Nanoporous films have potential applications in thermoelectric cooling on a chip, sensors, solar cells, and desalination. For phonon transport, amorphization and other pore-edge defects introduced by the nanofabrication processes can eliminate wave effects by diffusively scattering short-wavelength phonons and thus destroying the phonon phase coherence. As a result, phononic effects can only be observed at 10 K or below, when long-wavelength phonons become dominant for thermal transport. In this work, a 70-nm-thick silicon thin film with approximately 100-nm-diameter nanopores was annealed under a high vacuum, and the change of pore-edge defects was observed with in situ transmission electron microscopy. It was found that the pore-edge defects can be minimized to a sub-1-nm layer by annealing between 773 and 873 K for 30 min, without changing the pore sizes. The largely reduced pore-edge defects are critical to the desired phonon wave effects within a periodic nanoporous structure.

1.
J.
Maire
,
R.
Anufriev
,
R.
Yanagisawa
,
A.
Ramiere
,
S.
Volz
, and
M.
Nomura
, “
Heat conduction tuning by wave nature of phonons
,”
Sci. Adv.
3
(
8
),
e1700027
(
2017
).
2.
M.
Maldovan
, “
Narrow low-frequency spectrum and heat management by thermocrystals
,”
Phys. Rev. Lett.
110
(
2
),
025902
(
2013
).
3.
Y.
Xiao
,
Q.
Chen
,
D.
Ma
,
N.
Yang
, and
Q.
Hao
, “
Phonon transport within periodic porous structures—From classical phonon size effects to wave effects
,”
ES Mater. Manuf.
5
,
2
18
(
2019
).
4.
Q.
Li
,
Q.
Hao
,
T.
Zhu
,
M.
Zebarjadi
, and
K.
Takahashi
, “
Nanostructured and heterostructured 2D materials for thermoelectrics
,”
Eng. Sci.
13
,
24
50
(
2021
).
5.
Q. Y.
Li
,
T.
Feng
,
W.
Okita
,
Y.
Komori
,
H.
Suzuki
,
T.
Kato
,
T.
Kaneko
,
T.
Ikuta
,
X.
Ruan
, and
K.
Takahashi
, “
Enhanced thermoelectric performance of As-grown suspended graphene nanoribbons
,”
ACS Nano
13
(
8
),
9182
9189
(
2019
).
6.
H.
Kim
,
J.
Yun
,
M.
Gao
,
H.
Kim
,
M.
Cho
, and
I.
Park
, “
Nanoporous silicon thin film-based hydrogen sensor using metal-assisted chemical etching with annealed palladium nanoparticles
,”
ACS Appl. Mater. Interfaces
12
(
39
),
43614
43623
(
2020
).
7.
G.
Shi
and
E.
Kioupakis
, “
Electronic and optical properties of nanoporous silicon for solar-cell applications
,”
ACS Photonics
2
(
2
),
208
215
(
2015
).
8.
S. P.
Surwade
,
S. N.
Smirnov
,
I. V.
Vlassiouk
,
R. R.
Unocic
,
G. M.
Veith
,
S.
Dai
, and
S. M.
Mahurin
, “
Water desalination using nanoporous single-layer graphene
,”
Nat. Nanotechnol.
10
(
5
),
459
464
(
2015
).
9.
J.
Garg
and
G.
Chen
, “
Minimum thermal conductivity in superlattices: A first-principles formalism
,”
Phys. Rev. B
87
(
14
),
140302
(
2013
).
10.
J.
Ravichandran
,
A. K.
Yadav
,
R.
Cheaito
,
P. B.
Rossen
,
A.
Soukiassian
,
S. J.
Suresha
,
J. C.
Duda
,
B. M.
Foley
,
C.-H.
Lee
,
Y.
Zhu
et al, “
Crossover from incoherent to coherent phonon scattering in epitaxial oxide superlattices
,”
Nat. Mater.
13
(
2
),
168
172
(
2014
).
11.
J.
Tang
,
H.-T.
Wang
,
D. H.
Lee
,
M.
Fardy
,
Z.
Huo
,
T. P.
Russell
, and
P.
Yang
, “
Holey silicon as an efficient thermoelectric material
,”
Nano Lett.
10
(
10
),
4279
4283
(
2010
).
12.
A.
Jain
,
Y.-J.
Yu
, and
A. J.
McGaughey
, “
Phonon transport in periodic silicon nanoporous films with feature sizes greater than 100 nm
,”
Phys. Rev. B
87
(
19
),
195301
(
2013
).
13.
N. K.
Ravichandran
and
A. J.
Minnich
, “
Coherent and incoherent thermal transport in nanomeshes
,”
Phys. Rev. B
89
(
20
),
205432
(
2014
).
14.
Q.
Hao
,
D.
Xu
,
H.
Zhao
,
Y.
Xiao
, and
F. J.
Medina
, “
Thermal studies of nanoporous Si films with pitches on the order of 100 nm—Comparison between different pore-drilling techniques
,”
Sci. Rep.
8
(
1
),
9056
(
2018
).
15.
J.
Lee
,
W.
Lee
,
G.
Wehmeyer
,
S.
Dhuey
,
D. L.
Olynick
,
S.
Cabrini
,
C.
Dames
,
J. J.
Urban
, and
P.
Yang
, “
Investigation of phonon coherence and backscattering using silicon nanomeshes
,”
Nat. Commun.
8
,
14054
(
2017
).
16.
T.
Klitsner
and
R.
Pohl
, “
Phonon scattering at silicon crystal surfaces
,”
Phys. Rev. B
36
(
12
),
6551
(
1987
).
17.
D.
Xu
,
Q.
Wang
,
X.
Wu
,
J.
Zhu
,
H.
Zhao
,
B.
Xiao
,
X.
Wang
,
X.
Wang
, and
Q.
Hao
, “
Largely reduced cross-plane thermal conductivity of nanoporous In0.1Ga0.9N thin films directly grown by metalorganic chemical vapor deposition
,”
Front. Energy
12
,
127
136
(
2018
).
18.
Ç.
Girit
,
J. C.
Meyer
,
R.
Erni
,
M. D.
Rossell
,
C.
Kisielowski
,
L.
Yang
,
C. H.
Park
,
M. F.
Crommie
,
M. L.
Cohen
,
S. G.
Louie
et al, “
Graphene at the edge: Stability and dynamics
,”
Science
323
(
5922
),
1705
1708
(
2009
).
19.
X. T.
Jia
,
M.
Hofmann
,
V.
Meunier
,
B. G.
Sumpter
,
J.
Campos-Delgado
,
J. M.
Romo-Herrera
,
H. B.
Son
,
Y. P.
Hsieh
,
A.
Reina
,
J.
Kong
et al, “
Controlled formation of sharp zigzag and armchair edges in graphitic nanoribbons
,”
Science
323
(
5922
),
1701
1705
(
2009
).
20.
Q.-Y.
Li
,
K.
Takahashi
,
H.
Ago
,
X.
Zhang
,
T.
Ikuta
,
T.
Nishiyama
, and
K.
Kawahara
, “
Temperature dependent thermal conductivity of a suspended submicron graphene ribbon
,”
J. Appl. Phys.
117
(
6
),
065102
(
2015
).
21.
H. D.
Wang
,
S. Q.
Hu
,
K.
Takahashi
,
X.
Zhang
,
H.
Takamatsu
, and
J.
Chen
, “
Experimental study of thermal rectification in suspended monolayer graphene
,”
Nat. Commun.
8
,
15843
(
2017
).
22.
S. Q.
Hu
,
Z. W.
Zhang
,
P. F.
Jiang
,
J.
Chen
,
S.
Volz
,
M.
Nomura
, and
B. W.
Li
, “
Randomness-induced phonon localization in graphene heat conduction
,”
J. Phys. Chem. Lett.
9
(
14
),
3959
3968
(
2018
).
23.
S. Q.
Hu
,
J.
Chen
,
N.
Yang
, and
B. W.
Li
, “
Thermal transport in graphene with defect and doping: Phonon modes analysis
,”
Carbon
116
,
139
144
(
2017
).
24.
Q.
Hao
,
Y.
Xiao
, and
F. J.
Medina
, “
Annealing studies of nanoporous Si thin films fabricated by dry Etch
,”
ES Mater. Manuf.
6
,
24
27
(
2019
).
25.
J.
Ma
,
S.
Wang
,
X.
Wan
,
D.
Ma
,
Y.
Xiao
,
Q.
Hao
, and
N.
Yang
, “
The unrevealed 3D morphological evolution of annealed nanoporous thin films
,”
Nanoscale
14
(
45
),
17072
17079
(
2022
).
26.
A. J.
Storm
,
J. H.
Chen
,
X. S.
Ling
,
H. W.
Zandbergen
, and
C.
Dekker
, “
Fabrication of solid-state nanopores with single-nanometre precision
,”
Nat. Mater.
2
(
8
),
537
540
(
2003
).
27.
L.
Jacobsohn
,
D.
Cooke
,
B.
Bennett
,
R.
Muenchausen
, and
M.
Nastasi
, “
Effects of thermal annealing and ageing on porous silicon photoluminescence
,”
Philos. Mag.
85
(
23
),
2611
2620
(
2005
).
28.
N.
Ookubo
,
H.
Ono
,
Y.
Ochiai
,
Y.
Mochizuki
, and
S.
Matsui
, “
Effects of thermal annealing on porous silicon photoluminescence dynamics
,”
Appl. Phys. Lett.
61
(
8
),
940
942
(
1992
).
29.
M. L. V.
Gayler
, “
Melting point of high-purity silicon
,”
Nature
142
,
478
478
(
1938
).
30.
Y.
Pan
,
Y.
Tao
,
G.
Qin
,
Y.
Fedoryshyn
,
Y. N.
Raja
,
M.
Hu
,
C. L.
Degen
, and
D.
Poulikakos
, “
Surface chemical tuning of phonon and electron transport in free-standing silicon nanowire arrays
,”
Nano Lett.
16
(
10
),
6364
6370
(
2016
).
31.
F. M.
Chang
,
Z. Z.
Wu
,
J. H.
Huang
,
W. T.
Chen
,
S.
Brahma
, and
K. Y.
Lo
, “
Migration energy barriers for the surface and bulk of self-assembly ZnO nanorods
,”
Nanomaterials
8
(
10
),
811
(
2018
).

Supplementary Material

You do not currently have access to this content.