Nanometrology
This article includes a list of general references, but it lacks sufficient corresponding inline citations. (July 2017) |
Nanometrology is a subfield of
A challenge in this field is to develop or create new measurement techniques and standards to meet the needs of next-generation advanced manufacturing, which will rely on nanometer scale materials and technologies. The needs for measurement and characterization of new sample structures and characteristics far exceed the capabilities of current measurement science. Anticipated advances in emerging U.S. nanotechnology industries will require revolutionary metrology with higher resolution and accuracy than has previously been envisioned.[1]
Introduction
Control of the critical dimensions are the most important factors in nanotechnology. Nanometrology today, is to a large extent based on the development in semiconductor technology. Nanometrology is the science of measurement at the nanoscale level. Nanometer or nm is equivalent to 10^-9 m. In Nanotechnology accurate control of dimensions of objects is important. Typical dimensions of nanosystems vary from 10 nm to a few hundred nm and while fabricating such systems measurement up to 0.1 nm is required.
At nanoscale due to the small dimensions various new physical phenomena can be observed. For example, when the crystal size is smaller than the electron mean free path the conductivity of the crystal changes. Another example is the discretization of stresses in the system. It becomes important to measure the physical parameters so as to apply these phenomena into engineering of nanosystems and manufacturing them. The measurement of length or size, force, mass, electrical and other properties is included in Nanometrology. The problem is how to measure these with reliability and accuracy. The measurement techniques used for macro systems cannot be directly used for measurement of parameters in nanosystems. Various techniques based on physical phenomena have been developed which can be used for measure or determine the parameters for nanostructures and nanomaterials. Some of the popular ones are
Nanotechnology is an important field because of the large number of applications it has and it has become necessary to develop more precise techniques of measurement and globally accepted standards. Hence progress is required in the field of Nanometrology.
Development needs
Nanotechnology can be divided into two branches. The first being molecular nanotechnology which involves bottom up manufacturing and the second is engineering nanotechnology which involve the development and processing of materials and systems at nanoscale. The measurement and manufacturing tools and techniques required for the two branches are slightly different.
Furthermore, Nanometrology requirements are different for the industry and research institutions. Nanometrology of research has progressed faster than that for industry mainly because implementing nanometrology for industry is difficult. In research oriented nanometrology resolution is important whereas in industrial nanometrology accuracy is given precedence over
Standards
International standards
Metrology
National standards
Because of the importance of nanotechnology in the future, countries around the world have programmes to establish national standards for nanometrology and nanotechnology. These programmes are run by the national standard agencies of the respective countries. In the United States, National Institute of Standards and Technology has been working on developing new techniques for measurement at nanoscale and has also established some national standards for nanotechnology. These standards are for nanoparticle characterization, Roughness Characterization, magnification standard, calibration standards etc.
Calibration
It is difficult to provide samples using which precision instruments can be calibrated at nanoscale. Reference or calibration standards are important for repeatability to be ensured. But there are no international standards for calibration and the calibration artefacts provided by the company along with their equipment is only good for calibrating that particular equipment. Hence it is difficult to select a universal calibration artefact using which we can achieve repeatability at nanoscale. At nanoscale while calibrating care needs to be taken for influence of external factors like vibration, noise, motions caused by thermal drift and creep, nonlinear behaviour and hysteresis of piezoscanner[2] and internal factors like the interaction between the artefact and the equipment which can cause significant deviations.
Measurement techniques
In the last 70 years various techniques for measuring at nanoscale have been developed. Most of them based on some physical phenomena observed on particle interactions or forces at nanoscale. Some of the most commonly used techniques are Atomic Force Microscopy, X-Ray Diffraction, Scanning Electron Microscopy, Transmission Electron Microscopy, High Resolution Transmission Electron Microscopy, and Field Emission Scanning Electron Microscopy.
Atomic force microscopy (AFM) is one of the most common measurement techniques. It can be used to measure topology, grain size, frictional characteristics and different forces. It consists of a silicon cantilever with a sharp tip with a radius of curvature of a few nanometers. The tip is used as a probe on the specimen to be measured. The forces acting at the atomic level between the tip and the surface of the specimen cause the tip to deflect and this deflection is detected using a laser spot which is reflected to an array of photodiodes.
Scanning tunneling microscopy (STM) is another instrument commonly used. It is used to measure 3-D topology of the specimen. The STM is based on the concept of
Another commonly used instrument is the scanning electron microscopy (SEM) which apart from measuring the shape and size of the particles and topography of the surface can be used to determine the composition of elements and compounds the sample is composed of. In SEM the specimen surface is scanned with a high energy electron beam. The electrons in the beam interact with atoms in the specimen and interactions are detected using detectors. The interactions produced are back scattering of electrons, transmission of electrons, secondary electrons etc. To remove high angle electrons magnetics lenses are used.
The instruments mentioned above produce realistic pictures of the surface are excellent measuring tools for research. Industrial applications of nanotechnology require the measurements to be produced need to be more quantitative. The requirement in industrial nanometrology is for higher accuracy than resolution as compared to research nanometrology.
Nano coordinate measuring machine
A
List of some of the measurement techniques
This section is in prose. is available. (February 2017) |
Traceability
In metrology at macro scale achieving traceability is quite easy and artefacts like scales, laser interferometers, step gauges, and straight edges are used. At nanoscale a
Tolerance
Tolerance is the permissible limit or limits of variation in dimensions, properties, or conditions without significantly affecting functioning of equipment or a process. Tolerances are specified to allow reasonable leeway for imperfections and inherent variability without compromising performance. In nanotechnology the systems have dimensions in the range of nanometers. Defining tolerances at nanoscale with suitable calibration standards for traceability is difficult for different nanomanufacturing methods. There are various integration techniques developed in the semiconductor industry that are used in nanomanufacturing.
Integration techniques
- In hetero integration direct fabrication of nanosystems from compound substrates is done. Geometric tolerances are required to achieve the functionality of the assembly.
- In hybrid integration nanocomponents are placed or assembled on a substrate fabricating functioning nanosystems. In this technique, the most important control parameter is the positional accuracy of the components on the substrate.
- In monolithic integrationall the fabrication process steps are integrated on a single substrate and hence no mating of components or assembly is required. The advantage of this technique is that the geometric measurements are no longer of primary importance for achieving functionality of nanosystem or control of the fabrication process.
Classification of nanostructures
There are a variety of nanostructures like nanocomposites, nanowires, nanopowders, nanotubes, fullerenes nanofibers, nanocages, nanocrystallites, nanoneedles, nanofoams, nanomeshes, nanoparticles, nanopillars, thin films, nanorods, nanofabrics, quantumdots etc. The most common way to classify nano structures is by their dimensions.
Dimensional classification
Dimensions | Criteria | Examples |
---|---|---|
Zero-dimensional (0-D) | The nanostructure has all dimensions in the nanometer range. | Nanoparticles, quantum dots , nanodots
|
One-dimensional (1-D) | One dimension of the nanostructure is outside the nanometer range. | Nanowires , nanorods, nanotubes
|
Two-dimensional (2-D) | Two dimensions of the nanostructure are outside the nanometer range. | Coatings, thin-film-multilayers |
Three-dimensional (3-D) | Three dimensions of the nanostructure are outside the nanometer range. | Bulk |
Classification of grain structure
Nanostructures can be classified on the basis of the grain structure and size there are made up of. This is applicable in the cas of 2-dimensional and 3-Dimensional Nanostructurs.
Surface area measurement
For
- D = 6/(ρ*A)
Where "D" is the effective diameter, "ρ" is the density and "A" is the surface area found from the B.E.T. method.
See also
References
- ^ a b "Programs of the Manufacturing Engineering Laboratory" (PDF). U.S. National Institute of Standards and Technology. March 2008. Archived from the original (PDF) on 2010-04-01. Retrieved 2009-07-04. This article incorporates text from this source, which is in the public domain.
- S2CID 250913438. (Russian translationis available).
- ^ "Co-Nanomet: Nanometrology in Europe". Archived from the original on 2009-06-29.
- ISSN 0034-6748.
- S2CID 119275633.
General references
- Whitehouse, David J. (2011). Handbook of surface and nanometrology. CRC Press. OCLC 703152969.
- Schulte, Jürgen (2005). Nanotechnology: global strategies, industry trends and applications. Wiley. OCLC 56733161.
- "Eighth Nanoforum Report: Nanometrology" (PDF). Nanoforum. July 2006.
- Aliofkhazraei, Mahmood; Rouhaghdam, Alireza Sabour (2010). "Synthesis and Processing of Nanostructured Films, and Introduction to and Comparison with Plasma Electrolysis" (PDF). Fabrication of nanostructures by plasma electrolysis. Wiley-VCH. OCLC 676709104.