Low-power-loss and high voltage X-ray tube with graphite nanospines cold cathode

We report a low-power-loss and high voltage X-ray tubes with a graphite nanospines (GNS) cold cathode. The cathode is encapsulated in a glass tube having a Beryllium window with a Tantalum film to generate X-rays. The internal tube pressure was below 10⁻⁷ Pa and a tube current exceeding 1 mA at a tube voltage of 22.9 kV was observed in the fabricated X-ray tube. The tube current dispersion, defined as standard deviation/mean (σ/mean), was relatively small at 2.4%. An X-ray radiation dose rate exceeding 5 Sv/h was obtained from the X-ray tube and the radiation dose rate dispersion was also small (σ/mean=0.3%). As an application of the X-ray tube, we demonstrated radiography for the rapid inspection of organic products.     

Greatly enhanced infrared normal spectral emissivity of microstructured silicon using a femtosecond laser

The infrared normal spectral emissivity of microstructured silicon prepared by femtosecond laser irradiation in SF₆ was measured for the wavelength range 2.5 μm to 25 μm. Greatly enhanced emissivity compared to that of flat silicon was observed over the entire wavelength range. For a sample with 13-14 μm high spikes, the emissivity at a temperature of 100 °C is approximately 0.96. The emissivity decreases slightly in the wavelength region above 8 μm, but remains higher than 0.9 over most of the measured wavelength range. Also the average emissivity is less than Nextel- Velvet-811-21 Coating, it can be used stably at more wide temperatures from 100 °C to 400 °C. These results show the potential for microstructured silicon to be used as a flat blackbody source or silicon-based pyroelectric and microbolometer devices.     

Electronic parameters of high barrier Au/Rhodamine-101/n-Inp Schottky diode with organic ?nterlayer

In this work, we present that Rhodamine-101 (Rh-101) organic molecules can control the electrical characteristics of conventional Au/n-InP metal-semiconductor contacts. An Au/n-InP Schottky junction with Rh-101 interlayer has been formed by using a simple cast process. A potential barrier height as high as 0.88 eV has been achieved for Au/Rh-101/n-InP Schottky diodes, which have good current-voltage (I-V) characteristics. This good performance is attributed to the effect of formation of interfacial organic thin layer between Au and n-InP. By using capacitance-voltage measurement of the Au/Rh-101/n-InP Schottky diode the diffusion potential and the barrier height have been calculated as 0.78 V and 0.88 eV, respectively. From the I-V measurement of the diode under illumination, short circuit current and open circuit voltage have been extracted as 1.70 μA and 240 mV, respectively.     

Optimization of parameters for silicon planar source of modulated infrared radiation

We report on the performance of planar silicon diodes operating in the double injection mode and emitting modulated infrared radiation at temperature range above 300 K. Results present theoretical analysis and experimental verification of an optimization aimed at maximal difference between emissivity of this structure for cases with and without forward bias applied to p-n junction. Several advantages of the structures were shown: wide emission spectrum (3÷12 μm), short rise-fall time (300 μs), high operating temperature (≈400 K). These planar photonic sources can be used as easily controlled sources of modulated infrared radiation in wide spectral range, image simulators, e.g. dynamic scene simulation devices with frame frequencies well above 200 Hz and for measurements of thermovision camera dynamic parameters.     

Study of SHI induced recrystallization effects in SOI structures synthesized by nitrogen and oxygen ion implantation in silicon

Silicon oxynitride (Si_xO_yN_z) buried insulating layers were synthesized by implantation of nitrogen (¹⁴N⁺) and oxygen (¹⁶O⁺) ions sequentially in the ratio 1:1 at 150 keV to ion-fluences ranging from 1 × 10¹⁷ to 5 × 10¹⁷ cm⁻² to prepare silicon on insulator (SOI) structures. The as implanted samples were held at 270 °C and irradiated to total fluence of 1 × 10¹⁴ cm⁻² by 60 MeV Ni⁺⁵ to study the structural changes/recrystallization of SOI structures induced by swift heavy ion (SHI) irradiation. Fourier transform infrared (FTIR) measurements on the as implanted samples (≤1 × 10¹⁸ cm⁻²) show a single absorption band in the wavenumber range 1300-750 cm⁻¹ attributed to the formation of silicon oxynitride (Si-O-N) bonds in the implanted silicon. It is observed that a nitrogen rich silicon oxynitride structure is formed after SHI irradiation. The study of X-ray rocking curves on the samples show the formation of small silicon crystallites due to swift heavy ion irradiation.     

Studies of semitransparent optoelectronic position sensors

Semitransparent optoelectronic position sensors (ALMY sensors) have been developed for high-precision multipoint position and angle measurements of collimated laser beams over a large measurement range. The sensors provide a position resolution in the order of a micrometer over sensitive areas of several square centimeters. They consist of a thin film of amorphous silicon deposited on a glass substrate between two transparent layers of crossed strip electrodes. A transmittance of 80%-90% has been achieved for 780-nm laser light produced by diode lasers. We report about recent optimizations of the sensor performance and tests of the long-term stability under laser illumination and of the radiation tolerance at high neutron doses. As expected, the radiation hardness of the amorphous silicon sensors exceeds the one of crystalline silicon devices. The custom-designed readout electronics allow for operation at sufficiently low laser intensities in order to prevent significant degradation of the performance of the amorphous silicon sensors under illumination with laser light.     

Influence of the diamond grain size on the electrical properties of nano-crystalline diamond film detectors

In this work, we developed X-ray radiation detectors with sandwich structure fabricated from nano-crystalline diamond (NCD) films. These NCD films with different grain size ranging from 15 nm to 160 nm were grown on silicon substrates using a hot-filament chemical vapor deposition technique. I-V measurement results indicate that with reducing of the grain size, the resistivity of diamond films decreases from 9.5 × 10⁸ to 6.20 × 10⁷ Ω cm and the ratio of the photocurrent to the dark-current (I_ph/I_d) of the detectors decreases rapidly from 0.45 to 0.09 at an electric field of 50 kV/cm. Typical spectral response to 5.9 keV ⁵⁵Fe X-rays shows that counting efficiency and energy resolution of NCD detectors with large grains are better than those of detectors with small grains, due to the less defects and grain-boundaries contained in the film.     

Structure, hardness and thermal stability of TiAlN and nanolayered TiAlN/CrN multilayer films

TiAlN films were deposited on silicon (1 1 1) substrates from a TiAl target using a reactive DC magnetron sputtering process in Ar+N₂ plasma. Films were prepared at various nitrogen flow rates and TiAl target compositions. Similarly, CrN films were prepared from the reactive sputtering of Cr target. Subsequently, nanolayered TiAlN/CrN multilayer films were deposited at various modulation wavelengths (Λ). X-ray diffraction (XRD), energy dispersive X-ray analysis, nanoindentation and atomic force microscopy were used to characterize the films. The XRD confirmed the formation of superlattice structure at low modulation wavelengths. The maximum hardness of TiAlN/CrN multilayers was 3900 kg/mm², whereas TiAlN and CrN films exhibited maximum hardnesses of 3850 and 1000 kg/mm², respectively. Thermal stability of TiAlN and TiAlN/CrN multilayer films was studied by heating the films in air in the temperature range (T_A) of 500-900 °C for 30 min. The XRD spectra revealed that TiAlN/CrN multilayers were stable up to 800 °C and got oxidized substantially at 900 °C. On the other hand, the TiAlN films were stable up to 700 °C and got completely oxidized at 800 °C. Nanoindentation measurements performed on the films after heat treatment showed that TiAlN retained a hardness of 2200 kg/mm² at T_A=700 °C and TiAlN/CrN multilayers retained hardness as high as 2600 kg/mm² upon annealing at 800° C.     

Modification of radiation hardness of silicon <Emphasis Type="Italic">p</Emphasis>-<Emphasis Type="Italic">n</Emphasis> junction photodiodes by hydrogen plasma treatment

The influence of treatment by a low energy hydrogen ions on degradation of the spectral response, diffusion length of minority carriers (L_D) and efficiency (η) of silicon p-n junction photodiodes (solar cells without antireflective coatings) under the effect of electron irradiation has been investigated. Evaluation of the radiation hardness was made by subjecting the unhydrogenated and hydrogenated photodiodes to 1 MeV electron irradiation with doses of (0.1÷3) × 10¹⁵ cm^-2. The measurements have shown that pre-hydrogenation of the silicon p-n junction devices significantly decreases the degradation rate of L_D and η thereby improving their radiation hardness.     

Fabrication of p-type ZnO nanowires based heterojunction diode

Vertically aligned p-type ZnO (Li–N co-doped) nanowires have been synthesized by hydrothermal method on n-type Si substrate. X-ray diffraction pattern indicated a strong peak from (0 0 0 2) planes of ZnO. The appearance of a strong peak at 437 cm⁻¹ in Raman spectra was attributed to E₂ mode of ZnO. Fourier transformed infrared studies indicated the presence of a distinct characteristic absorption peaks at 490 cm⁻¹ for ZnO stretching mode. Compositional studies revealed the formation of Li–N co-doped ZnO, where Li was bonded with both O and N. The junction properties of p-type ZnO nanowires/n-Si heterojunction diodes were evaluated by measuring I–V and C–V characteristics. I–V characteristics exhibited the rectifying behavior of a typical p–n junction diode.     

Growth and properties of transparent p-NiO/n-ITO (In2O3:Sn) p-n junction thin film diode

We have grown “all oxide” transparent p-n junction thin film nanostructure device by using chemical solution deposition and E-beam evaporation onto SiO₂ substrate. Combined grazing incidence X-ray diffraction and atomic force microscopy confirm phase pure, mono-disperse 30 nm NiO and 2 at. wt.% Sn doped In₂O₃ (ITO) nanocrystallites. Better than 70% optical transparency, at a wavelength of 600 nm, is achieved across 160 nm thick p-n junction. The optical band gap across the junction was found to decrease as compared to the intrinsic ITO and NiO. The current-voltage (I-V) characteristics show rectifying nature with dynamic transfer resistance ratio of the order of 10³ in the forward bias condition. Very small reverse leakage current with appreciable breakdown was observed under the reverse bias condition. The observed optical and electrical properties of oxide transparent diode are attributed to the heteroepitaxial nature and carrier diffusion at the junction interface.     

Characterization of electron irradiated GaN n-p diode

Electron-beam irradiated GaN n⁺-p diodes were characterized by deep level transient spectroscopy (DLTS) and optical responsivity measurements. The GaN n⁺-p diode structures were grown by metal organic chemical vapor deposition technique, and the electron irradiation was done by the energies of 1 MeV and 2 MeV with dose of 1 × 10¹⁶ cm^− 2. In DLTS measurement, the defect states of E_c − 0.36 eV and E_c − 0.44 eV in the electron irradiated diodes appeared newly. The optical responsivity of GaN n⁺-p diode was characterized in ultra-violet region, and then the maximum optical responsivity at 350 nm was decreased after electron-beam irradiation.     

A novel ozone detection at room temperature through UV-LED-assisted ZnO thick film sensors

In this work a novel ozone detection at room temperature (RT) has been investigated. Two functional materials, ZnO and (W_0.9Sn_0.1)O_3 − x (WS10) oxides, have been synthesized to prepare thick film gas sensors, both used in conventional heated mode as well as at RT assisted by UV irradiation. As a source of light, a light emitting diode (LED) of 400 nm peak wavelength was used. Under typical operating conditions of the UV-LED, the radiation flux density ? over the sensor was of about 5 · 10¹⁷ photons/cm². Powders and films have been characterized by means of TG-DTA, SEM, TEM and XRD. Finally, electrical measurements have been performed on sensing films with the aim to compare conductive properties, surface barrier heights and ozone sensing features with and without UV irradiation. Despite the fact that two types of conventional heated sensors offered quite similar results with respect to ozone sensing, it turned out that, at RT and with the assistance of UV light, ZnO behaved excellently fast detecting ozone at concentrations down to 10 ppb, while for WS10 under the same operating conditions an opposite result was observed, i.e. very low response and long response time.     

Investigation of the tribological behavior and its relationship to the microstructure and mechanical properties of a-SiC:H films elaborated by low frequency plasma assisted chemical vapor deposition

Amorphous hydrogenated silicon carbide (a-SiC:H) coatings are promising candidates for tribological applications in the mechanical and aeronautical industries. Alternately high values of hardness H (15 < H < 32 GPa) and elastic modulus E contribute to their good wear resistance as well as to a low friction coefficient. The latter has been found to vary in the range 0.1 < μ < 0.65, depending upon the microstructure of the layers. The roughness of the films determined by atomic force microscopy is in all cases low (Ra ~ 5 nm). Comparisons between the tests carried out in air and those performed under vacuum conditions point to a substantial role of the adhesive part of the friction coefficient in vacuum. They also highlight the role played by the transfer layer between the film and the pin in producing a low friction coefficient for several coatings. This transfer layer consists chiefly of silicon and oxygen (O/Si ~ 2), whilst low quantities of carbon are also present.     

Gamma-ray irradiation experiment of turbo molecular pump

A turbo molecular pump which can be operated when exposed to high radiation has been under development at Japan Atomic Energy Research Institute (JAERI) and Osaka Vacuum Ltd., for use in the 3 GeV-RCS of the J-PARC project. The target irradiation dose is 30 MGy. In order to determine the extent of radiation damage to the pump, gamma-ray irradiation testing was performed at JAERI. It was found that the turbo molecular pump could operate properly when given an absorption dose less than 3.5 MGy in a gamma-ray irradiation environment. Since the elasticity of elastomer vacuum seals decreases when exposed to radiation, leaks occur. Other components, for example motor coil, control sensor, etc., retained their high performance even when given more than a 7 MGy absorption dose. The outgassing rate of the cable was measured before and after irradiation.     

Studies on the growth and physical properties of nonlinear optical crystal: 2-Amino-5-nitropyridinium-toluenesulfonate

Single crystals of 2-amino-5-nitropyridinium-toluenesulfonate (2A5NPT) were grown by the slow cooling method. The unit cell dimensions were determined from single crystal X-ray diffraction studies. The thermal parameters - thermal diffusivity (α), thermal effusivity (e), thermal conductivity (K) and heat capacity (C_p) of 2A5NPT were measured by an improved photopyroelectric technique at room temperature. Single and multiple shot experiments performed on the grown crystals for the second harmonic of pulsed Nd:YAG laser (532 nm) show that it exhibits a high laser damage threshold which is a favorable property for nonlinear optical applications. Dielectric constant and dielectric loss of the grown crystal were evaluated for the frequency range 1 kHz-1 MHz in the temperature region 40-130 °C. Hardness values were measured using Vickers hardness measurement.     

Bias frequency dependence of pn junction charging damage induced by plasma processing

Plasma-induced charging damage to pn junction in metal-oxide-semiconductor field-effect transistors (MOSFETs) was studied by using an inductively coupled plasma (ICP) reactor with Ar gas. The junction leakage current (I_leak) was measured for various source/drain to well in MOSFETs and simple diode structures. Two different rf bias frequencies, 13.56 MHz and 400 kHz, were utilized to investigate the effect of frequency on an increase in I_leak. The I_leak of n⁺/p and p⁺/n junctions was found to increase by a plasma treatment. In particular, more severe damage was observed for n⁺/p junction in both n-channel MOSFETs and the diodes. These observed results imply that plasma plays a role primarily as a positive current source. With regard to the rf bias frequency effects, samples exposed to the 400-kHz plasma were found to suffer from larger I_leak than those to the 13.56 MHz. From capacitance-voltage (C-V) measurement of junction capacitance changes, we also clarified that the observed increase in I_leak was attributed to the defect density at pn junction created by the plasma charging damage.     

Fabrication and characterization of transparent MEH-PPV/n-GaN (0 0 0 1) heterojunction devices

n-GaN/MEH-PPV thin film heterojunction diode was fabricated by depositing MEH-PPV thin film using spin-coating process on n-GaN (0 0 0 1). The junction properties were evaluated by measuring I-V characteristics. I-V characteristics exhibited well defined rectifying behavior with a barrier height of 0.89 eV and ideality factor of 1.7. The optical band gap of the MEH-PPV film using optical absorption method was found to be 2.2 eV and the fundamental absorption edge in the film is formed by the direct allowed transitions. At higher electric fields, the conductivity mechanism of the film shows a trap charge limited current mechanism. The obtained results indicate that the electronic parameters of the heterojunction diode are affected by properties of MEH-PPV organic film.     

Enhanced variant designs and characteristics of the microstructured solid-state neutron detector

Silicon diodes with large aspect ratio perforated microstructures backfilled with ⁶LiF show a dramatic increase in neutron detection efficiency beyond that of conventional thin-film coated planar devices. Described in this work are advancements in the technology with increased microstructure depths and detector stacking methods to increase thermal neutron detection efficiency. The highest efficiency devices thus far have delivered over 37% intrinsic thermal neutron detection efficiency by device-coupling stacking methods. The detectors operate as conformally diffused pn junction diodes with 1 cm² square-area. Two individual devices were mounted back-to-back with counting electronics coupling the detectors together into a single dual-detector device. The solid-state silicon device operated at 3 V and utilized simple signal amplification and counting electronic components. The intrinsic detection efficiency for normal-incident 0.0253 eV neutrons was found by calibrating against a ³He proportional counter and a ⁶LiF thin-film planar semiconductor device. This work is a part of on-going research to develop solid-state semiconductor neutron detectors with high detection efficiencies and uniform angular responses.     

Characteristics of gold/cadmium sulfide nanowire Schottky diodes

Schottky diode junctions were formed between nanowires of cadmium sulfide and nanowires of gold, through sequential cathodic electrodeposition into the pores of anodized aluminum oxide (AAO) templates. Lengths of CdS and Au nanowires were 100-500 nm and 300-400 nm respectively, while the diameter was 30 nm, each. Analysis of Schottky diodes yielded an effective reverse saturation current (J_o), of 0.32 mA/cm² and an effective diode ideality factor (A) of 8.1 in the dark. Corresponding values under one sun illumination were, J_o = 0.92 mA/cm² and A = 10.0. Dominant junction current mechanisms are thought to be tunneling and/or interface state recombination.