In the double-slit experiment with single electrons, the behavior of individual electrons is described by a probability wave. This wave determines the likelihood of finding an electron at different positions on the screen. The wave can interfere with itself, leading to an interference pattern on the screen.
If we consider a situation where the two slits are close together, such that there is a material between them, it is possible for some electrons to hit the screen behind this material. However, the probability of electrons reaching that region is typically low, as the material acts as a barrier that reduces the probability of an electron passing through it.
The interference pattern observed on the screen in the double-slit experiment is a result of the constructive and destructive interference of the electron's probability wave. The regions of constructive interference correspond to bright spots on the screen, while regions of destructive interference correspond to dark spots.
While it is possible for a few electrons to hit the screen behind the material, the majority of electrons will exhibit the interference pattern associated with the double-slit experiment. The pattern emerges due to the probabilistic nature of quantum mechanics, where the electrons behave as both particles and waves simultaneously.