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As CMOS technology approaches its physical and technical limits, alternative technologies such as nanotechnology or quantum computing are needed to overcome the challenges of lithography, transistor scaling, interconnects, and miniaturization. This article introduces a novel nanotechnology that uses atomic-scale silicon dangling bonds (ASDB) to create high-performance, low-power, nanoscale logic circuits. DBs are atoms that can form basic logic gates on a silicon surface using a scanning tunneling microscope device. ASDB can also be an alternative to the existing complementary metal oxide semiconductor (CMOS) technology. The article also proposes a new bar-shaped pattern to design gates and logic circuits with ASDB nano tecnolgoy. The bar-shaped pattern improves the reliability of the output, reduces the area and power consumption, and solves the problem of interatomic energy effects of ASDB. The article demonstrates the efficiency of the bar-shaped pattern by implementing two-input gates such as AND, NAND, OR, NOR, XOR, XNOR, and a 2:1 multiplexer with ASDB. The article also uses a powerful tool called SiQAD to simulate and verify the performance of the proposed structures with ASDB. According to the simulation results, the proposed logic gates are more energy efficient, stable, and compact than the previous structures. They consume 35% and 24.34% less energy and have 14.18% more stability, respectively. [ABSTRACT FROM AUTHOR]

Abstract We review our recent studies of photochemistry and plasmon chemistry of dimethyl disulfide, (CH 3 S) 2 , molecules adsorbed on metal surfaces using a scanning tunneling microscope (STM). The STM has been used not only for the observation of surface structures at atomic spatial resolution but also for local spectroscopies. The STM combined with optical excitation by light can be employed to investigate chemical reactions of single molecules induced by photons and localized surface plasmons. This technique allows us to gain insights into reaction mechanisms at a single molecule level. The experimental procedures to examine the chemical reactions using the STM are briefly described. The mechanism for the photodissociation reaction of (CH 3 S) 2 molecules adsorbed on metal surfaces is discussed based on both the experimental results obtained with the STM and the electronic structures calculated by density functional theory. The dissociation reaction of the (CH 3 S) 2 molecule induced by the optically excited plasmon in the STM junction between a Ag tip and metal substrate is also described. The reaction mechanism and pathway of this plasmon-induced chemical reaction are discussed by comparison with those proposed in plasmon chemistry. [ABSTRACT FROM AUTHOR]

Abstract: Five fluorene-based derivatives (C1–C5) were conveniently synthesized and characterized. X-ray analysis revealed the molecular structures and column stacking in the single crystal of compound C1 and C4. Good thermal stability was observed by thermogravimetric analysis. Their optical properties were studied by UV–vis and fluorescence spectroscopy, and electrochemical properties were investigated by cyclic voltammetry (CV). Interestingly, SEM studies showed that C3 was assembled into 1D micron-scale ribbons with an average width of 1μm and an average length exceeding 50μm. STM imaging indicated that C1 can form ordered self-assembled monolayers on HOPG. Density functional theory method was employed to optimize the structure and analyze the electron distribution of compound C1–C3. [ABSTRACT FROM AUTHOR]

Abstract: The Review is devoted to recent progress made from the combination of Scanning Tunneling Microscope (STM) experiments and First Principles atomistic simulations in the chemical characterization of metal–organic interfaces. Density Functional Theory (DFT) has now reached the point to mimic in a quantitative way two pillars of the STM probe: the imaging mode convoluting the topographic and electronic properties and the spectroscopy modes comprising of elastic and inelastic detection ways. We present a selection of hybrid interfaces ranging from isolated benzene derivatives to thin honeycomb carbon film – a single graphene layer – deposited onto transition metal surfaces. The direct experimental analysis of these interfaces was error-prone, necessitating the confrontation with First Principles atomistic simulations. The few examples thus illustrate the power of different kinds of STM simulations to complement the STM data, in order to unambiguously identify the chemical structure of organic adsorbates. [ABSTRACT FROM AUTHOR]

Abstract: Adsorption states and thermal desorption behavior of self-assembled monolayers (SAMs) of 2-thiophenethiol (TT) and 2-thiophenemethanethiol (TM) on Au(111) were investigated by X-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy (STM), and thermal desorption spectroscopy (TDS), and were compared with those of thiophene (TP) SAMs. The S 2p XP spectra of thiophenethiol SAMs showed a variety of the adsorption states of the S atoms on the Au surface. STM imaging revealed that the surface structures of these thiophene derivative SAMs are markedly different from each other, possibly as result of a difference in the adsorption behaviors of the molecules. We found that although thiophene derivatives contain two active sulfur atoms with different chemical activities, the 2D SAM structure can be tuned by the insertion of a methylene group between the TP ring and the SH group. Decomposed desorption was observed in the TD spectra of TT and TM SAMs, as is observed in the TP SAM. Thiophenethiol SAMs show the different adsorption and desorption behaviors compared to alkanethiol SAMs. [Copyright &y& Elsevier]

Abstract: The porphyrin-based molecules including H2TBPP, ZnTBPP and PtTBPP as well as the perinone derivatives (PD) molecules were deposited on Au(100), Au(111) and Cu(100) substrates in the form of single molecule, molecular line, submonolayer, monolayer and multilayer. The features of the performed molecular nanostructures were characterized by an ultrahigh vacuum scanning tunneling microscopy (STM) at room temperature. The observed molecular topographies matched very well with the molecule structures in spite of the fact that the molecular adsorption states were influenced by different metal surface. STM-induced photon emission was generated from the surface of H2TBPP multilayer structures on Au(100) in tunneling junction when the applied bias exceeds the “turn-on” voltages ∼−1.6 V or +1.3 V at 0.5 nA. [Copyright &y& Elsevier]

Abstract: The growth behavior of iron(II) phthalocyanine (FePc) molecules on Cu(111) and on NaCl/Cu(111) surfaces has been studied by a variable-temperature scanning tunneling microscope. Upon deposition at room temperature, FePc molecules with different adsorption configurations form short-ranged ordered domains on Cu(111). In the second FePc monolayer long-range ordering is observed. Molecule–molecule and molecule–substrate interactions are discussed in comparison with previous findings for FePc on Au(111). In order to reduce molecule–substrate interaction insulating NaCl layers are introduced. FePc molecules adsorb on Cl− anion sites but show high mobility during preparation. Our results provide detailed insight into the growth behavior of organic molecules on metallic and insulating surfaces. [Copyright &y& Elsevier]

Abstract: This study investigated the dynamics of copper atoms adsorbed on Si(111)-7×7 surfaces between 300K and 623K using a variable-temperature scanning tunneling microscope (STM). The diffusion behavior of copper clusters containing up to ∼6 atoms into a particular half unit cell of the 7×7 reconstructed Si(111) surface was considered. The movements and the formation of copper clusters were tracked in detail. The activation energies and pre-exponential factors for various diffusion paths were estimated. Finally, the Cu-etching-Si process and the quasi-5×5 incommensurated phase of Cu/Si islands were discussed. [Copyright &y& Elsevier]

Abstract: Using scanning tunneling microscopy (STM) and time of flight secondary ion mass spectrometry (TOF/SIMS), we observed radiation effects on a Si(111)-(7×7) surface in the collision of a single highly charged ion (HCI) with a charge state q up to q =50. The STM observation with atomic resolution revealed that a nanometer sized crater-like structure was created by a single HCI impact, where the size increased rapidly with q. The secondary ion yields also increased with q in which multiply charged Si ions (Si n+) were clearly observed in higher q HCI-collisions. The sputtering mechanism is briefly discussed, based on the so-called Coulomb explosion model. [Copyright &y& Elsevier]

Abstract: This paper focuses on the nano-oxidation of a silicon surface using scanning probe microscopes in air ambient and in UHV. Special emphasis is put in air ambient on the preparation of the surfaces and on the oxidation mechanism. The characteristics of the patterned nanostructures are reviewed versus the parameters which govern the process (tip–surface voltage, tip speed, humidity) as well as the kinetics models of the oxidation process. The oxide patterns can act as robust masks for dry or wet etching. Fabrication of nanostructures is presented and allows to realize electronic nanodevices. In UHV, there is no direct nano-oxidation of the surface by the microscope tip. First the surface is hydrogenated, second a local hydrogen desorption is performed with the STM tip and finally the bare desorbed area is exposed to oxygen. The desorption process is analyzed versus tip–surface voltage and tunneling current. The oxidation of a desorbed area using molecular or atomic oxygen is actually difficult to achieve. [Copyright &y& Elsevier]

Abstract: We have investigated surface modification by highly charged ions (HCIs) on highly oriented pyrolytic graphite (HOPG) surfaces with Raman spectroscopy and scanning tunneling microscopy. The xenon-HCIs having various charges up to 48+ were incident on HOPG samples with an identical collision velocity (5×105 m/s). In Raman spectra, disorder induced peaks (D peak) appeared around 1355cm−1 in addition to narrower, persistent peaks (G peak) at 1580cm−1 which are characteristic of unirradiated HOPG. The intensity ratio of the D peak to the G peak is much larger than that of HOPG irradiated with singly charged ions (SCIs) at the same fluence. By the annealing treatment, the intensity of the D peak decreased as small as practically unobservable. In the microscopic observation, on the other hand, protrusion nanostructures induced by HCI impacts did not disappear completely although their volume decreased drastically. From such relaxation dynamics, it is made clear that not only point and dimmer vacancies which is created in common with SCI irradiation, but also “cluster vacancies” are formed at the surface and subsurface. [Copyright &y& Elsevier]

In situ site-control techniques for self-organized InAs quantum dots (QDs) have been developed using an electron beam (EB) and a scanning tunneling microscope (STM) probe combined with molecular beam epitaxy. In the in situ EB-assisted process, InAs dots are preferentially formed in shallow, sub-μm-size GaAs holes with the InAs supply. We find that the specific slope of a hole acts as a favorable site for dot formation. In the in situ STM probe-assisted process, the size and pitch of the holes are considerably reduced into nanoscale. InAs QDs are then self-organized only at the hole sites due to strain-induced selective nucleation. Using this process, two- and three-dimensional QD arrays are fabricated with nanometer precision. [Copyright &y& Elsevier]

Abstract: Under excitation with an external electromagnetic field, gold nanocones act as efficient optical antennas. In this work, a process developed for the fabrication of sharp-tipped gold nanocones on silicon is extended to transparent substrates covered by a thin conducting layer. In this configuration, the cones can be investigated in scanning probe microscopes while illuminating from below. The electric coupling between cones and substrate and between individual cones can be varied by a precise thinning of the conducting layer via a fine-tuning of the original layer thicknesses. [Copyright &y& Elsevier]

The behavior of magnetoresistance in NiFe (permalloy) point junctions was investigated using an STM set-up, where the junction resistance was continuously varied from 108 Ω-10³ Ω. Our results reveal an enhancement of magnetoresistance of more than 80% at one conductance quantum, and the decaying magnetoresistance as one moves away from 12.9 kΩ to either the diffusive regime or the tunneling regime, as supported by independent theories on spin-dependent transport. The suppression of magnetoresistance with incorporation of a 35-nm-thick Au barrier was observed, as well as the dependence of magnetoresistance on the relative orientations of the electrodes. [ABSTRACT FROM AUTHOR]