Results 1 - 10 of 16410
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[en] The development of the sampling device with pulsed heating of the intermediate carrier for ion mobility spectrometer is described in this article. Numerical simulation of a pulse heater structure of is presented. The design of the sampling device using a pulsed heating of the intermediate carrier is developed. Experimental results of approval of the sampling device are presented.
[en] In portable hand-held devices for trace explosive and narcotic detection the most perspective is use of a principle of ion mobility spectrometry [,] owing to the best combination of cost, compactness, parameters of detection and a wide range of found out substances. Classical designs of a ion mobility spectrometer are represented by a set of the metal electrodes forming area with homogeneous longitudinal electric field, in a combination to an electric shutter and area of ionization to a source of ionization on the basis of a radioactive isotope. The extremely perspective problem is development of a compact not radioactive source of the ionization, allowing to generate ions both positive, and negative polarity and having low power consumption. The use pulse corona discharge as a source of ionization for a ion mobility spectrometer is represented to the most perspective. Application in a design of a pulse corona discharge ionization source allows, unlike systems with isotope 63Ni ionization, to do without application of an electrostatic ion shutter which separates ionization and drift chambers. However application of an ion shutter allows to achieve the best parameters of resolution and sensitivity. In the given work the scheme of operation and results of application of an electrostatic ion shutter as a part of a ion mobility spectrometer with a pulse corona discharge ionization source will be considered.
[en] Using first-principles calculations coupled with deformation potential (DP) theory, we have systematically studied the band structure, carrier mobility and strain modulation of monolayer graphane (CH), silicane (SiH) and germanane (GeH) nanoribbons. It is found that all the CH (SiH, GeH) nanoribbons are semiconductor with a wide range of band gap. The carrier mobility results show that the armchair germanane nanoribbon (AGeNR) has the characteristic of p -type semiconductor in electrical conduction because its hole mobility is larger than the electron mobility. While the graphane nanoribbon (CNR) behaves as n-type semiconductor in electrical conduction. Compared to AGeNR and CNR, the mobilities of other nanoribbons are much smaller. Moreover, the band structure and carrier mobility of AGeNR and CNR can be effectively tuned by strain. There are different state competing for the valence band maximum (VBM). When the strain exceeds certain value, the VBM is transited to a new band-edge state accompanied with a large increase of hole mobility. The new band-edge state has smaller DP constant because its bond character makes it less sensitive to strain, and thus resulting in higher hole mobility. (paper)
[en] We have investigated the pre-breakdown ionization processes in a pulsed capillary discharge using a capacitive probe array to measure ionization growth with time and space resolution. The experimental results indicate that pre-breakdown processes in shielded capillary discharges are characterized by the formation of a fast ionization wave. Depending on voltage polarity, the ionization wave can be associated with a mobile virtual anode with characteristic speed 105 m s-1, in the case of positive polarity, or with the propagation of a high speed potential wave, of characteristic speed 107 m s-1, in negative polarity case. The time and space evolution of the ionization waves is closely related with the formation of high energy electron beams, which originate due to the hollow cathode geometry of the open end capillary. A qualitative model based on the hollow cathode effect is proposed to explain the initial formation and later time evolution of the observed ionization waves
[en] Application of thick (∼50 μm) a-Si p-i-n diodes as a direct radiation detector for minimum ionizing particles is hampered by the need to apply large bias voltages in order fully to deplete the detecting intrinsic layer, which typically contains 5 - 10 x 1014 ionizable dangling bonds per CM3. By insertion of thin p-type layers at intervals within the intrinsic layer, the required depletion voltage can be reduced by a factor of at least 1/(n+l) where n is the number of layers inserted. This principle is demonstrated for devices approximately 12μm in thickness. It is shown that electron losses within the p type layer can be kept to minimum by choice of a low doping concentration for the introduced players
[en] A study of OSL variation with preheat temperature showed, in a majority of cases, that OSL recorded at room temperature, increases above 200 deg. C before the normal drainage at higher temperature. To explain this behaviour, an alternative interpretation to the common 'electronic thermal transfer' mechanism is suggested, supported by a study of hydrothermally grown quartz crystals. This interpretation involves impurities in substitution of Si4+, specially Al3+, which are associated with species like, in the case of quartz, hydrogen (H+, in fact, OH-) and alkali ions (Li+, Na+, K+). These monovalent ions usually act as charge compensators and are mobile during heating. As a consequence of the mobility and a possible irreversible exchange between compensators, the number of radiative recombination centres associated with the OSL trap(s), observable within the detection spectral window used (250-400 nm), increases during preheating. This phenomenon could lead to a wrong ED determination
[en] Rhenium disulfide (ReS_2) is a semiconducting layered transition metal dichalcogenide that exhibits a stable distorted 1 T (Re in octahedral coordination) phase. The reduced symmetry in ReS_2 leads to in-plane anisotropy in various material properties. In this work, we performed a comprehensive first-principle computational study of strain effect on the anisotropic mechanical and electronic properties of ReS_2 monolayers. We found that the anisotropic ratio in electron mobility along two principle axes is 2.36 while the ratio in hole mobility reaches 7.76. The study of strain applied along different directions shows that the elastic modulus is largest for out-of-plane direction, and the strain along a-direction induces indirect bandgap while strain along b- or c-direction does not. In addition, the carrier mobility can be significantly improved by the c-direction tensile strain. This study indicates that the ReS_2 monolayer has promising applications in nanoscale strain sensor and conductance-switch FETs.
[en] The transport properties of free charge carriers, photo- and cathodo-luminescence (CV) in GaN and AlN films obtained by MOCVD technique on sapphire and Si substrates, are investigated. The concentration of free charge carriers in GaN is of order 1017-1019 cm-3 whereas AlN thin films are insulating. The Hall mobility of electrons are 80-140 cm2/V s). In undoped GaN films the spectral composition of CL is close to photoluminescence (PL) when excited in the region of band-band transitions. The decay time constant of the 3.44 eV UV emission attributed to the bound exciton is considerably less than 1 ns, whereas the 3.26 eV violet (VI) band shows a slow hyperbolical decay over about 1 μs. The known yellow band appears at 2.25 eV due to transitions via localised states. In AlN the spectral composition of the broad CL band is close to that from bulk materials attributed to charge transfer transitions in deep oxygen-related donor-acceptor centres