Problem Statement Scope And Limitation Engineering Essay

Problem Statement Scope And Limitation Engineering Essay In this research ZnO thin film will be doped with aluminium using sol-gel spin-coating method. Then the Al-doped ZnO thin film (as seed catalyst) on a glass substrate will be then layered bottom of an aligned ZnO nanorod structure which was prepared using sonicated sol-gel immersion technique. The nanorod thin film parameters will be characterizing through its I-V curve characteristics and also the optical and absorbance of aligned ZnO nanorod thin film. INTRODUCTION 1.2.1 Background study UV sensor or stands for ultraviolet sensor are important devices that can be used in commercial and military applications. The applications are including gas sensing, space research, high temperature flame detection, air quality monitoring and many more. UV detectors currently used silicon-based detectors and photomultiplier tubes. These materials require costly filters and attenuators. However by replacing those technologies with wide band-gap semiconductors such as zinc oxide (ZnO) have been suggested [1]. UV light emitting or receiving devices, solar cells, gas sensor and transparent electrodes are some of the zinc oxide applications. Various deposition methods such as chemical vapor deposition, sputtering and molecular beam epitaxy were used to fabricate ZnO thin films. However, these deposition methods are high production cost because required high temperature processing and vacuum technology [2]. In this paper, the purpose of this research is to fabricate ultraviolet sensor using zinc oxide thin film and characterize the sensor performances by its electrical properties. Furthermore, this research is to characterize aluminum doping concentration and the nanostructure of zinc oxide thin film. In this research, sol-gel spin coating method was used to prepare Al doped zinc oxide thin film and an aligned ZnO nanorod structured thin films on a glass substrate by the sonicated sol-gel immersion method. 1.2.2 Literature Review ZnO is an n-type semiconductor with a direct band gap of 3.42eV and because of the oxygen vacancies and intrinsic defects such as interstitial zinc atoms, the electrical conductivity of the films is large [3]. It is very good material for electronic device application due to its wide band gap and large exciton binding energy of 60meV [4]. The properties of ZnO thin film can be improve by a doping process and annealing process [3]. There are that focus on the doping process. To improved electrical or optical properties of ZnO, ZnO were frequently doped with group 3, 4 and 5 elements such as Gallium (Ga), Sn and Aluminium (Al) [5]. Al doping is most suitable because its cheap, abundant and non-toxic material and will produce Al doped ZnO thin film with higher optical transmittance and low resistivity in infrared region [4]. From the journal [6], radio-frequency (RF) reactive magnetron sputtering method was used to deposit Al-doped ZnO on the smooth nucleation side of FSD films by. The electrical properties were discussed. The first electron concentration increased and next decreased with the increase of Al doping concentration. The maximum carrier concentration achieve when the film is doped with 2at% Al. Hall mobility is inversely proportional to the Al doping concentration. The high temperature annealing process is use to enhance the Hall mobility of the films [6]. From the journal [7], ZnO thin films with various weight percentages of aluminium and the electrical properties were discussed using sol-gel dip-coating method. The conductivity shows higher response of the doped ZnO thin films under UV compared with dark condition. Both condition proof that the conductivity of ZnO is directly proportional to doping concentration. The optical band gap energy is also directly proportional with doping concentration. The transmittance of ZnO thin films is about 75% when wavelength from 390nm to 850nm. From the journal [8], at different dopant concentration the electrical properties of Al-doped ZnO thin films were discussed using sol-gel method. The resistance first decrease with increase aluminium ion concentration. Then the resistance of doped thin films increased with increasing dopant concentration and it decreases at higher Al concentration. The transmittance of ZnO thin films is about 80% when wavelength from 370nm to 850nm. The advantage of gallium is an excellent dopant for increasing the conductivity and this source is less reactive and more resistive oxidation. Based on the journal [5], Ga-doped ZnO nanowires were growth using thermal deposition method. The ZnO nanowires have grown uniformly with high yield and average length of each nanowire is about 1.3um. From the XRD pattern, it can be deduced that the Ga element doped into the nanowires creates a clear broadening. The Ga-doped ZnO nanowires have a greater field-enhancement factor than the undoped ZnO nanowires [5]. Aqueous solution process with post-growth rapid photothermal processing (RPP) was used to prepare Sn-doped ZnO nanorods to develop aligned Sn-doped ZnO nanostructure. Aqueous solution method was chosen in preparation of metal oxide nanoparticles structure due to its cost and environment friendly. Rapid photothermal processing (RPP) as an alternatives of thermal annealing was combine with aqueous solution due to short cycle time, reduced exposure and flexibility [9]. Based on journals [6], [7] and [8], the optimum doping concentration of aluminium is 2at%, 5at% and 1.5at% respectively. Optimal aluminium doping concentration will gives highly semiconducting properties of Al-doped ZnO thin film for application UV sensor [4]. A research had done on various Al doping concentration and the optimum doping concentration is at 1at% Al. This research will used 1at% Al concentration based on journal [4]. Aligned ZnO nanorods that were prepared using sonication method are a simple way and very low cost method compared to other techniques. It also will growth high quality ZnO nanorod with a small diameter size [10]. 1.2.3 Problem Statement, Scope and Limitation Most people are aware of the effects of UV through the painful condition of sunburn, but the UV spectrum has many other effects whether its benefits or damaging to human health. Too much exposure to UV radiation can affect human health. UV application for optical sensor used 230 nm to 400nm wavelength which is ultraviolet B (UVB) which is harmful to human skin. Since it is harmful to human skin, metal oxide semiconductor films have been considered due to its excellent chemical and physical properties. One of them is zinc oxide material. Zinc oxide is not only good in optoelectronic but also in electrical properties. Zinc oxide is then will be doped with aluminium to enhanced the zinc oxide thin film properties by using sol-gel spin-coating method. It is important to choose the right method for preparing aligned ZnO nanorod. The scope of this research is to investigate the electrical properties (I-V characteristic) and the optical properties of the ZnO nanorod thin film at different i mmersion time. The limitations of this research are on the solution preparation and deposition condition which are different for different groups and on the fix parameter. 1.2.4 Significant of the research The nanomaterials based sensors are raising the advantage of size reduction and enhanced functionality [12]. This research will used a simple method to prepare an aligned ZnO nanorod thin film which is sol-gel immersion method which is this method has not been reported by any research group. Moreover it is very low-cost method. 1.2.5 Objectives To prepare Al-doped ZnO thin film as seed catalyst layer. To prepare aligned ZnO nanorod thin film at different immersion time. To fabricate aligned ZnO nanorod thin film based UV photoconductive sensor. To characterize fabricated UV sensor. 1.2.6 Research Questions To achieve the objective of this research, some research questions would need to focus on which are: What is the I-V curve characteristic of aligned ZnO nanorod thin films before and after exposing to the UV illumination? What is the optical and absorbance characteristic of aligned ZnO nanorod thin films? How to fabricate ZnO thin film? What is the factor affecting the nanostructure ZnO thin film before and after exposing to the UV illumination? CHAPTER 2 2.1 Research Methodology 2.1.1 Al doped ZnO thin films Sol-gel spin-coating method was used to prepare Al doped ZnO thin films. The solution include zinc acetate dihydrate (Zn(CH3COO)2 2H2O) as precursor, aluminium nitrate nonahydrate (Al(NO3)3 9H2O) as a dopant source,monoethanolamine (MEA, C2H7N14) as a stabilizer and 2-methoxyethanol as a solvent were prepared. The concentration of aluminium nitrate was 1.0at% Al doping and the molar ratio of MEA to zinc acetate was fixed at 1.0. At 3 hours before aged at room temperature for 24hours to yield clear and homogeneous solutions the solution was stirred at 80Â °C. The solutions were then used for deposition process by spin-coating technique. Substrates used were microscope on the glass substrates. At room temperature, the spin-coating was performed using 10 drops of solution per deposition with a speed of 3000rpm for 60s. The films were preheated in atmosphere ambient at 150Â °C for 10 minutes to evaporate the solvent each time after deposition process. The films were annealed at 500Â ° C for 1 hour in air ambient using a furnace (Protherm) after repeating the coating procedure 10 times. The crystal structure and orientation of ZnO thin films were investigated by X-ray diffractometer (XRD). The cross-section of the film thickness is observed by using scanning electron microscope (SEM). By using UV-vis-NIR spectrophotometer, the optical properties of ZnO thin films were measured in the wavelength range from 200 nm to 1500nm. The electrical properties were measured by dc probing system [4]. Start Prepare the solution of zinc oxide Precursor : zinc acetate dehydrate Stabilizer : monoethanolamine Dopant source : aluminium nitrate nonahydrate Solvent : 2-methoxyethanol Heat and stir the solution Temperature : 80Â °C Time : 3hr Solution stirring and aging Temperature : room temperature Time : 24hr Thin film deposition using spin-coating tech. Speed : 3000rpm Time : 60s Temperature : room temperature Solution : 10 drops of solution per deposition Thin film drying Temperature : 150Â °C Time : 10min Repeat 10 times Thin film annealing Temperature : 500Â °C Time : 1hr End 2.1.2 Aligned ZnO nanorod structure An aligned ZnO nanorod structure was prepared using the sonicated sol-gel immersion method on a glass substrate coated with a ZnO thin film that had been doped with 1at% Al. The sol-gel coating method was used to prepare the Al-doped ZnO thin film as a seeded catalyst that was prepared on the glass substrate. A solution was prepared of 0.1M zinc nitrate hexahydrate (Zn (NO3)2 .6H2O) and 0.1M hexamethylenetetramine (HMT, H2NCH2CH2OH) in deionized water (DI). At 50Â °C for 30 minutes using an ultrasonic water bath, this solution was sonicated. The solution was then aged and stirred for 3 hours at room temperature. The sonicated and aged solution was poured into a Schott bottle, at the bottom which had been placed the horizontal Al-doped ZnO thin film coated glass substrate. The capped bottle was then immersed in a 95Â °C water bath for 4 hours. After the immersion process, the sample was cleaned with DI water and allowed to dry in ambient air. By using field emission scanning electro n microscope (FESEM) and X-ray diffraction (XRD), the resulting ZnO nanorod structure was characterized for surface morphology and crystallinity. The optical transmittance and absorbance properties of the sample were characterized by UV-vis-NIR spectrophotometer [10]. Start Prepare the solution in deionized water 0.1M zinc nitrate hexahydrate 0.1M hexamethylenetetramine Sonicated solution using an ultrasonic water bath Temperature : 50Â °C Time : 30min Solution stirring and aging Temperature : room temperature Time : 3hr Placed the horizontal Al-doped ZnO thin film coated glass substrate at the bottom Schott bottle. Poured sonicated and aged solution Immersion process Temperature : 95Â °C water bath Time : 4hr Clean with DI water and dry in ambient air Nanorod structure characterization Electrical properties Optical properties End CHAPTER 3 3.1 Conclusion The electrical properties of ZnO thin film improved when ZnO thin film was doped with aluminium. Optimum aluminium doping concentration will gives highly semiconducting properties of Al-doped ZnO thin film for application UV sensor. It is important to find low cost method. The ZnO nanorods have an average diameter of 100nm. An average optical transmittance of 78% was observed. The electrical properties and optical properties of an aligned ZnO nanorod thin film were affected when varying the immersion time. High degree of crystalline, large surface area availability, a visible wavelength transparency and high UV absorption properties, this method show its suitable for UV sensor application.

Buy Essay Online: The Trials of Odysseus :: Odyssey essays

The Trials of Odysseus      Ã‚  Ã‚   Much of modern literature and beliefs can be found in The Odyssey. The epic stands as the basis for the adventure genre. Heroes, mystery, action, and bloodshed can all be found in Homer’s timeless classic. However, The Odyssey also contains one major concept that is a part of everyone’s life. Everyone must at one time or another prove themselves. And that is the foundation of Odysseus’ story. He, a warrior meant to die on the battleground at Troy, survived to set sail back to his home of Ithaca. For this the gods had him prove himself. Throughout The Odyssey it is constantly shown that in order for one to earn his right to live, he must first prove himself in the battle of life where his only weapons are his intellect, his sense of trust, and the strength of pure determination. Throughout The Odyssey, often times Odysseus is forced to call upon his intellect rather than his warrior instinct in order to pass another godly test. At one point in The Odyssey, Odysseus and his comrades are taken prisoner in the titanic cave of Polyphemus the Cyclops. A colossal boulder keeps Odysseus and his men from escaping. Rather than slaying the formidable adversary, Odysseus devises a plan more of a scholar than a relentless warrior. This becomes known as Odysseus recounts his story to the Phaecians, telling them that, â€Å" ‘I [Odysseus] formed the plan within my daring heart of closing on him [Polyphemus the Cyclops], drawing my sharp sword from my thigh, and stabbing him†¦ Yet second thoughts restrained me†¦ for we could never with our hands have pushed from the lofty door the enormous stone which he had set against it’ † (85). Odysseus’ strong intelligence outweighs those of his warrior comrades, who would have been quick to slay t he giant. Had Odysseus sent the Cyclops to Hades, he and his men would surely have followed. However, this was not to be, as Odysseus does not let the warrior in him direct his actions as a leader. Throughout his adventures, Odysseus must also rely on his intellect to rid of those who restrain him from reaching Ithaca. On the island of Ogygia, Odysseus is kept a reluctant guest at the halls of the goddess-nymph Calypso. Odysseus, who sees that he cannot escape by means of battle, turns to flattery. Buy Essay Online: The Trials of Odysseus :: Odyssey essays The Trials of Odysseus      Ã‚  Ã‚   Much of modern literature and beliefs can be found in The Odyssey. The epic stands as the basis for the adventure genre. Heroes, mystery, action, and bloodshed can all be found in Homer’s timeless classic. However, The Odyssey also contains one major concept that is a part of everyone’s life. Everyone must at one time or another prove themselves. And that is the foundation of Odysseus’ story. He, a warrior meant to die on the battleground at Troy, survived to set sail back to his home of Ithaca. For this the gods had him prove himself. Throughout The Odyssey it is constantly shown that in order for one to earn his right to live, he must first prove himself in the battle of life where his only weapons are his intellect, his sense of trust, and the strength of pure determination. Throughout The Odyssey, often times Odysseus is forced to call upon his intellect rather than his warrior instinct in order to pass another godly test. At one point in The Odyssey, Odysseus and his comrades are taken prisoner in the titanic cave of Polyphemus the Cyclops. A colossal boulder keeps Odysseus and his men from escaping. Rather than slaying the formidable adversary, Odysseus devises a plan more of a scholar than a relentless warrior. This becomes known as Odysseus recounts his story to the Phaecians, telling them that, â€Å" ‘I [Odysseus] formed the plan within my daring heart of closing on him [Polyphemus the Cyclops], drawing my sharp sword from my thigh, and stabbing him†¦ Yet second thoughts restrained me†¦ for we could never with our hands have pushed from the lofty door the enormous stone which he had set against it’ † (85). Odysseus’ strong intelligence outweighs those of his warrior comrades, who would have been quick to slay t he giant. Had Odysseus sent the Cyclops to Hades, he and his men would surely have followed. However, this was not to be, as Odysseus does not let the warrior in him direct his actions as a leader. Throughout his adventures, Odysseus must also rely on his intellect to rid of those who restrain him from reaching Ithaca. On the island of Ogygia, Odysseus is kept a reluctant guest at the halls of the goddess-nymph Calypso. Odysseus, who sees that he cannot escape by means of battle, turns to flattery.

Child Development Essay -- Child Rearing, Natural Growth

Lareau (2003) reports that social class plays a very important role in a child’s upbringing because it helps determine the way a child will be raised. In Lareau’s (2003) study she came to the conclusion that there were two different patterns of child rearing: concerted cultivation and natural growth. Concerted cultivation is the child rearing method that middle class parents use focusing on not only caring for their child, but developing a personality by enrolling their children in many structured activities and developing language skills (Lareau, 2003). Natural growth is the child-rearing method that working class and poor parents use to raise their children because there is not a lot of time and money for structured activities and long verbal discussions with the children (Lareau, 2003). Families who practice natural growth child rearing practices need to focus on providing the simpler needs of the child like providing shelter, clothing, food, and water therefore unab le to have the structured activities and worry about establishing communication skills. This is important to consider because the way children are raised because this has a social impact. The children that are being raised today will eventually grow up to be a part of their own society; there are social impacts on the current society because of the methods of child-rearing and the consequences that these child-rearing practices are having on children with the way they interact in society, There are benefits and disadvantages to both childrearing methods reported by Lareau (2010) however there are definitive differences in the child’s outcome due to the child’s social class and thus the method the child was raised with. In concerted cultivation children spend a ... ...nd sometimes talk to my extended family I seldom see them or would by any means categorize our relationships as strong kinship ties (Lareau, 2003). This I feel has been an unfortunate result of concerted cultivation because I see how some of my other cousins behave towards each other as they are so close talking everyday and meet several times a week for lunch or dinner. I feel this is sad because while I would love to have stronger ties with my extended family I realize it is not a part of the way I was brought up because of my middleclass child-rearing. The concept of my social connections often being mostly in homogenous age groups as a child is very accurate (Lareau, 2003). Because of the activities I participated in and the area in which I lived and went to school I predominately have friendships through activities with children much like I was at the time.

Wealth and Power in the United States

Wealth and Power in the United States Hugo Lindgren Chief Editor New York Time Magazine [email  protected] com This letter is to inform the public of how social class division is related to the concentration of wealth in the United States and support the need to redistribute wealth in America. Today our communities are divided by social class poor citizens live in poor areas of the community while citizens who make more money live in better areas of the community. Social class determines a great deal about citizens circumstances.Circumstances like education, health care, shelter, food and clothing. Generally the wealthiest or privileged citizens only associate themselves with other citizens who are in the same social class. The same concept comes into play with the middle, working and poor class. Today the top 1 percent is increasing in wealth while the middle and working class are decreasing. This inequality of wealth in America is becoming more and more of a problem for the middl e and working class. Wealth is the positive value of what a citizen owns. For example if a citizen owns a house the bank ay own half of the house until the loan is paid off but whatever the value is of the other half is how much wealth the citizen has from the house. Redistribution of wealth is raising taxes on citizens that have already made it to provide relief for the ones who haven’t. The Class theories best describes the distribution of wealth because it breaks down how the wealth is broken up amongst citizens of the United States. The rich have done much better than the middle or working class. The Top 1 percent had 22. 9 percent of national income in 2006 a number that hasn’t been matched since 1929 said CBS News Jeff Green inAmerica’s Class Warfare. While a citizen from the top 1 percent has already achieved success, wealth and power. The middle and working class has not and with a constant increase in cash flow for the wealthy and a constant decrease in cash flow for the less fortunate come a concern for those in public office. President Obama proposes lowering taxes for the less fortunate and a small increase for the citizens who have achieved success with wealth and power. However, other Officials have opposed President Obama’s approach to redistributing wealth.Mitt Romney stated â€Å"I think it’s about envy, I think it’s about class warfare When you have a president encouraging the idea of dividing America based on 99 percent vs. 1 percent those people who have been most successful will be in the 1 percent you’ve opened up a whole new wave of approach to this country which is entirely inconsistent with concept of one nation under god†. President Obama insists that by helping others will spread the wealth by having the rich pay a little more taxes so the middle class receive a tax credit because the middle class needs it most (Obama, 08).President Obama stated â€Å"I believe in redistributio n at least at a certain level to make sure that everybody’s got a shot† Everyone has the chance to maintain a roof over their heads and send their kids to college. Everybody that works hard can make it. Social class segregation is visible in all 52 states of America. Upper, middle and working classes have their own geographical residential areas within communities. Ethnic segregation begins within the social class groups because the majority of working and poor classes of Americans are minorities. The high class and elites are mostly white Americans.Therefore, geographically America is in fact more divided by this social class system. In 2006 10 percent of whites have been recorded as being below the poverty line while 24 percent of blacks remain below the poverty line (Harrison & Dye, 2010). In 2010 the top 1 percent had a 35. 4 percentage over the bottom 80 percent with 11. 1 percent of total net worth (Domhoff, 2005). However, it is this system that provides Amer ica with the unique opportunity that people from all over the world are drawn to. The fact that in America if you work hard and play by the rules you can reap he rewards by becoming successful and climbing up the social class ladder. Power in America is achieving higher education, owning property, financial freedom, maintaining a good credit. Power is measured by materialistic items such as expensive cars, jewelry, clothing, electronics, Vacations. It was William Thompson who said â€Å"Our position in the social hierarchy affects our health, happiness, and even how long we will live† (Thompson, 2005) Reference Harrison, B, C &Dye, T. R. (2011) Power and society: An introduction to the social sciences (12th Edition) Boston, Ma G.William Domhoff, September, 2005 retrieved October 15 2012 from http://www2. ucsc. Edu /who rules america/power/wealth. html Jeff Green (2006) America’s Class Warfare retrieved October 15 2012 form http:// www. youtube. Com /watch? v=bGS2G7 9IxTc&feature=fvst Mitt Romney Quote retrieved October 15, 2012 from http://www. youtube. com/watch? v=5wtLKcAU4wQ Barrack Obama Retrieved October 15, 2012 from http://www. youtube. com/watch? v=BRPbCSSXyp0 Obama Loyola University, C-SPAN October 19, 1998. http://www. youtube. com/watch? v=z0PUUpa5X4E William Thompson, Joseph Hickey, Society in Focus, 2005