Ivo W. Rangelow

Micromachined piezoresistive cantilever array with integrated resistive microheater for calorimetry and mass detection

We describe a microcantilever calorimeter consisting of an array of ten cantilevers. Each single cantilever is capable of detecting heat energy with the resolution of 50 nW Hz(−0.5). The device is based on a Si microcantilever coated with a 1 μm thick layer of SiO2 deposited with a 700 nm thick layer of aluminum which forms a resistive microheater. Heat fluxes are monitored by detecting the cantilever deflection (bending) due to the bimaterial structure of the cantilever (dissimilar thermal expansion properties of SiO2 and Al). The resistive microheater serves for calibration of the heat flux and for temperature sensing. In our design a piezoresistive Wheatstone bridge detector is applied for measurements of the cantilever beam deflection. The cantilever displacement detection system enables investigations in ultrahigh vacuum and low temperature conditions. The microcantilevers are manufactured in a one-dimensional array having ten individual microcantilevers which is the first step in the fabrication of ...

Micromachined atomic force microscopy sensor with integrated piezoresistive sensor and thermal bimorph actuator for high-speed tapping-mode atomic force microscopy phase-imaging in higher eigenmodes

This article describes microprobes for noncontact scanning force microscopy that make use of a direct-oscillating thermally driven bimorph actuator with integrated piezoresistive readout sensor. The sensitivity has been increased using direct current for biasing and alternating current for exciting the thermally driven cantilever in a higher flexural mode. The cantilever operates in the phase-shift atomic force microscopy (AFM) detection technique. The main advantage of phase imaging is the higher z resolution at high scan rates and much lower forces than in height imaging with contact AFM. Critical dimensions measurements illustrating the imaging capability and resolution of our new scanning proximal probe are demonstrated.

Novel high resolution scanning thermal probe

Scanning thermal microscopy is a scanning proximal probe technique, which can be used for mapping spatial variation of thermal properties of a surface such as temperature, thermal conductivity, and thermal diffusivity. The sensor presented here is a resistance based probe consisting of a nanometer-sized filament formed at the end of a piezoresistive atomic force microscope type cantilever. The freestanding filament is deposited by focused electron beam deposition using methylcyclopentadienyl trimethyl platinum as a precursor gas. The filament height is in the range of 2–5 μm, with typical “wire” diameters between 30 and 100 nm. Typical deposition times are between 2 and 5 min, and might be further shortened by optimizing the precursor gas flux. Because of its small size, the new probe has a high spatial resolution (<20 nm tip end radius) and, due to the low thermal mass, a high thermal sensitivity and fast response time. In this article, experiments designed to characterize the mechanical stability and el...

Fabrication of multipurpose piezoresistive Wheatstone bridge cantilevers with conductive microtips for electrostatic and scanning capacitance microscopy

The fabrication and performance of a microprobe with multipurpose capabilities for scanning probe microscopy is presented in this article. Atomic force microscopy (AFM), scanning capacitance microscopy, and electrostatic force microscopy measurements can be simultaneously performed with the probe in which a silicon tip is integrated with a piezoresistive cantilever. Fabrication of the microprobe is based on double side bulk/surface micromachining of silicon on insulator (SOI) substrates. The novelty of this device is a highly doped silicon tip with a curvature radius of about 20 nm which is electrically isolated from the silicon cantilever by the buried oxide layer of the SOI substrate. At the beam supporting point a piezoresistive Wheatstone bridge is fabricated to allow the deflection of the microtip to be monitored. This cantilever displacement detection system enables measurements in vacuum and simplifies the design of the AFM head. Experimental measurements agree well with theoretical estimates of th...

Chemical recognition based on micromachined silicon cantilever array

We report on the performance of a measurement system for the recognition of individual analytes and their binary mixtures which is based on a multiarray of four micromachined silicon cantivelers actuated at their resonance frequency. The cantilevers have been functionalized by organic polymers [polydimethylsiloxane (PDMS) and polyvinylpyridine (PVP)] and amorphous nitrogen-rich carbon nitride films. We found that the sensitivity and selectivity of the cantilevers coated with CNx films change according to the layer thickness. Our results show that the selected combination of sensitive layers ensures a wide range of specific, reversible and reproducible sensor responses upon exposure to methanol, 2-propanol, water and their binary mixtures. Further, it was found that the differences in recovery times of PDMS and CNx films after exposure to the two alcohols and their mixtures could be used especially for low analyte concentrations as a second characteristic in addition to the resonance frequency shift for th...

Use of self-actuating and self-sensing cantilevers for imaging biological samples in fluid

In this paper, we present a detailed investigation into the suitability of atomic force microscopy (AFM) cantilevers with integrated deflection sensor and micro-actuator for imaging of soft biological samples in fluid. The Si cantilevers are actuated using a micro-heater at the bottom end of the cantilever. Sensing is achieved through p-doped resistors connected in a Wheatstone bridge. We investigated the influence of the water on the cantilever dynamics, the actuation and the sensing mechanisms, as well as the crosstalk between sensing and actuation. Successful imaging of yeast cells in water using the integrated sensor and actuator shows the potential of the combination of this actuation and sensing method. This constitutes a major step towards the automation and miniaturization required to establish AFM in routine biomedical diagnostics and in vivo applications.

Batch fabricated scanning near field optical microscope/atomic force microscopy microprobe integrated with piezoresistive cantilever beam with highly reproducible focused ion beam micromachined aperture

In scanning near field optical microscope (SNOM), an optical probe with aperture diameter well below the optical wavelength is moved over the sample. The sample-probe distance control is one of the key problems in SNOM. Our earlier approach allowed for fabrication of the piezo-SNOM/atomic force microscopy (AFM) probe, however, reproductivity of the process and optical quality of the device were not satisfactory. Now we report an innovative processing sequence, which offers highly reproductive batch processing, typical for semiconductor technology and renders it possible to produce cantilevers playing role of an AFM detector as well as a nanoaperture detector. Moreover, illumination of the aperture is easier because of a wide input opening and its big cone angle. The throughput is in the range of 10−5 and higher. Apertures in hollow pyramids have been formed by direct ion beam drilling with a focused beam of 30 keV Ga+ ions. Direct focused ion beam (FIB) drilling is a reproducible process for hole formatio...

Ion Implantation with Scanning Probe Alignment

We describe a scanning probe instrument which integrates ion beams with the imaging and alignment function of a piezoresistive scanning probe in high vacuum. The beam passes through several apertures and is finally collimated by a hole in the cantilever of the scanning probe. The ion beam spot size is limited by the size of the last aperture. Highly charged ions are used to show hits of single ions in resist, and we discuss the issues for implantation of single ions.

Increased imaging speed and force sensitivity for bio-applications with small cantilevers using a conventional AFM setup

Highlights ► Development of small cantilever. ► Speed increase by a factor of ten using small cantilevers on a commercial AFM. ► Force sensitivity increase by a factor of five using small cantilever prototypes for force spectroscopy measurements.

Single ion implantation with scanning probe alignment

We present results from our development of a single ion implantation technique integrated with a scanning force microscope. Accurate alignment at the 5nm level is a crucial requirement for reliable single ion placement. We address this through integration of the ion beam with a scanning probe tip containing an aperture. Single ion registration is based on detection of secondary electron bursts from single, high charge state ions. We describe formation of scanning probe tips with holes and sensing poles by focused ion and electron beam processing (drilling and thin film deposition). Ion transport studies through apertures show stable transmission for >10h with 1nA scale beam intensities on precollimators.