**1. Introduction**

*Forensic science* is an umbrella term incorporating an innumerable professions where they uses their skills to help law enforcement agencies in reaching to the truth during any investigations. Forensic scientist succors in investigating and adjudicating both criminal and civil cases. Criminal activities have their footprints from ancient time and the nature of crime has considerably changed over a time period. Criminal activities are neither limited to geographical boundary, nor technical limitations. Moreover terrorist's activities, drug trafficking eco-crimes, high profile crimes, robbery hit and run cases, building collapse, petroleum products adulteration are some of the latest forms of crimes. In many cases, forensic evidence plays key role in obtaining conviction and often only trace evidences are existent on a suspect.

In past 20 years, scanning probe microscopes have emerged as an essential technique in various fields. The atomic force microscope (AFM) uses the most common scanning probe technique for materials characterization [1, 2]. Major advantages of AFM involves its high resolution in three dimensions, the sample is not necessary to be conductive and it does not need to be operated within a vacuum. It help in studying a large range of topographies and many types of materials can be imaged under it. AFM is capable of imaging 3D topography information from the angstrom level to the micron scale with extraordinary resolution. In AFM, the *Z*-axis resolution (perpendicular to the surface) is better than the *X*–*Y* scan plane resolution of the sample surface. The *Z*-resolution in AFM is on the sub-angstrom level under ambient atmospheric condition while the resolution in *X*–*Y* scan is limited due to the diameter of the probe and is on the order of a few nanometers. In the *X* and *Y* axis, AFM images shows complication of the probe geometry and sample texture, however, if the probe is much smaller than the surface features, the image distortions lead by the probe are nominal. The AFM sensitivity is derived from a force sensor which measures the forces between the probe and target surface which is usually less than 1 nN/nm. **Figure 1** shows a representation of the AFM [3].

Evidences such as blood, fibers, hair, soil, finger prints, gunshot residue, pollen etc. are found on the crime scene at nano or even at molecular level. At present, different nanotechnologies such as the application of nanoscale powders, high resolution scanning and transmission electron microscopy and atomic force microscopy are applied for the examination of various evidences for forensic investigations [4, 5]. Nevertheless, forensic trace depiction of forensic evidences at the nanoscale does not yield applicable forensic information as explained by Inman and Rudin [6, 7] with the principle of divisible matter. Examination of such type of evidences require combination of sophisticated instrumentation which can help in proving the facts and can provide a conclusive results which can provide justice to the society. As mentioned earlier AFM technique has showed application for the examination of such type of evidences which is centered with an extremely high resolution scanning probe microscope to sense intermolecular and interatomic forces between a sharp probe and the specimen. AFM is highly applied in forensic field as it has the biggest advantage of examination of evidences in minimal non-destructive manner as well as possess imaging capabilities to examine the sample in various environmental conditions. As it possess highly accurate piezoelectric scanners its lateral resolution is hundreds of times better than the diffraction limit of traditional optical microscope. The sample is scanned by the tip of the cantilever which results into the deflection because of the attractive or repulsive forces between sample and tip molecules. The cantilever's deflection is measured by

**Figure 1.** *A representation of the AFM.*

the laser beam which is later converted into an electrical signal by photodiodes, thus helping in imaging of the topography surfaces of the sample at the nano-level.
