Interface design in nanosystems of Advanced Superionic Conductors

152

Ionics 11 (2005)

Interface Design in Nanosystems of Advanced Superionic Conductors A.V. Andreeva and A.L. Despotuli Institute of Microelectronics Technology, Russian Academy of Sciences 142432 Chernogolovka, Moscow Region, Russia Electronic mail: [email protected] (A.V. Andreeva)

Abstract. First attempt of practical realization of new interface engineering approach "from advanced materials to advanced devices" for nanosystems of Advanced Superionic Conductors (ASICs), based on AgI (CuI) compounds is presented. Crystallochemical method of symmetry perfect ASIC//electrode interface searching is developed. Some new theoretical results of ASIC//indifferent electrode conjugated commensurate heteropairs with coherent interfaces and preliminary experimental results of the creation of thin-film supercapacitor - prototype based on the lattice matched heterojunction - are given. Future perspectives of the ASIC//electrode interface design suited for micro(nano)electronics and microsystem technology (MST) are discussed.

1. Introduction Interfaces play a central role in the nanoscience and nanotechnology and the progression: "possibleachievable-desirable" in this area can be realized by modern methods of interface engineering [ 1]. The terms and approaches such as "grain boundary design", "interface engineering" first formulated and developed by T. Watanabe [2,3] were successfully applied for the creation of advanced micro(nano)composite materials with significantly improved mechanical [2-4], electronic, magnetic properties [5-7] etc. Nanoscience and nanotechnology combine a great number of fundamentals and applied directions, in overwhelming majority cases, they have been dealing with electronic conduction materials, their properties and applications. As electronic devices continue to become smaller, a larger percentage of the atoms reside at the boundaries (for micro- and nanodevices, the relationship surface~volume is in the order of 103-106 larger than that for the tablet analogs) and therefore, the interfaces are subjected to increasing importance at submicron scale. However, the general level of understanding of interface physics is noticeably lacking in many cases of technological interest. It is the reason of large actuality to investigate the influence of the interface atomic structure on the functional possibilities of low- dimensional solid

state devices. The aim is to gain control of materials and devices at the atomic level, allowing us to design materials with properties tailored needs of Hi-Tech. Nature's achievements are therefore benchmarks for our increasing control of nanomaterials and their properties. To optimize structure design, to predict and to achieve desired characteristics or to control nanosystem properties so that a given state is reached, the processes of internal structure self-organization must be in accordance with processes of external influence of different fields (composition, temperature, substrate orien-tation, deformation, electrical, magnetic fields etc.). In general, the synergy principle governing the behavior of any system consists of laws relating to internal interaction as well as to laws concerning the external influences [8]. Modern technology provides wide possibilities for the application of the interface engineering in the sphere of micro- and nanodevices. The achievements in the creation of semiconductor "super-lattices" (L. Esaki) and semiconductor micro(nano)devices with definite zone structure, based on artificial lattice commensurate heterostmctures (Zh.I. Alferov [9]) were marked by Nobel Prises. Among the electronic materials, there is a class of partially ordered crystal solids with high level of the unipolar ionic conductivity (oi > 0.001 ~~2-1cm-1) and very low level of the electronic conductivity (oi >> %). It is

153

Ionics 11 (2005)

of nanoionics and creation o f new type

Table 1. Some ASICs based on AgI (CuI).

ionic devices (nanoionic supercapacitors, ASIC

o i (T ~ ~2-,cm-~

1.3 (147)

ct-AgI

Activation energy (eV)

=0.1

Space group & lattice Parameters (A)

Electronegativity

Im3m,

1.7

0.3 (22)

~0.1

P4332,

The c o n c e p t u a l l y new a p p r o a c h "from

advanced materials to advanced devices" was introduced for the creation o f nanoionic devices on the base o f ASICs in [15,16].

2.09

The p a p e r is devoted to first attempt o f

P4j32

practical realization o f this new interface

a = 11.24 CsAg 4-

0.3 (22)

Br3_~I2+x

x = 0.3

KAg415

0.221(22)

-'0.1

cube

2.16-2.17

a = 10.96 0.1

P4:32

0.23 (22)

Ag19115P207

> 0.01(22)

2.09

cube,

0.14 0.17

= 0.34 (22)

,-0.1

C1128

2.41

RbCuaC13I2

0.1-0.2 (160-240)

~ 0.1

Fm3m,

2.25

0.35 (>25)

0.112

P433 2

0.112(>150)

0.3

P4332

ASIC//indifferent electrode with coherent experimental results of the creation o f the capacitor with FIT conservation based on g i v e n . The future p e r s p e c t i v e s o f the

2.29

ASIC//electrode interface design suited for micro(nano)electronics

and

MST

are

discussed. 2.22

2.

Experimental Procedure

To find conjugated lattice commensurate 2.28

a = 10.00, 10.032

CsCn4C1312

perfect ASIC//electrode interface searching

the lattice m a t c h e d h e t e r o j u n c t i o n are

a = 10.36 P4332

The

p r o t o t y p e o f thin-film n a n o i o n i c super-

a = 9.916; 9.93; 9.974, 10.01; 10.03

RbCu4Br3I2

compounds.

interfaces are presented. First preliminary

cube a~

P4132,

(CuI)

of conjugated commensurate heteropairs of 2.09

a = 6.15; 6.16; 6.17 Rb4CU1617.2 -

AgI

is developed. Some new theoretical results

a = 11.19

0.09(450)

ct-CuI

0.1

engineering approach for A S I C s , based on crystallochemical method of symmetry

a = 11.13, 11.14 Ko.sRbo.5Ag415

W e are convinced that new advanced devices should be based on the advanced materials.

a = 5.106, 5.069, 5.062 ct-RbAg4I5

sensors etc.) was pointed out in [15-17].

pares o f A S I C / / e l e c t r o d e w i t h

coherent

s y m m e t r y perfect interfaces, some earlier d e v e l o p e d algorithms and programs were 2.27

*The table data are from "PCPDFWin" [21], some original papers.

e m p l o y e d [18-20]. W e also used data base " P C P D F W i n " for search of electrode materials. The calculations were made for the

the group o f superionic conductors (SIC) and solid elec-

different types o f the A S I C s (Table 1), mainly based on

trolytes (SE) simultaneously (SIC A SE). A m o n g this

A g I (CuI) compounds. The first experimental data are

group, we mark out a sub-group o f advanced superionic

obtained for CsAg4Br3_xI2+x A S I C isomorphous belonging

conductors (ASIC) [10,11] with very high level o f cr~ (oi

to the RbAg4Is-family.

> 0.01 ff2-1cm-l) and low activation energy (E _< 0.15-

Thin-films o f incongruently melted CsAg4gr3_xI2+x (x

0.17 eV). Crystal structure o f A S I C is close to the

0.3), first synthesized in [22,23]) were prepared by flash

optimal one for a fast ion transport (FIT). Just for com-

thermal evaporation (T = 950 K) o f nonstoichiometric

pounds

compositions of AgI,

with F I T , the " n a n o i o n i c s "

t e r m and the

RbI,

CsI

and

AgBr.

The

conception was proposed in 1992 [12]. Now nanoionics

CsAg4Br3_xI2+x A S I C s have recorded high values of A g §

is progressing towards molecular manufacturing for the

conductivity in a wide temperature range, including 300 K

creation o f new advanced materials and devices for the

(o~ ~- 0.3 ~2-:cm-1 concentration of Ag*-ions = 1022 cm -3,

energy storage and transformation [13-16]. The steadfast

Oe ~ t0 ~0 _ 10-:~ g2-:cm-~ at 300 K) and stable temporary

necessity of the interface engineering for the development

characteristics. Distinctive feature o f CsAg4Br3_xI2+x (x -=

154

Ionics 11 (2005) (a)

R (ballast resistance)

to iraputresistance of oscillograph

_r-u-t

(b)

" qnnn, ~

,

mlpulse of voltage expmmmtal cell of Sg/ASIC heteroslructure

Fig. 1. The layout of the M/CsAg4Br~ xI2+x/Ag(M: metallic alloys) capacitive heterostructure: 1: metallic alloy; 2: CsAg4Br 3 xIz+x ASIC (200 nm); 3: Ag electrode; 4: epoxide.

0.3) is its stability (without decomposition) in contact with metallic silver [22], that may be used in devices with reverse to Ag+-ions silver electrode. After thermal deposition on the substrates, thin-films were annealed in vacuum for ~20 min at T = 350 K. The obtained thinfilms were monophase and rather stable. By

this

technology, the M/CsAgeBr3_xI2+~/Ag (M: metallic alloys) capacitive heterostructures were fabricated. In this paper,

Fig. 2. The oscillograph measuring on the experimental cells: (a) R - a ballast resistor which determines the time constant of electric circuit -t - RCwhere C is a capacity of experimental cell, U~- the pulse of voltage from a generator; (b) time dependence voltage on the generator (Us) and experimental cell (U~) sockets.

point defects always exist on the boundaries of ionic crystals [27]. The DEL thickness is in the order of Debye length hD and is determined by the concentration of the mobile ions n~. According to [10], nanosystems of solid state ionics can be divided into two classes which differ by an opposite influence of the crystal structure defects on the ionic conductivity o~

(energy

activation

E):

1)

due to patent information restriction, only the first experimental preliminary results of the investigation of the

nanosystems on the base of compounds with initially small o i (large values of E); lI) nanosystems on the base

ASIC//electrode heterojunctions (prototypes of new thin film supercapacitors) are presented. These results obtained

of ASICs, with E = 0.1 eV. In nanocomposites of "poor" ionic conductors (class i)

in IMT RAS by one of the author (D.A.L.) in 1991-1992 and published in 2003 [16,24-26] are based on the clear

of crystallite sizes comparable with the DEL thickness, the integral values of o~ may be much higher than that in

idea of the electrode selection with lattice parameters close to ASIC. The layout-type of the investigated heterostructure is shown in Fig. 1.

component substances [14]. However, the ion-transport

Measurements

of the heterostructure

capacitive

characteristics were done by means of the oscillograph or impedancemeter (BM 653). Scheme of the oscillograph

properties (o~, E, n~) in such nanocomposites are significantly worse (energy of activation E in 4-8 times larger) than in ASICs (c~-AgI, RbAg4Is). Thus, at the high concentration of defects in nanosystems of "poor" ionics (class I), enhanced integral 0~ arises but, in ASICs

registration and experimental heterostructure (cell) res-

(class 11), the influence of defects is opposite. Con-

ponse in a charge-discharge mode are shown in Fig. 2. The oscillograph registered the change of the voltage of

sequently, the structured design for these two classes of the nanosystems must be fundamentally different by the

the cell. The value of the cell capacity was determined by

nature for achievement of the FIT.

the comparison of the responses of the experimental cell and the standard capacitor.

In general, the structure of ASICs at the electrode interface can be of two types: 1) disordered, like in liquid

3.

perfect with minor structure distortions, i.e. with para-

or solid electrolyte in contact with nanoporous carbon; 2) Results and Discussion

3.1. Interface Engineering of ASIC//Electrode Heterojunctions 3.1a. Structure Design of Two Classes of Solid State Ionic: Nanosystems. The double electric layers (DEL)

ASIC//electrode interfaces. The design and investigation

with a high concentration (comparatively to bulk) of

of structurally perfect ASIC//electrode interfaces are new

meters close to those of a crystal structure in the bulk of A S I C Therefore, for FIT conservation in nanosystems of ASICs, there are necessarily stable and structurally perfect

155

Ionics 11 (2005) important directions of basic research in solid state ionics and nanoionics.

3.lb. Special and General-Type Interfaces. From the macroscopic viewpoint, two crystals conjugated at the interface can differ in their chemical nature, structure, and relative orientation. These factors, working together or individually, form interphase (hetero-), and grain (homo-) boundaries which include domain boundaries, stacking faults, dislocation walls, etc. From the microscopic crystallographical viewpoint, as formulated by J. Friedel [28], interfaces can be divided into two large groups: (i) broad diffusion boundaries whose structure varies continuously ("incoherent boundaries") and (ii) narrow boundaries with structure varies sharply ("coherent and semicoherent boundaries"). These terms are based on the degree of atomic matching across the interface. External effects (temperature, pressure, composition, electric and magnetic fields, etc.) can make coherent boundaries incoherent and vice versa upon phase transitions. Therefore, to obtain film heterostructures with predictable and stable characteristics, the processes of their formation should be controlled by external fields with the account of crystallochemical properties of materials used. Device-quality films with high and stable electrical properties must have perfect structures and high density. Thin-films are nonequilibrium systems with a multivariant type of behavior during growth and there is a lot of controlling parameters of the nucleation and growth processes. Epitaxial growth of single crystalline layer on the nonisomorphous substrates is the most frequently used method of monolayer structure fabrication in microelectronics. In this method, an oriented layer growth is due to anisotropic effect of the substrate, therefore, the relationship between the symmetry of the substrate and the epitaxial layer (epilayer) is determined by the NeumannCurie principle [29-31 ]. Compared to an ideal lattice plane inside a crystal, any intercrystallite boundary has an excess free volume ("porosity"), which accumulates the impurity atom and the precipitates. These processes are fairly characteristic of the disordered boundaries of "general type". Among all homo- and heterophase boundaries, special low-energy coincidence boundaries of high coherence stand out along with non-coherent disordered boundaries of the general type. Special boundaries are mathematically described by the coincidence lattices (CL) and the reciprocal density of the coincidence sites ( Z ) [29]. Special coincidence interfaces arise at definite misorientation angles 0, determined by the rotation matrix operator (Rl't). Such

special orientations (RI'~) and (Z) values of CL are determined by the following formulas: ~cL = ~lA(RIx) " qb2(Rl't)q ; TeL = T1N(RI"t) Y~I :

qbi = T 9 G ~

(1) (2)

9 T 2 ( R I ' c ) -1

(3)

index ( T c I J T i ) ,

where (I)i, Ti and Gi (i = 1, 2) are the Fedorov's space, translation and the point symmetry groups of conjugated crystals (i = 1, 2) respectively and, ~cL ,TeL - space and translation groups of coincidence lattice.

3.1c. The Lattice Matching Algorithm, Energy Extremum and ASIC//electrode Conjugated Commensurate Heteropairs. The translation period of heterophase boundary is characterized by lattice match precision (e = {21dl-d21/dl+d2)})and by size of the boundary CL supercell (A). These parameters are interconnected. For weakly strained thick layer growth, the lattice mismatch (e) is usually less 1-3% but for strained epilayers with film thickness ~ 10 monolayers e can achieve 10%. The supercell size (A) apparently limited to a value which is reasonable for surface reconstruction, i.e. A < 30-60 nm. The lattice matching algorithm [18-20] includes: 1. Determination of equal vectors 4k (with precision e) in conjugated lattices Tk (k = 1,2) Ili11/llj21 = m2/ml, m k -- integers > 0, di k = .

Determination of equal angles q)ij k between commensurate v e c t o r s lik q)ijk : arcos{lik'ljk/ Ilikl Iljkl}

.

4.

ii k m k

(4)

pairs of

(5)

The reduction procedure of searching the boundary supercell unit; Determination of the unit supercell area (A) and boundary orientation N Aij = (

di k 9 dj k

)sin (q)ij k)

(6)

The orientation conditions of lattice matching determine the aspect of the (RIx) matrix which enables to find the common elements of boundary point symmetry Gb. Since low energy crystal surfaces correspond to high point symmetry and dense atomic packing, it can be proposed that G b and (A) characterize the contributions of boundary and elastic energy in the whole heterosystem

156

Ionics 11 (2005)

energy indirectly. The lattice matching is apparently a minor factor for epilayer formation at the first growth stages compared to point symmetry determined the local

Table 2. Some Lattice matched electrode materials with symmetry perfect ASIC {001}//{001}electrode interfaces for a-AgI and RbAg4Is ASICs.

symmetry of atomic ordering. The following interface analysis of symmetry dictated energy e x t r e m u m [18,19,32,33] allows to realize the selection o f optimal materials and phases o f epitaxial growth. Energy functional is a scalar function E(x) of

ASIC,space group,lattice parameter

Electrode material, space group, lattice parameter, some remarks of interface coincidence

cc-AgI,

Nb3Pt, Pm3m, a = 5.11

symmetry G, where (x) is a vector which components are

Im3m

independent physical parameters, then gradient V~o E(x)

a = 5.106 A,

has the same local symmetry group G~o as point Xo, Gxo ---" g E Gxo : {g t Vg E G ; gXo = xo}.

(7)

Ti3Au, Pm3n, a = 5.096 Ni2824S2, F43m, a = 5.087

5.069

Ni3Ge, Pm3m, a = 3.573, (45 ~ rotation)

5.062

GeNi3C0 ~5, Pm3m, a = 3.58, (45 ~ rotation) Co3GeCo 25, Pm3m,a = 3.615, (45 ~ rotation)

Then

Co3Ta, Pm3m, a = 3.647, (45 ~ rotation)

G(V~o E(x)} : {g I Vg E G; g{Vxo E(x)} -~ Vxo E(x) = Gxo (8)

Ag0.35Cut 75Ino.6Yb0.4, Fd3m, a = 7.185, (45 ~ rotation, multiple interface coincidence supercell)

The base of Gxo (M Gx~ is a locus of configuration vector

RbAg415,

space {x} of all points x, invariant to action o f all

P4332,

symmetry elements of group Gxo:

P4132,

M ax~

gx=x}

(9)

a =

11.24

If M GX~= 0 then Vxo E(x) = 0, i.e. there are special points

Li2MnBr4, Fd3m, a = 11.235 (owing to centering multiple cell) CuS2, Pa3, a = 5.625, (multiple cell x2 = 11.25) NiS 2, Pa3, a = 5.619, (multiple cell x2 = 11. 238)

of configuration space with local energy minimum. Some lattice matched conjugated

CdHo2S4, Fd3m, a = 11.24, (owing to centering there is multiple cell)

commensurate

AuCu3 Pm3m, a = 3.749, (multiple cell x3 = 11.247)

heteropairs ASIC//electrode are given in Table 2. Note that lattice commensurate heterojunctions with optimal combination of translation (A) and point (Go) symmetry can be realized for A S I C based heterojunctions by using isomorphic nmlticomponent continuous solid

F o r c o m p l e x phase d i a g r a m s with eutectic phase

solutions. That allows to carry out a close linear depen-

transformations the effective heat o f phase formation

dence of the lattice parameter from composition according

(AH') is concentration dependent [34]. By using postulate

V e g a r d rule, as it was made for commensurate semi-

[35] that the interface between two components has an

conductor heterojunctions [9,18,19].

initial concentration which is near the composition of the

3.1d. Crystallochemical Restrictions on the Electrode

lowest eutectic, the effective heat of phase formation

S e l e c t i o n . Side by side with s y m m e t r y analysis the

( A H ' ) can be calculated for any compound in a binary

possible interface chemical reactions must be taken into

system by formula:

account. It is necessary to analyze appropriate phase diagrams and growth kinetics. In [18-20] the crystallo-

AH' = AH*C/p

(10)

chemical method of symmetry perfect interface searching has been developed. The method includes: 1) search and

where AH* is the heat of compound formation, C is a

d e t e r m i n a t i o n o f the material c o m b i n a t i o n s and the

fractional atomic concentration o f limiting atoms, p is a

epitaxial orientation conditions; 2) thermodynamic ana-

the number of limiting atoms in the compound compared

lysis o f phase sequence and h o m o l o g y o f structure

to the lowest eutectic concentration. Thus, subsequent

element inheritance in solid state reactions occurring in

phase sequence in the investigated chemical system can be

the investigated system.

predicted.

Ionics 11 (2005) In addition to space group relation, the electrode and ASIC must be chemically and physically compatible with each other. That is at the ASIC//electrode interface. The electrode should be chemically indifferent and ideally polarizable (without Faraday processes) with respect to ASIC. And, the interfacial region must not be damaged by physical processes such as interdiffusion, formation of voids, dendritic growth etc. For instance, solid solutions are chemically stable and suitable for manufacture of long-lived heterostructures and devices. Special algorithm of the indifferent electrode selection criteria was developed. It is based on thermodynamic constraints on the evolution of the system imposed by interface energy and comparison of mean orbit electronegativity and some energy and crystallochemical characteristics [18,19,36-38] of electrode and film components (when thermodynamic data are unknown). Some simple thermodynamic considerations of new phase formation are: 9 In all cases of thin film deposition nucleation phenomena are controlled by the necessity of creating an interface between the nucleated phase and substrate. When two solids A and B in contact with each other they interact and form a new phase AB. The system originally containing one interface A//B (with energy o~) evolves into a system with two interfaces A//AB//B (with energies o2 and o3), which will be generally accompanied by an in-

9

crease in surface energy zXcrs = o2 + o3 - o~. In a case of epitaxy (coherent interface) ol is small, and Aos is large, in case of noncoherent interface o~ is large and Aos is small. In diffusion couples nucleation effects are become experimentally prominent wherenever AH (enthalpy of chemical reaction) is small. The threshold is of the order 100 cal/cm~ [36]. The nucleation phenomena of new phase is defined by the competition between a driving force (AG Gibbs energy) and opposing interface effects.

Note, because of the small AH, the nucleation phenomena should be sensitive to relatively small perturbations such as weak ion implantation or use of amorphous substrate instead of crystalline one, Thus, more perfect thin films may be grown in more nonequilibrium conditionsi if the processes of internal selforganization of investigated nanosysytems are carefully considered (as example, the self-ion assisted deposition method (E < 100 eV) in [6]).

157

3.1 e. High Functional ASIC//Electrode Heterostructures and Arrangement of the Fast Ionic Transport Channels. The FIT in RbAg4Is-family ASICs is determined by high concentration of Ag+-ions, flying over the low potential barriers (= 0.1 eV) at any moment. According evaluations made in recent papers [11,15] the DEL thickness in the RbAg4I5 ASIC is less ~-0.5 nm and the c a p a c i t a n c e of ASIC//indifferent electrode heterojunctions C > eS/?~D~20-100 sxF/cm2 (e ~ 1) should be achieved within a time interval N 1 0 -9 S for a perfect interface. First of all these high capacitive properties are determined by conservation of the bulk ASIC structure at the interface and reversible FIT of ions in the ASIC channels. In the RbAg415 the common structural motif (creating by face-shared Hal-ion tetrahedral polyhedra) forms passageways (channels) parallel to the three cubic axes for moving Ag+-ions [39,40]. Within each unit cell there are two such channels parallel to each of the axes. Crystal structure of ASICs is closely to an optimal one for FIT (Table 1). Therefore another necessary condition for high functional coherent interface ASIC// electrode is the arrangement of FIT-channels perpendicular to interface plane (for the RbAg4Is-family A S I C it is orientation). In the absence of coherent interface, the characteristics of capacitors fall because of large potential barriers (significantly exceed 0.1 eV) arising in the ASIC distorted structure for mobile ions. Experimental data [22] are indicative of suppression of the FIT in ASIC nanosystems with high density of disordered boundaries of the general type, which generate high concentration of defects and sharply raise the activation energy E. Fabrication of heterojunctions with coherent interfaces is the key task for development of nanoionics and creation of creating new types of ASIC-based devices (nanoionic supercapacitors and sensors [10]). 3.2. Thin-Film Nanoionic Supercapacitors and the Capacitive Properties of Lattice Matched Heterojunction ASIC//Metallic Alloy. In Fig. 3 the specific energy & power diagram [15] for different types of current sources and capacitors is shown. The presumptive energy and power characteristics for thin film nanoionic supercapacitors designed with coherent interfaces are presented in ellipse region. Specific characteristics and frequency response of projected ASICdevices would be better than ones for the present types of capacitors and supercapacitors.

158

Ionics 11 (2005) .- ........

; ....

: ....

: ....

~ ....

: .....

"'.:

tandartc a p a c i ~

: >| - '

f .

.

Fig. 3. The specific energy & power diagram for different types of current sources and capacitors [15].

.

.

~

. . . . . . . . . . . . .

9

O.S.S~.F: ....

junctions CsAg4Br3_xIz+~//electrode the chemically indifferent metal alloy of cubic symmetry (space group Fd3m) with spinel-type structure, ideally polarizable and with lattice parameters close to ASIC (elementary cell parameter 1.124 nm) was chosen. This first attempt of the purposeful electrode selection allowed to increase specific capacitance of CsAg4Br~_~Iz+x //electrode heterostructure in several times even for polycrystalline electrode structure and not sufficient vacuum conditions of synthesis. The polycrystalline structure of the electrode-substrate is inherited by the ASIC-fihn, forming columnar grain boundaries. These grain boundaries interacting with ASIC//alloy phase boundary in arbitrary junctions considerably reduce the capacitive characteristics. In dry air or vacuum the ASIC//alloy heterostructures had specific capacity 3 ~tF/cm2. The further steps to improve capacitive properties of investigated heterostructure can include applying of monocrystal alloy substrate with definite surface orientation, manipulation of grain boundary character distribution in the film by introduction of definite sharp textures intopolicrystalline substrate and others. Charge-discharge oscillograms for ASIC//alloy heterostructure by square pulse of voltage with the amplitude 0.4 V (on the alloy), are presented in Fig. 4. For designed heterostructure ASIC//alloy unusual great change of heterostructure capacity by a factor of 5-10 with changing

:

~ 1 7 6 1 7 6

+0.4Vmm :

~

. . . .

;

I

rt"capacitor'0.88 ~ ~ p,

i

!

~t" ....

! ....

.:.....~'~experimental

....

.....

], .

.

.

: .

.

.

.

.

.

i .

.

.

:

.... !-i.! :1...:

: ....

:]:

.. '"

!

i'"

i

i

heterostructures

.

:

~tand,irtc a i ~ a c i t ( ~ r ~

. ....

. ....

:0.08g....:

:

relativehumidity50%,RT :

!

/

....

:

:2" :~da

~>

....

o ~ 1 7 6 1 7 6

>

. . . .

The first attempt of the ASIC-supercapacitor prototype creation based on the ideas of interface design was realized in the M//CsAg4Br3_xI2+x//Ag (M-metallic alloy) thin film lateral heterostructure with auxiliary silver electrode (Fig. 1). For creation of lattice-matched hetero-

....2

~ivehumidityS0%,RT

i .... !l...i .... ! .... ~.

.....

.

,..;

.

.

o

2.~,.

v .......

,.,,

: ....

,~

]

:

I.~.:

Fig. 4. Voltage - time oscillogram for CsAg~Br3_Jz.]/alloy interface: (a) charge of capacitor at the square polar pulses of +0.4 V amplitude (on the alloy electrode); (b) discharge of capacitor when at constant voltage +0.4 V (on the alloy electrode) the square pulses of -0.4 V amplitude were applied.

relative air humidity within the range 0-50% (T = 300 K) was discovered (usually for capacitive humidity sensors the effect is not exceed 10-20%). For dry air the curve form V = f(t) (initial section of oscillogram) corresponds to the charge of 0.08 ~tF capacitor. The value of capacitor increases up to 0.88 gF at the relative humidity 50 %. The revealed effect can be used for the creation of a new type of high-sensitive humidity sensors. The same values of capacitance were obtained at the discharge of heterostructure (Fig. 4b) when the constant voltage +0.4 V was applied to the alloy electrode and then in addition the square pulse with the amplitude -0.4 V was applied. The value of electric field in the DEL at discharge at the moment t = 0 was ~0.4 V/ 5"108 cm ~- 107 V/cm. It follows from the experimental data that the capacity of DEL in the fields l 0 6 - 1 0 7 V/cm is constant. The behavior of ASIC//alloy heterostructures in dry and open air can be determined admittedly by the

Ionics 11 (2005) following: (i) the H20 molecules adsorbed on grain and phase boundaries modify interaction between the particles of electrode and ASIC decreasing the distortions of the ASIC crystalline structure at the interface; (ii) dissociation of the H20 molecules [41] on alloy surface causes the appearance of high concentration of protons decreasing the thickness of DEL; (iii) the molecule interlayer of H20 decreases of surface tension and distortion of crystal structure of adjacent ASIC layers [15,16]. Additional investigations are required to find out the reasons of such a behavior of the capacity of the ASIC//alloy heterostrnctures in dry and open air. Though the first results of interface engineering approach "from advanced superionic materials to advanced nanoionic supercapacitors" are rather unassuming, we sure that the comprehensive control of interface atomic structure (including selection of pairs of the high coherence conjugated materials, creating of sharp textures, application of an external fields of definite symmetry, understanding and taking into account the internal selforganization processes in nanosystems) has the highest potential in future development of high performance solid state ionic nanomaterials and devices. 4.

Conclusions

The challenges presented by nanoscience and nanotechnology are not simply restricted to the description of nanoscale systems and objects themselves, but extend to their design, synthesis, interaction with the macroscopic world, and ultimately largescale production. In this paper the first attempt of practical realization of new interface engineering approach "from advanced materials to advanced d e v i c e s " is applied to nanosystems of advanced superionic conductors (ASIC) solid electrolytes with exceptionally large unipolar ionic conductivity. The crystallochemical method of symmetry perfect ASIC//electrode interface searching is developed. Some new theoretical results of ASIC//indifferent electrode conjugated commensurate heteropairs with coherent interfaces and preliminary experimental result of the creation of nanoionic thin-film supercapacitor - prototype based on the lattice matched heterojunction are presented. It is shown thar fabrication of heterojunctions with coherent interfaces is the key task and a powerful tool for future development of high performance ASIC -based advanced materials and devices. The interface engineering methods are urgent for R&D in nanoionics of ASICs.

159 The further ways for increasing of nanodevice operating characteristics by controllable interface engineering and external field application with comprehensive consideration of internal selforganization processes are discussed.

5. References [1] K.E. Drexler, Engines of Creation. The Coming Era of Nanotechnology // Anchor Publishers, 1990, p. 381. [2] T. Watanabe, Res. Mechanica. 11, 47 (1984). [3] T. Watanabe, Acta Mater. 4, 4171 (1999). [4] T. Watanabe, Int. Conf. "Interfaces in advanced materials", Book of abstracts, Chernogolovka, 2630 May, 2003, p. 2. [5] A.I. II'in, A.V. Andreeva, B.N. Tolkunov, Mat. Sci. Forum 206-207,625 (1996). [6] O.V. Kononenko., A.V. Andreeva, A.I. II'in, V.N. Matveev, MRS-Proceedings, 2002, Texture & Microstructure of Magnetic and Electronics Films, 574. [7] A.V Andreeva., N.M. Talijan, et al., e-pulication, (http://preprint.chemweb.com/inorgchem/0302001) (2003). [8] A.V. Andreeva, Proc. 5th Russian Conference on Physicochemistry of Ultra-Disperse Systems, MEPHI, Moscow, 2000, p. 32 (in Russian). [9] Zh.I. Alferov, Uspehi Phys. Sci. 1"/2, 1068 (2002) (in Russian). [10] A.L. Despotuli, A.V. Andreeva, in: Book of Abstracts, 7th International Meeting "Fundamental Challenges of Solid State Ionics", Chernogolovka, June 16-18, 2004, p. 22 ( in Russian). [11] A.L. Despotuli., A.V, Andreeva, B. Rambabu, Proc. Patras Conference on Solid-State Ionics Transport Properties, September 14 - 18, 2004, p. 66. [12] A.L. Despotuli., V.I. Nikolaichik, Solid State Ionics 60,275 (1993). [13] J.H. Choy, Y.I. Kim, S.J. Hwang, J. Phys. Chem. B 102, 9191 (1998). [14] N. Sata, K. Eberman, K. Eberl, J. Maier, Nature 408,946 (2000). [ 15] A.L. Despotuli, A.V. Andreeva, Microsystem engineering, 11, 2 (2003) (in Russian). [16] A.L. Despotuli, A.V. Andreeva, Microsystem engineering, 12, 2 (2003) (in Russian).

160 [17] A.V. Andreeva, A.L. Despotuli, in: Book of abstracts International Conference "Interfaces in advanced materials", Chernogolovka, May 26-30, 2003, p. 32. [ 1 8] A.V. Andreeva, Surface: Physics, Chemistry, Mechanics 46, 117 (1990) (in Russian). [19] A.V. Andreeva, Mat. Sci. Forum 69, III (1991). [20] A.V. Andreeva, A.A. Firsova, "Interface symmetry: algorithms, programs, tables", Preprint of IMT Academy of Sci. USSR, Chernogolovka, 1990, p. 44. [21] S. Chandra, Superionic Solids. Principles and Applications, North-Holland Publishing Company, 1981, p. 404. [ 2 2 ] A . L . Despotuli, N.V. Lichkova., N.A. Minenkova., S.V. Nosenko, Electrochemistry 26, 1524 (1990) (in Russsian). [23] A.L. Despotuli, V.N. Zagorodnev, N.V. Lichkova, et al., Solid State Phys. 31, 242 (1989) (in Russian). [24] A.L. Despotuli, A.V. Andreeva, in: Proceeding of International workshop "Micro Robots, Micro Machines and Micro Systems", Institute for Problems in Mechanics RAS, Moscow, April 2425, 2003, p. 129. [25] A.L. Despotuli, A.V. Andreeva, e-publication, http://preprint.chemweb.com/physchem/0309001 (2003). [26] A.L. Despotuli, A.V. Andreeva, e-publication, http://preprint.chemweb.com/physchem/0306011 (2003). [27] K.J. Lehovec, J. Chem. Phys. 21, 1123 (1953). [28] J. Friedel, NATO ASI, (R. Balian, M. Kleman, J.P. Poirier, Eds.) 1981, p. 5. [29] A.P. Sutton, R.W. Baluffi, Interfaces in crystalline materials, Clarendon Press, Oxford, 1995, p. 819.

Ionics 11 (2005) [30] A.V. Shubnikov, V.A. Koptsik, "Symmetry in science and art", M. Nauka, 1972, p. 340 (in Russian). [31] A.V. Andreeva, "Structural symmetry and its manifestation, in properties of homo- and heterophase boundaries of crystals", Preprint of Institute of Microelectronics Technology of Academy of Sciences of USSR, Chernogolovka, 1987, p. 73 (in Russian). [32] G. Kalonji, J.W. Cahn, J. Physique t43, Col. C6, 25 (1982). [33] G. Kalonji, J. Physique 46, Col. C4,249 (1985). [34] R. Pretorius, in: Thin films and Interfaces, II, Mat. Res. Soc. Sympos. Proc., North-Holland, 25, 15 (1984). [35] R.M. Walser, R.W. Bene, Appl. Phys. Lett. 28, 624 (1976). [36] D'Heurle, in: Thin films and Interfaces, II, Mat. Res. Soc. Sympos. Proc., North-Holland, 25, 3 (1984). [37] E.G. Avvakumov, Chemistry in interests of steady evolution, 10, 725 (2002) (in Rusian). [38] A.L. Despotuli, V.1. Levashov, L.A. Matveeva, Electrochemistry 39,526 (2003) (in Russian). [39] S. Geller, Science 157,310 (1967). [40] D. Raleigh, J. Electrochem. Soc. 1 2 4 , 1157 (1977). [41] K.C. Hass, W.F. Schneide, A. Curioni, W. Andreoni, Science 282,265 (1998).

Paper presented at the Patras Conference on Solid State Ionics - Transport Properties, Patras, Greece, Sept. 14 18, 2004. Manuscript rec. Sept. 16, 2004; acc. Jan. 15, 2005.