graphene

Carbon Kopi

Carbon Kopi, coffee Hammersmith, coffee Fulham
Carbon Kopi, the sign in the window above giving a clue to the name without being a direct reference.

The name of this relatively new cafe in Hammersmith/Fulham was intriguing on several levels. Kopi means coffee in both Malay and Indonesian and, having recently travelled back from SE Asia, it was interesting to see what the link to this cafe may be. Then there was the pun in the name. The website explains it as representative of a desire to make a consistently good coffee, each being a carbon copy of the other. So both the name, and the cafe’s symbol have appeals for a coffee-science website. And so it was that we wandered down Fulham Palace Road to finally arrive at Carbon Kopi a few Saturdays ago.

The cafe occupies a corner building and is much larger than you may expect it to be. It is also friendly, airy and light with large windows giving plenty of illumination to the space. Allergen information was clearly labelled on the cakes and edibles (with extra information in a folder), which is always great to see.

Coffee was by Square Mile with guest roasters on batch brew and so we had a long black and oat milk hot chocolate which came served in huskee cups. Huskee cups are produced by re-using the husks otherwise discarded during the coffee milling stage. A re-usable cup that reduces waste certainly, but does it reduce the carbon footprint? An answer that depends on how many times you use it. Continuing the environmental theme, near the door, there was a separate bin for compostable cups. This was excellent to see because if compostable cups do not get to an industrial composting facility, they can take an absolute age to break down in a conventional compost heap.

Hat and huskee
Coffee in a huskee cup at Carbon Kopi. A protrusion on the saucer fits into the base of the huskee cup and stops it slipping across the saucer. Unlike graphite where the regular hexagons of carbon form layers that slip over each other to form a solid lubricant.

Across the road, the St Alban’s Church was made of brick. One row upon another, the set of bricks formed a layered structure. Where they met at corners or against the pavement they formed abrupt discontinuities, a sort of dislocation. Together with the small protrusion on the middle of the huskee cup saucer (to stop the cup slipping?), and the speaker above the door entertaining us with 80s music, the natural connection here was graphene.

Graphene is a form of carbon that is a single atomic layer thick. Each carbon atom is arranged into a flat hexagonal structure exactly like graphite but, unlike graphite, there is only one layer of these atoms in graphene. The strength and strange electrical properties of this material, together with its lightweight form, have made this material an intense subject of research for the past 15 years or so. A recent Physics World podcast tested a set of headphones with the vibrating membrane made of graphene. The idea being that the strength of the material combined with its relatively low mass, would enhance the way that we heard the sound coming through the speakers. You can listen to the review (though not the speakers) here.

coffee Hammersmith
Each layer of bricks forms a regular set of layers. But where they come up against each other discontinuities are formed. These can cause special problems in sheets of graphene.

But are there aspects of graphene that may be more applicable to the cafe and coffee industry? Various teams around the world have been working to make membranes of graphene work as single molecule detectors. The idea is that molecules adsorbed onto the surface of a graphene membrane change the electrical properties of the membrane to an extent that can be measured even in the case of single molecule adsorption. The sensitivity of the electrical properties of the graphene to different molecules could mean that graphene based devices would make very sensitive contamination detectors, including allergen detectors. Such sensors are the subject of a research collaboration at the National Physical Laboratory in Teddington and could mean that, rather than be in any doubt as to whether a substance contains an allergen, it could be quickly tested by passing it through a graphene sensor.

All this is quite far from the coffee and cakes at Carbon Kopi. But if you are in the area, it is a lovely place to stop, enjoy a coffee and contemplate the bricks of the church opposite.

Carbon Kopi is at 11 Margravine Road, W6 8LS

Semi skimmed at Full Fat, Balham

exterior of Full Fat Balham

The shopfront almost seemed to skinny for the name of this cafe.

Just around the corner from Balham tube station, on Chestnut Grove is a new (old) café, Full Fat. Although it has only been in its current location since September 2018, it was previously known as the Balham Kitchen and was apparently quite popular, not just because it was a friendly local café, but also because of the coffee and the chapatis.

We had chanced upon Full Fat while in Balham and took the opportunity for a chapati brunch. During our coffee break several customers came in and had a chat with the two people behind the counter. With coffee roasted by Workshop and an excellent range of homemade chapatis, along with friendly people, what is not to like? We enjoyed an Americano and an oat milk hot chocolate together with two chapatis. My egg chapati was perfectly done, just the right amount of pepper-to-egg balance. And the coffee was also very well made with plenty to think about just by gazing into it.

Although the café itself is quite small, there are three tables and several seats, enough to be able to ensure that you can probably perch somewhere to enjoy your coffee and chapati. There are even entertaining drawings on the walls of the café that make me wonder whether these are previous customers, immortalised on the walls enjoying a cup of coffee with their morning paper? Certainly they are a good reason to put down your smart phone and just soak in the atmosphere here.

pencil drawings in Full Fat

Pencil drawings at Full Fat Balham

Apart from the drawings, the other decoration in the café that caught my attention was behind another table: a striped piece of woodwork that was reminiscent of a type of cake served in Malaysia and Singapore, kueh lapis. It is a layered cake, the idea being that you peel each layer off to eat it, extending the enjoyment that you can get out of a cake. Although the layers peel easily, ordinarily the cake holds together as a cake, the layers do not glide over each other as if they are wholly separate, perhaps like chapatis stacked on top of each other. No, whether the cake works or not, as a kueh lapis, is down not just to the flavour, but also to the texture and to the way that each layer peels from the next, the subtle tug of one layer held, but not quite, by the last.

These interlayer or interface effects are often, ultimately, an atomic phenomenon. Just as when you drop a drip of coffee on the table, the thing that ultimately determines the shape of the droplet is the attraction between the molecules in the water and the atoms on the table surface*, so the stickiness of the cake has to be occurring, ultimately, at the atomic level.

Interface effects can be crucial in other solids too, not just coffee and cake. Consider sapphire. Sapphire has the molecular formula Al2O3. Ordinarily it is colourless and transparent, it becomes blue when impurities are added to it. But sapphire has another property which is that it is electrically insulating: a sapphire would not conduct any electricity if you tried to use it to connect to your light bulbs. This insulating behaviour is shared with another oxide, strontium titanate, SrTiO3, which is also a colourless and transparent material. Nothing of any interest there then. But, and this is the key thing, if you took a piece of strontium titanate and grew the sapphire on top of it, under certain growth conditions, this bilayer becomes extraordinarily electrically conducting, far better than many metals that you can think of. And it is because of the atomic effects that occur at the interface between the strontium titanate and the Al2O3.

Layering of wood at Full Fat

Can you see the layering on the wooden panel behind the table? Thought not, you’ll just have to visit Full Fat and see for yourself.

But then another example, a new finding that is perhaps more closely associated with coffee. When you take the semiconductor molybdenum ditelluride (MoTe2) and sandwich a thin layer of it between two sheets of graphene, some atomic-level interactions occur. In the case of MoTe2, the “band gap” of the semiconductor (which determines how it conducts electricity when light is shone on it) is altered by the van der Waals forces associated with the graphene layers: the interface effects are changing the way that the semiconductor reacts to light. Ordinarily if you shine a pulsed laser at such a semiconductor, the electrons† that get excited across the band gap are few enough that they behave as a gas within the semiconductor. This means that if you add more electrons (by pulsing the light on the semiconductor again), the density of the electron ‘gas’ will increase. What researchers have just shown is that for this 2D layer, if you shine very high powered lasers at the MoTe2 layer for a short length of time, so many electrons get excited that the semiconductor no longer behaves as if it contains an electron gas, but an electron ‘liquid’. A sort of droplet of electrons in the locality of the laser beam. And because of the way that the band structure had been affected by the interface layers, they managed to obtain this behaviour at room temperature. Although such liquids had been created before, the new thing about this result was that previously these experiments were usually done at very low (-269C) temperatures. Quite a temperature increase on previous results!

Droplets of an electron-hole excitation may seem a far step from the droplets of coffee that you could be enjoying at Full Fat. However, it is just a short hop for the imagination if you stopped to give it time to think. What will you notice next time you are in a café?

Full Fat is on Chestnut Grove, literally just around the corner from Balham tube station.

*Assuming that the table is flat. If the table is nanostructured, the structure itself can influence the ‘wettability’ of the table.

†Yes, and holes.

Diamonds are forever at Violet, Hackney

the outside of Violet

Violet in Hackney

Violet is not quite where I expected it to be. I had expected it to be in a row of shops on a main street, instead it is tucked away, a little cafe in a back street in Hackney. Despite the relative anonymity, Violet has won awards for the quality of its cakes. Award winning cakes are hard to resist and so, a few weeks ago I went along to Violet to try the coffee. With a couple of seats outside and a large room upstairs with seating, it is very easy to enjoy a good coffee and a cake while taking in the surroundings. The cakes certainly do not disappoint and, importantly for Bean Thinking, they know exactly what goes in them, meaning that if you are allergic to nuts or have other food allergies or intolerances, they are incredibly helpful. They definitely get a tick in the “cafe with good nut knowledge” category.

As it had been raining when we tried Violet, we decided to take a seat upstairs. Stacked in one corner of the room were a set of wooden chairs, reminiscent of those chairs that we had to stack at school. Each chair fitted almost exactly onto the previous one. At the top of the stack of chairs however, the uppermost chair did not fit exactly onto the previous chair, it was as if there was a defect in the stack.

stack of chairs, Violet

The chair stack in Violet.

The diagonal legs of the chairs resembled the multiple strata in a layered substance such as graphite. Each layer of graphite features a hexagonal arrangement of carbon atoms forming a structure very much like the chair legs in the chair stack. Graphene, a material of which there is currently a lot of hype, is a single layer of graphite. The carbon equivalent of one chair leg on its own. Carbon is a fascinating element. If, rather than being arranged in layers, it is arranged into a more 3D crystal structure, then you get diamond, a colourless, extremely hard crystal structure, very different from graphite. It is in diamond that defects in the stacking structure (such as with the uppermost chair) can cause spectacular effects.

If the carbon atoms are arranged into a perfect crystal structure, (the equivalent to the chairs being perfectly stacked), then diamond is colourless. If on the other hand, something happens to disrupt the structure, perhaps there is one carbon atom missing in the structure or maybe another, impurity element, such as nitrogen, has got in, the way that the electrons in the diamond react to light changes. This means that it can take on a colour. The introduction of nitrogen for example, in concentrations of only 0.1% will make the diamonds more yellow or orange. Red diamonds are a consequence not of impurities but simply defects in the crystal arrangement. The equivalent to that one last chair in the chair stack changing the properties of the stack completely. Knowing that the colour of a diamond is a result of a defect in the arrangement of carbon atoms in the structure offers us two possible viewpoints. Either people who buy red diamonds are paying a premium for defective goods, or, beauty takes many forms and what is beautiful is not necessarily what is regular and perfect. I know which view of the world I prefer to take.

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Violet is at 47 Wilton Way, E8 3ED