Staircase Structures Research Articles

Diamond tips for automated electrical probing inside a scanning electron microscopy system

Pyramidal tips made from boron doped diamond have become the ultimate choice for electrically measuring semiconductor device structures in electrical atomic force microscopy (AFM). An advanced measurement setup with diamond probing units directly integrated inside a scanning electron microscopy (SEM) system is highly wanted as this allows for accurate tip positioning compared to the optical microscope of a standard AFM and enables also multiple tip measurements. Therefore, we have developed highly conductive in-plane diamond tips with a triangular shape and attached them to Ni cantilevers. We have established a LabVIEW-based setup enabling automated electrical measurements inside a SEM system using stick-and-slip motion nanomanipulators and a parameter analyzer system. To our best knowledge, this paper presents first 1- and 2-tip electrical measurements of microfabricated diamond probes inside a SEM system. Measurements of Si staircase and Ge structures are shown and compared to scanning spreading resistance (SSRM) results. Our work demonstrates that doped diamond tips clearly outperform common tungsten probe needles enabling nanoprobing experiments which were impossible so far. Based on our results, we predict that doped diamond is going to be the standard tip material not only for electrical AFM but also for nanoprobing of semiconductor materials.

Luminescence properties of “double-stranded staircase” copper(i) halide coordination polymers with N-containing ligands

A set of CuIXL coordination polymers (X = Cl, Br, I; L = derivatives of pyrazine and bipyridine) with double-stranded staircase structures was analyzed by X-ray crystallography and luminescence spectroscopy to find a relationship between the structure and luminescence properties of the polymers. Our measurements have proved that luminescence emission wavelengths varied between 500–750 nm, after the polymers were irradiated by light with a wavelength of 370 nm. Although each coordination polymer has shown different emission maximum, we observed several interesting trends related to the structure of the compounds. There is a clear correlation between the emission maxima and the halide size and/or Cu–X distance, respectively. On the other hand, the substitution of the ligand L (pyrazine derivatives, 4,4′-bipyridine) has no significant contribution to the emission spectra. This observation supports the theory that the halide to metal charge transfer (XMCT) plays a key role in the photoluminescence of staircase polymers.

Vision-based approach to automated analysis of structure boundaries in scanning electron microscope images

In this article, a vision-based approach is presented for the automatic measurement of feature dimensions from cross-section scanning electron microscope images of three-dimensional structures. The cross-sections of fabricated structures are represented by a set of boundary points. The geometric distortion incurred during the imaging process is compensated for by matching the cross-section of a target structure to that of the fabricated one. Control points are defined on the boundary of the target structure, and their locations in the cross-section image are estimated using line fitting. The feature dimensions are measured based on the control points. The proposed automatic analysis method has been successfully applied to measuring dimensions of sawtooth and staircase structures transferred onto resist.

Local density of states of a finite-sized rectangular-lattice photonic crystal with separable profile of permittivity

A different approach in the calculation of two-dimensional local density of states has been presented for a two-dimensional finite rectangular-lattice photonic crystal with a separable profile of permittivity. Approximate staircase structures are already shown to be useful for their ability to reproduce actual properties of practical square lattice photonic crystals. Using the effective resonance approach in a Fabry–Perot resonator and transfer matrix method an analytical expression for calculating a two-dimensional local density of states can be derived for both polarisations in the structure. It is shown that for this geometry one can resolve the modes as a product of two separate functions each being a function of x- and y-coordinates. The results have been investigated for the two-dimensional local density of states in the ordered finite structure and in the disordered structure. The main advantage of this method in calculating the local density of states is its extremely efficient numerical evaluations. As an application we introduce a cavity-like defect in the vicinity of a waveguide-like defect and examine the variation of local density of states in the plane of the structure at band gap frequency.

Step-width adjustment in fabrication of staircase structures

Three-dimensional structures increasingly find applications in various devices such as diffractive optical elements, photonic element, microelectromechanical systems, etc., and are often fabricated by e-beam lithography. Their performance is known to be highly sensitive to their dimensions. Therefore, it is critical to achieve high dimensional accuracy for the desired characteristics. However, as the feature size in three-dimensional structures decreases down to nanoscale, the lateral development of the resist and the proximity effect due to electron scattering can make dimensions of the written features in a device substantially different from the target dimensions. In this study, this issue is addressed for staircase structures; specifically, minimizing the difference between the target and the actual widths of each step. Through computer simulation and experiments, it has been shown that significant improvement in dimensional accuracy, especially the step widths of the staircase structures, can be achieved by the proposed practical width-adjustment scheme.

Diagonal stripes in the spin glass phase of cuprates

Based on the unrestricted Gutzwiller approximation we study the possibility that the diagonal incommensurate spin scattering in the spin glass phase of lanthanum cuprates originates from stripe formation. Similar to the metallic phase two types of diagonal stripe structures appear to be stable: (a) site-centered textures which have one hole per site along the stripe and (b) ferromagnetic stair-case structures which are the diagonal equivalent to bond-centered stripes in the metallic phase and which on average have a filling of 3/4 holes per stripe site. We give a detailed analysis of the stability of both diagonal textures with regard to the vertical ones.

PAIRWISE ENTANGLEMENT IN THE TETRAHEDRAL LATTICE WITH HEISENBERG INTERACTIONS

By using the concept of negativity, we determine entanglement features of the tetrahedral lattice with Heisenberg interactions. It is found that except [Formula: see text] for the case of (1/2-1/2-1-1) mixed spins, there is no pairwise entanglement between any two spins at any temperature when B = 0. When B increases after B = 0, the ground-state negativities exhibit square wave or stepwise structures, and experience sharply descents to lower values at some energy-level crossing points. For thermal entanglement, the negativities exhibit ridge-like or staircase structures as B increases, and there are regions in the B–T plane where an increase of temperature may help to enhance the entanglement.

Electronic transport characteristics of a single wall carbon nanotube field effect transistor wrapped with deoxyribonucleic acid molecules

A SWCNT-FET device wrapped with DNA molecules was fabricated and the electronic transport properties were investigated. The gate modulated current-voltage characteristics of a bare SWCNT-FET device showed a p-type conduction behavior, which was consistent with generally characteristics in previous studies. However, the characteristics of the DNA-wrapped SWCNT-FET showed clear staircase structures. In addition, the conduction type was changed from p-type to n-type and the transconductance of the DNA-wrapped SWCNT-FET became smaller than that of the bare SWCNT-FET. All these observations provided the evidences of DNA wrapping on the surface of SWCNTs. Especially, the observed type conversion was interpreted as a result of oxygen transport from the surface of SWCNT to DNA molecules across the SWCNT-DNA interface.

Double‐diffusive layers in the Adriatic Sea

A microstructure profiler was deployed to make turbulence measurements in the upper layers of the southern Adriatic Sea in the Mediterranean during the Naval Research Laboratory (NRL) DART06A (Dynamics of the Adriatic in Real Time) winter cruise in March 2006. Measurements in the Po river plume along the Italian coast near the Gargano promontory displayed classic double‐diffusive layers and staircase structures resulting from the relatively colder and fresher wintertime Po river outflow water masses overlying warmer and more saline water masses from the Adriatic Sea. We report here on the water mass and turbulence structure measurements made both in the double‐diffusive interfaces and the adjoining mixed layers in the water columns undergoing double‐diffusive convection (DDC). This dataset augments the relatively sparse observations available hitherto on the diffusive layer type of DDC. Measured turbulence diffusivities are consistent with those from earlier theoretical and experimental formulations, suggesting that the wintertime Po river plume is a convenient and easily accessible place to study double diffusive convective processes of importance to mixing in the interior of many regions of the global oceans.

Further evidence for non-reemergence of winter SST anomalies in the North Pacific eastern subtropical mode water area

Following our previous study (Sugimoto and Hanawa, 2005b), we further investigate the reason why reemergence of winter sea surface temperature anomalies does not occur in the North Pacific eastern subtropical mode water (NPESTMW) area, despite its occurrence in the North Pacific subtropical mode water and North Pacific central mode water areas. We use vertical temperature and salinity profiles of the World Ocean Circulation Experiment Hydrographic Program and Argo floats with high vertical and temporal resolution, together with heat flux data through the sea surface. We point out first that one of the causes for non-occurrence of reemergence is that the thickness of NPESTMW is very thin. In addition to this basic cause, two major reasons are found: a vigorous mixing in the lower portion of NPESTMW and less heat input from the atmosphere in the warming season. Since, in the lower portion of NPESTMW and deeper, the stratification is favorable for salt-finger type convection to occur compared with the other mode water areas, vigorous mixing takes place. This is confirmed by both a large Turner Angle there and the existence of staircase structures in vertical temperature and salinity profiles. From the viewpoint of heat input, the NPESTMW area gradually gains heat in the warming season compared with other mode water areas. As a result, NPESTMW cannot be capped so quickly by the shallow summer mixed layer, and water properties of NPESTMW are to be gradually modified, even in the upper portion.

Quantitative Measurement of Dopant Concentration Profiling by Scanning Nonlinear Dielectric Microscopy

AbstractUsing a scanning nonlinear dielectric microscopy (SNDM), we observed two standard Si samples with epitaxial staircase structures, which have known dopant density values calibrated by using secondary ion mass spectroscopy (SIMS). As the result, good quantitative correlation between dopant density values and SNDM signals was obtained without the phenomenon of contrast reversal effect, which is associated with conventional scanning capacitance microscopy (SCM) measurements. Thus, it is expected that SNDM will be an effective method for observing the quantitative measurement of two-dimensional dopant profiling on semiconductor devices.

Electron transport through individual Ge self-assembled quantum dots on Si

Electrical properties of self-assembled quantum dots have been the subject of intensive research due to quantum confinement. Here the authors report on the fabrication of Ge quantum dots (QDs) onto Si (100) by ultrahigh-vacuum ion beam sputtering and the electrical properties of individual QDs. Transmission electron microscopy images show that samples with completely incoherent or coherent semispherical islands can be produced under different ion energies. The current-voltage (I-V) characteristics with conductive atomic force microscopy at room temperature. exhibit linear behavior at low bias and nonlinear behavior at large bias from coherent islands, whereas the staircase structures are clearly observed in the I-V curve from incoherent islands, which are attributed to electron tunneling through the quantized energy levels of a single Ge QD.

Irreducible decomposition of monomial ideals

In this paper we present two algorithms for irreducible decomposition of monomial ideals. We first use staircase structures to study the monomial ideals. We generalize the shifting degrees rule from two variables to three variables and then arbitrary case. With the aid of monomial tree representation, a new algorithm for irreducible decomposition of monomial ideals is provided. For the second method, we associate a monomial ideal with a Scarf complex, which is introduced by Herbert Scarf. Every facet of the Scarf complex corresponds to an irreducible component, and vice versa. Milowski(2004) developed a method to enumerate all the facets based on reverse search by exchanging one monomial at a time. We define a facet graph where nodes are facets and there is an edge from a facet F A to another facet F B if F B can be obtained from F A by exchanging one vertex. We give a new generic deformation called ordinal deformation and prove that the facet graph of an ordinally generic monomial ideal is strongly connected. This yields a simpler and more efficient enumeration algorithm.

Collective behavior of single electron effects in a single layer Si quantum dot array at room temperature

In this paper, we report direct experimental evidence of collective single electron effects in a single layer Si quantum dot (Si-QD) array at room temperature. The unique peak structure, observed in both the $I\text{\ensuremath{-}}V$ and the capacitance-voltage $(C\text{\ensuremath{-}}V)$ characteristics, differs remarkably from the peaks and the staircase structures reported for the case of an individual quantum dot and reveals the collective Coulomb blockade and the quantum confinement effects in the weakly coupled Si-QD array. Simple theoretical estimations have been made to interpret the origin of the unique peak structure. Moreover, the number of charged electrons for each peak calculated from the underlying area of the peaks both in the $I\text{\ensuremath{-}}V$ (after subtracting the background current) and the $C\text{\ensuremath{-}}V$ characteristics is found to be consistent with the number of coupled quantum dots under the electrode. This good agreement supports the assumption that each peak in the characteristics corresponds to a collective charging process of single electron into a subband in the Si-QD array arising from the weakly interdot coupling. This collective single electron effect in Si-QD array is important for its future application in the nanoelectronic devices.

Mn(II) Staircase Structures Stitched by Water Clusters to a 3D Metal-Organic Open Framework: X-ray Structural and Magnetic Studies

4-Hydroxypyridine-2,6-dicarboxylic acid (chelidamic acid, cdaH2) reacts with Mn(OAc)2 x 4H2O to form a 1D staircase structure with dimeric Mn(II) units connected by water clusters to form a 3D framework, {[Mn2(cda)2 x 4H2O] x 4H2O}n, 1, in aqueous pyridine at room temperature. The compound crystallizes in the triclinic space group P1 with a = 9.495(3), b =10.733(5), c = 11.065(4) A, alpha = 87.42(5), beta = 74.14(5), gamma = 80.07(2) degrees, U = 1068.5(9) A3, Z = 2, rho(calcd) = 1.915 g cm(-3), T = 100 K, mu = 1.28 mm(-1), R1 = 0.0453 (I > 2sigma(I)), wR2 = 0.1046, GOOF = 1.282. Upon removal of the water molecules by heating, the 3D structure breaks down. Thermogravimetric analysis, infrared, X-ray powder diffraction studies, and X-ray crystallography were performed to characterize this compound. Since the coordination polymer has diaqua-bridged Mn(II) centers, it was subjected to variable-temperature magnetic studies.

A viscous froth model for dry foams in the Surface Evolver

An implementation of the recent viscous froth model of Kern et al. [N. Kern, D. Weaire, A. Martin, S. Hutzler, S.J. Cox, The two-dimensional viscous froth model for foam dynamics, Phys. Rev. E 70 (2004) 041411.] in the Surface Evolver is described, along with examples of the simulations that can be achieved. In particular, results are given for steady shear of both periodic and confined staircase structures, and contrasted with the quasi-static case. Also discussed are the case of Couette shear and the relaxation due to coarsening after an initial step-strain. It is shown how the viscous froth model allows the investigation of strain-rate dependent effects and that it gives improved resolution of the topological events which govern the foam’s evolution, leading to structures that could not previously have been predicted.

Self-Assembly of Patchy Particles.

Molecular simulations are performed to study the self-assembly of particles with discrete, attractive interaction sites - "patches" - at prescribed locations on the particle surface. Chains, sheets, rings, icosahedra, square pyramids, tetrahedra, and twisted and staircase structures are obtained through suitable design of the surface pattern of patches. Our simulations predict that the spontaneous formation of two-dimensional sheets and icosahedra occurs via a first-order transition while the formation of chains occurs via a continuous disorder-to-order transition as in equilibrium polymerization. Our results show how precise arrangements of patches combined with patch "recognition" or selectivity may be used to control the relative position of particles and the overall structure of particle assemblies. In this context, patchy particles represent a new class of building block for the fabrication of precise structures.

First systematic investigation of C-H...Cl hydrogen bonding using inorganic supramolecular synthons: lamellar, stitched stair-case, linked-ladder, and helical structures.

Using a group of six neutral M(II)Cl(2)-containing coordination compounds as building blocks, the first systematic investigation of C-H...Cl hydrogen-bonding interactions was performed. Single-crystal X-ray structural analyses of four new compounds (pseudo-tetrahedral Co(II) and Zn(II); distorted trigonal bipyramidal Zn(II)) authenticate the metal coordination geometry. To provide a unified view of the presence of noncovalent interactions in this class of compounds, we have re-examined the packing diagram of two previously reported compounds (a distorted square-pyramidal Cu(II) complex and a trans-octahedral Co(II) complex). The organic ligands of our choice comprise bidentate/tridentate pyrazolylmethylpyridines and an unsymmetrical tridentate pyridylalkylamine. This systematic investigation has allowed us to demonstrate the existence of versatile C-H...Cl(2)M interactions and to report the successful application of such units as inorganic supramolecular synthons. Additional noncovalent interactions such as C-H...O and O-H...Cl hydrogen bonding and pi-pi stacking interactions have also been identified. Formation of novel supramolecular architectures has been revealed: 2D lamellar (p-cyclophane) and 3D lamellar, 3D "stitched staircase" (due to additional hydrogen-bonding interactions by water tetramers, with an average O-O bond length in the tetramer unit of 2.926 A, acting as "molecular clips" between staircases), 3D linked ladder, and single-stranded 1D helix.

Thin element approximation for the analysis of blazed gratings: simplified model and validity limits

The thin element approximation is widely used to predict the diffraction efficiency of thin periodic diffractive optical elements (DOEs). However, as the period-to-wavelength ratio is reduced, the approximation becomes inaccurate. A model based on a “shadow concept” can be used to predict the diffraction efficiency with high accuracy. Hereby we extend the model to include the effect of multi-level staircase structures and non-perpendicular incident angles. We also present an error map and define regions of validity for the thin element approximation (TEA) and the shadow model.

Controllable step motors and rectifiers of magnetic flux quanta using periodic arrays of asymmetric pinning defects

We study the transport of vortices in superconductors with regular arrays of asymmetric pinning wells when applying an alternating electrical current. The asymmetric traps are modelled by the superposition of two interpenetrating square lattices of weak and strong pinning centers with separation smaller than the lattice constant. We show that this system can induce a net rectifying or diode effect for the vortex motion, including collective step-motor-type dynamics, where many vortices move forward a controlled and exact number of pin-lattice spacings at each cycle of the ac driving force. This system exhibits a remarkable net dc response with striking sawtooth-type oscillations. The net dc voltage response ${V}_{\mathrm{dc}}$ of the ac-driven vortices versus both the half period P and the amplitude ${F}_{L}$ of the ``square wave'' ac drive has been detailed in the present work. The influence of the equilibrium thermal noise, the shift between the two pinning sublattices, the degree of translational and orientational disorder, and the size of the simulation system on the ${V}_{\mathrm{dc}}$ response of the vortex motion at ac drive has also been addressed. Devil staircase and Arnold's tongue structures are revealed. We also analytically derive all the key features of our numerical results. This system provides a very controllable stepmotor for the control of collective motion. Our results apply mutatis mutandis to arrays of Josephson junctions, colloidal systems with optical traps, Wigner crystals, and any system with repelling movable objects that can be pinned by a lattice of traps.