Shachar Richter

Broad Band Enhancement of Light Absorption in Photosystem I by Metal Nanoparticle Antennas

The photosystem I (PS I) protein is one of natures most efficient light harvesting complexes and exhibits outstanding optoelectronic properties. Here we demonstrate how metal nanoparticles which act as artificial antennas can enhance the light absorption of the protein. This hybrid system shows an increase in light absorption and of circular dichroism over the entire absorption band of the protein rather than at the specific plasmon resonance wavelength of spherical metal nanoparticles (NPs). This is explained by broad-resonant and nonresonant field enhancements caused by metal NP aggregates, by the high dielectric constant of the metal, and by NP-PS I-NP antenna junctions which effectively enhance light absorption in the PS I.

Solid-state biophotovoltaic cells containing photosystem I.

The large multiprotein complex, photosystem I (PSI), which is at the heart of light-dependent reactions in photosynthesis, is integrated as the active component in a solid-state organic photovoltaic cell. These experiments demonstrate that photoactive megadalton protein complexes are compatible with solution processing of organic-semiconductor materials and operate in a dry non-natural environment that is very different from the biological membrane.

Large-Scale Fabrication of 4-nm-Channel Vertical Protein-Based Ambipolar Transistors

We suggest a universal method for the mass production of nanometer-sized molecular transistors. This vertical-type device was fabricated using conventional photolithography and self-assembly methods and was processed in parallel fashion. We used this transistor to investigate the transport properties of a single layer of bovine serum albumin protein. This 4-nm-channel device exhibits low operating voltages, ambipolar behavior, and high gate sensitivity. The operation mechanism of this new device is suggested, and the charge transfer through the protein layer was explored.

Efficient Separation of Dyes by Mucin: Toward Bioinspired White‐Luminescent Devices

The production of organic white-light-emitting devices is one of the main technological and scientifi c challenges in the fi eld of optoelectronics [ 1–4 ] because the formation of such a broad emission spectrum with the use of a single dye is diffi cult to accomplish. [ 5 , 6 ] In practice, the emission of white light is achieved by the use of a mixture of the three primary dyes, which emit red (R), green (G), and blue (B) light. [ 7 ] However, as a result of nonradiative interactions between very close color elements, such as Förster resonance energy transfer (FRET), an undesirable shift in the emission spectrum is often observed, which prevents the achievement of white-light emission. [ 8 ]

1-nanometer-sized active-channel molecular quantum-dot transistor.

One of the most debated and an unresolved issue in the field of molecular electronics is the conduction mechanism of charged molecular junctions. In contrast to solid-state quantum-dot (SQD) systems, in which the conduction is governed by repulsive coulombic interactions, this is not always the case when molecules are charged. The latter arrangement, sometimes termed molecular quantum dot (MQD) is often accompanied by strong electron–phonon interactions that can dramatically affect the way in which MQDs conducts. The outcome of this phenomenon is usually manifested by the formation of a stabilized energy level (polaron) that opens additional paths for charge transfer. Theoretical studies suggest that some unique characteristics of molecular conduction such as Negative Differential Resistance (NDR) and voltage-controlled hysteresis can be explained by the polaronic effect. Although some initial observation of NDR and hysteresis in two-terminal molecular devices were thought to be polaron related, this was not fully confirmed and the issue is still extensively debated. Moreover, although theoretical studies predict strong dependence of polaron-driven phenomena, such as a hysteresis in MQD systems upon application of an external voltage (gate voltage, VG), this has never been demonstrated experimentally. Several attempts were made to explore this gate dependence but the results revealed either evidence for strong coulomb interactions or very poor gate dependence. These results can be understood in view of the demanding conditions needed for successful measurements of voltage-driven switching and of other polaronic-related phenomena: One of the most critical conditions for the attainment of hysteresis in MQD systems is the requirement that the injected electron ‘‘stays’’ on the molecular bridge long enough for its energy to be reduced to the polaronic level; i.e, G v0, where G is the coupling frequency of the molecule to the source and/or the drain leads and v0 is the vibrational polaron frequency. Analysis of the previously demonstrated molecular transistors indicates that in all of the latter experiments the molecular system was strongly coupled to the transistor leads via covalent bonds, thus essentially reducing the polaronic effect.

UV induced formation of transparent Au–Ag nanowire mesh film for repairable OLED devices

The next generation of optoelectronic devices requires transparent conductive electrodes to be flexible, cheap, and compatible with large scale manufacturing processes. Indium Tin Oxide (ITO) electrodes are often used due to their superior transparency and conductance, however they are brittle, expensive and their fabrication requires vacuum conditions which restrict scale-up. One possible alternative to the traditional ITO electrode is the metal nanowire mesh (MNWM) electrode, which is transparent, conductive, flexible and easy to produce. In this work we present the preparation and characterization of a simple organic light emitting diode (OLED) device based on a transparent electrode made of ultrathin MNWM and a comparison to an ITO based device. We have found that MNWM electrodes offer a suitable alternative to ITO electrodes in OLED devices. We have also found that the failure rate for devices due to short circuits between the top and bottom electrodes was smaller in MNWM based devices compared to ITO based devices since the MNWM devices could be repaired to present normal OLED behavior by selectively burning the nanowires forming the short. The ability to “heal” organic devices presents an important advantage and also allows for future uses in applications such as roll to roll printing.

Tuning the Critical Temperature of Cuprate Superconductor Films with Self‐Assembled Organic Layers

Control over the T(c) value of high-T(c) superconductors by self-assembled monolayers is demonstrated (T(c) = critical temperature). Molecular control was achieved by adsorption of polar molecules on the superconductor surface (see scheme) that change its carrier concentration through charge transport or light-induced polarization.

Spatial modulation of light transmission through a single microcavity by coupling of photosynthetic complex excitations to surface plasmons.

Molecule-plasmon interactions have been shown to have a definite role in light propagation through optical microcavities due to strong coupling between molecular excitations and surface plasmons. This coupling can lead to macroscopic extended coherent states exhibiting increment in temporal and spatial coherency and a large Rabi splitting. Here, we demonstrate spatial modulation of light transmission through a single microcavity patterned on a free-standing Au film, strongly coupled to one of the most efficient energy transfer photosynthetic proteins in nature, photosystem I. Here we observe a clear correlation between the appearance of spatial modulation of light and molecular photon absorption, accompanied by a 13-fold enhancement in light transmission and the emergence of a distinct electromagnetic standing wave pattern in the cavity. This study provides the path for engineering various types of bio-photonic devices based on the vast diversity of biological molecules in nature.

Surface-Induced Conformational Changes in Doped Bovine Serum Albumin Self-Assembled Monolayers

Evidence for considerable stabilization of doped bovine serum albumin (BSA) molecules upon adsorption on gold surfaces is provided. This is compared to the surface-induced conformational changes of the bare BSA and its corresponding monolayer. The BSA unfolding phenomenon is correlated with dehydration, which in turn enables improved monolayer coverage. The stabilization mechanism is found to be partially controllable via nanodoping of the BSA molecules, upon which the dehydration process is suppressed and molecular rigidity can be varied. Our experimental data and calculations further point to the intermixing of structural characteristics and inherent molecular properties in studies of biological monolayers.

Resolving the Mystery of the Elusive Peak: Negative Differential Resistance in Redox Proteins.

Vertical molecular transistors are used to explain the nonconformal electron transfer results obtained for redox proteins. The transport characteristics of a negative differential resistance peak as appears in the transport data of azurin and its nonredox derivative are explored. A correlation between the peak and its redox center is demonstrated.