Strong optical absorption of LaMn
0.6
Al
0.4
O
3
thin
films in the mid-infrared atmospheric window
Hongguang Wang,
ab
Lei Wang,
*
a
PengFei Hu,
c
Wei Ren,
*
a
Jinbao Xu,
a
Pengjun Zhao
ab
and Aimin Chang
a
Strong light absorption in the mid-infrared atmosphere window (3–5
mm) was reported for a complete (100)-oriented LaMn
0.6
Al
0.4
O
3
thin
film. It is attributed to Al-doping induced electron transitions from the
polar center of a [MnO
6
10
]
JT
pseudo-Jahn–Teller electron cluster to
a[MnO
6
8
]
JT
pseudo-Jahn–Teller hole cluster and strain intensification.
The infrared atmospheric windows, which let some infrared
radiation from the cloud tops and land–sea surface pass directly
into space without intermediate absorption and re-emission,
reect the overall dynamic property of the earth's atmosphere.
They have been investigated intensively, especially by infrared
detectors in those spectral ranges. Among them, an infrared
detector for the mid-infrared atmospheric window (3–5 mm) is
a research focus owing to its signicant application in the
infrared guidance systems of weapons and remote sensing
systems of residential areas.
1–3
Hitherto, kinds of detector materials have been investigated
in the mid-infrared (MIR) eld, which are classi ed into photon
detector material and thermal detector material. The typical
photon detector material HgCdTe is broadly used in this region
because of its excellent signal-to-noise performance and a very
fast response attributing to the principles of electronic transi-
tion.
4
Cooling requirement is the main obstacle to the more
widespread use because it makes IR systems bulky, heavy,
expensive and inconvenient to use.
5
By contrast, thermal
detectors typically operate at room temperature. The incident
radiation is absorbed to change the temperature of material and
the resultant changes in some physical properties are used to
generate an electrical output. They are usually characterized by
modest sensitivity and slow response. However, being cheap
and easy to use, they have been applied in low cost elds, above
all in civilian eld, such as aircra aid,
6
industrial process
monitoring,
7
reghting,
8
portable mine detection, night
vision,
9
etc.
10
As for resistive bolometer infrared detectors,
extensive studies have been carried out on various types of
thermally sensitive resistor materials, such as germanium–
silicon-oxide (Ge
x
Si
1x
O
y
),
11
vanadium oxide (VO
2
),
12
super
conducting yttrium–barium–copper-oxide (Y–Ba–Cu-O) and
binary and ternary oxides of manganese, nickel and cobalt.
13
For
them, one advantage is the nonselective absorption for a broad
spectral range, including mid-infrared atmospheric window.
However, the low optical absorption of infrared light restricts its
optical response for high sensitivity thermal detector applica-
tion and makes the fabrication of the infrared device more
complex. Therefore, it is urgent to nd thermo-sensitive mate-
rials that have strong light absorption in mid-infrared (3–5 mm)
atmospheric window for the progress of thermal detectors.
In this work, complete (100)-oriented LaMn
0.6
Al
0.4
O
3
(LMAO)
thin lms were prepared by spin coating. The microstructure
and morphology characteristics were observed by XRD and
TEM. The infrared optical properties were investigated by
Infrared Spectroscopic Ellipsometry. Its corresponding physical
mechanisms were analysed.
The LMAO thin lms were grown on (100)-oriented LaNiO
3
(LNO) as buffer layer Pt/Ti/SiO
2
/Si substrates by spin
coating. The raw materials include manganese acetate
[Mn(CH
3
COO)
2
$4H
2
O], aluminium nitrate [Al(NO
3
)
3
$9H
2
O],
and lanthanum nitrate [La(NO
3
)
3
$6H
2
O]. Acetic acid and
2-methoxyethanol were used as co-solvents. Initially, manga-
nese acetate and lanthanum nitrate were dissolved in acetic
acid and 2-methoxyethanol co-solvents according to the pre-
determined ratios and stirred at 60
C until complete dissolu-
tion. The aluminium nitrate was added at the desired ratios.
The nal solutions were stirred for 4 h at room temperature.
The concentration of LMAO solution was 0.1 M. Each coating
layer was spined at 3500 rpm for 20 s and annealed in air at
400
C on a hot plate for 5 min. The coating and heat treatment
procedures were repeated for 20 times. Finally, the samples
were annealed at 750
C for 30 min to crystallize the lms.
a
Key Laboratory of Functional Materials and Devices for Special Environments of CAS,
Xinjiang Key Laboratory of Electronic Information Materials and Devices, Xinjiang
Technical Institute of Physics & Chemistry of CAS, Urumqi 830011, China. E-mail:
wangl@ms.xjb.ac.cn; renw@ms.xjb.ac.cn; Tel: +86 13319895680
b
University of Chinese Academy of Sciences, Beijing 100049, China
c
Laboratory for Microstructures, Shanghai University, Shanghai 200444, China
Cite this: RSC Adv. ,2016,6, 53389
Received 21st April 2016
Accepted 26th May 2016
DOI: 10.1039/c6ra10308a
www.rsc.org/advances
This journal is © The Royal Society of Chemistry 2016 RSC Adv.,2016,6, 53389–53392 | 53389
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