arXiv subjects

C. Yang

Publications and source records attributed to C. Yang.

107 records · Page 6Linked to original sources

arXiv2008

Theory of the leak-rate of seals

Seals are extremely useful devices to prevent fluid leakage. However, the exact mechanism of roughness induced leakage is not well understood. We present a theory of the leak-rate of seals, which is based on percolation theory and a recently developed contact mechanics theory. We study both static and dynamics seals. We present molecular dynamics results which show that when two elastic solids with randomly rough surfaces are squeezed together, as a function of increasing magnification or decreasing squeezing pressure, a non-contact channel will percolate when the (relative) projected contact area, A/A_0, is of order 0.4, in accor dance with percolation theory. We suggest a simple experiment which can be used to test the theory.

cond-mat.soft↗

arXiv2008

Isospectral Deformations of Eguchi-Hanson Spaces as Nonunital Spectral Triples

We study the isospectral deformations of the Eguchi-Hanson spaces along a torus isometric action in the noncompact noncommutative geometry. We concentrate on locality, smoothness and summability conditions of the nonunital spectral triples, and relate them to the geometric conditions to be noncommutative spin manifolds.

math.OA↗

arXiv2008

Contact mechanics: contact area and interfacial separation from small contact to full contact

We present a molecular dynamics study of the contact between a rigid solid with a randomly rough surface and an elastic block with a flat surface. The numerical calculations mainly focus on the contact area and the interfacial separation from small contact (low load) to full contact (high load). For small load the contact area varies linearly with the load and the interfacial separation depends logarithmically on the load. For high load the contact area approaches the nominal contact area (i.e., complete contact), and the interfacial separation approaches zero. The numerical results have been compared with analytical theory and experimental results. They are in good agreement with each other. The present findings may be very important for soft solids, e.g., rubber, or for very smooth surfaces, where complete contact can be reached at moderate high loads without plastic deformation of the solids.

cond-mat.soft↗

arXiv2008

Gate-controlled charge transfer in Si:P double quantum dots

We present low temperature charge sensing measurements of nanoscale phosphorus-implanted double-dots in silicon. The implanted phosphorus forms two 50 nm diameter islands with source and drain leads, which are separated from each other by undoped silicon tunnel barriers. Occupancy of the dots is controlled by surface gates and monitored using an aluminium single electron transistor which is capacitively coupled to the dots. We observe a charge stability diagram consistent with the designed many-electron double-dot system and this agrees well with capacitance modelling of the structure. We discuss the significance of these results to the realisation of smaller devices which may be used as charge or spin qubits.

cond-mat.mes-hall↗

arXiv2008

Bias spectroscopy and simultaneous SET charge state detection of Si:P double dots

We report a detailed study of low-temperature (mK) transport properties of a silicon double-dot system fabricated by phosphorous ion implantation. The device under study consists of two phosphorous nanoscale islands doped to above the metal-insulator transition, separated from each other and the source and drain reservoirs by nominally undoped (intrinsic) silicon tunnel barriers. Metallic control gates, together with an Al-AlOx single-electron transistor, were positioned on the substrate surface, capacitively coupled to the buried dots. The individual double-dot charge states were probed using source-drain bias spectroscopy combined with non-invasive SET charge sensing. The system was measured in linear (VSD = 0) and non-linear (VSD <> 0) regimes allowing calculations of the relevant capacitances. Simultaneous detection using both SET sensing and source-drain current measurements was demonstrated, providing a valuable combination for the analysis of the system. Evolution of the triple points with applied bias was observed using both charge and current sensing. Coulomb diamonds, showing the interplay between the Coulomb charging effects of the two dots, were measured using simultaneous detection and compared with numerical simulations.

cond-mat.mes-hall↗

arXiv2007

High quality mechanical and optical properties of commercial silicon nitride membranes

We have measured the optical and mechanical loss of commercial silicon nitride membranes. We find that 50 nm-thick, 1 mm^2 membranes have mechanical Q > 10^6 at 293 K, and Q > 10^7 at 300 mK, well above what has been observed in devices with comparable dimensions. The near-IR optical loss at 293 K is less than 2E-4. This combination of properties make these membranes attractive candidates for studying quantum effects in optomechanical systems.

quant-ph↗

arXiv2007

Molecular dynamics study of contact mechanics: contact area and interfacial separation from small to full contact

We report a molecular dynamics study of the contact between a rigid solid with a randomly rough surface and an elastic block with a flat surface. We study the contact area and the interfacial separation from small contact (low load) to full contact (high load). For small load the contact area varies linearly with the load and the interfacial separation depends logarithmically on the load. For high load the contact area approaches to the nominal contact area (i.e., complete contact), and the interfacial separation approaches to zero. The present results may be very important for soft solids, e.g., rubber, or for very smooth surfaces, where complete contact can be reached at moderate high loads without plastic deformation of the solids.

cond-mat.soft↗

arXiv2007

Effect of surface roughness and adsorbates on superlubricity

We study the sliding of elastic solids in adhesive contact with flat and rough interfaces. We consider the dependence of the sliding friction on the elastic modulus of the solids. For elastically hard solids with planar surfaces with incommensurate surface structures we observe extremely low friction (superlubricity), which very abruptly increases as the elastic modulus decreases. We show that even a relatively small surface roughness or a low concentration of adsorbates may completely kill the superlubricity state.

cond-mat.soft↗

arXiv2006

How do liquids confined at the nanoscale influence adhesion?

Liquids play an important role in adhesion and sliding friction. They behave as lubricants in human bodies especially in the joints. However, in many biological attachment systems they acts like adhesives, e.g. facilitating insects to move on ceilings or vertical walls. Here we use molecular dynamics to study how liquids confined at the nanoscale influence the adhesion between solid bodies with smooth and rough surfaces. We show that a monolayer of liquid may strongly affect the adhesion.

cond-mat.soft↗

arXiv2006

Influence of surface roughness on superhydrophobicity

Superhydrophobic surfaces, with liquid contact angle theta greater than 150 degree, have important practical applications ranging from self-cleaning window glasses, paints, and fabrics to low-friction surfaces. Many biological surfaces, such as the lotus leaf, have hierarchically structured surface roughness which is optimized for superhydrophobicity through natural selection. Here we present a molecular dynamics study of liquid droplets in contact with self-affine fractal surfaces. Our results indicate that the contact angle for nanodroplets depends strongly on the root-mean-square surface roughness amplitude but is nearly independent of the fractal dimension D_f of the surface.

cond-mat.soft↗

arXiv2006

Ion implanted Si:P double-dot with gate tuneable interdot coupling

We report on millikelvin charge sensing measurements of a silicon double-dot system fabricated by phosphorus ion implantation. An aluminum single-electron transistor (SET) is capacitively coupled to each of the implanted dots enabling the charging behavior of the double-dot system to be studied independently of current transport. Using an electrostatic gate, the interdot coupling can be tuned from weak to strong coupling. In the weak interdot coupling regime, the system exhibits well-defined double-dot charging behavior. By contrast, in the strong interdot coupling regime, the system behaves as a single-dot.

cond-mat.mes-hall↗

arXiv2006

Coulomb blockade in a nanoscale phosphorus-in-silicon island

We study the low temperature electrical transport behaviour of a silicon single electron transistor. The island and leads are defined by patterned phosphorus doped regions achieved by ion implantation through a polymer resist mask. In the device a 50 nm diameter island, containing ~600 donors and having a metallic density of states, is separated from source and drain leads by undoped silicon tunnel barriers. The central island and tunnel barriers are covered by a surface gate in a field effect transistor geometry allowing the coupling between the leads and island to be controlled. Coulomb blockade due to charging of the doped island is measured, the oscillation period is observed to be constant while the charging energy is dependent on the surface gate voltage. We discuss the possibilities of approaching the few electron regime in these structures, with the aim of observing and manipulating discrete quantum mechanical states.

cond-mat.mes-hall↗

arXiv2006

Controlled single electron transfer between Si:P dots

We demonstrate electrical control of Si:P double dots in which the potential is defined by nanoscale phosphorus doped regions. Each dot contains approximately 600 phosphorus atoms and has a diameter close to 30 nm. On application of a differential bias across the dots, electron transfer is observed, using single electron transistors in both dc- and rf-mode as charge detectors. With the possibility to scale the dots down to few and even single atoms these results open the way to a new class of precision-doped quantum dots in silicon.

cond-mat.mes-hall↗

arXiv2006

A multiscale Molecular Dynamics approach to Contact Mechanics

The friction and adhesion between elastic bodies are strongly influenced by the roughness of the surfaces in contact. Here we develop a multiscale molecular dynamics approach to contact mechanics, which can be used also when the surfaces have roughness on many different length-scales, e.g., for self affine fractal surfaces. As an illustration we consider the contact between randomly rough surfaces, and show that the contact area varies linearly with the load for small load. We also analyze the contact morphology and the pressure distribution at different magnification, both with and without adhesion. The calculations are compared with analytical contact mechanics models based on continuum mechanics.

cond-mat.soft↗

arXiv2005

An ion-implanted silicon single-electron transistor

We report on the fabrication and electrical characterization at millikelvin temperatures of a novel silicon single-electron transistor (Si-SET). The island and source-drain leads of the Si-SET are formed by the implantation of phosphorus ions to a density above the metal-insulator-transition, with the tunnel junctions created by undoped regions. Surface gates above each of the tunnel junctions independently control the tunnel coupling between the Si-SET island and leads. The device shows periodic Coulomb blockade with a charging energy e$^2$/2C$_Σ$ $\sim$ 250 $μ$eV, and demonstrates a reproducible and controllable pathway to a silicon-based SET using CMOS processing techniques.

cond-mat.mes-hall↗

arXiv2003

Charge-based silicon quantum computer architectures using controlled single-ion implantation

We report a nanofabrication, control and measurement scheme for charge-based silicon quantum computing which utilises a new technique of controlled single ion implantation. Each qubit consists of two phosphorus dopant atoms ~50 nm apart, one of which is singly ionized. The lowest two energy states of the remaining electron form the logical states. Surface electrodes control the qubit using voltage pulses and dual single electron transistors operating near the quantum limit provide fast readout with spurious signal rejection. A low energy (keV) ion beam is used to implant the phosphorus atoms in high-purity Si. Single atom control during the implantation is achieved by monitoring on-chip detector electrodes, integrated within the device structure, while positional accuracy is provided by a nanomachined resist mask. We describe a construction process for implanted single atom and atom cluster devices with all components registered to better than 20 nm, together with electrical characterisation of the readout circuitry. We also discuss universal one- and two-qubit gate operations for this architecture, providing a possible path towards quantum computing in silicon.

cond-mat↗

arXiv1993

Hubble Space Telescope Images of the Subarcsecond Jet in DG Tau

We have applied a new restoration technique to archival [O~I], H$α$, and continuum HST images of DG~Tau. The restored [O~I] and H$α$ images show that DG~Tau has a jet with a projected length of 25~AU and width $\leq$10~AU, and is already collimated at a projected distance of $\sim$~40~AU (0\farcs25) from the star. Such a narrow width and short collimation distance for a stellar jet places important constraints on theoretical models of jet formation.

astro-ph↗