Organic Molecules Challenge Essay Example For Students

Organic Molecules Challenge Essay Organic Molecules ChallengeSilicons Reign as King of SemiconductorsThere is a revolution fomenting in the semiconductor industry. It may take 30years or more to reach perfection, but when it does the advance may be so greatthat todays computers will be little more than calculators compared to whatwill come after. The revolution is called molecular electronics, and its goal isto depose silicon as king of the computer chip and put carbon in its place. The perpetrators are a few clever chemists trying to use pigment, proteins,polymers, and other organic molecules to carry out the same task thatmicroscopic patterns of silicon and metal do now. For years these researchersworked in secret, mainly at their blackboards, plotting and planning. Now theyare beginning to conduct small forays in the laboratory, and their few successesto date lead them to believe they were on the right track. We have a long way to go before carbon-based electronics replace silicon-basedelectronics, but we can see now that we hope to revolutionize computer designand performance, said Robert R. Birge, a professor of chemistry, Carnegie-Mellon University, Pittsburgh. Now its only a matter of time, hard work, andsome luck before molecular electronics start having a noticeable impact.Molecular electronics is so named because it uses molecules to act as thewires and switches of computer chips. Wires, may someday be replaced bypolymers that conduct electricity, such as polyacetylene andpolyphenylenesulfide. Another candidate might be organometallic compounds suchas porphyrins and phthalocyanines which also conduct electricity. Whencrystallized, these flat molecules stack like pancakes, and metal ions in theircenters line up with one another to form a one-dimensional wire. Many organic molecules can exist in two distinct stable states that differ insome measurable property and are interconvertable. These could be switches ofmolecular electronics. For example, bacteriorhodpsin, a bacterial pigment,exists in two optical states: one state absorbs green light, the other orange. Shinning green light on the green-absorbing state converts it into the orangestate and vice versa. Birge and his coworkers have developed high density memorydrives using bacteriorhodopsin. Although the idea of using organic molecules may seem far-fetched, it happensevery day throughout nature. Electron transport in photosynthesis one of themost important energy generating systems in nature, is a real-world example ofwhat were trying to do, said Phil Seiden, manager of molecular science, IBM,Yorkstown Heights, N.Y. Birge, who heads the Center for Molecular Electronics at Carnegie-Mellon, saidtwo factors are driving this developing revolution, more speed and less space. Semiconductor chip designers are always trying to cram more electroniccomponents into a smaller space, mostly to make computers faster, he said. Andtheyve been quite good at it so far, but they are going to run into troublequite soon.A few years ago, for example, engineers at IBM made history last year when theybuilt a memory chip with enough transistors to store a million bytes ifinformation, the megabyte. It came as no big surprise. Nor did it when they cameout with a 16-megabyte chip. Chip designers have been cramming more transistorsinto less space since Jack Kilby at Texas Instruments and Robert Noyce atFairchild Semiconductor first showed how to put multitudes on electroniccomponents on a slab of silicon. But 16 megabytes may be near the end of the road. As bits get smaller and losertogether, crosstalk between them tends to degrade their performance. If thecomponents were pushed any closer they would short circuit. Physical limits havetriumphed over engineering. That is when chemistry will have its day. Carbon, the element common to allforms of life, will become the element of computers too. That is when we seeelectronics based on inorganic semiconductors, namely silicon and galliumarsenide, giving way to electronics based on organic compounds, said Scott E. Rickert, associate professor of macromolecular science, Case Western ReserveUniversity, Cleveland, and head of the schools Polymer Microdevice Laboratory. As a result, added Rickert, we could see memory chips store billions of bytesof information and computers that are thousands times faster. The science ofmolecular electronics could revolutionize computer design.But even if it does not, the research will surely have a major impact on organicchemistry. Molecular electronics presents very challenging intellectualproblems on organic chemistry, and when people work on challenging problems theyoften come up with remarkable, interesting solutions, said Jonathan S. Lindsey,assistant professor of chemistry, Carnegie-Mellon University. Even if the wholefield falls through, well still have learned a remarkable amount more aboutorganic compounds and their physical interactions than we know now. Thats why Idont have any qualms about pursuing this research.Moreover, many believe that industries will benefit regardless of whether anorganic-based computer chip is ever built. For example, Lindsey is developing anautomated system, as well as the chemi stry to go along with it, for synthesizingcomplex organic compounds analogous to the systems now available for peptide andnucleotide synthesis. And Rickert is using technology he developed foe molecularelectronic applications to make gas sensors that are both a thousand timesfaster and more sensitive than conventional sensors. Peyotism EssayIn their system, Poehler and Potember use compounds formed form either copper orsilver- the electron donor-and the tetracyaboquinodimethane (TCNQ) or variousderivatives-the electron acceptor. The researchers first deposit the metal ontosome substrate-it could be either a silicon or plastic slab. Next, they deposita solution of the organic electron acceptor onto the metal and heat it gently,causing a reaction to occur and evaporating the solvent. In the equilibrium state between these two molecular components, an electron istransferred from copper to TCNQ, forming a positive metal ion and a negativeTCNQ ion. Irradiating this complex with light from an argon laser causes thereverse reaction to occur, forming neutral metal and neutral TCNQ. Two measurable changed accompany this reaction. One is that the laser-lit areachanges color from blue to a pale yellow if the metal is copper or from violetif it is silver. This change is easily detected using the same or another laser. Thus, metal TCNQ films, like those made from bacteriorhodopsin, could serve asoptical memory storage devices. Poehler said that they have already builtseveral such devices and are now testing their performance. They work at roomtemperature. The other change that occurs, however, is more like those that take place onstandard microelectronics switches. When an electric field id applied to theorganometallic film, it becomes conducting in the irradiated area, just as asemiconductor does when an electric field is applied to it. Erasing a data or closing the switch is accomplished using any low-intensitylaser, including carbon dioxide, neodymium yttrium aluminum garnet, or galliumarsenide devices. The tiny amount of heat generated by the laser beam causes themetal and TCNQ to return to their equilibrium, non-conducting state. Turning offthe applied voltage also returns the system to its non-conducting state. The Hoptkins researchers found they could tailor the on/off behavior of thissystem by changing the electron acceptor. Using relative weak electron acceptors,such as dimethoxy-TCNQ, produced organometallic films with a very sharp on/offbehavior. But of a strong electron acceptor such as tetrafluoro-TCNQ is used,the film remains conductive even when the applied field is removed. This effectcan last from several minutes to several days; the stronger the electronacceptor, the longer the memory effect. Poehler and his colleagues are now working to optimize the electrical andoptical behavior of these materials. They have found, for example, that filmsmade with copper last longer than those made of silver. In addition, they aretesting various substrates and coatings to further stabilize these systems. Weknow the system works, Poehler said. Now were trying to develop it into asystem that will work in microelectronics applications.At Case Wester Rickert is also trying to make good organic chemistry and turn itinto something workable in microelectronics. He and his coworkers have foundthat using Langmuir-Blodgett techniques they can make polymer films actuallylook like and behave like metal foils. The polymer molecules are arranged in avery regular, ordered array, as if they were crystalline, said Rickert. These foils, made from polymers such as polyvinylstearate, behave much as metaloxide films do in standard semiconductor devices. but transistors made with theorganic foils are 20 percent faster than their inorganic counterparts, andrequire much less energy to make and process. Early in 1986, Rickert made adiscovery about these films that could have a major impact on the chemicalindustry long before any aspect of molecular electronics. the electricalbehavior of these foils is very sensitive to environmental changes such astemperature, pressure, humidity and chemical composition, he said. As a result,they make very good chemical sensors, better than any sensor yet developed.He has been able to develop an integrated sensor that to date can measure partsper billion concentrations of nitrogen oxides, carbon dioxide, oxygen, andammonia. Moreover, it can measure all four simultaneously. Response times for the new supersniffer, as Rickert calls the sensor, are inthe millisecond range, compared to tens of seconds for standard gas sensors,Recovery times are faster too; under five seconds compared to minutes or hours. The Case Western team is now using polymer foils as electrochemical andbiochemical detectors. In spite of such successes, molecular electronics researchers point out thatMEDs will never replace totally those made of silicon and other inorganicsemiconductors. Molecular electronics will never make silicon technologyobsolete, said Carnegie-Mellons Birge. The lasers we will need, for example,will probably be built from gallium arsenide crystals on silicon wafers. But molecular electronic devices will replace many of those now made withsilicon and the combination of the two technologies should revolutionizecomputer design and function.