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1.
J Phys Chem Lett ; 12(33): 8039-8045, 2021 Aug 26.
Artigo em Inglês | MEDLINE | ID: mdl-34402624

RESUMO

Calcite dissolution is initiated by the formation of a nanoscale etch pit followed by step edge propagation and hence strongly influenced by the interactions between surface diffusing ions and step edges. However, such atomic-scale dynamics are mostly inaccessible with current imaging tools. Here, we overcome this limitation by using our recent development of high-speed frequency modulation atomic force microscopy. By visualizing atomic-scale structural changes of the etch pits at the calcite surface in water, we found the existence of mobile and less-mobile surface adsorption layers (SALs) in the etch pits. We also found that some etch pits maintain their size for a long time without expansion, and their step edges are often associated with less-mobile SALs, suggesting their step stabilization effect.


Assuntos
Carbonato de Cálcio/química , Microscopia de Força Atômica/métodos , Nanoestruturas/química , Adsorção , Cristalografia , Estrutura Molecular , Solubilidade , Propriedades de Superfície , Água/química
2.
Phys Chem Chem Phys ; 20(36): 23522-23527, 2018 Sep 19.
Artigo em Inglês | MEDLINE | ID: mdl-30183018

RESUMO

Investigating interfacial water ordering on solid surfaces with different hydrophobicities is fundamentally important. Here, we prepared hydrophilic mica substrates with some areas covered by mildly hydrophobic graphene layers and studied the resulting hydration layers using three-dimensional (3D) force measurements based on frequency-modulation atomic force microscopy. Hydration layers of 0.3-0.6 nm were detected on bare graphene regions; these layers were considerably larger than the spacing measured on mica (0.2-0.3 nm). On the graphene-covered regions, we also observed the formation of special ordered structures of adsorbates over time, on which, surprisingly, no prominent hydration layers were detected. Based on these findings, we present one possible scenario to describe the formation process of the ordered interfacial structures and the enhanced oscillation period in the force profiles. This work also demonstrates the capability and significance of 3D force measurements in probing hydration behaviors on a heterogeneous substrate with a lateral resolution smaller than several nanometers.

3.
Beilstein J Nanotechnol ; 9: 1844-1855, 2018.
Artigo em Inglês | MEDLINE | ID: mdl-30013878

RESUMO

A phase-locked loop (PLL) circuit is the central component of frequency modulation atomic force microscopy (FM-AFM). However, its response speed is often insufficient, and limits the FM-AFM imaging speed. To overcome this issue, we propose a PLL design that enables high-speed FM-AFM. We discuss the main problems with the conventional PLL design and their possible solutions. In the conventional design, a low-pass filter with relatively high latency is used in the phase feedback loop, leading to a slow response of the PLL. In the proposed design, a phase detector with a low-latency high-pass filter is located outside the phase feedback loop, while a subtraction-based phase comparator with negligible latency is located inside the loop. This design minimizes the latency within the phase feedback loop and significantly improves the PLL response speed. In addition, we implemented PLLs with the conventional and proposed designs in the same field programmable gate array chip and quantitatively compared their performances. The results demonstrate that the performance of the proposed PLL is superior to that of the conventional PLL: 165 kHz bandwidth and 3.2 µs latency in water. Using this setup, we performed FM-AFM imaging of calcite dissolution in water at 0.5 s/frame with true atomic resolution. The high-speed and high-resolution imaging capabilities of the proposed design will enable a wide range of studies to be conducted on various atomic-scale dynamic phenomena at solid-liquid interfaces.

4.
Phys Rev Lett ; 120(11): 116101, 2018 Mar 16.
Artigo em Inglês | MEDLINE | ID: mdl-29601750

RESUMO

It seems natural to assume that defects at mineral surfaces critically influence interfacial processes such as the dissolution and growth of minerals in water. The experimental verification of this claim, however, is challenging and requires real-space methods with utmost spatial resolution, such as atomic force microscopy (AFM). While defects at mineral-water interfaces have been resolved in 2D AFM images before, the perturbation of the surrounding hydration structure has not yet been analyzed experimentally. In this Letter, we demonstrate that point defects on the most stable and naturally abundant calcite (10.4) surface can be resolved using high-resolution 3D AFM-even within the fifth hydration layer. Our analysis of the hydration structure surrounding the point defect shows a perturbation of the hydration with a lateral extent of approximately one unit cell. These experimental results are corroborated by molecular dynamics simulations.

5.
Nano Lett ; 17(7): 4083-4089, 2017 07 12.
Artigo em Inglês | MEDLINE | ID: mdl-28650174

RESUMO

The microscopic understanding of the crystal growth and dissolution processes have been greatly advanced by the direct imaging of nanoscale step flows by atomic force microscopy (AFM), optical interferometry, and X-ray microscopy. However, one of the most fundamental events that govern their kinetics, namely, atomistic events at the step edges, have not been well understood. In this study, we have developed high-speed frequency modulation AFM (FM-AFM) and enabled true atomic-resolution imaging in liquid at ∼1 s/frame, which is ∼50 times faster than the conventional FM-AFM. With the developed AFM, we have directly imaged subnanometer-scale surface structures around the moving step edges of calcite during its dissolution in water. The obtained images reveal that the transition region with typical width of a few nanometers is formed along the step edges. Building upon insight in previous studies, our simulations suggest that the transition region is most likely to be a Ca(OH)2 monolayer formed as an intermediate state in the dissolution process. On the basis of this finding, we improve our understanding of the atomistic dissolution model of calcite in water. These results open up a wide range of future applications of the high-speed FM-AFM to the studies on various dynamic processes at solid-liquid interfaces with true atomic resolution.

6.
Nanotechnology ; 27(41): 415709, 2016 Oct 14.
Artigo em Inglês | MEDLINE | ID: mdl-27609045

RESUMO

Frequency modulation atomic force microscopy (FM-AFM) experiments were performed on the calcite (10[Formula: see text]4) surface in pure water, and a detailed analysis was made of the 2D images at a variety of frequency setpoints. We observed eight different contrast patterns that reproducibly appeared in different experiments and with different measurement parameters. We then performed systematic free energy calculations of the same system using atomistic molecular dynamics to obtain an effective force field for the tip-surface interaction. By using this force field in a virtual AFM simulation we found that each experimental contrast could be reproduced in our simulations by changing the setpoint, regardless of the experimental parameters. This approach offers a generic method for understanding the wide variety of contrast patterns seen on the calcite surface in water, and is generally applicable to AFM imaging in liquids.

7.
J Biol Chem ; 291(13): 7004-16, 2016 Mar 25.
Artigo em Inglês | MEDLINE | ID: mdl-26865635

RESUMO

Aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor regulating the expression of genes involved in xenobiotic response. Recent studies have suggested that AhR plays essential roles not only in xenobiotic detoxification but also energy metabolism. Thus, in this study, we studied the roles of AhR in lipid metabolism. Under high fat diet (HFD) challenge, liver-specific AhR knock-out (AhR LKO) mice exhibited severe steatosis, inflammation, and injury in the liver. Gene expression analysis and biochemical study revealed thatde novolipogenesis activity was significantly increased in AhR LKO mice. In contrast, induction of suppressor of cytokine signal 3 (Socs3) expression by HFD was attenuated in the livers of AhR LKO mice. Rescue of theSocs3gene in the liver of AhR LKO mice cancelled the HFD-induced hepatic lipotoxicities. Promoter analysis established Socs3 as novel transcriptional target of AhR. These results indicated that AhR plays a protective role against HFD-induced hepatic steatosis and the subsequent lipotoxicity effects, such as inflammation, and that the mechanism of protection involves the direct transcriptional regulation ofSocs3expression by AhR.


Assuntos
Fatores de Transcrição Hélice-Alça-Hélice Básicos/genética , Dieta Hiperlipídica , Gorduras na Dieta/efeitos adversos , Fígado Gorduroso/genética , Receptores de Hidrocarboneto Arílico/genética , Proteínas Supressoras da Sinalização de Citocina/genética , Animais , Fatores de Transcrição Hélice-Alça-Hélice Básicos/deficiência , Sítios de Ligação , Fígado Gorduroso/etiologia , Fígado Gorduroso/metabolismo , Fígado Gorduroso/patologia , Regulação da Expressão Gênica , Metabolismo dos Lipídeos , Fígado/metabolismo , Fígado/patologia , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Regiões Promotoras Genéticas , Ligação Proteica , Receptores de Hidrocarboneto Arílico/deficiência , Transdução de Sinais , Proteína 3 Supressora da Sinalização de Citocinas , Proteínas Supressoras da Sinalização de Citocina/metabolismo , Transcrição Genética
8.
Rev Sci Instrum ; 85(12): 126106, 2014 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-25554342

RESUMO

High-speed atomic force microscopy has attracted much attention due to its unique capability of visualizing nanoscale dynamic processes at a solid/liquid interface. However, its usability and resolution have yet to be improved. As one of the solutions for this issue, here we present a design of a high-speed Z-tip scanner with screw holding mechanism. We perform detailed comparison between designs with different actuator size and screw arrangement by finite element analysis. Based on the design giving the best performance, we have developed a Z tip scanner and measured its performance. The measured frequency response of the scanner shows a flat response up to ∼10 kHz. This high frequency response allows us to achieve wideband tip-sample distance regulation. We demonstrate the applicability of the scanner to high-speed atomic-resolution imaging by visualizing atomic-scale calcite crystal dissolution process in water at 2 s/frame.


Assuntos
Microscopia de Força Atômica/instrumentação , Carbonato de Cálcio/química , Desenho de Equipamento , Análise de Elementos Finitos , Microscopia de Força Atômica/métodos , Modelos Teóricos , Vibração , Água/química
9.
Rev Sci Instrum ; 84(4): 043705, 2013 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-23635201

RESUMO

We have developed a liquid-environment atomic force microscope with a wideband and low-noise scanning system for atomic-scale imaging of dynamic processes at solid/liquid interfaces. The developed scanning system consists of a separate-type scanner and a wideband high-voltage amplifier (HVA). By separating an XY-sample scanner from a Z-tip scanner, we have enabled to use a relatively large sample without compromising the high resonance frequency. We compared various cantilever- and sample-holding mechanisms by experiments and finite element analyses for optimizing the balance between the usability and frequency response characteristics. We specifically designed the HVA to drive the developed scanners, which enabled to achieve the positioning accuracy of 5.7 and 0.53 pm in the XY and Z axes, respectively. Such an excellent noise performance allowed us to perform atomic-resolution imaging of mica and calcite in liquid. Furthermore, we demonstrate in situ and atomic-resolution imaging of the calcite crystal growth process in water.

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