  Nitrogen-Vacancy centers in diamond possess an electronic spin resonance that
strongly depends on temperature, which makes them efficient temperature sensor
with a sensitivity down to a few mK/$\sqrt{\rm Hz}$. However, the high thermal
conductivity of the host diamond may strongly damp any temperature variations,
leading to invasive measurements when probing local temperature distributions.
In view of determining possible and optimal configurations for diamond-based
wide-field thermal imaging, we here investigate, both experimentally and
numerically, the effect of the presence of diamond on microscale temperature
distributions. Three geometrical configurations are studied: a bulk diamond
substrate, a thin diamond layer bonded on quartz and diamond nanoparticles
dispersed on quartz. We show that the use of bulk diamond substrates for
thermal imaging is highly invasive, in the sense that it prevents any
substantial temperature increase. Conversely, thin diamond layers partly solve
this issue and could provide a possible alternative for microscale thermal
imaging. Dispersions of diamond nanoparticles throughout the sample appear as
the most relevant approach as they do not affect the temperature distribution,
although NV centers in nanodiamonds yield lower temperature sensitivities
compared to bulk diamond.
