Glossary

Atom : This is the smallest, most basic part of matter. An atom is full of protons and neutrons in the nucleus and electrons. The protons, themselves, are all the same. The electrons, themselves, are all the same. The neutrons, themselves, are all the same. Most of the atom is empty space.

Atom: The blue circles represent electrons. Electrons are mostly (described by quantum mechanics) found in certain regions called orbitals of specific energies. The red circle is the nucleus, which is composed of protons and neutrons. The nucleus in in actual atom is much smaller than the nucleus shown in this picture. 

Band: This is a grouping of energy levels (see Quantum Mechanics) that are so close together that there is enough energy naturally in the environment to allow electrons to jump between them without any difficulty.


Band Gap: The difference in energies between the valence and conduction bands (see valence and conduction band) . It is sort of like the strip between two subway lines. Riders can't exist in that strip. However, riders can go from one side of the strip to the other and can more easily travel on a given side of the strip.

The band gap of semiconductors and insulators is shown in this figure as energy difference between the conduction and valence bands. Metals do not have a band gap. Electrons can only exist in the colored boxes. They are mostly found in the orange boxes (the lower-energy valence band).

CdTe : CdTe (pronounced cadmium telluride) is a material used to absorb sunlight in some solar cells that you can buy. This material is very inexpensive and only a thin film of it is needed to absorb most of the light.

Charge : Charge describes how particles respond to an electric field (see electric field). It is a basic and conserved property of matter (you always have the same amount of it). Charge can either be negative, positive or neutral. A negative charge is attracted to a positive charge. An electric field points away from a positive charge and towards a negative charge. A negatively-charged particle is forced in a direction opposite the direction of an electric field. A positively-charged particle is forced in the direction of an electric field. A neutral particle is not affected by an electric field.

Chemical : A chemical is an atom or a grouping of atoms chemically bonded together (electrons are exchanged or shared between atoms). Water is a chemical. Air is composed of chemicals. The term "chemical" does not denote anything special. Some chemicals are dangerous, while other ones are safe to eat. Food is made of chemicals. Plants are made of chemicals. The world is made of chemicals.

Chemical bond : Electrons are shared (covalent) or exchanged (ionic) between atoms.

Compound : A grouping of atoms and/or ions chemically bonded together that can't be physically separated (such as by cutting). It looks roughly the same at all points in the material when you look at it with your eye (you can impress your teachers and say that it looks homogeneous).

Conduction Band : The band of energy levels that have energies greater than those of the valence band, but as close in energy to the valence band as possible. See Band gap for an illustration.

Cu(In,Ga)Se (CIGS) : CIGS is a material used to absorb sunlight in some solar cells. Cells based on this material are just now starting to be bought and sold. The Rockett research group researches this material system.

Current : Current describes the flow of electric charge. Imagine that you have a box full of charge. The current out of the box describes the amount of charge that would leave the box in a given amount of time. The units used to measure current are amperes (A).

Cu2ZnSn(S,Se)4 (CZTS) : CZTS is another material used to absorb sunlight in some solar cells. People do not understand it as well as silicon, CIGS, or CdTe. However, the earth has more of the elements that make up this material and, if we understood it better, we might be able to decrease the cost of solar cells.

Deposit : To put or lay down.

Electric field : An electric field is like a net surrounding a charged particle that tells you what direction a positive charge at that location, if it existed, would be forced and the amount of force for a unit charge due to the electric field that unit charge would experience. The electric field is related to a change in voltage (see Voltage) over a distance.

Electron : A negatively-charged particle that is much smaller than an atom. They can be found within an atom. Electrons are involved in all chemical bonds.

Electronics : Anything that uses electrons and electric fields to work, often alongside magnets and magnetic fields.

Element : An element is a type of atom with a specific number of protons. You can tell the difference between different elements by the number of protons the element has. Each element has the number of protons stated in the Periodic Table of the Elements shown below.

The Periodic Table of the Elements: Image courtesy of www.ptable.com

Energy : Energy is the ability to work. Something can either be already moving or have a significant potential (is ready) to move or change.

Film : A film is a thin layer of material. When you see oil spilled on top of water, you see a film. This is what causes you to see different colors. You also have films on glasses  or camera lenses to prevent reflections. We use thin films of material to absorb sunlight.

Force : A push or pull.

Glow Discharge: A glow discharge is a silent electrical discharge (silent lightning) through a low-pressure gas. It has areas of positive charge and negative charge, although taken as a whole, the discharge is neutral.

Isotope : An isotope is a different form of the same element. Although two isotopes of the same element have the same number of protons, they have different numbers of neutrons. Some isotopes are found more often than others.

Ion : A negatively or positively charged atom or molecule. One ionizes an atom or molecule when one adds or removes an electron from the atom or molecule.

Junction : A junction is where two things meet.

Matter : Anything that takes up space and has mass.

Mass : The amount of stuff that's in something.

Molecule : A group of atoms chemically bonded together with shared electrons (in what are called covalent bonds--impress your teacher!).

Momentum : Momentum is something that is conserved (you end up with the same amount that you started with). When you push something, it keeps on moving. When something lies still, it stays lying still.

Nucleus : Something found at the center of an atom that is full of protons and neutrons. It is extremely small and dense compared to the rest of the atom.

Neutron : A neutron is a particle without a charge that can be found in the nucleus of an atom. Differences in the number of neutrons in an element are called isotopes.

Plasma : A state of matter in which a large amount of atoms are ionized with unbound electrons, although most of the material has a neutral charge.

Photovoltaic : A device that is used to convert sunlight into electrical energy by creating charges that can move in a material.

P-N Junction : A p-n junction is when two semiconducting materials (see semiconductor) that have different energies meet. A solar cell is based on a P-N junction.

Proton : A proton is a particle with a positive charge that can be found in the nucleus of an atom. The number of protons present in an atom defines the element.

Semiconductor : A material that has a filled valence band, but an empty conduction band (see image in band gap). The difference between the valence and conduction bands, the band gap, is small enough that many electrons are excited by energy in the environment into the conduction band. You can have electrons go from the valence to the conduction band and back again.

Silicon : Silicon is an element with 14 protons and 14 electrons (when neutral). It is a semiconductor in its pure form (not mixed with other stuff). Silicon is used in many solar cells and is used in the chips inside your computer.

Solar : Having to do with the sun.

Solar Cell : A device that is used to convert energy from the sun into electrical energy (current and/or voltage).

Sputter : You can use sputtering to lay down layers of material. Ions (charged atoms and molecules) in a glow discharge (like lightning) are sent by an electric field to a target, which they bump into. These ions knock off atoms in the target, which then can deposit on another material called a substrate.  It is kind of like when you throw a tennis ball at a garage (do not try this at home), flecks of paint can come off.

Substrate : The material that you are growing a thin film on.

Valence : Only certain energies are allowed for electrons in a material. The highest energy grouping of energy levels (called a band) in a material that are full of electrons is called the valence band. See band gap for an illustration of the valence band.

Voltage : Voltage is a difference in the electrical potential energy a charge would have between two points. Think of it like a hill. At the top of the hill, you have a lot of potential energy. At the bottom of the hill, you have little potential energy. The energy difference between the two is like the voltage. For a hill, you are dealing with potential energy from gravity, while for electronics, you are dealing with charge.

Quantum Mechanics : A branch of physics in which only certain things can be known at a certain time. It makes the biggest difference on really tiny things. It is useful for, for example, describing the atom, chemical bonding, and the operation of and limitations on modern computer chips. A good description may be found here. Also, Alice in Quanumland by Robert Gilmore is a good book that illustrates many of these concepts in an entertaining and clear way (it also makes later classes very entertaining).