Photoemission tuning of nanodiamond particles treated in variable percentages of H2H_2-N2N_2 plasmas

This work deals with photochatodes (PCs) based on as-received and treated nanodiamond (ND) particles, 250 nm in size. The aim of this study is the hydro-, hydro-/nitro- and nitro-genation of NDs performed in microwave plasmas adding different $N_2$ percentages (0, 50 and 100 %) to pure $H_2$ gas. Untreated and treated NDs are dispersed in solvents such as 1,2-dichloroethane and deionized water, and then deposited, as continuous layers, on p-Si and kapton substrates by the pulsed spray technique. The produced layers are characterized by Raman, photoluminescence spectroscopies and photoemission measurements. The quantum efficiency (QE), a merit figure for photocathodes, is assessed in the UV spectral range from 146 to 210 nm. The results show an enhancement of the photoemission for PCs based on hydro-, hydro-/nitro- and nitro-genated NDs that exhibit at 146 nm QE values of about 23, 21 and 13 %, respectively. The advantage of nitrogenated PCs is the good stability to air exposure against their lowest QE values

Analysis of the Radish Seed Germination and Growth by Radiofrequency Stresses

In this work we report a study on the behavior of radish seed (Raphanus sativum L.) germination and growth under radiofrequency stresses. Groups of uniform seeds were irradiated at five duration time values of 60, 210, 375, 470 and 830 h at medium frequency of 1 Mhz, (MF/1), (MF/2), (MF/3), (MF/4) and (MF/5), respectively; at very high frequency of 100 Mhz, (VHF/1), (VHF/2) f(VHF/3), (VHF/4) and (VHF/5), respectively; at ultra high frequency of 900Mhz, (UHF/1), (UHF/2), (UHF/3), (UHF/4) and (UHF/5), respectively. The exhibited magnetic field for the three frequencies was of about 240 nT and the associate electric field inside the samples was less than 71 V/m, owing to the electric permittivity exposed sample. Another group of uniform radish seeds, irradiated by static magnetic (SM) field of 80 mT for the same time duration, was used as comparison, whereas untreated ones were used as control. The results showed that all physical stresses induced by magnetic fields did not have effect on seed germination as well as on cell elongation growth of the radish hypocotyls. On the contrary, a stimulating effect was observed on root growth

Production and Extraction of Protons by Solid Hydrogenated Targets via UV Laser Ablation

In this work we present the preliminary investigations about the production of proton beams by pulsed laser ablation of solid disks produced by compressed Titanium dihydride powder. The laser we used was an excimer KrF, operating at low intensity and ns pulse duration. The ion emission was analyzed by the time-of-flight technique using a Faraday cup as ion collector. We performed studies on the produced plasma for different laser fluence values and accelerating voltage. In free expansion mode we obtained protons and titanium ions having kinetic energy of some hundred of eV; by applying a postaccelerating voltage we obtained beams up to 15 keV

Effect of temperature on the physical, optical and photocatalytic properties of TiO2 nanoparticles

In this paper we describe the effect of calcination temperature on the structural, morphological, optical and photocatalytic properties of TiO2 nanoparticles. The titanium dioxide powders were produced by the sol–gel method starting from titanium tetraisopropoxide (TTIP) in neutral aqueous medium (pH 5.5). After that, the TiO2 nanoparticles were treated at three different calcination temperatures for 4 h: 100, 450 and 800 °C. Then, the powders were characterized by XRD, Raman and photoluminescence techniques. We observed the anatase phase for the powders treated at 100 and 450 °C and rutile for that treated at 800 °C. The photocatalytic activity of the TiO2 powders was investigated using Methylene Blue test and showed a strong correlation with the temperature (i.e. TiO2 phase). The better photocatalysis exhibited by the nanoparticles treated at 100 and 450 °C compared to the powder at 800 °C was due to the higher recombination of photo-generated electrons and holes of rutile with respect to anatase

Determination of recombination length of a non-equilibrium plasma produced by laser ablation

An experimental study of the laser ablation produced plasma evolution is necessary for its deeper understanding, since plasma expansion has both spatially and temporally varying characteristics. We irradiated a Cu target with a KrF laser beam. A small Faraday cup array and an axial Faraday cup were used as diagnostic systems, in order to study the spatial variation in the total charge carried by plasma ions. Charge loss during the plasma expansion was observed, which was attributed to the charged species recombination. This occurred upstream to the critical distance where the plasma density is high enough. Downstream the critical distance the plasma particles collisions were negligible and the ion charge remained frozen. In these experiments it was observed that the critical distance for charge recombination was a function of laser fluence

Biomedical prostheses coated by tailored MWPECVD nanocrystalline diamond films

Different aspects concerning the use of nanocrystalline diamond (NCD) film, as coating for biomedical prostheses, is discussed. An overview is done on diamond implementation in prostheses, on the NCD mechanical properties and on the technological aspects concerning the NCD growth process i.e. Microwave Plasma Enhanced Chemical Vapor deposition. Then, the attention is focused on a possible improvement of NCD growth on titanium (Ti) substrate. Further, a theoretical study by finite element method is discussed in order to model the adhesion properties of a NCD layer on Ti and Ti/Titanium Carbide (TiC) substrates. The goal of the proposed work is to provide a study about the use of thin NCD coating on Ti based prostheses. The function of the NCD coating on Ti material is to improve the implanted prosthesis with a long duration time, thus decreasing the total costs and the invasive surgery treatments

Short Soft X-Ray Sources

EnWe report on the characterization of pulsed soft X-rays emitted from laser-produced plasma. The plasma was generated by 40, 80 and 120 mJ laser energies provided by a pulsed KrF excimer laser focused on pure Si, Cu and Ta targets. The utilized detector was a very sensitive Faraday cup which opportunely biased was able to record time resolved signals of X-rays and to estimate their energy. The found X-rays energy values were compared with the ion temperature of the plasma obtained by fitting the time resolved ion current signals with a shifted Maxwell-Boltzmann velocity distribution. The results showed that the laser produced Ta plasma induced bunch of X-rays having in average the highest energy values and it was also characterized by ion temperature higher than the ones of the laser produced Si and Cu plasmas

Effects of physical stresses on radish seed germination and growth

In this work we explore the consequences on variable magnetic fields applied to radish seeds (Raphanus sativum L.) on germination and seedling growth. Three, different alternate magnetic fields have been tested having a high intensity, 40 mT, at very low frequency, 0.2 Hz (B0.2), a low intensity, 577 µT, at low frequency, 370 kHz (B370), and a very low intensity, about 250 nT, at ultra high frequency, 900 MHz (RF900). These last generate electromagnetic waves which are nowadays very used for mobile communications. Groups of uniform radish seeds were exposed to alternate magnetic fields at three duration time values: i) 120 h (BO.2/1), 260 h (B0.2/2) and 360 h (B0.2/3) at high intensity and very low frequency, 0.2 Hz; ii) 120 h (B370/1), 260 h (B370/2), 360 h (B370/3) at low intensity and low frequency, 370 kHz; iii) 120 h (RF/1), 260 h (RF/2), 360 h (RF/3) at very low intensity and ultra high frequency, 900 MHz. Furthermore, another group of seeds was treated by laser beams of 248 nm wavelength whose magnetic field is coupled to an electric field. These two fields, by the Planck theory, origin the quantum energy, expresses by photons. Therefore, in the laser-matter interaction photons are absorbed dependent on laser shots. Again, we performed experiments at three duration time values that applied: 30 kshots (KrF/1), 80 kshots (KrF/2) and 135 kshots (KrF/3) at 40 mJcm2/ fluence. The magnetic field and electric field presented by the laser beam are approximatively 250 kVm/ and 850 µT, respectively. All treatments were performed at room temperature. Both untreated seeds and each group of seeds exposed to the physical stresses were transferred in Petri dishes and followed for their germination and seedling growth up to 96 h. The results showed that all physical stresses induced by alternate magnetic fields, radiofrequency and laser radiations did not have effect on seed germination as well as on cell elongation growth of the radish hypocotyls in comparison to control seeds. On the contrary, all physical stresses showed a significate stimulation on root growth

Electron beams produced by innovative photocathodes based on nanodiamond layers

The investigation of two different photocathodes (PCs) based on nanodiamond (ND) layers, irradiated by a KrF nanosecond excimer laser (wavelength, \ensuremath{\lambda}=248\text{ }\text{ }\mathrm{nm}; photon energy, ${E}_{\mathrm{Ph}}=5\text{ }\text{ }\mathrm{eV}$) is reported. The ND layers were deposited by means of a pulsed spray technique. Specifically, the active layer of each PC consisted of untreated (as-received) and hydrogenated ND particles, 250 nm in size, sprayed on a $p$-doped silicon substrate. The ND-based photocathodes were tested in a vacuum chamber at {10}^{\ensuremath{-}6}\text{ }\text{ }\mathrm{mbar} and compared to a Cu-based one, used as reference. All the photocathodes were irradiated at normal incidence. The quantum efficiency (QE) of the photocathodes was assessed. QE values of the ND-based photocathodes were higher than that of the reference one. In particular, the hydrogenated ND-based PC exhibited the highest QE due to the negative electron affinity that results from the surface terminated by hydrogen. Additionally, the photocathode surface/local temperature and the multiphoton process contribution to the electron emission were studied