Annotated Bibliography

Moore, J. S., Jones, K. S., Kennel, H., & Corcoran, S. (2008). 3-D analysis of semiconductor dopant distributions in a patterned structure using LEAP. Ultramicroscopy, 108(6), 536-539. Twitchett-

This analysis provides an interesting view of the three-dimensional structure of doped semiconductors on an atomic level. This then allows a useful analysis of the atomic structure of silicon as it relates to function. Thus, we can see how - not only silicon, but also other potential semiconductors - works as it relates to how it is made up. This can then allow us to see what properties of a material, on the atomic level, are most necessary or helpful in creating a semiconductor.

Harrison, A. C., Yates, T. J., Newcomb, S. B., Dunin-Borkowski, R. E., & Midgley, P. A. (2007). High-resolution three-dimensional mapping of semiconductor dopant potentials. Nano Letters, 7(7), 2020-2023.

This piece from a highly acclaimed journal, in many ways, logically continues the previous. It provides a mapping of the dopant potentials of various semiconductors, with a focus on silicon as a "typical" semiconductor. Thus, we can see how - not only silicon, but also other potential semiconductors - works as it relates to how it is made up.This lens allows us to view other potential semiconductors critically.

Byrnes, S. (2013, December 1). Maximum possible efficiency of a solar thermal energy system. Retrieved November 23, 2015, from http://sjbyrnes.com/ultimate_PV.html Cummings, T. (2013, June 8).

This article provides fascinating insight into the modes and methods of measuring efficiency. It poses the question - "what is efficiency?". From there, its data and analysis serves to expand upon this question, answering it and many others. The exploration into the efficiency of solar panels. Solar panels that are made with silicon, as well as solar panels that have been made with other materials.

Lens Experiment. Retrieved November 24, 2015, from http://laser.physics.sunysb.edu/~thomas/report1/lens_report.html Hall, N. (2015, May 5).

Second Law of Thermodynamics. Retrieved November 25, 2015, from https://www.grc.nasa.gov/www/k-12/airplane/thermo2.html Lewis, N. S. (2007). Toward cost-effective solar energy use. science,315(5813), 798-801.

The Science of the Silicon Solar Cell. (n.d.). Retrieved November 22, 2015, from http://science.sbcc.edu/~physics/flash/siliconsolarcell/index.html.

This analysis provides an interesting view of the three-dimensional structure of doped semiconductors on an atomic level. This then allows a useful analysis of the atomic structure of silicon as it relates to function. Thus, we can see how - not only silicon, but also other potential semiconductors - works as it relates to how it is made up. This can then allow us to see what properties of a material, on the atomic level, are most necessary or helpful in creating a semiconductor.

Redarc Electronics. (n.d.). Retrieved November 22, 2015, from http://www.redarc.com.au/solar/about/solarpanels/.

This website provides an insight into the actuality of solar panels. It is a look into how solar panels are currently sold in the real world. Having real world websites and sources is very, very helpful because it provides a nice complement to being mired in a the philosophical conceptions of "what if".

What's the difference between climate change and global warming? (Climate Change FAQ #2)

Climate change is defined as a change in global or regional climate patterns, in particular a change apparent from the mid to late 20th century onwards and attributed largely to the increased levels of atmospheric carbon dioxide produced by the use of fossil fuels.

Global warming, in contrast, a gradual increase in the overall temperature of the earth's atmosphere generally attributed to the greenhouse effect caused by increased levels of carbon dioxide, chlorofluorocarbons, and other pollutants.

(Source: Merriam-Webster)

(Source: XKCD)

In general, “global warming” refers to the long-term warming of the planet - a well-documented rise since the early 20th century, particularly since the late 1970s. Worldwide, since 1880 the average surface temperature has gone up by about 0.8 °C (1.4 °F), relative to the mid-20th-century baseline (of 1951-1980).

“Climate change” includes global warming as well as many other changes Earth is undergoing.such as rising sea levels, shrinking mountain glaciers, accelerating ice melt in Greenland, Antarctica and the Arctic, and shifts in flower/plant blooming times. These are all consequences of the warming, which is - in turn - caused mainly by people burning fossil fuels and putting out heat-trapping gases into the air.

The terms “global warming” and “climate change” are sometimes used interchangeably, but they technically refer to slightly different things.

(Source: NASA)

No Internship Meeting

I could not go to my internship this week because the lab was working with a dangerous gas I had neither the training nor the clearance to handle. 

What is the difference between weather and climate? (Climate Change FAQs #1)

Weather is the state of the atmosphere with respect to heat or cold, wetness or dryness, calm or storm, clearness or cloudiness. In turn, climate is defined as the average course or condition of the weather at a place usually over a period of years as exhibited by temperature, wind velocity, and precipitation. 

(Source: Merriam-Webster)

In general, weather describes short-term oscillations and states of being. When you ask what you should wear tomorrow, or weather the roads will be good on Friday, you are asking questions about weather. In contrast, climate is a long-term trend or condition. When you wonder if a house you are building needs a strong roof to withstand snow or whether an area has good conditions for farming you are thinking about climate.

(Source: XKCD) 

Non-Solar Sustainable Energy: Wind

Wind energy research began in the 1970s, with NASA’s analytical model to predict the power generated by wind turbines. Currently, Sandia National Laboratories and National Renewable Energy Laboratory have programs dedicated to wind research. Sandia’s laboratory focuses on the advancement of materials, while the NREL wind projects are centered around making wind energy more cost effective. The president of Sky WindPower Corporation predicts wind turbines will eventually generate electricity at $0.01/kWh, a fraction of the cost of coal. Today, 3.1% of electricity globally is harnessed from the wind.

Wind power shows that solar energy is but one of multiple valid options in the realm of sustainable energy.

(Source: XKCD)

No Internship Meeting

I was unable to attend my internship this week because I was sick. 

Why Do We Need Sustainable Energy?: An Introduction to Climate Change

The Earth's climate has changed throughout history. Most of these changes are caused by vagaries in its orbit that affect the amount of solar energy Earth gets. However, the current warming trend is singular because it is caused by human actions and is extremely rapid. Increased levels of greenhouse gases warm the Earth; ice cores drawn from Greenland, Antarctica, and tropical mountain glaciers show that the Earth’s climate responds to changes in greenhouse gas levels. 

On Earth, human activities are changing the natural greenhouse. Over the last century the burning of fossil fuels like coal and oil has increased the concentration of atmospheric carbon dioxide. This happens because the coal or oil burning process combines carbon with oxygen in the atmosphere and produces as a byproduct carbon dioxide. 

(Source: XKCD)

Global climate change has already observably impacted the environment, such as a loss of sea ice, accelerated sea level rise, and longer, more intense heat waves. What's more, plant and animal ranges have shifted and trees are flowering sooner. As the Intergovernmental Panel on Climate Change wrote, "taken as a whole, the range of published evidence indicates that the net damage costs of climate change are likely to be significant and to increase over time."

What is Sustainable Energy?

Sustainable energy is defined as energy obtained from non-exhaustible resources. By this definition, sustainable energy does not run out or compromise the ability of future generations to meet their needs.

The underpinning of sustainable energy is sustainable development, or development that meets the needs of the present without compromising the ability of future generations to meet their own needs. This takes into account ecology, economics, politics and culture. Technologies that promote sustainable energy include hydroelectricity, solar energy, wind energy, wave power, geothermal energy, bioenergy, tidal power, and technologies designed to improve energy efficiency.

Costs for sustainable energy sources have fallen dramatically in recent years. Further, government policies have increasingly supported this green solutions. The result of both of these trends is the markets expanding.

(Source: XKCD)

No Internship Meeting

I did not attend my internship this week because my mentor was traveling.

The I-V Curve

A current-voltage (I-V) curve is meant to display a photovoltaic device's possible combinations of current and voltage output. The x-axis displays voltage, measured in volts, while the y-axis shows current, expressed in amps.

A solar panel, which is a type of photovoltaic device, produces its maximum current when there is no resistance in the circuit. This describes a situation in which the panel short circuits. This maximum current is known as the short circuit current and is abbreviated "Isc". Under this circumstance, the voltage in the circuit is zero.

Conversely, the maximum voltage occurs when there is a break in the circuit. This is called the open circuit voltage, "Voc". Here, the resistance is infinitely high and there is no current. This describes an incomplete circuit. These two extremes and the range between them, are shown on the I-V curve.

The power available from a photovoltaic device at any point along the curve is the product of the current and the voltage at that point. Units of power are called watts. At the short circuit current point, the power output is zero, since the voltage is zero. At the open circuit voltage point, the power output is also zero, because the current is zero.

The maximum power output, as displayed on the I-V curve is thus somewhere between these points. The exact location varies from solar panel to solar panel because each device's I-V curve is a little bit different.

The I-V curve is dependent on the device being under direct sunlight and having a constant device temperature. Standard sunlight conditions on a clear day are 1,000 watts of solar energy per square meter. This is referred to as 'one sun'. Less than one sun will reduce the current output of the PV device by a directly proportional amount.

Ohm’s Law

Ohm's law states that the current through a conductor between two points is directly proportional to the voltage across the two points:

I is the current through the conductor in units of amperes, V is the voltage measured across the conductor in units of volts, and R is the resistance of the conductor in units of ohms. Further, Ohm's law holds that the R in this relation is constant, independent of the current.

The law was named after the German physicist Georg Ohm. Georg Ohm was a German physicist and school teacher. He researched the then-novel electrochemical cell using equipment of his own creation. In doing so, Ohm found that a direct relationship between the voltage applied across a conductor and the electric current. He published a treatise in 1827 describing this relationship through the example of the flow of voltage and current through simple electrical circuits containing various lengths of wire. The above equation is the modern form of Ohm's original law.

Ohm’s law serves as an algebraic method for calculating the current if we know the electric potential difference and the resistance. What’s more, this equation indicates the two variables that would affect the amount of current in a circuit. The current in a circuit is directly proportional to the electric potential difference and inversely proportional to the resistance.

Charge flows at the greatest rates when the battery voltage is increased and the resistance is decreased. A twofold increase in the battery voltage would lead to a twofold increase in the current (if all other factors are kept equal). And an increase in the resistance of the load by a factor of two would cause the current to decrease by a factor of two to one-half its original value.

Voltage, Current, and Resistance

Voltage, current, and resistance are the three basic building blocks required to manipulate and utilize electricity.

Voltage, also known as electric potential difference, electric pressure, or electric tension, is denoted by ∆V. It is the difference in electric potential energy between two points per unit electric charge. Usually, voltage is caused by a combination of static electric fields, electric current through a magnetic field, and time-varying magnetic fields. We use voltmeters to measure the voltage between two points in a system. Often, we use a common reference potential – such as the ground of the system – as one of the points. A voltage may represent or lost, used, or stored energy.

An electric current is a flow of electric charge carried by electrons moving along a wire. The unit for measuring an electric current is the “ampere,” which is the flow of electric charge across a surface at the rate of one coulomb per second. Electric current is measured using an ammeter. Electric currents allow incandescent light bulbs, motors, inductors and generators to exist and function as they do.

The resistance of an object is the measure of how difficult it is to pass an electric current through that object. The unit by which electrical resistance is measured is “ohm” (Ω). An object of uniform cross section has a resistance proportional to its resistivity and length and inversely proportional to its cross-sectional area. All materials show some level of resistance.

What is a Semiconductor?

Semiconductors are elements whose conductivity is between that of an insulator - which has almost no conductivity - and a conductor - which has almost full conductivity. Most semiconductors are crystals, with silicon being the most common.


Some background: The electrons in an atom are organized in layers called shells, with the outermost layer being the valence shell. When atoms form bonds, the electrons in the valence shells are the ones that are shared or exchanged. Most conductors have just one electron in the valence shell. Semiconductors, on the other hand, typically have four electrons in their valence shell.

If all of an atom’s the neighbors are the same element, then all of its valence electrons will bond with valence electrons from other atoms. As a result, the atoms will arrange themselves into crystals. Semiconductors are made out of these distinct crystals.

Pure silicon crystals are useful for their conductivity. However, if trace amounts of other elements are introduced to a crystal, the atoms take on new and interesting qualities with respect to their conductivity. This process, called ‘doping’, introduces impurities to an element in order to modulate its conductivity. Semiconductors that are doped lightly or moderately are called ‘extrinsic semiconductors’. A semiconductor that is doped so much that it acts almost like a conductor is referred to as a degenerate semiconductor.

 The element introduced by doping is called a dopant, and the type of dopant affects the type of semiconductor and its properties. In fact, crystals can transform into one of two types of conductors dependent on the dopant used.

 When the dopant has five electrons in its valence layer, the result is an n-type semiconductor. For example, phosphorus atoms join the crystal structure of the silicon, each bonding with four adjacent silicon atoms. Because the phosphorus atom has five electrons in its valence shell, but only four of them are bonded to adjacent atoms, the fifth valence electron is left hanging without a bond. N-type semiconductors, then, are characterized by having extra electrons.

When the dopant has only three electrons in the valence shell, the result is a p-type semiconductor. The atom is able to bonds with four other atoms, but since it has only three electrons to offer, a hole is created. This hole behaves like a positive charge, which is what ‘p’ stands for.

Much like a positive charge, holes attract electrons. But when an electron moves into a hole, the electron leaves a new hole at its previous location. Thus, in a p-type semiconductor, holes are constantly moving around within the crystal as electrons constantly try to fill them up.
 

References

Moore, J. S., Jones, K. S., Kennel, H., & Corcoran, S. (2008). 3-D analysis of semiconductor dopant distributions in a patterned structure using LEAP. Ultramicroscopy, 108(6), 536-539.

Twitchett-Harrison, A. C., Yates, T. J., Newcomb, S. B., Dunin-Borkowski, R. E., & Midgley, P. A. (2007). High-resolution three-dimensional mapping of semiconductor dopant potentials. Nano Letters, 7(7), 2020-2023.