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Zr–N films were grown on glass substrates via radio-frequency magnetron sputtering using an Ar + N2 + H2 mixture. Hydrogen was employed in order to reduce oxygen contamination coming from background pressure, as confirmed by secondary ion mass spectroscopy analysis. The tuned process parameter was the nitrogen flux percentage (RN2) in the mixture. The crystallographic structure of the films was studied using x-ray diffraction. The measurements show that the films deposited at low RN2 (lower than or equal to 50%) crystallize in the rocksalt ZrN structure. As RN2 exceeds 50%, the film exhibits the co-presence of ZrN and Zr3N4 (denoted as o-Zr3N4) phases. When the deposition is performed in only nitrogen atmosphere (RN2 = 100%), a broad peak located at 2θ ≈ 32.2° is mainly attributed to the contribution coming from (320) planes of the o-Zr3N4. An envelope method, based on the optical reflection and transmission spectra taken at normal incidence, has been applied for the optical characterization of the nitride films. Such a method allows the determination of the samples’ average thickness and optical constants (refractive index n and extinction coefficient k) in the ultraviolet-visible-near infrared regions. The evaluated thickness was about 2500 nm, which is in good agreement with the value obtained from profilometry. The absorption coefficient α was calculated from reflectance and transmittance spectra. The energy bandgap ranges from 2.3 eV to 2.4 eV. Electrical characterization was performed using capacitance-voltage measurements, which showed that the films evolve from insulating to semiconductor behavior when the nitrogen content in the sputtering atmosphere is decreased, confirming structural and optical results.

This paper presents a new AlN-based MEMS devices suitable for vibrational energy harvesting applications. Due to their particular shape and unlike traditional cantilever which efficiently harvest energy only if subjected to stimulus in the proper direction, the proposed devices have 3D generation capabilities solving the problem of device orientation and placement in real applications. Thanks to their particular shape, the realized devices present more than one fundamental resonance frequencies in a range comprised between 500 Hz and 1.5 kHz, with a voltage generation higher than 300μV and an output power up to 0.4 pW for single MEMS device

A photoemission model for low work function coated metal surfaces and its experimental validationStudies of electron emission by photoelectric process from pure Zn cathodes by UV laser beams were performed. As UV sources, two different wavelength excimer lasers were utilized in order to investigate the photoemission as pure photoelectric process and multiphoton process. The Schottky effect was also considered. The utilized laser sources were a KrF operating at 248 nm wavelength ͑5 eV͒, 23 ns full width at half maximum ͑FWHM͒, and a XeCl operating at 308 nm wavelength ͑4.02 eV͒, 10 ns FWHM. The cathode work function was 4.33 eV, a value lower and higher than the photon energies of KrF and XeCl lasers, respectively. The photocathodes were tested in a vacuum photodiode cell at 10 −7 mbar. The cathodes were irradiated at normal incidence and the anode-cathode distance was set to 3.7 mm. Due to the electrical breakdown into the photodiode gap, the maximum applied accelerating voltage was 20 kV. Under the above experimental conditions a maximum of 5.4 MV/ m electric field resulted. Under the space charge effect, the electron emission was higher than the one expected by the Child-Langmuir law. In saturation regime the electron emission increased with the accelerating voltage owing to the Schottky effect and plasma formation. The highest output current was achieved with the KrF laser at 14 mJ laser energy. Its value was about 12 A, corresponding to a global quantum efficiency of approximately 1 ϫ 10 −4 , while the temporal quantum efficiency presented a maximum value of 1.1ϫ 10 −4 located at the tail of the laser pulse. The estimated efficiencies with the XeCl laser were lower than the KrF ones as well as the output current and the plasma formation, although higher energy values than the KrF ones were utilized. By the results obtained, we conclude that the plasma generation is strongly due to the extracted current but weakly to the used laser intensity.

In this paper, we report investigations of the electron emission from pure Zn cathodes irradiated by UV laser pulses of 23 ns (full-width at half-maximum) at a wavelength of 248 nm (5 eV). The metal cathodes were tested in a vacuum photodiode chamber at 10 −5 Pa. They were irradiated at normal incidence and the anode-cathode distance was set at 3 mm. The maximum applied accelerating voltage was 18 kV, limited by the electrical breakdown of the photodiode gap. Under the above experimental conditions, a maximum applied electric field of 6 MV/m resulted. In the saturation regime, the measured quantum efficiency value increased with the accelerating voltage due to the plasma formation. The highest output current was achieved with 14 mJ laser energy, 18 kV accelerating voltage and its value was 12 A, corresponding to a global quantum efficiency (GQE) approximately of 1 × 10 −4 . The temporal quantum efficiency was 1.0 × 10 −4 at the laser pulse onset time and 1.4 × 10 −4 at the pulse tail. We calculated the target temperature at the maximum laser energy. Its value allowed us to obtain output pulses of the same laser temporal profile. Tests performed with a lower laser photon energy (4.02 eV) demonstrated a GQE of two orders of magnitude lower.