Electronic Properties Of Nanostructures Research Articles

Investigation of drug delivery capability of single-walled carbon and boron-nitride nanotubes, boron-nitride (B16N16), and C32 fullerenes as nanocarriers of captopril drug; DFT study

Density functional theory (DFT) calculations were performed on M062X/6-31G (d) and M062X/6-311G (d, p) surfaces to investigate the interaction of captopril molecules with single-walled carbon nanotubes (SWCNT) and C32 nanoclusters. In order to enhance adsorption, a doping method was employed, and structures of single-walled boron nitride nanotubes (SWBNNT) and boron nitride nanoclusters (B16N16) were selected for improved drug delivery purposes in this study. The adsorption energy of captopril on the nanostructures was calculated in both phases. In both phases, captopril adsorption energy on nanostructures was calculated. The negative values of adsorption energy showed that the interaction between captopril and nanostructures is exothermic. The adsorption energy values were higher in the gas phase compared to the aqueous phase, indicating a stronger interaction in the gas phase. The density of states (DOS) study was employed to evaluate the effect of molecular adsorption on the electronic properties of nanostructures. The results revealed that the B16N16 nanocluster approached the Fermi level more closely after drug adsorption compared to other nanostructures. Quantum Theory of Atoms in Molecules (QTAIM) calculations showed that there is a weak interaction between captopril and both nanostructures. Based on the adsorption energy values obtained from both methods, the interaction between captopril and SWCNT was found to be stronger than that between captopril and SWBNNT, whereas the interaction in the B16N16 nanocluster was found to be equal to that in C32-fullerene. Significant changes in ΔEg values were observed for Captopril@SWCNT and Captopril@B16N16-fullerene in each method, indicating the conductivity of these two structures increased more after captopril adsorption compared to other nanostructures. Therefore, SWBNNT and B16N16-fullerene can serve as captopril nanosensors.

(Invited, Digital Presentation) Synthesis and Atomic Scale Characterization of 2D Layered Heterostructures Atom by Atom: An Ultra-high Resolution Aberration-corrected Electron Microscopy Study

Defects can have a profound effect on the macroscale physical, chemical, and electronic properties of nanostructures. They can lead to structural distortions, introduce extra states in the band gap and give rise to excess potential locally at buried interfaces. While defects and interfaces have been a well-studied subject for decades, little is known about their local atomic and chemical structure, sub-Angstrom structural distortions within their vicinity.Using ultra-high-resolution aberration-corrected S/TEM imaging and spectroscopy, this talk will discuss our recent efforts on the determination of the defect chemistry and sub-Angstrom relaxation effects in nanostructures around at the interfaces in the family of 2D crystal heterostructures. In the family of 2D crystal transition metal dichalcogenides (TMDs) alloys, we report how on anisotropy of the building blocks in the 2D heterostructure, such as ReS2/MoS2 and WS2/Graphene, and their epitaxy and strain at the interface can affect their nucleation and growth. This work will further uncover the structural distortions that occur in these heterostructure across various length scales and reveals the underlying physics of the formation of such heterostructures and their strain state resulting from CVD synthesis.

(Invited) Probing the Structure and Dynamic Behaviors of Heterogeneous Functional Materials with the Atomic Resolution in Real-Time

The recent advancement of aberration-corrected transmission electron microscopy (TEM) and in situ techniques unlocks a door to a new era of discovery in materials science. It allows us to study the local structure, chemical composition, and electronic properties of nanostructures with the atomic resolution, and observe the dynamic evolution of materials in response to applied fields and to changes in environments in real-time. In this talk, I will present our work on the development of in-situTEM techniques for imaging electric polarization, probing the nucleation and growth of ferroelectric domains during electric polarization switching, and observing thedynamic reaction and structural evolution of heterogeneous functional materials under realistic conditions with atomic precisionthrough a MEMS-based, electron-transparent closed cell with a heating stage.

Chirality and Nanophotonics

Due to advances in nanofabrication and in the theoretical understanding of their properties, chiral nano/metamaterials allow us to explore the limits of interaction between circularly polarized light (CPL) and matter. The essential geometrical property of these materials is that they lack mirror symmetry.1, 2 Nowadays, nanofabrication allows an unprecedented degree of control over the geometry and symmetries of materials, at scales much smaller than the wavelength of light. The relevant nanofabrication methods involve lithography and bioassembly from both top-down and bottom-up strategies. In addition, the strong field enhancements at the surface of plasmonic materials can locally sculpt the electromagnetic fields and achieve exotic states of light. As a consequence, remarkable physical phenomena have emerged, such as negative refractive index and superchiral light. Chiral nanomaterials are currently considered for numerous technological applications, including chiral molecular sensing, separation and synthesis, super-resolution imaging, nanorobotics, and ultra-thin broadband optical components for CPL. The latter include CPL absorbers, polarizers and mirrors. This special issue covers a wide variety of subjects that illustrate well the richness of the research field.1, 2 Among the topics addressed here are: control of the chiroptical properties, circular dichroism, plasmonic and biomolecular chiral responses, circular birefringence, superchiral light, asymmetric transmission, optical forces, helical waveguides, orbital angular momentum, quantum mechanical theory of chiral nanostructures, bioassemblies and hybrid nanostructures, photoluminescence in chiral particles, optical activity from hierarchical chiral systems, photoacoustic circular dichroism, extrinsic chirality, interactions of nanocrystals with chiral biomolecules that are of interest for the development of pharmaceuticals, chiral meta-atoms and metamaterials, magnetochiral effects, nonlinear optical chiroptics, surface-enhanced Raman optical activity, and chiral negative refractive index materials. Finally, it has been a great pleasure and honor to edit this special issue referring to the Chirality & Multiphoton NanoPhotonics 2016 International Scientific Seminar of the Royal Society. We thank all our colleagues who attended the event, as well as those who provided their excellent contributions to this issue. We are also very grateful to Dr. Anja Wecker and the entire editorial team of Advanced Optical Materials for their assistance in preparing the special issue. Ventsislav K. Valev is a Research Fellow of the Royal Society and Reader in the Department of Physics, at the University of Bath, UK, where he heads the MultiPhoton NanoPhotonics group. Prior to taking up this post, he was a Research Fellow in the Cavendish Laboratory, at the University of Cambridge. He received his Ph.D. in 2006 from Radboud University Nijmegen in the Netherlands. His research focusses on the application of chiral plasmonic nano/metamaterials to achieve enhanced chiroptical effects, especially in nonlinear optics. Alexander O. Govorov is Distinguished Professor of Theoretical Physics at Ohio University in Athens, USA. He received his Ph.D. in 1991 from the Institute of Semiconductor Physics, Novosibirsk, Russia. His research is focused on the theory of optical and electronic properties of nanostructures and bioassemblies. John Pendry is a condensed matter theorist and has worked at Imperial since 1981. He has worked extensively on electronic and structural properties of surfaces developing the theory of low energy diffraction and of electronic surface states. He founded the field of “metamaterials”, a concept for engineered structures whose electromagnetic properties depend on their internal structure rather than their chemical constitution. He discovered that a perfect lens manufactured from negatively refracting material would circumvent Abbe's diffraction limit to spatial resolution, which has stood for more than a century. His most recent innovation of transformation optics gives the metamaterial specifications required to rearrange electromagnetic field configurations at will.

Effects of edge reconstruction on the common groups terminated zigzag phosphorene nanoribbon

Edge configuration plays an important role in the electronic properties of nano-structures. In this work, we perform first-principles calculations to study the effects of the cooperation between neighbor groups on the edge configuration and the electronic properties of zigzag-PNRs (ZPNRs) terminated by common groups H, F, O, S and OH. We find that the cooperation has little effect on the H(F)-terminated ZPNRs, but gives rise to an edge reconstruction for the O(S)-terminated ZPNRs. The edge reconstruction derives from the repulsion between neighbor O atoms and the distortion of the P skeleton induced by the p state coupling among the edge, second edge and third edge P atoms. In comparison to the H-terminated ZPNRs, O-terminated ZPNRs are also a semiconductor and enlarge the band gap, but bring about an extra transport channel for the charge transport at the edge and decreases the effective mass of the electron and hole. OH-terminated ZPNRs also undergo a doubling of the unit cell (UC) along the periodic direction because of the different directions of the neighbor O–H bonds. In comparison with the H-terminated ZPNRs, OH-terminated ZPNRs show a similar band gap and electronic effective mass, but increase the effective mass of the hole.

A New Approach for Calculating the Band Gap of Semiconductors within the Density Functional Method

Within the framework of the density functional theory, the method was developed to calculate the band gap of semiconductors. We have evaluated the band gap for a number of monoatomic and diatomic semiconductors (Sn, Ge, Si, SiC, GaN, C, BN, AlN). The method gives the band gap of almost experimental accuracy. An important point is the fact that the developed method can be used to calculate both localized states (energy deep levels of defects in crystal), and electronic properties of nanostructures.

UV resonant Raman scattering facility at Elettra

We present a newly developed resonant Raman scattering instrument working in the UV spectral range. This set-up, which exploits the UV synchrotron radiation source available at Elettra (Trieste, Italy), results in an innovative spectroscopic facility to be used for addressing a large array of open problems, ranging from the electronic properties of nanostructures and strongly correlated materials to biochemistry.

Nanomaterials for Neural Interfaces

AbstractThis review focuses on the application of nanomaterials for neural interfacing. The junction between nanotechnology and neural tissues can be particularly worthy of scientific attention for several reasons: (i) Neural cells are electroactive, and the electronic properties of nanostructures can be tailored to match the charge transport requirements of electrical cellular interfacing. (ii) The unique mechanical and chemical properties of nanomaterials are critical for integration with neural tissue as long‐term implants. (iii) Solutions to many critical problems in neural biology/medicine are limited by the availability of specialized materials. (iv) Neuronal stimulation is needed for a variety of common and severe health problems. This confluence of need, accumulated expertise, and potential impact on the well‐being of people suggests the potential of nanomaterials to revolutionize the field of neural interfacing. In this review, we begin with foundational topics, such as the current status of neural electrode (NE) technology, the key challenges facing the practical utilization of NEs, and the potential advantages of nanostructures as components of chronic implants. After that the detailed account of toxicology and biocompatibility of nanomaterials in respect to neural tissues is given. Next, we cover a variety of specific applications of nanoengineered devices, including drug delivery, imaging, topographic patterning, electrode design, nanoscale transistors for high‐resolution neural interfacing, and photoactivated interfaces. We also critically evaluate the specific properties of particular nanomaterials—including nanoparticles, nanowires, and carbon nanotubes—that can be taken advantage of in neuroprosthetic devices. The most promising future areas of research and practical device engineering are discussed as a conclusion to the review.

Analysis of strain fields in silicon nanocrystals

Strain has a crucial effect on the optical and electronic properties of nanostructures. We calculate the atomistic strain distribution in silicon nanocrystals up to a diameter of 3.2 nm embedded in an amorphous silicon dioxide matrix. A seemingly conflicting picture arises when the strain field is expressed in terms of bond lengths versus volumetric strain. The strain profile in either case shows uniform behavior in the core, however, it becomes nonuniform within 2–3 Å distance to the nanocrystal surface: tensile for bond lengths whereas compressive for volumetric strain. We reconcile their coexistence by an atomistic strain analysis.

Atomic-Scale Templates Patterned by Ultrahigh Vacuum Scanning Tunneling Microscopy on Silicon

The ultrahigh vacuum (UHV) scanning tunneling microscope (STM) enables patterning and characterization of the physical, chemical, and electronic properties of nanostructures on surfaces with atomic precision. On hydrogen-passivated Si(100) surfaces, selective nanopatterning with the STM probe allows the creation of atomic-scale templates of dangling bonds surrounded by a robust hydrogen resist. Feedback-controlled lithography, which can remove a single hydrogen atom from the Si(100):H surface, demonstrates high-resolution nanopatterning. The resulting patterns can be used as templates for a variety of materials to form hybrid silicon nanostructures while maintaining a pristine background resist. The versatility of this UHV-STM nanolithography approach has led to its use on a variety of other substrates, including alternative hydrogen-passivated semiconductor surfaces, molecular resists, and native oxide resists. This review discusses the mechanisms of STM-induced hydrogen desorption, the postpatterning deposition of molecules and materials, and the implications for nanoscale device fabrication.

Monochromatic high frequency coherent phonons propagation with superlattice transducers

The availability of efficient and compact phonons transducers in the THz range would be very interesting for phonons spectroscopy, acoustic microscopy and study of vibrational and electronic properties of nanostructures. Thanks to epitaxial growth of semiconductors multilayers, high quality phononic nanostructures with standard semiconductors, such as superlattices (SL) and nanocavities can be obtained for the GHz and THz transduction. Picosecond ultrasonics experiments have been performed in transmission geometry with pump and probe incident on opposite sides of the substrate, allowing discoupling acoustic generation and detection processes. By these means, we have shown independently that SL are very efficient high frequency monochromatic phonon generators and detectors. We report on experiments where two superlattices have been grown on the opposite sides of a substrate: a first SL with uniform layer thickness over the whole surface sample is used as a generator; the other one, used as the detector, presents a thickness gradient and the location of the detection is chosen in order to have the best matching with the emitted frequency. This setup is used to study the propagation of monochromatic high frequency coherent phonons as a function of temperature.

Scanning tunneling microscopy and spectroscopy of nanostructures

Recent advances in low-temperature scanning tunneling microscopy and spectroscopy have provided new opportunities for investigating locally the geometric and electronic properties of nanostructures on surfaces. Four examples are chosen from our laboratory, which illustrate the power and the potential of this local approach. (i) Light emission from individual C 60 molecules on a Au(1 1 0) surface––challenges for an optical spectroscopic analysis on the scale of single molecules. (ii) Kondo effect of a single magnetic Ce adatom on Ag(1 1 1)––new perspectives for probing magnetic nanostructures. (iii) Two-dimensional self-assembly of supramolecular structures on metal surfaces––a step towards understanding and control of supramolecular aggregation. (iv) MgO on Ag(0 0 1): insulator at the ultrathin limit––new frontiers for the development of oxide heterostructure-based nanodevices.

High spatial resolution imaging and spectroscopy in nanostructures

The challenge during the characterization of nanostructures is in extracting consistent local and spatially varying information from the structure and correlating it to the new physics that appears at the nanoscale. Recent years have seen exciting advances in imaging and spectroscopy techniques that can achieve this goal. The techniques offer the possibility to directly investigate local properties of materials with sub-nanometre spatial resolution. In this paper we review, from the perspective of our own contributions to the field of carbon nanostructures, recent advances in the application of nanoanalysis. Complementary techniques of spatially resolved electron, and scanning tunneling microscopy and spectroscopy, can be used to characterize and correlate the structure, topology, chemistry and electronic properties of nanostructures. Often the interpretation of the data needs to come from comparison with adequate theoretical models.