In this work, we performed temperature-dependent studies of the THz transient amplitude FeCo waveformes, from a FeCo/graphene nanobilayer sample, triggered by fs pulsed laser in the 80–400 K range. We show that a due-twofold extension, in the range 80–300 K the amplitude increases with temperature and tends to saturate above this range. This dependence contrasts sharply with the temperature dependence of the FeCo film's magnetization, which shows a typical ferromagnetic (FM) trend with Curie temperature well above 400 K. We explain this discrepancy, as the presence of an antiferromagnetic (AFM) at the FeCo/graphene interface, which is associated with the native oxide formed at the FeCo surface. The Angle Resolved X-ray Photoelectron Spectroscopy studies of a bare FeCo film revealed coexistence of the metallic [Co(0), Fe(0)] and antiferromagnetic [Co(II)O and the Fe(III)2O3] phases, at the sample surface. The observation of the exchange bias in our magnetization hysteresis loop of a FeCo film confirms presence of an FM/AFM interface layer at the FeCo surface. In summary, we conclude that the temperature dependence of the THz transient amplitude is governed by the AFM phase.
Pancreatic ductal adenocarcinoma (PDAC) ranks among the malignancies with the highest fatality and morbidity rates. This is predominantly attributable to an absence of understanding the intricate and diverse microenvironment of the tumor. We use terahertz time-domain spectroscopy (THz-TDS) imaging in transmission geometry to probe ex-vivo the heterogenous microenvironment of the genetically modified murine PDAC tissue that closely resembles the PDAC heterogeneity in human malignancy. We introduced a maximum a-posteriori probability estimation algorithm to objectively the tumor’s heterogenous microenvironment using the average values of refractive index and absorption coefficient within the useable terahertz bandwidth as imaging markers. Direct comparison of stained histopathologic images and the refractive index and the absorption coefficient high-resolution, two-dimensional maps of the same PDAC samples confirms the high potential of the THz-TDS method for tumor tissue characterization.
We present a photodetector capable of detecting both optical and x-ray picosecond pulses, based on our in-house grown cadmium magnesium telluride (Cd,Mg)Te single crystals. We focused on a specific Cd0.97Mg0.03Te, In-doped crystal composition, because of its bandgap suitable for 800-nm-wavelength light detection and a single-picosecond optical photoresponse. The detector was fabricated as a planar metal-semiconductor-metal structure with interdigitated electrodes and exhibited a linear, Schottky-free, current-voltage characteristics with <40-pA dark current and up to 20-mA/W responsivity. The detector temporal resolution was measured to be ~200-ps full-width-at-half-maximum transient, in response of ~100-fs-wide pulses consisting of either optical (800-nm wavelength) or x-ray (4.5-keV) photons and was limited by the detector housing and 15-GHz bandwidth of the readout oscilloscope. The latter demonstrates the detector is suitable for coarse timing in x-ray free-electron laser/optical femtosecond pump-probe spectroscopy applications. We also demonstrated that due to its very high stopping power, the Cd0.97Mg0.03Te detector responded well to various nuclear gamma sources with energy ranging from 59.6-keV to 660-keV.
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