Nanoscale manipulation of Ge nanowires by ion hammering

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Title I Nanoscale Manipulation of Ge Nanowire by ion hammering

Author(s) I S Thomas Picraux LANL SG Choi NREL Golden CO Lucia Romano UF Gainesville Nicholas G Rudawski UF Gainesville Monta R Holworth UF Gainesville Kevin S Jones UF Gainesville

Intended for I Nature Nanotechnology

pLosAlamos NATIONAL LABORATORY --- EST1943 --shy

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Nanoscale manipulation of Ge nanowires by ion hammering

Lucia Romano Nicholas G Rudawski Monta R Holzworth and Kevin S Jones

Department of Materials Science and Engineering University ofFlorida Gainesville FL 32611

USA

S G Choi2 and S T Picraux

Center for Integrated Nanotechnologies Los Alamos National Laboratory Los Alamos NM 87545

USA

1 Present address Departement of Physics and Astronomy University of Catania Italy

2 Present address National Renewable Energy Laboratory Golden CO 80401 USA

corresponding author

Correspondence and requests for materials should be addressed to LR luciaromano(iljcLinfnit KJ kjones(liengufledu TP picrauxlanlgov

Nanoscale manipulation of Ge nanowires by ion hammering by lRomano

1

Nanowires generated considerable interest as nanoscale interconnects and as active

components of both electronic and electromechanical devices However in many cases

manipulation and modification of nanowires are required to realize their full potential It is

essential for instance to control the orientation and positioning of nanowires in some specific

applications This work demonstrates a simple method to reversibly control the shape and the

orientation of Ge nanowires by using ion beams Initially crystalline nanowires were

partially amorphized by 30 keY Ga+-implantation After amorphization viscous flow and

plastic deformation occurred due to the ion hammering effect causing the nanowires to bend

toward the beam direction The bending was reversed multiple times by ion-implanting the

opposite side of the nanowires resulting in straightening of the nanowires and subsequent

bending in the opposite direction This ion hammering effect demonstrates the detailed

manipulation of nanoscale structures is possible through the use of ion irradiation

Crystalline Si and Ge nanowires (NWs) can be grown by vapor-liquid-solid (VLS) epitaxy

with Au catalyst nanoparticles (see Figure la-b) resulting in pillars with nanometer-scale diameters

and high aspect ratios [I] The NWs exhibit exceptional mechanical and electrical properties that

are attractive for a variety of applications [2-7] However manipulation and modification ofNWs is

required for many applications It is highly desirable to be able to manipulate the orientation of

either individual NWs or an entire surface covered with NWs This work investigates the

application of ion beam processing as a new method of controllably and reversibly manipulating the

orientation of a nanowire after it has been grown

The damage from ion irradiation is usually an undesirable phenomenon unless one is

preamorphizing a material like Si prior to doping[8] One might expect that irradiation should have

the same detrimental effects on nanosystems as on bulk solids But recent experiments on electron

or ion irradiation of various nanostructures demonstrate that it can have beneficial effects as well

and these results suggest that electron or ion beams may be used to tailor the structure and

properties ofnanosystems with high precision [9] These studies suggest that ion hammering may

be used to alter surfaces However no demonstrated effect of ion hammering on NWs has been

reported

When an energetic ion penetrates into a solid it loses energy mainly via two independent

processes with the relative magnitude of each process related to the ion velocity i) nuclear energy

loss (Sn) which dominates at low energy and results from a direct transfer of kinetic energy to the

target nuclei (elastic collisions) and ii) electronic energy loss (Se) which prevails at high energy and

Nanoscale manipulation of Ge nanowires by ion hammering by LRomano

2

results from electronic excitation andor ionization of the target atoms (inelastic collisions) [10] It

has been shown that energetic ion bombardment of amorphous thin films results in unsaturable

plastic flow in the form of anisotropic deformation at negligible density change In this case the ion

beam induces ~ompressive (tensile) deformation parallel (perpendicular) to the beam direction for

sufficiently high Se ( 1 keYom) and sufficiently low target temperatures [11] This is known as

the ion hammering effect This phenomenon has been found to occur only in amorphous material

systems including metallic ceramic and polymer glasses thus indicating that it is universal for the

amorphous state [12 13] No deformation occurs in materials that remain crystalline during ion

bombardment The ion-irradiation-induced deformation of amorphous solids has been explained in

terms of a viscoelastic thermal spike model [14] In this model the deformation is attributed to the

high degree of anisotropy of the ion-induced thermal spike For high values of Se a cylindrical

region around the ion track is heated Shear stresses generated by the thermal expansion of the

highly anisotropic heated region then relax resulting in a local in-plane expansion perpendicular to

the ion track which freezes in upon cooling of the thermal spike The macroscopic anisotropic

deformation is thus the result of a large number of individual ion impacts High energy irradiation

experiments indicated an apparent threshold of Se - 1 keVnm below which no deformation would

be expected [15] although Van Dillen et al [16] demonstrated that ion-irradiation at energies as low

as 300 keY (Se - 04 keVnm) can cause dramatic anisotropic plastic deformation in colloidal Si02

particles Since the plastic deformation is maximized when the specimen thickness is much less

than the ion projected range this phenomenon has been observed primarily with high energy (Me V)

ion irradiation in bulk samples There have been no previous reports to our knowledge of the ion

hammering effect in this electronic-energy loss regime below Se = 04 keVnm The present results

(Se - 01 keVnm for 30 keY Ga ions implantation in Ge) indicate that ion hammering is operative

in this low energy regime and thus may playa significant role in altering the structure of nanoscale

materials

The ion hammering effect was observed during Ga+-irradiation ofGe NWs at 30 keY (Seshy

01 keYom) with the beam incident at 45deg relative to the elongated direction of the NWs Figure 2

presents a series of scanning electron microscopy (SEM) images of the gradual and ultimately

spectacular bending of the Ge NWs from Ga+-irradiation to difference doses (Q) in a specific beam

direction (left or right) With the Ga + beam incident from the right with Q= 34x 1013 cm-2 the

NWs initially start to bend slightly towards left as shown in Figure 2b After an ion dose of Q=

15xl014 cm-2 the NWs are almost vertical (see Figure 2c-d) and tending to bend towards the right

(beam direction) The gradual bending towards the beam direction is clearly evident in Figures 2d

and 2e after Q = 31 X 1014 and 61 x1014 cm-2 respectively The deformation is stable The different


3

bending of crystalline and amorphous NWs is summarized schematically in Figure ld-e After

irradiation to Q= 6x 10 14 cm-2 from the right the beam direction was reversed in order to impinge

from the left as indicated by the arrows in Figures 2f - j which correspond to additional doses ofQ 2

= 27x 10 13 - 38x 1014 cm- bull A spectacular reversal of the bending is observed with the NWs

bending towards the beam direction Once again reorienting the beam to impinge from the right

the NWs were once again observed to bend towards the beam as shown in Figures 2k - 0

2corresponding to Q= 30x 10 13 - 80xI014 cm- bull A decrease in NW diameter due to sputtering was

observed for doses greater than 3xl015 cm-2 for the Ga beam perpendicular to the NWs while for the

NWs aligned parallel to the beam direction much higher doses were possible without observable

loss of Ge Thus the NW shape can be manipulated numerous times by the ion hammering effect

without sputtering limitations and is estimated to survive at least twice the 3 cycles demonstrated

above

Ion beam-induced bending effects have been reported for C nanotubes having diameters of a

few to several hundred nanometers [17 18] and for ShN4membranes [19] Park et at [17] have

discussed mechanisms involving dipole-to-field interaction but have concluded that the electric

fields generated are too low to cause the bending Tripathi et at [18] proposed a model to explain

the bending phenomenon which is based on irradiation induced temperature rise and the

temperature gradient produced along the length and breadth of the structure However this model

assumes the material has a negative thermal expansion coefficient whereas Ge has been shown to

have a positive coefficient over a broad temperature range [20] Thus this proposed explanation for

ion bombardment-induced bending ofnanotubes cannot explain the present observations

The amorphization process of the Ge NWs is presented in Figure 3 Figures 3a - c present

SEM and transmission electron microscopy (TEM) images of an as-grown NW indicating a single

crystal of Ge with a diameter of 50 nm and the lt IIIgt axis oriented along the wire direction Partial 2amorphization of the NW was observed after an implanted dose ofQ = 35x 10 13 cm- which was

responsible for the initial bending of the NW away from the beam direction as shown in Figure 3d

Ge is known to exhibit -10 expansion upon amorphization [21] and thus expansion of the

amorphized side is constrained by the crystalline side causing the nanowire initially to bend away

from the beam SEM and TEM imaging indicated that bending looks more accentuated near the top

of the NW this is due to the base being constrained by the substrate Low- and high-resolution

TEM images shown in Figures 3e and 3findicated uniform implantation along one side of the

NW and amorphization of approximately two-thirds of the structure thus indicating that

amorphization proceeds from the beam-exposed side of the implanted NW It should be noted that

NWs are three dimensional structures that can be approximated as a cylinder Therefore the


4

surface exposed to the ion beam is curved and the beam incidence becomes more grazing moving

from the center of the NW towards the side Consequently the implanted ions have a cylindrical

distribution The distribution of 30 ke V Ga + ions implanted at 0deg (45deg) tilt into a planar Ge substrate

covered with 5 nm Ge02 (as observed in Figure3) has a projected range and longitudinal range

straggling of - 18 (14) and 9 (8) nm respectively as calculated by SRIM simulations [22] Thus

simulations predict an amorphous layer -25 nm thick However since TEM analysis is averaged

over the whole NW thickness the measured depth is larger than the SRIM value Ultimately the

NWs were completely amorphized after Q - 10x 1014 cm-2(not shown) in agreement with the

reported bulk Ge amorphization threshold dose by Si+-implantation at 40 keY [23]

Once completely amorphized the NWs exhibit gradual bending towards the ion beam

direction This behavior is analogous to a strip of metal laying on a hard surface bending upward

when struck in the middle by a hammer Moreover this deformation was reversible as NWs bent

towards the right subjected to additional irradiation from the left bend back towards the left Figure

4 shows SEM images of a bending NW at the extreme points of deformation Additionally several

SEM images at different tilt and rotation angles were collected in order to identify the threeshy

dimensional movement of the NWs during bending (not presented) Comparing the three different

extremes presented in Figures 4b - d it was revealed that almost all of the bending occurs directly

toward the ion beam There are however small differences in the NW length (between 10 and 20

) observed between each extreme due to a small amount of torsion that can be caused by a slight

misalignment of the FIB stage after each irradiation step (see methods for details) this effect has

been assumed to negligibly impact the bending process

After the NWs were amorphized by ion-irradiation viscous flow and plastic deformation

occurred during implantation due to the ion hammering effect [24 25] The time (ion dose)

dependence of this bending can be used to infer the local stress based on a viscoelastic thermal

spike model [13] The NW shown in Figure 4 was discretized along the length in order to measure

the progressive bending as a function of the ion beam dose A schematic of the bending of a single

NW is shown in Figure 5a with the Xs and Zs axes corresponding to the substrate normal and inshy

plane directions as viewed two-dimensionally with the ion beam direction B always incident on the

substrate at 45deg with the origin located at the base of the wire Thus B = lt-1 -1gt in vector

notation The shift of each section of the NW has been measured assuming a negligible variation

along the perpendicular direction to the Xs-Zs plane Thus zs(xs) is the displacement of the wire from

the unbent state at position Xs For the NW it is useful to define Xw and Zw as the local Cartesian

axes parallel and perpendicular to the irradiated side of the wire Thus in the unbent state Xs and Zs

are identical to Xw and Zw


5

Since the ion beam and bent NW always remain in the Xs-Zs plane and boundary conditions

require the exposed surface of the wire to be traction-free [26-28] a localized internal normal stress

axxw along Xw in the wire will be generated which causes the deformation and bending of the wires

In the case of a flat planar surface being irradiated with the ion-beam incident at an angle of () the

generated in-plane stress along the direction coinciding with the surface projection of the ion-beam

will eventually reach a steady-state value of -3A17lt1gt2(cos2laquo())- sin2laquo()raquo where A is the deformation

yield 17 is the viscosity of the amorphous substrate and lt1gt is the ion flux The stress is considered

steady-state because the plastic flow behavior of the substrate is not changing with time though

plastic flow is occurring This also corresponds to macroscopic deformation of the substrate not

changing with time For the case of amorphous Ge under the presented irradiation conditions 17

-2x1013 Pa-s [2930] and lt1gt = 43x1012 cm-2s-1with A further defined as [26]

A = 0427(~) aSe (1)

5-4v pCp

where v = 028 is the Poisons ratio [31] a = 79x 10-6 Kl is the thermal expansion coefficient [30]

Se = 012 keVnm assuming all energy lost is converted to heat [30] p = 532 gcm3 is the density

[31] and cp = 04 JgK is the heat capacity of amorphous Ge [32] Thus assuming Eq (1) can be

extrapolated down to very low implant energies laquolt -05 GeV) A = 10x10-2nm2 for Ga+shy

implantation at 30 keY into amorphous Ge

For the case of the NWs presented here it is therefore predicted that axxw under steady-state

conditions (wire curvature not changing with time) will be given by

CTXXw = - A 77lt1gt(cos 2 (OJ - sin 2 (OJ) (2)

where () is assumed to be constant over the whole wire and only the bottom half portion of the NW

was used for stress analysis since any imaging misalignment will produce less deviation from the

actual bending behavior than if the whole NW was used The time-dependent nature ofaxxw

a(t)xxw generated in the NW is given by

c-E - (3)a(tLw - ret)

where E = 86 GPa is the Youngs modulus of amorphous Ge [30] c = 25 nm is the wire halfshy

thickness and r(t) is the local radius of curvature of the NW as a function of time t It is evident

from Figures 2 and 4 that () is variable with time due to bending though the lower portion of the

NWs is roughly linear such that () can be reasonably assumed constant over this whole portion of

the wire The measured time- (dose-) dependence ofaxxw [Eq (3)] was compared with the steadyshy

state value [Eq (2)] predicted to result with () at a given value of t (Q) as shown in Figure 5b with

both values considered as averaged over the whole of the lower portion of the NWs and Q Only 29


6

I (L25x 1014 cm2 Q) was considered in this analysis (approximately corresponding to the SEM

images in Figures Ic e) since the NWs were fully amorphized for this regime and the ionshy

hammering effect was homogeneous over the whole wire The error in a()xxw is reflective of the

error in measuring r(1) due to the possibility of minor misalignment during SEM imaging Thus a

10 error in ret) (corresponding to approximately the same relative error in a(1)xx w) was adopted

to sufficiently account for any minor imaging misalignments that may have arisen It appears the

measured stresses are of lower magnitude compared to the predicted steady-state values However

the time- (dose-) dependence of Uxxbullw is similar to the predicted steady-state stress since the

measured stress in the NW increases as the wire continues to bend towards the beam At present

understanding of the evolution of Uxxw in the NWs is not entirely understood but the threeshy

dimensional nature of the NWs and possible though slight misalignment issues during imaging may

have also played a role The much lower magnitude of generated stress compared to steady-state

predictions based on extrapolation of the high energy ion hammering thermal model to this very

low energy regime is noteworthy [26-28] These results demonstrate that the ion hammering effect

is still significant at unanticipatedly [15] low electronic energy loss values (~ 1 keVnm) and thus

relevant for the manipulation of the shape of structures extending into the nanoscale regime

n is evident from Figure 4 that mechanical work is being done on the NWs by the ion beam

The work done on the NW by the ion beam over of the time interval of implantation II I 12 is

given by

12

W = JFbea)t)Vwiret)dt (4) I

where Fbeam (t) is the I-dependent net force acting on the nanowire as generated by the ion beam

and vwire (t) is the I-dependent velocity of the NW measured at the NW center The whole of the

NW was considered for work analysis The nature of Fbeam (I) is dependent on the momentum of an

incoming ion pion = 333x 1020 N-s the time required for an ion to come to rest after impacting the

surface Ires and the number of ions instantaneously absorbed as a function of I Nins() Thus the

force generated on the beam by the impact of a single ion is equal to pion tres with Nins()

approximated as

ltIgt hP(I)(Ozs(t) )NiTA) - ffresl r- w J-- 1 dx (5)

2 0 ax where hp(t) is the projected height of the nanowire as a function of I and w-50 nm is the crossshy

sectional width of the wire Thus Fbeam (I) in vector notation is approximated as


7

- ltIgt hp(ll(OZs(t) )FbeaJt)~ Pion -w f ---1 cUs(-l-l) (6)

2 0 OXs

with typical values of FbeaJt) on the order of~Olx 10-15 N

Numerically computing the integral in Eq (4) for 29S tS 143 s (corresponding to 125x 1014

s QS 6l5x 1014 cm-2 where the NWs have been fully amorphized) produces W= ~ -3 plusmn 1 eV It

should be noted that these values are orders of magnitude lower than the work required to elastically

bend non-irradiated crystalline Si NWs over comparable length scales [33] Therefore our

experiment clearly shows that it is easier to perform mechanical work during ion-irradiation of an

amorphous material compared to the crystalline counterpart due to viscous flow from the ionshy

hammering effect

The ion beam can act like an artists hammer to model the NW shape as desired and thus

loops or springs can be realized by suitably changing the impinging beam location and direction

Using the same procedure it is presumably possible to bend Si NWs (after amorphization) or Si02

NWs However the bending mechanism ofSi NWs as a function of ion dose would show a higher

threshold dose since the amorphization threshold of Si by Ga implantation is higher than Ge

(displacement energy ofSi and Ge are about 15 and 10 eV [34] respectively) Then amorphous Si

NWs would bend with approximately the same dose dependence as the Ge NWs irradiated by

30keV Ga ions since the electronic energy loss Se is of the same order of magnitude for both

materials Moreover silica NWs can bend without the initial step of amorphization since these

NWs can be grown amorphous In this case the capability of directly modifying the NWs shape

may open up vast opportunities for making versatile building blocks for micro- and nanoscale

photonic circuits and components [35] as well as functionalizing photonic glasses on the nanometer

scale

In conclusion the ion hammering effect was observed for low energy ion implantation of

amorphized Ge nanowires Dramatic reversible bending of the wires toward the incident beam

direction was attributed to stresses induced by viscous flow generated from the ion-hammering

effect Such deformation is highly suitable for in situ manipulation of three-dimensional shapes by

focused ion beams Moreover the work produced by the ion beam due to the viscous flow is

significantly lower than the mechanical work necessary to observe similar bending in crystalline

material


8

Methods

Sample preparation

To facilitate the TEM examination the NWs were grown on (111) Si pillars ~ 40~m tall and

~ 2~m in diameter The pillars were prepared by a deep reactive ion etching of a lithographically

patterned Si (111) substrate After forming the pillars the coupons were cleaned with acetone

followed by methanol rinse in order to remove the residual photoresist Even though a small number

of craters were present on the top surface of the pillars flat Si (111) surface regions existing on the

surface which enabled growth of epitaxial Ge NWs on the top of the pillars

Ge NWs were grown epitaxially via the vapor-liquid-solid (VLS) mechanism in a high-vacuum

cold-wall chemical vapor deposition (CYD) system on (111) Si [36] Prior to loading into the CYD

chamber the native oxide on the Si pillars was removed by a dilute hydrofluoric (HF) acid (2 vol

in DI water) dip and acidified Au nanoparticles with the nominal diameter of 50 nm were

dispersed on the coupons The coupons were further outgassed at 200degC inside the CYD chamber

under vacuum (mid 10-8 Torr range) for 5 hours and pre-annealed at 450degC for 10 min immediately

before the growth ofGe NWs The growth ofGe NWs proceeded via a two-step growth where

the growth is initialized at 425degC and subsequently continued at 375degC This procedure is shown to

increase the proportion of vertically aligned Ge NWs while ensuring minimum tapering Ge~

(30 in H2) was used as the process gas with a partial pressure of900 mTorr during the growth

The growth duration was 10 min The Ge NWs grew in the four lt111gt directions with only the

ones grown normal to the surface (ie [111] direction) used in this study

In-situ ion-irradiation

An FEI Strata DB 235 scanning electron microscopefocused ion beam system was used to

perform in-situ ion beam irradiation Electron and ion beams were oriented with an angle of 52deg

between them The stage was rotated in order to vary the ion beam direction with respect to the

NWs The NWs were irradiated at a stage tilt such that the ion beam was incident at 45deg relative to

the vertical of the NWs All irradiations were performed using a 30 keY Ga+ beam with a square

scanning pattern of 38x38 um2 current of 10 pA (corresponding to an ion of flux 3x 10 12 ions cm-2

S-I) dwell time of 01 ~s and beam spot size of30 nm Thus the dose received depended on the

time of exposure and ion beam incidence angle After each irradiation step the stage was tilted and

rotated 52deg and 90deg respectively in order to take SEM images of the NWs perpendicular to the

beam direction

9


Structural characterization

Transmission electron microscopy was used to characterize the structure of the NWs in the

as-grown condition and after ion irradiation The samples were imaged on a JEOL 2010F

transmission electron microscope using on-axis multi-beam imaging conditions The pillar was

attached to an in-situ micromanipulator by selective ion beam Pt deposition and lifted out from the

parent material taking care to avoid any ion beam irradiation of the pillar top in order to protect the

NWs The free pillar was then attached to a special Cu grid and loaded into the microscope for

imaging


10

Acknowledgements

The authors acknowledge the Major Analytical Instrumentation Center at the University of

Florida for use of the transmission electron microscope and focused ion beam facilities and

Clarence Tracy at Arizona Institute ofNanoelectronics (Arizona State University Tempe) for his

work on patterning substrates This work was performed in part at the Center for Integrated

Nanotechnologies a US Department of Energy Office of Basic Energy Sciences user facility at

its Los Alamos National Laboratory (Contract DE-AC52-06NA25396) site


11

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13

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14

Figure Legends

Figure 1 Illustration of the effects of ion implantation on nanowires a) VLS growth ofGe

nanowires on (Ill) Si b c) as-grown nanowires with diameters -50 run d) after low dose 30 keY

Ga+ implantation at 45deg (Rp - 20 run) which amorphizes part of the wire (slight bend away due to

lower density of amorphous Ge) and e) ion hammering effect dominates as dose increases causing

the nanowire to bend toward the ion beam

Figure 2 SEM images of three ion irradiation sequences showing reversible bending ofGe

nanowires epitaxially grown on (111) Si during Ga+-irradiation at 30 keY incident at 45deg with

respect to the vertical ofthe nanowires Ion beam incident from the right with Q = a) 0 (as-grown

non-irradiated) b) 34x1013 c) 15x1014

d) 3l x I014 and e) 6lx1014 cm2 Ion beam subsequently

incident from the left on the resulting nanowires with additional Q = t) 27x 1013 g) lOx 1014

h)

16x 1014 i) 32x 1014

andj) 38x 1014 cm2 Ion beam subsequently incident from the right on the

resulting nanowires with Q = k) 30x 1013 1) 15x 1014 m) 34x 1014

n) 49x 1014 and 0) 80x 1014

cm2

Figure 3 Effect of low dose implantation on the side of the nanowire Before implantation a) SEM

image b) low magnification TEM micrograph c) high resolution TEM micrograph After 30 keY

Ga + implantation at 45deg with respect to the nanowire axis at a dose of Q = 35 X 1013 cm2 d) SEM

image e) low magnification TEM micrograph and t) high resolution TEM micrograph Crystalline

(c) amorphous (n) and oxidized (ox) portions of the nanowires are schematically indicated the ion

beam direction is from the right

Figure 4 SEM images showing the reversibility of bending at three different extremes for a single

Ge nanowire during Ga+-irradation at 30 keY a) an as-grown Ge nanowire b) after irradiation from

the right with a dose of Q 61 x1014 cm2 c) after irradiation from the left with Q = 38x 1014 cm2

and d) after irradiation from the right with Q= 80x 1014 cm2 Each value ofadditional dose Q is

given with respect to a specific beam direction (left or right)

Figure 5 a) Schematic discretization of a bending Ge nanowire depicting the coordinate systems

used for the measurement of internal stresses and mechanical work performed during ionshy

irradiation b) Plot of the measured in-plane compressive stress Oxxw (open circles) generated in

the nanowire as determined from the curvature along the bottom portion of the nanowire shown in


15

Figure 4b as a function of ion dose and irradiation time during the initial irradiation step using Eq

(3) The predicted steady-state values ofUn bullw (solid squares) that would be generated in the

NANOWIRE (corresponding to observed irradiation angles at specific times and doses) as predicted

by Eq (2) are provided for reference


16

O Ge

a) O H b)

O Au

(111)Si -------------

Crystalline nanowires Amorphous nanowires

Figure 15 in Nanoscale manipulation of Ge nanowires by ion hammering by LRomano et al




a) Initial b)

+ Ion dose [x1 014 attcm2]

2 3 4 5 6 I I I I I

10 _ bull Predicted Steady-State 1-

1 shy

QQ bullbullQ Q

Qbull +1 z~~ Q middotmiddotmiddot0middotmiddotmiddot Measured -01 shy Q

I I I I I I

20 40 60 80 100 120 140

time [s]

(111) Si Substrate

r~middotl ~-~--~--bull ~ i

I i bullbull

I +


Nanoscale manipulation of Ge nanowires by ion hammering

Lucia Romano Nicholas G Rudawski Monta R Holzworth and Kevin S Jones

Department of Materials Science and Engineering University ofFlorida Gainesville FL 32611

USA

S G Choi2 and S T Picraux

Center for Integrated Nanotechnologies Los Alamos National Laboratory Los Alamos NM 87545

USA

1 Present address Departement of Physics and Astronomy University of Catania Italy

2 Present address National Renewable Energy Laboratory Golden CO 80401 USA

corresponding author

Correspondence and requests for materials should be addressed to LR luciaromano(iljcLinfnit KJ kjones(liengufledu TP picrauxlanlgov


1




























reported






2

























materials











3












above























4




































5












A = 0427(~) aSe (1)

5-4v pCp






















6



















given by

12








approximated as





7


2 0 OXs








hammering effect













scale







material


8

Methods

Sample preparation





























beam direction

9









imaging


10

Acknowledgements








11

References


Phys Lett 4 89-90 (1964)







889 (2007)



(2004)



3636-3639 (2008)



84326-4329(2008)



872910-2913 (2000)











Res B 65 228-231 (1992)


12





(2000)







205307 (2008)



252184-2187(2007)



Methods Phys B 175 193-196 (2001)






Def Solids 108 131-135 (1989)










J Appl Phys 70 3521-3527 (1991)


13


Appl Phys 74 7154-7161 (1993)







Nano Lett 6 622-625 (2006)





819 (2003)




14

Figure Legends












h)

16x 1014 i) 32x 1014



n) 49x 1014 and 0) 80x 1014

cm2

















15






16

O Ge

a) O H b)

O Au

(111)Si -------------






a) Initial b)


2 3 4 5 6 I I I I I


1 shy

QQ bullbullQ Q


I I I I I I

20 40 60 80 100 120 140

time [s]

(111) Si Substrate


I i bullbull

I +





























reported






2

























materials











3












above























4




































5












A = 0427(~) aSe (1)

5-4v pCp






















6



















given by

12








approximated as





7


2 0 OXs








hammering effect













scale







material


8

Methods

Sample preparation





























beam direction

9









imaging


10

Acknowledgements








11

References


Phys Lett 4 89-90 (1964)







889 (2007)



(2004)



3636-3639 (2008)



84326-4329(2008)



872910-2913 (2000)











Res B 65 228-231 (1992)


12





(2000)







205307 (2008)



252184-2187(2007)



Methods Phys B 175 193-196 (2001)






Def Solids 108 131-135 (1989)










J Appl Phys 70 3521-3527 (1991)


13


Appl Phys 74 7154-7161 (1993)







Nano Lett 6 622-625 (2006)





819 (2003)




14

Figure Legends












h)

16x 1014 i) 32x 1014



n) 49x 1014 and 0) 80x 1014

cm2

















15






16

O Ge

a) O H b)

O Au

(111)Si -------------






a) Initial b)


2 3 4 5 6 I I I I I


1 shy

QQ bullbullQ Q


I I I I I I

20 40 60 80 100 120 140

time [s]

(111) Si Substrate


I i bullbull

I +


























materials











3












above























4




































5












A = 0427(~) aSe (1)

5-4v pCp






















6



















given by

12








approximated as





7


2 0 OXs








hammering effect













scale







material


8

Methods

Sample preparation





























beam direction

9









imaging


10

Acknowledgements








11

References


Phys Lett 4 89-90 (1964)







889 (2007)



(2004)



3636-3639 (2008)



84326-4329(2008)



872910-2913 (2000)











Res B 65 228-231 (1992)


12





(2000)







205307 (2008)



252184-2187(2007)



Methods Phys B 175 193-196 (2001)






Def Solids 108 131-135 (1989)










J Appl Phys 70 3521-3527 (1991)


13


Appl Phys 74 7154-7161 (1993)







Nano Lett 6 622-625 (2006)





819 (2003)




14

Figure Legends












h)

16x 1014 i) 32x 1014



n) 49x 1014 and 0) 80x 1014

cm2

















15






16

O Ge

a) O H b)

O Au

(111)Si -------------






a) Initial b)


2 3 4 5 6 I I I I I


1 shy

QQ bullbullQ Q


I I I I I I

20 40 60 80 100 120 140

time [s]

(111) Si Substrate


I i bullbull

I +













above























4




































5












A = 0427(~) aSe (1)

5-4v pCp






















6



















given by

12








approximated as





7


2 0 OXs








hammering effect













scale







material


8

Methods

Sample preparation





























beam direction

9









imaging


10

Acknowledgements








11

References


Phys Lett 4 89-90 (1964)







889 (2007)



(2004)



3636-3639 (2008)



84326-4329(2008)



872910-2913 (2000)











Res B 65 228-231 (1992)


12





(2000)







205307 (2008)



252184-2187(2007)



Methods Phys B 175 193-196 (2001)






Def Solids 108 131-135 (1989)










J Appl Phys 70 3521-3527 (1991)


13


Appl Phys 74 7154-7161 (1993)







Nano Lett 6 622-625 (2006)





819 (2003)




14

Figure Legends












h)

16x 1014 i) 32x 1014



n) 49x 1014 and 0) 80x 1014

cm2

















15






16

O Ge

a) O H b)

O Au

(111)Si -------------






a) Initial b)


2 3 4 5 6 I I I I I


1 shy

QQ bullbullQ Q


I I I I I I

20 40 60 80 100 120 140

time [s]

(111) Si Substrate


I i bullbull

I +





































5












A = 0427(~) aSe (1)

5-4v pCp






















6



















given by

12








approximated as





7


2 0 OXs








hammering effect













scale







material


8

Methods

Sample preparation





























beam direction

9









imaging


10

Acknowledgements








11

References


Phys Lett 4 89-90 (1964)







889 (2007)



(2004)



3636-3639 (2008)



84326-4329(2008)



872910-2913 (2000)











Res B 65 228-231 (1992)


12





(2000)







205307 (2008)



252184-2187(2007)



Methods Phys B 175 193-196 (2001)






Def Solids 108 131-135 (1989)










J Appl Phys 70 3521-3527 (1991)


13


Appl Phys 74 7154-7161 (1993)







Nano Lett 6 622-625 (2006)





819 (2003)




14

Figure Legends












h)

16x 1014 i) 32x 1014



n) 49x 1014 and 0) 80x 1014

cm2

















15






16

O Ge

a) O H b)

O Au

(111)Si -------------






a) Initial b)


2 3 4 5 6 I I I I I


1 shy

QQ bullbullQ Q


I I I I I I

20 40 60 80 100 120 140

time [s]

(111) Si Substrate


I i bullbull

I +













A = 0427(~) aSe (1)

5-4v pCp






















6



















given by

12








approximated as





7


2 0 OXs








hammering effect













scale







material


8

Methods

Sample preparation





























beam direction

9









imaging


10

Acknowledgements








11

References


Phys Lett 4 89-90 (1964)







889 (2007)



(2004)



3636-3639 (2008)



84326-4329(2008)



872910-2913 (2000)











Res B 65 228-231 (1992)


12





(2000)







205307 (2008)



252184-2187(2007)



Methods Phys B 175 193-196 (2001)






Def Solids 108 131-135 (1989)










J Appl Phys 70 3521-3527 (1991)


13


Appl Phys 74 7154-7161 (1993)







Nano Lett 6 622-625 (2006)





819 (2003)




14

Figure Legends












h)

16x 1014 i) 32x 1014



n) 49x 1014 and 0) 80x 1014

cm2

















15






16

O Ge

a) O H b)

O Au

(111)Si -------------






a) Initial b)


2 3 4 5 6 I I I I I


1 shy

QQ bullbullQ Q


I I I I I I

20 40 60 80 100 120 140

time [s]

(111) Si Substrate


I i bullbull

I +




















given by

12








approximated as





7


2 0 OXs








hammering effect













scale







material


8

Methods

Sample preparation





























beam direction

9









imaging


10

Acknowledgements








11

References


Phys Lett 4 89-90 (1964)







889 (2007)



(2004)



3636-3639 (2008)



84326-4329(2008)



872910-2913 (2000)











Res B 65 228-231 (1992)


12





(2000)







205307 (2008)



252184-2187(2007)



Methods Phys B 175 193-196 (2001)






Def Solids 108 131-135 (1989)










J Appl Phys 70 3521-3527 (1991)


13


Appl Phys 74 7154-7161 (1993)







Nano Lett 6 622-625 (2006)





819 (2003)




14

Figure Legends












h)

16x 1014 i) 32x 1014



n) 49x 1014 and 0) 80x 1014

cm2

















15






16

O Ge

a) O H b)

O Au

(111)Si -------------






a) Initial b)


2 3 4 5 6 I I I I I


1 shy

QQ bullbullQ Q


I I I I I I

20 40 60 80 100 120 140

time [s]

(111) Si Substrate


I i bullbull

I +



2 0 OXs








hammering effect













scale







material


8

Methods

Sample preparation





























beam direction

9









imaging


10

Acknowledgements








11

References


Phys Lett 4 89-90 (1964)







889 (2007)



(2004)



3636-3639 (2008)



84326-4329(2008)



872910-2913 (2000)











Res B 65 228-231 (1992)


12





(2000)







205307 (2008)



252184-2187(2007)



Methods Phys B 175 193-196 (2001)






Def Solids 108 131-135 (1989)










J Appl Phys 70 3521-3527 (1991)


13


Appl Phys 74 7154-7161 (1993)







Nano Lett 6 622-625 (2006)





819 (2003)




14

Figure Legends












h)

16x 1014 i) 32x 1014



n) 49x 1014 and 0) 80x 1014

cm2

















15






16

O Ge

a) O H b)

O Au

(111)Si -------------






a) Initial b)


2 3 4 5 6 I I I I I


1 shy

QQ bullbullQ Q


I I I I I I

20 40 60 80 100 120 140

time [s]

(111) Si Substrate


I i bullbull

I +


Methods

Sample preparation





























beam direction

9









imaging


10

Acknowledgements








11

References


Phys Lett 4 89-90 (1964)







889 (2007)



(2004)



3636-3639 (2008)



84326-4329(2008)



872910-2913 (2000)











Res B 65 228-231 (1992)


12





(2000)







205307 (2008)



252184-2187(2007)



Methods Phys B 175 193-196 (2001)






Def Solids 108 131-135 (1989)










J Appl Phys 70 3521-3527 (1991)


13


Appl Phys 74 7154-7161 (1993)







Nano Lett 6 622-625 (2006)





819 (2003)




14

Figure Legends












h)

16x 1014 i) 32x 1014



n) 49x 1014 and 0) 80x 1014

cm2

















15






16

O Ge

a) O H b)

O Au

(111)Si -------------






a) Initial b)


2 3 4 5 6 I I I I I


1 shy

QQ bullbullQ Q


I I I I I I

20 40 60 80 100 120 140

time [s]

(111) Si Substrate


I i bullbull

I +









imaging


10

Acknowledgements








11

References


Phys Lett 4 89-90 (1964)







889 (2007)



(2004)



3636-3639 (2008)



84326-4329(2008)



872910-2913 (2000)











Res B 65 228-231 (1992)


12





(2000)







205307 (2008)



252184-2187(2007)



Methods Phys B 175 193-196 (2001)






Def Solids 108 131-135 (1989)










J Appl Phys 70 3521-3527 (1991)


13


Appl Phys 74 7154-7161 (1993)







Nano Lett 6 622-625 (2006)





819 (2003)




14

Figure Legends












h)

16x 1014 i) 32x 1014



n) 49x 1014 and 0) 80x 1014

cm2

















15






16

O Ge

a) O H b)

O Au

(111)Si -------------






a) Initial b)


2 3 4 5 6 I I I I I


1 shy

QQ bullbullQ Q


I I I I I I

20 40 60 80 100 120 140

time [s]

(111) Si Substrate


I i bullbull

I +


Acknowledgements








11

References


Phys Lett 4 89-90 (1964)







889 (2007)



(2004)



3636-3639 (2008)



84326-4329(2008)



872910-2913 (2000)











Res B 65 228-231 (1992)


12





(2000)







205307 (2008)



252184-2187(2007)



Methods Phys B 175 193-196 (2001)






Def Solids 108 131-135 (1989)










J Appl Phys 70 3521-3527 (1991)


13


Appl Phys 74 7154-7161 (1993)







Nano Lett 6 622-625 (2006)





819 (2003)




14

Figure Legends












h)

16x 1014 i) 32x 1014



n) 49x 1014 and 0) 80x 1014

cm2

















15






16

O Ge

a) O H b)

O Au

(111)Si -------------






a) Initial b)


2 3 4 5 6 I I I I I


1 shy

QQ bullbullQ Q


I I I I I I

20 40 60 80 100 120 140

time [s]

(111) Si Substrate


I i bullbull

I +


References


Phys Lett 4 89-90 (1964)







889 (2007)



(2004)



3636-3639 (2008)



84326-4329(2008)



872910-2913 (2000)











Res B 65 228-231 (1992)


12





(2000)







205307 (2008)



252184-2187(2007)



Methods Phys B 175 193-196 (2001)






Def Solids 108 131-135 (1989)










J Appl Phys 70 3521-3527 (1991)


13


Appl Phys 74 7154-7161 (1993)







Nano Lett 6 622-625 (2006)





819 (2003)




14

Figure Legends












h)

16x 1014 i) 32x 1014



n) 49x 1014 and 0) 80x 1014

cm2

















15






16

O Ge

a) O H b)

O Au

(111)Si -------------






a) Initial b)


2 3 4 5 6 I I I I I


1 shy

QQ bullbullQ Q


I I I I I I

20 40 60 80 100 120 140

time [s]

(111) Si Substrate


I i bullbull

I +






(2000)







205307 (2008)



252184-2187(2007)



Methods Phys B 175 193-196 (2001)






Def Solids 108 131-135 (1989)










J Appl Phys 70 3521-3527 (1991)


13


Appl Phys 74 7154-7161 (1993)







Nano Lett 6 622-625 (2006)





819 (2003)




14

Figure Legends












h)

16x 1014 i) 32x 1014



n) 49x 1014 and 0) 80x 1014

cm2

















15






16

O Ge

a) O H b)

O Au

(111)Si -------------






a) Initial b)


2 3 4 5 6 I I I I I


1 shy

QQ bullbullQ Q


I I I I I I

20 40 60 80 100 120 140

time [s]

(111) Si Substrate


I i bullbull

I +



Appl Phys 74 7154-7161 (1993)







Nano Lett 6 622-625 (2006)





819 (2003)




14

Figure Legends












h)

16x 1014 i) 32x 1014



n) 49x 1014 and 0) 80x 1014

cm2

















15






16

O Ge

a) O H b)

O Au

(111)Si -------------






a) Initial b)


2 3 4 5 6 I I I I I


1 shy

QQ bullbullQ Q


I I I I I I

20 40 60 80 100 120 140

time [s]

(111) Si Substrate


I i bullbull

I +


Figure Legends












h)

16x 1014 i) 32x 1014



n) 49x 1014 and 0) 80x 1014

cm2

















15






16

O Ge

a) O H b)

O Au

(111)Si -------------






a) Initial b)


2 3 4 5 6 I I I I I


1 shy

QQ bullbullQ Q


I I I I I I

20 40 60 80 100 120 140

time [s]

(111) Si Substrate


I i bullbull

I +







16

O Ge

a) O H b)

O Au

(111)Si -------------






a) Initial b)


2 3 4 5 6 I I I I I


1 shy

QQ bullbullQ Q


I I I I I I

20 40 60 80 100 120 140

time [s]

(111) Si Substrate


I i bullbull

I +


O Ge

a) O H b)

O Au

(111)Si -------------






a) Initial b)


2 3 4 5 6 I I I I I


1 shy

QQ bullbullQ Q


I I I I I I

20 40 60 80 100 120 140

time [s]

(111) Si Substrate


I i bullbull

I +





a) Initial b)


2 3 4 5 6 I I I I I


1 shy

QQ bullbullQ Q


I I I I I I

20 40 60 80 100 120 140

time [s]

(111) Si Substrate


I i bullbull

I +




a) Initial b)


2 3 4 5 6 I I I I I


1 shy

QQ bullbullQ Q


I I I I I I

20 40 60 80 100 120 140

time [s]

(111) Si Substrate


I i bullbull

I +



a) Initial b)


2 3 4 5 6 I I I I I


1 shy

QQ bullbullQ Q


I I I I I I

20 40 60 80 100 120 140

time [s]

(111) Si Substrate


I i bullbull

I +


a) Initial b)


2 3 4 5 6 I I I I I


1 shy

QQ bullbullQ Q


I I I I I I

20 40 60 80 100 120 140

time [s]

(111) Si Substrate


I i bullbull

I +


Documents

Nanoscale manipulation of Ge nanowires by ion hammering