Metal matrices and diamond injections

Today is just a quick roundup of some of the latest diamond news. I have some deadlines looming...

A project called ExtreMat has just come into my attention, where Professor H. Peter Degischer and Co. are in the process of fabricating new materials for extreme environements. Degischer is using 100µm diamond particles coated in silver and connected with tiny silicon bridges to create a new composite material for extreme application.

"We examined some metal matrix composites and their interfacial bonding which are promising for use in nuclear reactor heat sinks, rocket engines or in power electronics. The characterisation of these heterogeneous materials falls within our area of competency", says Degischer, Head of the Institute of Materials Science and Material Technology at the TU Vienna. The team hope the material to be resistant to very high heat fluxes and temperatures, physico-chemically aggressive media, complex mechanical loads and highly energetic radiation field.

The second news item reminds me of a previous post I wrote on Nanodiamond printing. A team of researchers at Northwestern University have developed a tool called the Nanofountain Probe that functions in two different ways. Firstly, the probe acts like a fountain pen. The drug-coated nanodiamonds serve as the ink, allowing researchers to create devices by "writing" with it. The second mode functions as a micro syringe for single cell application, permitting direct injection of biomolecules or chemicals into individual cells.

The research was led by Horacio Espinosa, a Professor of mechanical engineering, and Dean Ho, an assistant Professor of mechanical and biomedical engineering, both at the McCormick School of Engineering and Applied Science at Northwestern University. Their results were recently published online in the scientific journal Small.

Thinner than theory: Diamond nanorods

How thin can diamond nanorods be? Theory would lead you to believe that 2.7nm is the smallest possible diamond-diameter, however Shang et al. from the University of Ulster have recently shown diamond nanorods (DNRs) can be grown to the ultrathin size of 2.1nm.

Below 2.7nm thickness DNRs are thought to be energetically unstable. Shang et al. have ascribed the existence of their thinner-than-theory DNRs to a tapered graphene sheath around the DNR, which they claim could be responsible for the system's low free energy, and thus stability.

As well as housing the DNR, Shang et al. also speculate that the graphene sheath could act as a 'high pressure reactive nanocell' that self-assembles and catalyses DNR growth during PECVD. The group suggest that the curvature of a piece of graphene (seeded onto a surface) could possibly give rise to a surface tension or additional pressure that creates a thermodynamic nano-climate in favour of DNR growth over carbon nanotubes (CNTs) or amorphous carbon.

Upon measuring the threshold field emission of the DNRs, Shang et al. found them to compare favourably to most nanostructured emitters (CNT, ZnO, CNx, GaAs, GaN, AlN, BCN, etc.); however they did fair worse than oriented high density multiwall CNTs. The group measured 1mA/cm2 at 1.9V/µm, and performed admirably against the metric of field emission for flat panel displays.

The full paper, which employs a host of imaging techniques to characterise the DNRs, can be found here.

When Semi Turns To Super

I haven't posted much on Boron-doped diamond (BDD) superconductivity yet as I'm fairly unacquainted with it, so it was a pleasant surprise recently to see the cover of Nature Materials devoted to an initiating review of 'Superconducting group-IV semiconductors', by Blase et al.

It's a review so I'll leave the scientific details for you to discover, but I would like to point you in the direction of a good figure on the 'evolution of the electronic density of states and band structure with increasing p-type doping'.

Also in the news, here is a recent interview with the De Beers Group Managing Director Gareth Penny from the IDEX website.

$6.1 million and 50 nanometers

This week I'm killing two birds with one post by highlighting some recent stories from the diamond community. Last week the University of California, Santa Barbara, (UCSB) received a $6.1 million grant from DAPRA and AFOSR to develop diamond as the material of choice for quantum computing processing. The project will cover all corners of quantum computing, bringing together physicists, electrical engineers, material scientists and computer scientists to deliver the complete diamond-computing package.

"We are extremely excited by the rapid pace of discoveries in this emerging area of science and technology. This vital support offers extraordinary collaborative research opportunities for students to engage at the frontiers of the field in areas spanning fundamental physics to materials science," said David Awschalom, principal investigator for both projects and Professor of Physics and Electrical and Computer Engineering at UCSB.

On the other side of the pond, Dr. David Moran from the University of Glasgow has recently unveiled his group's most recent creation - the smallest diamond transistor in the world. The diamond gate measures only 50nm, which halves the previous record held by NTT (Japan).

Dr. Moran explains, “by developing a diamond transistor technology, we aim to tap into the truly amazing properties of this exciting material which could prove fundamental to the development of several next generation technologies. These require a very fast and ideally high-power transistor technology that needs to be able to operate in adverse weather/temperature conditions. This is where a diamond transistor technology would excel.”

Ultralong spin coherence in quantum-grade diamond brings quantum computing a step closer

Quantum computing is at the forefront of popular diamond research at the moment - and rightly so. This month's Nature Materials (AOP) has presented a letter from the EQUIND project entitled, 'Ultralong spin coherence time in isotropically engineered diamond', which describes an important step that has been taken into improving the viability of using diamond as a processor for quantum information.

The paper is reporting the longest-ever, room-temperature spin dephasing in N-V centres observed in the solid state, with dephasing times weighing in at 1.8 ms. This long dephasing time is the mainstay of quantum computing and will possibly allow coherent coupling between spins separated by a few nanometers in a quantum information processor. This impressive time has been achieved by almost eradicating all other non-zero spin states in diamond (during its growth), in order to minimise any unwanted interactions between the purposeful N-V centres and other paramagnetic impurities.

The 'quantum grade' single crystal diamond was grown at E6 under the direction of Daniel Twitchen, where the non-zero spin states were minimised by depleting the content of carbon 13 atoms in the diamond lattice from 1.1% to 0.3%. Other impurities such as nitrogen and hydrogen were also minimised resulting in long-lived quantum states.

Nanodiamonds in blue

Nanodiamonds can come in a variety of colours. Red and green NDs are made by knocking N-V and N-V-N centres into diamond via ionic bombardment and annealing, however blue nanodiamonds are not so easy. Mochalin and Gogotsi from Drexel University have now managed to light up nanodiamonds in blue, but without using the conventional ion bombardment approach.

"When we started this work, we did not intend to produce a fluorescent material, we just explored ways to make hydrophobic nanodiamond that could be easily mixed with motor oils and hydrophobic polymers," says Mochalin. "Octadecylamine is used as a strongly hydrophobic protective coating for boilers. It was a natural choice for us to bind it to nanodiamond. Somewhat surprisingly, this modification resulted not only in highly hydrophobic nanodiamond, but also rendered it fluorescent. And the fluorescence was so bright that it could be detected with bare eyes under a laboratory UV lamp even at high dilutions."

Mochalin and Gogotsi functionalised the nanodiamonds using conventional amine chemistry and are now working to uncover the mechanism for this fluorescence. The full paper, published in JACS can be found here.

Light sensitive p-type surface conduction channels on diamond

Last September I wrote a post on the work of Rezek et al., which described the illumination-induced charge transfer between Polypyrrole (PPy) and an H-terminated diamond surface. I left you on the edge of your seats by saying 'there is much work that needs to be done to uncover the possible transfer mechanism between the two substances', so without much further ado...

Cermák et al. have recently fabricated a device in order to gauge the influence of charge transfer between PPy and diamond on H-terminated surface conductivity. The device consists of a contacted and passivated thin strip of H-terminated diamond, upon which there is a non-passivated, covalently bonded PPy cluster. Cermák et al. report that, upon exposure to visible light, the device shows linear IV characteristics with resistivities being an order of magnitude lower than that of dark measurements. Switching the light source on and off, the device has demonstrated a 1 second response time, and a strong dependence on the wavelength of the light source has been reported.

The group ascribes the effect down to exciton creation at the PPy/diamond interface. Since the energetic positions of the trap states of PPy and diamond are similar, holes excited in the PPy can move from the PPy into the diamond, enhancing the p-type surface conduction in the diamond. Unfortunately the conductivity of the PPy-device is 4 orders of magnitude lower than its equivalent solely H-terminated device because of the removal of H-termination during PPy covalent bonding; however, a consolation prize of the large differences in light/dark conductivities is gained.

The full, rather emotionally written paper can be found here!

STED microscopy of N-V centres with nanometric resolution

The optical detection of N-V (nitrogen-vacancy) centres in diamond is limited by diffraction and resolution is limited to half the wavelength of light used. However in the latest issue of Nature Photonics, Rittweger et al. report sub-Angstrom precision at pinpointing N-V centres in type IIa CVD diamond - 3 orders of magnitude below the conventional diffraction limit.

Rittweger et al. have used stimulated emission depletion (STED) microscopy to image the N-V centres. STED resolves close-spaced objects by ensuring only one object fluoresces at one time. Employing stimulated emission on the optically-active objects allows them to be transiently switched off, allowing STED to achieve nanometric resolution and Angstrom precision.

The group observed outstanding photostability in the N-V centres, indicating that N-V centres engrained in nanodiamonds will be excellent fluorescent markers for biological nanoscopy. Rittweger et al. now hope to investigate the effects of magnetic and microwave fields on STED microscopy, which may lead to great simplifications in magnetic imaging at the nanoscale.

The full paper can be found here.