Due to their self-assembly function, DNA sensors have gained much attention as next-generation sensors that require an extremely low power supply.
Study: Spin transport properties in DNA & electrically doped iron QD organo-metallic junction. Image Credit: marie_mi/Shutterstock.com
Scientists have recently used iron (Fe) quantum dots (QD) electrodes to determine the spin transport properties and quantum scattering transmission characteristics of DNA sensors at room temperature. This study is available in Materials Today: Proceedings.
The Role of Spintronics in Nanotechnology
Spintronics is an emerging field of next-generation nanoelectronics devices, which is based on the intrinsic spin property of electrons along with their magnetic moment. Spintronics has exhibited immense potential in developing devices that require low power for their operation, high density, and high-speed processing, all of which are ideal for memory electronic devices. These properties are used in optoelectronic devices, primarily for circularly polarized light. Interestingly, spintronics is also applied in a semiconductor tunnel junction.
The decay rate of spin current is directly proportional to effective spin diffusion length. Furthermore, the spin chemical potential and spin accumulation rate are directly proportional to the decay rate of spin current.
In the application of spintronics, spin current plays the most crucial role. The spin transport phenomenon includes two important configurations, i.e., parallel configuration (PC) and anti-parallel configuration (APC), which are linked to spin transmission. In semiconductors, the effective spin diffusion length is dependent on the charge flowing in the same direction as the spin current.
Typically, very thin metal oxide layers are used to develop Magneto-Tunnel Junctions (MTJ). Magnesium oxide (MgO), silicon dioxide (SiO2), and zirconium dioxide (ZrO2) are popularly utilized materials for the fabrication of tunnel junctions. Nevertheless, the limited effective function of these materials, metal oxide defects, and interdiffusion, significantly affect the development of tunnel junction devices.
Nanoparticles, such as Fe-doped carbon nanotubes (CNT), are used to fabricate tunnel junction devices. Interestingly, a group of researchers proposed the substitution of CNT with silicon carbide nanotube (SiCNT) because of its improved performance concerning density, strength, operating frequency, thermal shock resistance capacity, and resistance against adverse environments. Another nanomaterial used for spin transport study is the boron nitride nanotube.
The process of adding ions and protons to the atom or molecule is known as protonation. This process plays a catalytic role in the spin transport phenomenon. A proton is incorporated into the organo-metallic interface to facilitate efficient spin transport current.
Development of the Organo-Metallic Junction Using DNA and Fe QD
The new study investigates the organo-metallic junction, which has been developed using DNA (biomolecule) and Fe (metal) QD. This newly developed device constitutes a single-stranded DNA bound to two Fe QDs. The extended regions of these QDs are considered electrodes.
Both ends of the atomistic model are composed of QDs. A weak Coulomb interaction was maintained between electrodes and DNA. Importantly, the electrodes were doped to generate a rapid and significantly higher spin transport quantum-ballistic current flow across the central molecular region, which is basically the single DNA molecule with the extended areas of Fe QDs.
Spin Transport Properties for DNA and Fe QD Organo-Metalic Junction
The first principle approach, i.e., Non-Equilibrium Green’s Function (NEGF) and Density Functional Theory (DFT), were used to examine PC and APC configurations to understand the spin transport properties. Furthermore, the DNA sensor’s quantum scattering transmission characteristics were evaluated through Fe QD electrodes at room temperature.
The doping concentration was modified based on the applied voltage at the two ends of the electrodes. The change in the doping concentration altered the spin transport current transmission for both PC and APC configurations, which were calculated using the Landauer Büttiker formula. Transmission peaks depended on electrical doping concentration. The spin transport current for APC configuration was found to be lower, responsible for thermodynamic stability and higher channel conductivity with decreased barrier height.
In PC, more spin transport current was observed along with a greater transmission peak that represented a large number of quantum scattering channels. An increased electrical doping concentration led to a lower barrier height, facilitating a larger current flow through the central region. Nevertheless, the transmission was marginally reduced owing to the back-scattering effect. In both spin-up and spin-down PC configurations, a high current flow was observed. However, the spin-up current was significantly more compared to the spin-down current.
Estimation of Tunneling Organo Metallic Contact Resistance (TOMCR) revealed that at zero voltage, TOMCR was 99.99%, which was maintained by increasing the voltage up to 0.4. The TOMCR decreased by further increasing the voltage beyond 0.4.
The newly developed device can provide ~100% spin filtration effect for PC as well as APC at higher bias voltage and it could be a potential candidate for the development of next-generation spin-dependent devices.
Dey Roy, D. et al. (2022) Spin transport properties in DNA & electrically doped iron QD organo-metallic junction. Materials Today: Proceedings. https://www.sciencedirect.com/science/article/pii/S2214785322055110