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A great number of chemical and mechanical phenomena, ranging from catalysis to friction, are dictated by the atomic-scale structure and properties of material surfaces. Yet, the principal tools utilized to characterize surfaces at the atomic level rely on strict environmental conditions such as ultrahigh vacuum and low temperature. Results obtained under such well-controlled, pristine conditions bear little relevance to the great majority of processes and applications that often occur under ambient conditions. Here, we report true atomic-resolution surface imaging via conductive atomic force microscopy (C-AFM) under ambient conditions, performed at high scanning speeds. Our approach delivers atomic-resolution maps on a variety of material surfaces that comprise defects including single atomic vacancies. We hypothesize that atomic resolution can be enabled by either a confined, electrically conductive pathway or an individual, atomically sharp asperity at the tip-sample contact. Using our method, we report the capability of in situ charge state manipulation of defects on MoS2 and the observation of an exotic electronic effect: room-temperature charge ordering in a thin transition metal carbide (TMC) crystal (i.e., an MXene), α-Mo2C. Our findings demonstrate that C-AFM can be utilized as a powerful tool for atomic-resolution imaging and manipulation of surface structure and electronics under ambient conditions, with wide-ranging applicability.

We present results of atomic-force-microscopy-based friction measurements on Re-doped molybdenum disulfide (MoS2). In stark contrast to the widespread observation of decreasing friction with increasing number of layers on two-dimensional (2D) materials, friction on Re-doped MoS2exhibits an anomalous, i.e. inverse, dependence on the number of layers. Raman spectroscopy measurements combined withab initiocalculations reveal signatures of Re intercalation. Calculations suggest an increase in out-of-plane stiffness that inversely correlates with the number of layers as the physical mechanism behind this remarkable observation, revealing a distinctive regime of puckering for 2D materials.

Atomic-scale characteristics of surfaces dictate the principles governingnumerous scientific phenomena ranging from catalysis to friction. Despite thisfact, our ability to visualize and alter surfaces on the atomic scale isseverely hampered by the strict conditions under which the related methods areoperated to achieve high spatial resolution. In particular, the two prominentmethods utilized to achieve atomic-resolution imaging - scanning tunnelingmicroscopy (STM) and noncontact atomic force microscopy (NC-AFM) - aretypically performed under ultrahigh vacuum (UHV) and often at low temperatures.Perhaps more importantly, results obtained under such well-controlled, pristineconditions bear little relevance for the great majority of processes andapplications that often occur under ambient conditions. As such, a method thatcan robustly image surfaces on the atomic scale under ambient conditions haslong been thought of as a "holy grail" of surface science. Here, by way of aproof-of-principle measurement on molybdenum disulfide (MoS2), we report thatthe method of conductive atomic force microscopy (C-AFM) can be utilized toachieve true atomic-resolution imaging under ambient conditions as proven bythe imaging of a single atomic vacancy, without any control over theoperational environment or elaborate sample preparation. While the physicalmechanisms behind this remarkable observation are not elucidated yet, ourapproach overcomes many of the classical limitations associated with STM andNC-AFM, and the findings herald the potential emergence of C-AFM as a powerfultool for atomic-resolution imaging under ambient conditions.

Abstract: We present the results of friction experiments performed by manipulation of oxidized platinum nanoislands on highly oriented pyrolytic graphite (HOPG) substrates through atomic force microscopy (AFM). The oxidation of the platinum nanoislands, performed via mild plasma exposure, is confirmed through X-ray photoelectron spectroscopy (XPS) and high-resolution energy-dispersive X-ray spectroscopy (EDX), the latter of which reveals partial oxidation on the sliding surfaces of the nanoislands. Oxidized platinum nanoislands are found to exhibit higher friction than non-oxidized islands, with a ~ 70% increase in mean shear stress over the investigated contact size regime. An increase in chemical interaction forces between the oxidized platinum and the graphite substrate is proposed to explain the increase in friction forces. Our results reveal that alteration of interfacial chemistry through oxidation leads to a noticeable modulation of friction forces, but not a total breakdown of the superlubric state (as evidenced by the signature observation of decreasing shear stress with increasing contact size), providing further feasibility for the design of superlubric mechanical systems to be operated under ambient conditions. Graphic Abstract

Abstract: Conductive-atomic force microscopy (C-AFM) and molecular dynamics (MD) simulations are used to investigate time-dependent electrical contact resistance (ECR) at the nanoscale. ECR is shown to decrease over time as measured using C-AFM and estimated using two approaches from MD simulations, although the experiments and simulations explore different time scales. The simulations show that time dependence of ECR is attributable to an increase in real contact area due to atoms diffusing into the contact. This diffusion-based aging is found to be a thermally activated process that depends on the local contact pressure. The results demonstrate that contact aging, previously identified as an important mechanism for friction, can significantly affect electrical conduction at the nanoscale. Graphical Abstract:

Candida albicans is an opportunistic fungal pathogen of humans known for its ability to cause a wide range of infections. One major virulence factor of C. albicans is its ability to form hyphae that can invade host tissues and cause disseminated infections. Here, we introduce a method based on atomic force microscopy to investigate C. albicans hyphae in situ on silicone elastomer substrates, focusing on the effects of temperature and antifungal drugs. Hyphal growth rates differ significantly for measurements performed at different physiologically relevant temperatures. Furthermore, it is found that fluconazole is more effective than caspofungin in suppressing hyphal growth. We also investigate the effects of antifungal drugs on the mechanical properties of hyphal cells. An increase in Young's modulus and a decrease in adhesion force are observed in hyphal cells subjected to caspofungin treatment. Young's moduli are not significantly affected following treatment with fluconazole; the adhesion force, however, increases. Overall, our results provide a direct means of observing the effects of environmental factors and antifungal drugs on C. albicans hyphal growth and mechanics with high spatial resolution.IMPORTANCECandida albicans is one of the most common pathogens of humans. One important virulence factor of C. albicans is its ability to form elongated hyphae that can invade host tissues and cause disseminated infections. Here, we show the effect of different physiologically relevant temperatures and common antifungal drugs on the growth and mechanical properties of C. albicans hyphae using atomic force microscopy. We demonstrate that minor temperature fluctuations within the normal range can have profound effects on hyphal cell growth and that different antifungal drugs impact hyphal cell stiffness and adhesion in different ways.

Abstract: Electrical contact resistance (ECR) measurements performed via conductive atomic force microscopy (C-AFM) suffer from poor reliability and reproducibility. These issues are due to a number of factors, including sample roughness, contamination via adsorbates, changes in environmental conditions such as humidity and temperature, as well as deformation of the tip apex caused by contact pressures and/or Joule heating. Consequently, ECR may vary dramatically from measurement to measurement even on a single sample tested with the same instrument. Here we present an approach aimed at improving the reliability of such measurements by addressing multiple sources of variability. In particular, we perform current-voltage spectroscopy on atomically flat terraces of highly oriented pyrolytic graphite (HOPG) under an inert nitrogen atmosphere and at controlled temperatures. The sample is annealed before the measurements to desorb adsorbates, and conductive diamond tips are used to limit tip apex deformation. These precautions lead to measured ECR values that follow a Gaussian distribution with significantly smaller standard deviation than those obtained under conventional measurement conditions. The key factor leading to this improvement is identified as the switch from ambient conditions to a dry nitrogen atmosphere. Despite these improvements, spontaneous changes in ECR are observed during measurements performed over several minutes. However, it is shown that such variations can be suppressed by applying a higher normal load.

We present a comparative study of the tribological properties of Pd-, Pt-, and Zr-based bulk metallic glasses (BMG-Pd, BMG-Pt, and BMG-Zr, respectively) under unlubricated conditions. In particular, micro-tribometry is utilized with a 52,100 steel ball, showing that BMG-Pt exhibits a significantly higher coefficient of friction (COF) (0.58 ± 0.08) when compared with BMG-Pd (0.30 ± 0.02) and BMG-Zr (0.20 ± 0.03). Topographical roughness on and off wear scars is characterized via atomic force microscopy (AFM), with results that do not correlate with the observed frictional behavior. On the other hand, scanning electron microscopy (SEM) is utilized to reveal contrasting wear mechanisms for the three samples: while BMG-Pd and BMG-Zr exhibit predominantly abrasive wear, there is evidence of adhesive wear on BMG-Pt. Consequently, the occurrence of adhesive wear emerges as a potential mechanism behind the observation of relatively high coefficients of friction on BMG-Pt, suggesting stronger interactions with steel when compared with the other BMG samples.

AbstractTheory predicts that two-dimensional (2D) materials may only exist in the presence of out-of-plane deformations on atomic length scales, frequently referred to as ripples. While such ripples can be detected via electron microscopy, their direct observation via surface-based techniques and characterization in terms of interaction forces and energies remain limited, preventing an unambiguous study of their effect on mechanical characteristics, including but not limited to friction anisotropy. Here, we employ high-resolution atomic force microscopy to demonstrate the presence of atomic-scale ripples on supported samples of few-layer molybdenum disulfide (MoS2). Three-dimensional force/energy spectroscopy is utilized to study the effect of ripples on the interaction landscape. Friction force microscopy reveals multiple symmetries for friction anisotropy, explained by studying rippled sample areas as a function of scan size. Our experiments contribute to the continuing development of a rigorous understanding of the nanoscale mechanics of 2D materials.

We present the results of atomic-force-microscopy-based friction measurementson Re-doped molybdenum disulfide (MoS2). In stark contrast to the seeminglyuniversal observation of decreasing friction with increasing number of layerson two-dimensional (2D) materials, friction on Re-doped MoS2 exhibits ananomalous, i.e. inverse dependency on the number of layers. Raman spectroscopymeasurements revealed signatures of Re intercalation, leading to a decouplingbetween neighboring MoS2 layers and enhanced electron-phonon interactions, thusresulting in increasing friction with increasing number of layers: a newparadigm in the mechanics of 2D materials.

We perform atomic force microscopy (AFM) experiments on mechanically exfoliated, single-layer and bulk molybdenum disulfide (MoS2) in order to probe friction forces as a function of sliding speed. The results of the experiments demonstrate that (i) friction forces increase logarithmically with respect to sliding speed, (ii) there is no correlation between the speed dependence of friction and the number of layers of MoS2, and (iii) changes in the speed dependence of friction can be attributed to changes in the physical characteristics of the AFM probe, manifesting in the form of varying contact stiffness and tip-sample interaction potential parameters in the thermally activated Prandtl-Tomlinson model. Our study contributes to the formation of a mechanistic understanding of the speed dependence of nanoscale friction on two-dimensional materials.

An approach to measuring electrical contact resistance as a direct function of the true contact size at the nanoscale is presented. The approach involves conductive atomic force microscopy (C-AFM) measurements performed on a sample system comprising atomically flat interfaces (up to several hundreds of nanometers in lateral size) formed between gold islands and a highly oriented pyrolytic graphite (HOPG) substrate. The method overcomes issues associated with traditional C-AFM such that conduction can be correlated with a measurable true, conductive contact area. Proof-of-principle experiments performed on gold islands of varying size point toward an increasing contribution of the island-HOPG junction to the measured total resistance with decreasing island size. Atomistic simulations complement and elucidate experimental results, revealing the maximum island size below which the electrical contact resistance at the island-HOPG junction can be feasibly extracted from the measured total resistance.

Molybdenum disulfide (MoS2) is one of the most broadly utilized solid lubricants with a wide range of applications, including but not limited to those in the aerospace/space industry. Here we present a focused review of solid lubrication with MoS2 by highlighting its structure, synthesis, applications and the fundamental mechanisms underlying its lubricative properties, together with a discussion of their environmental and temperature dependence. The review also includes an extensive overview of the structure and tribological properties of doped MoS2, followed by a discussion of potential future research directions.

We present a review of superlubricity: the state of ultra-low friction between surfaces in relative motion. Various approaches to achieving this state are considered in a broad sense, including structural superlubricity, superlubricity via normal force control, and contact actuation, as well as thermolubricity, liquid superlubricity, and quantum lubricity. An overview of the physical fundamentals associated with each approach is presented, with particular emphasis on recent theoretical and experimental developments that constitute milestones in our scientific understanding. The review also includes a discussion of perspectives on future research in the context of existing challenges. It is projected that interest in superlubricity from the basic science and engineering communities will continue to accelerate in the near future, accompanied by a transition from fundamental studies to technologically relevant applications.

Purpose: To evaluate the efficacy and safety of oral azithromycin treatment combined with topical antibiotic and anti-inflammatory agents in pediatric patients with chronic severe bilateral blepharokeratoconjunctivitis. Methods: Patients younger than 14 years with chronic and severe bilateral blepharokeratoconjunctivitis were reviewed retrospectively. Consecutive patients receiving oral azithromycin treatment were included. All patients received oral azithromycin (5 mg/kg/single dose daily) for at least 4 weeks combined with topical antibiotic and anti-inflammatory agents. Before and after the treatment, clinical symptoms were noted, and corneal and conjunctival fluorescein staining and corneal neovascularization were graded. Meibomian gland secretion and meibomian gland plugging were also assessed. All patients completed at least 3 months of follow-up after completion of the oral azithromycin treatment. Patients' clinical data at the time of diagnosis and last follow-up visit were statistically compared. Results: Twenty-nine children (58 eyes, mean age of 6.51 years) were included. The mean time of oral azithromycin use was 5.87 weeks (range: 4 to 10 weeks). Clinical symptoms and signs and visual acuity were significantly improved after treatment. The mean fluorescein staining and corneal neovascularization grades and meibomian gland secretion and meibomian gland plugging scores also improved after treatment (P <.001). Eyelid distortion or fornix shortening was not observed. At the last follow-up visit, all patients were stable with treatment only with daily eyelid hygiene, topical cyclosporine, and artificial tears. Conclusions: Long-term, low-dose oral azithromycin combined with topical antibiotic and anti-inflammatory agents is an effective treatment option for pediatric patients with chronic severe bilateral blepharokeratoconjunctivitis. [J Pediatr Ophthalmol Strabismus. 2024;61(5):358–364.] [ABSTRACT FROM AUTHOR]

In this study, latanoprost-loaded polyvinyl alcohol (PVA/LAT) nanofibers were developed as an ocular drug delivery system for glaucoma treatment. The nanofibers were constructed via electrospinning and crosslinked by glutaraldehyde. The characterization studies were conducted by scanning electron microscopy, Fourier Transform infrared spectroscopy, Brunauer, Emmett, and Teller analyses, water contact angle measurements, and also swelling and degradation studies. The PVA/LAT nanofibers crosslinked with 0.5% glutaraldehyde solution for 20 min had a cumulative release of 52% for 23 days. The results demonstrated that the PVA/LAT nanofibers have a usage potential as an ocular drug delivery system for glaucoma treatment. [ABSTRACT FROM AUTHOR]

Despite its fundamental importance, physical mechanisms that govern friction are poorly understood. While a state of ultra-low friction, termed structural lubricity, is expected for any clean, atomically flat interface consisting of two different materials with incommensurate structures, some associated predictions could only be quantitatively confirmed under ultra-high vacuum (UHV) conditions so far. Here, we report structurally lubric sliding under ambient conditions at mesoscopic (∼4,000-130,000 nm(2)) interfaces formed by gold islands on graphite. Ab initio calculations reveal that the gold-graphite interface is expected to remain largely free from contaminant molecules, leading to structurally lubric sliding. The experiments reported here demonstrate the potential for practical lubrication schemes for micro- and nano-electromechanical systems, which would mainly rely on an atomic-scale structural mismatch between the slider and substrate components, via the utilization of material systems featuring clean, atomically flat interfaces under ambient conditions.

Atomic-scale characteristics of surfaces, including their structure, chemical reactivity, and electronic properties, determine their roles in multiple fields of science and technology, e.g., as coatings, catalysts, and device components. As such, it is of utmost importance to study the atomic arrangement and atomic-scale physico-chemical properties of surfaces in real space in a robust and reliable manner. A powerful technique for achieving this goal is scanning probe microscopy (SPM). Here, we present an overview of SPM-based techniques for atomic-resolution surface imaging and spectroscopy and highlight selected advances in the field. We also discuss current challenges of SPM-based techniques for atomic-resolution surface studies. [ABSTRACT FROM AUTHOR]

AIM: To evaluate the results of mitomycin-C(MMC)-augmented viscocanalostomy in patients with open-angle glaucoma.METHODS: This retrospective study included 104 patients who underwent viscocanalostomy surgery between December 2007 and March 2014. Pre- and postoperative intraocular pressure(IOP), number of glaucoma medications, visual acuity, complications, adjunctive procedure(laser goniopuncture and/or glaucoma medication), and success rate were recorded. Complete success was defined as IOP≤21 mmHg without additional medication, and qualified success was defined as IOP≤21 mmHg with or without glaucoma medication.RESULTS: Mean preoperative IOP was 27.5±9.2 mmHg and mean postoperative IOP was 14.5±6.6 mmHg at the last visit(PP=0.726). Qualified success was achieved in 106(86.9%)eyes and complete success was achieved in 62(50.8%)eyes. Laser goniopuncture was performed in 43(35.2%)eyes and glaucoma medication usage rate was 49.1%. The mean postoperative followup period was 27.29±16.78(1-79)mo.CONCLUSION:Although viscocanalostomy is a safer option due to low complication rates and stable visual acuity, without laser goniopuncture(LGP), surgical success rate is still very low. Further comparative studies are necessary to evaluate the contribution of MMC to viscocanalostomy surgery.