Increase Of Space Charge Density Research Articles

Dynamic interplay between thionine and DNA under carbon ion irradiation: a real-time first-principles study

Understanding the interactions between deoxyribonucleic acid (DNA) and photosensitizer under ion irradiation benefits the development of aptasensors, DNA biosensors and cancer diagnosis. Using real-time time-depended density functional theory, by simulating high-energy C ion passing through DNA with poly(dG)·poly(dC) sequence and that with embedded thionine (3,7-diamino-5-phenothiazinium, TH), we compared the electronic stopping power (ESP), evolution of the structure and charge, and absorption spectrum. TH inserting leads the increase in space charge density, a larger electron de-excitation and a larger ESP, but the speed corresponding to the maximum ESP is almost same. When C ion passes through TH–DNA, the structure of TH slightly changes and there still exists noncovalent interaction between TH and DNA, but the absorption coefficient depends on the electron occupied state of TH when the ion passes through. These results indicate that at low radiation doses, TH still can be a DNA detector, although its response wavelength and intensity have been slightly changed, and provide a theoretical reference to improve the possible application of phenothiazine dye in DNA biosensor under ion irradiation.

Effects of sub-bandgap illumination on electrical properties and detector performances of CdZnTe:In

The effects of sub-bandgap illumination on electrical properties of CdZnTe:In crystals and spectroscopic performances of the fabricated detectors were discussed. The excitation process of charge carriers through thermal and optical transitions at the deep trap could be described by the modified Shockley-Read-Hall model. The ionization probability of the deep donor shows an increase under illumination, which should be responsible for the variation of electrical properties within CdZnTe bulk materials with infrared (IR) irradiation. By applying Ohm's law, diffusion model and interfacial layer-thermionic-diffusion theory, we obtain the decrease of bulk resistivity and the increase of space charge density in the illuminated crystals. Moreover, the illumination induced ionization will further contribute to improving carrier transport property and charge collection efficiency. Consequently, the application of IR irradiation in the standard working environment is of great significance to improve the spectroscopic characteristics of CdZnTe radiation detectors.

Optimal width of barrier region in X/γ-ray Schottky diode detectors based on CdTe and CdZnTe

The spectral distribution of quantum detection efficiency of X- and γ-ray Schottky diodes based on semi-insulating CdTe or Cd0.9Zn0.1Te crystals is substantiated and obtained in analytical form. It is shown that the width of the space charge region (SCR) of 6–40 μm at zero bias in CdTe (Cd0.9Zn0.1Te) Schottky diode is optimal for detecting radiation in the photon energy range above 5–10 keV. Based on the Poisson equation, the relationship between the SCR width and the composition of impurities and the degree of their compensation are investigated. It is shown that the presence of deep levels in the bandgap leads to a considerable increase in space charge density and electric field strength near the crystal surface. However, this effect contributes a small error in the determination of the SCR width using the standard formula for the Schottky diode. It is also shown that the concentration of uncompensated impurities in CdTe and Cd0.9Zn0.1Te crystals within the 4 × 1011–1013 cm–3 range is optimal for the detection efficiency of X- and γ-rays in the photon high-energy range. The record-high values of energy resolution have been obtained in the spectra of 241Am, 57Co, 133Ba and 137Cs isotopes measured using CdTe crystals with Schottky diodes because the concentration of uncompensated donors in the CdTe crystals (1–2) × 1012 cm–3 falls on an interval of maximum detection efficiency. In the spectrum of 57Co isotope, the limiting energy resolution has been achieved.

Ultra High Resolution Linear Ion Trap Orbitrap Mass Spectrometer (Orbitrap Elite) Facilitates Top Down LC MS/MS and Versatile Peptide Fragmentation Modes

Although only a few years old, the combination of a linear ion trap with an Orbitrap analyzer has become one of the standard mass spectrometers to characterize proteins and proteomes. Here we describe a novel version of this instrument family, the Orbitrap Elite, which is improved in three main areas. The ion transfer optics has an ion path that blocks the line of sight to achieve more robust operation. The tandem MS acquisition speed of the dual cell linear ion trap now exceeds 12 Hz. Most importantly, the resolving power of the Orbitrap analyzer has been increased twofold for the same transient length by employing a compact, high-field Orbitrap analyzer that almost doubles the observed frequencies. An enhanced Fourier Transform algorithm—incorporating phase information—further doubles the resolving power to 240,000 at m/z 400 for a 768 ms transient. For top-down experiments, we combine a survey scan with a selected ion monitoring scan of the charge state of the protein to be fragmented and with several HCD microscans. Despite the 120,000 resolving power for SIM and HCD scans, the total cycle time is within several seconds and therefore suitable for liquid chromatography tandem MS. For bottom-up proteomics, we combined survey scans at 240,000 resolving power with data-dependent collision-induced dissociation of the 20 most abundant precursors in a total cycle time of 2.5 s—increasing protein identifications in complex mixtures by about 30%. The speed of the Orbitrap Elite furthermore allows scan modes in which complementary dissociation mechanisms are routinely obtained of all fragmented peptides.

Electrical Characterization of Phosphorus Doped Ion Beam Synthesised CoSi2/Si Schottky Barrier Diodes.

ABSTRACTThe current/voltage characteristics of ion beam synthesised CoSi2/Si (n - type) Schottky barrier diodes implanted with phosphorus to doses between 5 × 1012 and 2 × 1013 ions cm-2are examined after annealing at temperatures in the range 400° - 1000°C. For each dose of implanted phosphorus, the effective barrier height of the CoSi2/Si interface is successively reduced as the anneal temperature increases. The results of Secondary Ion Mass Spectroscopy (SIMS) analysis indicate that these changes are due to an increase in the space charge density at the interface. For lower annealing temperatures the increase in space charge density is attributed to activation of the phosphorus in the tail of the dopant distribution which extends across the CoSi2/Si interface. For higher annealing temperatures larger increases in the space charge density are attributed to a modified dopant distribution resulting from phosphorus diffusion and activation at the interface. For doses of 1 × 1014 P* cm-2and 2×1015P*cm2, ohrnie characteristics are seen after annealing at temperatures of 1000°C and 500°C respectively.

Dielectric properties of CsBr single crystals-effect of d.c. bias

The dielectric properties of CsBr single crystals, both virgin and γ-irrddiated have been measured as a function of frequency (103–105Hz), temperature (300–575 K) and d.c. bias (0–350 Vcm−1). γ-irradiation produces colour centres in these crystals and consequently an increase in space charge density is observed. D.c. bias has brought in considerable changes in dielectric constant (ϵ') and loss (tanδ) of these crystals particularly at low frequencies and high temperatures. An attempt has been made to understand these data qualitatively through barrier layer formation.

Two-dimensional numerical analysis of turn-off process in a GTO under inductive load

The turn-off process for a gate turn-off thyristor (GTO) with a shorted anode emitter is analyzed under an inductive load with high applied voltage using a two-dimensional numerical model. The role of the shorted anode emitter is discussed in conjunction with the current-flow lines. Furthermore, the behavior of plasma squeezing and the electric field under high applied voltage are investigated. Plasma squeezing during the storage period is relieved during the fall period due to the hole-current component generated overall of the center junction by the extension of the depletion layer. The hole-current component causes an increase in space-charge density which in turn generates a high electric field around the center junction. At the same time, the electron-current component causes a reduction in space-charge density in the n-base side. Therefore, the electric field under the cathode is lower than under the gate; however, its value becomes over 100 kV/cm. On the other hand, temperature rise is low.

Photovoltage profiling of hydrogenated amorphous Si solar cells

We have used Surface Photovoltage Profiling (SPVP) to study hydrogenated amorphous Si (a-Si:H) p-i-n solar cells grown on glass/conductive-transparent oxide (CTO) or stainless-steel substrates. This technique involves the measurement by a Kelvin Probe of photoinduced changes in the surface potential with respect to a fixed back contact as tha cahh is layers of a-Si:H are consistent with these interface voltages. The junctions of the solar cell are analyzed in terms of their barrier heights (obtained by measuring Δφ at very high illumination levels at low temperature), their depletion widths (obtained from the photovoltage profiling), and their space-charge densities (estimated from published density-of-states curves). The principal reasons for poor cells were found to be: (1) poor i/n junction photovoltages, and (2) the presence of a low- or zero-field region in the i layer, caused primarily by high space-charge densities and correspondingly narrow depletion widths, leading to poor minority carrier current collection and fill factor. Similar low- or zero-field regions can also exist in cells of very good quality (efficiency ∼10%), but their harmful effects can be compensated for by higher diffusion lengths. Such zero-field regions may also play a pivotal role in the optically induced degradation of a-Si:H solar cells; we have found that in an unstable cell prolonged illumination can produce a fivefold increase in space-charge density above that before illumination, with a concommitant decrease in p/i junction depeletion width.