Guruprasad Sahoo

This study explores the magnetic and electronic properties of 3d transition metal doped phosphorene monolayers using first principles calculations, with a focus on their potential two dimensional (2D) spintronics applications. We identify Ti, V, Cr, Mn and Fe doping induces magnetism in otherwise non-magnetic phosphorene with respective magnetic moment of 1μB, 2μB, 3μB, 4μB and 3μB per dopant. The induced magnetic moment is attributed to the intra-atomic charge transfer (from 4s to 3d) and subsequent spin-dependent electronic redistribution at the dopant site. Among the doped systems, Cr and Mn doped phosphorene exhibit ferromagnetic ground states with critical temperatures of 217.8 K and 733.5 K, respectively. On the other hand, Ti, V and Fe doping favor antiferromagnetic ordering with relatively lower critical temperatures, 147.1 K, 58.7 K and 52.2 K, respectively. While Ti and V doping retains semiconducting character with a band gap of 0.31 eV and 0.17 eV, respectively, the Cr, Mn and Fe doped systems are found to be metallic in nature. Notably, the Fe and V doped phosphorene monolayers exhibit unconventional compensated magnetism that combines the privilege of both ferromagnetism (spin-split band structure) and antiferromagnetism (zero net magnetization). While the former doped system is identified as a quasi-altermagnetic material, the latter one is predicted to be a Luttinger compensated magnetic semiconductor. Since they can facilitate an effective spin transport without any unwanted ferromagnetic coupling, therefore, the Fe and V doped phosphorene monolayers are the preferred superior materials for applications in next-generation 2D spintronics.

The present study demonstrates the structural, elastic, thermal, and electronic properties of copper nitride (Cu₃N) doped with transition metal M (M: Fe, Co, and Ni) using pseudopotential-based density functional calculations as implemented in the Quantum ESPRESSO simulation code. The exchange-correlation is approximated by Perdew-Burke-Ernzerhof functional within the framework of generalized gradient approximation. The doped matrices, represented as Cu₃NM, are verified to be stable structures, both thermodynamically and mechanically. Tailoring of elastic properties and their anisotropy due to M doping is successfully demonstrated through a comprehensive analysis of the computed elastic stiffness coefficients, elastic moduli, elastic anisotropy factors, and spatial variation of the elastic moduli, which have not been explored yet. An increase in bulk modulus due to M doping ensures enhanced mechanical stability under isotropic stress. Conversely, while doping of Co and Ni enhances the shear resistance of the host material, Fe doping slightly reduces it. The superior ductile nature of all the studied systems predicts their suitability for applications in flexible electronics. It is evident that doping of M substantially reduces the elastic anisotropy of Cu₃N. Using the calculated elastic moduli, the velocity of acoustic waves and its anisotropy for Cu₃N and Cu₃NM are also predicted. The anisotropy in the acoustic velocity of the studied materials recommends their potential application in acoustic devices with directional selectivity. It is also noticed that, while the average acoustic velocity is reduced due to Fe doping, it increases for Co and Ni doping. Furthermore, analysis of the computed Debye temperature and minimum thermal conductivity forecasts their employability as thermal barrier coatings. Finally, the calculations reveal the ferromagnetic nature of Cu₃NFe and Cu₃NCo with respective induced magnetic moments of 2.71 and 1.47 μ _B/cell, recommending their potential applications in spintronics. It is also proved that the M-d–Cu-d coupling stabilizes the ferromagnetic ordering in such magnetic systems. On the other hand, Cu₃NNi is observed to be non-magnetic.

Using ab initio density functional calculations, we have investigated the stability and electronic structure of pure and oxygen doped semiconducting Cu₃N. The oxygen can be accommodated in the system without structural instability as the formation energy either decreases when oxygen substitutes nitrogen, or remains nearly same when oxygen occupies the interstitial position. The interstitial oxygen (O^I) prefers to stabilize in the unusual charge neutral state and acts as an acceptor to make the system a p-type degenerate semiconductor. In this case the hole pockets are formed by the partially occupied O^I-p states. On the other hand, oxygen substituting nitrogen (O^S) stabilizes in its usual −2 charge state and acts as a donor to make the system an n-type degenerate semiconductor. The electron pockets are formed by the conducting Cu-p states. In the case of mixed doping, holes are gradually compensated by the donor electrons and an intrinsic gap is obtained for stoichiometry. Our calculations predict the nature of doping as well as optical band gap variation in experimentally synthesized copper oxynitride. While interstitial doping contracts the lattice and increases the substitutional doping increases both lattice size and Mixed doping reduces Additionally we show that a rare intra-atomic d–p optical absorption can be realized in the pristine Cu₃N as the Fermi level lies in the gap between the Cu-d dominated anti-bonding valence state and Cu-p conducting state.

We have investigated the temperature dependent carrier transport properties of nano-crystalline copper nitride thin films synthesized by modified activated reactive evaporation. The films, prepared in a Cu-rich growth condition are found to be highly disordered and the carrier transport in these films is mainly attributed to the impurity band conduction. We have observed that no single conduction mechanism is appropriate to elucidate the carrier transport in the entire temperature range of 20 – 300 K. Therefore, we have employed different conduction mechanisms in different temperature regimes. The carrier transport of the films in the low temperature regime (20 – 150 K) has been interpreted by implementing quantum correction to the conductivity. In the high temperature regime (200 – 300 K), the conduction mechanism has been successfully analyzed on the basis of Mott’s variable range hopping mechanism. Furthermore, it can be predicted that copper ions present at the surface of the crystallites are responsible for the hopping conduction mechanism.

Zn_1-xCd_xO thin films have been prepared by sol-gel spin coating method. Structural analysis shows that the Cd substitution into the wutrzite ZnO lattice is achieved up to about 20 mol %. The optical band gap is found to decrease with the increase in Cd content. Increase in the annealing temperature up to a certain critical temperature leads to band gap narrowing because of the proper substitution of Zn by Cd and thereafter the band gap increases due to Cd re-evaporation from the lattice sites. This critical temperature lowers down with the increase in Cd doping concentration. The resistivity decreases with the increase in Cd content and increases with the increase in annealing temperature.

Copper nitride thin films have been prepared by pulsed direct current reactive magnetron sputtering. Structural, morphological and optical properties of the as-deposited films have been studied. X-ray diffraction analysis shows that the films are polycrystalline single phase of Cu ₃ N. Prominent growth along (100) plane is observed for higher nitrogen flow rate whereas growth along (111) plane is observed for relatively lower nitrogen flow rate. The band gap of this material changes from 1.02 to 1.40 eV by varying the nitrogen flow rate and deposition time.