Types of Uncertainty
Uncertainty in measurement can be classified into two main types:
Type A and
Type B:
Type A: Evaluated using statistical methods. This involves repeated measurements and the application of statistical analysis to determine uncertainty.
Type B: Evaluated using non-statistical methods. This includes uncertainties arising from factors like instrument calibration, environmental conditions, and theoretical models.
Identify all
sources of uncertainty.
Quantify each source of uncertainty using Type A or Type B evaluation.
Combine these individual uncertainties to obtain a total uncertainty, usually through a method called
root-sum-square (RSS).
Express the combined uncertainty along with the measurement result.
Common Sources of Uncertainty in Nanotechnology
Several sources of uncertainty are particularly relevant in nanotechnology: Instrumental Uncertainty: Caused by the limitations and calibration of measurement instruments such as
atomic force microscopes (AFM) and
scanning electron microscopes (SEM).
Environmental Factors: Variations in temperature, humidity, and other environmental conditions can impact measurements at the nanoscale.
Sample Preparation: Differences in sample preparation methods can introduce variability and uncertainty.
Human Factors: Operator skill and experience can contribute to measurement uncertainty.
Expressing Uncertainty
After evaluating the uncertainty, it must be expressed in a clear and standardized format. The GUM recommends expressing uncertainty as an expanded uncertainty, which is usually obtained by multiplying the combined standard uncertainty by a coverage factor (k). This provides an interval within which the true value is expected to lie with a certain level of confidence (typically 95%).
Example: If a measurement result is 10 nm with an expanded uncertainty of ±2 nm, it means the true value is expected to lie between 8 nm and 12 nm with a 95% confidence level.Challenges and Best Practices
Several challenges can arise when applying GUM in nanotechnology: Complexity of Measurements: Nanotechnology measurements often involve complex and multi-step processes, making it difficult to identify and quantify all sources of uncertainty.
Rapid Technological Advancements: The fast pace of innovation in nanotechnology can outstrip the development of standardized measurement techniques and uncertainty evaluation methods.
To address these challenges, it is essential to:
Keep abreast of the latest developments in
measurement techniques and uncertainty evaluation methods.
Collaborate with
interdisciplinary teams to ensure comprehensive evaluation of all sources of uncertainty.
Adopt and follow standardized protocols and guidelines, such as those provided by the GUM.
Conclusion
The Guide to the Expression of Uncertainty in Measurement (GUM) offers a vital framework for ensuring the accuracy and reliability of measurements in nanotechnology. By understanding and applying the principles of uncertainty evaluation, researchers and practitioners can enhance the reproducibility and validity of their findings, thereby advancing the field of nanotechnology.
