Search

Summary The ingenious construction of electron donor-acceptor (D-A) systems has been proven to be the major trend for advanced performance optoelectronic materials. However, the related development is undiversified and has become stereotyped in recent years, and the explorations of innovative architecture with both prominent optoelectronic properties and innovatively coined optoelectronic mechanisms are appealing, yet significantly challenging tasks. Here, we exploit a series of unique Janus luminogens, namely TAOs, with unique charge separation in a simple five-membered mesoionic ring. TAOs, having low molecular weight (∼329 g mol−1), present efficient aggregation-induced red/near-infrared emission (550–850 nm) with up to 21.5% of fluorescence quantum yield. An original mechanism, termed bended intramolecular charge transfer (BICT), is proposed to understand the fluorescence behavior. It is experimentally demonstrated that TAOs exhibit great potential for use as molecular transistors and can be efficiently utilized in living cells, bacteria, and brain imaging in a straightforward manner by using intravenous postinjection with outstanding photostability and biocompatibility.

Quantum transport in a single molecular transistor device is studied at finite temperature in the presence of electron-electron and electron-phonon interactions and dissipation using the Anderson-Holstein-Caldeira-Leggett model. The dissipation due to substrate is treated exactly by a canonical transformation and the electron-phonon interaction is eliminated by the Lang-Firsov transformation. Finally the effective Hamiltonian is studied using the Keldysh non-equilibrium Green function technique and the tunnelling current through the single molecular transistor is obtained at finite temperature.

A single molecular transistor is considered in the presence of electron-electron interaction, electron-phonon interaction, an external magnetic field and dissipation. The quantum transport properties of the system are investigated using the Anderson-Holstein Hamiltonian together with the Caldeira-Leggett model that takes care of the damping effect. The phonons are first removed from the theory by averaging the Hamiltonian with respect to a coherent phonon state and the resultant electronic Hamiltonian is finally solved with the help of the Green function technique due to Keldysh. The spectral function, spin-polarized current densities, differential conductance and spin polarization current are determined.

The ingenious construction of electron donor-acceptor (D-A) system has been proven to be the major trend for novel advanced-performance optoelectronic materials. However, the related development is undiversified and become stereotyped in recent years, and the explorationsof new architecture with both prominentoptoelectronic property and innovatively coined optoelectronic mechanism are appealing yet significantly challenging tasks. We herein exploit a series of novel Janus luminogens, namely TAOs, with unique charge separation in asimple five-membered mesoionic ring.TAOs having low molecular weight present efficient aggregation-induced red/near-infrared emission with up to 21.5% of fluorescence quantum yield. A new mechanism termed as bended intramolecular charge transfer (BICT) is proposed to understand the fluorescence behavior. It is experimentally demonstrated that TAOs exhibit great potential for the use as molecular transistor, and can be efficiently utilized in brain imaging straightforwardly through intravenous postinjection.

The potential of proton transfer reactions as a fundamental mechanism to realize a nanoscale molecular transistor is investigated. Employing density functional theory and the nonequilibrium Green’s function formalism, we identify molecule–graphene nanojunctions, which exhibit high- and low-conducting states depending on the specific location of protons in the molecular bridge. In addition, we show that an electrostatic gate field can control the proton transfer process and thus allow specific conductance states to be selected. In this way, the current in the junction can be switched on and off as in a field-effect transistor. The underlying mechanism is analyzed in detail., This work has been supported by the German Research Foundation (DFG) through SFB 953 and a research grant. P.B.C. acknowledges financial support from Banco Santander and Spanish MICINN (PGC2018-095953-B-I00).

Made available in DSpace on 2019-10-06T16:59:18Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-02-15 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) We demonstrated here that molecular redox films are electrochemical capacitive devices possessing specific field effect in which molecular moieties within films act as sensitive gates. We confirm that the field effect present in these redox switches is suitable in detecting, in a label-free manner (without needs of redox probe in the biological samples), biomarkers of essential importance for dengue, heart risks and inflammation, Parkinson's disease and tumors. Though the sensitiveness is high, it is governed by Thomas Fermi screening and thus depends on the target-to-receptor size ratio. Thus, we also demonstrated how this target-to-receptor size ratio affects the sensitivity. We concluded that the smaller the biological receptor the greater the sensitivity. Consequently, a larger molecular target associated with a smaller receptor provides a considerable (predictable) improvement of the sensitiveness. Institute of Chemistry São Paulo State University (UNESP Universidade Estadual Paulista), CP 355 Institute of Chemistry São Paulo State University (UNESP Universidade Estadual Paulista), CP 355

The quantum transport properties of a single molecular transistor are studied in the presence of an external magnetic field using the Keldysh Green function technique. The Anderson-Holstein-Caldeira-Leggett model is used to describe the single molecular transistor that consists of a molecular quantum dot (QD) coupled to two metallic leads and placed on a substrate that acts as a heat bath. The local electron-phonon (el-ph) interaction in the QD is decoupled by the Lang-Firsov (LF) transformation and the effective Hamiltonian is used to study the effects of an external magnetic field on the tunneling current and spin polarization of a SMT at zero temperature.The quantum transport properties of a single molecular transistor are studied in the presence of an external magnetic field using the Keldysh Green function technique. The Anderson-Holstein-Caldeira-Leggett model is used to describe the single molecular transistor that consists of a molecular quantum dot (QD) coupled to two metallic leads and placed on a substrate that acts as a heat bath. The local electron-phonon (el-ph) interaction in the QD is decoupled by the Lang-Firsov (LF) transformation and the effective Hamiltonian is used to study the effects of an external magnetic field on the tunneling current and spin polarization of a SMT at zero temperature.

Molecular electronics is one of the promising technologies for future electronic applications that is currently gaining a lot of interest. This is because if single molecule could be used as active electronic components this would provide an ultimate device miniaturization. Previously studied molecules provide almost exclusively two terminal devices. In this paper, three-leg molecular devices are examined employing a first-principles study based on density functional theory coupled to the non-equilibrium Green’s function formalism. We illustrate the feasibility of building a prototype molecular transistor using three-leg molecules directly contacted to gold electrodes. We discuss the different factors that control the transport through this molecular transistor. Moreover, we show that a functional standalone NAND logic gate can be implemented using a single three-leg molecular device.

The electron transport properties of an electrostatic gated single molecular transistor are investigated by using self-consistent semi-empirical method. The charge transport characteristics of the molecular device are analysed through the current-voltage I SD−V SD characteristics transmission characteristics T (E), and molecular projected self-consistent Hamiltonian states analysis. It is revealed that the gate bias V G can effectively tune the transport properties to greater extent. The mechanisms governing the gate bias tuned transport properties in this device were discussed. The proposed device also exhibits gate modulated negative differential resistance feature, which is exploited in realising basic logic gates. Thus, by using source-drain resistance R as a function of V G, the application of using gated thiophene based molecular device to realise a set of five basic logic gates at particular V SD is shown. The significant feature of the proposed device is the possibility of realising different logic gates with just one molecular transistor using computationally inexpensive semi-empirical method.

Мета роботи – проведення досліджень фізичних процесів в молекулярних структурах, які мають властивості, необхідні у випадках використання молекул у ролі перемикачів, транзисторів або інших електронних елементів комп’ютерів майбутнього, а також пошук структур, які в результаті самоорганізації набувають необхідні досліднику властивості. При цьому зменшення їх розмірів може призводити до появи нових властивостей або функцій..

Для подальшого моделювання транспорту електрона через транзистор на основі однієї молекули необхідно визначити основні параметри цієї молекули, до числа яких можна віднести ємнісні характеристики. Для визначення ємності молекул необхідно використовувати інший підхід, ніж для класичних об'єктів, а саме, розглядаючи структуру молекули і просторовий розподіл потенціалу. У даній роботі взятий до розгляду зв'язок енергетичних параметрів молекули (її енергії спорідненості та іонізації, повної енергії) від її заряду.

This Letter proposes a realistic design of a single-molecule quantum-interference-based transistor. The transistor consists of a cross-conjugated donor–bridge–acceptor molecule and is chemically ga...

Molecular-based devices are widely considered as significant candidates to play a role in the next generation of "post-complementary metal-oxide-semiconductor" devices. In this context, molecular-based transistors: molecular junctions that can be electrically gated-are of particular interest as they allow new modes of operation. The properties of molecular transistors composed of a single- or multimolecule assemblies, focusing on their practicality as real-world devices, concerning industry demands and its roadmap are compared. Also, the capability of the gate electrode to modulate the molecular transistor characteristics efficiently is addressed, showing that electrical gating can be easily facilitated in single molecular transistors and that gating of transistor composed of molecular assemblies is possible if the device is formed vertically. It is concluded that while the single-molecular transistor exhibits better performance on the lab-scale, its realization faces signifacant challenges when compared to those faced by transistors composed of a multimolecule assembly.

Molecular Field Effect Transistor (MFET) is a promising alternative candidate of traditional MOSFET in future due to its small size, low power consumption and high speed. In this work, we introduce a model of three-terminal MFET. The structure of the MFET is in shape like traditional MOSFET, but its conductive channel is replaced by a benzene-1,4-dithiolate molecule. We use non-equilibrium Green's function method to compute transport function of charges and ultimately, the current-voltage (1-V) characteristics. The program is written by using graphic user guide (GUI) in Matlab. We have found significant difference of I-V characteristics between MOSFET and MFET. In addition, impacts of types of material, temperature, and bias on I-V characteristics of the MFET have been considered. Using GUI in Matlab, obtained results of simulations are intuitively displayed.

The Anderson-Holstein model with Caldeira-Leggett coupling with environment is considered to describe the damping effect in a single molecular transistor (SMT) which comprises a molecular quantum dot (with electron-phonon interaction) mounted on a substrate (environment) and coupled to metallic electrodes. The electron-phonon interaction is first eliminated using the Lang-Firsov transformation and the spectral density function, charge current and differential conductance are then calculated using the non-equilibrium Keldysh Green function technique. The effects of damping rate and electron-electron and electron-phonon interactions on the transport properties of SMT are studied at zero temperature.

Molecular transistor is a good candidate as substitute of CMOS device due to small size, expected good performance and suitability to be included in high density-circuits. To date a lot of effort has been carried out to understand the conduction properties in molecular devices. However, minor effort has been devoted to reduce their computational complexity to obtain a compact molecular model. First-principle based methods frequently used are highly computational demanding for a single device, thus they are not suitable for complex circuit design. In this paper we present an accurate and at the same time computationally efficient method (named Efficient and Effective model based on Broadening level, Evaluation of peaks, SCF and discrete levels, ee-besd) to calculate the electron transport characteristics of molecular transistors in presence of applied bias and gate voltages. The results obtained show a remarkable improvement in terms of computational time with respect to existing approaches, while maintaining a very good accuracy. Finally, the ee-besd model has been embedded in a circuit level simulator in order to show its functionalities and, particularly, its computational cost. This is shown to be affordable even for circuits based on a high number of devices.

The effect of overheating of the electron subsystem on the Coulomb blockade in a structure (molecular transistor) based on a metal cluster containing a finite number of atoms has been theoretically studied. The electron energy spectrum in such quantum grains of cylindrical and spherical shape has been calculated. An increase in the electron subsystem temperature in the cluster leads to vanishing of the current gap and pronounced smoothening of the quantum and Coulomb steps on the current-voltage characteristic of the structure, in agreement with experimental observations.

Recently, several molecular devices have been realized with interesting properties like conductance, switching, gate modulation and negative differential resistance. In this paper we present a new modular framework based on VHDL-AMS that allows a comparison among different Molecular-FET models in terms of capability to capture an accurate I–V characteristics. It also allows to analyze the impact of Molecular-FET and to inspect the circuit proper behavior and its possible use in an architecture organized as a cascade of basic crossbars. This comparison exhibits technological choices, capability of different models features to capture physical quantities and models computational efforts.

Due to ongoing experimental advances, nanoelectromechanical systems represent a fascinating field of study which receives increasing attention. Because of their small size, these systems allow for exploring fundamental physics and give rise to a wide range of applications such as high frequency resonators and ultra-sensitive sensors. Because of strong electron-phonon coupling, nanoelectromechanical sys- tems provide a paradigmatic model for bosonic degrees of freedom coupled to an out-of-equilibrium fermionic environment. Many of the applications require a general understanding of the forces which are induced by a quantum environment on a classical system. By considering the na- nosystem as a generic time-dependent scatterer, these reaction forces have recently been expressed via an adiabatic expansion in terms of the scattering matrix and its first adiabatic correction. In this thesis, we present a more efficient and direct derivation of these forces by solely using scattering theory which is natural to the considered problem. Due to the Anderson orthogonality catastrophe small local changes of a scattering potential can drastically affect properties of large quantum systems. In equilibri- um, the orthogonality exponent was related to the friction coefficient of a classical particle moving in a free electron gas. Based on our knowledge on the environment- induced forces, we generalise this idea to out-of-equilibrium situations. To this end, we study the fidelity amplitude and the Loschmidt echo, which are dynamical mea- sures of the Anderson orthogonality catastrophe. A molecular transistor at the ultimate miniaturisation limit has recently been ex- perimentally realised. Atomically precise gating is achieved via repositioning of individual charges by scanning tunnelling microscopy. Remarkably, a pronounced conductance gap instead of the expected charge degeneracy is observed. Motiva- ted by the experimental observations, we explain this behaviour by the presence of two different molecular conformational states, which generalises the conventional picture of single- electron tunnelling through molecular transistors., Aufgrund fortschreitender experimenteller Fortschritte stellen nanoelektromecha- nische Systeme ein faszinierendes Gebiet mit steigender Aufmerksamkeit dar. We- gen ihrer kleinen Ausmaße erlauben diese Systeme die Erforschung fundamenta- ler Physik und ermöglichen eine Vielzahl von Anwendungen, u.a. als Hochfre- quenzresonatoren und ultrasensitiven Sensoren. Wegen starker Elektron-Phonon- Wechselwirkung sind diese Systeme ein Paradebeispiel von bosonischen Freiheits- graden, die an eine fermionische Umgebung im Nichtgleichgewicht koppeln. Viele der Anwendungen erfordern ein generelles Verständnis der umgebungsindu- zierten Kräfte auf ein klassisches System. Indem das Nanosystem als generelle zeit- abhängige Streuregion beschrieben wird, sind diese Kräfte kürzlich als Funktion der Streumatrix und seiner ersten adiabatischen Korrektur hergeleitet worden. In dieser Arbeit präsentieren wir eine effizientere und direkte Herleitung dieser Kräf- te ausschließlich unter Benutzung der Streutheorie, die auf natürlich Weise solche Systeme beschreibt. Kleine lokale Änderungen eines Streupotentials können aufgrund der Anderson Or- thogonalitätskatastrophe drastische Auswirkungen auf Eigenschaften großer Quan- tensysteme haben. Im Gleichgewicht wurde der Orthogonalitätsexponent direkt mit dem Reibungskoeffizienten eines klassischen System, das sich in einem freien Elek- tronengas bewegt, verknüpft. Mit den erworbenen Kenntnissen zu den umgebungs- induzierten Kräften verallgemeinern wir diese Idee ins Nichtgleichgewicht. Hierzu untersuchen wir das Verhalten der Fidelitätsamplitude und des Loschmidt Echos, die dynamische Grössen der Orthogonalitätskatastrophe darstellen. Ein molekularer Transistor im ultimativen Miniaturisierungslimit ist kürzlich expe- rimentell realisiert worden. Atomar präzise Steuerspannung ist erzielt durch Repo- sitionierung einzelner Ladungen durch Rastertunnelmikroskopie. Eine ausgeprägte Leitwertlücke anstatt des erwarteten Ladungsentartungspunktes wurde gemessen. Motiviert durch die experimentellen Beobachtungen erklären wir dieses Verhalten mit der Existenz zweier molekularer Konformationszustände, was das konventionel- le Bild des Einzelelektronentunnelns durch molekulare Transistoren generalisiert.

Сучасні комп΄ютери набули стрімкого розвитку. З часом елементна база буде мініатюризована до розмірів молекули. Робота направлена на вивчення переносу електрона через молекулу, закріплену між дво- ма електродами. Використовувати слід стабільні молекули, які мають дві конформації. Дослідження проводились з молекулою дифенілу з різними замісниками.

The use of molecular devices in post-CMOS devices and structures is described. Particularly we demonstrate the fabrication and characterization of two-novel devices: a two-terminal device which exhibits a two-negative differential resistance peaks and a sub-10-nm-channel vertical molecular transistor which contains a molecular quantum-dot compound. We show that the latter device can be operated in two distinct modes: gate-controlled switch and gate-controlled hysteresis.