Searching for Trolls under the Electron Bridge (recording)

so good evening and welcome to the next installment of the SLAC public lectures So today we're very lucky to

have Liz Ryland from the pulse Institute here at slack and Stanford to talk to us

uh Liz is from Louisiana originally did her ba at Louisiana or BS I guess at

Louisiana Tech um then from there she got to the University of Illinois one of

the the big places actually for condensed matter physics um she apparently built her own little

x-ray laser and did so well that she got to come here and work with the big one that we have here at slack and so she's

been a post to at the pulse Institute um she's going to talk to us about uh

looking for trolls under the electron Bridge so we'll find out what that means

good luck all right thanks for the introduction Michael so as Michael said

we're going to search for trolls under an electron Bridge today and we're going to spend a while figuring out what on Earth I'm talking about so when I gave

this practice talk they wanted more info about me so I am indeed from Louisiana uh yeah it's a great place

it's the land of Marty gr food and like aggressively hot sunlight and a lot of plants that grow from that and that's

really all that I'm about I'm from sh for so the northern part of the state not exactly New Orleans which is way

down there but I have family in Lafia kind of capital of Cajun Country and kind of have been all over the state and

really there is sunlight everywhere sunlight and plants grow big and strong and the older I get the more impressed I

got by how massive plants can grow and how much they can do deriving energy

just from sunlight and Soil and Water so as Michael said I

after like childhood in high school and stuff I went to Louisiana Tech University it's a big engineering school

in Louisiana and I got my degree in chemistry and I worked at a college radio station and from doing those two

things I realized that chemistry is cool and with my undergraduate degree I really just only had got the bearest

foundation so I really wanted to know more and so I applied to graduate school and I decided to go to the University of Illinois at Urbana-Champaign as Michael

said it's a very big school and there I joined the Josh verise group where we built this tabletop XUV instrument which

instead of making really high energy x-rays in about a mile we made really

soft energy X-rays and about six feet inside our own lab and we got to kind of build that all from scratch it was

really cool and I used that to really start studying molecules on a fundamental level really tracking the

electron movement at the speed that they actually move at from there I went to the US Naval Research lab for a post to I

kind of expanded into IR spectroscopy and that's where I spent the Lost plague year of 2020 and then from there I moved

on to slack uh you know Co not a great time for anyone so I moved on to Slack and

even though I had been working in IR spectroscopy I wanted to expand my horizons I really like X-rays and all of

the different things you can do when you're using those as your primary instrument so at slack I joined uh Kelly

Gaffney and Amir cardones Han in the solution phase chemistry group of the Stanford pulse Institute of the slack

National accelerator lab really lots of titles what that means is that we are based at slack and we're really an

enduser for these giant instruments so we're not part of making the XR but we're part of using them to answer

fundamental scientific questions so getting into the bulk of the talk why we even want to study

photochemistry is it because there's a massive ball of energy in the sky that's glowing on us constantly pretty much so

the sun is really powerful so the sun is really powerful

it's constantly doing Fusion so it's taking two hydrogen smashing them into a helium atom and releasing tons and tons

of energy as I have up there it fuses over 600 million tons of hydrogen per

second and releases massive amounts of energy almost four time 10 26 watts per

day that's almost a trillion times a trillion times a trillion of watts of energy compared to what actually reaches

Earth because that's emitting an all you know directions from this sphere in the sky it's Crossing 93 million miles to

get to the Earth's surface and at the Earth's surface you're going to absorb almost 200,000 terawatts of energy just

distributed hitting every single continent things like that so really tons and tons of energy to put this in

context that is 10,000 times the global energy use

today we all know that the sun is powerful in California we use it to grow

nutrients inside plants and create harvests and fruits and vegetables and weeds use them to grow aggressively and

no matter what we can do we can't actually get rid of weeds because they're powered by the sun which is incredibly

powerful so we have been trying as chemist to figure out how can we utilize

the sun's energy for a long time starting with uh gako chiman an Italian

photo-chemist from the late 1800s he was Nobel nominated for the Nobel prize

Nobel Prize different times and he's thought to be the father of photochemistry so he did it the first

photochemistry experiment in 1886 he pretty much exposed things to

sunlight and was like this is wild there is going to be sometimes bubbling gasses evolving in situation there's color

changes anyone who's left a jacket they really like in their car over a hot summer has come back to find their jacket half a different color this is

because the sun it sends you this this light and is going to interact with materials at a fundamental level so Tron

he started the Department of Chemistry at the University of bologna and this is a picture of him on top of the roof

of the University just with a bunch of different folks all sitting out just seeing what chemistry is going to happen

it's a great picture if you zoom in really far he actually has two different buildings covered like he's like I don't

need a lab space guys there's a roof and I have these flasks and up in the left is kind of an example of the type of

reaction so basically you have molecule you expose to sunlight and suddenly the molecules connect together almost like a

polymerization and more than that he's also thought of as the father of the idea of green chemistry so after the

turn of the century in around 1908 to 1912 he started writing these papers being like the sun is amazing guys why are

we using fossil fuels and in a seminal paper from 1912 published in science and then presented at International

conferences he pretty much announced we need to stop using fossil fuels I have this great vision of the future we don't

need to keep burning coals and polluting our environment we can convert to purely solar he had a very fun idea he didn't

quite think of solar panels instead he thought of giant glass tubes that kind of stretched out over Europe and all of

the Cities winding around and all of them were full with some gas absorbing light and for Sun and essentially just netting that straight into the

electrical grid so we didn't quite come up with his vision but we're still using the sun

today to power a lot of different sources there's three different ways we primarily Harvest energy from the Sun

there's going to be thermal energy which it gets really hot outs sometimes asphalt gets so hot you can cook eggs on

it that's basically doing chemistry so we have different ways we can Harvest this energy it's like contributes to uh

heating of the Earth's surface and you know we're all familiar with being warm in the recent years we started being

able to harvest electrical energy from sunlight solar panels so in California

alone in a year we generate around 20,000 Million per year that's around 15%

of total California energy consumption but that's not really what I'm talk today many of you are probably

familiar with those areas what instead I'm going to talk about is how can we use the sun to directly do chemical

reactions just like chimen was trying to do so there's two different main R we're

going to go for you're going to store energy in chemical bonds many of us are familiar with that how plants work

plants are going to take sunlight and use it to power the mechanism of converting water and CO2 into glucose

and oxygen which we need to breathe but glucose is very powerful and they use it to power all of these cellular functions

the other option is that you use that energy immediately or directly to power a chemical reaction an example we're all

familiar with is color change sunglasses all that is is sunlight comes in and you're making a molecular Bond or twist

or change in some way and that's going to have a different interaction with light so the way that we as a society

think we're going to imitate what plants are doing is instead of trying to make glucose and oxygen which is a very

complicated process using photosystem too a lot of great studies going on at slack about that but is this idea of

storing energy in chemical bonds so specifically hydrogen gas so that

instead of putting gasoline into your heart you'll put condensed hydrogen and then use those chemical bonds to power

uh your car so comparing hydrogen to gas

it's going to one kilogram of hydrogen is about a coil one gallon of gasoline a gallon gas will get you 25 miles and

will release a bunch of hydrocarbons into the atmosphere whereas one kilogram of condensed hydrogen is going to be

able to power your car 60 miles and more importantly when it combust hydrogen combusting with oxygen is going to have

a main output of water which is going to be better to put into the environment than any sort of

pollutant so we're already working on a bunch of different ways to make hydrogen mostly with electrolytic uh water

splitting you send in water you electricity hopefully green electricity and you're going to generate hygiene and

be able to release oxygen into the atmosphere the photo chemists dream is to just take out the middleman why are we

using this electricity that we had to generate and store and use batteries and put it into our grid why not make the

sunlight do it directly and that idea is is essentially taking water exposing it to sunlight and a catalyst and

generating hydrogen and oxygen so the question of course for a

chemist is how are we going to design a catalyst that harvests sunlights and then takes those electrons that it's

taking directly from the sunlight to do the specific chemistry needed to turn water into hydrogen so that's going to

be again breaking the bonds in water and then putting that energy and storing it into hydrogen that then breaks releases

energy and you can power a lot of things just like gasoline so how can we make this

Catalyst be powered by sunlight so a catalyst is let's call it just a molecule that does some specific chemist

like Mak hydrogen or really anything else chemistry can do a lot of stuff the idea is that when you expose it to

sunlight you're taking a ground state and you're act catalytically active so instead having to heat it up or

electrocute it or expose it to energy you ground state of some molecule this is an example of a common photocatalyst

has a ruum surrounded by some other stuff you expose it to light it moves it up an energy level into this excited

state which in essentially is taking an electron off of the ruum atom the metal

and moving it onto one of these outer sphere lians and then that electron is accessible to do some kind of chemistry

and that's great that's all well and good there's a bunch of great research on this there's actually a slack public lecture covering this topic from 2017 by

chrisan cunis talking about catching light is I believe the name of but really talking about this process so

today I'm going to talk about what do you do when that's not the chemistry you want to do that molecule can't do it you

instead want to use this it's a platinum Catalyst really commonly used in a lot of industrial processes but it has a

different system instead of from the metal to the LI you want your Li so your chlorine kind of around it to give an

electron to your metal so you shine some light on it and your light isn't quite enough doesn't work nothing happens you

don't reach the six side State this is because light as many of you know comes in a spectrum all

different colors of light are coming down from the Sun the yellow line is what hits in sunlight on top of the

atmosphere remember to the left is going to be shorter wavelength so higher

energy things like purple and x-rays eventually and then to the right is going to be your infrared light going

into microwaves and much longer wavelength and lower energy the M from here you can easily see the majority of

sunlight hitting their surface is going to be of this visible band that's actually why we see in the visible it's

the most important photons for our eyes to be able to see and this is at the top of the

atmosphere you go through the atmosphere and all the different substances absorb these specific bands of light so you

reduce the yellow into that red line so that's the radiation left over at sea level so a little bit weaker still

clearly dominated by the visible region and you can see notches in it that are going to be the specific absorption

bands of water and CO2 and other things in our atmosphere and the goal of this

is that you want to design some kind of catalyst A system that absorbs specifically in that visible region to

harvest as much of this sunlight as possible so for that system you can

actually separate it out and have a part that is going to absorb energy from the Sun and turn it into an electron and you

have a part that's going to do the specific chemistry rather than having one system that do you just connect them

you connect them using an electron bridge and that's really going to be the theme of today it's how do we make an

electron effectively move from donor the thing that is absorbing sunlight and

creating an electron to your electron acceptor which is going to be the thing that does some kind of chemistry this is

an example of what the molecule looks like in real space so going from one end to the

other however you have a competing pathway once your electron leaves your

electron doesn't really want to stay left it has all this energy it got up in the morning and was like I'm going to go on a trip but sometimes it gets there or

goes out and it loses that energy and so it's going to return home and so our entire job is kemus is trying to make a

unidirectional bridge where you have the electron go really fast and not turn

around and come back kind of similar to I'm sure one of someone in here has driven over one of these the wrong way I know that's what that laughter was so

you want uh they're called Road spikes where drive over one way the other way they puncture your tires we're trying to

design molecular Road spikes so the electron moves one way not the other and

you really want to do this because you want it to remain active as long as possible this is going to be at least

tens to hundreds of nanoseconds that's how long it takes for this molecule to run into other molecules and actually do

some chemistry this is okay though because the electron moves fast enough and we we

can do this so here's a slight less intimidating drawing of a molecule where you have the ranium portion is going to

generate electron and we're going to move across to the Platinum so upon photo excitation let's just kind

of watch what the electron does so you have an electron that's just hanging out in its Atomic home inside the ranium you

photo electron moves the closest part of the bridge and then a little bit of time passes it moves to the center a little

bit of time passes it moves SP a little and it finally arrives at the platinum

and we're ready to do some targeted chemistry this entire distance is going to be around 2 nanometers for comparison

the average width of human hair is around 50,000 nanometers so this is an incredibly incredibly small distance

that this electron is moving and the electron is moving incredibly fast it's going to be much much faster than a nanc

faster than a Pico thousandth of a nanc frequently on the orders of ftoc which

is a thousandth of a thousand of a nanc and then again needs to stay there

for 100 NS do that chemistry unidirectional the problem however is sometimes your electron never arrives

your collaborator Spends months making these beautiful molecules all of this theoretical design it's going to work

great it doesn't do any chemistry you look at it and the electron never arrives the question has a troll

consumed my electron and if so where has it been

several trolls how has it done this to me this is really the job of a physical

chemist which is what I identify as so there's many different kinds of chemistry there's people who do

calculations and design things there's people who stand in a lab a wet lab and do some amazing magic with vases not

vases and glasses to synthesize these molecules and then you have physical chemists who are kind of afraid of real

chemicals but are good at math and good at like using wrenches and so we build these really insane three mile long

instruments and convince everyone use them and we have a lot of fun really our goal is to figure are we're figuring out

how the molecule works and more importantly how it doesn't work and then we work with our collaborators to tell

them this is exactly where this molecule went wrong and so you can work together so they can do de novo design and fix

this Catalyst to you know make a brighter future so what do I mean by a

troll this can be the electron is stuck on the bridge your electron leaves home gets to the bridge and the bridge is

really nice why does it want to go all the way to the Platinum the bridge is really nice it feels sa stable and safe there it would be uphill in energy to go

onto the Platinum your option can also be that the bridge is too long and that there's a lot of traffic so the electron

it's going really slow and you know it would take longer to get away than it would to just turn around and go back

home that's where you have that competing back electron transfer problem and where we want to invent this idea of

like no don't go home it's very hard to go home and the last option that I'm going to talk about is maybe the

electron just gives its energy to Sol it goes on the bridge and then it meets like a really nice hobo and it gives all

its money to the hobo and the hobo like swims away into the sunset I don't I don't know how that would go anyway so

really my job is identifying how has the electron been eaten or been sent back home because it's afraid of a

troll so how do you do that how do you put cameras on an electron bridge this is really tiny this is only a few

nanometers long how are we going to put traffic cameras on a molecular Bridge

the answer is lasers because lasers are super fun all right so a quick rehash on

lasers lasers are light waves particle wave Duality they oscillate In Waves

they're very targeted and collinear so they can be powerful blue light is made of shorter waves than red light red

light is long longer waves but particle wave Duality lasers are also particles

you're delivering literal units of light energy a piece of blue light has more

energy than a pie piece of red light particle wave Duality they happen as both and that's incredibly important

for understanding how to manipulate lasers and use them to study things we can thank this kind of concept to plun

who around 1900 was like Hey things can exist in Quant of energy photons probably exist and then our favorite

dude Einstein who literally every era of science you just lead back to him somehow in 1917 he pretty much trolled

everyone and said hey guys I did some math you can definitely make laser you can build up this light and deliver it

in a coherent source so that you can shine a laser pointer woo laser pointer and have it go really long distance

without ever like losing sorry fumbled that they go in a straight line for a

really long time which means you can point them at things they aren't diffuse and I say he trolled people because he

said you could do this in 1917 and he clearly wrote out the math to do it and then it took 45 years for someone to

actually be able to physically make it the first laser that was made is a ruby laser and so imagine you have a brick of

Ruby literally we use crystals all the time Sapphire is one of the most commonly ones we use so a laser is just

any sort of gain medium coupled into an optical cavity the gain medium you shine

light on it in the Ruby laser case it was a flash lamp and by Shining Light on it you're giving a bunch of energy to

this system and everything's going to just start trying to get rid of that energy as a characteristic wavelength you

make it into a laser by putting mirrors on each end of the cavity and only something that matches like a multiple

of that cavity is going to oscillate this is why they are actually able to make a merer first so that is

microwave laser because you can imagine that making a cavity that's uh multiple

units of centimeters is much easier than one that's multiple units of nanometers and so just aligning and creating was

really hard then there was the the wild west of laser inventions in the 1960s there was

so much going on and there is actually was like a 30-year litigation on who really deserve the Nobel Prize and who

actually gets the patent for making lasers really cool stuff invented a bunch of things then came Donna

Strickland who in 1985 she made a came up with something called chirp pulse amplification which

essentially a way to make a very high power pulse laser and that enabled using

these to study chemical methods so Donna Strickland got the 2018 Nobel Prize for

this method and then the 1999 Nobel Prize went to this man named Ahmed zael

who is essentially the father of fto chemistry he's the one who took these lasers and used them to solve chemical

problems the the way you did this is that these

laser pointers that everyone's mostly familiar with these are called continuous wave lasers so they are constant L emitting in time however by

doing some interesting Optical cavity stuff you can have the lasers deliver instead

tiny at once and these pulses can be incredibly short and I'm talking microsc

and nanc followed in the 90s by PC lasers that you can control well and then after that ftoc lasers so a ftoc is

a millionth of a billionth of a second that's very very short and if you have

ftoc laser it's like a camera so you have a camera that has a very stop Fast

Flash speed so at a public lecture a few months ago someone use the example of a hummingbird with a really slow camera so

a long exposure time you can't see the hummingbird's wings but if you make your exposure time shorter and shorter and

shorter you can start resolving and seeing those hummingbird wings and that's why ftocs are really important

for studying chemistry because that is the rate at which electrons move along a bridge out of seconds even shorter than

that very great a lot of cool talks on that for interesting physics things and

then y'all can go and watch their lectures if you want to hear about them because I'm really only talking ftoc

so talking explicitly how you do this is what zel did is he was like okay one

laser is done what if we use two it's a technique called pump probe spectroscopy you use two lasers the first one

delivers a pump pulse that is going to be a piece of visible light it's going to imitate the Sun you give it to a

molecule and it goes into the excited state what happens to it if it gets exposed to light and then you come in

with a probe pulse and that again that's your camera you're taking a picture and by

changing the or not the exposure time but when you take the picture it's like if you take a picture one second two

seconds three seconds things like that and the great things about lasers is they're columnated and all light travels

at the same speed in a vacuum so by literally changing the distance that you are having on your alignment path you

change the arrival time between the two and you're taking photos throughout time

and you can really remap electron movement process so whales work all the light was

visible and we're at SLAC National Lab why am I talking about all this Optical stuff so energy describes uh the color

of the light so visible light we're now talking in EV is a unit of energy

visible light is going to be very short it's going to be like one or two EV x-rays are much much bigger they're

going to be a thousand EV or 100,000 EV the reason that uh this matters is

because this is going to be characteristic on an element by element

basis so we use slack because slack is an x-ray laser we can use tabletop

things to make Optical pulses of light but you really need these massive facilities to make incredibly short

pulses of X-ray light because they move completely different from other light and you need the source needs to be

really long because you want it to be really intense the more intense your pulse the better your resolution of your

camera so ex really short why do we use x-rays here you have a nucleus you have

a bunch of electrons sitting around your X-ray light comes in and it kicks out one of the electrons in an

inner shell and it moves it into the veilance level by absorbing that piece of light so if you have nitrogen it's a

very small distance just a little hop for that electron from home to the

veence Shell if you have a bigger atom like a metal like this ruum you have a lot more

layers of electrons and it's going to be a bigger distance that it has to go same

thing for platinum even bigger than renum so your electron has further to travel to get to to the veilance bander

to where it wants to go so a little bit of audience participation how much gas

does it take to go from the surface I'll give you an example nitrogen is 400 EV

who Brave and wants to guess what it is for

ranium no kids today adults are not

brave 1 1600 that is a good

guess so this is a huge difference and that is not because it is just a

distance change between these atoms as you get bigger and bigger the core of these atoms is pulling its electrons

even stronger and so the electrons are having to fight incredibly hard to get out of the center of the

atom Platinum I won't ask anyone to guess because I know everyone's feeling very nervous tonight is 72,000 EV so

again Platinum not that much bigger than but pulling those electrons even harder so it becomes very hard to escape but

the great thing about these being different energies is they're characteristic if you shoot a bunch of

different colored X-rays at things you can tell exactly what elements are there just by the energy that they

absorb so that's why we have free electron lasers and synchrotrons and R

there those are the energies that you're able to those are the energies you need

to identify if that element is present and different beam lines and different facilities all across the globe all have

different uh energies of x-rays that you do so the way you actually use the instrument is you write these proposals

you mail it off and they say we'll give you seven days in two years prepare really well because that's the only shot

you have uh can be very alarming but it's really amazing the information that

you can get from these facilities so what this looks like in practice is you have your X-ray light

and it goes in and it hits a sample this it as a powder the X-ray either transmits through the sample or you

measure it some other way and you really just see x-rays before you hit the sample and x-rays after you hit the

sample and you just subtract those and so if you have a ruum you expose it and

you see this peak remember this is my camera this is the X-ray camera I'm taking a photo of

it this is what my uh ruini looks like before it has a piece of light so before

it loses an electron so you photo excite it with your visible light pulse emulating the

sun nice lightning bolt on the renum and you can answer this question of has light created an electron and you're

going to answer that by if this peak moves left or right that Peak is going to change and if it changes you can say

hey the electron has left home lets you know no troll at the renum center you

can then go to a different beam line with a different amount of energy and you can look look at the Platinum same

exact thing you shine light on it start the electron leaving the renum

and if you see a change you can answer the question has the electron arrived on the Catalyst just by the movement in

this peak of this energy and again we're taking these x-ray photos incredibly fast using these lasers so your distance

and time can be fto or Pico so again every millionth of a billionth of a second you can take a picture take a

picture take a picture and so you can not only see has something arrived there how long did it take to arrive

there lastly I'm going to talk about nitrogen so nitrogen you can see much

lower energy but there's a lot more nitrogens throughout this molecule so if you shine light on it

start an electron moving you can identify exactly where on the molecule is the electron just by looking at one

of theen so if it's still around the ruini you're going to get a change in this

yellowish Peak if it's gone to the center of the bridge you're going to get a change on the greenish peak in the center if it uh is on the Platinum the

Catalyst part of your Bridge you're going to see a change in the highest energy Peak that blue one and this can

be incredibly diagnostic because now you're able to map the entire molecule and I uh with using one energy and

you're crucially able to look at the bridge step so why I mean you notice that you

might have noticed that the ranium had one Peak and the Platinum had one Peak but the nitrogen has three Peaks this is

because there's different chemical signatures you're measuring that in of the nitrogen so this is the where you're

moving an electron from the most core of the nitrogen to

the but this is a nitrogen atom it's just sitting in gas not interacting with anything when you put it into a molecule

it has a bunch of other atoms around it those other atoms are going to fill the veence shell so they're going to share

some electrons and the center of the nitrogen all the other electrons are going to respond to the presence of the

new ones they're going to pull in closer to the nucleus so kind of reacting back and forth what is around it and that's

going to what it's around it is going to change so the veence the core is much

closer the veence shell is full so it's having to go even further to escape this electron and just like we showed

earlier if the electron has further to go and it's a harder go job you have to

use more gas to get there and that's going to move your Peak and that's going to be diagnostic of what the nitrogen is

bound to so in this way we can start answering this question of what part of

the bridge is the electron getting stuck at if it's in the center of the bridge

you're going to see a change on the yellow and green Peak if it gets stuck on the ruum part of the bridge you'll

only see a change in the yellow Peak if it gets all the way to the Platinum part of the bridge and you see a change in

every single Peak you can then use that as traffic cameras and speed not speed

map do isn't word the speed how long it took to get somewhere um and that's incredibly

powerful so oh thought I already did that so let me talk a little about bit

about the actual experiment we're doing so this is a brand new inst station at

uh LCL so some of you might or might not know lcls is undergo an upgrade right now

we're becoming lcls 2 and what that means is we're super cooling an entire

portion of the accelerator and by super cooling it we can make our electrons multiply even more so the source is

going to be a million times brighter and once again you can imagine what that's going to do to your signal to noise if

you have a really bright light you can see better than a dim one like if you get a splinter you don't sit in your

living room you go into the bathroom under the brightest light you have to see as well as you possibly can so this

is going to really improve our signal to noise and so we built this new inst station called

kimri so this has a comedically complex sample delivery I say comedically

because you want to deliver these molecules to an x-ray beam but you don't want them to be a powder chemistry

doesn't happen in solid state it happens in solution interacting with the solvent in the environment you're mixing a bunch

of things together however uh sorry however nitrogen

absorbs at 400 EV I mentioned that a few times and that's because that's significant as soon as you go below

around a thousand EV of light energy you have these photons they're getting pretty weak and they're just going to

start interacting with everything including the atmosphere air any solvent you put it in any Optics so you have to

do the entire experiment under a vacuum chamber so this has to get to around 10

the minus 5 T that's you know space is something like 10us 12 to 10us 17 so not

quite at Space level but it's not very much air in there you have to use a

couple of different vacuum pumps to get it out there all right so do the entire experiment vacuum chamber people do that

but remember I said this is a liquid that I'm putting in so I'm shooting a liquid into a vacuum chamber and it

interacts with air so it's definitely going to interact with any sort of cell that I put this liquid in so going to

just shoot bare liquid I'm just going to Jet liquid into a vacuum chamber an exposed nozzle and you know I also I

don't one of the ways we do this is you sit a nice round jet people people know

how to make round Jets that's very reasonable and very nice but for x-ray

absorption you want a nice homogeneous surface so you want a really flat jet so

you want an ultra thin Jet and by ultra thin I mean you know a few Micron

thick so we designed this insane microfluidic chip design so instead of

jetting a round jet of water you have this micro chip and it has different channels and as the channels come in

they shoot liquid out the liquid hits into each other and splashes out in this Leaf form and then splashes out into a

leaf form and then splashes out into a leaf form and you can engineer these so delicately that you get something that's

maybe a millimeter wide and then only a micron

thick so over on the left is one of the first examples of this you had this kind of colliding chip and you can see there

was still a lot of interference it wasn't perfectly smooth I show that picture to show this converging nozzle

look how amazingly smooth that is you know that's smooth because you see those bands of light we actually use those

bands of light to figure out how thick this sample is and by the bands of light interacting you can figure out how thick

it is so again very thick this jet that this is a photo of is around five microns thick once again compared to

human hair that's 20 to 180 Micron thick so this is significantly thinner than

even the finest baby hair and it's a millimeter wide and we're shooting it into an exposed vacuum it's pretty

insane and you know we have one more problem this isn't reasonable at all

because these samples are precious they're so precious that just a few

grams of it is going to take a collaborator six months to years to synthesize you do not make friends if

you're like hey I want to do an experiment can I have like three years of your life making this one sample please and you know so we're like okay

we really want to do these measurements really precious samples you're going to synthesize those in like tens of

milligram amounts very very small and so you really want to ask someone for under a gram and so in order to do this we're

like great we're already shooting an insane liquid jet into a vacuum chamber let's also add this catcher so this is a

heated copper tube and it's like attached to its own vacuum chamber so you shoot a liquid jet exposed into

vacuum catch the water suck it out and recirculate the entire thing and so we only recirculate around 50 milliliters

of it that's significantly less than I have in this class um and this is just

it's so much engineering went into this I put the publication on there I know you're all going to rush out and read it

um it's very impressive because now instead asking for 16 or 20 grams of a

sample you can reduce that and ask for 500 milligrams which makes you lots of friends and has people actually want to

do an experiment with you um I went over this just

because I think this is one of the coolest things about science is the truly comedic things you do to make an

experiment work uh again 50 milliliters for around eight hours constantly being exposed to

things so we did this experiment last year and

we just did the first half of this bridge because this was a brand new inst station and again it was actually designed for LS2 when we have a million

times better Source but we went ahead and had to test it before we had that because of course just like do your

experiment with a million times less photons that's fine so we've did this experiment and we were able to show that

the electron does after being excited by light land on the bridge

however from preliminary results we're finding that uh there's also a troll

there the electron never wants to leave that bridge it's too stable it's too happy there's like a cafe on the bridge

and all kinds of other stuff it never actually wants to go all the way to platinum who wants to drive that far but the really important conclusion from

this isn't that we found one molecule that didn't work is that we found a mechanism for why it didn't work and we

built this system that's modular so the reason I have these drawn

in separate parts is because the entire ethos of this project is is to build these like building block linkers so

imagine these are Lego sets where you have a bunch of different electronic sceps and one Catalyst you pick the

electronic scepter that absorbs the color of light that you currently have or you have an electronic septer so

thing that turns sunlight into electrons and it's incredibly good at absorbing blue sunlight which hits your office at

the perfect angle each day to be very intense and so you can just swap out the electron acceptor the Catalyst and do

whatever chemistry you want using this Linker you've already designed so the example here if your Bridge doesn't work

like the ones we've used we can just substitute out a new bridge and again that still has nitrogens in it so this

technique I described is still going to be useful for figuring out if this system works so we've been presenting

this at conferences and scientific meetups recently every single person you

talk to is really excited about the ability to look at nitrogens this is because nitrogens are ubiquitous in

these types of systems here's a bunch of bridges you can notice that there's nitrogens everywhere nitrogen it's like

carbon it's one of the building blocks of all chemistry and it's incredibly important for understanding these

systems so so many people have come up to us and are really excited about when are you going to get the good enough

signal noise that you can move into harder solvents that you can move into this it's been really fun to talk to people about all of the different

experiments that you can do going forward and this is here at slack National Lab they've been building it the last few years it's going to be

really great so in conclusion kind of what I've talked about to you today is how you use

ultra short X-rays to track this electron movement in these kind of bridge system

in these light harvesting systems that are modular and this has a bunch of great applications uh it's going to be really

cool going forward so that is searching for trolls under the electron

Bridge

also always a plug for collaboration science as a team slack is a massive facility these are like 20 different

people who all work together just to do that one experiment and many many more again Christian Kunis catching light a

previous SLAC public lecture really great introduction to the chromophor so the light absorbing turning it into an

electron really great introduction on that highly recommend

that's all so uh Liz thank you very much I

guess there are some members of this team in the audience too want to raise your hand yeah team members over there

very good um so we have some time for questions so here's the deal with the

questions um this uh lecture is being recorded and it'll appear I guess in

about a week on YouTube on our SLAC YouTube channel if you'd like your question to be actually in the recording

which I hope you do uh please wait for the microphone to come to you and then talk into the microphone and then Liz

will answer the question so please raise your hand to ask a question and I'll recognize

you

sir hi thanks for the talk um I wanted to understand with the absorption lines

like like what what does that mean like a certain electron energy is being

absorbed and then you don't see it at the end or something or um do you mean

like from the solar Spectrum uh no no there was like the plots that you were showing to work out where the electron

had gone in that system yeah like this yeah yeah those ones yeah okay sorry can

you repeat your question just so sure yeah so what does that like peak mean does

that mean those electrons never reach the end or uh no this is the initial

Spectrum so this is at the ground state so before you ever photo excite it you're sending in this color of X-ray

light and it's going to based on just the identity of the

atom so an atom it exists at the center with the nucleus it's going to be positively charged and then you have

electrons existing in layers out of it is called a core level technique

x-rays are going to take one of the innermost electrons give it energy and leave and so that is the energy it takes

for an electron to leave the center of the atom and that energy the amount of

gas it takes and the distance it has to go that's going to change by everything that's around it so this is just a

ground state measurement and then if you photo excite it first these Peaks are going to move and you can identify what

part of the bridge it's on by which Peak moves oh but let's be a little could you go back to the

ranium the original Peak that you should yeah there we go so the question is why

is there a peak rather than a spread yeah and the yeah and oh um so it's a

bound transition versus ionization so ionization means the electron just leaves gets skyrocketed never sees home

again a bound transition means it's moving in between orbitals so it could be in between the closest Shell and the

one like third up or the closest Shell and the veilance and so it's a bound transition because it moves a specific

amount and then I don't show it here but each of these it has this pre Peak and

then there's kind of this big step function that happens after it and in atoms these levels are very discrete

they're definite energy so it's it's a very narrow band of x-rays that has this

large probability to go from exactly this shell to exactly that show and

that's used in all of these techniques and many other in the rest of chemistry too I should say and so Platinum is a

good example because you see that's sharp Peak and then you can already see the ledge and that's the ionization energy so it's a big shelf kind of with

a main Peak you thanks for the question uh who else

sir so I'm thinking about the exclusion PR ible and the fact that you can only have one electron with one quantum

number in one spot as these things move along the chain is it actually one electron going

each step or is one pushing on the end whole end the chain and pushing another

one out the other end can this technique actually just answer that question so the technique I think can't

actually answer that question because it's going to be a resolution issue and I think depending on the different system it's either going to be the same

electron because the electron it's moving in something called the lumo the lowest unoccupied orbital because

electron you know path of least resistance so it's hopping into the the lowest space and so the same electron is

moving because usually it's that one the idea is that the one electron has all this energy and so it's hopping it's

starting out it has been sent a bunch of energy and then you design it so that the bridge is lower is an easier path

for the electron than otherwise so it's usually the same electron that is just kind of bouncing around trying to find its lowest energy

place but I think like if you go into solid state materials they tend to think of it as like you know a phononic mode

of electrons bouncing against each other and things like

that yeah what made you decide to become a

scientist oh um I've always liked science and a lot

of stuff it's really fun but I had an internship as an engineer after my first

year of college and I hated it so much I changed my major I just yeah I worked in

a plant all summer and I just oh felt like I was selling happiness so like selling my soul

selling happiness for money I don't know how to phrase that and so I changed and a chemistry major and then at the end of

college I just really thought science was interesting thought I'd go see what grad school was

about thought it was

fun you me understand how you capture the data on the back end of these things

when you have ftoc resololution like what's the yeah what's the data

capture look that's coming out of this process so the data capture so it's ftoc

resolution but you measure the same step many many times and so the detectors only need to run out at like you know

per second or something like or per microsc something much much slower than that and so there's kind of three main

ways that you detect this this is a good slide to be on for that so you can either have transition mode which is

what I have documented here you just measure before and you put literally a CCD camera like a literal regular camera

that can detect afterwards or just a photo diode that's counting the number of

uh photons that are hitting it so that's one way the measurement that I actually have here is something called total

electron yield mode and so this is you grind up your sample into a powder and

put it onto conductive tape it's carbon tape that's sticky and you stick that onto a piece of uh copper something very

conductive and then you literally just pretty much attach a voltmeter and through the photoelectric effect a

photon hits this you create this electron and you measure the drain current that's just bleeding out of it

and that's called total electron yield mode so that's two different ways we can measure this the Third Way is

fluorescence so when shine a piece of light on it and generate this electron

that electron eventually loses its energy and if it loses it back to where it was it'll emit a characteristic uh

Photon and then you can put a photo out in front of it and so that's for when you have like a really cloudy sample or a solid or something like this so the

main three ways to detect it but luckily sample readout isn't a problem but that confused me so much when I started grad

school because I was like to seconds and what like our camera is reading out at half a second so yeah it's that you

do the same measurement many many times and then just by separating the distance

the the laser goes that gives you the ftoc resolution thank you can can I expand on

that question yeah please do how do you know how long it is between when the two laser pulses

hit uh so that is a really fun thing so you essentially measure something called

time zero and so it's a little bit harder in the X-ray but if you have two

Optical lasers you send one through a nonlinear material so you send an a

laser going this way you overlap another laser going this way and then you change the distance like a delay stage just add

a leg or something like that and through this material you actually will have it add photons together and it'll change

the momentum which is the angle so you have a crystal one laser goes this way one laser goes this way and when you

have time zero when they arrive at the same time a third laser comes out at an angle in between those and you stick a

white piece of paper behind your Crystal and you stare at it and stare at it and stare at it until you see a blue blip

and then you yell at your labmate go back go back go back and then you realign it and you just kind of manually move those so that calls time zero and

then again all light travels at about the same speed and especially the same speed

in a vacuum so literally by changing the distance of the path of the laser you're

changing the amount of time it takes to get there we literally we can literally have tape measures that will have like

millimeters on one side and Picoseconds on the other side and you can measure the distance because electron or light

moves at the same speed it's very fun it's very pretty please you have the next

question um I have two questions so the first is

um why do you only um push the electron from the innermost to the veence shell

and not just directly out of the at um so it's the type of measurement

I'm doing there's actually both kinds so you can have

um scattering so okay this is an absorption measurement so we are literally looking for that transition so

we're scanning standing across all these energies and seeing where it is because we're trying to identify the energy of

that veence band that's one of the things we're looking for so if you have a measurement where it kicks it out

that's going to be a lot of the scattering techniques which isn't what I do but basically they kick out that electron and then they track that

electron hitting other atoms and bouncing around and they see the energy of the electron after it's hit a bunch

of things so that is also an incredibly important technique uh um and then the

second is I know you showed a lot of the bridges where like nitrogen B because um

It's relatively versatile like carbon is there any other element that could achieve the same effect or that you've

experimented with so I haven't looked at a lot of uh other Bridges just because we're working on this nitrogen technique

but yes it's a huge field you actually have people who are even using like carbon Nanotubes or something like that

or yeah lots of different kinds of bridges um couple of the ones I show actually

have like zinc and carbons and stuff like that so there's so many different kinds of bridges and there's it's a huge

field of research uh let's see Fluorine and sulfur shows up a lot thank

you the

back um what what if you switched to heavy hydrogen duum would you expect any

new phenomenon from that I don't think I know what a heavy

hydrogen material is duum oh dyum yes you would expect a change from

that so if you do duum instead of water you're going to again be changing the

electron orbitals um I don't think I have a more specific

answer than that yeah it's duum in the um hydrogen generation process you want

to generate D2 instead of H2

it's just there's a lot more hydrogen so yeah there's a lot more hydrogen so duum and heavy atoms are really important

actually for this entire field of research and that is because this is chemistry so if it's hydrogen Evolution

you can deuterate your solvent the other parts of the Catalyst and you can actually use that to find out where did

the hydrogen that I'm using to do this reaction where did it come from am I harvesting hydrogen from the solvent is

it from like electron donor is it being ripped off of the like glass container

I'm making the experiment in you can deuterate various things and really track those to see what is contributing

the important part to the chemistry but for cars um we we just

don't it's expensive to collect enough dyum to power a car so you better do it

with ordinary hydrogen yeah plus slack narium is a big no no substance okay you

get a bunch of are really mean emails if they think you've lost a bottle of dyum it's very confusing especially if you

haven't lost a bottle of duum and you don't know what they're talking about okay um let's take two more questions

who has them uh

please so you mentioned uh lcs2 is that the right um and I think

there are two orders of magnitude higher Fidelity measurements that comes with that what what does that mean for your

experiments what are you going to be able to see uh that's going to be amazing for these experiments because

the sample right now we have to do it in water the reason you have to do this delivery in water to look at nitrogen is

because carbon absorbs at 250 EV and like that gentleman asked about there is

a shelf you're going to ionize your all of your solvent so it's going to make massive background and so uh if you have

a carbon solvent there's currently too big a background for you to be able to see your sample once you have these this

huge order of magnitude Improvement in your signal to noise you're going to be able to expand this experiment to

different solvents which is what it was designed for and you're going to be able to still have great signal to noise in

that and you're also of course going to be able to reduce the sample as we did this experiment at 100 Millar which

means that it's basically sludge and jetting sludge is like a huge problem I broke several pumps and probably made

enemies so yeah it's going to be really amazing said the inst was designed for the upgrade so it started receiving that

light maybe November and so they're really excited I think the first experiment is this February with the

upgraded light source so it's worth saying a little about this it's not that

the light is going to be a million times brighter it's that

you're going to have a million times more pulses per second of about the same size so the way that's achieved is by

using a different kind of accelerator than they're using now at slack the old

slack is based on a 1960s basically version copper accelerator they've just

cleared out a third of the tunnel at slack and put in an accelerator based on

superconductivity so you can bring that down to uh a degree or two above absolute zero and then this material is

um just it maintains High field and you don't lose power and you can shoot it

much more often and the idea is to shoot at a million pulses a second instead of

120 pulses a second for the ordinary slack and so um each each pulse can give

you data and so it's just G to be much more powerful it's gonna be amazing

we're gonna go from collecting something like a terabyte of data every few minutes to a terabyte of data per second

and yeah uh yeah I think there's a lot of concerns about how are we even going to

store that data and then I think we don't know how to do it right now and so like one example is there's someone

working on machine learning to look at all the pulses in real time and just be like never mind that's not real don't

even store that that's not real data well you know what I'm a particle physicist and we deal with this at the LHC already so yeah um in principle we

know how to do it and it's just bringing those techniques to this field uh which we hope is ready for it another really

cool thing about the upgrade that I'm excited about is uh x-ray sources like this these XLS the X-ray free electron

lasers there's six of them in the world they have this problem that that's called J and that's because this source

is so stochastic that your X-ray it's might not arrive exactly where you clock time zero it's going to be time zero

plus or minus a Picosecond and that Picosecond can be very frustrating if

you're looking for like a one PC Dynamic so you actually have to have a separate entire experiment that has to happen

during yours where you just clock when did the erex arrive and then you have to do a bunch of complicated math to like

Resort all of your data and something about super cooling the accelerator I understand I keep asking people is

something about this it's going to have significantly less Jitter something on the order of 20 ftto seconds rather than

900 ftto seconds and so that's going to simplify data processing and simplified

data collection for in time because again these are kind of high stress experiments where it's like 5 a and you

have a 12-hour shift and you're just like ah make this Choice make this Choice do we move the time or not so

it's I'm really excited about that it sounds cool okay anyone want to ask the last

[Music]

question please I may have missed this but I was

wondering how do you actually build the bridge is it just a solvent and you spr the lasers through them or can you

explain that a bit more how do you build the bridge so that's going to be a synthetic chemist and so uh these Bridge

so I have the molecule up here now so you basically take parts of the

bridge and then you sometimes expose them to light and it causes bonds to form I'm not a synthetic chemist I don't

know how to explain this well really impressive people mix things

together in weird temperatures with weird gasses and

great final question in your organic chemistry course in college you get um much

simpler problems like that assembling different bonds to get what you want but the complicated ones it's just black

magic yeah and it's really impressive people have gotten the Nobel Prize for

uh introducing new kinds of black magic that enable you to do previously inaccessible syntheses and so now we're

profiting from all of that to actually get these bridges in the first place yeah and that's actually one of the

coolest things about these donor Bridge acceptor applications is for this uh the area of photochemistry so literally

using light as a reagent in your chemical reaction is a booming field right now in the last 10 years there's

started to be lots of Publications on it and pharmaceutical companies actually doing photochemistry as like inline

industrial processes basically uh light can be a very targeted reagent so it can

do something like helping you with the handedness of a molecule so handedness is called chirality in chemistry and so

that's going to be take an orange and a lemon the thing you're smelling literally the same molecule just

different handedness they're mirror reflections of each other and another example of that is a lot of medicines

are amazing and if you have the wrong handedness that turns the wrong way that's actually going to be a poison there's something called the thalidomide

Scandal where in France in the seven 7s maybe the 80s a bunch of pregnant women

huh 60s great so okay y'all know about the fomite Scandal for those of you who

don't basically one-handedness of the molecule is a treatment for morning

sickness and so a lot of French women were given this to treat morning sickness and it caused the other

handedness of the molecule causes extreme birth defects and so there's a generation of the lamide babies who are

born with these extreme birth defects and plug for women's scientists uh was in and it was approved throughout Europe

but the FDA it was not approved for use in America which is why a lot of Americans don't know about it and it was

a single woman at the FDA who had a chemistry background and was like the research on this is not good this we

should not be giving this to pregnant women and she had a lot of political pressure from her boss and a like bosses

being like no no just pass it it's fine everyone else said it's fine and so just an example of one person thinking

something through carefully can really change and yeah got to be very conscientious and careful in science but

uh point of that story was that light can be a very targeted reagent and so it can help you synthesize just one-h

handedness of a molecule rather than the others just because those are going to be slightly slightly different energies and so maybe synthesizing at 455

nanometer versus 465 nanometer light which is both blue but it'll have a slight difference in the outcome of that

reaction thank you well let's thank Liz again this has been

very okay um I apologize that uh this

Auditorium is going to go out of commission during March so we will not have the traditional March public

lecture but we will have one at the end of May it'll be pretty fascinating and every two months we'll bring up another

one of these if you want to get on our mailing list uh go to the slack website look for public lectures and there will

be a way to get on the mailing list for these events and we hope to see you in May and in the future so thanks to you

all for coming and I hope you've had a good

time

 

SLAC National Accelerator Laboratory