This work demonstrates that chiral imprinted CdSe quantum dots (QDs) can act as spin selective filters for charge transport. The spin filtering properties of chiral nanoparticles were investigated by magnetic conductive-probe atomic force microscopy (mCP-AFM) measurements and magnetoresistance measurements. The mCP-AFM measurements show that the chirality of the quantum dots and the magnetic orientation of the tip affect the current-voltage curves. Similarly, magnetoresistance measurements demonstrate that the electrical transport through films of chiral quantum dots correlates with the chiroptical properties of the QD. The spin filtering properties of chiral quantum dots may prove useful in future applications, for example, photovoltaics, spintronics, and other spin-driven devices.

We review a recently discovered phenomenon, the chiral induced spin selectivity (CISS) effect, that can enable a new technology for the injection of spin polarized current without the need for a permanent magnetic layer. The effect occurs in chiral molecules and systems without parity symmetry, i.e. systems that do not have inversion symmetry. The theoretical foundations for the effect are presented first and then followed by several examples of spin-valves that are based on chiral systems. The CISS-based spin valves introduce the possibility to inject spin current without the use of a permanent magnet and to achieve relatively large magnetoresistance at room temperature.

It is shown that "spontaneous magnetization" occurs when chiral oligopeptides are attached to ferrocene and are self-assembled on a gold substrate. As a result, the electron transfer, measured by electrochemistry, shows asymmetry in the reduction and oxidation rate constants; this asymmetry is reversed between the two enantiomers. The results can be explained by the chiral induced spin selectivity of the electron transfer. The measured magnetization shows high anisotropy and the "easy axis" of magnetization is along the molecular axis.

We discuss spin injection and spin valves, which are based on organic and biomolecules, that offer the possibility to overcome some of the limitations of solid-state devices, which are based on ferromagnetic metal electrodes. In particular, we discuss spin filtering through bacteriorhodopsin in a solid state biomolecular spin valve that is based on the chirality induced spin selectivity (CISS) effect and shows a magnetoresistance of ∼2% at room temperature. The device is fabricated using a layer of bacteriorhodopsin (treated with n-octyl-thioglucoside detergent: OTG-bR) that is adsorbed on a cysteamine functionalized gold electrode and capped with a magnesium oxide layer as a tunneling barrier, upon which a Ni top electrode film is placed and used as a spin analyzer. The bR based spin valves show an antisymmetric magnetoresistance response when a magnetic field is applied along the direction of the current flow, whereas they display a positive symmetric magnetoresistance curve when a magnetic field is applied perpendicular to the current direction.

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We report here the investigations on the size dependent variation of magnetic properties of nickel ferrite nanoparticles. Nickel ferrite nanoparticles of different sizes (14 to 22 nm) were prepared by the sol-gel route at different annealing temperatures. They are characterized by TGA-DTA, XRD, SEM, TEM and Raman spectroscopy techniques for the confirmation of the temperature of phase formation, thermal stability, crystallinity, morphology and structural status of the nickel ferrite nanoparticles. The magnetization studies revealed that the saturation magnetization (Ms), retentivity (Mr) increase, while coercivity (Hc) and anisotropy (Keff) decrease as the particle size increases. The observed value of Ms is found to be relatively higher for a particle size of 22 nm. In addition, we have estimated the magnetic domain size using magnetic data and correlated to the average particle size. The calculated magnetic domain size is closely matching with the particle size estimated from XRD. Impedance spectroscopy was employed to study the samples in an equivalent circuit to understand their transport phenomena. It shows that nickel ferrite nanoparticles exhibit a non-Debye behavior with increasing particle size due to the influence of increasing disorders, surface effects, grain size and grain boundaries, etc.

The carrier density dependent current–voltage (J−V) characteristics of electrochemically prepared poly(3-methylthiophene) (P3MeT) have been investigated in Pt/P3MeT/Al devices, as a function of temperature from 280 to 84 K. In these devices, the charge transport is found to be mainly governed by different transport regimes of space charge limited conduction (SCLC). In a lightly doped device, SCLC controlled by exponentially distributed traps (Vl+1 law, l > 1) is observed in the intermediate voltage range (0.5–2 V) at all temperatures. However, at higher bias (>2 V), the current deviates from the usual Vl+1 law where the slope is found to be less than 2 of the logJ–logV plot, which is attributed to the presence of the injection barrier. These deviations gradually disappear at higher doping level due to reduction in the injection barrier. Numerical simulations of the Vl+1 law by introducing the injection barrier show good agreement with experimental data. The results show that carrier density can tune the charge transport mechanism in Pt/P3MeT/Al devices to understand the non-Ohmic behavior. The plausible reasons for the origin of injection barrier and the transitions in the transport mechanism with carrier density are discussed.

Polypyrrole (PPy) has been synthesized electrochemically on platinum substrate by varying synthesis temperature and dopant concentration. The charge transport in PPy has been investigated as a function of temperature for both in-plane and out-of-plane geometry in a wide temperature range of 5 K–300 K. The charge transport showed strong anisotropy and various mechanisms were used to explain the transport. The conductivity ratio, σr = σ(300 K)/σ(5 K) is calculated for each sample to quantify the relative disorder. At all the temperatures, the conductivity values for in-plane transport are found to be more for PPy synthesized at lower temperature, while the behavior is found to be different for out-of-plane transport. The carrier density is found to play a crucial role in case of in-plane transport. An effort has been made to correlate charge transport to morphology by analyzing temperature and frequency dependence of conductivity. Charge transport in lateral direction is found to be dominated by hopping whereas tunneling mechanisms are dominated in vertical direction. Parameters such as density of states at the Fermi level [N(EF)], average hopping distance (R), and average hopping energy (W) have been estimated for each samples in both geometry.