Effect Of Single Atom Or Small Molecule Adsorption On The Transport Mechanism Of Nanodevices

With the rapid development of technology and life,the miniaturization of integrated circuits has become an inevitable development direction,and people have turned their research direction to nanodevices.In the early days,the construction of molecular devices was modeled on metal electrodes-organic molecules-metal electrodes,and in experiments,precious metal materials were mostly used as electrodes,which could be made to adsorb organic molecules by stretching and fracturing due to their low hardness.However,the process loss is large and the manipulation is not stable and precise enough,so more functional materials are needed to replace them.The discovery and application of the giant magnetoresistance effect(GMR)has led scientists to recognize the existence of spin.Today,the subject of spintronics is a worthy direction to explore,both in terms of theoretical research and practical applications.In fact,although electronics has been developed and applied for more than a hundred years,what has been used and studied in circuits and electronic devices is basically the flow of electric current,that is,the flow of electric charge,which has nothing to do with spin at all.Spintronics is the use of the spin and magnetic moment of electrons,so that not only the charge transport but also the spin and magnetic moment of electrons are included in solid state devices.Since then,there has been a great deal of theoretical and experimental research on spintronics.The materials used in spintronics require high electron polarization rates and long electron spin relaxation times.Many new materials,such as magnetic semiconductors,semimetals,etc.,have been extensively studied in recent years to show the properties required for spintronics applications.Such spintronics-based devices will be significantly better than conventional electronic devices,with faster response time and lower energy consumption than charge transport of electrons.From the basic theory and experimental techniques,it is demonstrated that molecules often have weak spin-orbit coupling and hyperfine interactions,which makes it possible to maintain spin coherence over longer relaxation times and distances in molecular electronics systems than in conventional metal and semiconductor materials.Therefore,molecular spintronic devices have more important development prospects.In conclusion,for traditional electronics and electronic properties,spin is related to magnetism and charge is related to current.Magnetism is used for long-term memory,and current is used for logical operations.Therefore,the direction of spintronics development points to:superior magnetic storage technology;traditional logic circuits combined with spin such as spin semiconductor devices;spin-related logic circuits combined with magnetoelectronics.In this paper,we analyzed the spin electron transport properties of different molecular devices by first-principles calculations based on density generalized function theory(DFT)combined with the nonequilibrium Green’s function approach(NEGF).In our first job,the transport properties of a single perylene-3,4,9,10-tetracarboxylic dianhydride(PTCDA)molecular device before and after adsorbing single heavy metal atoms Ni,Pd,Cd,Cu,Zn,and Ag have been investigated.We find that the adsorption of a single Ni or Pd atom has a little modulation on the I-V characteristic of the junction.However,the adsorptions of a single Cd,Cu,Zn,and Ag atom can redistribute the charge of the junction,leading to the obvious shift of the transmission spectra.The results of this study have certain guiding significance for the practical preparation of heavy metal atom sensors for organic molecules in the future.In the second job,the physical mechanism of oxygen molecule adsorption on the regulation of spin-polarized transport properties of mono-anthracene molecular devices with graphene nanoribbons as electrodes was investigated.The calculated results show that when the oxygen molecules are not adsorbed,the mono-anthracene molecules attached to the graphene nanoribbons in a transverse manner have a better spin filtering effect than the mono-anthracene molecules attached to the graphene nanoribbons in a longitudinal manner.When oxygen adsorbs the mono-anthracene molecules,the spin currents of both configurations decrease significantly,but the spin filtering effect is enhanced.In particular,the devices with mono-anthracene molecules attached to the graphene nanoribbons in atransverse manner consistently maintain nearly 100%spin filtering efficiency in the ± 0.5 V region.The spin-polarization transport spectrum,transport eigenstates and spin-filtration efficiency of the devices were analyzed to explain in detail the physical mechanism of the spin transport properties of the devices and the improvement of spin-filtration behavior of the devices by adsorption of oxygen molecules.In the third job,we investigate the spin-resolved transport properties of sawtooth-shaped silicon carbon nanoribbons with different edge hydrogenations.Double hydrogenation on either edge carbon or silicon atoms can break the magnetic simplicity under single hydrogenation and change it from initial metallicity to semimetallicity in the ferromagnetic state.Under the P magnetic structure,the double hydrogenation on the edge carbon or silicon atoms can induce and reverse a perfect spin-filtering behavior with a spin-filtering efficiency close to 100%.Under the AP magnetic structure,the double hydrogenation on the edge carbon or silicon atoms can significantly improve the spin rectification behavior of zSiCNR devices,and the corresponding spin rectification ratios of α-spin or β-spin currents are significantly increased.The above findings are useful for their functional applications in SiC spin-related nanodevices.In the fourth work,we present the spin polarization transport properties of the devices composed of H-zSiCNRs-2H and 2H-zSiCNRs-H in this paper to study the spin polarization transport properties of the devices composed of asymmetric hydrogenated silicon carbide nanoribbons.The computational results show that when the electrode is set as a P spin structure,the device exhibits a double spin rectification effect and the two spin rectifications are in the same direction.When the electrode is set to AP spin structure,the device exhibits a significant spin filtering effect,and the up spin current exhibits a superior spin rectification effect compared to the down spin.These properties provide design ideas for future design of functional devices.