The CiCs(SiI)n defect in silicon from a density functional theory perspective

Carbon is an important defect in silicon (Si) as it can interact with intrinsic point defects and affect the operation of devices. In heavily irradiated Si containing carbon the initially produced carbon interstitial - carbon substitutional (CiCs) defect can associate with self-interstitials (SiI’s) to form, in the course of irradiation, the CiCs(SiI) defect and further to form larger complexes namely CiCs(SiI)n defects by the sequential trapping of self-interstitials defects. In the present study, we use density functional theory to clarify the structure and energetics of the CiCs(SiI)n defects. Here we report that the lowest energy CiCs(SiI) and CiCs(SiI)2 defects are strongly bound with -2.77 eV and -5.30 eV, respectively

Controlling A-center concentration in silicon through isovalent doping: Mass action analysis

It has been determined experimentally that doping silicon with large isovalent dopants such as tin can limit the concentration of vacancy-oxygen defects, this in turn, can be deleterious for the materials properties and its application. These results have been supported by recent calculations based on density functional theory employing hybrid functional. In the present study, we employ mass action analysis to calculate the impact of germanium, tin and lead doping on the relative concentrations of vacancy-oxygen defects and defect clusters in silicon under equilibrium conditions. In particular, we calculate how much isovalent doping is required to constrain vacancy-oxygen concentration in silicon and conclude that Sn and Pb doping are the most effective isovalent dopants. The results are discussed in view of recent experimental and computational results

Carbon related defects in irradiated silicon revisited

Electronic structure calculations employing hybrid functionals are used to gain insight into the interaction of carbon (C) atoms, oxygen (O) interstitials, and self-interstitials in silicon (Si). We calculate the formation energies of the C related defects C(i)(Si(I)), C(i)O(i), C(i)C(s), and C(i)O(i)(Si(I)) with respect to the Fermi energy for all possible charge states. The C(i)(Si(I))(2+) state dominates in almost the whole Fermi energy range. The unpaired electron in the C(i)O(i)(+) state is mainly localized on the C interstitial so that spin polarization is able to lower the total energy. The three known atomic configurations of the C(i)C(s) pair are reproduced and it is demonstrated that hybrid functionals yield an improved energetic order for both the A and B-types as compared to previous theoretical studies. Different structures of the C(i)O(i)(Si(I)) cluster result for positive charge states in dramatically distinct electronic states around the Fermi energy and formation energies

Infrared study of defects in nitrogen-doped electron irradiated silicon

Nitrogen is a key dopant in Czochralski silicon widely used to control properties of Si wafers for applications in the microelectronics industry. Most of these properties are affected by defects and their processes. Here we employ Fourier transform infrared spectroscopy to investigate the existence of radiation induced N-related defects in Si. Besides well-known signals of substitutional (Ns) at 653 cm−1, interstitial (Ni) at 691 cm−1, N2 at 766 cm−1, N–O complexes at 801, 996 and 1026 cm−1 and N2O at 973 and 996 cm−1 we determined some additional signals. The pair of bands at 646 and 663 cm−1 has been tentatively correlated with the Ns V pair in agreement with previous theoretical calculations. Similarly the pair of bands at 725 and 778 cm−1 has been tentatively correlated with the N2 V complex and another pair of bands at 930 and 953 cm−1 may be related with the N2SiI complex. Additionally, oxygen-vacancy defects such as the vacancy-oxygen pair (A-center or VO) are common in electron irradiated Si and can impact the material and electronic properties of Si. We investigate and compare the effect of N doping on oxygen-vacancy defects in electron irradiated Si. It is determined that nitrogen reduces the production of VO defects

The C_iO_i(Si_I)₂ defect in silicon:Density functional theory calculations

Carbon–oxygen-self-interstitial defects in silicon (Si) are technologically important as they can impact the operation of devices through the concentration of intrinsic point defects. In irradiated Si the CiOi defect attracts self-interstitials (SiI’s) and leads to the formation of the CiOi(SiI). Experimental studies have determined that annealing at 150 °C results in the capturing of more SiI’s leading to the formation of the CiOi(SiI)2 defect. Recent experimental studies proposed that the CiOi(SiI)2 defect is bistable and considered possible configurations. In the present study we aim to clarify the structure of the CiOi(SiI)2 defect and use density functional theory calculations to gain insights on the formation and stability of the CiOi(SiI)2 defect in Si. It is calculated that two configurations are energetically favourable differing in energy by only 0.19 eV.</p

Strategies to suppress A-center formation in silicon and germanium from a mass action analysis viewpoint

We investigate the impact of tin (Sn) doping on the formation and the thermal stability of the vacancy-oxygen (VO or A-center) in the electron-irradiated Czochralski silicon (Si) and its conversion to the VO2 defects. Previous experimental studies are consistent with the viewpoint that Sn (and other oversized isovalent atoms) doping suppresses the formation of the A-center. The results are discussed in view of recent density functional theory calculations, whereas we employ mass action analysis to calculate the impact of isovalent dopants on the suppression of the A-center. We propose point defect engineering strategies to suppress the concentration of the deleterious A-centers in Si and in related materials such as germanium

Quantification of myelin loss in frontal lobe white matter in vascular dementia, Alzheimer's disease, and dementia with Lewy bodies

The aim of this study was to characterize myelin loss as one of the features of white matter abnormalities across three common dementing disorders. We evaluated post-mortem brain tissue from frontal and temporal lobes from 20 vascular dementia (VaD), 19 Alzheimer’s disease (AD) and 31 dementia with Lewy bodies (DLB) cases and 12 comparable age controls. Images of sections stained with conventional luxol fast blue were analysed to estimate myelin attenuation by optical density. Serial adjacent sections were then immunostained for degraded myelin basic protein (dMBP) and the mean percentage area containing dMBP (%dMBP) was determined as an indicator of myelin degeneration. We further assessed the relationship between dMBP and glutathione S-transferase (a marker of mature oligodendrocytes) immunoreactivities. Pathological diagnosis significantly affected the frontal but not temporal lobe myelin attenuation: myelin density was most reduced in VaD compared to AD and DLB, which still significantly exhibited lower myelin density compared to ageing controls. Consistent with this, the degree of myelin loss was correlated with greater %dMBP, with the highest %dMBP in VaD compared to the other groups. The %dMBP was inversely correlated with the mean size of oligodendrocytes in VaD, whereas it was positively correlated with their density in AD. A two-tier regression model analysis confirmed that the type of disorder (VaD or AD) determines the relationship between %dMBP and the size or density of oligodendrocytes across the cases. Our findings, attested by the use of three markers, suggest that myelin loss may evolve in parallel with shrunken oligodendrocytes in VaD but their increased density in AD, highlighting partially different mechanisms are associated with myelin degeneration, which could originate from hypoxic–ischaemic damage to oligodendrocytes in VaD whereas secondary to axonal degeneration in AD

Isovalent doping and the CiOi defect in germanium

Oxygen–carbon defects have been studied for decades in silicon but are less well established in germanium. In the present study we employ density functional theory calculations to study the structure of the CiOi defect in germanium. Additionally, we investigate the interaction the CiOi defect with isovalent dopants such as silicon and tin. It is calculated that the CiOi defects will preferentially form near isovalent dopants in germanium. Interestingly the structure of the dopant-CiOi defects is different with the Sn residing next to the Oi whereas the Si atom bonds with the Ci. The differences in the structure of CiOi defects in the vicinity of isovalent dopants are discussed

A Polymorphism in a Gene Encoding Perilipin 4 Is Associated with Height but not with Bone Measures in Individuals from the Framingham Osteoporosis Study

There is increasing interest in identifying new pathways and candidate genes that confer susceptibility to osteoporosis. There is evidence that adipogenesis and osteogenesis may be related, including a common bone marrow progenitor cell for both adipocytes and osteoblasts. Perilipin 1 (PLIN1) and Perilipin 4 (PLIN4) are members of the PATS family of genes and are involved in lipolysis of intracellular lipid deposits. A previous study reported gender-specific associations between one polymorphism of PLIN1 and bone mineral density (BMD) in a Japanese population. We hypothesized that polymorphisms in PLIN1 and PLIN4 would be associated with bone measures in adult Caucasian participants of the Framingham Osteoporosis Study (FOS). We genotyped 1,206 male and 1,445 female participants of the FOS for four single-nucleotide polymorphism (SNPs) in PLIN1 and seven SNPs in PLIN4 and tested for associations with measures of BMD, bone ultrasound, hip geometry, and height. We found several gender-specific significant associations with the measured traits. The association of PLIN4 SNP rs8887, G>A with height in females trended toward significance after simulation testing (adjusted P = 0.07) and remained significant after simulation testing in the combined-sex model (adjusted P = 0.033). In a large study sample of men and women, we found a significant association between one SNP in PLIN4 and height but not with bone traits, suggesting that PATS family genes are not important in the regulation of bone. Identification of genes that influence human height may lead to a better understanding of the processes involved in growth and development