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The band structures, density of states and absorption spectra of un-doped and Co-doped ZnO supercells of Zn1−xCoxO (x = 0.0417, 0.0625 and 0.1250) have been investigated using first-principles plate-wave uitrasoft pseudopotential method based on the density functional theory. The calculated results showed that the band gaps are broadened by Co dopi...
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Context 1
... band structure, total density of states (TDOS) and partial density of states (PDOS) of the unit cell of un-doped ZnO have been calculated, we can known from Figure 1a that the band gap (E g ) of un-doped ZnO is 0.73 eV, which is in agreement with the previ- ously value [24,25]. However, it is less than the experimental value of 3.37 eV due to the limitation of DFT in GGA, the discontinuity in the exchange-correlation potential is not taken into account with- in the framework of DFT [26]. ...
Context 2
... the band gap calculated in GGA is always less than the experimental value, it can be corrected by scissors operator, in this work, the value of scissors operator is 2.64 eV. After corrected by scissors operator, the band structure and TDOS of the unit cell of un-doped ZnO have been shown in Fig- ure 1b, we can see from Figure 1b that the calculated results are good in agreement with the experimental results, so our analysis is reliable. In this Letter, the Fermi level has been specified to be 0 eV. ...
Context 3
... the band gap calculated in GGA is always less than the experimental value, it can be corrected by scissors operator, in this work, the value of scissors operator is 2.64 eV. After corrected by scissors operator, the band structure and TDOS of the unit cell of un-doped ZnO have been shown in Fig- ure 1b, we can see from Figure 1b that the calculated results are good in agreement with the experimental results, so our analysis is reliable. In this Letter, the Fermi level has been specified to be 0 eV. ...
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Citations
... The origin of the dilute magnetism may be due to the existent of defects which can be unambiguously attributed to the locally locked and polarized nonbonding electrons in Co-doped ZnO monolayer system. These electrons will be locally pinned and polarized by the deeply and densely trapped bonding and core electrons, these locked electrons have measurable magnetism [55,56]. ...
The graphene-like ZnO(gZnO) monolayer systems have been experimentally and theoretically widely studied. And recently, more specifically the preparation of Co-doped two-dimensional ZnO. In this work, the stability, band structures and absorption spectrum of Co doping gZnO monolayer systems with the varying doping concentrations and strains have been investigated by using the first-principles plane-wave ultra-soft pseudopotential method based on the density functional theory. The results show that the Co doped gZnO monolayer systems are stable. The band gap is narrowed by Co doping, and becomes narrower with the increase of doping concentration, in addition to that the band gap is narrowed as the strain increases. The estimated Curie temperature（Tc) value is about 695 K. The covalent bond becomes stronger and the ionic bond becomes weaker as Co doing concentration increases. The absorption spectrum has a red-shift by Co doping, and heavier doping level leads to more significant red-shift, meanwhile, the absorption spectrum has a blue-shift as the strain increases. This results may be helpful for the designing of new-type gZnO-based spintronic materials and optical devices.
... Results showed that the strong Co-Co interaction is responsible for the ferromagnetic state. Theoretical studies on Co-doped ZnO have been reported in various studies [15,16]. However, the doping systems' absorption spectrum is mainly distributed in the UV region, and the distribution in the visible region is lacking. ...
... The increase in substitutional Co doping results in a further apparent redshift in the absorption spectrum of substitutional Co-doped ZnO, which corresponds to the experimental results [15]. For the interstitial Co-doped ZnO, the absorption spectrum is redshifted relative to the undoped ZnO, which agrees with the experimental results [18] of the interstitial Cu-doped ZnO (Cu is a transition metal element in the same periodicity as Co). ...
... Moreover, the increase in Co doping concentration narrowed the bandgaps of the doped systems. The calculation results were consistent with the experimental results [15] (Different spatial scales of the systems led to slight differences in the bandgaps of the systems [31] that did not affect the comparison of relative values). Fig. 2(d) shows that the position of the Fermi level shifted into the conduction band, indicating that the doping system was degenerated while the tailing effect was produced. ...
The redshift and blueshift of the absorption spectrum of Co-doped ZnO have been reported experimentally. The effects on the bandgap and absorption spectrum of Co doping and interstitial H coexisting in ZnO have not been fully elucidated. The electronic structures and absorption spectra of Co-doped ZnO, interstitial Co-doped ZnO, and supercell model with four different spacings of substitutional Co and interstitial H co-doped ZnO systems were calculated using first-principle analysis. Results indicated that the multibody effect of the doped systems is greater than Burstein–Moss effect. The bandgap of the doped systems is narrowed, and the absorption spectra are significant and presented in order as follows: ZnO < Zn0.9722Co0.0278O < Zn0.9583Co0.0417O < Zn0.9583Co0.0417Hi0.0417O < Zn0.9583Coi0.0417O.
Nowadays, the experimental results of absorption spectrum distribution of Ni doped ZnO suffer controversy when the mole fraction of impurity is in a range from 2.78% to 6.25%. However, there is still lack of a reasonable theoretical explanation. To solve this problem, the geometry optimizations and energies of different Ni-doped ZnO systems are calculated at a state of electron spin polarization by adopting plane-wave ultra-soft pseudo potential technique based on the density function theory. Calculation results show that the volume parameter and lattice parameter of the doping system are smaller than those of the pure ZnO, and they decrease with the increase of the concentration of Ni. The formation energy in the O-rich condition is lower than that in the Zn-rich condition for the same doping system, and the system is more stable in the O-rich condition. With the same doping concentration of Ni, the formation energies of the systems with interstitial Ni and Ni replacing Zn cannot be very different. The formation energy of the system with Ni replacing Zn increases with the increase of the concentration of Ni, the doping becomes difficult, the stability of the doping system decreases, the band gap becomes narrow and the absorption spectrum is obviously red shifted. The Mulliken atomic population method is used to calculate the orbital average charges of doping systems. The results show that the sum of the charge transitions between the s state orbital and d state orbital of Ni²⁺ ions in the doping systems Zn0:9722Ni0:0278O, Zn0:9583Ni0:0417O and Zn0:9375Ni0:0625O supercells are all closed to +2. Thus, it is considered that the valence of Ni doped in ZnO is +2, and the Ni is present as a Ni²⁺ ion in the doping system. The ionized impurity concentrations of all the doping systems exceed the critical doping concentration for the Mott phase change of semiconductor ZnO, which extremely matches the condition of degeneration, and the doping systems are degenerate semiconductors. Ni-doped ZnO has a conductive hole polarization rate of up to nearly 100%. Then the band gaps are corrected via the LDA (local density approximation)+U method. The calculation results show that the doping system possesses high Curie temperature and can achieve room temperature ferromagnetism. The magnetic moment is derived from the hybrid coupling effect of p-d exchange action. Meanwhile, the magnetic moment of the doping system becomes weak with the increase of the concentration of Ni. In addition, the absorption spectrum of Ni-interstitial ZnO is blue-shifted in the ultraviolet and visible light bands.
Contradictory experimental absorption spectra blue shift and red shift results have been reported in the literatures. To solve this problem, this study investigates the electronic structure and absorption spectra of Zn1-xCuxO (x= 0, 0.0313 and 0.0625, respectively) and Zn32CuO32 supercells employing first-principles calculations with GGA+U method. By increasing the Cu substitutional doping concentration from 3.13% to 6.25%, the following results are obtained: increased magnetic properties, narrower band gaps, and a significant red shift in the absorption spectrum. These findings are in good agreement with the experimental results. The changes of band gap and absorption spectrum for interstitial doping and substitutional doping are opposite.
Objective:
Prognostic biomarkers that distinguish between patients with good or poor outcome can be used to guide decisions of whom to treat and how aggressively. In this sense, several groups have proposed genetic polymorphisms as potential susceptibility and prognostic biomarkers; however, their validity has not been proven. Thus, the main goal of the present work was to investigate the potential role of single and combined CYP1A1, GSTM1, and GSTT1 genotypes as modifiers of cancer survival in Chilean patients with prostate cancer.
Methods and materials:
A total of 260 histologically confirmed patients were recruited from a voluntary screening, and genomic DNA was obtained from their blood samples for genotyping analyses to detect the CYP1A1*2A polymorphism and GSTM1 and GSTT1 deletions. The progression of illness and mortality were estimated with a median follow-up of 8.82 years. Adjusted estimated genotype risks were evaluated by hazard ratio and 95% CI using the Cox proportional model. In addition, the Kaplan-Meier survival method and log-rank test were used to evaluate patient survival with regard to genotype.
Results:
The 9-year overall and specific survival rates were 67.6% and 36.6% in the GSTT1null group, 67.6% and 58.7% in the GSTM1non-null group, 69.0% and 51.6% in the *1A/*2A group, 63.9% and 61.5% in the *2A/*2A group vs. 76.2% and 62.3% in the GSTT1non-null group, 82.3% and 50% in the GSTM1null group, and 83.7% and 56.3% in the *1A/*1A group, respectively. The hazard ratios and the Kaplan-Meier curve results demonstrate that the GSTM1non-null, GSTT1null, and CYP1A1*2A genotypes are significantly associated with mortality. Our study has two main limitations: a relatively small sample size and a low global mortality percentage (25.4%); thus, we need to continue the follow-up to confirm these findings.
Conclusions:
Our results suggest that the GSTM1non-null, GSTT1null, and CYP1A1*2A genotypes may be good prognosis markers, particularly in patients with high-risk tumors.
This paper presents the influence of process parameters, such as argon (Ar) flow rate, sputtering power and substrate temperature on the band gap of Al-doped ZnO film, Al-doped ZnO thin films were fabricated by radio frequency (RF) magnetron sputtering technology and deposited on polyimide and glass substrates. Under different Ar flow rates varied from 30 to 70 sccm, the band gap of thin films were changed from 3.56 to 3.67 eV. As sputtering power ranged from 125 to 200W, the band gap was varied from 3.28 to 3.82 eV; the band gap was between 3.41 and 3.88 eV as substrate temperature increases from 150°C to 300°C. Furthermore, the correlation between carrier concentration and band gap was investigated by HALL. These results demonstrate that the band gap of the Al-doped ZnO thin film can be adjusted by changing the Ar flow rate, sputtering power and substrate temperature, which can improve the performance of semiconductor devices related to Al-doped ZnO thin film.
