Nanoarhitectonics of Inorganic-Organic Silica-Benzil Composites: Synthesis, Nanocrystal Morphology and Micro-Raman Analysis.

The synthesis of nanosized organic benzil (C6H5CO)2 crystals within the mesoporous SiO2 host matrix was investigated via X-ray diffraction, transmission electron microscopy, Raman spectroscopy, and ab initio lattice dynamics analysis. Combining these methods, we have proved that the main structural properties of benzil nanocrystals embedded into SiO2 host membranes with pore diameters of 6.0, 7.8, 9.4, and 13.0 nm are preserved compared to a bulk benzil crystal. Space confinement has an insignificant impact on the lattice vibrational properties of benzil crystals implanted into the host matrices. The ab initio lattice dynamics calculation of the phonon spectrum in the Brillouin zone center shows the mechanical and dynamical stability of benzil lattice, revealing very low optical frequency of 11 cm-1 at point Γ.

Scale-up synthesis of high-quality solid-state-processed CsCuX (X = Cl, Br, I) perovskite nanocrystal materials toward near-ultraviolet flexible electronic properties.

High-quality CsCu2X3 and Cs3Cu2X5 (X = Cl, Br, I) nanocrystals (NCs) exhibit excellent optoelectronic, physical, and chemical properties for detection of UV radiation due to large carrier mobility and lifetime, and heavy atoms. The nanocrystal materials can be prepared via a low-cost and simple solid-state synthesis. However, poor reproducibility and complex synthesis methods of obtaining perovskite NC thin films represent a drawback for the fabrication of the commercial photoelectric device. To address these issues, we develop highly stable CsCu2X3 and Cs3Cu2X5 NC materials using a facile solid-state reaction method for the scale-up production of halogen lead-free perovskites. We suggest a distinctive way to design a series of nanocrystalline perovskites using short-term synthesis and study the mechanism of perovskite formation using thermal solid-state synthesis. These all-inorganic and lead-free CsCu2X3 and Cs3Cu2X5 exhibit large photoluminescence quantum yields (PLQYs) up to 95.2%. Moreover, flexible paper photodetectors based on this series of lead-free perovskites show strong photoselectivity and bending stability at 254 nm, 365 nm, and 405 nm wavelengths. High-quality responses with a responsivity of 1.1 × 10-3 A W-1 and detectivity of 2.71 × 109 jones under UV illumination (10 µW cm-2) at a bias voltage of 5 mV are demonstrated. These results open prospects for designing photodetectors, LEDs, and other photosensitive devices.

Microwave characterization of aqueous amino acid solutions using the multifrequency WGM resonator technique.

Amino acids play essential role for humans. We studied the dielectric properties of the basic aliphatic amino acids and polar positive amino acids in solutions of different concentrations. The high-Q single microwave whispering gallery-mode (WGM) quartz dielectric resonator based technique, enhanced to a number of measurement frequencies, was applied. The technique allows liquid investigation of micro- to nano- liter volumes filled in microfluidic channel on six discrete frequencies in the 30-40 GHz range. The dependencies of the complex permittivity on the molar mass show almost linear behavior for aliphatic amino acids at different concentrations. The study results are in good agreement with the calculated data obtained by Cole-Cole equation.

On the issue of textured crystallization of Ba(NO3)2 in mesoporous SiO2: Raman spectroscopy and lattice dynamics analysis.

The lattice dynamics of preferentially aligned nanocrystals formed upon drying of aqueous Ba(NO3)2 solutions in a mesoporous silica glass traversed by tubular pores of approximately 12 nm are explored by Raman scattering. To interpret the experiments on the confined nanocrystals polarized Raman spectra of bulk single crystals and X-ray diffraction experiments are also performed. Since a cubic symmetry is inherent to Ba(NO3)2, a special Raman scattering geometry was utilized to separate the phonon modes of Ag and Eg species. Combining group-theory analysis and ab initio lattice dynamics calculations a full interpretation of all Raman lines of the bulk single crystal is achieved. Apart from a small confinement-induced line broadening, the peak positions and normalized peak intensities of the Raman spectra of the nanoconfined and macroscopic crystals are identical. Interestingly, the Raman scattering experiment indicates the existence of comparatively large,∼10-20 µm, single-crystalline regions of Ba(NO3)2 embedded in the porous host, near three orders of magnitude larger than the average size of single nanopores. This is contrast to the initial assumption of non-interconnected pores. It rather indicates an inter-pore propagation of the crystallization front, presumably via microporosity in the pore walls.

Noise suppression beyond the thermal limit with nanotransistor biosensors.

Transistor biosensors are mass-fabrication-compatible devices of interest for point of care diagnosis as well as molecular interaction studies. While the actual transistor gates in processors reach the sub-10 nm range for optimum integration and power consumption, studies on design rules for the signal-to-noise ratio (S/N) optimization in transistor-based biosensors have been so far restricted to 1 µm2 device gate area, a range where the discrete nature of the defects can be neglected. In this study, which combines experiments and theoretical analysis at both numerical and analytical levels, we extend such investigation to the nanometer range and highlight the effect of doping type as well as the noise suppression opportunities offered at this scale. In particular, we show that, when a single trap is active near the conductive channel, the noise can be suppressed even beyond the thermal limit by monitoring the trap occupancy probability in an approach analog to the stochastic resonance effect used in biological systems.

Amyloid-beta peptide detection via aptamer-functionalized nanowire sensors exploiting single-trap phenomena.

New highly sensitive direct methods for the early detection of peptides involved in Alzheimer's disease (AD) are required in order to prolong effective and healthy memory and thinking capabilities and also to stop the factors resulting in AD. In this contribution, we report the successful demonstration of a label-free approach for the detection of amyloid-beta (Aß) peptides by highly selective aptamers immobilized onto the SiO2 surface of the fabricated sensors. A modified single-stranded deoxyribonucleic acid (ssDNA) aptamer was specially designed and synthesized to detect the target amyloid beta-40 sequence (Aß-40). Electrolyte-insulator-semiconductor (EIS) structures as well as silicon (Si) nanowire (NW) field-effect transistors (FETs) covered with a thin SiO2 dielectric layer have been successfully functionalized with Aß-40-specific aptamers and used to detect ultra-low concentrations of the target peptide. The binding of amyloid-beta peptides of different concentrations to the surface of the sensors varied in the range from 0.1 pg/ml to 10 µg/ml resulting in a change of the surface potential was registered by the fabricated devices. Moreover, we show that the single-trap phenomena observed in the novel Si two-layer (TL) NW FET structures with advanced characteristic parameters can be effectively used to increase the sensitivity of nanoscale sensors. The obtained experimental data demonstrate a highly sensitive and reliable detection of ultra-low concentrations of the Aß-40 peptides. This opens up prospects for the development of real-time electrical biosensors for studying and understanding different stages of AD by utilizing Si TL NW FET structures fabricated on the basis of cost-efficient CMOS-compatible technology.

Towards pharmacological treatment screening of cardiomyocyte cells using Si nanowire FETs.

Silicon nanowires (Si NWs) are the most promising candidates for recording biological signals due to improved interfacing properties with cells and the possibility of high-speed transduction of biochemical signals into detectable electrical responses. The recording of extracellular action potentials (APs) from cardiac cells is important for fundamental studies of AP propagation features reflecting cell activity and the influence of pharmacological substances on the signal. We applied a novel approach of using fabricated Si NW field-effect transistors (FETs) in combination with fluorescent marker techniques to evaluate the functional activity of cardiac cells. Extracellular AP signal recording from HL-1 cardiomyocytes was demonstrated. This method was supplemented by studies of the pharmacological effects of stimulations using noradrenaline (NorA) as a modulator of functional activity on a cellular and subcellular levels, which were also tested using fluorescent marker techniques. The role of calcium alteration and membrane potential were revealed using Fluo-4 AM and tetramethylrhodamine, methyl ester, perchlorate (TMRM) fluorescent dyes. In addition, chemical treatment with sodium dodecyl sulfate (SDS) solutions was tested. The results obtained demonstrate positive prospects for AP monitoring in different treatments for studies related to a wide range of myocardial diseases using lab-on-chip technology.

Microwave characterization of low-molecular-weight antioxidant specific biomarkers.

Antioxidants play a crucial role in the life sciences, as the regulators of biochemical reactions. We studied the dielectric properties of the low-molecular weight antioxidant specific biomarkers sodium ascorbate and glutathione in solutions of different concentrations. The biomarkers are multifunctional metabolites relevant to the reactive oxygen species (ROS) scavenging system of cells. The newly developed high-Q microwave whispering-gallery-mode (WGM) dielectric resonator based technique was applied. The technique allows investigation of liquids of nanoliter volumes filled in microfluidic channel within several milliseconds. The revealed peculiarities in the dependence of permittivity on concentrations of the sodium ascorbate and glutathione solutions are explained by differences in relaxation times and loses introduced by molecules of different shapes. We suggest that this novel approach offers the potential for the detection and characterization of ROS-relevant biomarkers with millisecond-time resolution.

Liquid-Gated Two-Layer Silicon Nanowire FETs: Evidence of Controlling Single-Trap Dynamic Processes.

We fabricate two-layer (TL) silicon nanowires (NW) field-effect transistors (FETs) with a liquid gate. The NW devices show advanced characteristics, which reflect reliable single-electron phenomena. A strong modulation effect of channel conductivity with effectively tuned parameters is revealed. The effect opens up prospects for applications in several research fields including bioelectronics and sensing applications. Our results shed light on the nature of single trap dynamics which parameters can be fine-tuned to enhance the sensitivity of liquid-gated TL silicon nanowire FETs.

Noise spectroscopy of tunable nanoconstrictions: molecule-free and molecule-modified.

Devices with metallic nanoconstrictions functionalized by organic molecules are promising candidates for the role of functional devices in molecular electronics. However, at the moment little is known about transport and noise properties of nanoconstriction devices of this kind. In this paper, transport properties of bare gold and molecule-containing tunable cross-section nanoconstrictions are studied using low-frequency noise spectroscopy. Normalized noise power spectral density (PSD) S I /I 2 dependencies are analyzed for a wide range of sample resistances R from 10 Ohm to 10 MOhm. The peculiarities and physical background of the flicker noise behavior in the low-bias regime are studied. It is shown that modification of the sample surface with benzene-1,4-dithiol molecules results in a decrease of the normalized flicker noise spectral density level in the ballistic regime of sample conductance. The characteristic power dependence of normalized noise PSD as a function of system resistance is revealed. Models describing noise behavior for bare gold and BDT modified samples are developed and compared with the experimental data for three transport regimes: diffusive, ballistic and tunneling. Parameters extracted from models by fitting are used for the characterization of nanoconstriction devices.

Photoconductivity, pH Sensitivity, Noise, and Channel Length Effects in Si Nanowire FET Sensors.

Silicon nanowire (NW) field-effect transistor (FET) sensors of various lengths were fabricated. Transport properties of Si NW FET sensors were investigated involving noise spectroscopy and current-voltage (I-V) characterization. The static I-V dependencies demonstrate the high quality of fabricated silicon FETs without leakage current. Transport and noise properties of NW FET structures were investigated under different light illumination conditions, as well as in sensor configuration in an aqueous solution with different pH values. Furthermore, we studied channel length effects on the photoconductivity, noise, and pH sensitivity. The magnitude of the channel current is approximately inversely proportional to the length of the current channel, and the pH sensitivity increases with the increase of channel length approaching the Nernst limit value of 59.5 mV/pH. We demonstrate that dominant 1/f-noise can be screened by the generation-recombination plateau at certain pH of the solution or external optical excitation. The characteristic frequency of the generation-recombination noise component decreases with increasing of illumination power. Moreover, it is shown that the measured value of the slope of 1/f-noise spectral density dependence on the current channel length is 2.7 which is close to the theoretically predicted value of 3.

Effect of Gamma Irradiation on Dynamics of Charge Exchange Processes between Single Trap and Nanowire Channel.

In the present study, transport properties and single trap phenomena in silicon nanowire (NW) field-effect transistors (FETs) are reported. The dynamic behavior of drain current in NW FETs studied before and after gamma radiation treatment deviates from the predictions of the Shockley-Read-Hall model and is explained by the concept taking into account an additional energy barrier in the accumulation regime. It is revealed that dynamics of charge exchange processes between single trap and nanowire channel strongly depend on gamma radiation treatment. The results represent potential for utilizing single trap phenomena in a number of advanced devices.

Sensitivity enhancement of Si nanowire field effect transistor biosensors using single trap phenomena.

Trapping-detrapping processes in nanostructures are generally considered to be destabilizing factors. However, we discovered a positive role for a single trap in the registration and transformation of useful signal. We use switching kinetics of current fluctuations generated by a single trap in the dielectric of liquid-gated nanowire field effect transistors (FETs) as a basic principle for a novel highly sensitive approach to monitor the gate surface potential. An increase in Si nanowire FET sensitivity of 400% was demonstrated.

Liquid and back gate coupling effect: toward biosensing with lowest detection limit.

We employ noise spectroscopy and transconductance measurements to establish the optimal regimes of operation for our fabricated silicon nanowire field-effect transistors (Si NW FETs) sensors. A strong coupling between the liquid gate and back gate (the substrate) has been revealed and used for optimization of signal-to-noise ratio in subthreshold as well as above-threshold regimes. Increasing the sensitivity of Si NW FET sensors above the detection limit has been predicted and proven by direct experimental measurements.

Features of transport in ultrathin gold nanowire structures.

The origin of the interface formation appearing due to the realization of contacts to ultrathin gold nanowire devices is revealed. Such interfaces play an important role in transport mechanisms in nanowire structures and can determine the electrical and operating parameters of a nanodevice. Based on experimental results, the specific electrical properties of bundles of ultrathin gold nanowires fabricated by wet chemical synthesis and subsequently assembled and contacted with gold electrodes are reported. It is demonstrated that these properties are strongly affected by the monolayers of organic molecules inevitably present on the surface of the nanowires due to synthetic conditions. In particular, such layers form a potential barrier to tunneling of the electrons from contacts to the nanowires. The electric transport behavior of the investigated nanowire structures in the temperature range from 500 mK to 300 K obeys the model of thermal fluctuation-induced tunneling conduction through the nanowire-metal electrode molecular junction. Application of this model allows calculation of the parameters of the molecular potential barrier. The formation of such a molecular barrier is verified by scanning tunneling microscope (STM) and transmission electron microscope (TEM) measurements performed using a supporting graphene layer. These findings are important for designing novel nanodevices for molecular electronics on the basis of ultrathin nanowires.