Quantum dots reveal spin transport properties of DNA sensors

Due to their self-assembly feature, DNA sensors have gained much attention as next-generation sensors that require an extremely low power supply.

​​​​​​​​​​​​Study: Spin transport properties in the organometallic QD junction of DNA and electrically doped iron. Image credit: marie_mi/Shutterstock.com

Scientists have recently used iron (Fe) quantum dot (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 nanoelectronic devices, which is based on the intrinsic spin property of electrons together with their magnetic moment. Spintronics has shown immense potential in the development of devices that require low power for operation, high density and high speed processing, all of which are ideal for electronic memory devices. These properties are used in optoelectronic devices, mainly for circularly polarized light. Interestingly, spintronics is also applied in a semiconductor tunnel junction.

The decay rate of the spin current is directly proportional to the effective spin diffusion length. Furthermore, the spin chemical potential and the rate of spin accumulation are directly proportional to the decay rate of the spin current.

In the application of spintronics, the spin current plays the most crucial role. The phenomenon of spin transport includes two important configurations, namely parallel configuration (PC) and antiparallel configuration (APC), which are linked to spin transmission. In semiconductors, the effective spin diffusion length depends 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 (MTJs). Magnesium oxide (MgO), silicon dioxide (SiO2) and zirconium dioxide (ZrO2) are popularly used materials for making tunnel joints. However, 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 (CNTs), are used to fabricate tunnel junction devices. Interestingly, a group of researchers proposed the replacement of CNTs with silicon carbide nanotubes (SiCNTs) due to their improved performance in terms of density, strength, operating frequency, thermal shock resistance and resistance to adverse environments. Another nanomaterial used for the study of spin transport 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 organometallic interface to facilitate an efficient spin transport current.

Development of organometallic bonding using DNA and Fe QDs

The new study investigates organometallic bonding, which has been developed using DNA (biomolecule) and Fe (metal) QDs. 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 between the electrodes and DNA was maintained. Importantly, the electrodes were doped to generate a fast and significantly higher spin transport quantum ballistic current flow through the central molecular region, which is basically the single DNA molecule with the extended Fe QD areas .

Spin transport properties for DNA and Fe organometallic QD binding

The first major 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 quantum scattering transmission characteristics of the DNA sensor were evaluated using Fe QD electrodes at room temperature.

The doping concentration was modified as a function of the voltage applied to both ends of the electrodes. The change in the doping concentration altered the transmission of the spin transport current for both PC and APC configurations, which were calculated using the Landauer Büttiker formula. The transmission peaks depended on the electrical doping concentration. The spin transport current for the APC configuration was found to be lower, responsible for the thermodynamic stability and higher channel conductivity with decreased barrier height.

In PC, more spin transport current was observed along with a larger transmission peak representing a large number of quantum scattering channels. An increased electrical doping concentration led to a lower barrier height, facilitating greater current flow through the central region. However, the transmission was marginally reduced due to the backscatter effect. In both spin-up and spin-down PC configurations, high current flow was observed. However, the spin-up current was significantly more compared to the spin-down current.

Estimation of tunnel organ metal contact resistance (TOMCR) revealed that at zero strain, TOMCR was 99.99%, which was maintained by increasing the strain up to 0.4. The TOMCR decreased further increasing the strain beyond 0.4.

The newly developed device can provide ~100% spin-filtering effect for PC as well as APC at higher bias voltage and could be a potential candidate for the development of next-generation spin-dependent devices.

reference

Dey Roy, D. et al. (2022) Spin transport properties in DNA and electrically doped iron QD organometallic junction. Materials Today: Proceedings. https://www.sciencedirect.com/science/article/pii/S2214785322055110

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