Matt’s back in town! (with pictures of black silicon…)

 

I’m back in Richmond now, having just returned from a year-long research sabbatical in France working on a new project involving “Black Silicon.” When a smooth surface of pure silicon is subjected to plasma etching under certain special conditions, it can spontaneously form a dense forest of microscopic spikes and holes, typically a few hundred nanometers across and a handful of microns high.  As a result of this extreme roughness, light which is incident on the surface becomes trapped, and is eventually absorbed by the material, making it appear black to the naked eye.  Beyond the many interesting physics questions this material raises (How does this happen?  What determines the length scale?) this material has several potential applications, including the possibility for more efficient solar cells.

A scanning electron microscope image of black silicon

My work in France was at ESIEE Paris, an engineering school in the eastern suburbs of Paris.  I will continue to work on this project here at Richmond, collaborating with my French colleagues remotely.   Although we don’t have the plasma etching equipment here, we do have access to microscopy and analysis tools.   I also expect to return to Paris for several weeks at a time during the summers.

Review of Global Specialties PB-503 (do not buy)

I normally don’t review products here, but I’ve had a recent experience with the Global Specialties PB-503 that’s left a particularly bad taste in my mouth.  Since many of the vendors who sell it don’t post product reviews, I’ll write mine here.

On the plus side, this unit is a compact and convenient way to combine several DC power supplies and a function generator with a conveniently large breadboard area.  The design is well-suited to my introductory electronics course, for instance.

However, I have been unimpressed with the durability of these units.  Used in a classroom setting, I have had to repair several of these that failed over a semester. (By contrast, the multimeters I have used in the classroom have gone through many fuses, but have never been damaged.)  Repairs have included blown regulators in the DC power supplies and damaged voltage adjustment knobs (trim pots). Another had a bad solder joint.

Worse yet, these units have a known design flaw which the company seems uninterested in addressing.  The TTL output on the function generator does not work when the unit is in sine wave or triangle wave mode (which, after all, is when the TTL output is actually needed).  According to Global Specialties, this is due to a forced redesign of the unit when one of their parts became obsolete and unavailable.  I notified Global Specialties of the TTL issue in January 2010.  Initially, they assured me they would inform me of a fix for this problem within a few weeks.  Almost one year later, I have heard no news of a resolution to this design issue, and the company has not responded to my latest inquiries.

As it stands, this product does not do what it is supposed to do; if the company has plans to fix it, they have kept those plans from me.  I recommend against purchasing these units until this defect is addressed.

Vampire power: unplug the cable box!

The other day I became curious about how much power was being used by various electrical appliances in my house.  In particular, I was curious about “standby power” or “vampire power”: the electrical power drawn by devices when they are idle or even completely turned off.  So I stole borrowed a digital multimeter from work, connected it to an extension cord (had to cut open the cord), and voila–my own power meter!  To get the power usage in Watts, I measure AC current (amps, rms) and multiply by 120 volts.

The results surprised me!

First, the good news: the little power supply that I use to recharge my cell phone is actually quite efficient.  With no phone plugged into it, it draws only 0.0009 amps, for a power consumption of about 0.1 Watt.  At 10 cents per kilowatt-hour, that works out to about 10 cents per year.  I still unplug it when not in use, just out of habit, but leaving it plugged in clearly wouldn’t ruin either me or our planet.

Next, the bad news.   Many other power bricks were very inefficient, drawing 4 to 6 Watts even when hooked up to no load!  Other appliances clearly have similarly inefficient power supplies inside them, like my Braun coffee maker, which draws 3.5 Watts even when it’s turned off–all to run a stupid little LCD clock which I’ve never even bothered to set to the correct time.   Other losers were a boom box (6.8 watts when off) and a pair of computer speakers (7.9 watts when off).

Why are some of these so bad?  The answer, unfortunately, seems to be just bad design.  Old style power supplies often use transformers to step down the voltage from the 120 volts in a standard outlet to the handful of volts needed for the appliance.  These are the large, heavy black bricks that often feel warm to the touch when they are plugged in.  By contrast, the small power brick for my cell phone feels very light; it uses silicon-based electronics instead of the heavy iron-core transformer, and is much more efficient.  When the phone isn’t plugged in, the power supply doesn’t feel warm at all.

But the single worst offender was my cable box, made by Motorola and supplied to me by Comcast.  When it’s on, it draws 35 Watts.  But when it’s off, it still draws 34.5 watts! That’s costing me an extra $30 per year, for absolutely no benefit to me.  That’s  unconscionable!

The solution is simple: I have now put several of the worst offending devices on power strips with off switches.  Now when they’re off, they’re really off.  🙂  With a small amount of effort on my part, I should easily be able to save about $70 per year, which of course also reduces my carbon footprint and is generally good for the planet.

Do you have a story or question about “vampire power” you’d like to share?  Leave a comment and let me know.

Bad wiring in my house!

I was installing a ceiling fan in a bedroom in my house last weekend when I found that my home was badly miswired by the original builders.  The current wiring works, but is unsafe and clearly in violation of the national electric code.  (The home was built in 1995, when the builders REALLY should have known better.)  This turned out to be a nice circuits example for my intro physics class, so I thought I’d also post it here as an example of stuff you can learn in school that’s actually practical in real life.

The issue is the wiring of some hallway lights which are controlled by two switches at the top and bottom of the staircase.  The picture below shows how it’s supposed to be wired, using two “three-way switches.”  (Confusingly, they’re apparently called “two-way switches” in the UK.)  Note that three separate wires (as in 3-wire cable) are required between the two switches.

bad_wiring1b.gif

What happened in my house is this: the electrical contractors apparently ran out of 3-wire cable, and instead ran only 2-wire cable between the two switches.  This left them with no neutral wire to complete the circuit from the hallway lights.  Instead, they ran a cable to the bedroom, and connected to a neutral from a completely different branch circuit.  The wiring they did is shown below:

bad_wiring2b.gif

Here’s a quick quiz: what’s wrong with what they did?

Actually, there are three things wrong with it:

  1. In general, you want the supply and return current paths of a circuit to be near each other.  Big open loops in a circuit path tend to cause interference, degrading circuit performance.  (In some cases, they can also lead to inductive heating of metal structures near the wires, though not here.)  But this is the least of the problems.
  2. A much more serious problem is that the neutral wire in circuit #2 (for the bedroom) gets more current than it’s designed for.  The wires in circuit #2 are designed to handle only 15 Amps; any more, and the circuit breaker is supposed to shut the circuit off.  But in the diagram above, if the other lights and outlets in the bedroom draw 14 Amps through the breaker, and the hallway lights draw 2 Amps, then the neutral (return) wire for Circuit #2 carries 16 Amps, which is above its limit.  That’s a fire hazard.
  3. Another serious problem with this scheme is that a person working on circuit #2 (say, me, installing a ceiling fan) would typically turn off the breaker for circuit #2 and assume that he is safe.  But in fact, the neutral wire in this circuit still carries current from the hallway lights.  Breaking the neutral wire and touching it could lead to a nasty shock.  That’s how I found out something was wrong with my house: my hand brushed against a neutral wire and I got zapped.  I was uninjured, but this is serious: people have died because of this.

Now the really technical part:

I’m not a licensed electrician, but I believe this work is in violation of the National Electric Code, also known as NFPA 70.  In the situation above, the possibility of overcurrent in the neutral wire (grounded conductor) of circuit #2 appears to violate article 210.20.

Interestingly, I actually have two different places in my house that suffer from this defect.  One is exactly as I described above; the second is a little more subtle, because the two circuits are actually on different phases.  If the two hot wires (ungrounded conductors) are 180 degrees out of phase, the current in the shared neutral wire is actually the difference between the two currents, avoiding the overcurrent situation.  Bizarrely, I believe this makes the out-of-phase wiring scheme technically legal under older (pre 2005) versions of the code, when my house was built.  I think the two circuits would fall under the category of “multiwire branch circuits,” defined in article 100 and governed by article 210.4  (also known as “edison circuits” or “shared neutral circuits” or “common neutral circuits”).  Fortunately, this section of the code has been modified, and the newest version (2008) includes provisions in articles 210.4(B) and 210.7(B) that the two branch circuits must be equipped with a means to disconnect them simultaneously, such as a double pole breaker with a common trip tie in the panel box.  This prevents someone from disconnecting only one of the two circuits and mistakenly believing the circuit is safe to touch.  In my opinion, this update to the code is long overdue.

A quick note of clarification: although the preferred method of wiring a three way switch is to run a neutral wire from the same feed as the hot wire (using three-wire cable between the switches), there’s nothing sacred about that arrangement.  As long as the neutral wire coming from the lights is eventually connected back to the same branch circuit that the hot wire came from, there is no safety issue, though wrongness aspect #1 above still applies.  Three-wire cable is more expensive than two-wire cable, and two-wire cable can be safely used between three way switches, provided that the wire with white insulation is permanently reidentified by color as an ungrounded conductor, consistent with article 200.7(C)(1) and 200.7(C)(2).  (Were the white wires in my house between the two switches reidentified?  Of course not.)

The LHC: the world’s purest diamond and my 50 micron contribution to a 17 mile tunnel

With the recent news of the successful startup of the large hadron collider (LHC) at CERN, I’m reminded that I actually worked on a small piece of it back in the late 1990s, in one of my former lives as a graduate student at Ohio State University.  The LHC is the new, big, expensive, high energy particle accelerator, a 17 mile long tunnel that will accelerate particles to very high speeds, ultimately making collisions which will  mimic the conditions of the early universe just after the big bang. 

My own tiny piece of the project involved making tracking devices to detect the particles ejected from these high energy collisions. These tracking devices consist of a thin slab of insulating or semiconducting material, with a grid of tiny metal wires running horizontally on one side and vertically on the other.  When a high energy particle comes tearing through, it ionizes atoms in the material, creating small voltages on the nearby wires.  By monitoring the voltages on all of the wires, scientists can measure the precise x-y location of the high energy particle.  The actual detector at the end of the 17 mile long tunnel consists of many thousands of these devices, arranged in a sphere surrounding the area where the collision occurs.  By accurately tracking all of the particles ejected from a collision, scientists can work backwards to understand the physics of the collision itself.

In an accelerator as powerful as the large hadron collider, the spray of ejected particles would basically shred ordinary tracking devices, which are normally made of silicon.  I worked briefly with the RD42 collaboration to help develop tracking devices made of diamond, which is much less susceptible to radiation damage.  As part of the project, the group helped develop very high purity synthetic diamonds made by a chemical vapor deposition (CVD) technique.  The chemical and electrical purity of these diamonds easily surpasses that of any naturally occurring diamond on the earth, and at one point I actually held in my hand what at the time was the most perfect diamond the world had ever seen.  (It looked like a small piece of glass, about a centimeter square, maybe a couple of millimeters thick.) 

I helped the group to perform the lithography required to pattern the diamond’s surfaces with a dense array of 50 micron gold wires, about the thickness of a human hair.  (It was a fairly standard application of existing lithography technology, made only slightly trickier by the roughness and optical properties of the diamond surface.)  Interestingly, I never set out to be a high energy physicist, and initially I didn’t have anything to do with the group working on the LHC at Ohio State University.  At the time, I was actually using lithography to attach electrodes to tiny superconducting crystals for a completely unrelated experiment; I just happened to be the local expert there when the LHC group needed some help to prepare for some upcoming “beam time” at another accelerator.  I took time away from my normal Ph.D. work to help them out, and it ended up being a very interesting and ultimately successful collaboration.

The moral of the story, for those of you who like that sort of thing, is to pay attention to what your colleagues are working on, even if it seems unrelated to what you’re doing.  There may be connections to your own work that aren’t so obvious.  The LHC is a huge project, and many thousands of people have contributed to it; I sometimes wonder how many of those are accidental contributors like me.  Accidental or not, I’m proud to have played even a tiny technical part in the experiment, and I look forward to the new physics it will tell us.

Shout Out to Prospective Students

One of my goals for this blog is to provide a window into the physics department for prospective students interested in physics or engineering who are considering whether to come to Richmond.   Are you reading?  Is anybody out there?  Please drop me a quick comment here (or fire me an email if you’d rather) to let me know that you’re reading.  You can also ask a question, or tell me if there’s anything you’d particularly like to see here.  Thanks!  –Matt

We Put the “YOU” in NYOU-ton’s Laws…

Finding out I’m a physicist apparently evokes bad memories for some people I meet.  “Ooh, I hated physics in high school,” they often say, or “That was my worst class in college!”  Why so many negative reactions?  (Do people say the same about their history classes?)

Over the years, I’ve begun to realize that at least some of the problem probably comes from how physics is taught: often in a large lecture format, with a teacher filling the board with dense equations…and a room of compliant students dutifully copying them down.  Fortunately, that doesn’t describe the physics department at UR.  Cheesy puns about Newton aside, the culture in our department tilts strongly away from standard chalk-n-talk lectures, and we really do try to teach our courses in a way that focuses on the student and builds real understanding.  Below are some of the general principles I personally try to teach by.

Teach concepts and build intuition first, use math later.  Some students are very skilled at mathematics, and for them a short mathematical description of a physics principle is all they need.  Mathematics is the natural language of physics–quantitative and logically precise–and it’s an extremely powerful tool.   But for many students, mathematics serves as a barrier to entry, at least initially.  I always try to teach by first “getting the gist” of something across: an idea, an analogy, or just a mental picture of how something works.  Once that’s in place, then mathematics can really help pin the concept down.

Use inductive as well as deductive reasoning.  Humans are hard-wired to find patterns.  We learn to associate light with heat by using inductive reasoning through our daily experiences, observing that the two usually come together.  (Few of us have used deductive reasoning to make that connection based on the absorption of photons, blackbody radiation, etc.)  Yet physics is often taught deductively: Given A and B, we can prove C, from which we can then derive principle D, which has the special cases E, F, and G.  While it’s certainly important to understand the logical structure of our physics knowledge, that’s probably not the most natural way to learn it, at least for most people.  In my classes, I often teach inductively: I note the often familiar cases E, F, and G, then show how they are all special cases of a general principle D, which happens to be related to yesterday’s lesson about A, B, and C.  (As a professor who knows the subject well already, the deductive sequence A to G always seems the most logical; and that’s always how the textbooks teach it, too.  It’s hard to remember that that’s not always the most natural way to learn the subject.)

Above all: make learning active–without making it embarassing.  If you have to fix your bicycle, the very last thing you’d do would be to read an entire book about bicycle repair from cover to cover before ever getting your hands dirty.  (Or worse: attend a 14 week series of long-winded lectures on the subject, where you have to write down your own notes!)  Instead, you might look at a book, then try to tinker with the bike, read some more, get some advice, then tinker some more.  Over the course of a few repairs, you’d eventually get to be a real expert in bicycle repair, building up some real understanding about how bikes work.  Why should physics be any different? 

The small class size at UR let’s me teach my classes so that all of my students are active learners.  I can talk at the board for 10 minutes or so, and then ask my students “now, everybody draw me a graph of velocity versus time,” as I circulate around the room to see how they’re doing.  We also use many other modes of active learning (interactive laboratories, group problem solving etc.) that force students to use what they learn immediately, building connections and creating real understanding.   For example, all of our introductory classes are “workshop physics” courses, where the laboratory and lecture are integrated together (typically three 2-hour meetings a week, with 1 professor and about 20 students), which makes the laboratories a truly useful tool for learning concepts and building intuition, as opposed to a once-a-week chore that may or may not have to do with what’s being covered in the lecture portion.  (Incidentally, calling on students at random to answer questions in class is “active learning” too–but often only for the one student who gets picked.  Many students in my classes don’t like to be called on, and that’s fine with me.  I don’t care if my students are calling out answers, as long as they’re all thinking–and there are plenty of other ways to make that happen without the public humiliation.)

None of this is about watering down the content of physics courses.  (In fact, I’m as much of a hard-ass numbers guy as anybody I know.  Try one of my exams if you don’t believe me.)  It’s about teaching material in a way that’s consistent with how most humans learn best.  If that makes me too much of an old softie, then I’m guilty as charged.  I simply call it “doing my job well.”

Visiting campus? Look me up.

Just a quick note to pass along to anyone who’s planning on visiting the University of Richmond.  If you’re interested in physics and want to find out more than is usually possible from a campus tour, please feel free to contact me directly, either by phone or by email.  (Or, for that matter, you can post a question here on my blog.)  I often meet with prospective students and their families on campus, and I’m happy to do it.  Looking forward to meeting you!

What is Undergraduate Research, Anyway?

I’ve gotten several questions recently from prospective students and their parents asking how undergraduate research works.  Who does it?  When does it start?  What do they do?  What is undergraduate research, anyway?

As a professor, I have two jobs.  One is to teach students, as I do every day in my classes.  The other is to do research, which in my case involves doing experiments, taking data, figuring things out, and then presenting it at conferences and in articles in scientific journals.  At big universities like Ohio State and Princeton (where I was before), research is done in groups involving at least one professor plus a small army of post-docs and graduate students.  At Richmond, we do the same thing but with undergraduates.  We study the same kinds of problems, present at the same national and international conferences, and publish in the same journals.  (Does size and lack of graduate students put us at a disadvantage?  Only a little bit.  Some projects require millions of dollars and dozens of graduate students; other projects don’t.  I have to be a little bit careful picking my projects, but there are plenty of unanswered questions out there that I can find the answers to just fine here, thanks.  In fact, most of us collaborate with colleagues from other schools, too.)

In our physics department, all six of the tenure-line faculty are research active.  (That’s not true at all small colleges, where it’s common for some of the faculty, particularly senior professors who were hired under different expectations, to support their school’s mission in other ways.  Some other colleges may also lack the resources to support research at the level we do.)  If each of us works with three or four students, the total number of physics students involved in undergraduate research is…well, pretty much all of them, including students only in their first or second year.  Note that in our department, research is not just for seniors doing “senior projects” or for only the top honors students.  Students typically do research during the year for course credit, and most do research over the summers for money, paid by the University or from a professor’s research grant.

Students here do research on whatever topics the faculty are studying.  For me, that means copolymer materials, nanotechnology, and atomic force microscopy.  (Other professors here study nuclear physics, particle physics, biological physics, and cosmology.)  Although in principle a student could pursue a topic independently, in practice that never happens, simply because figuring out what problems are truly new and interesting (and practical) at the forefront of human knowledge is virtually impossible for a novice.   (And if it’s not at the forefront of human knowledge, we’re not generally interested in it here at UR.  Topics like “the physics of skiing” are fun and might even be a good learning experience, but that’s just not what we do.)  There is no formal process for matching students with faculty; by their sophomore years at the latest, our students generally recognize the benefits of doing research and tend to be drawn to one professor’s lab or another.  The professors are always on the lookout for new students too, and in a department as small and informal as ours, connections just happen.

Doing research is a great experience for our students.   They are often authors on journal articles, and they get to travel to national and international conferences to present their work–all of which looks pretty good on a resume for graduate school or for jobs.  The skills they learn, both specific technical skills and a more general ability to tackle open-ended problems and deal with complexity,  are applicable wherever they go.  And for me, it’s great to see how students grow from their first tentative steps as incoming students, to confident and capable seniors who go on to do great things.  In this way, my two jobs–teaching and research–are really just one job, like two faces of the same coin.