Odd-even effects in aryl-substituted alkanethiolate SAMs: nonsymmetrical attachment of aryl unit and its impact on the SAM structure.

Aryl-substituted alkanethiolate (AT) self-assembled monolayers (SAMs) exhibit typically so-called odd-even effects, viz. systematic variations in the film structure, packing density, and molecular inclination depending on the parity of the number of the methylene units in the alkyl linker, n. As an exception to this rule, ATs carrying an anthracen-2-yl group (Ant-n) as tail group were reported to have different behavior due the non-symmetric attachment of the anthracene unit to the AT linker, providing additional degree of freedom for the molecular organization and allowing for partial compensation of the odd-even effects. In this context, the structure of SAMs formed by adsorption of anthracene-substituted ATs (Ant-n; n = 1-6) at room temperature on Au(111) substrate was investigated by high-resolution scanning tunnelling microscopy (STM). Most of these SAMs exhibit a coexistence of two different ordered phases, some of which are common for either n = odd or n = even while other vary over the series, showing a broad variety of different structures. The average packing density of the Ant-n SAMs, derived from the analysis of the STM data, varies by 7.5-10% depending on the parity of n, being, as expected, higher for n = odd. The respective extent of the odd-even effects is noticeably lower than that usually observed for other aryl-substituted monolayers (∼25%), which goes in line with the previous findings and emphasizes the impact of the non-symmetric attachment of the aromatic unit.

Polymorphism and Building-Block-Resolved STM Imaging of Self-Assembled Monolayers of 4-Fluorobenzenemethanethiol on Au(111).

Self-assembled monolayers (SAMs) of 4-fluorobenzenemethanethiol (p-FBMT) on Au(111), prepared by immersion procedure (1 mM ethanolic solution; 60 °C; 18 h), were characterized by scanning tunneling microscopy (STM). The data suggest the formation of highly ordered monolayer with a commensurate structure, described by the 2 3 × 13 R 13 ∘ unit cell. The STM appearance of this cell occurs, however, in two different forms, with either well-localized individual spots or splitting of these spots in two components. These components are assigned to the tunneling through the entire molecule or sulfur docking group only. The respective spots correspond then to the terminal fluorine atom and sulfur docking group, manifesting, thus, building-block-resolving STM imaging. The accessibility of the docking group for direct tunneling is most likely related to a specific molecular organization for one of the two possible internal structures of the unit cell. The above results represent a showcase for potential of STM for imaging of upright-arranged and densely packed molecular assemblies, such as SAMs.

Annealing effect for self-assembled monolayers formed from terphenylethanethiol on Au(111).

The structure and morphology of self-assembled monolayers (SAMs) prepared on Au(111) from solutions of terphenylethanethiol (TP2) at room temperature and subsequently annealed at temperatures up to 473 K were investigated using scanning tunneling microscopy. This system is of particular interest because of its metastable character, holding potential for its tailored modification. Indeed, the data suggest the formation of several different structural phases, viz. α, ß, γ, and δ, appearing progressively for the as-prepared and annealed samples. The consecutive α → ß â†’ γ → δ phase transitions occurring with increasing annealing temperature involved a continuous reduction of the molecular packing density and significant changes in the substrate morphology. The major morphological changes were the appearance and progressive growth of monoatomic gold islands, on top of which the TP2 phases were formed, representing in all cases a single domain for a particular island and restricted only by the island size. For all the phases, inclined molecular orientation was assumed while a so-called lying-down arrangement, in which the TP2 backbones are orientated parallel to the gold surface, was not observed. A nearly complete desorption of the TP2 molecules was recorded at an annealing temperature of 473 K, accompanied by the drastic change in the surface morphology.

Side-Group-Induced Polymorphism in Self-Assembled Monolayers: 3,5-Bis(trifluoromethyl)benzenethiolate Films on Au(111).

The structure and molecular organization of self-assembled monolayers (SAMs) depend on a complex interplay of intermolecular and molecule-substrate interactions, so that even a small change in molecular composition can result in noticeable changes in the SAM structure. Herein we show that decoration of the most basic aromatic SAM constituent, benzenethiol, with two trifluoromethyl groups leads to distinct polymorphism in the respective SAMs, in which the appearance of a specific structural phase or a combination of several different phases is dependent on the parameters of the preparation procedure. High-quality films with a single crystallographic phase and significantly large domains could only be prepared after a short immersion time (5 min) and an additional re-immersion of the sample in pure ethanol at an elevated temperature. A standard 24 h immersion at room temperature led to poorly defined films with a large defect density and only a small portion of the surface covered by well-ordered molecular domains.

Charge carrier mobilities in organic semiconductors: crystal engineering and the importance of molecular contacts.

We have conducted a combined experimental and theoretical study on the optimization of hexa-peri-hexabenzocoronene (HBC) as organic semiconductor. While orientations with high electronic coupling are unfavorable in the native liquid crystalline phase of HBC, we enforced such orientations by applying external constraints. To this end, self-assembled monolayers (SAMs) were formed by a non-conventional preparation method on an Au-substrate using electrochemical control. Within these SAMs the HBC units are forced into favorable orientations that cannot be achieved by unconstrained crystallization. For simulating the charge transport we applied a recently developed approach, where the molecular structure and the charge carrier are propagated simultaneously during a molecular dynamics simulation. Experiments as well as simulations are mutually supportive of an improved mobility in these novel materials. The implication of these findings for a rational design of future organic semiconductors will be discussed.

Knowledge, Awareness and Practice of Artificial Intelligence and Types of Realities Among Healthcare Professionals: A Nationwide Survey From Pakistan.

Background Artificial intelligence (AI) refers to the simulation of human intelligence processes by machines, enabling them to perform tasks. The advancements in AI have also improved virtual reality (VR), augmented reality (AR) and mixed reality (MR) experience allowing a greater opportunity for use in the field of medicine. Objective To evaluate the knowledge, attitude and practice of AI and types of realities among Pakistani healthcare professionals (HCPs). Materials and methods This was a prospective, nationwide study designed at the Department of Neurosurgery at Punjab Institute of Neurosciences (PINS), Lahore, was conducted between January 2024 to February 2024. More than 500 HCPs were approached, out of which 176 participated in this survey consensually. A pre-formed general questionnaire based on knowledge, attitude and practices of AI and types of realities was modified according to local conditions. Google Forms (Google Inc., USA) was used to conduct the one-time sign up response. Statistical Package for Social Sciences (IBM SPSS Statistics for Windows, Version 24, USA) was used to analyze submitted responses. Results About 69.9% respondents were male HCPs. Most of the respondents were from the fields of neurosurgery, medicine and general surgery, i.e., 10.80%, 10.20% and 4%, respectively. More than 90% HCPs used Internet and electronic devices daily. A majority of 62.50% respondents agreed that AI brings benefits for the patients, while at the same time, 45.50% agreed that they would not trust the assessment of AI more than that of HCPs. 61% HCPs feared that AI-based systems could be manipulated from the outside sources, like terrorists and hackers. Although 90% respondents knew the definition of AR and VR, a strikingly low 40% respondents could only identify the practical applications of these realities when asked in a mini-quiz. About 61.40% HCPs never used any AI-based application throughout their clinical practice, but Google Health was used by 29.50% respondents, followed by Remote Patient Monitoring AI application used by 3.4% individuals. Conclusion There is an evident under-utilization of AI and types of realities in clinical practice in Pakistan. Lack of awareness, paucity of resources and conventional clinical practices are the key reasons identified. Pakistan is on the path towards the point where the developed world is currently. There is a potential to move past the initial stages of AI implementation and into more advanced modes of adopting AI and types of realities.

Post-infectious Moyamoya Syndrome: A Review of Existing Scientific Literature From 2000 to 2023.

Moyamoya disease (MMD) is considered a primary disorder of an unknown etiology. In contrast, Moyamoya syndrome (MMS) refers to MMD associated with other underlying diseases, such as meningitis in childhood, neurofibromatosis type II, Down syndrome, cranial irradiation, and different types of anemias, particularly hemoglobinopathies. We aimed to provide a comprehensive clinicopathological overview of MMS. All case reports and case series published from 2000 to 2023 pertaining to MMD were included in the study. Case studies, original articles, editorials, letters to editors, and clinical images were excluded. The search was conducted using the Boolean operators ("AND" and "OR") on PubMed and Google Scholar. A total of 13 case reports and one case series study were included. The study suggests infection might be a trigger in susceptible individuals. The autoimmune antibody findings (anti-double stranded DNA IgG) suggest a potential autoimmune component in some cases. There were diverse presentations and outcomes of post-infectious MMS, with a striking predominance of pediatric cases (66.66%) and a possible female predominance. Both computerized tomography (CT) and magnetic resonance imaging (MRI) showed evidence of restricted blood flow. CT showed that stenosis, occlusion, and collateral formation were frequent vascular findings, but often unspecified in severity. Infarction, hypodensities, and hematoma were the most common parenchymal findings (22.22% each). The findings on MRI were stenosis (50%) and collateral formation (44.44%). Infarction was the most common finding (66.66%) in parenchyma. Hydrocephalus, encephalomalacia, and atrophy were less frequent. Lesions were most frequent in the internal carotid artery (66.66%), middle cerebral artery (66.66%), and anterior cerebral artery (50%). Lesions were less frequent in the posterior cerebral, vertebral, and basilar arteries. The frontal lobe (38.89%) and basal ganglia (33.33%) were commonly affected parenchymal regions. The most common risk factor was human immunodeficiency virus (HIV) infection (50%), followed by trisomy 21, cryptococcal, and other types of meningitides. Aspirin (50%) and antiretroviral therapy (38.89%) were the cornerstones of treatment for MMS. This review accentuates the noteworthy obstacles presented by post-infectious MMS, especially its catastrophic effect on children and its correlation with HIV/AIDS. According to our elaborate literature search using PubMed and Google Scholar, this is the first narrative review in the existing scientific literature summarizing the literature on post-infectious MMS.

Polymorphism in self-assembled terphenylthiolate monolayers on Au(111).

Self-assembled monolayers (SAMs) of terphenylthiol (TPT) on gold Au(111) substrates exhibit well-ordered structures over large scales if they are annealed in ethanol at 40 °C after their formation. Using high-resolution STM, two distinct, ordered phases could be observed. The simpler phase, designated as α-phase, consists of closely packed molecules in the well-known (2√3 × âˆš3)R30° structure. It could be demonstrated that under less suitable imaging conditions this phase can be mistaken as the hexagonal (√3 × âˆš3)R30°, which resolves a discrepancy in between previous reports. The second phase is characterized by a stripe pattern with a periodicity of 2.0 nm and can be described by a point-on-line incommensurate (4 × n) ([Formula: see text]) lattice with n close to 8. This ß-phase contains four pairs of terphenylthiolate molecules, which might be held together by either disulfide bonds or the recently discussed S-Au-S motif, and is thus 35% ± 15% less densely packed than the α-phase. The coexistence of these phases explains the variability of spectroscopic results obtained in the past for terphenylthiolate layers, since their relative proportion determines the average thicknesses/tilt angles found in these studies.

Formation of highly ordered and orientated gold islands: effect of immersion time on the molecular adlayer structure of pentafluorobenzenethiols (PFBT) SAMs on Au(111).

Self-assembled monolayers (SAMs) of pentafluorobenzenethiol (PFBT) on Au(111) substrates, prepared with different immersion times (ITs) at room temperature, were studied using scanning tunneling microscopy (STM) and infrared reflection-absorption spectroscopy (IRRAS). In the present study, the focus was on several important points of interest in the field of SAMs. First, the gold islands formed upon adsorption of PFBT molecules on the gold surface were monitored at different ITs in terms of their size, density, and shape. After short ITs (5 to 30 min), small gold islands with rounded shape were formed. These gold islands were arranged in a rather regular fashion and found to be quite mobile under the influence of the STM-tip during the scanning. When the IT was increased to 16 h, the results revealed the formation of highly ordered and orientated gold islands with very unusual shapes with straight edges meeting at 60° or 120° running preferentially along the [11(-)0] substrate directions. The density of the gold islands was found to decrease with increasing IT until they almost disappeared from the SAMs prepared after 190 h of IT. On top of the gold islands, the PFBT molecules were found to adopt the closely packed (10√3 × 2) structure. Second, a number of structural defects such as disordered regions at the domain boundaries and dark row(s) of molecules within the ordered domains of the PFBT SAMs were observed at different ITs. The SAMs prepared after 190 h of IT were found to be free of these defects. Third, at low and moderate ITs, a variation in the PFBT molecular contrast was observed. This contrast variation was found to depend mainly on the tunneling parameters. Finally, our results revealed that the organization process of PFBT SAMs is IT-dependent. Consequently, a series of structural phases, namely, α, ß, γ, δ, and ε were found. The α-, ß-, γ-, and δ-phases were typically accompanied by the ε-phase that appeared on top of gold islands. With increasing IT, the α→ß→ γ→δ→ε phase transitions took place. The resulting ε-phase, which covered the entire gold surface after 190 h of IT, yielded well-ordered self-assembled monolayers with large domains having a (10√3 × 2) superlattice structure.

On the complexation kinetics for metallization of organic layers: palladium onto a pyridine-terminated araliphatic thiol film.

Palladium nanoparticles have been deposited electrochemically onto self-assembled monolayers (SAMs) of 4-(4-(4-pyridyl)phenyl)phenylmethanethiol. A pronounced correlation between the kinetics of the complexation between pyridine nitrogens and Pd cations and the sample potential has been observed. The amount of the Pd deposit significantly increases by adjusting the sample potential during the complexation step to values below the point of zero charge. The size of the spherical shaped Pd nanoparticles varies within a certain limit according to the amount of Pd(2+) ions initially coordinated on top of the SAM. The metallic state of these particles was confirmed by X-ray photoelectron spectroscopy and infrared reflection-absorption spectroscopy. Moreover, CO adsorption on the clean Pd deposit revealed further information about the crystallographic orientation of the nanoparticles.

Initiation and inhibition of dealloying of single crystalline Cu3Au (111) surfaces.

Dealloying is widely utilized but is a dangerous corrosion process as well. Here we report an atomistic picture of the initial stages of electrochemical dealloying of the model system Cu(3)Au (111). We illuminate the structural and chemical changes during the early stages of dissolution up to the critical potential, using a unique combination of advanced surface-analytical tools. Scanning tunneling microscopy images indicate an interlayer exchange of topmost surface atoms during initial dealloying, while scanning Auger-electron microscopy data clearly reveal that the surface is fully covered by a continuous Au-rich layer at an early stage. Initiating below this first layer a transformation from stacking-reversed toward substrate-oriented Au surface structures is observed close to the critical potential. We further use the observed structural transitions as a reference process to evaluate the mechanistic changes induced by a thiol-based model-inhibition layer applied to suppress surface diffusion. The initial ultrathin Au layer is stabilized with the intermediate island morphology completely suppressed, along an anodic shift of the breakdown potential. Thiol-modification induces a peculiar surface microstructure in the form of microcracks exhibiting a nanoporous core. On the basis of the presented atomic-scale observations, an interlayer exchange mechanism next to pure surface diffusion becomes obvious which may be controlling the layer thickness and its later change in orientation.

Electrochemical investigations on stability and protonation behavior of pyridine-terminated aromatic self-assembled monolayers.

Based on electrochemical methods such as cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), Au(111) electrodes modified by self-assembled monolayers (SAMs) of a homologous series of pyridine-terminated thiols with aromatic backbones have been investigated. An important correlation between the chain structure and film integrity in electrolytic media was found. Monolayers with odd numbers of methylene spacers in the molecular chain showed superior barrier properties compared to even numbered counterparts. A positive influence of an increase in the number of attached phenyl rings on the integrity of SAMs was observed. Furthermore, cathodic desorption of the investigated SAMs is characterized by multiwave desorption peaks and extraordinarily large cathodic charges indicating an unusual desorption process. Moreover, protonation behavior of the SAMs has been investigated by X-ray photoelectron spectroscopy (XPS) and electrochemical methods. Protonation has been found to be reversible and surface pK(a) values have been determined to be around 5 for all investigated monolayers.

Self-assembled monolayers of aromatic omega-aminothiols on gold: surface chemistry and reactivity.

Amino-terminated self-assembled monolayers on gold substrates were studied by X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption fine structure (NEXAFS) measurements, and atomic force microscopy (AFM). Two different omega-amino-4,4'-terphenyl substituted alkanethiols of the general structure H(2)N-(C(6)H(4))(3)-(CH(2))(n)-SH (ATPn) were used: 2-(4''-amino-1,1':4',1''-terphenyl-4-yl)ethane-1-thiol (n = 2, ATP2) and 3-(4''-amino-1,1':4',1''-terphenyl-4-yl)propane-1-thiol (n = 3, ATP3). Moreover, the addressability of amino groups within the films was investigated by chemical derivatization of ATPn SAMs with 3,5-bis(trifluoromethyl)phenyl isothiocyanate (ITC) forming fluorinated thiourea ATPn-F films. Evaluation of high-resolution C 1s and N 1s XPS data revealed successful derivatization of at least 50% of surface amino species. Furthermore, it could be demonstrated by angle-resolved NEXAFS spectroscopy that chemical derivatization with ITC has no noticeable influence on the preferential upright orientation of the molecules in the SAMs.

A highly ordered, aromatic bidentate self-assembled monolayer on Au(111): a combined experimental and theoretical study.

Self assembled monolayers (SAMs) made from an aromatic organodithiol, 2-mercaptomethylbenzenethiol (C(6)H(4)SHCH(2)SH) on Au(111) have been investigated in the context of a combined experimental and theoretical approach. The SAMs prepared by immersion of an Au-substrate in corresponding ethanolic solutions were characterized using scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), infrared reflection absorption spectroscopy (IRRAS) and thermal desorption spectroscopy (TDS). Adapted from the experimentally obtained unit cell of the SAM, density functional theory (DFT) calculations were applied to get a deeper insight into the structure of these dithiolate based SAMs. On the basis of the experimental and theoretical findings we provide a detailed structural model for this aromatic SAM consisting of the phenyl-group rigidly anchored to the substrate by two thiolate-bonds.

Influence of OH groups on charge transport across organic-organic interfaces: a systematic approach employing an "ideal" device.

The charge transport across a pentacene/SAM interface has been studied by scanning tunnelling spectroscopy (STS) as a function of temperature and film thickness in order to obtain information on the transport mechanisms and in particular on the importance of interfacial OH-groups on n-transport in organic semiconductors. The current-voltage (I-V) characteristics of pentacene thin films deposited on a mercaptoundecanol self-assembled monolayer (SAM) on Au(111) reveal an asymmetric behaviour. At positive sample bias the onset currents shift towards higher voltages for decreasing temperatures, whereas such changes are not seen at negative bias. For lower temperatures, the variation of current onset with layer thickness is absent. These observations are explained by OH-groups at the SAM-surface effectively acting as charge traps. When electrons are caught in these traps at the organic-organic interface, charge transport is severely affected. Imaging of the SAM after loading the traps suggests that the attachment of electrons to the OH-groups exposed at the organic surface is a reversible process.

Structural characterization of self-assembled monolayers of pyridine-terminated thiolates on gold.

Self-assembled monolayers (SAMs) fabricated on Au(111) substrates from a homologous series of pyridine-terminated organothiols have been investigated using ultra high vacuum infrared reflection adsorption spectroscopy (UHV-IRRAS), X-ray photoelectron spectroscopy (XPS), scanning tunnelling microscopy (STM) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. A total of 4 different pyridine-based organothiols have been investigated, consisting of a pyridine unit, one or two phenyl units, a spacer of between one and three methylene units and, finally, a thiol unit. For all pyridine-terminated thiols the immersion of Au-substrates in the corresponding ethanolic solutions was found to result in the formation of highly ordered and densely packed SAMs. For an even number of the methylene spacers between the SH group and the aromatic moieties, the SAM unit-cell is rather large, (5sq.rt(3) x 3)rect, whereas in case of an odd number of methylene units a smaller unit cell is adopted, (2sq.rt(3) x sq.rt(3))R30 degrees. The tilt angle of the molecules amounts to 15 degrees . In contrast to expectation, the pyridine-terminated organic surfaces exposed by the corresponding SAMs showed a surprisingly strong resistance with regard to protonation.