SI traceability: Current status and future trends for forces below 10 microNewtons (original) (raw)
Related papers
Traceability of small force measurements and the future international system of units (SI)
International Journal of Metrology and Quality Engineering, 2016
The unit of force is connected to the international prototype of the kilogramme, unit of mass in the international system of units (SI), via dead weight machines using calibrated masses. However, forces below 10 mN, ubiquitous in nature and in some devices cannot be measured with a traceability to the SI. The measurement, with the uncertainty of these forces has implications for both basic and applied science. Today, many emerging sectors in micro/nanotechnology and biotechnology have started producing and using systems to implement low forces that, for various reasons, require them to be traceable. Also, the revision of the SI, scheduled for 2018 year, of linking the definitions of the kilogramme, the ampere, the kelvin and the mole to fixed numerical values of fundamental constants, has aroused particular interest in the measurement and calibration of small forces. In this paper, we will give some indications of the state of the art on the small force with a focus on the development of a force sensor using a photoelastic crystal as a monolithic solid-state laser. Basically, the force to be measured is applied to the crystal induces a birefringence in the laser medium which in turn manifests itself by the appearance of a splitting between the frequencies associated with the two polarization components of the oscillating laser mode. This difference is then exploited because, within the elastic limit of the crystal, it is proportional to the force acting on the laser.
Recent advances in traceable nanoscale dimension and force metrology in the UK
Measurement Science & Technology, 2006
It is now fully appreciated that metrology will play an integral role in the successful development and commercialization of micro-and nanotechnology. To this end, the UK Government, through the National Measurement System, funded several groundbreaking projects in its 2002-2005 Programme for Length. This paper will briefly describe the background of the research, concentrating on the technical details of the projects. The Programme for Length normally only funds work into dimensional metrology but this funding cycle also funded work into low force metrology as this area is crucial to most mechanical probing techniques. The projects described include a traceable areal contacting instrument designed to calibrate areal transfer artefacts and hence offer traceability for industrial areal instruments, the production of the areal transfer artefacts, the development of Internet-based softgauges for profile parameters, a primary low force balance with a force resolution of 50 pN and the development of methods for measuring complex micro-scale structures. Amongst others, the projects involved collaboration with PTB, TNO, Taylor Hobson, AWE, Rubert & Co. and the Universities of Warwick, Huddersfield and Eindhoven.
The nist microforce realization and measurement project
IEEE Transactions on Instrumentation and Measurement, 2003
The National Institute of Standards and Technology (NIST) has launched a five-year Microforce Realization and Measurement Project focusing on the development of an instrument and laboratory capable of realizing and measuring the SI unit of force below 5 10 6 N using the electrical units as the link to the International System of Units (SI). As a proof of principle, a prototype electromechanical balance has been developed to allow comparisons between mechanically and electrically derived forces up to 300 N with a resolution of 15 nN. Results from force comparisons using 1-, 10-, and 20-mg deadweights are presented.
Towards a Traceable Infrastructure for Low Force Measurements
IFIP — International Federation for Information Processing, 2008
Over the past ten years or so the need for the measurement of low forces ranging from newtons down to attonewtons has become increasingly important. As we begin to manufacture and manipulate structures on the micrometre to nanometre scale, the forces that are exerted in such processes must be controlled. To control such forces requires some form of measurement, either a direct measurement of the force, or a measurement of the effect the force has on the structure it is applied to. This paper is primarily concerned with the development of a traceability infrastructure for forces in the range from 1 nN to 10 |xN. The lower end of this force range does not cover chemical or most biological forces (usually in the femto-to piconewton range) despite the increasing importance of accurately measuring such forces. Further work is still requu-ed to push the limits of force traceability to these levels. At the upper end of the force range considered here, more traditional methods for measuring forces can be used that are traceable to the unit of mass, i.e. the force is realised as a mass in a gravitational field. The force range discussed in this paper applies to many nano-and micrometre scale manipulation and assembly applications, including micro-grippers, handlers and force feedback devices. Further applications that fall into the force range discussed here include the force exerted on a surface by atomic force microscopes and other scanning probe instruments, forces in the area of materials property measurement using indentation technology, the forces found in micro-electromechnical systems (MEMS) and the forces exerted by artificial biological tissues, for example muscle fibres. The two main force generation mechanisms that are found in nature and engineering are the weight of the mass of an object in a gravitational field and the deflection of an element with a finite spring constant. On the micro-to nanometre scale the spring force is more usually used to produce or react to a force, for example an AFM cantilever.
Methods for transferring the SI unit of force from millinewtons to piconewtons
The establishment of standards for small force measurement requires a link to an absolute measurement of force traceable to the international system of units (SI). To this end, a host of different means are being employed by the NIST small force measurement project to realize and transfer forces between 5 millinewtons and 5 piconewtons. Realizations based on deadweights and electrostatic forces, as well as transfer artifacts based the mechanical properties of single DNA molecules will be discussed. The application of each of these approaches will also be discussed as a calibration method for different kinds of instruments requiring the measurement of small forces.
CALIBRATION OF MICROFABRICATED CANTILEVERS FOR SI TRACEABLE SMALL FORCE MEASUREMENT
A procedure is described by which the spring constant of a microfabricated cantilever bea m can be calibrated for the measurement of small forces i n an atomic force microscope (AFM) or other device. The procedure utilizes dynamic force instrumented indentation to determine the mechanical properties of the beam by applying a well-characterized oscillating f orce and measuring resulting displacement of the system. An uncertainty analysis is carried out, and by intercomparison with the U.S. National Institute of Standards and Technology (NIST) Electrostatic Force Balance (EFB). The spring constants determined usi ng the indentation method agree within 2 % of the valu es determined using the EFB for spring constants as lo w as 2 N/m.
A New Microdevice for SI-Traceable Forces in Atomic Force Microscopy
A new self-excited micro-oscillator is proposed as a velocity standard for dissemination of nanonewton-level forces that are traceable to the International System of Units (SI). The microfabricated oscillator is top-coated with magnetic thin films and closely surrounded with conductive microwires to enable both magnetic sensing and actuation. An analog control system will keep the actuation side of the device oscillating sinusoidally with a frequency up to 200 kHz and a nanometerlevel amplitude that is fairly insensitive to the quality factor. Consequently, the device can be calibrated as a velocity standard in air and used in ultra-high vacuum with a velocity shift of less than one percent. Because of the nanometer-level oscillation amplitude, the microdevice could be used to probe capacitance gradients near tips of cantilevers used for atomic force microscopy (AFM). Hence, the calibrated micro-oscillator could be used with electrostatic forces to calibrate AFM cantilevers as SI-traceable force transducers for fundamental metrology of electrical and mechanical nanoscale quantities.
2014
Reliability of measurement is a crucial element of both research and industry. Metrological traceability to the SI unit metre guarantees commensurate units, also at nanometre range. In this thesis, a traceability chain is established for nanometre scale measurements. Measurement instruments and methods were developed for accurate measurements, calibration of instruments and transfer standards, and uncertainty estimations. A metrological atomic force microscope (MAFM) was developed and characterized. The MAFM can be used in the calibration of transfer standards and in accurate AFM measurements. Calibration methods for commercial AFMs were developed. A laser diffractometer was also developed for accurate calibration of 1-D and 2-D gratings with a standard uncertainty of several tens of picometres. Laser interferometric position measurement with a calibrated vacuum wavelength is directly traceable to the realization of the metre if measuring full interferometer fringes, but there is small nonlinearity in sub-fringe measurements. Therefore, in sub-nanometre measurements the nonlinearity of the interferometer needs to be corrected. A method for this correction was developed. Laser diffraction measurement is a very accurate method for characterization of grating pitch. One of the main uncertainty sources is the uncertainty of the measured diffraction angle. Therefore, a method for calibration of the rotary table of the laser diffraction setup was developed. The method can be used also in the realization of angle scale. Methods for transfer standard calibration were developed for both pitch and step height calibration by MAFM. An acoustic method was developed for compensation of the refractive index of air in interferometric measurements. Sub-nanometre uncertainty can be reached with this method. Characterization of instruments, validation of methods and uncertainty estimations are a crucial part of traceability. Therefore, uncertainty estimates based on the characterization of the instruments are given for all measurements in this thesis. Comparisons between laboratories are the best way to ensure commensurate measurements. International comparison results between national metrology institutes for pitch and step height transfer standards are listed. I would like to thank all my colleagues at MIKES, especially MSc Jeremias Seppä, Mr Asko Rantanen, PhD Hannu Husu and MSc Aarni Iho, and the whole length group. It has been a pleasure working with you. Many thanks to PhD Mikko Merimaa for the discussions and comments on the thesis. Thanks also to PhD Kaj Nyholm for his valuable comments. I am grateful to Mr Leonid Mihaljov and AcWaCo Ltd for their kind cooperation. I would like to thank all my international colleagues for their cooperation and valuable input throughout the years. I am also thankful to the University of Helsinki, Department of Physics, and Professor Juhani Keinonen for the inspiring atmosphere during my studies and initial years in the academic world, and to Professor Jyrki Räisänen for his support at the very end of the work. Many thanks to the preliminary examiners Professor Janne Ruokolainen and Professor Markus Ahlskog for their effort. Thanks to Adelaide Lönnberg for revising the English language of the thesis. I would like to acknowledge the Academy of Finland for the financial support, and NGS-NANO for their support. Finally, I would thank my family, Ilkka and Lassi, for their encouragement and support.