Correlation of work function and stacking fault energy through Kelvin probe force microscopy and nanohardness in diluteα-magnesium

Electronic interactions of the Group 2A elements with magnesium have been studied through the dilute solid solutions in binary Mg-Ca,Mg-Sr and Mg-Ba systems.This investigation incorporated the difference in the‘Work Function'(ΔWF)measured via Kelvin Probe Force Microscopy(KPFM),as a property directly affected by interatomic bond types,i.e.the electronic structure,nanoindentation measurements,and Stacking Fault Energy values reported in the literature.It was shown that the nano-hardness of the solid-solutionα-Mg phase changed in the order of Mg-Ca>Mg-Sr>Mg-Ba.Thus,it was shown,by also considering the nano-hardness levels,that SFE of a solid-solution is closely correlated with its‘Work Function'level.Nano-hardness measurements on the eutectics andΔWF difference between eutectic phases enabled an assessment of the relative bond strength and the pertinent electronic structures of the eutectics in the three alloys.Correlation withΔWF and at least qualitative verification of those computed SFE values with some experimental measurement techniques were considered important as those computational methods are based on zero Kelvin degree,relatively simple atomic models and a number of assumptions.As asserted by this investigation,if the results of measurement techniques can be qualitatively correlated with those of the computational methods,it can be possible to evaluate the electronic structures in alloys,starting from binary systems,going to ternary and then multi-elemental systems.Our investigation has shown that such a qualitative correlation is possible.After all,the SFE values are not treated as absolute values but rather become essential in comparative investigations when assessing the influences of alloying elements at a fundamental level,that is,free electron density distributions.Our study indicated that the principles of‘electronic metallurgy'in developing multi-elemental alloy systems can be followed via practical experimental methods,i.e.ΔWF measurements using KPFM and nanoindentation.

Quantitative measurement of the charge carrier concentration using dielectric force microscopy

The charge carrier concentration profile is a critical factor that determines semiconducting material properties and device performance.Dielectric force microscopy(DFM)has been previously developed to map charge carrier concentrations with nanometer-scale spatial resolution.However,it is challenging to quantitatively obtain the charge carrier concentration,since the dielectric force is also affected by the mobility.Here,we quantitative measured the charge carrier concentration at the saturation mobility regime via the rectification effect-dependent gating ratio of DFM.By measuring a series of n-type GaAs and GaN thin films with mobility in the saturation regime,we confirmed the decreased DFM-measured gating ratio with increasing electron concentration.Combined with numerical simulation to calibrate the tip–sample geometry-induced systematic error,the quantitative correlation between the DFM-measured gating ratio and the electron concentration has been established,where the extracted electron concentration presents high accuracy in the range of 4×10^(16)–1×10^(18)cm^(-3).We expect the quantitative DFM to find broad applications in characterizing the charge carrier transport properties of various semiconducting materials and devices.

Magnetic Microstructures of 2∶17 Type Sm(Co,Fe,Cu,Zr)_z Magnets Detected by Magnetic Force Microscopy

The magnetic microstructures of 2：17 type Sm （Co, Fe, Cu, Zr）z magnets were detected by magnetic force microscopy. Comparing the microstructures of the specimens eoated with and without Ta thin film before and after heat-treatment, it is found that： （a） as a protection layer, Ta coating layer about 20 nm thick can effectively restrain Sm volatilization under high temperature; （b） the stress built in the 2.17 type Sm-Co magnets during specimen preparation only affects some local parts of the domain structures; （c） the magnetic microstructures vary largely for specimens heat-treated at high temperature without Ta film coating due to Sm volatilization. In addition, by comparing with high coercivity Fe-Pt point tips, it is found that the Co-Cr thin-film tips are not suitable for detecting the magnetic microstructures of strong permanent magnets.

AN ATOMIC FORCE MICROSCOPY STUDY ON THE AGGREGATION OF ISOTACTIC POLY(METHYL METHACRYLATE)

Aggregation process of isotactic poly（methyl methacrylate） （i-PMMA） has been studied extensively for many years, and considerable progress has been made in both experimental and theoretical studies. They are, however, seldom sustained by real-space observations of the underlying morphology. In this paper, the aggregation process of i-PMMA in concentrated acetone solutions and the fractal structure of the resulting three-dimensional clusters were characterized on the basis of real-space AFM observations of their two-dimensional projection. It was found that spherical multiple-chain particles formed upon collapse and aggregation of the involving chains as a whole during quenching the solution to room temperature. By keeping the solution at room temperature, the initially formed particles stick together upon contact to form larger particles through reassembling very slowly. The succeeding collision of the enlarged spherical particles leads to the formation of small clusters. These newly formed small clusters grow when they meet with other clusters or single Brownian particles. This leads to the formation of large clusters with fractal dimension of 1.95 ± 0.05, which suggest a reaction-limited cluster aggregation of i-PMMA in a concentrated acetone solution. This is in accordance with the conclusion obtained by light scattering measurements.

Analysis of the injection layer of PTCDA in OLEDs using x-ray photoemission spectroscopy and atomic force microscopy

Through the investigation of the sample surface and interface of 3, 4, 9, 10-perylenetetracarboxylic dianhydride （PTCDA）/indium-tin-oxide （ITO） thin films using atomic force microscopy, it has been found that the surface is complanate, the growth is uniform and the defects cover basically the surface of ITO. Furthermore, the number of pinholes is small. The analysis of the sample surface and interface further verifies this result by using x-ray photoemission spectroscopy. At the same time, PTCDA is found to have the ability of restraining the diffusion of chemical constituents from ITO to the hole transport layer, which is beneficial to the improvement of the performance and the useful lifetime of the organic light emitting diodes （OLEDs）.

Effect of Rho-kinase pathway on neurite outgrowth of rat hippocampal neurons under atomic force microscopy

Hippocampal neurons of neonatal rats were cultured in serum-free culture medium for 5 days in vitro, and treated with the Rho-kinase inducer lysophosphatidic acid. Atomic force microscopy revealed that the numbers of level-1, -2 and -3 neurites protruding from rat hippocampal neurons was significantly reduced. After treatment with the Rho kinase inhibitor Y27632, a significant increase in the numbers of these neurites was observed. Our experimental findings indicate that the Rho-kinase pathway is closely associated with the neurites of hippocampal neurons.

Effects of caveolin-1 on bone marrow mesenchymal stem cells differentiating into neuron-like cells An atomic force microscopy observation

Bone marrow mesenchymal stem cells （MSCs） from rats were transfected with Rn-siRNA-caveolin-1 and differentiated into neuron-like cells using fasudil hydrochloride. Membrane ultrastructural changes in MSCs were observed under atomic force microscopy. Caveolin-l-transfected rat MSCs exhibited weak nuclear refraction, dense caveolae and long finger-like cellular processes prior to fasudil hydrochloride treatment. MSCs differentiating into neuron-like cells exhibited weak nuclear refraction and large cellular processes without caveolae. We hypothesize that caveolin-1 plays an important role in the regulation of bone marrow MSC differentiating into neuron-like cells.

Characterizing silicon intercalated graphene grown epitaxially on Ir films by atomic force microscopy

An efficient method based on atomic force microscopy（AFM） has been developed to characterize silicon intercalated graphene grown on single crystalline Ir（111） thin films. By combining analyses of the phase image, force curves,and friction–force mapping, acquired by AFM, the locations and coverages of graphene and silicon oxide can be well distinguished. We can also demonstrate that silicon atoms have been successfully intercalated between graphene and the substrate. Our method gives an efficient and simple way to characterize graphene samples with interacted atoms and is very helpful for future applications of graphene-based devices in the modern microelectronic industry, where AFM is already widely used.

Environmental temperature effect on dimensional measurements of atomic force microscopy

Atomic force microscopy(AFM)is increasingly being used as a fundamental tool for dimensional measurements at the nanoscale in the laboratory and in industry.Since the environmental temperature is not controlled in many measurements,or is even varied on purpose,quantification of its effects on AFM dimensional measurements is needed.In this paper,the influences of the temperature in the entire environment of the AFM(excluding only the controller and computer)and that in the local environment around the tip–sample are investigated.The results show that lateral dimensional measurements are affected mainly by the entire environmental temperature.However,vertical measurements are influenced by the temperature of both the entire environment and the local environment.The effects become significant for temperatures higher than some threshold,here between 35 and 40 XC.

Investigation of Adsorption of Xanthan Gum on Enamel by Tapping Mode Atomic Force Microscopy

By using tapping mode atomic force microscopy(TMAFM), a polymer layer was found on the enamel surface after the exposure to xanthan gum solutions. The layer thickness is closely related to the exposure time and the concentration of xanthan gum solution. The thickness data were evaluated by a Kruskal-Wallis test and Box-Whisker Plot at a 95% confidence level(p<0.05), and a statistically significant difference among the thickness data groups was demonstrated. After the exposure to 1000, 400, 100 mg/L xanthan gum solutions, the mean of layer thickness at the adsorption equilibrium is in the ranges of 103.5_122.06, 82.4_88.94 and 45.27_55.55 nm, respectively. This phenomenon suggests that the viscosity modifying agents in the beverage might be adsorbed on the enamel surface during consumption, which may form a barrier that can protect the enamel from being attacked by acid and therefore reduce dental erosion.

Effects of Environments on the Noise of Atomic Force Microscopy Cantilevers

Thermal vibration of the cantilevers is the main source of noise in atomic force microscopy(AFM).When immersed in liquids,the dynamic behavior of the cantilevers will be significantly affected by the environment.In this study,the effects of environments on the noise of AFM were investigated.The results show that the V⁃shaped cantilever exhibited very low noise in high vacuum.The noise in atmospheric environment was also satisfactory.In liquid environments,the noise dramatically increased.The systematic noise was low and dependent on the distance between the tip and substrate.As the velocity increased,the noise of V⁃shaped cantilever was increased in a similar trend.It is also found that the variation trend was more pronounced as the liquid viscosity increased.The noise of rectangular cantilever was lower than that of V⁃shaped cantilever in the same environment.The present study indicates that high vacuum is an ideal environment for single molecule force spectroscopy(SMFS)due to the lower noise and higher resolution.For a better signal⁃to⁃noise ratio,both the cantilever velocity and liquid viscosity should be as low as possible.These results will be helpful when a lower noise is desired in weak force detection.

Microstructure Morphologies of Asphalt Binders using Atomic Force Microscopy

We investigated microstructure morphologies of three asphalts（SK, Karamay, and Esso） used in China using atomic force microscopy（AFM）. The topography and phase contrast images were obtained. Topographic profile and three dimensional images were described. Roughnesses of microstructure were calculated. And the chemical compositions of asphalt were tested to explain the microstructural mechanism of the asphalt. The results show that the topography and phase image in atomic force microscopy are appropriate to evaluate the microstructure of the asphalt binder. There are significant differences in microstructural morphologies including bee-like structure, topographic profile, 3D image, and roughness for three asphalts in this study. There are three different phases in microstructure of asphalt binder. The oil source and chemical composition of asphalt, especially asphaltenes content have a great influence on the microstructure.

Minimizing electrostatic interactions from piezoresponse force microscopy via capacitive excitation

Piezoresponse force microscopy(PFM)has emerged as one of the most powerful techniques to probe ferroelectric materials at the nanoscale,yet it has been increasingly recognized that piezoresponse measured by PFM is often influenced by electrostatic interactions.In this letter,we report a capacitive excitation PFM(ce-PFM)to minimize the electrostatic interactions.The effectiveness of ce-PFM in minimizing electrostatic interactions is demonstrated by comparing the piezoresponse and the effective piezoelectric coefficient measured by ce-PFM and conventional PFM.The effectiveness is further confirmed through the ferroelectric domain pattern imaged via ce-PFM and conventional PFM in vertical modes,with the corresponding domain contrast obtained by ce-PFM is sharper than conventional PFM.These results demonstrate ce-PFM as an effective tool to minimize the interference from electrostatic interactions and to image ferroelectric domain pattern,and it can be easily implemented in conventional atomic force microscope(AFM)setup to probe true piezoelectricity at the nanoscale.

Theory of higher harmonics imaging in tapping-mode atomic force microscopy

The periodic impact force induced by tip-sample contact in a tapping mode atomic force microscope （AFM） gives rise to the non-harmonic response of a micro-cantilever. These non-harmonic signals contain the full characteristics of tip-sample interaction. A complete theoretical model describing the dynamical behaviour of tip-sample system was developed in this paper. An analytic formula was introduced to describe the relationship between time-varying tip-sample impact force and tip motion. The theoretical analysis and numerical results both show that the timevarying tip-sample impact force can be reconstructed by recording tip motion. This allows for the reconstruction of the characteristics of the tip-sample force, like contact time and maximum contact force. It can also explain the ability of AFM higher harmonics imaging in mapping stiffness and surface energy variations.

Improvement of the high-k/Ge interface thermal stability using an in-situ ozone treatment characterized by conductive atomic force microscopy

In this work, an in-situ ozone treatment is carried out to improve the interface thermal stability of HfO_2/Al_2O_3 gate stack on germanium（Ge） substrate. The micrometer scale level of HfO_2/Al_2O_3 gate stack on Ge is studied using conductive atomic force microscopy（AFM） with a conductive tip. The initial results indicate that comparing with a non insitu ozone treated sample, the interface thermal stability of the sample with an in-situ ozone treatment can be substantially improved after annealing. As a result, void-free surface, low conductive spots, low leakage current density, and relative high breakdown voltage high-κ/Ge are obtained. A detailed analysis is performed to confirm the origins of the changes.All results indicate that in-situ ozone treatment is a promising method to improve the interface properties of Ge-based three-dimensional（3D） devices in future technology nodes.

Electron trapping properties at HfO_2/SiO_2 interface, studied by Kelvin probe force microscopy and theoretical analysis

Electron trapping properties at the HfO2/SiO2 interface have been measured through Kelvin Probe force microscopy,between room temperature and 90 ℃.The electron diffusion in HfO2 shows a multiple-step process.After injection,electrons diffuse quickly toward the HfO2/SiO2 interface and then diffuse laterally near the interface in two sub-steps：The first is a fast diffusion through shallow trap centers and the second is a slow diffusion through deep trap centers.Evolution of contact potential difference profile in the fast lateral diffusion sub-step was simulated by solving a diffusion equation with a term describing the charge loss.In this way,the diffusion coefficient and the average life time at different temperatures were extracted.A value of 0.57 eV was calculated for the activation energy of the shallow trap centers in HfO2.

Atomic Force Microscopy Measurement in the Lignosulfonate/Inorganic Silica System:From Dispersion Mechanism Study to Product Design

Designing and preparing high-performance lignin-based dispersants are crucial steps in realizing the value-added utilization of lignin on an industrial scale.Such process depends heavily on an understanding of the dispersion mechanism of lignin-based dispersants.Here,atomic force microscopy(AFM)is employed to quantitatively investigate the dispersion mechanism of a lignosulfonate/silica(LS/SiO_(2))system under different pH conditions.The results show that the repulsive force between SiO_(2)particles in LS solution is stronger than it is in water,resulting in better dispersion stability.The Derjaguin–Landau–Verwey–Overbeek(DLVO)formula as well as the DLVO formula combined with steric repulsion is utilized for the fitting of the AFM force/distance(F/D)curves between the SiO_(2)probe and substrate in water and in LS solution.Based on these fitting results,electrostatic and steric repulsive forces are respectively calculated,yielding further evidence that LS provides strong steric repulsion between SiO_(2)particles.Further studies indicate that the adsorbance of LS on SiO_(2)(Q),the normalized interaction constant(A),and the characteristic length(L)are the three critical factors affecting steric repulsion in the LS/SiO_(2)system.Based on the above conclusions,a novel quaternized grafted-sulfonation lignin(QAGSL)dispersant is designed and prepared.The QAGSL dispersant exhibits good dispersing performance for SiO_(2)and real cement particles.This work provides a fundamental and quantitative understanding of the dispersion mechanism in the LS/inorganic particle system and provides important guidance for the development of high-performance lignin-based dispersants.

Adaptive semi-empirical model for non-contact atomic force microscopy

Non-contact atomic force microscope is a powerful tool to investigate the surface topography with atomic resolution.Here we propose a new approach to estimate the interaction between its tips and samples,which combines a semi-empirical model with density functional theory(DFT)calculations.The generated frequency shift images are consistent with the experiment for mapping organic molecules using CuCO,Cu,CuCl,and CuO_(x)tips.This approach achieves accuracy close to DFT calculation with much lower computational cost.

LOW TEMPERATURE MAGNETIC FORCE MICROSCOPY STUDY OF VORTEX IN A YBa_2Cu_3O_(7-x) THIN FILM

A low temperature magnetic fore microscope for the study of high temperature superconductor is developed. It has been applied to spatially resolve single vortices at law temperature (77K) in a YBa2Cu3O7-x thin film deposited by laser ablation on a NdGaO3 substrate. The images of disordered vortex arrangements are obtained. The movement of single vortices after a contact mode scanning of the detecting tip over the thin film surface is observed. The reason for the movement is discussed.