Electrical Resistance Tomography of Conductive Thin Films

The Electrical Resistance Tomography (ERT) technique is applied to the measurement of sheet conductance maps of both uniform and patterned conductive thin films. Images of the sheet conductance spatial distribution, and local conductivity values are obtained. Test samples are tin oxide films on glass substrates, with electrical contacts on the sample boundary, some samples are deliberately patterned in order to induce null conductivity zones of known geometry while others contain higher conductivity inclusions. Four-terminal resistance measurements among the contacts are performed with a scanning setup. The ERT reconstruction is performed by a numerical algorithm based on the total variation regularization and the L-curve method. ERT correctly images the sheet conductance spatial distribution of the samples. The reconstructed conductance values are in good quantitative agreement with independent measurements performed with the van der Pauw and the four-point probe methods.Comment: IEEE Transactions on Instrumentation and Measuremen

A correlation noise spectrometer for flicker noise measurement in graphene samples

We present a high-resolution digital correlation spectrum analyzer for the measurement of low frequency resistance fluctuations in graphene samples. The system exploits the cross-correlation method to reject the amplifiers' noise. The graphene sample is excited with a low-noise DC current. The output voltage is fed to two two-stage low-noise amplifiers connected in parallel; the DC signal component is filtered by a high-pass filter with a cutoff frequency of 34 mHz. The amplified signals are digitized by a two-channel synchronous ADC board; the cross-periodogram, which rejects uncorrelated amplifiers' noise components, is computed in real time. As a practical example, we measured the noise cross-spectrum of graphene samples in the frequency range from 0.153 Hz to 10 kHz, both in two- and four-wire configurations, and for different bias currents. We report here the measurement setup, the data analysis and the error sources

Thermal emittance measurements of a cesium potassium antimonide photocathode

Thermal emittance measurements of a CsK2Sb photocathode at several laser wavelengths are presented. The emittance is obtained with a solenoid scan technique using a high voltage dc photoemission gun. The thermal emittance is 0.56+/-0.03 mm-mrad/mm(rms) at 532 nm wavelength. The results are compared with a simple photoemission model and found to be in a good agreement.Comment: APL 201

Ultrafast laser pulse heating of metallic photocathodes and its contribution to intrinsic emittance

The heating of the electronic distribution of a copper photocathode due to an intense drive laser pulse is calculated under the two-temperature model using fluences and pulse lengths typical in RF photoinjector operation. Using the finite temperature-extended relations for the photocathode intrinsic emittance and quantum efficiency, the time-dependent emittance growth due to the same photoemission laser pulse is calculated. This laser heating is seen to limit the intrinsic emittance achievable for photoinjectors using short laser pulses and low quantum efficiency metal photocathodes. A pump-probe photocathode experiment in a standard 1.6 cell S-band gun is proposed, in which simulations show the time dependent thermal emittance modulation within the bunch from laser heating can persist for meters downstream and, in principle, be measured using a slice emittance diagnostic

Site, artefacts and landscape: Prehistoric Borg in-Nadur, Malta

In the past decade, Computer Graphics have become strategic for the development of projects aimed at the interpretation of archaeological evidence and the dissemination of scientific results to the public. Among all the solutions available, the use of 3D models is particularly relevant for the reconstruction of poorly preserved sites and monuments destroyed by natural causes or human action. These digital replicas are, at the same time, a virtual environment that can be used as a tool for the interpretative hypotheses of archaeologists and an effective medium for a visual description of the cultural heritage as it is crosses linguistic barriers. In this paper, the methodology, aims and outcomes of a virtual reconstruction of the Borġ in-Nadur megalithic temple, carried out by Archeomatica Project of the University of Catania, are offered as a case study for a Virtual Archaeology of prehistoric Malta.peer-reviewe

Cold electron beams from cryo-cooled, alkali antimonide photocathodes

In this letter we report on the generation of cold electron beams using a Cs3Sb photocathode grown by co-deposition of Sb and Cs. By cooling the photocathode to 90 K we demonstrate a significant reduction in the mean transverse energy validating the long standing speculation that the lattice temperature contribution limits the mean transverse energy or thermal emittance near the photoemission threshold, opening new frontiers in generating ultra-bright beams. At 90 K, we achieve a record low thermal emittance of 0.2 $\mu$m (rms) per mm of laser spot diameter from an ultrafast (sub-picosecond) photocathode with quantum efficiency greater than $7\times 10^{-5}$ using a visible laser wavelength of 690 nm