Study On Quantum Transport Properties Of The Novel Low-Dimensional Nanomaterial Devices

In nanomaterials and devices quantum effects begin to play a role,which results in many excellent characteristics of nanomaterials over the traditional materials.Thus Nano materials and devices have been one of the hot topics in scientific research due to the potential applications in supercomputer chips,energy storage and conversion,sensors and so forth.It is urgent and necessary to explore new and efficient low-dimension materials and further improve and enrich their properties by modifying,doping and constructing heterostructures,et.al.In this thesis,the electronic structures of several novel lowdimension materials and the quantum transport of devices have been studied systematically based on the first principles.Moreover,we discussed the influences of external conditionals(such as the strain,the bias voltage,the gate voltage,etc.)on the devices and analyzed physical and chemical mechanism,and revealed the possible applications in related fields.The main contents and innovations of this thesis are as follows:(1)The electronic structures of Ge P3 nanoribbons and the quantum transport behaviors of their tunneling junctions.We find that the monolayer Ge P3 nanoribbon exhibit semiconducting properties,whereas trilayer one shows metallicity.The quantum transport properties of trilayer-monolayer-trilayer tunneling junction depend on the connecting form between the central monolayer Ge P3 nanoribbon and the trilayer Ge P3 nanoribbon electrodes at two ends.With the gate voltage increasing,the conductance increases for the bottom-connecting and middle-connecting tunneling junction and decreases for the topconnecting tunneling junction.In addition,the I–V curves are approximately linear for the bottom-connecting and middle-connecting structures,and bexhibit negative differential conductance for the top-connecting structures.(2)The pure spin current and thermoelectric transport properties in a triangulene-based molecular junction.The results show that the molecular junction exhibits a perfect gate controlled spin filter effect.The pure spin current and the spin-dependent thermopower can be obtained in the molecular junction by modulating the temperature,temperature gradient and gate voltage.More importantly,a large thermospin figure of merit can be achieved by optimizing configuration of the temperature,gate voltage and chemical potential.(3)Novel two-dimensional layered material KAg Se and its potential applications in the photovoltaic devices.The KAg Se monolayer is proved to exhibit high carrier mobility and remarkable optical absorption coefficients in the visible light.Moreover,huge photocurrent can be obtained in the monolayer KAg Se-based nano devices,so is the larger photon responsivity than that in the monolayer chalcogenides and graphene based devices.In addition,layered KAg Se shows a ~ 1.5 e V direct band gap,which is among the optimum band gaps of excitonic solar cells(1.2-1.6 e V)and roughly independent of the number of layers.This is one of the innovations in the thesis.(4)A new-type of boride lateral heterojunctions(LHSs)and related properties.The results show that the monolayer boride lateral heterojunctions show a moderate direct band gaps,ultrahigh carrier mobilities,and efficient visible light absorptions.In the nano devices based on monolayer BP-BAs LHSs,the large photocurrents and photovoltaic response as the important parameters for solar cell systems are obtained in the visible range,which are far larger than those of the Mo S2-WSe2 LHS under the same external conditions,and provide a new strategy on the applications in the field of solar cells.This is another innovations in the thesis.