Tanya L. Wright

Electrical, Thermal, and Mechanical Characterization of Silicon Microcantilever Heaters

Silicon atomic force microscope (AFM) cantilevers having integrated solid-state heaters were originally developed for application to data storage, but have since been applied to metrology, thermophysical property measurements, and nanoscale manufacturing. These applications beyond data storage have strict requirements for mechanical characterization and precise temperature calibration of the cantilever. This paper describes detailed mechanical, electrical, and thermal characterization and calibration of AFM cantilevers having integrated solid-state heaters. Analysis of the cantilever response to electrical excitation in both time and frequency domains aids in resolving heat transfer mechanisms in the cantilever. Raman spectroscopy provides local temperature measurement along the cantilever with resolution near 1 mum and 5degC and also provides local surface stress measurements. Observation of the cantilever mechanical thermal noise spectrum at room temperature and while heated provides insight into cantilever mechanical behavior and compares well with finite-element analysis. The characterization and calibration methodology reported here expands the use of heated AFM cantilevers, particularly the uses for nanomanufacturing and sensing

Thermal conduction from microcantilever heaters in partial vacuum

This paper reports the thermal and electrical characteristics of a heated microcantilever in air and helium over a wide range of pressures. The cantilever heater size modulates thermal conductance between the cantilever and its gaseous surroundings; and the Knudsen number, Kn characterizes this thermal conductance. When Kn 1, thermal transport from the cantilever heater remains constant. This measurement of thermal conductance around Kn=1 could aid the design and analysis of Pirani sensors and other microscale thermal sensors and actuators.

Room-temperature chemical vapor deposition and mass detection on a heated atomic force microscope cantilever

This letter reports the localized room-temperature chemical vapor deposition of carbon nanotubes (CNTs) onto an atomic force microscope cantilever having an integrated heater, using the cantilever self-heating to provide temperatures required for CNT growth. Precise temperature calibration of the cantilever was possible and the CNTs were synthesized at a cantilever heater temperature of 800°C in reactive gases at room temperature. Scanning electron microscopy confirmed the CNTs were vertically aligned and highly localized to only the heater area of the cantilever. The cantilever mechanical resonance decreased from 119.10kHzto118.23kHz upon CNT growth, and then returned to 119.09kHz following cantilever cleaning, indicating a CNT mass of 1.4×10−14kg. This technique for highly local growth and measurement of deposited CNTs creates new opportunities for interfacing nanomaterials with microstructures.

Thermal Metrology of Silicon Microstructures Using Raman Spectroscopy

Thermal metrology of an electrically active silicon heated atomic force microscope cantilever and doped polysilicon microbeams was performed using Raman spectroscopy. The temperature dependence of the Stokes Raman peak location and the Stokes to anti-Stokes intensity ratio calibrated the measurements, and it was possible to assess both temperature and thermal stress behavior with resolution near 1mum. The devices can exceed 400degC with the required power depending upon thermal boundary conditions. Comparing the Stokes shift method to the intensity ratio technique, non-negligible errors in devices with mechanically fixed boundary conditions compared to freely standing structures arise due to thermally induced stress. Experimental values were compared with a finite element model, and were within 9% of the thermal response and 5% of the electrical response across the entire range measured

Thermal metrology of silicon microstructures using Raman spectroscopy

The effects of temperature and stress on the Raman shift in single crystal silicon and polycrystalline silicon films were calibrated. Polysilicon films were grown by LPCVD using a range of temperatures to produce amorphous and crystalline materials followed by doping and annealing. The dependencies of the linear coefficients were related to the polysilicon microstructure using AFM surface scans to determine any possible links. Finally, the technique was utilized in measuring the temperature distribution in a thermal MEMS cantilever device with micron spatial resolution.

Fabrication and Characterization of Liquid and Gaseous Micro- and Nanojets

This paper reports on the fabrication and characterization of liquid and gaseous jets ejected from microfabricated nozzles with dimensions ranging from 500 nm to 12 μm. Unlike previous work reporting the fabrication of nano-orifices defined within the thickness of the substrates [1-4], the in-plane nanonozzles presented in this paper are designed to sustain the high pressures necessary to obtain substantial nanofluidic jet flows. This approach also allows important three-dimensional features of nozzle, channel and fluidic reservoir to be defined by design and not by fabrication constraints, thereby meeting important fluid-mechanical criteria such as a fully-developed flow. The shrinking jet dimensions demand new metrology tools to investigate their flow behavior. A laser shadowgraphy technique is used to visualize and image the jet flows. Micromachined heated and piezoresistive cantilevers are used to investigate the thrust and heat flux characteristics of the jets.Copyright

Micro-cantilever metrology tool for flow characterization of liquid and micro/nanojets

This paper reports the development of MEMS metrology tools to characterize liquid and gaseous jets ejected from micro/nanofabricated nozzles. To date few highly local measurements have been made on micro/nanojets, due in part to the lack of characterization tools and techniques to investigate their characteristics. Atomic force microscope cantilevers are well-suited for interrogating these flows due to their high spatial and temporal resolution. In this work, cantilever sensors with either integrated heating elements or piezoresistive elements have been fabricated to measure thrust, velocity, and heat flux characteristics of micro/nanojets.Copyright

Transport in Thermal Dip Pen Nanolithography

The manufacture of nanoscale devices is at present constrained by the resolution limits of optical lithography and the high cost of electron beam lithography. Furthermore, traditional silicon fabrication techniques are quite limited in materials compatibility and are not well-suited for the manufacture of organic and biological devices. One nanomanufacturing technique that could overcome these drawbacks is dip pen nanolithography (DPN), in which a chemical-coated atomic force microscope (AFM) tip deposits molecular ‘inks’ onto a substrate [1]. DPN has shown resolution as good as 5 nm [2] and has been performed with a large number of molecules, but has limitations. For molecules to ink the surface they must be mobile at room temperature, limiting the inks that can be used, and since the inks must be mobile in ambient conditions, there is no way to stop the deposition while the tip is in contact with the substrate. In-situ imaging of deposited molecules therefore causes contamination of the deposited features.Copyright

Characterization of heated atomic force microscope cantilevers in air and vacuum

This paper presents characterization of heated atomic force microscope (AFM) cantilevers in air and helium, both at atmospheric pressure and in a partially evacuated environment. The cantilevers are made of doped single-crystal silicon using a standard silicon-on-insulator cantilever fabrication process. The electrical measurements show the link between the cantilever temperature-dependant electrical characteristics, electrical resistive heating, and thermal properties of the heated AFM cantilever and its surroundings. Laser Raman thermometry measures temperature along the cantilever with resolution near 1 μm and 4°C. By modulating the gaseous environment surrounding the cantilever, it is possible to estimate the microscale thermal coupling between the cantilever and its environment. This work seeks to improve the calibration and design of heated AFM cantilevers.Copyright

Nanoscale inking, melting, and soldering with a heated atomic force microscope cantilever tip

Thermal dip pen nanolithography (tDPN) is a nanolithography technique that leverages previous advances in dip pen nanolithography and the design and fabrication of heated atomic force microscope cantilevers. In tDPN a heated atomic force microscope cantilever tip deposits high-melting temperature materials from the tip onto a surface. This technique is distinct from conventional DPN in that the ink molecules are not mobile at room temperature, allowing local control of deposition allowing the tip to be used for metrology of written features without contamination. tDPN represents an advancement in nanometer-scale lithography and manufacturing, which could enable the rapid prototyping and economical manufacture of nanodevices.Copyright