Delivered by Ingenta toStevens Institute of Technology

IP 15524615220Wed 05 Jan 2011 153948

Copyright copy 2010 American Scientific PublishersAll rights reservedPrinted in the United States of America

Nanoscience andNanotechnology LettersVol 2 181ndash184 2010

Fabrication and Characterization of a NanoscaleNindashAl Bimorph for Reconfigurable Nanostructures

Onejae Sul1 Seongjin Jang1 Danial S Choi2 and Eui-Hyeok Yang1lowast1Mechanical Engineering Department Stevens Institute of Technology Hoboken NJ 07030 USA

2Material Engineering University of Idaho Moscow ID 83844 USA

This paper presents the fabrication and characterization of nanoscale nickelndashaluminum (NindashAl)bimorphs towards self-adjustable nanostructures Nickel nanowires were grown by a template basedgrowth method using anodized aluminum oxide membrane and positioned at the edge of an oxi-dized silicon substrate A thin aluminum film was deposited on the sidewall of a Ni nanowire usingpulsed laser deposition (PLD) creating the bimorph nanostructure The deposition status and thick-ness of the film were monitored using transmission electron microscope (TEM) The tip deflection ofNindashAl bimorphs under temperature change was measured on a temperature-controlled stage insidea scanning electron microscope (SEM) The displacements of the nanoactuator tips were recordedusing SEM by comparing those data in different temperatures The measured tip deflections wereup to 700 nm from an 18 m long bimorph at a 380 K temperature change which agreed well withthe modeled prediction

Keywords Nanowire Actuator Bimorph

1 INTRODUCTION

Nowadays electrical components and devices dimensionsare decreasing while device performance increases Themajor constraints which limit (or determine) the ability toshrink electrical component feature size are (1) the inte-gration feasibility of the nanodevices with macroscopicsystems and (2) the relatively large parasitic effects experi-enced by a signal during transmission through narrow wireinterconnects Both issues can be resolved by integrating ananoantenna directly on the chip12 Micro-scale labs-on-chips would require transfer of information between mul-tiple chips or between a chip and a macroscopic externalreceiver Here the most important unit for interconnec-tion is an integrated reconfigurable nanoantenna In orderto tune the frequency and maximize the transmission effi-ciency the antenna needs the ability to vary the shape of itsown structure3 On the microscale using microelectrome-chanical systems (MEMS) devices loop-shaped variableinductors in the form of thermal bimorph actuators havebeen demonstrated to tune the radio frequency4ndash6 Vari-able diameter annular antennas have also been reported78

where a microscale thermal bimorph switch is the key fac-tor to vary the diameter of the antenna ring7 The per-formance of an antenna such as its gain bandwidth and

lowastAuthor to whom correspondence should be addressed

efficiency of a given electrical size is governed by physicallaws of nature9 Therefore reconfigurable antenna archi-tecture would take advantage of combined multiple func-tions in a single antenna which results in a significantreduction in the area occupied by the multiple antennaelements with potentially enhanced functionality and per-formance To enable a reconfigurable antenna the elec-trical current distribution over the volume of the antennaneeds to be changed where each distribution correspondsto a different mode of operation To this end one canchange the geometry of the antenna by switching on andoff various geometrical metallic segments that make up theantenna as shown in Figure 1 For switching in a Gigahertzmode MEMS switches have been employed1011 By fabri-cating these structures on the nanoscale higher frequencyantennas may be created for several applications1213

The first nano-bimorph was fabricated by Ikuno14 usinga multiwalled carbon nanotube as the cantilever base Bythe thermal expansion rate mismatch between the carbonnanotube and the deposited oxide materials they observedthe deflection of the bimorph under temperature varia-tion Recently the authorrsquos group measured the amount ofthe force generation from the tip of such a carbon nano-tube based bimorph through lateral force microscopy15

Although the carbon nanotube has its own mechanicaladvantages such as robustness the problem of fabrica-tion in the desired dimensions and arrangement makes

Nanosci Nanotechnol Lett 2010 Vol 2 No 2 1941-490020102181004 doi101166nnl20101079 181

Delivered by Ingenta toStevens Institute of Technology

IP 15524615220Wed 05 Jan 2011 153948

Fabrication and Characterization of a Nanoscale NindashAl Bimorph for Reconfigurable Nanostructures Sul et al

(a) (c)

(b) (d)

Fig 1 (a) and (b) A nanobimorph actuator can electrically connect or disconnect neighboring antenna elements by curving its shape Red indicatesthat the bimorph actuator is curved by thermal energy and the connection is disconnected Blue indicates that the actuator is released and the connectionis restored (c) Changing the antenna area can modulate transmission frequency (d) Changing patterns create different polarization

the metallic nanowires alternative materials for nanobi-morphs Compared to the carbon nanotubes the metallicnanowire such as nickel nanowires fabrication by anodicalumina template method16 or lithographic methods17 gen-erates better control of their aspect ratio and arrangementOther groups developed novel nanobimorphs using vari-ous fabrication techniques A focused ion beam chemicalvapor deposition technique was used to grow a doublelayer nanobimorph from a tungsten-based-conductor anddiamond-like-carbon18 Using this method up to 600 nmof deflection was obtained at the tip of the bimorphIn addition to thermal actuation piezoelectricity froman aluminum-nitride based bimorph19 or electrochemicalswelling of the polypyrrole under charging20 were reportedto create nanobimorph actuators Here the field of nanobi-morph actuator is still in its infancy in terms of fabricationand characterization In this paper we present nickelndashaluminum bimorph nanoactuators as the first step towarddeveloping a reconfigurable nanoantenna technology

2 EXPERIMENTAL DETAILS

Ni nanowires were electrochemically deposited in a com-mercially available anodized aluminum oxide (AAO)membrane of 200 nm nominal pore size The nanowireswere extracted by dissolving the membrane in 5 M NaOHand then cleaned several times with deionized water Aftersuspending in water a droplet of the nanowire suspen-sion was dispensed on silicon substrate and dehydratedThe substrate was then broken into smaller pieces to form

cantilevered nanowires at substrate edges A pulsed laserdeposition (PLD) system was used to deposit Al on onlyone side of the Ni nanowire with a precisely controlledthickness and uniformity89 because of the low kineticenergy of ejected atoms from the target in the PLD systemIn this experiment an NdYAG (Quanta Ray DCR2-10)laser was used to evaporate an Al target with a depositionrate of 06 Aring per 1 min at 70 mJ10 ns pulse When thefabricated nanoscale bimorphs were pulled out from thePLD chamber after evaporation the aluminum film oxi-dized naturally with atmospheric oxygen This aluminumoxide layer is only present on the surface and is much thin-ner than the aluminum layer To image the double layerstructure several individual nickel nanowires were dis-persed on a TEM grid (Ted Pella 300 Mesh Copper Gridswith lacey carbon) where the grid was dried in air Somecantilevered nanowires were imaged in the TEM (PhillipsCM20) The double layer structure of the bimorph wasconfirmed from TEM images taken at 200 kV (Fig 2)If two layers of homogeneous materials a and b are

stacked with thicknesses da db and modified Youngrsquosmoduli Ya and Yb respectively the resulting bimorphdeflects at one end with a temperature variation T by21

= 3L2AlminusNiT dAlminusdNi

dAldNi

times[(

dAl

dNi

)2YAlYNi

+4dAl

dNi

+6

+4dNi

dAl

+(dNi

dAl

)2YNiYAl

]minus1

(1)

182 Nanosci Nanotechnol Lett 2 181ndash184 2010

Delivered by Ingenta toStevens Institute of Technology

IP 15524615220Wed 05 Jan 2011 153948

Sul et al Fabrication and Characterization of a Nanoscale NindashAl Bimorph for Reconfigurable Nanostructures

Fig 2 Angled transmission electron microscope (TEM) image of aNindashAl bimorph The aluminum (Al) layer is on top of the nickel (Ni)nanowire (arrow) The scale bar is 500 nm

where Y = E1minus E is Youngrsquos modulus is Pois-son ratio and is the thermal expansion rate assuming arectangular cross section for each layer Here Aluminum =231 times 10minus6K22 Nickel sim 134 times 10minus6K23 EAluminum =70 GPa24 ENickel = 200 GPa25 Aluminum = 03326 and Nickelwas 03127

The diameter of a fabricated Ni nanowire was 270plusmn20 nm which was a little larger than the nominal poresize of AAO membrane as similarly shown in otherreports1528 The diameter was confirmed by scanning elec-tron microscope (SEM) images These nanobimorphs usedin the actuation experiment were made from individualnanowires not from nanowire bundles which was alsoconfirmed by SEM images The measured thickness ofaluminum was 70plusmn 10 nm which was confirmed usingan atomic force microscope (AFM) from a separatelyand simultaneously deposited aluminum film on a sepa-rately prepared substrate Three different lengths of NindashAlbimorphs were used in this experimental study 10 13 and18 mThe silicon substrate containing the bimorphs was

loaded on top of a miniature heater (Heat wave labs ultrahigh vacuum button heater Model 101136) which wasmounted on a custom built SEM stage (Fig 3) A thermo-couple was attached to the surface of the heater to monitorits temperature The power cables and the thermocouplewire were extended to the outside of the SEMrsquos vacuumchamber through a feedthrough Because it was difficultto accurately measure the temperature of the substratedirectly the temperature of the heater was continuouslymonitored by a thermometer outside the chamber until itwas stabilized at a targeted temperature The temperaturestabilization could also be monitored using ldquoliverdquo SEMimaging As the temperature is raised the SEM imagingshowed lsquodriftingrsquo of the substrate due to thermal expan-sion of the heater and the substrate To track the iden-tical bimorph the SEM stage was manually controlledAfter temperature stabilization was achieved the driftingstopped Then the heater and the substrate remained for

Fig 3 An SEM stage for thermal control The silicon substrate wasmounted on top of the button heater The thermocouple tip was attachedon the surface of the button heater to monitor the temperature

some time (about an hour) with the heater turned on con-tinuously to achieve thermal equilibrium We assumed thatat thermal equilibrium the heater and the substrate wereat the same temperatureFor a temperature change from 295 K to 675 K with

an 18 m long bimorph the calculated deflection usingEq (1) is 890 nm The measured deflection from the SEMimages shown in Figures 4(a) and (b) was 700plusmn200 nmThe deviation between the calculation and the measure-ment is attributed to the effect of oxidation at the surfacesof both metallic materials2930 especially because of thereduced thermal expansion rate of aluminum oxide on thesurface of aluminum layer31 Figure 5 shows a comparison

Fig 4 Thermal deflections of NindashAl bimorph nanoactuators (a) Anoverlay of two SEM images of an 18 m long bimorph taken at roomtemperature (295 K white) and at 675 K (black) during a temperaturerising phase The tip moved toward left (arrow) The oxide film is on theright side of the image Scale bar is 10 m (b) An overlay image ofthe same bimorph during the temperature decreasing phase The bimorphtip moves to the right when temperature is decreased to 295 K (c) Anoverlay image of a bimorph with 10 m in length at room temperature(white) and at 675 K (black) respectively The oxide film is on the topThe scale bar is 2 m The tip moved downward (d) Another over-lay image of the same bimorph in the decreasing phase The tip movedupward

Nanosci Nanotechnol Lett 2 181ndash184 2010 183

Delivered by Ingenta toStevens Institute of Technology

IP 15524615220Wed 05 Jan 2011 153948

Fabrication and Characterization of a Nanoscale NindashAl Bimorph for Reconfigurable Nanostructures Sul et al

Fig 5 Deflection measurements from the three bimorphs agree wellwith the prediction from Eq (1)

between measurements and prediction by Eq (1) for allthree bimorphs

3 CONCLUSIONS

We have created a bimorph nanoactuator by depositing athin Al film on top of an electrodeposited Ni nanowireThe amount of deflection generated from this nanoscalebimorph was measured using SEM images Compared topreviously reported approaches our fabrication methodutilizing PLD could possibly be utilized for generation ofmultiple devices with high yield Thermal actuation has theadvantage of a simpler actuation method because it doesnot require electrical wiring or a charging environment forthe devices Comparisons were made with bimorph theorybased on the limited data obtained in this study The resultsand analyses suggest that the measured deflections agreewith the prediction while more actuation data with variousthicknesses and diameters of nickel nanowires are neededthrough further study This work is the first step towarddeveloping reconfigurable nanostructures for an antennatechnology

Acknowledgment The authors appreciate valuableadvice and comments on the YAG laser by ProfessorsStrauf and Whittaker in the Department of Physics atStevens Institute of Technology The authors also thankKitu Kumar for her technical assistance This work hasbeen partially supported by the National Science Founda-tion Major Research Instrumentation Program Award NoDMI-0619762

References and Notes

1 Y Qian and T Itoh IEEE Trans Microwave Theory Tech 46 1891(1998)

2 J Lin and T Itoh IEEE Trans Microwave Theory TechMTT-42 2186 (1994)

3 P J Burke Proceeding of SPIE 5593 52 (2004)4 I Zine-El-Abidine and M Okoniewski J Micromech Microeng

17 2280 (2007)5 I Zine-El-Abidine M Okoniewski and J G McRory

J Micromech Microeng 15 2063 (2005)6 V M Lubecke B Barber E Chan D Lopez M E Cross

and P Gammel IEEE Trans Microw Theory Tech 49 2093(2001)

7 B A Cetiner H Jafarkhani J Y Qian H J Yoo A Grauand F De Flaviis IEEE communication magazine 42 62(2004)

8 B A Cetiner G R Crusats L Jofre and N Biyikli IEEE Trans-actions on Antennas and Propagation 58 626 (2010)

9 L Jofre B A Cetiner and F De Flaviis IEEE Trans on Antennasand Propagat 50 658 (2002)

10 J Muldavin C O Bozler S Rabe P W Wyatt and C L KeastIEEE Transaction on Microwave Theory and Techniques 56 522(2008)

11 M Rais-Zadeh P A Kohl and F Ayazi J Microelectromech Syst17 78 (2008)

12 D A Czaplewski G A Patrizi G M Kraus J R WendtC D Nordquist S L Wolfley M S Baker and M P DeBoerJournal of Micromechanics and Microengineering 19 085003(2009)

13 A Subramanian A R Alt L Dong B E Kratochvil C RBolognesi and B J Nelson ACS Nano 3 2953 (2009)

14 T Ikuno S Honda T Yasuda K Oura M Katayama J G Leeand H Mori Appl Phys Lett 87 213104 (2005)

15 O Sul and E H Yang Nanotechnology 20 095502 (2009)16 I Z Rahman K M Razeeb M A Rahman and M D

Kamruzzaman J Magn Magn Mater 262 166 (2003)17 N A Melosh A Boukai F Diana B Gerardot A Badolato P M

Petroff and J R Heath Science 300 112 (2003)18 J Chang B K Min J Kim and L Lin Microelectron Eng

86 2364 (2009)19 N Sinha G E Wabizewski R Mahameed V V Felmetsger S M

Tanner R W Carpick and G Piazza Appl Phys Lett 95 053106(2009)

20 V A Pedrosa X Luo J Burdick and J Wang Small 4 738(2008)

21 G A Gehring M D Cooke I S Gregory W J Karl and R WattsSmart Mater Struct 9 918 (2000)

22 W Fang and C Y Lo Sensors and Actuators 84 310(2000)

23 Y Kuru M Wohlschlogel U Welzel and E J Mittemeijer SurfCoat Technol 202 2306 (2008)

24 A V Kulkarni and B Bhushan Thin Solid Films 290 206(1996)

25 H Majjad S Basrour P Delobelle and M Schmidt Sens Actua-tors A Physical 74 148 (1999)

26 G Cornella S H Lee W D Nix and J C Brevman Appl PhysLett 71 2949 (1997)

27 G Simmons and H Wang Single Cyrstal Elastic Constants and Cal-culated Aggregate Properties A Handbook 2nd edn MIT PressCambridge MA (1971)

28 W C West N V Myung J F Whitacre and B V RatnakumarJ Power Sources 126 203 (2004)

29 H Over and A P Seitsonen Science 297 2003 (2002)30 J Trost H Brune J Wintterlin R J Behm and G Ertl J Chem

Phys 108 1740 (1998)31 J B Wachtman Jr T G Scuderi and G W Cleek J Amer

Ceramic Soc 45 319 (2006)

Received 30 April 2010 Accepted 4 June 2010

184 Nanosci Nanotechnol Lett 2 181ndash184 2010

Delivered by Ingenta toStevens Institute of Technology

IP 15524615220Wed 05 Jan 2011 153948

Fabrication and Characterization of a Nanoscale NindashAl Bimorph for Reconfigurable Nanostructures Sul et al

(a) (c)

(b) (d)

Fig 1 (a) and (b) A nanobimorph actuator can electrically connect or disconnect neighboring antenna elements by curving its shape Red indicatesthat the bimorph actuator is curved by thermal energy and the connection is disconnected Blue indicates that the actuator is released and the connectionis restored (c) Changing the antenna area can modulate transmission frequency (d) Changing patterns create different polarization

the metallic nanowires alternative materials for nanobi-morphs Compared to the carbon nanotubes the metallicnanowire such as nickel nanowires fabrication by anodicalumina template method16 or lithographic methods17 gen-erates better control of their aspect ratio and arrangementOther groups developed novel nanobimorphs using vari-ous fabrication techniques A focused ion beam chemicalvapor deposition technique was used to grow a doublelayer nanobimorph from a tungsten-based-conductor anddiamond-like-carbon18 Using this method up to 600 nmof deflection was obtained at the tip of the bimorphIn addition to thermal actuation piezoelectricity froman aluminum-nitride based bimorph19 or electrochemicalswelling of the polypyrrole under charging20 were reportedto create nanobimorph actuators Here the field of nanobi-morph actuator is still in its infancy in terms of fabricationand characterization In this paper we present nickelndashaluminum bimorph nanoactuators as the first step towarddeveloping a reconfigurable nanoantenna technology

2 EXPERIMENTAL DETAILS

Ni nanowires were electrochemically deposited in a com-mercially available anodized aluminum oxide (AAO)membrane of 200 nm nominal pore size The nanowireswere extracted by dissolving the membrane in 5 M NaOHand then cleaned several times with deionized water Aftersuspending in water a droplet of the nanowire suspen-sion was dispensed on silicon substrate and dehydratedThe substrate was then broken into smaller pieces to form

cantilevered nanowires at substrate edges A pulsed laserdeposition (PLD) system was used to deposit Al on onlyone side of the Ni nanowire with a precisely controlledthickness and uniformity89 because of the low kineticenergy of ejected atoms from the target in the PLD systemIn this experiment an NdYAG (Quanta Ray DCR2-10)laser was used to evaporate an Al target with a depositionrate of 06 Aring per 1 min at 70 mJ10 ns pulse When thefabricated nanoscale bimorphs were pulled out from thePLD chamber after evaporation the aluminum film oxi-dized naturally with atmospheric oxygen This aluminumoxide layer is only present on the surface and is much thin-ner than the aluminum layer To image the double layerstructure several individual nickel nanowires were dis-persed on a TEM grid (Ted Pella 300 Mesh Copper Gridswith lacey carbon) where the grid was dried in air Somecantilevered nanowires were imaged in the TEM (PhillipsCM20) The double layer structure of the bimorph wasconfirmed from TEM images taken at 200 kV (Fig 2)If two layers of homogeneous materials a and b are

stacked with thicknesses da db and modified Youngrsquosmoduli Ya and Yb respectively the resulting bimorphdeflects at one end with a temperature variation T by21

= 3L2AlminusNiT dAlminusdNi

dAldNi

times[(

dAl

dNi

)2YAlYNi

+4dAl

dNi

+6

+4dNi

dAl

+(dNi

dAl

)2YNiYAl

]minus1

(1)

182 Nanosci Nanotechnol Lett 2 181ndash184 2010

Delivered by Ingenta toStevens Institute of Technology

IP 15524615220Wed 05 Jan 2011 153948

Sul et al Fabrication and Characterization of a Nanoscale NindashAl Bimorph for Reconfigurable Nanostructures

Fig 2 Angled transmission electron microscope (TEM) image of aNindashAl bimorph The aluminum (Al) layer is on top of the nickel (Ni)nanowire (arrow) The scale bar is 500 nm

where Y = E1minus E is Youngrsquos modulus is Pois-son ratio and is the thermal expansion rate assuming arectangular cross section for each layer Here Aluminum =231 times 10minus6K22 Nickel sim 134 times 10minus6K23 EAluminum =70 GPa24 ENickel = 200 GPa25 Aluminum = 03326 and Nickelwas 03127

The diameter of a fabricated Ni nanowire was 270plusmn20 nm which was a little larger than the nominal poresize of AAO membrane as similarly shown in otherreports1528 The diameter was confirmed by scanning elec-tron microscope (SEM) images These nanobimorphs usedin the actuation experiment were made from individualnanowires not from nanowire bundles which was alsoconfirmed by SEM images The measured thickness ofaluminum was 70plusmn 10 nm which was confirmed usingan atomic force microscope (AFM) from a separatelyand simultaneously deposited aluminum film on a sepa-rately prepared substrate Three different lengths of NindashAlbimorphs were used in this experimental study 10 13 and18 mThe silicon substrate containing the bimorphs was

loaded on top of a miniature heater (Heat wave labs ultrahigh vacuum button heater Model 101136) which wasmounted on a custom built SEM stage (Fig 3) A thermo-couple was attached to the surface of the heater to monitorits temperature The power cables and the thermocouplewire were extended to the outside of the SEMrsquos vacuumchamber through a feedthrough Because it was difficultto accurately measure the temperature of the substratedirectly the temperature of the heater was continuouslymonitored by a thermometer outside the chamber until itwas stabilized at a targeted temperature The temperaturestabilization could also be monitored using ldquoliverdquo SEMimaging As the temperature is raised the SEM imagingshowed lsquodriftingrsquo of the substrate due to thermal expan-sion of the heater and the substrate To track the iden-tical bimorph the SEM stage was manually controlledAfter temperature stabilization was achieved the driftingstopped Then the heater and the substrate remained for

Fig 3 An SEM stage for thermal control The silicon substrate wasmounted on top of the button heater The thermocouple tip was attachedon the surface of the button heater to monitor the temperature

some time (about an hour) with the heater turned on con-tinuously to achieve thermal equilibrium We assumed thatat thermal equilibrium the heater and the substrate wereat the same temperatureFor a temperature change from 295 K to 675 K with

an 18 m long bimorph the calculated deflection usingEq (1) is 890 nm The measured deflection from the SEMimages shown in Figures 4(a) and (b) was 700plusmn200 nmThe deviation between the calculation and the measure-ment is attributed to the effect of oxidation at the surfacesof both metallic materials2930 especially because of thereduced thermal expansion rate of aluminum oxide on thesurface of aluminum layer31 Figure 5 shows a comparison

Fig 4 Thermal deflections of NindashAl bimorph nanoactuators (a) Anoverlay of two SEM images of an 18 m long bimorph taken at roomtemperature (295 K white) and at 675 K (black) during a temperaturerising phase The tip moved toward left (arrow) The oxide film is on theright side of the image Scale bar is 10 m (b) An overlay image ofthe same bimorph during the temperature decreasing phase The bimorphtip moves to the right when temperature is decreased to 295 K (c) Anoverlay image of a bimorph with 10 m in length at room temperature(white) and at 675 K (black) respectively The oxide film is on the topThe scale bar is 2 m The tip moved downward (d) Another over-lay image of the same bimorph in the decreasing phase The tip movedupward

Nanosci Nanotechnol Lett 2 181ndash184 2010 183

Delivered by Ingenta toStevens Institute of Technology

IP 15524615220Wed 05 Jan 2011 153948

Fabrication and Characterization of a Nanoscale NindashAl Bimorph for Reconfigurable Nanostructures Sul et al

Fig 5 Deflection measurements from the three bimorphs agree wellwith the prediction from Eq (1)

between measurements and prediction by Eq (1) for allthree bimorphs

3 CONCLUSIONS

We have created a bimorph nanoactuator by depositing athin Al film on top of an electrodeposited Ni nanowireThe amount of deflection generated from this nanoscalebimorph was measured using SEM images Compared topreviously reported approaches our fabrication methodutilizing PLD could possibly be utilized for generation ofmultiple devices with high yield Thermal actuation has theadvantage of a simpler actuation method because it doesnot require electrical wiring or a charging environment forthe devices Comparisons were made with bimorph theorybased on the limited data obtained in this study The resultsand analyses suggest that the measured deflections agreewith the prediction while more actuation data with variousthicknesses and diameters of nickel nanowires are neededthrough further study This work is the first step towarddeveloping reconfigurable nanostructures for an antennatechnology

Acknowledgment The authors appreciate valuableadvice and comments on the YAG laser by ProfessorsStrauf and Whittaker in the Department of Physics atStevens Institute of Technology The authors also thankKitu Kumar for her technical assistance This work hasbeen partially supported by the National Science Founda-tion Major Research Instrumentation Program Award NoDMI-0619762

References and Notes

1 Y Qian and T Itoh IEEE Trans Microwave Theory Tech 46 1891(1998)

2 J Lin and T Itoh IEEE Trans Microwave Theory TechMTT-42 2186 (1994)

3 P J Burke Proceeding of SPIE 5593 52 (2004)4 I Zine-El-Abidine and M Okoniewski J Micromech Microeng

17 2280 (2007)5 I Zine-El-Abidine M Okoniewski and J G McRory

J Micromech Microeng 15 2063 (2005)6 V M Lubecke B Barber E Chan D Lopez M E Cross

and P Gammel IEEE Trans Microw Theory Tech 49 2093(2001)

7 B A Cetiner H Jafarkhani J Y Qian H J Yoo A Grauand F De Flaviis IEEE communication magazine 42 62(2004)

8 B A Cetiner G R Crusats L Jofre and N Biyikli IEEE Trans-actions on Antennas and Propagation 58 626 (2010)

9 L Jofre B A Cetiner and F De Flaviis IEEE Trans on Antennasand Propagat 50 658 (2002)

10 J Muldavin C O Bozler S Rabe P W Wyatt and C L KeastIEEE Transaction on Microwave Theory and Techniques 56 522(2008)

11 M Rais-Zadeh P A Kohl and F Ayazi J Microelectromech Syst17 78 (2008)

12 D A Czaplewski G A Patrizi G M Kraus J R WendtC D Nordquist S L Wolfley M S Baker and M P DeBoerJournal of Micromechanics and Microengineering 19 085003(2009)

13 A Subramanian A R Alt L Dong B E Kratochvil C RBolognesi and B J Nelson ACS Nano 3 2953 (2009)

14 T Ikuno S Honda T Yasuda K Oura M Katayama J G Leeand H Mori Appl Phys Lett 87 213104 (2005)

15 O Sul and E H Yang Nanotechnology 20 095502 (2009)16 I Z Rahman K M Razeeb M A Rahman and M D

Kamruzzaman J Magn Magn Mater 262 166 (2003)17 N A Melosh A Boukai F Diana B Gerardot A Badolato P M

Petroff and J R Heath Science 300 112 (2003)18 J Chang B K Min J Kim and L Lin Microelectron Eng

86 2364 (2009)19 N Sinha G E Wabizewski R Mahameed V V Felmetsger S M

Tanner R W Carpick and G Piazza Appl Phys Lett 95 053106(2009)

20 V A Pedrosa X Luo J Burdick and J Wang Small 4 738(2008)

21 G A Gehring M D Cooke I S Gregory W J Karl and R WattsSmart Mater Struct 9 918 (2000)

22 W Fang and C Y Lo Sensors and Actuators 84 310(2000)

23 Y Kuru M Wohlschlogel U Welzel and E J Mittemeijer SurfCoat Technol 202 2306 (2008)

24 A V Kulkarni and B Bhushan Thin Solid Films 290 206(1996)

25 H Majjad S Basrour P Delobelle and M Schmidt Sens Actua-tors A Physical 74 148 (1999)

26 G Cornella S H Lee W D Nix and J C Brevman Appl PhysLett 71 2949 (1997)

27 G Simmons and H Wang Single Cyrstal Elastic Constants and Cal-culated Aggregate Properties A Handbook 2nd edn MIT PressCambridge MA (1971)

28 W C West N V Myung J F Whitacre and B V RatnakumarJ Power Sources 126 203 (2004)

29 H Over and A P Seitsonen Science 297 2003 (2002)30 J Trost H Brune J Wintterlin R J Behm and G Ertl J Chem

Phys 108 1740 (1998)31 J B Wachtman Jr T G Scuderi and G W Cleek J Amer

Ceramic Soc 45 319 (2006)

Received 30 April 2010 Accepted 4 June 2010

184 Nanosci Nanotechnol Lett 2 181ndash184 2010

Delivered by Ingenta toStevens Institute of Technology

IP 15524615220Wed 05 Jan 2011 153948

Sul et al Fabrication and Characterization of a Nanoscale NindashAl Bimorph for Reconfigurable Nanostructures

Fig 2 Angled transmission electron microscope (TEM) image of aNindashAl bimorph The aluminum (Al) layer is on top of the nickel (Ni)nanowire (arrow) The scale bar is 500 nm

where Y = E1minus E is Youngrsquos modulus is Pois-son ratio and is the thermal expansion rate assuming arectangular cross section for each layer Here Aluminum =231 times 10minus6K22 Nickel sim 134 times 10minus6K23 EAluminum =70 GPa24 ENickel = 200 GPa25 Aluminum = 03326 and Nickelwas 03127

The diameter of a fabricated Ni nanowire was 270plusmn20 nm which was a little larger than the nominal poresize of AAO membrane as similarly shown in otherreports1528 The diameter was confirmed by scanning elec-tron microscope (SEM) images These nanobimorphs usedin the actuation experiment were made from individualnanowires not from nanowire bundles which was alsoconfirmed by SEM images The measured thickness ofaluminum was 70plusmn 10 nm which was confirmed usingan atomic force microscope (AFM) from a separatelyand simultaneously deposited aluminum film on a sepa-rately prepared substrate Three different lengths of NindashAlbimorphs were used in this experimental study 10 13 and18 mThe silicon substrate containing the bimorphs was

loaded on top of a miniature heater (Heat wave labs ultrahigh vacuum button heater Model 101136) which wasmounted on a custom built SEM stage (Fig 3) A thermo-couple was attached to the surface of the heater to monitorits temperature The power cables and the thermocouplewire were extended to the outside of the SEMrsquos vacuumchamber through a feedthrough Because it was difficultto accurately measure the temperature of the substratedirectly the temperature of the heater was continuouslymonitored by a thermometer outside the chamber until itwas stabilized at a targeted temperature The temperaturestabilization could also be monitored using ldquoliverdquo SEMimaging As the temperature is raised the SEM imagingshowed lsquodriftingrsquo of the substrate due to thermal expan-sion of the heater and the substrate To track the iden-tical bimorph the SEM stage was manually controlledAfter temperature stabilization was achieved the driftingstopped Then the heater and the substrate remained for

Fig 3 An SEM stage for thermal control The silicon substrate wasmounted on top of the button heater The thermocouple tip was attachedon the surface of the button heater to monitor the temperature

some time (about an hour) with the heater turned on con-tinuously to achieve thermal equilibrium We assumed thatat thermal equilibrium the heater and the substrate wereat the same temperatureFor a temperature change from 295 K to 675 K with

an 18 m long bimorph the calculated deflection usingEq (1) is 890 nm The measured deflection from the SEMimages shown in Figures 4(a) and (b) was 700plusmn200 nmThe deviation between the calculation and the measure-ment is attributed to the effect of oxidation at the surfacesof both metallic materials2930 especially because of thereduced thermal expansion rate of aluminum oxide on thesurface of aluminum layer31 Figure 5 shows a comparison

Fig 4 Thermal deflections of NindashAl bimorph nanoactuators (a) Anoverlay of two SEM images of an 18 m long bimorph taken at roomtemperature (295 K white) and at 675 K (black) during a temperaturerising phase The tip moved toward left (arrow) The oxide film is on theright side of the image Scale bar is 10 m (b) An overlay image ofthe same bimorph during the temperature decreasing phase The bimorphtip moves to the right when temperature is decreased to 295 K (c) Anoverlay image of a bimorph with 10 m in length at room temperature(white) and at 675 K (black) respectively The oxide film is on the topThe scale bar is 2 m The tip moved downward (d) Another over-lay image of the same bimorph in the decreasing phase The tip movedupward

Nanosci Nanotechnol Lett 2 181ndash184 2010 183

Delivered by Ingenta toStevens Institute of Technology

IP 15524615220Wed 05 Jan 2011 153948

Fabrication and Characterization of a Nanoscale NindashAl Bimorph for Reconfigurable Nanostructures Sul et al

Fig 5 Deflection measurements from the three bimorphs agree wellwith the prediction from Eq (1)

between measurements and prediction by Eq (1) for allthree bimorphs

3 CONCLUSIONS

We have created a bimorph nanoactuator by depositing athin Al film on top of an electrodeposited Ni nanowireThe amount of deflection generated from this nanoscalebimorph was measured using SEM images Compared topreviously reported approaches our fabrication methodutilizing PLD could possibly be utilized for generation ofmultiple devices with high yield Thermal actuation has theadvantage of a simpler actuation method because it doesnot require electrical wiring or a charging environment forthe devices Comparisons were made with bimorph theorybased on the limited data obtained in this study The resultsand analyses suggest that the measured deflections agreewith the prediction while more actuation data with variousthicknesses and diameters of nickel nanowires are neededthrough further study This work is the first step towarddeveloping reconfigurable nanostructures for an antennatechnology

Acknowledgment The authors appreciate valuableadvice and comments on the YAG laser by ProfessorsStrauf and Whittaker in the Department of Physics atStevens Institute of Technology The authors also thankKitu Kumar for her technical assistance This work hasbeen partially supported by the National Science Founda-tion Major Research Instrumentation Program Award NoDMI-0619762

References and Notes

1 Y Qian and T Itoh IEEE Trans Microwave Theory Tech 46 1891(1998)

2 J Lin and T Itoh IEEE Trans Microwave Theory TechMTT-42 2186 (1994)

3 P J Burke Proceeding of SPIE 5593 52 (2004)4 I Zine-El-Abidine and M Okoniewski J Micromech Microeng

17 2280 (2007)5 I Zine-El-Abidine M Okoniewski and J G McRory

J Micromech Microeng 15 2063 (2005)6 V M Lubecke B Barber E Chan D Lopez M E Cross

and P Gammel IEEE Trans Microw Theory Tech 49 2093(2001)

7 B A Cetiner H Jafarkhani J Y Qian H J Yoo A Grauand F De Flaviis IEEE communication magazine 42 62(2004)

8 B A Cetiner G R Crusats L Jofre and N Biyikli IEEE Trans-actions on Antennas and Propagation 58 626 (2010)

9 L Jofre B A Cetiner and F De Flaviis IEEE Trans on Antennasand Propagat 50 658 (2002)

10 J Muldavin C O Bozler S Rabe P W Wyatt and C L KeastIEEE Transaction on Microwave Theory and Techniques 56 522(2008)

11 M Rais-Zadeh P A Kohl and F Ayazi J Microelectromech Syst17 78 (2008)

12 D A Czaplewski G A Patrizi G M Kraus J R WendtC D Nordquist S L Wolfley M S Baker and M P DeBoerJournal of Micromechanics and Microengineering 19 085003(2009)

13 A Subramanian A R Alt L Dong B E Kratochvil C RBolognesi and B J Nelson ACS Nano 3 2953 (2009)

14 T Ikuno S Honda T Yasuda K Oura M Katayama J G Leeand H Mori Appl Phys Lett 87 213104 (2005)

15 O Sul and E H Yang Nanotechnology 20 095502 (2009)16 I Z Rahman K M Razeeb M A Rahman and M D

Kamruzzaman J Magn Magn Mater 262 166 (2003)17 N A Melosh A Boukai F Diana B Gerardot A Badolato P M

Petroff and J R Heath Science 300 112 (2003)18 J Chang B K Min J Kim and L Lin Microelectron Eng

86 2364 (2009)19 N Sinha G E Wabizewski R Mahameed V V Felmetsger S M

Tanner R W Carpick and G Piazza Appl Phys Lett 95 053106(2009)

20 V A Pedrosa X Luo J Burdick and J Wang Small 4 738(2008)

21 G A Gehring M D Cooke I S Gregory W J Karl and R WattsSmart Mater Struct 9 918 (2000)

22 W Fang and C Y Lo Sensors and Actuators 84 310(2000)

23 Y Kuru M Wohlschlogel U Welzel and E J Mittemeijer SurfCoat Technol 202 2306 (2008)

24 A V Kulkarni and B Bhushan Thin Solid Films 290 206(1996)

25 H Majjad S Basrour P Delobelle and M Schmidt Sens Actua-tors A Physical 74 148 (1999)

26 G Cornella S H Lee W D Nix and J C Brevman Appl PhysLett 71 2949 (1997)

27 G Simmons and H Wang Single Cyrstal Elastic Constants and Cal-culated Aggregate Properties A Handbook 2nd edn MIT PressCambridge MA (1971)

28 W C West N V Myung J F Whitacre and B V RatnakumarJ Power Sources 126 203 (2004)

29 H Over and A P Seitsonen Science 297 2003 (2002)30 J Trost H Brune J Wintterlin R J Behm and G Ertl J Chem

Phys 108 1740 (1998)31 J B Wachtman Jr T G Scuderi and G W Cleek J Amer

Ceramic Soc 45 319 (2006)

Received 30 April 2010 Accepted 4 June 2010

184 Nanosci Nanotechnol Lett 2 181ndash184 2010

Delivered by Ingenta toStevens Institute of Technology

IP 15524615220Wed 05 Jan 2011 153948

Fabrication and Characterization of a Nanoscale NindashAl Bimorph for Reconfigurable Nanostructures Sul et al

Fig 5 Deflection measurements from the three bimorphs agree wellwith the prediction from Eq (1)

between measurements and prediction by Eq (1) for allthree bimorphs

3 CONCLUSIONS

We have created a bimorph nanoactuator by depositing athin Al film on top of an electrodeposited Ni nanowireThe amount of deflection generated from this nanoscalebimorph was measured using SEM images Compared topreviously reported approaches our fabrication methodutilizing PLD could possibly be utilized for generation ofmultiple devices with high yield Thermal actuation has theadvantage of a simpler actuation method because it doesnot require electrical wiring or a charging environment forthe devices Comparisons were made with bimorph theorybased on the limited data obtained in this study The resultsand analyses suggest that the measured deflections agreewith the prediction while more actuation data with variousthicknesses and diameters of nickel nanowires are neededthrough further study This work is the first step towarddeveloping reconfigurable nanostructures for an antennatechnology

Acknowledgment The authors appreciate valuableadvice and comments on the YAG laser by ProfessorsStrauf and Whittaker in the Department of Physics atStevens Institute of Technology The authors also thankKitu Kumar for her technical assistance This work hasbeen partially supported by the National Science Founda-tion Major Research Instrumentation Program Award NoDMI-0619762

References and Notes

1 Y Qian and T Itoh IEEE Trans Microwave Theory Tech 46 1891(1998)

2 J Lin and T Itoh IEEE Trans Microwave Theory TechMTT-42 2186 (1994)

3 P J Burke Proceeding of SPIE 5593 52 (2004)4 I Zine-El-Abidine and M Okoniewski J Micromech Microeng

17 2280 (2007)5 I Zine-El-Abidine M Okoniewski and J G McRory

J Micromech Microeng 15 2063 (2005)6 V M Lubecke B Barber E Chan D Lopez M E Cross

and P Gammel IEEE Trans Microw Theory Tech 49 2093(2001)

7 B A Cetiner H Jafarkhani J Y Qian H J Yoo A Grauand F De Flaviis IEEE communication magazine 42 62(2004)

8 B A Cetiner G R Crusats L Jofre and N Biyikli IEEE Trans-actions on Antennas and Propagation 58 626 (2010)

9 L Jofre B A Cetiner and F De Flaviis IEEE Trans on Antennasand Propagat 50 658 (2002)

10 J Muldavin C O Bozler S Rabe P W Wyatt and C L KeastIEEE Transaction on Microwave Theory and Techniques 56 522(2008)

11 M Rais-Zadeh P A Kohl and F Ayazi J Microelectromech Syst17 78 (2008)

12 D A Czaplewski G A Patrizi G M Kraus J R WendtC D Nordquist S L Wolfley M S Baker and M P DeBoerJournal of Micromechanics and Microengineering 19 085003(2009)

13 A Subramanian A R Alt L Dong B E Kratochvil C RBolognesi and B J Nelson ACS Nano 3 2953 (2009)

14 T Ikuno S Honda T Yasuda K Oura M Katayama J G Leeand H Mori Appl Phys Lett 87 213104 (2005)

15 O Sul and E H Yang Nanotechnology 20 095502 (2009)16 I Z Rahman K M Razeeb M A Rahman and M D

Kamruzzaman J Magn Magn Mater 262 166 (2003)17 N A Melosh A Boukai F Diana B Gerardot A Badolato P M

Petroff and J R Heath Science 300 112 (2003)18 J Chang B K Min J Kim and L Lin Microelectron Eng

86 2364 (2009)19 N Sinha G E Wabizewski R Mahameed V V Felmetsger S M

Tanner R W Carpick and G Piazza Appl Phys Lett 95 053106(2009)

20 V A Pedrosa X Luo J Burdick and J Wang Small 4 738(2008)

21 G A Gehring M D Cooke I S Gregory W J Karl and R WattsSmart Mater Struct 9 918 (2000)

22 W Fang and C Y Lo Sensors and Actuators 84 310(2000)

23 Y Kuru M Wohlschlogel U Welzel and E J Mittemeijer SurfCoat Technol 202 2306 (2008)

24 A V Kulkarni and B Bhushan Thin Solid Films 290 206(1996)

25 H Majjad S Basrour P Delobelle and M Schmidt Sens Actua-tors A Physical 74 148 (1999)

26 G Cornella S H Lee W D Nix and J C Brevman Appl PhysLett 71 2949 (1997)

27 G Simmons and H Wang Single Cyrstal Elastic Constants and Cal-culated Aggregate Properties A Handbook 2nd edn MIT PressCambridge MA (1971)

28 W C West N V Myung J F Whitacre and B V RatnakumarJ Power Sources 126 203 (2004)

29 H Over and A P Seitsonen Science 297 2003 (2002)30 J Trost H Brune J Wintterlin R J Behm and G Ertl J Chem

Phys 108 1740 (1998)31 J B Wachtman Jr T G Scuderi and G W Cleek J Amer

Ceramic Soc 45 319 (2006)

Received 30 April 2010 Accepted 4 June 2010

184 Nanosci Nanotechnol Lett 2 181ndash184 2010