N1005 IBM Research: materials science

Farming at nanoscale dimensions

<div class="MsoNormal"><b style="mso-bidi-font-weight: normal;"><span style="font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;"></span></b></div><div class="MsoNormal"><i style="mso-bidi-font-style: normal;"><span style="font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;">Why understanding how nanowires self-assemble could lead to a new crop of nanodevices</span></i></div><div class="MsoNormal" style="mso-margin-bottom-alt: auto; mso-margin-top-alt: auto;"><br /></div><div class="MsoNormal" style="mso-margin-bottom-alt: auto; mso-margin-top-alt: auto;"><span style="font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;">by Dr. Frances Ross, materials scientist at IBM Research</span></div><div class="MsoNormal" style="mso-margin-bottom-alt: auto; mso-margin-top-alt: auto;"><br /></div><div class="MsoNormal" style="mso-margin-bottom-alt: auto; mso-margin-top-alt: auto;"><table cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: right; margin-left: 1em; text-align: right;"><tbody><tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhKaQNqJ-0L_Z3hyXQVtipDs4_0skmUZxEGeW3g1ombIez0m4FcoAXff6Hf4KKCtViBzV0n3HhMpY4gHpYBoe2kixcZ13FXY2o2HiIJP4ixKOUpNh5jXboFERkYFS_Ch_xpx-sowQkl6b0/s1600/Panciera-CoverImage1.jpg" imageanchor="1" style="clear: right; margin-bottom: 1em; margin-left: auto; margin-right: auto;"><img border="0" height="400" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhKaQNqJ-0L_Z3hyXQVtipDs4_0skmUZxEGeW3g1ombIez0m4FcoAXff6Hf4KKCtViBzV0n3HhMpY4gHpYBoe2kixcZ13FXY2o2HiIJP4ixKOUpNh5jXboFERkYFS_Ch_xpx-sowQkl6b0/s400/Panciera-CoverImage1.jpg" width="303" /></a></td></tr><tr><td class="tr-caption" style="text-align: center;">Artistic rendering of self-assembled nanowires<br />composed of different crystal structures<br />that spontaneously grow with the help of a<br />catalytic nanoparticle at the tip of each nanowire.<br />(credit: <a href="http://aidansugano.com/">Aidan Sugano</a>.)</td></tr></tbody></table><span style="font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;">Building transistors today is done with lithography, which is a “top-down” process that uses patterning to create the complex layers that make up the transistor structure. It’s a bit like exposing a negative on photographic paper to get the pattern you want and then using this pattern as a template to place each material – metal, insulator or semiconductor – in exactly the right location. This process has worked successfully since the 1950s, and our scientists have even demonstrated the </span><span style="font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;">first working test chips with features approaching </span><span style="font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;"><a href="http://asmarterplanet.com/blog/2015/07/a-new-wave-innovation-chips.html"><span style="mso-bidi-font-family: "Times New Roman"; mso-fareast-font-family: "Times New Roman";">7 nanometers</span></a></span><span style="font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;">, the equivalent of placing more than 20 billion tiny switches on chips the size of a fingernail</span><span style="font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;">. But as we get to ever-smaller dimensions, new approaches to building nanoscale devices will be required.</span><span style="font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;"> </span></div><div class="MsoNormal" style="mso-margin-bottom-alt: auto; mso-margin-top-alt: auto;"><br /></div><div class="MsoNormal" style="mso-margin-bottom-alt: auto; mso-margin-top-alt: auto;"><span style="font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;">At IBM’s T. J. Watson Research Center we use a technique called </span><span style="font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;"><a href="http://ibmresearchnews.blogspot.com/2015/07/self-assembling-nano-whiskers.html"><span style="mso-bidi-font-family: "Times New Roman";">self-assembly</span></a></span><span style="font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;"> to grow and directly control nanostructures that could one day form parts of integrated circuits. Self-assembly looks at chip building from the other end of the spectrum: a “bottom-up” approach that builds nanostructures in a way that is dictated by physics rather than by an imposed pattern. In some ways it’s like farming, in that that you plant seeds to grow a crop, and then support the growth with the right conditions to get the result you want.</span><br /><a name="more"></a></div><div class="MsoNormal" style="mso-margin-bottom-alt: auto; mso-margin-top-alt: auto;"></div><div class="MsoNormal" style="mso-margin-bottom-alt: auto; mso-margin-top-alt: auto;"><span style="font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;">But exploring self-assembly doesn’t mean we are ready to throw away today’s approach; instead, we want to use top-down strategies that we have already learned over many years, and combine them with new tricks that use self-assembly.</span><span style="font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;"> </span></div><div class="MsoNormal" style="mso-margin-bottom-alt: auto; mso-margin-top-alt: auto;"><br /></div><div class="MsoNormal" style="mso-margin-bottom-alt: auto; mso-margin-top-alt: auto;"><span style="font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;">Think of water splashing onto a pane of glass. It spontaneously forms little hemispheres. The droplets are hemispherical because </span><span class="renderedqtext"><span style="font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;">surface tension pulls the water molecules into this shape to minimize the surface area and energy of each droplet. But there is no reason for the droplets to form in any particular location or to be any particular size, so their positions and sizes are random. The spontaneous formation of the hemispherical shape is an example of self-assembly, but other aspects of the process (position, size) are not controlled.</span></span><br /><br /><span class="renderedqtext"><span style="font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;">Now imagine there is a scratch on the glass. Water droplets form on the scratch, because it is a good, low energy place for the water molecules to stick. We have now </span></span><span style="color: black; font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;">combined self-assembly – “make a hemispherical droplet on this surface” – with an imposed pattern – “make a droplet <i style="mso-bidi-font-style: normal;">on this part of the surface </i>by using carefully placed scratches.” The result is that we can build more complicated patterns. Flexible, customized patterns like this water example, but on the nanoscale, help us build integrated circuits.</span></div><div class="MsoNormal" style="mso-margin-bottom-alt: auto; mso-margin-top-alt: auto;"><br /></div><div class="MsoNormal" style="mso-margin-bottom-alt: auto; mso-margin-top-alt: auto;"><span style="color: black; font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;">The more precisely we can direct this self-assembly, the more versatility we can achieve. We can choose different materials for our nanostructures, build them with different sizes, and control their chemical compositions in ways that allow them to be tuned to have the properties we need. The properties of some nanomaterials could include the ability to do the job of a transistor but with less power, or at extreme temperatures beyond what silicon can handle.</span><span style="font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;"></span><b style="mso-bidi-font-weight: normal;"><span style="color: black; font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;"> </span></b></div><div class="MsoNormal" style="mso-margin-bottom-alt: auto; mso-margin-top-alt: auto;"><br /></div><div class="MsoNormal" style="mso-margin-bottom-alt: auto; mso-margin-top-alt: auto;"><b style="mso-bidi-font-weight: normal;"><span style="color: black; font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;">How to direct a nanowire</span></b></div><div class="MsoNormal" style="mso-layout-grid-align: none; mso-pagination: none; text-autospace: none;"></div><div class="MsoNormal" style="mso-layout-grid-align: none; mso-pagination: none; text-autospace: none;"><br /></div><span style="color: black; font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;">In order to direct self-assembly, we have to understand the physical stimuli that influence atoms to assemble in a certain way as they form a nanostructure. The particular nanostructures we find most interesting are called nanowires. </span><span style="font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;">These are long thin crystals whose amazing <span style="mso-bidi-font-weight: bold;">length-to-width ratio</span> could help create very densely packed transistors.</span><span style="font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;"> Using a combination of imposed patterning and self-assembly, we can grow nanowires spontaneously using the help of catalytic particles. And we can watch the nanowires as they grow, recording the process on video using a one-of-a-kind Ultra High Vacuum Transmission Electron Microscope in our lab.</span><br /><br /><span style="font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;">We load a flat substrate into the microscope, place catalytic particles onto it (this is the directed part of the process), then heat it and add some reactive gases. We watch what happens to the catalytic particles (this is the self-assembly part of the process) by magnifying the </span><span style="color: black; font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;">image by 50,000 times or more. The reaction can be slow – it takes hours for the whole experiment to be finished – but the videos show how the nanostructures grow, one layer of atoms after another. </span><span style="font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;">Recording videos, for example at different temperatures or with different added gases, is central to understanding every step of the nanowires’ growth. We get to see cause and effect when the conditions change, so we can work out the laws of physics that control the growth.</span><span style="font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;"> </span><br /><br /><div class="MsoNormal" style="mso-layout-grid-align: none; mso-pagination: none; text-autospace: none;"><div class="separator" style="clear: both; text-align: center;"></div><div class="separator" style="clear: both; text-align: center;"><iframe allowfullscreen="" frameborder="0" height="315" src="https://www.youtube.com/embed/toKPzF-QnkE" width="420"></iframe></div><div style="text-align: center;"><i>This video was recorded in an ultra high vacuum transmission electron microscope</i><br /><i>showing a silicon nanowire growing from a gold-based catalyst. The silicon is the vertical post and the catalyst is the liquid droplet on the tip. The diameter of the nanowire is 70 nanometers; in other words, about 1/1,000th of the diameter of a human hair. The stripes in the silicon and the zigzag shape along its edge provide information about the atomic arrangement within the nanowire.<br />This movie was recorded at 500 degrees C and is sped up by 30 times.</i> </div><br /></div><div class="MsoNormal" style="mso-layout-grid-align: none; mso-pagination: none; text-autospace: none;"><span style="color: black; font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;">Recently, we have become especially interested in growing nanowires made of gallium arsenide that form with the help of catalysts made of gold nanoparticles. For this we need two reactive gases, trimethylgallium and arsine. We chose these because they supply the two components needed to build the nanowire, gallium and arsenic. When we record our movies, the first reaction we see is between gallium and gold. This reaction turns the original gold nanoparticles into hemispherical liquid gold-gallium droplets. As we continue to watch, gallium and arsenic combine within each droplet to start growing a gallium arsenide nanowire beneath the droplet. </span></div><div class="MsoNormal" style="mso-layout-grid-align: none; mso-pagination: none; text-autospace: none;"><br /></div><div class="MsoNormal" style="mso-layout-grid-align: none; mso-pagination: none; text-autospace: none;"><span style="color: black; font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;">Gallium arsenide nanowires grown this way are particularly special because it is possible to change the way the gallium and arsenic atoms stack up within each nanowire. Two arrangements of the atoms are possible, and we can change from one to the other simply by altering the temperature of the reaction or even just varying the ratio of the two gases as they flow past the catalysts. The videos show how these changes in growth conditions modify the way the atoms arrange themselves at the junction between the nanowire and the catalyst. And that causes a change in how the atoms eventually stack up when they form the nanowire. We still have the same material, gallium arsenide, but the two possible arrangements of the atoms lead to different electrical properties for the whole nanowire. </span><br /><br /><span style="color: black; font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;">Understanding what drives atoms to take up one arrangement versus another gives us a better chance of growing nanowires that have the particular electrical properties that are needed for a device </span><span style="color: black; font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;">such as a nano-transistor</span><span style="color: black; font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;">. It’s akin to having more colors on your palette so that you can paint a better picture. </span></div><div class="MsoNormal" style="mso-layout-grid-align: none; mso-pagination: none; text-autospace: none;"><br /></div><div class="MsoNormal" style="mso-layout-grid-align: none; mso-pagination: none; text-autospace: none;"><span style="color: black; font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;">These special nanowires, composed of regions with different atomic arrangement, have applications in photonics or single electron transistors, both important building blocks for electronic circuits. And simply knowing that we can control the crystal arrangement in a nanowire will open up the microprocessor community’s imagination for new devices. In particular, optoelectronics, where light and electricity are combined in photonics structures, is a good bet. But that’s just the “tip of the crystal.”</span></div><div class="MsoNormal" style="mso-layout-grid-align: none; mso-pagination: none; text-autospace: none;"><br /></div><div class="MsoNormal" style="mso-layout-grid-align: none; mso-pagination: none; text-autospace: none;"><span style="color: black; font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;"><span style="font-family: "helvneue light for ibm" , sans-serif;">O</span>ur latest results, "Interface dynamics and crystal phase switching in Gallium Arsenide nanowires", will be published <span style="font-family: "helvneue light for ibm" , sans-serif;">in </span>this week’s <i style="mso-bidi-font-style: normal;">Nature.</i></span></div>

Why understanding how nanowires self-assemble could lead to a new crop of nanodevices by Dr. Frances Ross, materials scientist at IBM Resear...

How to build a better cell through engineering

6:00 AM N1000 0

<br /> <div class="MsoNormal"><div class="separator" style="clear: both; text-align: center;"><a href="http://researcher.watson.ibm.com/researcher/photos/3293.jpg" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" height="199" src="http://researcher.watson.ibm.com/researcher/photos/3293.jpg" width="200" /></a></div><i><span style="font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;">Editor's note: this article is by IBM Research Staff Member Simone Bianco, PhD</span></i></div><div class="MsoNormal"><br /></div><div class="MsoNormal"><span style="font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;">There’s nothing better on a hot day than a cold beer. Hefeweizen? Lager? Maybe a pilsner? It’s a matter of yeast that gives all beer its flavor. Yeast is the single-celled organism that makes an otherwise simple list of ingredients, complex. And it’s not just for common brewing or baking. Because different strains perform in different ways – some fermenting at high temperatures, other at cold temperatures – yeast is the one of the most-studied organisms in the world.</span><br /><a name="more"></a><span style="font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;"> </span></div><div class="MsoNormal"><br /></div><div class="MsoNormal"><span style="font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;">If we were to take a look at the microscopy, we would see that these yeast strains are morphologically different. Their internal organization differs, sometimes dramatically. The effect of that is reflected in the way the organism performs specific functions. In this case fermentation. A paradigm of cell biology is that the alterations of cell morphology are connected to alterations of chemical reactions inside the various cell structures, called organelles. Changes in the architecture of the cell will correspond to a difference in cell behavior, with either suppression or modification of existing cellular capabilities, or even the emergence of new functionalities. </span></div><div class="MsoNormal"><br /></div><div class="MsoNormal"><b style="mso-bidi-font-weight: normal;"><span style="font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;">Engineering a cell</span></b><span style="font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;"></span></div><div class="MsoNormal"><br /></div><div class="MsoNormal"><span style="font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;">There is, however, little mechanistic understanding of the links between cell morphology and cell function. Evolution has provided all living organisms with a genetic code that contains all the information necessary for each and every cell to function properly, from single cell organisms, like yeast, to multi-cellular, incredibly complex higher organisms like us humans. </span></div><div class="MsoNormal"><br /></div><div class="MsoNormal"><span style="font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;">Yet, decoding all the information contained in the genetic code is still an impossible task, today. Tens of thousands of genes are activated at specific times during the existence of just one yeast cell, and even more chemical reactions will occur during its lifespan. Hundreds of protein species will inhabit the cell, providing the building blocks of life. Monitoring this activity is a task that cannot be tackled with today's technology. Fundamental understanding of such an important part of the life of our cells needs a paradigm shift. </span></div><div class="MsoNormal"><br /></div><div class="MsoNormal"><span style="font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;">We need a new discipline: cellular engineering.</span></div><div class="MsoNormal"><br /></div><div class="MsoNormal"><span style="font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;">It is evident that such a task cannot be accomplished by a single research institution. Exceptional experimental capabilities need to go hand in hand with top-of-the-line computational and analytical tools. This is why the University of California, San Francisco, the University of California, Berkeley, Stanford University, San Francisco State University, the San Francisco Exploratorium, and IBM Research have joined forces. The collaboration wants to design, build, and test models of cellular organization. And ultimately develop cells that can perform specific functions.</span></div><div class="MsoNormal"><br /></div><div class="MsoNormal"><span style="font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;">Think of cell morphology as a proxy for cellular state and function. We can study it through microscopy methods, which are orders of magnitude cheaper than genetic screens, and provide enough accuracy to be used routinely in almost any laboratory. But building relationships between morphology and functionality requires extensively targeted experimental efforts, where cells, like beer yeasts, need to be subject to specific stimuli, and then imaged. </span></div><div class="MsoNormal"><br /></div><div class="MsoNormal"><span style="font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;">At the same time, it requires computational capabilities that need supercomputing-level power, and need new analysis tools to extract meaningful information, and learn from the wealth of data that will be produced. Furthermore, informed mathematical models are needed to quickly generate novel hypotheses from principles of cellular organization that can be tested in the laboratory. Finally, molecular information of a cell – its chemistry, genetics, proteomics -- will be needed in order to generate the ontology necessary to engineer cells that perform specific functions.</span></div><div class="MsoNormal"><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjoiCz_T3LQmGdFYXo1DexcWa-nW60iJqOx-N9MQ6O3LhRneWn9S6ce6QFTv_bWsXP4kIMpkW6WaQrTNeQBdvsV3IsbhizLoQw2WL8mEVDcofSHFP7g8sX1x-sMnB1Gpl7GPJa3aWj2el8/s1600/cellgraph4.jpg" /><span style="font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;"> </span></div><div class="separator" style="clear: both; text-align: center;"></div><div class="separator" style="clear: both; text-align: center;"></div><div class="MsoNormal"><span style="font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;">Mapping of the entire cell structure can be broken down to useable information using techniques like PCA and LDA, then machine learning is applied to understand the parsed data. <span style="mso-spacerun: yes;"> </span></span> </div><div class="MsoNormal"><span style="font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;"><br /></span></div><div class="MsoNormal"><b style="mso-bidi-font-weight: normal;"><span style="font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;">Modeling the morphology of cancer</span></b></div><div class="MsoNormal"><br /></div><div class="MsoNormal"><span style="font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;">The model example of the usefulness of fundamental understanding of the connection between cell morphology and cell behavior is cancer pathology.</span></div><div class="MsoNormal"><br /></div><div class="MsoNormal"><span style="font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;">When a doctor suspects that a patient has a tumor, the doctor will perform a biopsy: the removal of tissue samples of that are imaged and reviewed by a pathologist. The doctor then relies on an extensive set of image correlations to existing cases to compare the shape of the patient’s organelles (a cell’s wall, nucleus, mitochondria, and other internal parts) to those imaged from tumor tissues at different stages of progression. The correlation in the morphology becomes a correlation in functionality: the patient’s cells, if indeed cancerous, will replicate indefinitely, providing the hallmark behavior of any tumor. </span></div><div class="MsoNormal"><br /></div><div class="MsoNormal"><span style="font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;">This is, in many cases, an art, and it relies on invasive techniques, the expertise of the doctor, the state of the tumor, and different levels of understanding of the involved cellular mechanisms. A general mechanistic understanding of the morphological transformation processes does not yet exist, but it could dramatically improve the efficiency of diagnosis, and even reduce the need for invasive tests and further genetic screens. Moreover, cellular engineering could help introduce innovative therapeutic measures, as protection of other cells by aggregating and dividing labor between cells, or creation of new complex organizations for novel bio-materials to protect against cancerous cells.</span></div><div class="MsoNormal"><br /></div><div class="MsoNormal"><b style="mso-bidi-font-weight: normal;"><span style="font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;">The perfect cell for the perfect job</span></b><span style="font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;"></span></div><div class="MsoNormal"><br /></div><div class="MsoNormal"><span style="font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;">What is our goal with this research? If we know how cells adjust their morphology, we could control these mechanisms, predict their performance, and increase their range of capabilities. Engineered cells could be used to monitor the activity of bioreactors, devices to carry out specific chemical processes in a lab environment. NASA recently used advanced bioreactors to grow tissue samples of liver, muscle, cartilage and bone. Scientists could soon have an endless reservoir of tissues to test their research hypothesis, with a clear impact on the future of bioengineering and therapeutic sciences.</span></div><div class="MsoNormal"><br /></div><div class="MsoNormal"><span style="font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;">The disposal of organic pollutants are increasingly done by bioremediation, or using specific enzymes to convert waste into an output that is non-toxic and can serve another purpose within its environment. Specific detectors monitor the production of the product to generate useful information by proper modulation of the enzymes’ internal morphology. We can also build novel organic toxicity sensors by sensing cells’ morphology, and understanding their modifications. </span></div><div class="MsoNormal"><br /></div><div class="MsoNormal"><span style="font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;">This isn’t science fiction. The spirotox test estimates the toxicity of a volatile compound, like a gas, by monitoring cell organelles’ deformation after toxic exposure.</span></div><div class="MsoNormal"><br /></div><div class="MsoNormal"><span style="font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;">These sorts of sentinels cells, engineered to respond to changes in composition or concentration, could also be used to prevent food adulteration and protect people from food fraud. Or, more efficient biofuels can be engineered through reprogramming cell morphologies to maximize the efficiency of energy production.</span></div><div class="MsoNormal"><br /></div><span style="font-family: "helvneue light for ibm" , sans-serif; font-size: 13.0pt;">The hope is that, one day, we will be able to build cells that do what we want. Even make better beer.</span><br /><br />

Almaden cell biology cellular engineering materials science How to build a better cell through engineering

Editor's note: this article is by IBM Research Staff Member Simone Bianco, PhD There’s nothing better on a hot day than a cold beer. He...

Self-assembling nano… whiskers?

9:53 AM N1000 0

<div class="MsoNormal"><span style="font-size: 13.0pt; line-height: 107%; mso-ascii-font-family: Calibri; mso-ascii-theme-font: minor-latin; mso-hansi-font-family: Calibri; mso-hansi-theme-font: minor-latin;">by Dr. Frances Ross, materials scientist at IBM Research</span><br /><br /><table cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: right; margin-left: 1em; text-align: right;"><tbody><tr><td style="text-align: center;"><a href="http://graphics8.nytimes.com/images/2009/08/31/science/01trans2_600.jpg" imageanchor="1" style="clear: left; margin-bottom: 1em; margin-left: auto; margin-right: auto;"><img border="0" height="176" src="http://graphics8.nytimes.com/images/2009/08/31/science/01trans2_600.jpg" width="320" /></a></td></tr><tr><td class="tr-caption" style="text-align: center;">Dr. Frances Ross at the IBM Thomas J Watson<br />Research Center. Photo credit: Chris Ramirez<br />for <a href="http://www.nytimes.com/2009/09/01/science/01trans.html?pagewanted=all&_r=1&" target="_blank">The New York Times</a></td></tr></tbody></table><span style="font-size: 13.0pt; line-height: 107%; mso-ascii-font-family: Calibri; mso-ascii-theme-font: minor-latin; mso-hansi-font-family: Calibri; mso-hansi-theme-font: minor-latin;">“Whiskers” have been recorded in natural ores since the 1500s. These crystal formations indeed look like a cat’s whiskers, but function as wires. And since Bell Labs in the 1960s began to grow whiskers deliberately out of many different substances, materials scientists have been molding them into everything from photovoltaic devices, transistors, sensors, solid state lighting and batteries. At IBM Research, with colleagues from academia and the Brookhaven National Laboratory, we have developed a way to make these structures grow in an electron microscope. By recording the atoms <a href="http://spectrum.ieee.org/nanoclast/semiconductors/materials/new-selfassembly-technique-embeds-quantum-dots-into-nanowires">self-assembling</a>to form the whiskers – renamed in modern fashion as <i style="mso-bidi-font-style: normal;">nanowires</i> – we hope to understand how they grow and how to tune the growth conditions to build nano-devices.</span><br /><a name="more"></a><br /><span style="font-size: 13.0pt; line-height: 107%; mso-ascii-font-family: Calibri; mso-ascii-theme-font: minor-latin; mso-hansi-font-family: Calibri; mso-hansi-theme-font: minor-latin;">The term nanowire describes any crystal that is thin in diameter, down to tens of nanometers, but with a length maybe hundreds or thousands of times greater. The material that the nanowire is made of, and its exact dimensions, determine its performance. For example, how solar energy is absorbed, in the case of photovoltaics. Or how lithium moves along a nanowire, in the case of rechargeable batteries. And how magnetic fields arrange themselves along its length, in the case of IBM’s <a href="http://www-03.ibm.com/ibm/history/ibm100/us/en/icons/racetrack/">racetrack memory</a>. The big bang in these tiny structures comes from the fact that at nanoscale dimensions, even conventional materials can behave in remarkable and unexpected ways.</span><br /><br /><span style="font-size: 13.0pt; line-height: 107%; mso-ascii-font-family: Calibri; mso-ascii-theme-font: minor-latin; mso-hansi-font-family: Calibri; mso-hansi-theme-font: minor-latin;">One exciting opportunity for nanowires is as building blocks for transistors in microelectronics. While getting to the <a href="http://asmarterplanet.com/blog/2015/07/a-new-wave-innovation-chips.html">7 nanometer</a> node is heroic, the lithographic process conventionally used to define the circuits is ultimately limited. Using self-assembled nanowires as the cores of the transistors can provide a pathway to smaller circuits, and perhaps even new designs that need less power to perform computations.</span><br /><br /><span style="font-size: 13.0pt; line-height: 107%; mso-ascii-font-family: Calibri; mso-ascii-theme-font: minor-latin; mso-hansi-font-family: Calibri; mso-hansi-theme-font: minor-latin;">Our experiments started with the goal of understanding how the atoms spontaneously arrange themselves into the simplest sorts of nanowires, those that are made up of only one material. We chose our favorite element, silicon, the semiconductor that forms the basis of microelectronics. The nanowires grow with the help of a catalyst. So, we start with a flat wafer of silicon, add a couple of layers of gold atoms and heat until the gold and silicon react chemically and form tiny liquid droplets. The reaction takes place at 370<sup>o</sup>C, and results in something that looks a lot like a pane of glass covered by raindrops – at the nano-scale.</span><br /><br /><table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody><tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhWCP3D2U4GBbnA4j14-Z57h5LW_PWjWMnynMsovP1BSvCqgWGord3R4X8Pj-TERHdqIrZHdsq8whdj0_-P8B2dM0FX8MoLnHp25Eb5F9Fx2XuzPxOAOXokJPCt1yZS8sALoqzBpVPcTov7/s1600/nanowires_electron_microscope.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="243" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhWCP3D2U4GBbnA4j14-Z57h5LW_PWjWMnynMsovP1BSvCqgWGord3R4X8Pj-TERHdqIrZHdsq8whdj0_-P8B2dM0FX8MoLnHp25Eb5F9Fx2XuzPxOAOXokJPCt1yZS8sALoqzBpVPcTov7/s400/nanowires_electron_microscope.jpg" width="500" /></a></td></tr><tr><td class="tr-caption" style="text-align: center;">A silicon nanowire at 5nm and 20nm.</td></tr></tbody></table><span style="font-size: 13.0pt; line-height: 107%; mso-ascii-font-family: Calibri; mso-ascii-theme-font: minor-latin; mso-hansi-font-family: Calibri; mso-hansi-theme-font: minor-latin;">The trick is then to flow disilane gas, which contains silicon atoms, across the hot, droplet-covered silicon surface. When a molecule touches the surface of the silicon wafer, it bounces off and nothing changes. But when a molecule hits the surface of the gold droplet, it sticks and breaks apart, and its silicon atoms enter the droplet. As more silicon enters a droplet, the excess settles out as solid silicon beneath the droplet. Think of gradually adding spoonfuls of sugar to your coffee: excess sugar eventually settles at the bottom of the cup. In the case of the nanowires, the settling does not form disordered sludge, but instead a perfect layer of silicon atoms. The droplet stays at the top, and the nanowire keeps growing as long as we keep the gas flowing. The photo shows a nanowire during growth: the liquid droplet, labeled Au-Si, sits on top of the nanowire.<br /> </span><br /><span style="font-size: 13.0pt; line-height: 107%; mso-ascii-font-family: Calibri; mso-ascii-theme-font: minor-latin; mso-hansi-font-family: Calibri; mso-hansi-theme-font: minor-latin;">Watching this process in our electron microscope, and later in a microscope at Brookhaven National Laboratory with a high-speed (400 frames–per-second) movie camera, was an amazing experience. The video below shows the nanowire and the droplet, where the rows of dots indicate positions of silicon atoms in the nanowire. Layers of silicon atoms add onto the nanowire beneath the liquid droplet.</span></div><div class="MsoNormal"><br /><span style="font-size: 13.0pt; line-height: 107%; mso-ascii-font-family: Calibri; mso-ascii-theme-font: minor-latin; mso-hansi-font-family: Calibri; mso-hansi-theme-font: minor-latin;"><iframe allowfullscreen="" frameborder="0" height="360" src="https://www.youtube.com/embed/AS06F4YwvnM" width="480"></iframe></span><br /><span style="font-size: x-small;"><i><span style="font-size: 10.0pt; line-height: 100%; mso-ascii-font-family: Calibri; mso-ascii-theme-font: minor-latin; mso-hansi-font-family: Calibri; mso-hansi-theme-font: minor-latin;">Watch how a silicon nanowire self-assembles under a gold-silicon droplet,<br />and grows around a nanocrystal of nickel disilicide</span></i></span><br /><br /><span style="font-size: 13.0pt; line-height: 107%; mso-ascii-font-family: Calibri; mso-ascii-theme-font: minor-latin; mso-hansi-font-family: Calibri; mso-hansi-theme-font: minor-latin;">Droplet size determined the nanowire’s diameter. Temperature determined how long, and how quickly, the nanowire grew. We also tested other important semiconductors – germanium, gallium arsenide and gallium phosphide – and showed that their nanowires grew in a similar way. This finding helps us to understand how to build more complicated structures. So, we watched what happened as we switched from one gas to another, and learned the rules that govern which semiconductors could be stacked layer by layer, within a single nanowire. </span><br /><br /><span style="font-size: 13.0pt; line-height: 107%; mso-ascii-font-family: Calibri; mso-ascii-theme-font: minor-latin; mso-hansi-font-family: Calibri; mso-hansi-theme-font: minor-latin;">Because each layer has different electronic behavior, these complicated nanowires could form versatile nano-devices. And it’s possible to grow even more complicated nanowires.</span><br /><br /><span style="font-size: 13.0pt; line-height: 107%; mso-ascii-font-family: Calibri; mso-ascii-theme-font: minor-latin; mso-hansi-font-family: Calibri; mso-hansi-theme-font: minor-latin;">Our most recent experiments show what happens when we add metals, such as nickel or cobalt, to the catalytic droplet. Instead of settling out as a flat layer, the metal forms a single nanocrystal that floats in the droplet. Eventually this nanocrystal settles out, and we can grow the nanowire around it. This sequence of events was completely unexpected to us – imagine if you add that extra spoonful of sugar to your coffee and then find a perfect cube of sugar floating in the liquid! Electron microscope videos help us understand why the atoms assemble in this way, and how to control the resulting nanowire to optimize the shape, size and position of the embedded nanocrystals.</span><br /><br /><span style="font-size: 13.0pt; line-height: 107%; mso-ascii-font-family: Calibri; mso-ascii-theme-font: minor-latin; mso-hansi-font-family: Calibri; mso-hansi-theme-font: minor-latin;">Self-assembling nanowires creates new concepts for nanomaterials, helping us build structures that cannot be fabricated using conventional techniques. The self-assembly process is still challenging because every nanowire comes out slightly different – perhaps imperfect for use in a device. We are not yet precise enough to exactly replicate the process across an entire wafer, much less build reliable nano-devices. However, each step forward, such as the nanowires with embedded nanocrystals, suggests new opportunities for electronics and other applications.</span><br /><br /><span style="font-size: 13.0pt; line-height: 107%; mso-ascii-font-family: Calibri; mso-ascii-theme-font: minor-latin; mso-hansi-font-family: Calibri; mso-hansi-theme-font: minor-latin;">Self-assembly will succeed when we can harness the spontaneous behavior of atoms. That’s an exciting prospect. We need to change our way of thinking to avoid the need for perfection, but still control how the self-assembled structures behave under certain conditions – allowing us to create wholly unique devices and capabilities.</span><br /><br /><span style="font-size: 13.0pt; line-height: 107%; mso-ascii-font-family: Calibri; mso-ascii-theme-font: minor-latin; mso-hansi-font-family: Calibri; mso-hansi-theme-font: minor-latin;">Read <a href="http://www.nature.com/nmat/journal/v14/n8/full/nmat4352.html">Synthesis of nanostructures in nanowires using sequential catalyst reactions</a> in <i style="mso-bidi-font-style: normal;">Nature Materials</i>.</span></div>

materials science nanodevices nanotechnology nanowires Nature Materials Self-assembling nano… whiskers?

by Dr. Frances Ross, materials scientist at IBM Research Dr. Frances Ross at the IBM Thomas J Watson Research Center. Photo credit: Chris Ra...