Flake thickness is one of the defining properties of graphene-related 2D materials (GR2Ms), and therefore requires reliable, accurate, and reproducible measurements with well-understood uncertainties. This is needed regardless of the production method or manufacturer because it is important for all GR2M products to be globally comparable. An international interlaboratory comparison on thickness measurements of graphene oxide flakes using atomic force microscopy has been completed in technical working area 41 of versailles project on advanced materials and standards. Twelve laboratories participated in the comparison project, led by NIM, China, to improve the equivalence of thickness measurement for two-dimensional flakes. The measurement methods, uncertainty evaluation and a comparison of the results and analysis are reported in this manuscript. The data and results of this project will be directly used to support the development of an ISO standard.
Core-shell nanoparticles have attracted much attention in recent years due to their unique properties and their increasing importance in many technological and consumer products. However, the chemistry of nanoparticles is still rarely investigated in comparison to their size and morphology. In this review, the possibilities, limits, and challenges of X-ray photoelectron spectroscopy (XPS) for obtaining more insights into the composition, thickness, and homogeneity of nanoparticle coatings are discussed with four examples: CdSe/CdS quantum dots with a thick coating and a small core; NaYF4-based upconverting nanoparticles with a large Yb-doped core and a thin Er-doped coating; and two types of polymer nanoparticles with a poly(tetrafluoroethylene) core with either a poly(methyl methacrylate) or polystyrene coating. Different approaches for calculating the thickness of the coating are presented, like a simple numerical modelling or a more complex simulation of the photoelectron peaks. Additionally, modelling of the XPS background for the investigation of coating is discussed. Furthermore, the new possibilities to measure with varying excitation energies or with hard-energy X-ray sources (hard-energy X-ray photoelectron spectroscopy) are described. A discussion about the sources of uncertainty for the determination of the thickness of the coating completes this review. Graphical abstract.
Nanoparticles , Quantum Dots , Nanoparticles/chemistry , Photoelectron Spectroscopy , Polymers , Polystyrenes
OBJECTIVE: The treatment of acne presents a major clinical and dermatological challenge. Investigating the nanomechanical properties of the microcomedone precursor lesions using atomic force microscopy (AFM) may prove beneficial in understanding their softening, dissolution and prevention. Although the exact biochemical mechanism of NaSal on microcomedones is not fully understood at present, it appears to exhibit a significant exfoliation effect on the skin via corneodesmosome dissolution. METHODS: Therefore, to support this exploration, sodium salicylate (NaSal), a common ingredient employed in skin care products, is applied ex vivo to microcomedones,collected by nose strip adhesive tape, and their nanomechanical properties are assessed using AFM. Although the exact biochemical mechanism of NaSal on microcomedones is not fully understood at present, it appears to exhibit a significant exfoliation effect on the skin via corneodesmosome dissolution. RESULTS: Herein, our findings demonstrate that when microcomedones are treated with 2% NaSal, samples appeared significantly more compliant ('softer') ((1.3 ± 0.62) MPa) when compared to their pre-treated measurements ((7.2 ± 3.6) MPa; p = 0.038). Furthermore, elastic modulus maps showed that after 2% NaSal treatment, areas in the microcomedone appeared softer and swollen in some, but not in all areas, further proving the valuable impact of 2% NaSal solution in altering the biomechanical properties and morphologies in microcomedones. CONCLUSION: Our results are the first of their kind to provide qualitative and quantitative mechanobiological evidence that 2% NaSal decreases the elastic modulus of microcomedones. Therefore, this study provides evidence that NaSal can be beneficial as an active ingredient in topical treatments aimed at targeting microcomedones.
OBJECTIF: Le traitement de l'acné présente un défi clinique et dermatologique majeur. L'étude des propriétés nanomécaniques des lésions précurseurs en tant que microcomédons à l'aide de la microscopie à force atomique (AFM) peut s'avérer bénéfique pour comprendre leur ramollissement, leur dissolution et leur prévention. MÉTHODES: Par conséquent, pour soutenir cette exploration, le salicylate de sodium (NaSal), un ingrédient couramment utilisé dans les produits de soins de la peau, est appliqué ex vivo aux microcomédons et leurs propriétés nanomécaniques sont évaluées à l'aide de l'AFM. Bien que le mécanisme biochimique exact du NaSal sur les microcomédons ne soit pas entièrement compris à l'heure actuelle, il semble présenter un effet exfoliant significatif sur la peau via la dissolution des cornéodesmosomes. RÉSULTATS: Ici, nos résultats démontrent que lorsque les microcomédons sont traités avec 2% de NaSal, les échantillons semblaient significativement plus conformes ("plus doux") ((1.3 ± 0.62) MPa) par rapport à leurs mesures pré-traitées ((7.2 ± 3.6) MPa ; P = 0,03826). De plus, les cartes du module d'élasticité ont montré qu'après un traitement à 2 % de NaSal, les zones du microcomédon semblaient plus molles et gonflées dans certaines zones, mais pas dans toutes, prouvant ainsi l'impact précieux d'une solution de NaSal à 2 % dans la modification des propriétés biomécaniques et de la morphologie des microcomédons. CONCLUSION: Nos résultats sont les premiers du genre à fournir des preuves mécanobiologiques qualitatives et quantitatives que 2% de NaSal diminue le module d'élasticité des microcomédons. Par conséquent, cette étude fournit des preuves que NaSal peut être bénéfique en tant qu'ingrédient actif dans les traitements topiques visant à cibler les microcomédons.
Acne Vulgaris/drug therapy , Dermatologic Agents/chemistry , Sodium Salicylate/chemistry , Administration, Topical , Elastic Modulus , Healthy Volunteers , Humans , Microscopy, Atomic Force , Skin/drug effects
Quantitative determination of the geometry of an atomic force microscope (AFM) probe tip is critical for robust measurements of the nanoscale properties of surfaces, including accurate measurement of sample features and quantification of tribological characteristics. Blind tip reconstruction, which determines tip shape from an AFM image scan without knowledge of tip or sample shape, was established most notably by Villarrubia [J. Res. Natl. Inst. Stand. Tech. 102 (1997)] and has been further developed since that time. Nevertheless, the implementation of blind tip reconstruction for the general user to produce reliable and consistent estimates of tip shape has been hindered due to ambiguity about how to choose the key input parameters, such as tip matrix size and threshold value, which strongly impact the results of the tip reconstruction. These key parameters are investigated here via Villarrubia's blind tip reconstruction algorithms in which we have added the capability for users to systematically vary the key tip reconstruction parameters, evaluate the set of possible tip reconstructions, and determine the optimal tip reconstruction for a given sample. We demonstrate the capabilities of these algorithms through analysis of a set of simulated AFM images and provide practical guidelines for users of the blind tip reconstruction method. We present a reliable method to choose the threshold parameter corresponding to an optimal reconstructed tip shape for a given image. Specifically, we show that the trend in how the reconstructed tip shape varies with threshold number is so regular that the optimal, or Goldilocks, threshold value corresponds with the peak in the derivative of the RMS difference with respect to the zero threshold curve vs. threshold number.
Algorithms , Microscopy, Atomic Force/methods
Finite element analysis (FEA) is used to model nanoindentation by a rigid, spherically shaped indenter, axially indenting an elastic two phase polymer system comprised of a cylindrical nanoparticle of compliant polymer set in a semi-infinite matrix of stiffer polymer. The cylindrical nanoparticle is normal to the sample surface. An axisymmetric finite element model is used to determine the reduced modulus measured as a function of the indentation depth for various nanoparticle radii and extensions below the surface. We show how the previous simple analytical equations may be extended to describe these situations with accuracy. This gives excellent agreement with the FEA and provides a clear guide to the maximum indentation depth as a function of both the nanoparticle radius and its thickness consistent with a choice of either computation from the analytical equations or direct measurement with a maximum of 10% error in the measured reduced modulus.
Hardness Tests/methods , Microscopy, Atomic Force/methods , Models, Chemical , Models, Molecular , Nanoparticles/chemistry , Nanoparticles/ultrastructure , Polymers/chemistry , Computer Simulation , Elastic Modulus , Finite Element Analysis , Hardness
The characterisation of nanoscale surface properties of textile and hair fibres is key to developing new effective laundry and hair care products. Here, we develop nanomechanical methods to characterise fibres using an atomic force microscope (AFM) to give their nanoscale modulus. Good mounting methods for the fibre that are chemically inert, clean and give strong mechanical coupling to a substrate are important and here we detail two methods to do this. We show, for elastic nanoindentation measurements, the situation when the tip radius significantly affects the result via a function of the ratio of the radii of the tip and fibre and indicate the importance of using an AFM for such work. A valid method to measure the nanoscale modulus of fibres using AFM is thus detailed and exampled on hair to show that bleaching changes the nanoscale reduced modulus at the outer surface.
Hair/chemistry , Hair/ultrastructure , Microscopy, Atomic Force/methods , Nanotechnology/methods , Humans
Finite element analysis (FEA) is used to investigate the effect of the Poisson's ratios of both the overlayer and the substrate on the nanoindentation of an elastic two-phase system where the elastic overlayer is more compliant than the underlying elastic substrate. A rigid spherical indenter is used as a probe. It is found that nanoindentation results may be expressed analytically using a simple extension of the previously described equation (Clifford and Seah 2006 Nanotechnology 17 5283). This simple function describes the reduced modulus value measured using Oliver and Pharr's method (1992 J. Mater. Res. 7 1564) for any modulus values or Poisson's ratio values of the overlayer and substrate, overlayer thickness or indenter tip radius. This equation and the FEA behind it are tested using experimental published data for the nanoindentation of a silicon dioxide layer on silicon.
