Metal samples in small dimensions (few µm and less) show different mechanical behavior compared to bulk material. This mechanical size effect, which is important for miniaturized devices and the fundamental understanding of deformation behavior, is still not fully understood. Since it is determined by the movement and interaction of dislocations, these mechanisms should be further investigated. Transmission electron microscopy (TEM) is a powerful tool that can be used to image and further analyze dislocations and the use thereof is a logical choice for these studies. In this work a focused ion beam (FIB) workstation was used to manufacture micromechanical tensile samples (3x3x15µm) from single crystalline bulk copper. After in situ tensile testing in the scanning electron microscope the FIB was used to thin interesting areas to electron transparency. These were then analyzed in the TEM. Furthermore the dislocation density of the single crystalline bulk material was determined. This work shows the formation of a subgrain at a glide plane which lead to the shut down of a source that was important for deformation. The analysis of another sample in the region near the sample head reveals the accumulation of dislocations with the same burgers vector on the primary slip system. Their existence is due to the fact that they cannot exit the sample because the glide planes run through the sample head. The results of µLaue experiments are congruent with those found in this work.