Select
Surface dynamics studied by time-dependent tunneling current
Qin LIU (刘琴), Ke-dong WANG (王克东), Xu-dong XIAO (肖旭东)
Front Phys Chin. 2010, 5 (4 ): 357-368.
https://doi.org/10.1007/s11467-010-0108-5
Scanning tunneling microscopy (STM) is not only an excellent tool for the study of static geometric structures and electronic structures of surfaces due to its high spatial and energy resolution, but also a powerful tool for the study of surface dynamic behaviors, including surface diffusion, molecular rotation, and surface chemical reactions. Because of the limitation of the scanning speed, the video-STM technique cannot study the fast dynamic processes. Alternatively, a time-dependent tunneling current, I–t curve, method is employed in the research of fast dynamic processes. Usually, this method can detect about 1000 times faster dynamic processes than the traditional video-STM method. When placing the STM tip over a certain interesting position on the sample surface, the changing of tunneling current induced by the surface dynamic phenomena can be recorded as a function of time. In this article, we review the applications of the time-dependent tunneling current method to the studies of surface dynamic phenomena in recent years, especially on surface diffusion, molecular rotation, molecular switching, and chemical reaction.
References |
Related Articles |
Metrics
Select
Corrugated single layer templates for molecules: From h -BN nanomesh to graphene based quantum dot arrays
Hai-feng MA (马海峰), Mario THOMANN, Jeanette SCHMIDLIN, Silvan ROTH, Martin MORSCHER, Thomas GREBER
Front Phys Chin. 2010, 5 (4 ): 387-392.
https://doi.org/10.1007/s11467-010-0137-0
Functional nano-templates enable self-assembly of otherwise impossible arrangements of molecules. A particular class of such templates is that of sp 2 hybridized single layers of hexagonal boron nitride or carbon (graphene) on metal supports. If the substrate and the single layer have a lattice mismatch, superstructures are formed. On substrates like rhodium or ruthenium these superstructures have unit cells with ~3-nm lattice constant. They are corrugated and contain sub-units, which behave like traps for molecules or quantum dots, which are small enough to become operational at room temperature. For graphene on Rh(111) we emphasize a new structural element of small extra hills within the corrugation landscape. For the case of molecules like water it is shown that new phases assemble on such templates, and that they can be used as “nano-laboratories” where many individual processes are studied in parallel. Furthermore, it is shown that the h -BN/Rh(111) nanomesh displays a strong scanning tunneling microscopy-induced luminescence contrast within the 3 nm unit cell which is a way to address trapped molecules and/or quantum dots.
References |
Related Articles |
Metrics
Select
Tailoring interacting magnetic nanodots via dimensionality variation of mediating electrons
Li-feng YIN, Jian SHEN
Front Phys Chin. 2010, 5 (4 ): 393-404.
https://doi.org/10.1007/s11467-010-0136-1
Nature produces ferromagnetic materials based on nearest neighbor exchange interaction between atomic spins. For artificially fabricated nanomagnets, it is those “small” magnetic energies, e.g. anisotropy, dipolar interaction and indirect exchange interaction that play crucial roles against the thermal fluctuation. We have developed strong capabilities to grow nanodot assemblies in ultrahigh vacuum with controllable size and density on/in both metallic and insulating templates. Based on our novel synthesis capability, we have studied artificial nanomagnets with tunable coupling strength via dimensionality control of the mediating electrons in one-dimensional (1-D), 2-D, and 3-D. We show that such kind of dimensional confinement provides a unique way to induce novel magnetic properties and to gain control of them. The research outlined in this work provides the science base to understand, modify, and manipulate the magnetic properties through dimensional confinement.
References |
Related Articles |
Metrics
Select
Investigation of gate-all-around silicon nanowire transistors for ultimately scaled CMOS technology from top–down approach
Ru HUANG (黄如), Run-sheng WANG (王润声)
Front Phys Chin. 2010, 5 (4 ): 414-421.
https://doi.org/10.1007/s11467-010-0110-y
The gate-all-around (GAA) silicon nanowire transistor (SNWT) is considered one of the best candidates for ultimately scaled CMOS devices at the end of the technology roadmap. This paper reviews our recent work on the key issues regarding SNWTs from the top-down approach including process integration, carrier transport, and fluctuation and variability in these unique one-dimensional stronglyconfined nanowire devices. A new process integration scheme for SNWTs is discussed, which features a fully-Si-bulk substrate, an epi-free process, a self-aligned structure and a large source/drain fan-out. The physical characteristics of the fabricated devices with 10-nm-diameter nanowires are further investigated. The carrier transport performance in SNWTs is experimentally estimated, with a modified extraction methodology which takes into account the impact of temperature dependence of parasitic source resistance. SNWTs with sub-40-nm gate lengths exhibit high ballistic efficiency at room temperature, indicating great potential for SNWTs as an alternative device structure for near-ballistic transport. For heat transfer in SNWTs, the self-heating effect is also characterized. However, due to the one-dimensional (1-D) nature of nanowires and increased phonon-boundary scattering in the GAA structure, the self-heating effect in SNWTs based on the bulk substrate is comparable or even a little bit worse than SOI devices, which may limit the ultimate performance of SNWT-based circuits and thus, special design consideration is expected. On the other hand, random variation has become a practical problem at nano-scale. The characteristic variability of SNWTs is experimentally studied in detail. The results of extracted variation sources indicate that, with suppressed random dopant fluctuations in the intrinsic channel, variations in radius and metal-gate work function of SNWTs dominate both the threshold voltage and on-current fluctuations. Comparing with conventional planar MOS devices, SNWT based SRAM cells exhibit better stability due to the superior electrostatic control in SNWTs.
References |
Related Articles |
Metrics
11 articles