Direct observation of the distribution of impurity in phosphorous/boron co-doped Si nanocrystals

Doping in Si nanocrystals is an interesting topic and directly studying the distribution of dopants in phosphorous/boron co-doping is an important issue facing the scientific community.In this study,atom probe tomography is performed to study the structures and distribution of impurity in phosphorous/boron co-doped Si nanocrystals/SiO_(2) multilayers.Compared with phosphorous singly doped Si nanocrystals,it is interesting to find that the concentration of phosphorous in co-doped samples can be significantly improved.Theoretical simulation suggests that phosphorous-boron pairs are formed in co-doped Si nanocrystals with the lowest formation energy,which also reduces the formation energy of phosphorous in Si nanocrystals.The results indicate that co-doping can promote the entry of phosphorous impurities into the near-surface and inner sites of Si nanocrystals,which provides an interesting way to regulate the electronic and optical properties of Si nanocrystals such as the observed enhancement of conductivity and sub-band light emission.

Impurity distribution in metallic dysprosium during distillation purification

The distribution rules of impurities contents in distilled metallic dysprosium were researched, and a theoretical analysis was carried out. The research results indicated that, the content of impurity in distilled metal, such as Al and Fe, was lower in the ini-tial stage, increased slowly in the middle stage, and increased rapidly in the last stage during the process of distillation purification. The calculated method of separation coefficient of impurity in crude metal by content of impurity in distilled metal was not suitable for high pure metals, and the modified separation coefficient was proposed, and it equaled 1/6.1 and 1/16.9 for impurity Al and Fe. The physical process of distillation was coincident with that of solidification essentially, and solute re-distribution theory in solidify-ing front could be used to describe the impurity distribution near evaporating surface. In the former stage of distillation purification, the diffusion of impurity in liquid metal could reach a quasi-equilibrium state, the calculated result of impurity content in distilled metal agreed well with experiments. In the latter stage of distillation process, the diffusion rate of impurity in liquid metal decreased, and the content in distilled metal was larger than the calculated result.

A simple expression for impurity distribution after multiple diffusion processes

There are several diffusion processes with different temperatures in modern semiconductor technology.The impurity distribution after these diffusion processes is analyzed and a simple expression for describing the distribution is given.It is found that the impurity distribution after multiple diffusion processes can be characterized with an effective diffusion length.The relation between this effective diffusion length and the diffusion lengths of each diffusion process is given and shows itself to be very simple and instructive.The results of the expression agree well with numerical simulations by using SUPREMⅣ.An example of the application of the expression is also shown.

The variation of Mn-dopant distribution state with x and its effect on the magnetic coupling mechanism in Zn_(1-x) Mn_x O nanocrystals

Zn1-xMnxO （x = 0.0005, 0.001, 0.005, 0.01, 0.02） nanocrystals are synthesized by using a wet chemical process. The coordination environment of Mn is characterized by X-ray photoelectron spectroscopy, Raman spectroscopy, and its X-ray absorption fine structure. It is found that the solubility of substitutional Mn in a ZnO lattice is very low, which is less than 0.4%. Mn ions first dissolve into the substitutional sites in the ZnO lattice, thereby forming Mn2＋O4 tetrahedral coordination when x ≤ 0.001, then entering into the interstitial sites and forming Mn3＋O6 octahedral coordination when x ≥ 0.005. All the samples exhibit paramagnetic behaviors at room temperature, and antiferromagnetic coupling can be observed below 100 K.

Effects of oxygen vacancy location on the electronic structure and spin density of Co-doped rutile TiO_2 dilute magnetic semiconductors

According to density functional theory （DFT） using the plane wave base and pseudo-potential, we investigate the effects of the specific location of oxygen vacancy （Vo） in a （Ti,Co）06 distorted octahedron on the spin density and magnetic properties of Co-doped rutile Ti02 dilute magnetic semiconductors. Our calculations suggest that the Vo location has a significant influence on the magnetic moment of individual Co cations. In the case where two Co atoms are separated far away from each other, when the Vo is located at the equatorial site of a Co-contained octahedron, the ground state of the two Co cations is d6（t3g↑, t23g ↓） without any magnetic moment. However, if the Vo is located at the apical site, these two Co sites have different ground states and magnetic moments. The spin densities are also observed to be modified by the exchange coupling between the Co cations and the location of Vo. Some positive spin polarization is induced around the adjacent O ions.

Migration regularities of impurities C,O,Fe,Co and Ni and effect of crystal transition on C,O and Fe in purification of metal La by solid-state electrotransport

Migration regularities of impurities C,O,Fe,Co and Ni and the effect of crystal transition on C,O and Fe in purification of metal La by solid-state electrotransport(SSE)were studied.The impurity migration direction,removal extent and difficulty were intuitively judged by impurity residual rate distribution curve.It is indicated that major impurities Fe,Co,Ni,C and O in metal La are found to significantly migrate to anode and migration effects are much better with the increase in temperature and prolongation of time in purification of La by SSE.Impurities Fe,Co and Ni in La may be fast diffusion elements,which are very extreme to be removed,and removal difficulty is in the order of Fe<Co<Ni<O<C.When La was migrated for 100 h at 800℃by SSE,the residual rates of impurity Fe,Co,Ni,O and C are 0.25%,10.10%,40.04%,64.00%and 70.04%,respectively.The crystal transition of La,transformed from fcc crystal to bcc crystal,has significant effect on migration of interstitial impurities,and removal effect of interstitial impurities C and O can be significantly improved when purification was performed above crystal transition temperature of 865℃of La.However,there is little effect on Fe.When La was migrated at 880℃for 100 h,residual rates of impurities C and O are,respectively,19.90%and 32.67%lower than those at 820℃for 100 h,while that of Fe is lower than0.25%in both situations.Therefore,more pure metal La can be obtained through further increasing temperature,especially above crystal transition temperature of 865℃of La.