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Subsurface imaging capability of liquid-environment higher-harmonic atomic force microscopy (AFM) was investigated using a reference artifact. A series of cylindrical cavities with pre-known dimensions were fabricated on a silicon substrate via electron beam lithography and then covered by a set of highly oriented pyrolytic graphite (HOPG) pieces with different thicknesses. Experiments on these structures demonstrated that the higher-harmonic amplitude sensitivity to the local stiffness in liquids was at least an order of magnitude larger than that in ambient air under the same parameter settings. The harmonic AFM in liquids could detect the cavities beneath over a 200 nm thick HOPG cover. Theoretical analyses based on the cantilever dynamics and the membrane mechanical properties well interpreted the experimental results. Furthermore, it was verified that the momentary excitation of the non-driven higher eigenmode in a low-Q environment could play a critical role in the enhanced subsurface imaging capability of harmonic AFM in liquids. [ABSTRACT FROM AUTHOR]

Manufacture of aspheric microlens has always been technically challenging for conventional approaches due to their complex curved profile and tiny sizes. Two-photon polymerization is capable of producing arbitrary shape with high spatial resolution, apart from the disadvantage of ultra-low rate of yield resulting from point-by-point writing strategy. Here, we report parallel fabrication of aspheric microlens arrays (AMLAs) by taking advantage of holographic femtosecond laser direct-writing. The inherent constraints of the spatial light modulator are taken into consideration for achieving improved intensity uniformity and enhanced diffraction efficiency. Closely-packed AMLAs with designable optical parameters are readily fabricated with excellent optical performance. [ABSTRACT FROM AUTHOR]

We investigate the surface deformation in two-photon induced multi-dimensional data storage. Both experimental evidence and theoretical analysis are presented to demonstrate the surface characteristics and formation mechanism in azo-containing material. The deformation reveals strong polarization dependence and has a topographic effect on multi-dimensional encoding. Different stages of data storage process are finally discussed taking into consideration the surface deformation formation. [ABSTRACT FROM AUTHOR]

A technique based on two-dimensional nonperiodic grating is proposed to quantitatively measure the drift of scanning probe microscopy (SPM) instruments. Cross-correlation image analysis is adopted in determining the drift. The grating, named as zero-reference mark (ZRM), has specially designed codes and arrangement of the elements can be optimized to have maximum ratio of maximum peak to second maximum of the image correlation matrix. Design considerations of ZRM for drift measurement are discussed theoretically. Advantages of applying ZRM are analyzed by numerical simulation. Comparisons between ZRM and periodic grating show that ZRM has a sharper, less ambiguous correlation function. Adopting ZRM is much more insensitive to drift larger than one element width. Measurement sensitivity is improved by almost one order of magnitude. These characteristics of ZRM imply that it is suitable to be severed as a reference mark for SPM drift measurement. [ABSTRACT FROM AUTHOR]

The demand for ultrahigh resolution in positioning and alignment is increasing in the field of precision engineering. By superimposing a pair of specially coded two-dimensional (2D) gratings, the correct alignment position of the two gratings can be detected with high resolution and accuracy. Due to the small dimensions of the grating, the diffraction effect is strong and it cannot be ignored. In this article, design considerations for such 2D zero-reference gratings are presented and the behavior of the diffraction of the zero-reference gratings is analyzed theoretically. The transmission function obtained by diffraction analysis agrees with the result from the autocorrelation method by neglecting the diffraction effect. The alignment is independent of the small variation in the gap between two gratings. [ABSTRACT FROM AUTHOR]

We proposed a method for measuring undercut etching based on contact resonance atomic force microscopy (CR-AFM). Suspended undercut structures were fabricated through isotropic wet etching on a patterned SiNx/Si architecture. The materials beneath the SiNx masks with circular and rectangular shapes were partially etched to form center-supported thin plates. A clear contrast was observed between the supported and suspended regions by CR-AFM amplitude imaging, enabling accurate determination of the undercut boundary and the corresponding etched length. CR-spectroscopy measurements of the undercut dimensions were also applied by acquiring the contact stiffness distribution and by further fitting with models of analyzing the plate deflection. The etching rates given by both the imaging and spectroscopy measurements were in close accordance. The theoretical measurement error induced by finite CR-frequency to stiffness sensitivity was evaluated to be around 5% under our experimental settings. This work paves the way for in situ and real-time detection of undercut etching at the nanoscale and benefits relevant micro- and nano-fabrications. [ABSTRACT FROM AUTHOR]

As one of the fundamental sources of noise in atomic force microscopy (AFM), thermal fluctuations of the cantilever have been studied for the case of a free tip but not much for cantilevers in contact. In this paper, using the equipartition theorem, we calculated the thermal deflection amplitude for all normal modes of an elastically supported AFM cantilever, including the free cantilever as a special case. With increasing contact stiffness, the mean thermal fluctuation amplitude decreases for all cantilever modes when in the elastic contact. In addition, considering the optical lever detection scheme used in most AFMs, we calculated the corresponding output thermal noise amplitude. The experiments validated our theoretical calculations. Our investigation facilitates a more comprehensive understanding of the thermal noise in AFM. It provides guidance for thermally excited contact-resonance AFM, which is promising for quantitative viscoelastic measurements. [ABSTRACT FROM AUTHOR]

A human vestibular system is a group of devices in the inner ear that govern the balancing movement of the head, in which the saccule is responsible for sensing gravity accelerations. Imitating the sensing principle and structure of the Sensory Hair (SH) cell in the saccule, a Bionic Sensory Hair (BSH) was developed, and 9 BSH arrays were arranged in the bionic macular at the bottom of the spherical shell to prepare a Bionic Saccule (BS). Based on the piezoelectric equation, the electromechanical theoretical models of the BSH cantilever and BS were deduced. They were subjected to impact oscillations using an exciter, and their output charges were analyzed to check their sensing ability. The results showed that BSH could sense its bending deflection, and the BS could sense its position change in the sagittal plane and in space. They exhibited a sensitivity of 1.6104 Pc s2/m and a fast response and similar sensing principles and low resonance frequency to those of the human saccule. The BS is expected to be used in the field of robotics and clinical disease diagnosis as a part of the artificial vestibular system in the future. [ABSTRACT FROM AUTHOR]

Micro-/nano-scale roughness specimens are highly demanded to synthetically calibrate the scanning probe microscopy (SPM) instrument. In this study, three-dimensional (3D) specimens with controllable main surface evaluation parameters were designed. In order to improve the design accuracy, the genetic algorithm was introduced into the conventional digital filter method. A primary 3D calibration specimen with the dimension of 10 μm × 10 μm was fabricated by electron beam lithography. Atomic force microscopy characterizations demonstrated that the statistical and spectral parameters of the fabricated specimen match well with the designed values. Such a kind of 3D specimens has the potential to calibrate the SPM for applications in quantitative surface evaluations. [ABSTRACT FROM AUTHOR]