Author Archives: steve bush

Stanene: two-dimensional tin

Two dimensional tin has been fabricated by a Chinese-American team. It is potentially a large band-gap semiconductor with unusual properties that include topological superconductivity and near-room-temperature quantum anomalous Hall effect, according to the Nature Materials paper ‘Epitaxial growth of two-dimensional stanene‘.

Topological superconductivity is the free conduction of electrons along the outside edges of a two dimensional material.

Stanene now joins 2D silicon (silicene) and 2D germanium (germanene) from group IV of the periodic table.

The team found a suitable hexagonal crystal to grow it on – (111) Be₂Te₃ – and deposited it using molecular beam epitaxy – MBE was how other teams managed to fabricates silicene and germanene, and germanene has also been made by mechanical exfoliation.

What grows is not totally flat like graphene, but a molecule with a regular slight buckle – every second atom is either slightly up or slightly down from the molecular plane – resembling two layers when viewed from the side. The height difference is around 0.1nm.

This is early days for the material, which interacted with the substrate and could not be measured in isolation. Work with the bare substrate, the substrate plus stanene, and then further over-coated with potassium, allowed theoretical models to be confirmed and improved. “The synthesis of stanene and its derivatives will stimulate further experimental investigation of their theoretically predicted properties”, said researchers in the paper’s abstract.

Scientists took part from: Shanghai Jiao Tong University, Stanford University, Tsinghua University, Collaborative Innovation Center of Quantum Matter (Beijing) and Collaborative Innovation Center of Advanced Microstructures (Nanjing).

Stanene: two-dimensional tin

Two dimensional tin has been fabricated by a Chinese-American team. It is potentially a large band-gap semiconductor with unusual properties that include topological superconductivity and near-room-temperature quantum anomalous Hall effect, according to the Nature Materials paper ‘Epitaxial growth of two-dimensional stanene‘.

Topological superconductivity is the free conduction of electrons along the outside edges of a two dimensional material.

Stanene now joins 2D silicon (silicene) and 2D germanium (germanene) from group IV of the periodic table.

The team found a suitable hexagonal crystal to grow it on – (111) Be₂Te₃ – and deposited it using molecular beam epitaxy – MBE was how other teams managed to fabricates silicene and germanene, and germanene has also been made by mechanical exfoliation.

What grows is not totally flat like graphene, but a molecule with a regular slight buckle – every second atom is either slightly up or slightly down from the molecular plane – resembling two layers when viewed from the side. The height difference is around 0.1nm.

This is early days for the material, which interacted with the substrate and could not be measured in isolation. Work with the bare substrate, the substrate plus stanene, and then further over-coated with potassium, allowed theoretical models to be confirmed and improved. “The synthesis of stanene and its derivatives will stimulate further experimental investigation of their theoretically predicted properties”, said researchers in the paper’s abstract.

Scientists took part from: Shanghai Jiao Tong University, Stanford University, Tsinghua University, Collaborative Innovation Center of Quantum Matter (Beijing) and Collaborative Innovation Center of Advanced Microstructures (Nanjing).

L up and R down in 0402 inductors

The 0402DF series of chip inductors offers higher inductance and significantly lower resistance compared with previous 0402-sized inductors, claims maker Coilcraft.

There are 25 values from 20nH to 3.3µH (+/- 5%).

As an example of resistance, the 220nH value is 240mΩ – 55% lower than the same value in Coilcraft’s 0402AF sSeries “making it optimised for use as a harmonic filter element for NFC applications”, said the firm.

Other proposed applications are as elements in band-stop filters, low-pass filters, one-pole filters, an RF choke in cellular bands, or for ground-to-ground isolation.

The cores are ferrite, and terminations are RoHS 6/6-compliant matte tin over nickel over silver-palladium-glass frit.

L up and R down in 0402 inductors

The 0402DF series of chip inductors offers higher inductance and significantly lower resistance compared with previous 0402-sized inductors, claims maker Coilcraft.

There are 25 values from 20nH to 3.3µH (+/- 5%).

As an example of resistance, the 220nH value is 240mΩ – 55% lower than the same value in Coilcraft’s 0402AF sSeries “making it optimised for use as a harmonic filter element for NFC applications”, said the firm.

Other proposed applications are as elements in band-stop filters, low-pass filters, one-pole filters, an RF choke in cellular bands, or for ground-to-ground isolation.

The cores are ferrite, and terminations are RoHS 6/6-compliant matte tin over nickel over silver-palladium-glass frit.

Graphene and boron nitride make a semiconductor junction

Graphene and boron nitride nanotubes can form a digital switch, according to Michigan Technological University.

Respectively they are a zero band-gap conductor and wide band-gap insulator.

“When we put them together, you form a band gap mis-match that creates a potential barrier that stops electrons,”said Michigan professor Yoke Khin Yap.

The team took exfoliated graphene and grew BN tubes on it with chemical vapour deposition (see diagram): 60nm diameter hetrojunctions formed at the joins.

Tungsten scanning tunnelling microscope (STM) probes were used to contact the graphene and the tube.

When the probe was 1.23µm up the tube from the join there was no conduction (±30V bias).

At 620nm away from the join, a symmetrically-conducting junction formed – with a curve much like a diode conduction curve, but bidirectional, which was conducting significantly (0.5µA) with 30V bias in either duirection.

Shifting the distance to 100nm caused the junction to conduct significantly by ~12V.

Attempts to turn the junction into a transistor – the under-lying oxidised silicon wafer (500nm oxide) was used as a back-gate – were unsuccessful, even at ±100V. The team proposed that highly-conductive lower layers of the multi-layer graphene shielded the junction, and that a top-gated structure might work.

Simulation by density functional theory (DFT) suggests that mismatch of the density of states (DOS) is responsible for the voltage-dependant switching behaviour, according to ‘Switching behaviors of graphene boron nitride nanotube heterojunctions‘, a paper covering the work in Nature Scientific Reports.

Encoder offers 5,000 counts per revolution

Avago AEDT-981x is a family of industrial grade optical encoders offering from 2,000 to 5,000 counts per revolution (CPR) using a code wheel of 11mm optical radius.

The devices are three channel incremental encoders – two quadrature plus one index channel – and are rated from -40 to 115°C.

The package is ~ 27 x 21 x 10mm with straight or right-angled pins. Spatial mounting tolerance is 0.4mm and the code wheel gap can range ±0.15mm, “allowing easy motor shaft alignment”, said Mouser, which is stocking the encoder.

Supply is 55V and the encoders have automatic LED brightness regulation to minimise consumption, which is typically 20mA. Outputs deliver ±5mA without pull up resistors.

Applications are expected in motor control, robotics, and factory automation.

Water repellent coating improves capacitor reliability

Murata has developed a water-repellent coating that it claims will increase the reliability of multi-layer ceramic capacitors.

At issue is condensation – not just between the PCB and he capacitor, but on any capacitor surface that can gather condensation.

When water wets the surface of the capacitor – top diagram – electromigration of electrode metals can occur which can eventually grow into a short circuit between the capacitor electrodes.

With the anti-wetting coating, which is permemantly applied, water droplets can not bridge from electrode to electrode and the scope for electromigration is significantly reduced – middle diagram.

Murata water shedding capacitor

Diagram shows the ceramic die, electrodes, and coating

“This capacitor has applications particularly in navigation systems, body control electronic control units [ECUs], air conditioner ECUs, meter ECUs and engine ECUs,” said Murata.

Sample shipments have begun and mass production is scheduled within a year.

K computer claims super computer crown

Having fallen from the peak of the Top 500 list of super computers a few years ago, Japan’s K computer is back up there again, this time on the Graph 500 supercomputer ranking.

Graph 500 is a relatively new benchmark, from 2010, which seeks to measure supercomputers on data-intensive loads rather than simple speed, “with the goal of improving computing involving complex data problems in areas such as cybersecurity, medical informatics, data enrichment, social networks, symbolic networks, and modeling neuronal circuits in the brain”, said Fujitsi, builder of K computer.

A collaboration between RIKEN, the Tokyo Institute of Technology, University College Dublin, Kyushu University, and Fujitsu got the computer its top place – announced this month at the international conference on high-performance computing (ISC2015) in Frankfurt.

The Tokyo Institute of Technology and RIKEN used 82,944 of K computer’s 88,128 compute nodes (663552 SPARC64 cores) to solve a breadth-first search of a graph of 1 trillion nodes and 16 trillion edges in 0.45s, scoring 38,621 gigaTEPS.

Sequoia at the Lawrence Livermore Laboratory scored of 23,751 gigaTEPS, and Mira at the Argonne National Laboratory scored 14,982.

“In June last year we took the top spot with K computer, but we dropped to second place in the rankings of November that year,” said K computer scientist Koji Ueno. “In response, we identified problems in the performance of our previous implementation and developed a new algorithm that allowed us to make some important improvements.”

Key to K Computer’s high through put is its ‘6-dimensional mesh/torus‘ internal network.

Server power measured per programme by Fujitsu

Server power measured per programme by Fujitsu

Server power measured per programme by Fujitsu

Aiming to cut power waste in data centres, Fujitsu Labs has developed a way to determine how much energy each programme running on a CPU consumes.

It adds to the capability, called RAPL, of some Intel CPUs to measure overall power consumption.

“According to a report by the Japanese Ministry of Internal Affairs and Communications, Japan’s datacenters consume an average of 7.72 billion kWh per year,” said Fujitsu.

“One way to reduce energy consumption is through the use of more energy-efficient hardware. Another is to reduce the energy required to run programs on servers. A precondition for energy-efficient programming is to have an understanding of the energy being consumed by existing software. Until now, however, it was not possible to calculate the energy required to execute software on a core-by-core basis, so it has been difficult to take a software-based approach to reducing power consumption.”

Not a lot of detail has been revealed – it is to be presented at the Summer United Workshops on Parallel, Distributed and Cooperative Processing 2015 (SWoPP 2015) next week.

The Lab’s technique uses information that can be tracked at the individual core level such as clock cycles and cache-hit percentages to estimate energy consumption in detail, down to the program module level. It adds atound 1% processing over-head, and captures information by the millisecond.

Testing is underway, a practical implementation is expected in 2016, and the company is also looking into applying the technology to its own data centres.

Server power measured per programme by Fujitsu

Server power measured per programme by Fujitsu

Server power measured per programme by Fujitsu

Aiming to cut power waste in data centres, Fujitsu Labs has developed a way to determine how much energy each programme running on a CPU consumes.

It adds to the capability, called RAPL, of some Intel CPUs to measure overall power consumption.

“According to a report by the Japanese Ministry of Internal Affairs and Communications, Japan’s datacenters consume an average of 7.72 billion kWh per year,” said Fujitsu.

“One way to reduce energy consumption is through the use of more energy-efficient hardware. Another is to reduce the energy required to run programs on servers. A precondition for energy-efficient programming is to have an understanding of the energy being consumed by existing software. Until now, however, it was not possible to calculate the energy required to execute software on a core-by-core basis, so it has been difficult to take a software-based approach to reducing power consumption.”

Not a lot of detail has been revealed – it is to be presented at the Summer United Workshops on Parallel, Distributed and Cooperative Processing 2015 (SWoPP 2015) next week.

The Lab’s technique uses information that can be tracked at the individual core level such as clock cycles and cache-hit percentages to estimate energy consumption in detail, down to the program module level. It adds atound 1% processing over-head, and captures information by the millisecond.

Testing is underway, a practical implementation is expected in 2016, and the company is also looking into applying the technology to its own data centres.