Neutron Doping Research Articles

Computational Modeling of Doped 2D Anode Materials for Lithium-Ion Batteries.

Development of high-performance lithium-ion batteries (LIBs) is boosted by the needs of the modern automotive industry and the wide expansion of all kinds of electronic devices. First of all, improvements should be associated with an increase in the specific capacity and charging rate as well as the cyclic stability of electrode materials. The complexity of experimental anode material selection is now the main limiting factor in improving LIB performance. Computer selection of anode materials based on first-principles and classical molecular dynamics modeling can be considered as the main paths to success. However, even combined anodes cannot always provide high LIB characteristics and it is necessary to resort to their alloying. Transmutation neutron doping (NTD) is the most appropriate way to improve the properties of thin film silicon anodes. In this review, the effectiveness of the NTD procedure for silicene/graphite (nickel) anodes is shown. With moderate P doping (up to 6%), the increase in the capacity of a silicene channel on a Ni substrate can be 15-20%, while maintaining the safety margin of silicene during cycling. This review can serve as a starting point for meaningful selection and optimization of the performance of anode materials.

Improved lithium-ion batteries and their communication with hydrogen power

Self-contained power supplies and energy storage continue to improve. The criteria that determine their development include efficiency, safety, adaptability, modifiability, and a number of others. In this work, one of the ways to improve the lithium-ion battery by using a new negative electrode is considered. The possibilities of applicability of the improved lithium-ion battery are discussed, its advantages and disadvantages in relation to a hydrogen fuel cell and power sources using hydrogen fuel are considered. The study of the functioning of the new anode, the material of which is a two-layer silicene on a nickel substrate, is carried out at the atomic level. Improvement of the anode characteristics can be achieved by subjecting it to the neutron doping. Li-ion batteries with an improved anode will have higher charging capacity and power, faster charging and improved safety.

Promising two-dimensional nanocomposite for the anode of the lithium-ion batteries. Computer simulation

To create a high-performance lithium-ion battery, a new anode material is needed. We study the structure, dynamics, and mechanical properties of a promising anode silicene/graphite material subjected to the transmutation neutron doping. The motion of the lithium ion under electric field along a silicene channel located on a graphite substrate was studied. The concentration of phosphorus in the walls of the silicene channel varied from 3% to 18%. The concentration of nitrogen in the graphite substrate was 5%. Both the gap and the amount of phosphorus in the channel walls were found to affect the movement of the lithium ion along the channel. As a rule, strong stresses in the silicene sheets are not observed during the movement of the Li+ ion along the channel. The maximum values of local stresses arising in the walls of the channel turn out to be slightly sensitive both to the doping degree of silicene and to the size of the channel gap. The top sheet of the silicene channel always has a larger roughness than the bottom one. To use silicene in a lithium-ion battery, the maximum doping degree of silicene with phosphorus should not exceed 9%.

Thermal neutron transmutation doping of GaN semiconductors

High quality Ge doping of GaN is demonstrated using primarily thermal neutrons for the first time. In this study, GaN was doped with Ge to concentrations from 1016 Ge atoms/cm3 to 1018 Ge atoms/cm3. The doping concentrations were measured using gamma-ray spectroscopy and confirmed using SIMS analysis. The data from SIMS analysis also show consistent Ge doping concentration throughout the depth of the GaN wafers. After irradiation, the GaN was annealed in a nitrogen environment at 950 °C for 30 min. The neutron doping process turns out to produce spatially uniform doping throughout the whole volume of the GaN substrate.

Computer Test of a Modified Silicene/Graphite Anode for Lithium-Ion Batteries.

Despite the considerable efforts made to use silicon anodes and composites based on them in lithium-ion batteries, it is still not possible to overcome the difficulties associated with low conductivity, a decrease in the bulk energy density, and side reactions. In the present work, a new design of an electrochemical cell, whose anode is made in the form of silicene on a graphite substrate, is presented. The whole system was subjected to transmutation neutron doping. The molecular dynamics method was used to study the intercalation and deintercalation of lithium in a phosphorus-doped silicene channel. The maximum uniform filling of the channel with lithium is achieved at 3% and 6% P-doping of silicene. The high mobility of Li atoms in the channel creates the prerequisites for the fast charging of the battery. The method of statistical geometry revealed the irregular nature of the packing of lithium atoms in the channel. Stresses in the channel walls arising during its maximum filling with lithium are significantly inferior to the tensile strength even in the presence of polyvacancies in doped silicene. The proposed design of the electrochemical cell is safe to operate.

Getters in silicon

Gettering of rapidly diffusing metallic impurities and structural defects in silicon which is the main material for IC fabrication, high-power high-voltage devices and neutron doped silicon has been studied. Structural defect based getters and gas phase getters based on chlorine containing compounds have been analyzed. Formation of structural defect based getters requires producing intrinsic sources of dislocation generation and precipitate/dislocation agglomerate formation. We show that dislocations are generated at microcrack mouths and form a low-mobility dislocation network at inactive wafer sides. In the latter case the defects are generated in the wafer region adjacent to the active layer of the electronic component. The generation of intrinsic getters is based on the decomposition of the supersaturated oxygen solid solution in silicon which favors the formation of a complex defect system in silicon that consists of various precipitate/dislocation agglomerates. Stacking faults also form, i.e., oxide precipitates with Frank’s dislocation loop clouds. Two intrinsic getter formation methods have been considered: one is related to oxygen impurity drain from the wafer surface region and the other implies accurate control of vacancy distribution over wafer thickness. We have analyzed the effect of getters as defect structures on the reduction of the mechanical stress required for dislocation generation onset which may eventually determine the mechanical strength of silicon wafers. The mechanism of impurity and defect gettering by gas phase medium with chlorine-containing compound additions has been considered. We show that silicon atom interaction with chlorine in the surface wafer region at high temperatures may cause the formation of vacancies which may penetrate to the specimen bulk with some probability. This leads to the case ∆Сv > 0 and ∆Ci ≤ 0, which changes the composition and density of the microdefects. Examples have been given for practical use of heat treatment of silicon wafers in a chlorine-containing atmosphere during oxide film application with the aim to dissolve microdefects, drain rapidly diffusing impurities from crystal bulk and prevent the formation of generation/recombination centers during device fabrication and silicon neutron doping.

Backside doping profiles of irradiated silicon detectors

Silicon detectors are used in High Energy Physics (HEP) experiments as tracking and vertexing devices. The damage caused by radiation is of special interest for sensors to be used at the HL-LHC. The doping profiles of highly irradiated sensors can neither be measured with common capacitance voltage methods nor with methods of chemical analysis. Nevertheless, they need to be known for damage modelling or for simulations of the sensor performance. In this paper it is shown that highly neutron irradiated doping profiles can be measured by using a spreading resistance probe technique. It turned out that the implantation depth of the profiles of active dopants decreases with increasing fluences.

Neutron doping effects in epitaxially laterally overgrown n-GaN

Thermal neutron irradiation and annealing effects were studied for undoped n-GaN prepared by epitaxial lateral overgrowth (ELOG). Electron beam induced current (EBIC) imaging and profiling prior to irradiation showed that the residual donor doping in our ELOG samples was about three times higher in the high-dislocation-density ELOG wing than in the low-dislocation-density ELOG window regions. Irradiation with thermal neutrons and subsequent annealing led to greatly improved doping uniformity, as evidenced by EBIC imaging. The neutron transmutation doping avoids the anisotropy of donor incorporation efficiency for different planes during ELOG and provides a uniform doping environment. Capacitance-voltage profiling on such samples showed the presence of electrically active centers with concentration close to the concentration of Ge donors produced by Ga interaction with thermal neutrons.

Problems of homogeneous irradiation of Si ingots more than 200 mm in diameter under neutron doping

The problem of homogeneous irradiation of Si ingots of large diameter (i.e., comparable with the thermal neutron diffusion length in silicon—20 cm) by thermal neutrons is considered. The effect of neutron absorption on the irradiation homogeneity is discussed. It is established for some usual cases of neutron doping that the neutron distribution in the irradiation zone affects the irradiation homogeneity. The results obtained can be useful for choosing and designing the irradiation zone for neutron doping of silicon.

Effect of neutron irradiation and doping level on defect structure formation in gallium arsenide crystals

Effect of neutron irradiation and doping level on defect structure formation in gallium arsenide crystals

Broad band application of combined instrumental photon and neutron activation analysis

The use of INAA and IPAA is illustrated by several applications (Zn-traces in Cu, neutron doping of Zn in copper, implanted Sb in silicon, trace elements in sediment material and polyethylene). The two methods are used to complement or to cross-check each other. Validation by IDA-TIMS was performed in the case of neutron doping and turned out to be a valuable support. Even developed routines of activation analysis need improvement. Two technical solutions, the high energy photon screen (HEPS) and a twin detector assembly, are dealt with in detail.

Multivariate data analysis of process control data from neutron transmutation doping of silicon

Final resistivities obtained by neutron transmutation doping (NTD) of silicon can be measured only after an annealing process has been carried out at the manufacturer's plant. The reactor centre carrying out the neutron doping process by irradiation under selected conditions must control the process by indirect measurement of the product quality. The method of partial least squares was used to identify important parameters for improving the quality of the NTD-silicon, as well as for predicting the final quality data observed by the customer.

Changes in the structure of poly (vinyl alcohol)-CrCl3 composites irradiated by low level fast neutron doses

Cast thin films of the composites PVA-CrCl3 were prepared. The absorption spectra, X-ray diffraction, hardness number and dielectric constant were measured before and after irradiation by neutrons in the fluence range of 3.4 × 105 to 1.68 × 108 n/cm2. The Racah constant was calculated to be 600 cm-1 which is about 65% of the free ion value. A pronounced band characterizing the carbonyl group has developed at 220 nm by irradiation. The degree of crystallinity is enhanced with the increase of neutron fluence. The position of the glass transition and α-relaxation temperatures were dependent on neutron fluence and doping content.

Neutron doping of silicon in power reactors

It has been demostrated that conditions optimal for the production of large quantities of quality neutron-doped silicon (NDS) exist in power nuclear reactors of the RBMK type. Experimental investigations of the irradiation conditions and the electrophysical properties of NDS produced in RBMK-1000 under various regimes were carried out and methods developed for enhancing the uniformity of impurity, introduced as a result of neutron irradiation across the diameter and along the length of large ingots of semiconductor material. Methods of stabilization of the neutron flux in irradiation channels are proposed. Possibilities are explored of producing low-resistivity silicon as well as NDS for various semiconductor devices: superhigh-voltage pn junctions, high- and low-resistivity reference resistors, and detectors of nuclear radiation.

Carrier removal and changes in electrical properties of neutron irradiated GaAs

The changes in electrical properties of n-GaAs as a result of irradiations with fast neutrons have been studied. Epitaxial layers doped with Si at concentrations in the range 1.35×1015 to 1.599×1016 cm−3 were irradiated with reactor neutron fluences up to 1.31×1015 cm−2. When the changes in carrier concentration, Hall mobility, and resistivity were more than 25% of their initial values, nonlinear dependence on neutron fluence was apparent. New theory is proposed which explains the changes in electrical properties in terms of rates of trapping and release of charges. A theoretical relationship is derived for the change in carrier concentration as a function of neutron fluence and doping level. A linear relationship between neutron fluence and Fermi level shift was found to be consistent with the observed changes in carrier concentration.

Neutron doping of silicon in RBMK-1000

Neutron doping of silicon in RBMK-1000

Lattice defects in silicon doped by neutron transmutation

The method of silicon doping by thermal neutron transmutation (producing phosphorus atoms) is compared to the conventional method. Both the electronic and atomic lattice defects are considered. From accurate radioactive and electrical measurements, the numbers of carriers and phosphorus atoms are measured separately in order to derive the concentration of electronic defects. Diffusion profiles of gallium are determined by activation analysis as well as ion microprobe before and after neutron doping, which gives the influence of the doping on the concentration of the atomic defects responsible for diffusion. No difference between the methods of doping can be detected within the range of experimental errors.