Functionalized Self-Assembled Monolayers for High-Performance Perovskite Solar Cells
摘要： The family of organic-inorganic hybrid perovskite (OIHPs) materials is one of the most promising for very high efficiency photovoltaic solar cells application. In the present work, the effect of a series of self-assembled monolayers placed at the TiO2-perovskite junction, on the functioning of triple cation perovskite solar cells has been investigated. We show that employing 4-chlorobenzoic acid leads to the marked boosting of the solar cells performances. The starting pristine cell had a 20.3% power conversion efficiency (PCE) and the chemical engineering permitted to reach a PCE up to 21.35%. Our experimental study completed by density functional theory (DFT) calculations and modelling show that this improvement is due to the reduction of interfacial states, to the improvement of the quality of the OIHP material and to the structural continuity between TiO2 and the OIHP. Especially, we demonstrate that the interfacial chemical interactions are important to consider in the design of highly efficient devices.
关键词： Perovskite solar cells,Self-assembled monolayers,Hydrides,Benzoic acid derivatives,High efficiency,Density functional theory
更新于2025-09-12 10:27:22
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Nitrogen oxides sensing performance of thiols and dithiols self-assembled monolayer functionalized Au/GaAs-based Schottky diodes
摘要： In this work, GaAs-based Schottky diodes, functionalized by alkanethiolates, were used to fabricate NOx gas sensors with high-selectivity and low-power. Alkanethiolates were employed to form a self-assembled monolayer (SAM) on the surface of the Au (111) Schottky contacts of the n-GaAs substrate using immersion method. The adsorption behaviors between SAM and Au (111) with different terminal (functional) groups, carbon numbers (CN), immersion times (tim), and alkanedithiol concentrations were characterized by cyclic voltammetry (CV) measurement. The interaction between NOx molecules and SAM was determined by an ultraviolet/visible (UV-Vis) spectrophotometer. The NOx sensing performance of the studied device under proper conditions was investigated at different temperatures and NOx gas concentrations. Experimentally, at 25℃, good sensing responses of 49.6 and 35.5 in 100 ppm NO2 and NO ambiences were obtained, respectively. Furthermore, similar sensing properties of the studied device were found in air and in N2 ambience. Therefore, the studied device can be considered a promising candidate for NOx sensing applications.
关键词： Alkanedithiol,Nitrogen oxides,Gas sensors,Schottky diode,GaAs,Self-assembled monolayers (SAM)
更新于2025-09-12 10:27:22
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Self-assembled interface monolayers for organic and hybrid electronics
摘要： The state of the art in the field of self-assembled organic interface monolayers widely used in organic and hybrid electronics is analyzed and the results obtained are summarized. Recent advances in full and local substrate modification using interface layers are considered in detail. Examples of the most successful applications of interface monolayers as monolayer dielectrics, modifiers of the work function and adhesion promoters are given. The advantages of utilizing interface monolayers at semiconductor/dielectric interfaces and for modifying the semiconductor surface are demonstrated. Specific features of formation of nanostructured surfaces including those used in biosensoric applications are outlined.
关键词： adhesion promoters,work function modifiers,biosensors,organic electronics,interface layers,hybrid electronics,dielectrics,self-assembled monolayers
更新于2025-09-12 10:27:22