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General nanomoulding with bulk metallic glasses

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2015 Nanotechnology 26 145301

(http://iopscience.iop.org/0957-4484/26/14/145301)

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General nanomoulding with bulk metallicglasses

Ze Liu1,2 and Jan Schroers1,2

1Department of Mechanical Engineering and Materials Science, Yale University, New Haven, CT06520, USA2Center for Research on Interface Structures and Phenomena, Yale University, New Haven, CT 06511,USA

E-mail: ze.liu@yale.edu and jan.schroers@yale.edu

Received 24 November 2014, revised 30 January 2015Accepted for publication 19 February 2015Published 18 March 2015

AbstractBulk metallic glasses (BMGs) are ideal for nanomoulding as they possess desirable strength formolds as well as for moldable materials and furthermore lack intrinsic size limitations. Despitetheir attractiveness, only recently Pt-based BMGs have been successfully molded into poresranging 10100 nm (Kumar et al 2009 Nature 457 86872). Here, we introduce a quantitativetheory, which reveals previous challenges in lling nanosized pores. This theory considers, inaddition to a viscous and a capillary term, also oxidation, which becomes increasingly moreimportant on smaller length scales. Based on this theory we construct a nanomouldingprocessing map for BMG, which reveals the limiting factors for BMG nanomoulding. Based onthe quantitative prediction of the processing map, we introduce a strategy to reduce the capillaryeffect through a wetting layer, which allows us to mold non-noble BMGs below 1 m in air. Anadditional benet of this strategy is that it drastically facilitates demoulding, one of the mainchallenges of nanomoulding in general.

Keywords: bulk metallic glasses, nanomoulding, nanoimprinting, wetting/dewetting, surfaceoxide

(Some gures may appear in colour only in the online journal)

1. Introduction

A critical requirement for any moldable material is that itsintrinsic length scale is small compared to the size of themolds features. Polymers are ultimately limited by theirchain lengths and crystalline materials are limited by theirgrain sizes. Bulk metallic glasses (BMGs) lack intrinsic sizelimitation on the nanoscale [15]. In addition to this crucialattribute, BMGs are hard and tough compared to othermaterials used for nanomoulding, yet they can be softenedinto a state in which they can be readily molded [2]. Theseproperties are often combined with favorable chemistry forbiocompatibility, electrochemical activity, antibacterialbehavior, and biodegradability.

Despite their attractiveness, until recently, BMGs couldnot be molded into features below 100 nm. Kumar et al [1]was rst to mold Pt57.5Cu14.7Ni5.3P22.5 into pores of10100 nm in diameter and lengths that correspond to an

aspect ratio of over 20. The ability to mold BMGs in acontrollable manner has triggered broad research in exploringapplications, such as electrochemical catalysts [69], microfuel cell [10], MEMS/NEMS [5, 11, 12], programmablebiomaterials [1315] and wastewater treatment materials[16, 17]. Besides these applications, molded BMG nanos-tructures have also enabled the scientic community to studysize and connement effects on mechanical properties [1825], deformation modes [2629], crystallization [30, 31] andow behaviors [23]. However, Kumars ndings and all fol-lowing BMG nanomoulding has been limited to very few,noble-metals-based alloys such as Pt57.5Cu14.7Ni5.3P22.5 [1]and Pd43Ni10Cu27P20 [3234] with a high resistance to oxideformation. Enabling the broad potential applications of BMGnanomoulding requires the development of nanomouldingstrategies for more economic BMGs. Most BMGs, however,readily oxidize, particularly when heated into the supercooledliquid region (SCLR) like during thermoplastic forming

Nanotechnology

Nanotechnology 26 (2015) 145301 (9pp) doi:10.1088/0957-4484/26/14/145301

0957-4484/15/145301+09$33.00 2015 IOP Publishing Ltd Printed in the UK1

(TPF) [35]. Such oxidizing results in the formation of a rigidoxide layer which dramatically affects and ultimately prohi-bits the TPF lling of nanosized pores for the vast majority ofBMGs. We show here a general description for quantitativeprediction of molding of BMGs into nanoscale features,which accounts for possible oxide formation. Our modelincludes a threshold pressure and a capillary contribution,which are required to break the oxide lm and overcome thecapillary force to enter into a nanopore, respectively. Inaddition, a viscous term, which when compared to thestrength of the mold, denes the possible moldable aspectratios. Based on this quantitative model which we use toconstruct a nanomoulding processing map forZr35Ti30Cu8.25Be26.75, we introduce a strategy to reduce thecapillary effect, which allows us to fabricate nanorods in airfrom highly reactive, non-noble based BMGs such asZr35Ti30Cu8.25Be26.75, Zr44Ti11Cu10Ni10Be25 andMg65Cu25Y10.

2. Materials and methods

The nanomoulding experiments are operated in air with aheating-cell equipped Instron 5569 machine (50 kN maximumload capacity). The processing temperature forZr35Ti30Cu8.25Be26.75, Zr44Ti11Cu10Ni10Be25 andMg65Cu25Y10 with/without oils is 435 C and 175 C, respec-tively. The total processing time for all of the samples is2min and the maximum loading force is 50 KN. Demouldingof Zr35Ti30Cu8.25Be26.75 and Zr44Ti11Cu10Ni10Be25 nanorods isachieved through etching Al2O3 templates with KOH solution(3 mol L1, temperature of 85 C). For Mg65Cu25Y10, we useH3PO4 solution (concentration of 85%, temperature of 85 C)due to the high reactivity of the alloy with both alkaline andacidic solutions.

To demonstrate the use of BMGs as molds and moldablematerials, we choose as an example Pt57.5Cu14.7Ni5.3P22.5 as amoldable material and Pd43Ni10Cu27P20 as a mold material.Firstly, a Pd43Ni10Cu27P20 BMG disc is thermoplasticallyformed into a nanoporous Al2O3 template at 360 C. Themaximum loading force and processing time are 5 KN and2 min, respectively. Pd43Ni10Cu27P20 nanorods arrays to beused subsequently as a mold are exposed by etching theAl2O3 template. We then place a Pt57.5Cu14.7Ni5.3P22.5 discwhich is covered by a thin layer of high temperature oil on thePd43Ni10Cu27P20 nanorods array mold and thermoplasticallyform the mold-replicate combination at 270 C. Demouldingis realized by a small mechanical force applied at roomtemperature.

3. Processing map for BMG nanomoulding

Thermoplastic compression molding, a process in whichmoldable material is heated to ow into micro/nanoporeunder an applied pressure, has been widely used in surfacepatterning for polymers [3639] and BMGs [3, 12, 4045]due to its simplicity and scalability. Typically for a cylindrical

pore with diameter, d, the required pressure to drive a liquidinto a pore, p, can be calculated from HagenPoiseuille law

= p Ld

4 , (1)max

where is the liquids viscosity and max is the maximumshear strain rate. max is located at the liquid-mold interfacewhen assuming a parabolic velocity distribution. This owresistance linearly scales with the viscosity of the liquid(gure 1(a)). Typically for creep ow of BMGs in theirSCLRs, ~ 1 s ,max 1 and their minimum accessible viscositycan vary signicantly among BMG formers ranging 105109 Pa s [46]. For > 109 Pa s, the molding pressure of 10 GPais prohibitively high to ll an aspect ratio of three. Figure 1(a)and equation (1) also suggest that the viscous resistance ofBMG liquids is size independent, which has been experi-mentally conrmed for molds larger than approximately onemicron [47]. However, for nanosized molds,

oxide layer should be of the form of

=p

Ef

Ev

h

d, , , (5)0 c

where c is the strength of the oxide layer, and h the thicknessof the oxide layer. From linear theory of small deection andvon-Mises yielding criterion, equation (5) can be written as

= +

pv v

h

d

16

3 1, (6)0

c

2

2

which denes the pressure to break the oxide layer. Thispressure barrier scales with (1/d)2 and is more dramatic thanthe linear-scaling entering barrier from surface dewetting(second term in equation (2)). This scaling behavior revealsthat the oxide layer barrier is indeed dominating the llingrequirements of small pores. Considering the nonlinear effect,the more accurate pressure to break the oxide layer (p0/E) isrelated to the maximum deection value (wm/h) when rstyielding at clamped edges [48]

+

= + +

+ +

v

v v E

a

h

w

hv v

w

hv v

w

h

1

14

1

90(1 )(113 13 )

1

1890(1 ) (40 26 ) , (7)

2

2

c2

m

m2

2 m3

=

+p

E v

h

a

w

h

w

h

16

3

1

1, (8)0

2

4m m

3

where = + v v(1 )(173 73 ).1360

By substituting themechanical properties of the oxide layer (E 200 GPa,c 1 GPa, and v 0.3) and the oxide thickness (1 and10 nm) into equation (7), the maximum deection value (wm/h) at yielding is calculated. Then substituting this value intoequation (8), the critic pressure p0 to rupture the oxide layer isnally obtained (gure 1(c)). It is obvious that when moldinginto small pores, the surface oxide layer becomes increasinglyimportant. However, this is only the case for reactive alloyssuch as Zr-BMGs. For alloys with high corrosion resistancesuch as Pt-BMGs, the contribution of an oxide layer can beneglected.

The maximum aspect ratio that can be achieved inmolding nanorods is ultimately limited by the strength of themold (0), which denes the upper bound for the appliedpressure. As a consequence, the maximum aspect ratio thatcan be realized is given by

=

+L

d d

1

4

4 cos. (9)

max max0

Equations (2), (7), (8) and (9) describe the generalnanomoulding of supercooled BMGs (gures 1(a)(c)). Thisdescription can be used to construct a BMGs processingmap, which reveals the dominating effect of nanomouldingat different pore diameters. Taking Zr35Ti30Cu8.25Be26.75 forexample, parameters are ~ 1 s ,max 1 = 107 Pa s, = 150, = 1 J m2. Furthermore, we assume a maximum strength of0 = 300 MPa for Al2O3 template (with 200 nm diameter

Figure 1. Thermoplastic based nanomoulding of bulk metallic glasses. (a) Contribution of the viscosity term to the forming pressure for BMGliquids owing into a nanopore (equation (1)) for an aspect ratio of three, and a maximum shear strain rate of max 1 s1. (b) For nanosizedmolds, the capillary effect should be included in the pressure (second term in equation (2)) which inversely linearly scales with the diameterof a pore. (c) When nanomoulding supercooled BMGs in air, the BMG surface is typically covered with an oxide layer, which deforms as arigid lm under normal pressure exerted by the BMG liquid. The pressure needed to break the oxide layer scales with the square of thediameter of a nanopore. (d) Processing map for Zr35Ti30Cu8.25Be26.75 which is constructed based on (a)(c), with max 1 s1, = 107 Pa s,= 150, = 1 J m2, and h= 10 nm. The molding pressure is limited by the strength of the mold, approximately 300 MPa [49] for Al2O3template assuming a 0.2% elastic limit. Formation of nanorods is initially limited by the pressure requirement to break the oxide layer (blackline) and/or overcome capillary force (red line), which are the onset boundaries of nanomoulding.

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Nanotechnology 26 (2015) 145301 Z Liu and J Schroers

pores) from a 0.2% elastic limit [49]. Combiningequations (2), (3), and (5), the processing map can be con-structed (gure 1(d)), where the oxide thickness is set ash = 10 nm, the upper bound in our experiments. We measuresuch a thickness of the oxide layer by oxidizingZr35Ti30Cu8.25Be26.75 thin plate at 435 C for 4 min in air.Subsequently, the plate is stretched to break the surfaceoxide layer and the thickness is determined using SEM(gure 5).

4. Results and discussions

4.1. Nanomoulding non-noble BMGs by adding a wetting layer

The processing map (gure 1(d)) reveals the dominating

effects controlling molding into different size pores. Prior to

this work, Zr-BMGs have not been molded into features

smaller than 1 m. For this size region, the processing map

reveals that the dominating barrier originates from either the

Figure 2. (a) Molding reactive BMGs by reducing capillary force through the use of an interlayer wetting layer. Al2O3 templates are coatedwith high temperature oil (DuPont Kryto) prior to the molding operation. (b) After thermoplastic forming Zr35Ti30Cu8.25Be26.75 into a200 nm Al2O3 template at 435 C for 2 min. Left: without the use of a wetting layer, right: with the use of high temperature oil as a wettinglayer. (c) Nanorods do not form without oil. (d) Formation of nanorods under the same conditions as (c) but with oil.

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Nanotechnology 26 (2015) 145301 Z Liu and J Schroers

capillary effect or surface oxide. To reduce these barriers, andhence enable nanomoulding with non-noble BMGs, we pro-pose a simple strategy through introducing a wetting layer tothe Al2O3 template surface (gure 2(a)). Specically, weimmerse Al2O3 templates and/or BMGs into high temperatureoil prior to the molding operation. Oils typically wet ceramicsand metals. We choose DuPont Kryto oil which wets Al2O3template and Zr35Ti30Cu8.25Be26.75 well (contact angle< 45, gure 6). By reducing the surface energy throughthe surface wetting oil, we successfully moldZr35Ti30Cu8.25Be26.75 and Zr44Ti11Cu10Ni10Be25 into 100 nmnanopores. One of the results for 200 nm nanorods withaspect ratio over ve is shown in gure 2(d). In contrast,

molding under the same processing conditions but without oildoes not result in any lling of the 200 nm pores (gure 2(c)).

We attribute the successful nanomoulding of Zr-BMGwhen using an oil layer to the reduced surface energy ofBMG liquids which decreases the capillary (second term inequation (2)). When forming supercooled Zr35Ti30Cu8.25Be26.75into a nanopore wetted with oil, the capillary term inequation (2) changes to d4( )/ ,oil BMG oil and the interfacialtension between oil and supercooled BMG can be estimated by = + oil BMG oil BMG oil BMG [50]. The capillary termthus becomes ( ) d4 1 / / ,BMG oil BMG which suggests thatthe capillary effect can be reduced by using oil. In addition, the

Figure 3. Nanomoulding Zr44Ti11Cu10Ni10Be25 and Mg65Cu25Y10 by using oil-wetted Al2O3 templates. Zr44Ti11Cu10Ni10Be25 andMg65Cu25Y10 are molded at 435 C and 175 C, respectively. The total processing time is 2 min and the maximum loading force is 50 KN.(a) and (d) show the as-thermoplastic formed samples. The dark color in both of the BMGs suggests that nanorods formed. (b)(c) SEMimages of Zr44Ti11Cu10Ni10Be25 nanorods after removing the Al2O3 template through KOH etching. (e)(f) Mg65Cu25Y10 nanorods withAl2O3 template partially etched by using H3PO4. The reactivity of Mg65Cu25Y10 with both alkaline and acidic solutions which are required toetch the Al2O3 template causes degradation of the nanorods.

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Nanotechnology 26 (2015) 145301 Z Liu and J Schroers

Figure 4. BMGs used as mold or moldable materials. (a) Requirements for a BMG mold/moldable material combination are that one BMGhas sufciently softened, which is achieved by processing in its supercooled liquid region close to its crystallization temperature. The otherBMG to be used as a mold should have a 20% higher Tg than that of the moldable BMG. Such a difference guarantees several orders ofmagnitude difference in strength (ow stress). (b) Schematics of nanomoulding Pt-BMG using Pd-BMG nanorods as a mold. (c)(d)Pd43Ni10Cu27P20 nanorods after demoulding from Pt57.5Cu14.7Ni5.3P22.5. (e)(f) Replicated nanoholes in Pt57.5Cu14.7Ni5.3P22.5.

Figure 5. Surface oxide layer on Zr35Ti30Cu8.25Be26.75, formed during processing in air at 435 C. Subsequently the sample is deformed torupture the surface oxide, resulting in a total processing time of 4 min. (a) Optical microscopy image reveals the rupture of the surface oxidelayer. (b)(c) By using SEM (the sample stage is tilted 30 degrees), the oxide thickness is measured to about 156 nm, which corresponds toan oxidation rate of 0.65 nm s1 by assuming a linear oxidation process. Within our processing protocol, it takes 15 s to heat the sample,which gives the upper bound thickness of the oxide layer to 0.65*15 nm 10 nm.

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Nanotechnology 26 (2015) 145301 Z Liu and J Schroers

changing of sticky boundary to lubrication boundary may helpto reduce the owing resistance and thus enable the fabricationof nanorods with larger aspect ratio, which is still underinvestigation.

To demonstrate the general applicability of this strategy,we also mold Zr44Ti11Cu10Ni10Be25 and Mg65Cu25Y10 intopores of 200 nm in diameter (gure 3). When applying an oillm, both alloys can be nanomolded. The appearance of theMg65Cu25Y10 nanorods is affected by the subsequent H3PO4etching to remove the Al2O3 template.

4.2. BMGs used as molds and moldable materials

Besides using BMGs as ideal moldable materials, BMGsdrastic temperature dependent strength can also be utilized asa means to use them as molds. For example the softeningtemperatures of thermoplastics are usually below 200 C,which is lower than the glass transition temperatures (Tg) formost BMGs. Hence, BMGs are high strength at these tem-peratures, hence can be used as molds for thermoplasticpolymers. Due to the large range of glass transition tem-peratures among BMGs, nanomoulding one BMG withanother BMG mold is also possible. The selection of theappropriate BMGs depends on their relative glass transitiontemperatures. This attribute and requirement are schemati-cally shown in gure 4(a), where the viscosity (or ow stress)of BMGs can decrease by several orders of magnitude whenthe temperature approaches Tg. Compared with other moldmaterials such as silicon and Al2O3 molds, BMG nanomoldsare advantageous due to their high elasticity, strength, andtoughness. These attributes warrant long mold life, ability todemould, and precise and inexpensive fabrication of the mold.

To demonstrate this concept, Pd43Ni10Cu27P20 nanorodarrays of 200 nm in diameter are fabricated by replicatingAl2O3 mold at 360 C. Subsequently, these nanorod arrays actas a mold and are replicated at 270 C with oil-wettedPt57.5Cu14.7Ni5.3P22.5. Demoulding at room temperature canbe readily achieved by small mechanical forces. This method,in contrast to all previous BMG nanomoulding methods,allows the reuse of the mold. As such it represents a steptowards commercial usage of BMG nanostructures since itdrastically reduces fabrication costs which in the past inclu-ded the disposable Al2O3 template.

5. Conclusions

We identied the governing contributions for most generalBMG nanomoulding. These are viscous, capillary, and sur-face oxide layer fracture. The viscous contribution dominatesfor supercooled BMGs with large viscosity, when lled intohigh aspect ratios. The capillary term scales with the char-acteristic dimension of the nanopore and is determined byinterface wetting properties (surface energy/contact angle).The surface oxide layer controls the lling barrier at smallerscales since it scales with the square of the diameter of thenanopore. Our general description allows for quantitativepredictions, which can be used to create a processing map forBMG nanomoulding.

The processing map reveals the limiting factors, whichhave prevented nanomoulding for the majority of BMG alloysin the past. We used this knowledge to develop a moldingstrategy using a wetting layer to reduce the entering barriers.Using this method, reactive BMGs based on Zr and Mg canbe nanomolded under practical conditions. Furthermore, thewetting layer also dramatically reduces interfacial forces,which suggest the possibility for a non-disposable moldmethod for BMG nanomoulding.

Acknowledgment

This work was primarily supported by the National ScienceFoundation under MRSEC DMR-1119826. Facilities use wassupported by YINQE. We thank Dr Sungwoo for help castingMg-BMG.

Appendix

A.1. Oxidation rates

We oxidized Zr35Ti30Cu8.25Be26.75 in air at 435 C and sub-sequently stretched the BMG to break its surface oxide layer.The total processing time is 4 min. The ruptured surfaceoxide layer is clearly revealed under an optical microscope(gure 5(a)). Using SEM (gures 5(b)(c), the sample stage istilted 30), the oxide thickness is measured to 156 nm,which corresponds to a 0.65 nm s1 oxidation rate if assuming

Figure 6. Wetting of high temperature oil (DuPont Kryto) on Al2O3 template and polished Zr35Ti30Cu8.25Be26.75.

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Nanotechnology 26 (2015) 145301 Z Liu and J Schroers

a linear oxidation. During the TPF-based molding, we usuallyconsume 15 s to reach the processing temperature, whichdenes the upper bound thickness of the oxide layer to10 nm (0.65*15 nm).

A.2. Wetting properties of high temperature oil with templatesand BMGs

The contact angles of oil drops on surfaces of Al2O3 andpolished Zr35Ti30Cu8.25Be26.75 are smaller than 45 (gure 6),which suggests the high temperature oil (DuPont Kryto) usedin our experiments wet both of them well.

References

[1] Kumar G, Tang H X and Schroers J 2009 Nanomoulding withamorphous metals Nature 457 86872

[2] Schroers J 2010 Processing of bulk metallic glass Adv. Mater.22 156697

[3] Saotome Y, Itoh K, Zhang T and Inoue A 2001 Superplasticnanoforming of Pd-based amorphous alloy Scr. Mater. 4415415

[4] Kumar G, Desai A and Schroers J 2011 Bulk metallic glass: thesmaller the better Adv. Mater. 23 46176

[5] Sharma P, Kaushik N, Kimura H, Saotome Y and Inoue A2007 Nano-fabrication with metallic glassan exoticmaterial for nano-electromechanical systemsNanotechnology 18 035302

[6] Brower W E, Matyjaszczyk M S, Pettit T L and Smith G V1983 Metallic glasses as novel catalysts Nature 301 4979

[7] Sekol R C et al 2013 PdNiCuP metallic glass nanowires formethanol and ethanol oxidation in alkaline media Int. J.Hydrog. Energy 38 1124855

[8] Carmo M et al 2011 Bulk metallic glass nanowire architecturefor electrochemical applications ACS Nano 5 297983

[9] Zhao M, Abe K, Yamaura S, Yamamoto Y and Asao N 2014Fabrication of PdNiP metallic glass nanoparticles andtheir application as highly durable catalysts in methanolelectro-oxidation Chem. Mater. 26 105661

[10] Sekol R C et al 2013 Bulk metallic glass micro fuel cell Small9 20815

[11] Nakayama K S et al 2010 Controlled formation andmechanical characterization of metallic glassy nanowiresAdv. Mater. 22 872

[12] Schroers J, Pham Q and Desai A 2007 Thermoplastic formingof bulk metallic glassa technology for MEMS andmicrostructure fabrication J. Microelectromech. Syst. 162407

[13] Schroers J, Kumar G, Hodges T M, Chan S and Kyriakides T R2009 Bulk metallic glasses for biomedical applications Jom61 219

[14] Padmanabhan J et al 2014 Engineering cellular response usingnanopatterned bulk metallic glass ACS Nano 8 436675

[15] Zberg B, Uggowitzer P J and Lofer J F 2009 MgZnCa glasseswithout clinically observable hydrogen evolution forbiodegradable implants Nat. Mater. 8 88791

[16] Lin B, Bian X F, Wang P and Luo G P 2012 Application of Fe-based metallic glasses in wastewater treatment Mater. Sci.Eng. B 177 925

[17] Wang J Q et al 2012 Rapid degradation of Azo dye by Fe-based metallic glass powder Adv. Funct. Mater. 22256770

[18] Guo H et al 2007 Tensile ductility and necking of metallicglass Nat. Mater. 6 7359

[19] Lee C J, Huang J C and Nieh T G 2007 Sample size effect andmicrocompression of Mg65Cu25Gd10 metallic glass Appl.Phys. Lett. 91 081601

[20] Jang D C and Greer J R 2010 Transition from a strong-yet-brittle to a stronger-and-ductile state by size reduction ofmetallic glasses Nat. Mater. 9 2159

[21] Magagnosc D J et al 2013 Tunable tensile ductility in metallicglasses Sci. Rep. 3 1096

[22] Tnnies D, Maa R and Volkert C A 2014 Room temperaturehomogeneous ductility of micrometer-sized metallic glassAdv. Mater. 26 571521

[23] Shao Z et al 2013 Size-dependent viscosity in the super-cooledliquid state of a bulk metallic glass Appl. Phys. Lett. 102221901

[24] Chen D Z et al 2013 Nanometallic glasses: size reductionbrings ductility, surface state drives its extent Nano Lett. 1344628

[25] Gu X W et al 2014 Mechanisms of failure in nanoscalemetallic glass Nano Lett. 14 585864

[26] Volkert C A, Donohue A and Spaepen F 2008 Effect of samplesize on deformation in amorphous metals J. Appl. Phys. 103083539

[27] Chen C Q, Pei Y T and De H J T M 2010 Effects of size on themechanical response of metallic glasses investigated throughin situ TEM bending and compression experiments ActaMater. 58 189200

[28] Greer J R and De H J T M 2011 Plasticity in small-sizedmetallic systems: intrinsic versus extrinsic size effect Prog.Mater. Sci. 56 654724

[29] Wang Y B et al 2014 Ultrahigh-strength submicron-sizedmetallic glass wires Scr. Mater. 84-85 2730

[30] Gopinadhan M et al 2013 Finite size effects in thecrystallization of a bulk metallic glass Appl. Phys. Lett. 103111912

[31] Sun Y T et al 2014 Understanding glass-forming abilitythrough sluggish crystallization of atomically thin metallicglassy lms Appl. Phys. Lett. 105 14

[32] Mukherjee S et al 2012 Palladium nanostructures from multi-component metallic glass Electrochim. Acta 74 14550

[33] Liu X, Shao Y, Li J F, Chen N and Yao K F 2014 Large-areaand uniform amorphous metallic nanowire arrays preparedby die nanoimprinting J. Alloys Compd. 605 711

[34] Mukherjee S et al 2013 Tunable hierarchical metallic-glassnanostructures Adv. Funct. Mater. 23 270813

[35] Schroers J 2008 On the formability of bulk metallic glass in itssupercooled liquid state Acta Mater. 56 4718

[36] Chou S Y, Krauss P R and Renstrom P J 1996 Imprintlithography with 25-nanometer resolution Science 272 857

[37] Rohr T, Ogletree D F, Svec F and Frechet J M J 2003 Surfacefunctionalization of thermoplastic polymers for thefabrication of microuidic devices by photoinitiated graftingAdv. Funct. Mater. 13 26470

[38] Lendlein A, Jiang H Y, Junger O and Langer R 2005 Light-induced shape-memory polymers Nature 434 87982

[39] Nie Z H and Kumacheva E 2008 Patterning surfaces withfunctional polymers Nat. Mater. 7 27790

[40] Chu J P et al 2007 Nanoimprint of gratings on a bulk metallicglass Appl. Phys. Lett. 90 034101

[41] Li N, Xu X N, Zheng Z Z and Liu L 2014 Enhancedformability of a Zr-based bulk metallic glass in asupercooled liquid state by vibrational loading Acta Mater.65 40011

[42] Li N et al 2013 A thermoplastic forming map of a Zr-basedbulk metallic glass Acta Mater. 61 192131

[43] Xia T, Li N, Wu Y and Liu L 2012 Patternedsuperhydrophobic surface based on Pd-based metallic glassAppl. Phys. Lett. 101 081601

8

Nanotechnology 26 (2015) 145301 Z Liu and J Schroers

[44] Li N, Xia T, Heng L P and Liu L 2013 Superhydrophobic Zr-based metallic glass surface with high adhesive force Appl.Phys. Lett. 102 251603

[45] Chen W, Liu Z, Robinson H M and Schroers J 2014 Flawtolerance versus performance: a tradeoff in metallic glasscellular structures Acta Mater. 73 25974

[46] Kato H et al 2006 Fragility and thermal stability of Pt-and Pd-based bulk glass forming liquids and their correlation withdeformability Scr. Mater. 54 20237

[47] Chiu H M, Kumar G, Blawzdziewicz J and Schroers J 2009Thermoplastic extrusion of bulk metallic glass Scr. Mater.61 2831

[48] Chien W Z 1947 Large deection of a circular clamped plateunder uniform pressure Acta Phys. Sin. 7 6

[49] Ko S et al 2006 Mechanical properties and residual stress inporous anodic alumina structures Thin Solid Films 515 19327

[50] Fowkes F M 1964 Attractive forces at interfaces Ind. Eng.Chem. 56 40

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Nanotechnology 26 (2015) 145301 Z Liu and J Schroers

1. Introduction2. Materials and methods3. Processing map for BMG nanomoulding4. Results and discussions4.1. Nanomoulding non-noble BMGs by adding a wetting layer4.2. BMGs used as molds and moldable materials

5. ConclusionsAcknowledgmentAppendixA.1. Oxidation ratesA.2. Wetting properties of high temperature oil with templates and BMGs

References