  Thermal energy atom scattering at a surface with grazing incidence conditions
is an innovative method for investigating dispersive atom-surface interactions
with potential application in quantum sensing interferometry. The complete
establishment of this technique would require a detailed peak analysis, which
has yet to be achieved. We examined peak-width fluctuations in atomic and
molecular beams diffracted by a grating under grazing incidence conditions.
Careful measurements and analyses of the diffraction patterns of He atoms and
D$_2$ molecules from three square-wave gratings with different periods and
radii of curvature enabled the identification of factors influencing the
variations in the width as a function of the grazing incidence angle. The
effects of macroscopic surface curvature, grating magnification, and beam
emergence are substantial under these conditions but negligible for incidence
angles close to the normal. Our results shed light on the phenomena occurring
in grazing incidence thermal energy atom scattering.
