D.C. Chavan

Ferrule-top nanoindenter: An optomechanical fiber sensor for nanoindentation

Ferrule-top probes are self-aligned all-optical devices obtained by fabricating a cantilever on the top of a ferruled optical fiber. This approach has been proven to provide a new platform for the realization of small footprint atomic force microscopes (AFMs) that adapt well to utilization outside specialized laboratories [D. Chavan et al., Rev. Sci. Instrum. 81, 123702 (2010); ibid. 82, 046107 (2011)]. In this paper we now show that ferrule-top cantilevers can be also used to develop nanoindenters. Our instrument combines the sensitivity of commercial AFM-based indentation with the ease-of-use of more macroscopic instrumented indenters available today on the market. Furthermore, the all-optical design allows smooth operations also in liquids, where other devices are much more limited and often provide data that are difficult to interpret. This study may pave the way to the implementation of a new generation user-friendly nanoindenters for the measurement of the stiffness of samples in material sciences and medical research.

Top-down approach to fiber-top cantilevers

Taking inspiration from conventional top-down micromachining techniques, we have fabricated a low mass gold fiber-top cantilever via align-and-shine photolithography. The cantilever is characterized by measuring its resonance frequency and mechanical quality factor. Our results show that the device grants mass sensitivity comparable to that reported for similar standard cantilevers. This proof-of-concept paves the way to series production of highly sensitive fiber-top devices for remote detection of biochemical substances.

Ferrule-top atomic force microscope

Ferrule-top cantilevers are a new generation of all-optical miniaturized devices for utilization in liquids, harsh environments, and small volumes [G. Gruca et al., Meas. Sci. Technol. 21, 094033 (2010)]. They are obtained by carving the end of a ferruled fiber in the form of a mechanical beam. Light coupled from the opposite side of the fiber allows detection of cantilever deflections. In this paper, we demonstrate that ferrule-top cantilevers can be used to develop ultra compact AFMs for contact mode imaging in air and in liquids with sensitivity comparable to that of commercial AFMs. The probes do not require any alignment procedure and are easy to handle, favoring applications also outside research laboratories.

Note: Ferrule-top atomic force microscope. II. Imaging in tapping mode and at low temperature

In a recent paper [D.Chavan et al., Rev. Sci. Instrum. 81, 123702 (2010)] we have demonstrated that ferrule-top cantilevers, obtained by carving the end of a ferruled fiber, can be used for contact mode atomic force microscopy in ambient conditions. Here we show that those probes can provide tapping mode images at both room and cryogenic temperatures (12 K).

Collecting optical coherence elastography depth profiles with a micromachined cantilever probe

We present an experimental setup that combines optical coherence elastography depth sensing with atomic force microscope indentation. The instrument relies on a miniaturized cantilever probe that compresses a sample with a small footprint force and simultaneously collects an optical coherence tomography (OCT) depth profile underneath the indenting point. The deflection of the cantilever can be monitored via optical fiber interferometry with a resolution of 2 nm. The OCT readout then provides depth profiles of the subsurface layer deformation with 15 nm resolution and depth range of a few millimeters.

Fibre-top atomic force microscope probe with optical near-field detection capabilities

We present a fibre‐top probe fabricated by carving a tipped cantilever on an optical fibre, with the tip machined in correspondence of the fibre core. When approached to an optical prism illuminated under total internal reflection conditions, the tip of the cantilever detects the optical tunnelling signal, while the light coupled from the opposite end of the fibre measures the deflection of the cantilever. Our results suggest that fibre‐top technology can be used for the development of a new generation of hybrid probes that can combine atomic force microscopy with scanning near field optical microscopy.

Opto-mechanical probe for combining atomic force microscopy and optical near-field surface analysis

We have developed a new easy-to-use probe that can be used to combine atomic force microscopy (AFM) and scanning near-field optical microscopy (SNOM). We show that, using this device, the evanescent field, obtained by total internal reflection conditions in a prism, can be visualized by approaching the surface with the scanning tip. Furthermore, we were able to obtain simultaneous AFM and SNOM images of a standard test grating in air and in liquid. The lateral resolution in AFM and SNOM mode was estimated to be 45 and 160 nm, respectively. This new probe overcomes a number of limitations that commercial probes have, while yielding the same resolution.

Towards High Speed Ferrule-Top Atomic Force Microscopy

Abstract This paper introduces a high speed ferrule-top Atomic Force Microscope (AFM) system by integrating an all optic miniaturized ferrule-top cantilever probe with a high speed AFM scanner. The ferrule-top cantilevers are a new generation of AFM probes that are manufactured directly at the end of a ferruled optical fiber. With a laser coupled into the optical fiber from its opposite end, the cantilever deflection readout is directly available via interferometry. This paper is focused on integrating the ferrule-top probes into a high speed AFM system for simplification of the AFM adjustment towards automation and as a pre-step for a fast scanning tip AFM system. Recorded AFM images that are acquired by the ferrule-top AFM system demonstrate successful imaging at the speed of two frames per second, with 256 by 256 pixel resolution.

Fiber-top and ferrule-top cantilevers for atomic force microscopy and scanning near field optical microscopy

Fiber-top and ferrule-top cantilevers (FTC) are a new generation of all optical, monolithic, self-aligned microdevices. They are obtained by carving a cantilever on the cleaved end of an optical fiber (fiber-top) or on a ferrule terminated fiber (ferrule-top). FTCs rely on Fabry-Perot interferometry to measure the deflection of the cantilever with subnanometer deflection sensitivity. FTCs specially developed for scanning probe microscopy are equipped with a sharp tip that has the dual function of probing the topography and collecting/emitting light. We perform the scanning probe microscopy using these probes in air, liquid and at low temperature (12°K). The light emission/collection functionality of FTC probes also allows one to combine scanning near field optical microscopy (SNOM) and optical transmission microscopy with contact and non-contact mode atomic force microscopy (AFM). This makes FTCs ideal for AFM+SNOM on soft samples, polymers and biological specimen, where bent fiber probes and tuning fork based systems would not be recommended because of the high stiffness of those probes. We demonstrate here the capability of fiber-top cantilevers to measure deflection and collect near field optical signal, and also the capability of ferrule-top cantilevers for simultaneous optical transmission microscopy and topography of SNOM gratings. Thanks to their unique features, FTCs also open up possibilities for UV nanolithography and on-demand optical excitation at nanoscale.

Development of fiber optic ferrule-top cantilevers for sensing and beam-steering applications

Ferrule-top (FT) cantilevers are a new generation of all optical micromechanical sensors obtained by carving microstructures on the top of ferrule terminated fibers. In this paper, we will demonstrate how this plug and play design can be used for the development of a new generation of sensors and actuators for harsh environments, where commercially available devices would be prone to failure. Ferrule-top sensors can work in two main modes - static and dynamic. The static mode is based on recording elastic deflection of the cantilever; the dynamic mode relies on tracking changes in its mechanical properties (resonance frequency, quality factor). Depending on the application, one can choose which mode is most suitable or combine both to achieve best performance. We will illustrate the relation between specific measured quantity (humidity, flow) and the behavior of the sensor. Further, we will show the setup in which the sensor can be actuated using light, giving the possibility to excite the cantilever without any electronics on the sensing head. This technique might by use for the development of fully optical beamsteering microdevices.