S1  

Supporting Information for

Uniform doping of metal oxide nanowires using solid state diffusion Joaquin Resasco1, Neil P. Dasgupta2,3, Josep Roque Rosell4, Jinghua Guo4, and Peidong Yang2,5*

1Department of Chemical Engineering and 2Department of Chemistry, University of California, Berkeley, California 94720, United States. 3Department of Mechanical Engineering, University of Michigan, Ann Arbor, Michigan 48109, United States. Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States. 5Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States

Table S1. EXAFS Curve Fitting Parameters Path R(Å) N σ2(Å2) ΔE0(eV) S0 Rf (%) Mn-O 2.03 4 .00386 2.6576 0.8607

1.6

Mn-O 2.15 2 .00428 Mn-Ti 3.30 4 .0104 Mn-Ti 3.79 4 .0127 The coordination number N was taken to be fixed for the crystalline material. S0 and ΔE0 were fit to the same value for all paths as they are properties of the central atom. X-Ray Photoelectron Spectroscopy Sample Source Δ2p1/2 (eV) Δ3s (eV)

MnO This work Ref S1 Ref S2

6.0 6.0 5.4

6.1 6.0 6.1

Mn2O3 This work Ref S1 Ref S2

10.1 10.0 10.5

5.2 5.1 5.4

MnO2 This work Ref S1 Ref S2

12.0 11.8 11.9

4.7 4.5 4.5

As deposited 10.75 5.3 Annealed 6.2 6.0

 

Figure Sdiisopropreflects th

Figure S2of numbecycle of Mwas obse

1: XPS survpylacetamidihe thermal s

2: (A) Thicker of cyclesMnOx ALD

erved after 1

vey spectra inate) followstability of th

kness of MnOs. A linear g

films under.0 s.

of MnOx ALwing a 60 she amidinate

Ox ALD filmgrowth rate or increasing p

S2

LD films deec Ar sputt

e precursor.

ms measuredof ~1.0 Å/cpulse time o

eposited usinter. The lack

d by TEM anycle was ob

of the Mn am

ng the Mangk of carbon

nd ellipsomebserved. (B) midinate prec

ganese bis(Nin the spec

etry as a funGrowth rat

cursor. Satur

N,N’-ctrum

nction te per ration

 

Figure Sconformascan of cwire and

Figure S4unchange

3: (A) TEMal coating. Score-shell nathe Ti in the

4: XPS speced before an

M image of Scale bar is 2anowire aftere core. Scale

ctra of the Tnd after the c

a core-shell20 nm. (B,C)r 200 cycles

e bar is 100 n

Ti 2p region,onversion pr

S3

l TiO2|MnO) STEM mos showing conm.

, showing throcess.

x nanowire de EDS maponfinement

he binding e

after 100 cypping and coof the Mn t

energy and p

ycles, showorrespondingo the shell o

peak structur

wing a

g line of the

re are

 

Figure Sdiameter dopant. C

Figure S6

5: EDS line(A) and len

Correspondin

6: (A,B) STE

e scans of Mngth (B) of ng elemental

EM mode el

Mn:TiO2 nanothe wire, inl maps are sh

lemental map

S4

owires showndicating thehown in Figu

ps of Ti and

wing the Mne homogeneogure 1f and 1

Zr in conve

n:Ti intensityous incorpog.

erted wire.

y ratio acrosration of the

ss the e Mn

 

Calculat

Figure S7of ALD f

tion of Expe

7: Measuredfilm thickne

ected Mn Co

d and calculass.

oncentratio

ated atomic c

S5

n

concentratio

on of Mn in cconverted wwires as a fun

nction

 

Ternary

Figure StemperatuMnTiO3.

Figure S9form axiarates of M

y MnTiO3 Ph

S8: X-Ray ures. The te

9: (A,B) TEMal segments Mn2+ along c

hase Forma

Diffraction ernary phase

M images ofof pure MnT

c-axis. EDS

ation

patterns foe MnTiO3 is

f nanowires TiO3 and TiOconfirms rel

S6

or convertedformed at

converted atO2. Axial seglative stoichi

d wire sam1050°C. * i

t 1050°C. Ngmentation iiometry of M

mples at difindicates dif

anowires phis likely due Mn and Ti in

fferent anneffraction line

hase segregatto high diffu

n segments.

ealing es for

te to fusion

 

Figure Sbetween respectivwhich caedge disl

10: (A,B) HRMnTiO3 and

vely. (F) Moian form due tlocations are

RTEM imagd TiO2. (C-Eiré image shto the simila

e observed at

ges of nanowE) FFTs of Ti

ows epitaxiaarity of the ot the interfac

S7

wires convertiO2 section, al interface bxygen subla

ce.

ted at 1050°MnTiO3 sec

between Mnattice in the t

C, showing ction, and intnTiO3 110antwo structure

the interfaceterface nd TiO2 001es. However

e

1

r,

S8  

Transient Diffusion of Mn in TiO2 Nanowires The transient diffusion of Mn in the TiO2 nanowire can be described by Fick’s Second Law:

Where �� is the concentration of Mn and x is the distance from the edge of the nanowire. The solution for diffusion into a finite medium solution can be obtained numerically and is available in for simple geometric shapes in Gurney-Lurie charts. The numerical solution would predict a more rapid conversion than the solution for a semi-infinite medium but otherwise similar diffusion profiles. Therefore as a simple approximation, the nanowire can be considered a semi-infinite medium to yield an analytical solution:

erf2

The surface concentration of Mn (��� can be taken as unity as the nanowire shell is manganese oxide. The initial concentration of Mn in the nanowire (�� ) is zero. From single crystal studies the diffusion coefficients of various transition metals in rutile TiO2 at different partial pressures of oxygen are known.3 The diffusion coefficients of interest here are those orthogonal to the c-axis, which are lower than those parallel to the c-axis. The diffusion coefficients were also measured to be substantially higher at low partial pressures of oxygen. The diffusion coefficient of Mn in TiO2

is quite high: 1.1*10-10 cm2/s at 900°C in air. As the diffusion distance is quite small as the nanowire diameter is ~100 nm, the nanowires readily become fully converted at high temperature.

To observe the transient diffusion behavior the conversion process was investigated at lower temperatures. The expected distribution of Mn for the semi-infinite medium solution at T=600°C is shown in Figure S11, assuming a diffusion coefficient of 2.7*10-12 cm2/s for Mn diffusion orthogonal to the c-axis in an Ar environment. STEM elemental maps for incomplete conversion for different conversion times are shown in Figure S12. We see that at elevated temperatures the conversion is very rapid, and that the expected diffusion profiles are reproduced by the experimental data.

 

Figure Sin an Ar becomes

Figure S0, 1, 10,

11: Mn distrenvironmenfully conver

12: (A-D) STand 100 min

ributions in tt. The nanowrted in a rela

TEM mode En of conversi

the TiO2 nanwire is assumatively short

EDS elemenion at 600°C

S9

nowire as a fumed to be a s

conversion

ntal maps forC in Ar.

function of tisemi-infinitetime.

r transient co

ime for conve medium. T

onversion of

version at 60The nanowire

f nanowire a

00°C e

after

 

Mechani From sinsuggestedalong opeTi ions. DcrystalloginterstitiaHoweverthe c-axidriven byThe largechanges ipartial prdefect coFigure S

Figure Sin the 2p oxidation

ism for Diff

ngle crystal sd to be depeen channels Divalent iongraphic direcally. Both mr, in this systs. Thereforey Mn atoms er diffusion cin point deferessure of oxoncentration 13, however

13: (A,B) XPregion and t

n state.

fusion Proce

studies on mendent on theparallel to ths therefore hctions. Trivaechanisms atem, the con it is likely tdissolving scoefficients ect concentraxygen. In airand Mn is n

r, the mechan

PS spectra othe 3s multip

ess

etal ion diffue charge stathe c-axis andhave a large alent and tetrare importantncentration grthat the diffuubstitutionalobserved foations, name, the diffusio

not reduced tnism for diff

of the Mn 2pplet peak spl

S10

usion in rutile of the ion. d are pushedanisotropy iravalent ionst for mixed-vradient exist

usion of Mn lly and diffur conversion

ely oxygen von coefficiento the Mn2+ ofusion is like

and 3s regiolitting. The v

le TiO2, the Divalent im

d into substitin diffusion cs dissolve suvalent impurts in the radifrom the she

using throughn in an Ar envacancies andnts are reducoxidation staely unchange

ons, indicativalues are co

mechanism mpurity ions tutional Ti sicoefficient fubstitutionallrity ions sucial direction,ell into the wh an interstitnvironment ad interstitial

ced due to thate as showned.

ing the satellonsistent wit

of diffusiondiffuse rapidites by inters

for different ly and diffus

ch as Mn. , orthogonal

wire core is tial mechaniare a result o Ti atoms, w

he smaller pon in XPS in

lite peak distth a Mn3+

n is dly stitial

se

to

ism.3 of with oint

tance

S11  

References: S1. Gorlin, Y.; Jaramillo, T. J. Am. Chem. Soc. 2010, 132, 13612.

S2. Dicastro, V.; Polzonetti, G. J. Electron Spectrosc. Relat. Phenom. 1989, 48, 117.

S3. Sasaki, J.; Peterson, N.; Hoshino, K. J. Phys. Chem. Solids 1985, 46, 1267.