Decoupling absorption and radiative cooling in mid-wave infrared bolometric elements.

We present a spectrally selective, passively cooled mid-wave infrared bolometric absorber engineered to spatially and spectrally decouple infrared absorption and thermal emission. The structure leverages an antenna-coupled metal-insulator-metal resonance for mid-wave infrared normal incidence photon absorption and a long-wave infrared optical phonon absorption feature, aligned closer to peak room temperature thermal emission. The phonon-mediated resonant absorption enables a strong long-wave infrared thermal emission feature limited to grazing angles, leaving the mid-wave infrared absorption feature undisturbed. The two independently controlled absorption/emission phenomena demonstrate decoupling of the photon detection mechanism from radiative cooling and offer a new design approach enabling ultra-thin, passively cooled mid-wave infrared bolometers.

Comparative analysis of the sensitivity of nanometallic thin film thermometers.

Thin film platinum resistive thermometers are conventionally applied for resistance thermometry techniques due to their stability and proven measurement accuracy. Depending upon the required thermometer thickness and temperature measurement, however, performance benefits can be realized through the application of alternative nanometallic thin films. Herein, a comparative experimental analysis is provided on the performance of nanometallic thin film thermometers most relevant to microelectronics and thermal sensing applications: Al, Au, Cu, and Pt. Sensitivity is assessed through the temperature coefficient of resistance, measured over a range of 10-300 K for thicknesses nominally spanning 25-200 nm. The interplay of electron scattering sources, which give rise to the temperature-dependent TCR properties for each metal, are analyzed in the framework of a Mayadas-Shatzkes based model. Despite the prevalence of evaporated Pt thin film thermometers, Au and Cu films fabricated in a similar manner may provide enhanced sensitivity depending upon thickness. These results may serve as a guide as the movement toward smaller measurement platforms necessitates the use of smaller, thinner metallic resistance thermometers.

Thermal Conductivity Enhancement in Ion-Irradiated Hydrogenated Amorphous Carbon Films.

Amorphous solids are traditionally assumed to set the lower bound to the vibrational thermal conductivity of a material due to the high degree of structural disorder. Here, were demonstrate the ability to increase the thermal conductivity of amorphous solids through ion irradiation, in turn, altering the bonding network configuration. We report on the thermal conductivity of hydrogenated amorphous carbon implanted with C+ ions spanning fluences of 3 × 1014-8.6 × 1014 cm-2 and energies of 10-20 keV. Time-domain thermoreflectance measurements of the films' thermal conductivities reveal significant enhancement, up to a factor of 3, depending upon the preirradiation composition. Films with higher initial hydrogen content provide the greatest increase, which is complemented by an increased stiffening and densification from the irradiation process. This enhancement in vibrational transport is unique when contrasted to crystalline materials, for which ion implantation is known to produce structural degradation and significantly reduced thermal conductivities.