  We present a method for preparing a single two-dimensional sample of a
two-spin mixture of fermionic potassium in a single antinode of an optical
lattice, in a quantum-gas microscope apparatus. Our technique relies on
spatially-selective microwave transitions in a magnetic field gradient.
Adiabatic transfer pulses were optimized for high efficiency and minimal atom
loss and heating due to spin-changing collisions. We have measured the dynamics
of those loss processes, which are more pronounced in the presence of a spin
mixture. As the efficient preparation of atoms in a single antinode requires a
homogeneous transverse magnetic field, we developed a method to image and
minimize the magnetic field gradients in the focal plane of the microscope.
