<P> Once inserted into a TEM, the sample has to be manipulated to locate the region of interest to the beam, such as in single grain diffraction, in a specific orientation . To accommodate this, the TEM stage allows movement of the sample in the XY plane, Z height adjustment, and commonly a single tilt direction parallel to the axis of side entry bolders . Sample rotation may be available on specialized diffraction holders and stages . Some modern TEMs provide the ability for two orthogonal tilt angles of movement with specialized holder designs called double - tilt sample holders . Some stage designs, such as top - entry or vertical insertion stages once common for high resolution TEM studies, may simply only have X-Y translation available . The design criteria of TEM stages are complex, owing to the simultaneous requirements of mechanical and electron - optical constraints and specialized models are available for different methods . </P> <P> A TEM stage is required to have the ability to hold a specimen and be manipulated to bring the region of interest into the path of the electron beam . As the TEM can operate over a wide range of magnifications, the stage must simultaneously be highly resistant to mechanical drift, with drift requirements as low as a few nm / minute while being able to move several μm / minute, with repositioning accuracy on the order of nanometers . Earlier designs of TEM accomplished this with a complex set of mechanical downgearing devices, allowing the operator to finely control the motion of the stage by several rotating rods . Modern devices may use electrical stage designs, using screw gearing in concert with stepper motors, providing the operator with a computer - based stage input, such as a joystick or trackball . </P> <P> Two main designs for stages in a TEM exist, the side - entry and top entry version . Each design must accommodate the matching holder to allow for specimen insertion without either damaging delicate TEM optics or allowing gas into TEM systems under vacuum . </P> <P> The most common is the side entry holder, where the specimen is placed near the tip of a long metal (brass or stainless steel) rod, with the specimen placed flat in a small bore . Along the rod are several polymer vacuum rings to allow for the formation of a vacuum seal of sufficient quality, when inserted into the stage . The stage is thus designed to accommodate the rod, placing the sample either in between or near the objective lens, dependent upon the objective design . When inserted into the stage, the side entry holder has its tip contained within the TEM vacuum, and the base is presented to atmosphere, the airlock formed by the vacuum rings . </P>

What form of transmission is most resistant to transmission errors