Scanning transmission electron microscopy (STEM):

Materials
Scanning transmission electron microscopy (STEM): This instrument would be used for imaging. Images are formed by passing electrons through a minute specimen (Nellist, 2007). The concentration is on a specific spot, basically 0.2 – 0.6 nm. The particular technique utilized is STEM tomography. This technique allows the reconstruction of a 3D image composed of both internal and external structures of the sample to a 2D image. Incremental tilts are crucial in obtaining 2D images. After the specimen cut, and then observed using a STEM to produce images critical for nanometer and atomic scaling of the MTJ sensor. 
The principal mechanism is the concentration of a beam of electrons on a sample or specimen to produce an image (Nellist, 2007). The interaction of the electrons produces multiple signals. Hence information that can be obtained includes the surface of the topography, in this case, the roughness of layers, and composition of elements in the MTJ sensor, and how they change preceding the various processes incorporated. 
Transmission electron microscopy (TEM): This instrument uses electrons to illuminate the sample and produce imaged of the sample, which is to be used for analysis. The specific technique to be utilized is the scanning TEM, which is incorporated in TEM by adding a system capable of the raster of convergent beams across the specimen being observed for the formation of a definite image after combining various detectors. After sectioning the specimen, grinding and dimpling the specimens to miniatures of about 20nm, they are then stained and observed under the TEM.
The main working principle of this equipment is the creation of magnified images by focusing on a beam of electrons (Inkson, 2016). When the specimen is illuminated by electrons in this equipment, the subsequent result is the increased electron transmission wavelength. The specific information revealed by TEM includes the crystalline information and composition of the specimen under observation (Inkson, 2016). In addition, the texture and topographical information of the specimen under observation can also be obtained. 
Procedure
Magnetron sputtering method was utilized at room temperatures to deposit silicon oxide (SiO2), which was thermally oxidized. The substrate structure was a composition of Silicon (Si), SiO2, iron, and copper element with boron (CoFeB), Magnesium oxide (MgO), Tantalum (Ta) and Ruthenium (Ru). The first ferromagnetic material constituting CoFeB was then deposited, followed by deposition of MgO layers. The pressure used in MgO deposition was ten mTorr in the Ar atmosphere. Following this, MTJ sensor samples were then annealed successively at a temperature of 5000C for one hour, under a strong 400 mT magnetic field. 
Further, cross-sections of the MTJ sensor were cut, grounded and dimpled to miniature specimens of about 20nm. Subsequently, an argon ion-beam thinning process followed, and radiation damage was reduced by utilizing an incident beam incident at 4-60. The stated process helped in imaging observation in TEM and STEM. A conventional microscope was also utilized to take images for analysis. The specific images taken for both TEM and STEM were HRTEM and ABF STEM, respectively. 
 

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