Cutting Edge Nanotechnologylloporphyrin systems are excellent materials for molecular electronicsrse structural motifs and associated electrical, optical and chemicalnanostructures like tubes, spheres, wires, rods and structures withortunity fof these functionalmolecules into electronic and optoelectronic devices(Botti et al 2002) DNA provides basicbuilding blocks for constructing functionalized nanostructures with four major featuresmolecular recognition, self-assembly, programmability, and predictable nanoscale structure(Braunthis chapter, we review the formation of 5-(4-Hydroxyphenyl)-10, 15, 20-tri)nI) porphyrin SAMlicon dioxide(SiO2) and hydrogen silesqui(HSQ) andpplication as Cu diffusiofor UlSi metallization and in microfluidics, We discussSAM on gold and its interesting properties for molecularsome of the approaches and current research status inDNAlatedre fabrication and the potential use of DNAsnsistor realization2 Challenges in Nanoscale TechnologiesCMOS technolmicroprocessors, static/dynamic mmicrocontrollers and othets As weys of building logic andhbe considered One such approach is using bottom-up methods with the conventionalfabrication metodsthe sub-50 nm CMOSmultilevel interconnects with copper(Cu) are currentlybeing used to minimize interconnect delay, coupling, and power dissipation Copper is oneof the best known electrical conductors having a very low resistivity and highation resistance horough the dielectric is a sereliability issue(Dallaporta, 1990)
Diffusion of copper in Si, SiO and low-k inter layegrading the device performance and life time(Shacham-Diamond et al, 1991) Becausehese issues Cu needs a suitable drift/diffusion barrier whose thickness is scaleable alongth the other technoloNext section discusses the application of hydroxy l-phenyl porpAMs in nano-scaletechnologies First, we discuss, how 5-(4-Hydroxyphenyl)-10, 15, 20-tri (p-tolyl) Zn(llrphyrin SAM is useful in preventing copper diffusion in SiOz and HSQ Surfacedification of substrates like SiOz using porphyrin SAMs has a tremendousnanofluidics The porphyrins with meso-pyridyl groupuseful to prepare walublerphyrins, which can bind with biological molecules such as DNA and other proteins Weso review the formation of and characterization of SAM of meso-pyridyl porpa thiol linker [such as 5(4-(2(4-(S-Acetylthiomethyl)phenyl)ethynyl)pheny l)10, 15, 20-trisell known that the bottom-up approachsophisticated DNA networks, Section 4 describes how the DNA is used as a template forecularand in quantum computingntechopen
Bottom-up Approaches for NanoelectronicsUHV) or other specialized equipment Krishnamoorthy et al, in 2001 have reported the usediffusion barriers at the Cu-SiO interface Molecules with different side chains andt terminal groups have been studied toilize Cu through strong localinterfacial bonding and to improve interfacial adhesion (Ganesan et al, 2004) In thefollowing section, the potential application of hydroxy-phenyl Zn(l) porphyrin SAM asCu diffusion barrier for ULSI metallization has been explained342 Porphyrin SAMs as Cu Diffusion Barriers in ULSI metallizationUsing the porphyrin SAM as a diffusion barrier has multiple advantages like excellentthickness controlayer ), conformal layer formation and uncenter of the porphyrin macrocycle Zn in hydroxy-phenyl Zn(li) porphyrin moleculeprevents Cu ion diffusion into SiOz due to its electronegativity and strong binding to theporphyrin molecule Adding to the above effects, the pyrrole subunits within the porphyrinkey role in the piion of cu diffusionnds have been known for their involvement in diffusion barriermechanisms(Mrunal Khaderbad et al 2008; Urmimala Roy et al, 2009presented
It shows that the hydroxy-phenyl Zn(n porphyrin sAl p-Si hasisthe following sections, the resulture-stress(BTS)CV analysisis effective inpreventing the diffusion of mobile Cu ions into SiOz as well as HSQBias Stress Temperature effects on CisiOyp-Si and CwvsAMSiOyp-Si MOS capacitors(MOSCAPsdiffuse through sio,, Si or ILDs under highmperature stress(BTSnditions, Previous research showed that in atmospheric nitrogen ambient, copper driftigher In theectric field, at temperatureslow as 100C, positive Cu ions(Cu or Cu2) drift rapidly through inter-layer dielectricsILD)(Cluzel et al, 2002; Loke et al, 1998) The copper ion diffusion under BTS conditionsthe shift of moscap c-vcitance-voltage)characteristics This shift can becalculated using the following equationViBdms-1/Cox(Qr+ QmYm+ Qhere Cox is the oxide capacitance; poes is the difference in the work functions of the metalcharges respectively andm is the centroid of the mobile chargecarriedCu/SiOz(HsQ)/p-Si and Cu/SAM/SiO(HSQ)/p-sithe Cu diffusion SAM formation in thesedthe recipe explained in section 33 Fig 9(a) describes the pistress and post-stress C-v(normalized with respect to Cma)characteristics for the Cu mOScapacitors(tox=40nm) with and without the porphyrin SAM, obtained at 50 kHz frequenusing Agilent 4284-A precision LCR meter Fig 9(b) shows the C-v characteristics for theCu MIS capacitors (tHs150nm) with and without the porplequency The Cu/SiO /p-Si MOS capacitor was subjectedectric fielntechopen
Cutting Edge Nanotechnologystress at 100C for 30 minutes, where as, the Cu/HsQ/p-Si MIS capacitor was subjected toelectric field stres0608605-stress C-V characteristics for the Cu mosd without the porphyrin SAM (b) Pre-stress and post-stress HFCv plots ofCu/SAM/HSQ/p-Si MIS capacitor after BTS of 30 min (tH5Q= 150nm)g plots in figs
9(a)and 9(b), it is clear that Ce shift is less in thethat of mos structure without SAMAVab(Vab shift) versus stress time for MOS(MIS) structures with and withoutbjected to higher fields(45 Mv/cm) at theture (100 C) and stress time(30 mins), and still show superior properties(Fig15stressedAM were subjectedemperatures (c) Flatband Voltage(AVib) versus stress timeof Cu/HSQ/Si andoxy-Phenyl Porphyrin SAMs for micro/nancial for tfabrication of nanofluidic dThe hydrophobic and hydrophilicacterurface have been exploited to handle and control liquid flows in the abovphobic and hydrophilic regions inside microchannelsprinting ofntechopen
Bottom-up Approaches for NanoelectronicsPorphyrin self-assembled monolayer chemistry can be used to modify surface wettingf a variety of materialsThe contact angle meastts are known to be effecticharacterizing theetting propertiements of 50 HL of sessile DResistivity, p-182 MQ2-cm) drop on Sio surface and on hydroxy-phenyl porphyrinFig 11 Contact angle measurements(a)DI water drop on SiO2(b) Image showing a DI waterdrop on hydroxy-phenyl porphyrin SAMThe water drop on SiO2 surface exhibited contact angles of 30+20 showing hydrophilicg 1la)of hydroxy-pheto78±30shows that the patterning of hydrophilic substrates with porphyrin SAMs has tremendousapplications in micro/nanofluidics and that the SAMs are effective in modifying the surfaceproperties36 Meso-pyridil Porphyrin SAM on Gold for molecmolecules as buildiectronic devices such as transistors, has the potentialple che,d ang blocks for makingwith electronic or optical functionality and their self assembly to build active electronidevices CNTS, polyphenylenes, porphyrins and DNA strands are some of the moleculeshat are being actively researched upon for the above purposes Many techniques have beenproposed to probe the conductance of single molecules, either using a fixed gap betweentwo electrodes(fabricated by e-beam lithography or as a mechanically controllable breakunction or break-junction using electromigration) or using conductive atomic forcemicroscopy(AFM) and scanning tunneling microscopy(STM)techniques(Chen et al, 2007;Akkerman et al, 2008)
Apyridil SAM on gold with a thiol linker can be formed asexplained in section 331 Amarchand Satyapalan et at in 2005 reported its structural andheir applicationsbserved that the electronic characteristics measured by scanning tunneling spectroscopthat thissimilar to a serjunction with a barrier potential(Reed et al 1997) This barrier behavior can beth the help of alignment of molecular orbital levels(HOMO/LUMO) with thatgy level Dependingstrongly whenev>EL-eeositive substrate biasEf- ehnegative substrate bias)()ntechopen
Cutting Edge Nanotechnologywhere Et and EH are LUMO and HOMO energy levels of the molecule respectively and Ey isgiven by(Datta et al, 1997)ev>min [(Er-EH/n), (EL-Erl-n (positive substrate bias)(4)distance of substrate from the centre of the molecule to the distance ofsubstrate from the tipFig 12(a)I-V characteristics of bare gold substrate(b)I-v characteristics of the SAMFigure 12 shows the STS plots of the gold substrate and of the 5-(4-(2-(4-(SAcetylthiomethyl)heny l)ethyny l)phenyl)-10, 15, 20-tris(4-pyridyl) porphyrin SAM in ambient laboratoryonditions It is evident that the tunneling current is almost negligible before a certain cut-inharply afterf porphy4 DNA for Nanoelectronics ApplicationsDNA is fast becoming a material of choice for the bottom-up approach in the fabrication ofof DNA as molecular wires(Eley et al, 1961) Easy availability(second-most abundant claof biomolecules, next to proteins), self-assembly property andbe manipulatin vitro has put DNA into one of the top-priority alternatives febiomolecules are to be chosen for the bottom-up self-assemblapproach, DNAdbust toextreme physical and chemical conditions Inherent programmability of DNA througnce is another attractive feature ofabove points, DNA also offers the possibility of in vifro precise manipulation which makespossible interesting device applications for nanoelectronics applications4
1 RelevaDNA is a duplex (double-stranded) polymeric molecule Each strand is itself a polymensisting of nitrogenous basesd(thymine, cytosine and uracil) The only exception that contains uracil molecule in the dNAbacteriophage pbs1a,1995) Fig, 13 shows the chemical structure of the five basesntechopen
Bottom-up Approaches for NanoelectronicsGuanineCytosineUracilFig 13 Different bases in a DNA molecuases form hydrogen-bonds between each other so as to stabilize the duplexforms double H-bonds with thymine or uracil whea triple H-bond with cytosine (as shown in fig 14)canine- Cytosine2008)The DNA moleculegatively-supercoiled like a rope, twisted opposite to thedirection of helix thus pushing the basesfrom each other This structural propertyZ-DNA Out of these, B-DNA is the most common form of DNA available(hence mostwidely studied scientifically) and Z-DNA is the rarest form of DNA (formsstringent conformed due to the charof DNA, the amount and direction of supercoiling, chemical modifications of the bases andthe solution conditions (like the condn of electronic templates These attributes are listed in table-2 as followsA-formB-formight-handed right-handedMean bp/t/bp along axis 24 A(0 26 3 4 A(034 nm) 3
A(037 nm)Rise/turn of helix 246 A(246 nm) 332 A (332 nm) 456A(456 nm)ropeller20A(20nm)18A(18nm)2 Geometrical attributes of A, B- and Z-forms of DNA(Neidle, 2008; Ghosh2003)ntechopen
Cutting Edge NanotechnologyAnother important physical feature that needs a mention is the presence of major and minorn the DNa molecule(fitT03415 Schematic of DNA molecule showing major and minor grooves(Molecular BiologyWeb book, 2009)12A Differentterials like porphyrins and others that bind to DNA usually prefer major grooves for thispurpose This is because of the greater exposure of bases through the respective grooveMolecular Biology Web Book, 2009), DNA being a biological molecule could bebelated to the needs of electronics by bilecule is possible by the use of different enzymes(Molecular Biology Web Book, 2009)asNucleases: Enzymes that degrade dNa by hydrolysis of the phosphodiester bonExonucleases hydrolyze phosphodiester bonds from thef DNAEndonucleases hydrolyze phosphodiester bonds within the DNA
Mostfrequently used nucleasesLigases: Enzymes that close the nicks; recover the broken phosphodiester bonds ina double-stranded (ds)DNpolymerases: Synthesize polynucleotide chains from nucleoside triphosphatesuence of their products match with the pre-determined polynucleotide chainsork in 573 direction (by addirAfter thess is done, dnaule could be separated on the basis ofnumber of base-pairs in the molecule by gel-electrophoresis The amplification / selection of dna molecules could bepolymerase-chain reaction colloquialknown as PCR In this process, a RNa primer is required to start the reaction Then DNAntechopen
Bottom-up Approaches for Nanoelectronicslymerase takes over, adding individual dNTPs present in the reaction mixture accordinthe sequence as desired This process repeated n times give 2 copies of the desired DNolecule(Saiki et aL, 1985; Saiki et al, 198842 Transfer of charge through DNAThe much debated topic in the scientific community is the conductivity of bare dNAolecule Scientists have reported DNA as superconducting(Kasumov et al, 2001), metallic(Fink et al, 1999; Cai et al, 2000; Tran et al, 2000; Yoo et al, 2001), semiconducting( Poratht al, 2000; Rakitin et al, 2001) and insulating(Braun E, et998: dePablo et al 2000torm et al
2001)as well There coua plethora ofns for the ambigui
Bottom-up Approaches for Nanoelectronics3 Porphyrin Self-Assembled Monolayers for Nanoelectronic Application31 Self-Assembled MonolayersAMand selfon to the surfaces of different substrates Theecules that feare calledreactants Surfactanof a headwhich bindsat constitutes the outer surface of the film, and a backbone that connects head-group andend-group and affects the intermolecular separation and molecular orientation
A SAM hasthermodynamically stable system, it tends to eliminate faulous surfaces that have been employedAMctors such apalladium;conductorsdsme and cadmium sulfide and insulators such as silicon oxide(Abraham UAn impotem for itstechnological applications is thetures ofdroxyalkylalkoxysilanes, and alkylaminosilanes need hydroxylated surfaces as substrates Selfassembly of these molecules takes place through the formation of polysiloxane, which isnnected to surface silanol groups(-SiOH) via Si-O-Si bonds Fig la shows the process forthe formation of SAM on silicon dioxide using silanes, organometallics and alcohols(Aswalal,2006)SiHydroxylationbSihalogenation/Amination3333Silanization(RSiCl3)SiO2Au, Ag, Cu and PeSiO2SiO2Fig 1(a) Formation of SAM on SiOz(b)SAM on Goldntechopen
Cutting Edge Nanotechnologyubstrates on which thesequartz, glass, mica, zinc seler g the above process includeyers have been preparekanethiolates CH3(CH2)nsd well definedarrangement of organic surface phases was first observed in 1983 by the immersion of a gsubstrate in the dialkylsulfide solution Besides gold, thiols bind very strongly to sillladium and copper(Abraham Ulman, 1998) Fig 1b shows the formation of SAM onis well known that there are a number of head groups that bind to various dielectrics(Christopher Love et al
, 2005) The binding mechanism is given in the third column, bratconductors, Tabshows the ligands that bind to the vBindingSH, ArSH(thiols)RSMMg Cu, Pd)RSOHRSO-A1RNCRNC-PUGaAsRS-GaAsRS-GaAsSiO, glassRSiCl3, RSi(OR)Si-HIRCOOYCH, CHSi/Si-ClRLi, RMgXR-SiMetal oxidesRCOOHRCOO----MORCONHOHRCONHOI—MORPO:HRPO 2---Zr+In O3/SnO2RPO32---MTable 1 Substrates and ligands that form SAMsthe following sections, importance of porphyrins and porphyrin derivatives, formation ofus substrates and structural/ material characterization of thesentechopen
Bottom-up Approaches for Nanoelectronics32 Porphyrinsolecule The basic structure of the porphyrin macrocycle consists of four pyrroliclinked by four methine bridFig 2 Porphin moleculeFigure 2 shows the structure of a porphin molecule Porphyrins bind metals to formomplexes, usually with a charge of 2* or 3+, which resides in the central N4 cavity formedby the loss of two protons These metallo-porphyrins play an important roleChlorophyll is a Mg-porphyrin and the Fe(lI) porphyrin complex is the part of hemoglobinsglobins, whikygen transport and storage in living tissuesDavid Dolphin, 1978)wide variety of porphyrin arrays of ever increasing size have been constructed by thetraditional methodology of covalently linking porphyrins The importance of porphyrinslectrochemical properties, stability, and highly predictable and robust structure Theresearch developments in the formation and characterization of functional, porphyrinterials and devicesif-assembled porphyrin arrays into phototransistors andAs of porphyrin molecules for sensors and nanotechnologypplications: metalloporphyrins as stochastic sensand covalently bound arrays ofyrrole units as photonic materialsf these multi-functional nanostructures is in nanoelectronics andonducting properties(Kenneth S
Suslick et al, 2000)Photoconductivity and non-linear optical properties with visible light have also beenemonstrated in porphyrinic materials(Schwab et al, 2004) With porphyrins formingnanostructures such as tubes, spheres, wires, rods, and structuresmorphologies, an opportunity presents itself for integration of these functional porphybased nanostructures into electronic and optoelectronic devices(Anthony et al, 200(Grenoble et al, 2005), organic field effect transistors (OFETs)(Berliocchi Met al 2004), bio-sensorsky et al, 2000), explosive detectors( Shengyang tao et2007, Dudhe et al, 2008, 2009)and in TFTs, Wende et al, 2007, demonstrated the substrate-induced magnetic ordering and switching of iron porphyrin molecules Above studies openent molecular electronicspotential applications of porphyrins in memory storage devices Masahiro Kawao et alprepared conducting oligo-diethynyl-porphyrinwith length exceeding 600 nm Thntechopen
Cutting Edge Nanotechnologyptics33 Hydroxy-phenyl PoSAM formation on siO and HsQThe hydroxy-phenyl porphyrin SAMhnique(Onclin, 2005) The silicon dioxide substrate used to prepare porphyrin SAM wasSi wafer The substrate was then cut into the required size and cleaned byminutes This removes any native carbon impurities and creates OH groups on the Sio2ng siloxane bonds and forming silanol groups(SiOH)on the surface Aftertreatment, the Sio substrate was rinsed inter and driedunder Ar gas flow
M =Zn, cu, Co, Ni Mg5(4-Hydroxypheny l)-10, 15, 20-tri (p-tolyl) porphyrin This molecule 5(4-Hydroxyphenyl)-10, 15, 20-tri (p-tolyl) porphyrin is used to prepare a self-assembledressure-10-2mbar) the substrate at 1100Cfor 1 hour 4 mg of porphyrin was dissolved in 20 ml of toluene to prepare 10-M solutionThe Sio substrate was immersed in the above solution for 30 minutes During immersionhead groups of the porphyrin molecule chemically bond with the silanol groups on Sio2surface forming a self-assembled monolayer(Fig 4)ntechopen
Bottom-up Approaches for NanoelectronicsFig 4 Formation of hydronyl porphyrin SAM on Siog the substrate with toluene and drying under Ar gaFinally the substratheated at 120oc for 45 minutes to remove the water molecules andthen stored for characterization Almethod can be used to prepare SAM on HSQThe formation of sa ms is assessing various methods, which include surface probeicroscopies(such as AFM and STM), Fourier transform Infrared spectroscopy(FTIR), UVspectroscopy, tunnelingpy(TEM), sum frequtact angle, ellipsometry, and NEXAFSUltraviolet-visible spectroscopy200-400visible = 400-800 nm) corresponds tobetween the energy levels that correspond to the structure and orbitalsms
The following electronic transitionby the absorption ofultraviolet and visible light: o to o, n to o*, n to m01201freebase8008後000Wavelength(nm)isible spectrum of Zn-TPP-OH SAM on HScintense absorption(extinction coeffic200,000)in the neighborhood of 400 nm; thisbsorption maximum is referred to as the Soret Band", Visible spectra of porphyrins alsoeral weaker absorptions (Q Bands) at longer wavelengths (450 to 700 nntechopen
Cutting Edge NanotechnologyVariations of the peripheral substituents on the porphyrin ring cause minor changes to thetensity and wavelength of the absorption features The protonation of two of the innitrogen atoms or the insertion/removal of metal atoms into the macrocycle strongly changethe visible absorption spectrum Fig 5(a) illustrates the ground state UV absorpof the hydroxy-phenyl porphyrin SAM on SiO Spectra were recorded using Perkin-ElmerLambda 35 spectrophotometer at room temperature in the wavelength range of 350 to 800D2 substrate, relatively low absorbance was observed The Soret band of porphyre n cnm) For porphyrin inO2 was broadened and red shifted to 426 nm compared to the Soret band of porphyrinluene This red shift indicates that the porphyrin molecules are arranged-sideorientation in thecular self-assembly Fig 5(b) illustrates the ground state UVabsorption spectra of the hydroxy-phenyl porphyrin SAM on HSQ
Soret band shift and331 Preparation of meso-pyridyl Porphyrin SAM on Goldof meso-pyridyl porphyrin Self-Assembled Monolayer(SAM)explained in the work done by Amarchand Satwork, a meso-pyridyl porphyrin having a thiol linker such as 5-(4-(2-(4-(S-acetylthiomethyphenyl) ethynyl) phenyl) porphyrin shown in Fig 6 was synthesized and used for theon of seThe formation of self-assembled monolayers on gold surface is a spontaneous process Thecificity of the gold-sulfur interaction has providedxtremely convenient route to theormation of chemisorbed molecular films, The procedure of SAM formation that isfollowed is simple, and flexible enough to change it to suit different compounds The SAMsformed by this method are very stable due to the nature of the adsorption which is viachemical bondCH2SCOCH30-tris(4-pyridyl) porphyrinFourier transform infrared (FTIR) spectroscopy gives the molecular orientation and orderingin a self-assembled monolayer For this study, grazing incidence(80 to the surface normalntechopen
Bottom-up Approaches for Nanoelectronicsreflection absorption FTIR spectroscopy was used Fig 7 shows the FTIR spectrum of mesoa broad and strong band at 3433ecules bound to theband due to the stretching mode ofesolved at about 3315shoulder on the lonumber sid3o t hyrin a e inly from the O-H stretching mode of waterd at 3433 cm-1 Besides this high wavenumber band, twebands at 970 and 723to N-H in-plane and out-of-plane bending modesber region A strong band at 2924dium band at 2357ascribed to CH2 antisymmsymmetric stretchingmodes, respectively A strong band located at 1637 cml is ascribed to the C==N stretchingmode Some weak and medium bands due to the vibrational modes of the porphyrin ringon1600-680of the solid spectrum96095595
089459405001000150020002500300035004000Wavenumber (cm")Fig 7 FTIR spectrum ofpyridyl porphyrin SAM on goldThe surface coverage of a monolayer is examined by measuring the surface morphologyforce microscopy (AFM)(Fig 8) The 5-nlelutiondemonstrated the formation of SAMs meso-thiol porphyrins on gold surfaces Basichexagonal v3xv3 R 300 arrangement with highly ordered moneas observedntechopen
Cutting Edge NanotechnologyFig 8, AFMMs as Cu Diffusion Barriers in ULSI metallization341cion Barriers in ULSI metallizationFor the sub-nm CMOS technology, ultrathin diffusion barriers(1-3nm) are needed for thecopper interconnects to suppress the diffusion of Cu into silicon and into inter layerdielectrics(ILDs)(Awaya et al, 1996) In this regard, refractory metal binary and termarydes have been investigated for their copper diffusion barrier propeputtering is used to deposry nitride alloys, such as W-Ge-N, Ta-Si-N, W-Si-N, WB-N, and Ta-W-N Since the resistance of interconnects is affected by the thickness of thebarrier layer(Koike et al, 2005), thinner barrier layers(less than 10 nm)with TiSiN and WNhave been deposited by chemical vapor deposition(CVD)research groupsatomic layer deposition (ALn yer thickness by depositing ultra thin Tin or WNC layers byaddress the issue of barrier laydepositing conformal and thin barrier layers which a-2)
ALD is known to be effective inhous or polycrystallinehase ( ill S BeckerRoy G Gordon 2003) Thefailure mechanism of diffusiobarriers is the grain boundary diffusion and the barrier layers deposited by the abovediscussed methods tend to be ineffective due to their high defect densities and fast diffusipaths such as nano-pipes or grain boundaries(Rosenberg et al, 2000) Thus, deposition ofontinuous and uniform ultrathin layers is difficult by conventionalnd chemicalAn alternative and viable approach to this problem is tol - assembled monolaywhich can withstand back-end of line(BEOL) processing conditand meet the diffusion barrier requirements These methods are also extremely costffective compared to other deposition techniqeot require ultrahigh vntechopen