Explain and assess how a common policy issue is addressed in different countries.
• frame your essay around a central research puzzle/question (what is the policy problem?) • justify the comparative method used (most similar or most different?) • link your analysis to wider theoretical and/or empirical debates where relevant • explain why different countries respond to shared policy issues in different ways • evaluate how these different policy responses lead to different policy outcomes
Gas Sensing Properties of Te Thin Films: Thickness and UV Distributed: eighth August, 2018 Last Edited: eighth August, 2018 Disclaimer: This paper has been put together by an understudy. This isn't a case of the work composed by our expert paper authors. You can see tests of our expert work here. Any suppositions, discoveries, ends or suggestions communicated in this material are those of the writers and don't really mirror the perspectives of UK Essays. Thickness and UV light impacts on the gas detecting properties of Te thin movies Conceptual In this exploration, tellurium thin movies were researched for use as hydrogen sulfide gas sensors. To this end, a tellurium thin film has been stored on Al2o3 substrates by warm vanishing, and the impact of thickness on the affectability of the tellurium thin film for estimating H2S gas is contemplated. X-beam diffraction (XRD) examination, checking electron microscope(SEM) and Raman Spectrometer were used for describing the readied tests. XRD designs demonstrate that as the thickness expands, the crystallization makes strides. Watching the pictures acquired by SEM, it is seen that the grain measure increments as the thickness increments, and thusly, less imperfections will be found in the surface of the film. Concentrate the impact of thickness on H2S gas estimation, it ended up clear that as the thickness expands, the affectability diminishes and the reaction and recuperation time increments. Concentrate the warm impact of the thin film while estimating H2S gas, it winds up clear that as the location temperature of the thin film expands, affectability and the reaction and recuperation times lessen. To enhance the reaction and recuperation time of the tellurium thin film for estimating H2S gas, the impact of UV radiation while estimating H2S gas was likewise explored. The outcomes demonstrate that the reaction and recuperation times unequivocally diminish utilizing UV radiation. Presentation Tellurium is a P compose semiconductor with tight band hole and a hole vitality of 0.35eV which makes it perfect for use in thin film transistors , gas sensors [2-4], optical data stockpiling  and shields in aloof radiative cooling . As of late, it has been demonstrated that the tellurium thin film is delicate to some lethal gases like H2S . Hydrogen sulfide is a harmful and destructive gas which is shaped in coal mines, oil and gas enterprises, concoction items plants, and the sewers. Introduction to little measures of this gas (less 50 ppm) causes migraine, poor memory, loss of craving and fractiousness, while presentation to vast sums (a large portion of 500 ppm) will cause demise following 30-a hour . Up until this point, different semiconductor metal oxides have been delivered for distinguishing H2S gas, for example, SnO2, WO3, and CeO2 [9-11]. The fundamental issue of these sensors is that they require high temperature for estimating H2S gas, and this high temperature will abbreviate the life of the sensor. Estimating gas through semiconductor metal oxide relies on parameters like thickness of the thin film, statement temperature, and the substrate material. Up until now, few reports have been issued about the affectability of the tellurium thin film to some lessening and oxidizing gases, for example, NO2, CO, NH3, and H2S [4,7,13,14]. In this examination, the impact of the thickness of the tellurium thin film on distinguishing H2S gas and furthermore the impact of the film temperature and UV radiation while estimating H2S gas have been contemplated. Examination points of interest Tellurium thin movies with thicknesses of 100, 200, and 300 nm estimated by Quartz computerized thickness measure, were kept on Al2O3 substrate by warm vanishing of unadulterated tellurium in a tungsten pot. Substrates were cleaned for 30 minutes by liquor and CH3)2CO in ultrasonic shower. The underlying weight of the vacuum chamber and the temperature of substrate while keeping were separately 3×10-5 mbar and 373K. The development rate of the film and the testimony territory were individually 5nm/s and 100mm2. Gold cathodes were saved on the surface of film through warm dissipation and copper wires were connected to them by silver glue. The microstructure of the movies was described through X-beam diffraction (XRD). The morphology of the movies surface was controlled by filtering electron magnifying lens (SEM). Sensor reaction to different grouping of H2S gas was contemplated in a holder made of hardened steel with a volume of 250cm3 .The electrical obstruction of the sensors was estimated by a multimeter as a component of time. Gas confine identification was performed for the movies with various thicknesses and at various condition temperatures. The sensors were additionally presented to UV radiation while distinguishing H2S gas. The component of gas identification was explored by Raman spectroscopy method. The spectra were recorded when presentation to the gas. Raman spectra of the movies were recorded in back dissipating geometry with a phantom goals of 3 cm-1. The 785 nm line of Ar+ laser was utilized for excitation. Results and Discussion XRD examples of tellurium films with various thicknesses are appeared in fig. 1. In this figure, the pinnacles meant with star are identified with Al2O3 substrate. At 100 nm, Te thickness pinnacle of low power is seen at 27.77° which is identified with Te (101) with hexagonal structure. At 200 nm, notwithstanding Te (101), another pinnacle comparing to Te (100) shows up at 23.15°. At last, other than Te (100) and Te (101), another pinnacle is seen at 40.78°which is identified with Te (110) with hexagonal structure. From the XRD results, it tends to be derived that, thickness builds the outcomes in an expansion of film crystallinity because of the expansion of the quantity of planes that produce diffraction. Fig. 2 demonstrates the SEM pictures of arranged Te films at various thicknesses. [S1]At 100 nm, the grains are isolated from each other by an extensive separation, in this manner shaping irregular and harsh surface. Expanding film thickness prompts an expansion of surface homogeneity and coherence, grain measure increment also. Fig. 3 delineates the opposition variety of the tellurium thin movies with various thicknesses at room temperature before presentation to H2S gas. It very well may be seen that the film obstruction diminish with thickness increment because of decrease of anomaly in grain course of action and inhomogeneity on the film surface, which prompts a superior charge bearer versatility. The affectability of the movies to H2S is given by: S= Where Ra and Rg are the electrical obstruction of the film noticeable all around and the H2S separately. Fig. 4 demonstrates the impact of Te film thickness on affectability to 8ppm of H2S at room temperature. Note that the film affectability diminishes with an expansion in thickness. To clarify this conduct, it merits specifying that the proposed component for H2S gas estimation is as per the following: the oxygen noticeable all around is adsorbed by the film surface, particularly in the grain limits and film porosities. After adsorption, oxygen responds with Te film surface and in view of the film temperature, it very well may be ionized into O2-, O2-, O-(in the temperatures under 150CËš the ionization frame is O2-). These types of oxygen ionization increment the film gap thickness which implies a decrease of Ra in P compose semiconductor, for example, Te. As H2S gas is included, it responds with ionized oxygen and the outcome will be the arrival of electrons inside the film and decrease of the opening numbers and increment of Rg obstruction. The responses are demonstrated as follows: O2(gas) O2(ads)(1) O2(ads)+ e O2-(ads)(2) H2S(gas)+O2-(advertisements) H2(gas)+SO2(gas)+ e(3) At 100 nm Te thickness, the nearness of a high thickness of grain limits and imperfections results in a high H2S gas adsorption which causes perceptible varieties in film electrical opposition, showing an expansion of affectability. At higher thickness, where the grain limit and deformities densities diminish, the adjustments in obstruction are elusive including a reduction in the affectability as appeared in fig. 4. The other imperative normal for sensor is its selectivity. The affectability on introduction to 10 ppm of CO, NH3 and NO was observed to be 3 %,40 % and - 67 % (negative sign shows decrease in opposition), respectively. Hence we see that the Te films have significantly bigger affectability towards H2S gas in contrast with different gases. Fig. 5 demonstrates the reaction energy of Te films at various thickness (100 nm and 200 nm) after presentation to 8ppm H2S. Considering the reaction and recuperation times, the occasions for achieving 90% of relentless state estimations of Ra and Rg individually can be characterized. It tends to be plainly found in fig. 5 that thickness increment prompts an expansion of reaction and recuperation times. The previous and the last are because of high adsorption rate of H2S and O2 gases, individually, at 100 nm by the considerable quantities of grain limits and deformities . Fig. 6 demonstrates Raman spectra of 100 nm Te test when presentation to 8 ppm H2S gas at room temperature. In both spectra, tops at 123, 143 and 267 cm-1 are identified with tellurium. Two different pinnacles saw in test before instigating H2S gas at 680 and 811 cm-1 are allocated to TeO2 . Notice that the force of oxide stage is significantly less than that of Te stage demonstrating that a low portion of Te film is oxidized, which is because of Te molecules at first glance . After introduction to H2S gas, in light of the proposed response system the TeO2 crests have nearly vanished. What's more, no pinnacle comparing to H2S or mixes of sulfur or hydrogen is recognized in film after introduction to H2S gas. Fig. 7 demonstrates the sensors affectability as an element of H2S gas focus for 100, 200 and 300 nm tests at room temperature. The film to 100 nm Te thickness exhibits a straight reaction from the 8 to 34 ppm run and the film affectability appears to immerse at higher fixation. Not surprisingly, from fig. 7 it tends to be seen that the affectability diminishes as the film thickness is expanded. Figure 8 demonstrates the outcomes identified with reaction and re>GET ANSWER