Absence of Kondo resonance in high-resolution photoemission spectra of monocrystallineFe1−xCoxSi

${\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Co}}_{x}\mathrm{Si}$ single crystals with different Co concentrations were grown using the tri-arc Czochralski technique. Samples with 0, 5, and $20\phantom{\rule{0.3em}{0ex}}\mathrm{at.}\phantom{\rule{0.2em}{0ex}}%$ of Co were studied with photon energies of 21.2 and $40.8\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ with spectral resolutions as high as $8\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$ at the Fermi level. For FeSi, a full gap of $28\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$ has been found, which closes with 5% of Co. In the range between 20 and $150\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, energy dependent angle-resolved measurements in the [111] direction were made for FeSi. Through a comparison with theoretical calculations, the states at the Fermi energy can be directly assigned to $\mathrm{Fe}\phantom{\rule{0.2em}{0ex}}3d$ states. No sign of Kondo resonance is found.