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The resolution limit in an atomic force microscope image usually is attributed to the finite radius of the contacting probe. Here, it is shown that this assumption is valid only when adhesion forces are minimal. Relative to the tip-imposed geometrical limit, the resolution and contrast in AFM images can be degraded by increasing adhesion forces. The large adhesion forces observed for some tips at low humidity conditions are shown to be due to tip contamination or poorly formed tip apexes. Methods to determine and to reduce the extent of tip contamination are described. Cleaning carried out using UV-ozone or oxygen-plasma etching were found to significantly reduce the minimum adhesion force.

The conventional deflection-mode atomic force microscope operates by optically monitoring the slope near the end of a microcantilever in contact with the sample surface. This signal is usually interpreted as a measure of height change. Lateral forces from friction, surface geometry, or inclination of the cantilever to the surface also affect the slope due to cantilever buckling. We calculate the deflection of a hollow triangular model cantilever subject to both lateral and normal forces. The measured response of the servo circuit to an inclined, loaded cantilever is then determined. This shows (1) errors are always present in height measurements of structures on inhomogeneous surfaces; (2) the sensitivity to buckling can be reduced by repositioning the laser; (3) friction measurements can be accurately made by scanning in two directions and applying the proper calibration.

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Ultraviolet photovoltaic effect in BiFeO3/Nb-SrTiO3 heterostructure J. Appl. Phys. 112, 083506 (2012) The cooling effect on structural, electrical, and optical properties of epitaxial a-plane ZnO:Al on r-plane sapphire grown by pulsed laser deposition Appl. Phys. Lett. 101, 151907 (2012) Growth and ferromagnetic resonance properties of nanometer-thick yttrium iron garnet films Appl. Phys. Lett. 101, 152405 (2012) Stoichiometric controlling of boron carbide thin films by using boron-carbon dual-targets Appl.

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Background/Aims: MicroRNA-197 (miR-197) has been shown to play roles in epithelialmesenchymal transition (EMT) and metastasis. The Wnt/β-catenin pathway is associated with EMT, but whether miR-197 regulatesWnt/β-catenin remains unclear. This study was to demonstrate the role of miR-197 on the Wnt/β-catenin pathway in hepatocellular carcinoma (HCC). Methods: Quantitative reverse transcription polymerase chain reaction (qRT-PCR) was used to detect the expression of miR-197 in 105 HCC specimens and 15 HCC cell lines. We tested the predicted target gene of miR-197 using a genetic report system. The role of miR-197 in HCC cell invasion and migration (wound healingand cell invasion and migrationby Transwell assays) and in an HCC xenograft modelwas analyzed. Results: Using a miRNA microarray analysis of HCC specimens and compared with non-metastatic HCC, miR-197 was identified as one of the most upregulated miRNAs in metastatic HCC. miR-197 expression was positively associated with the invasiveness of HCC cell lines. Metastatic HCC cells with high miR-197 expression had Wnt/β-catenin signaling activation. High levels of miR-197 expression also promoted EMT and invasionHCC cells in vitro and in vivo. miR-197 directly targeted Axin-2, Naked cuticle 1 (NKD1), and Dickkopf-related protein 2 (DKK2), leading to inhibition of Wnt/β-catenin signaling. High miR-197 expression was found in HCC specimens from patients with portal vein metastasis;high miR-197 expression correlated to the expression of Axin2, NKD1, and DKK2. Conclusion: miR-197 promotes HCC invasion and metastasis by activating Wnt/β-catenin signaling. miR-197 could possibly be used as a prognostic marker and therapeutic target for HCC.