LetвЂ™s grow a solid How solids grow Put your own name here! What is special about a solid? пЃ® It keeps its shape. A man-made object A natural object 2 Liquids пЃ® Have no shape пЃ® When solids get hot they melt so atoms can move round freely. to form a liquid - like chocolate on a hot day. 3 Solids remember how they grew! пЃ® We look at 2 ways that solids grow. п‚Ё and the types of solid formed. пЃ® Water can form: 1. frost and snowflakes вЂ“ formed out of 2. ice in icicles or on a pond вЂ“ formed the air from water 4 1. Snowflakes and frost пЃ® пЃ® пЃ® are very irregular, have many points or edges, have lots of space inside them. 5 2. Ice in icicles Ice on a pond It is transparent with very flat surfaces 6 Water from the tap and water from melted ice Which is which? пЃ® Liquids do not remember. пЃ® 7 How do solids grow? Why is it interesting and useful to know? пЃ® We make modern devices by growing a solid atom-by-atom п‚Ё to give us the form that we want. 8 1 9 Snowflakes grow from vapour пЃ® We have air with very few water molecules in it. Cold surface пЃ® When the water molecule hits a cold surface it will stick just where it lands Molecule вЂ“ a new word? A molecule of water is the tiniest particle of water that can exist and still be water. 10 A computer can show this пЃ® We use a simulation from Hong Kong http://apricot.polyu.edu.hk/~lam/dla/dla.html 11 http://apricot.ap.polyu.edu.hk/dla/dla.html 12 Growing a snowflake пЃ® 100 molecules 11 000 molecules 13 2 14 Ice from a puddle пЃ® Why is it perfectly flat? 15 Crystals пЃ® пЃ® пЃ® When solids grow the atoms add on row by row to form a layer. Then another layer grows on top. Then another - A tiny natural crystal in a stone 16 How many layers of atoms in this chunk of quartz crystal? One layer is very, very thin. пЃ® About 10000 layers make the thickness of paper. пЃ® The crystal has about 100 million layers of atoms! How big can a crystal grow? See http://news.bbc.co.uk/1/hi/8466493.stm пЃ® 17 Growing a solid from liquid or a solution пЃ® пЃ® пЃ® An atom will join the solid only if the conditions are exactly right. If the solid is near to its melting point the atoms can move around so as to get a more perfect pattern. We call this annealing. 18 Growing a solid atom by atom пЃ® пЃ® Send a beam of atoms through a vacuum and on to a flat surface. Keep the surface hot so that the atoms can move around and find the best place to settle. 19 What is the arrangement of atoms? пЃ® Each atom wants to be close to other atoms. пЃ® What pattern do we get? We see lines пѓ crystals ! 20 More atoms пЃ® Can you see a pattern? 21 Lines 22 More lines 23 - in 3 directions 24 Bubble rafts show thisWe will make some soon. 25 How to make a bubble raft Bowl of water Add one spoonful of detergent very carefully - stir gently. Put in the yoghurt pot - you will get a stream of bubbles. The yoghurt pot is below the water surface and above the bottom of the bowl. Move your hand slowly from side to side to spread the bubbles. 26 A bubble raft is a вЂ�solidвЂ™ layer water. on the surface of the A bubble raft grown quickly. 27 What do we see ? пЃ® пЃ® пЃ® пЃ® The bubbles attract each other. They all move a little so that a new bubble goes in the best place. The bubbles are attracted to the edge of the container and to your fingers! If a bubble bursts or the raft is disturbed it will repair itself вЂ“ this is called annealing. 28 A bubble raft grown very slowly пЃ® Can you see the rows? University of Cambridge 29 The bubbles are in rows пЃ® In 3 directions 30 Who are the experts at creating this order? пЃ® Bees п‚Ё honeycomb 31 What else do we learn ? пЃ® Bubbles are made from air and soapy water BUT пЃ® пЃ® They do not look like air, or water. They do not behave like air, or water. A foam dance! 32 What is special about bubbles? пЃ® пЃ® пЃ® The soap films are very thin. A thin film of water is very different from water in a bucket or glass. We have a very thin sandwich air- water вЂ“air 33 Now back to solids All crystalline solids have atoms in layers like lots of bubble rafts. пЃ® We can grow crystals from a solution of salt in water. пЃ® пЃ® Special вЂ�sandwichвЂ™ crystals can be grown, which have different atoms in different layers. 34 Sandwich crystals can now be grown layer by layer пЃ® пЃ® пЃ® MBE (Molecular Beam Epitaxy) п‚Ё 1 layer per second п‚Ё 2,000,000 seconds for 1 mm = 23 days for 1 mm These special crystals are used inп‚Ё LEDs п‚Ё and----- 35 You use manufactured crystals in вЂ“ Computer вЂ�chipsвЂ™ Chips are in: mobile phones games consoles laptops MP3 players-36 What have we learned ? вЂўA solid remembers the way it is formed. вЂўA solid formed from vapour may be like a snowflake. вЂўWe get perfect solids from liquids and if the solid is free to readjust, anneal. вЂўWe grew a bubble raft on water and watched it anneal. вЂўWe saw that soap bubbles look very different from water and air and behave differently too! вЂўWe learned that modern devices depend on atomic layer sandwiches. 37 Scientists do amazing things! There is lots to find out! Keep asking questions!