Contents
Functional, Medical and Electronic Coatings

Thin Film Characterization for Surface Engineering: Contact Angle and Surface Energy on Thin Films and Coatings, Nanomaterials and Ultra Thin Layers

A water contact angle reads the outermost few angstroms of a thin film, so it shows whether a deposition, treatment or cleaning step changed the surface you made. Add two or three test liquids for surface free energy, fix the model, and read the result alongside AFM, XPS and nanoindentation.

Who this is for: Thin film and surface engineering researchers, coating process engineers in microelectronics, optical and sensor work, and teams developing nanomaterials and functional films.

Where it fits: Checking each deposition, plasma, monolayer or cleaning step, comparing film recipes, and tracking ageing of fresh films in air.

What it does not do: It does not measure film thickness, composition, hardness, modulus, roughness or adhesion to the substrate.

Method
Sessile drop water contact angle; advancing and receding angles; two or three liquid surface free energy
Standard
Follows ASTM D7334 advancing angle practice and ISO 19403-2 surface free energy methods
Setup
About 2 minutes
Book a 15 minute demo Request a quote
Surface Nano Coatings
Abhimanyu Photo
Written by
Abhimanyu Bhandankar
Holds an MBA from Schulich School of Business and a BE in IT. He joined Droplet Lab in July 2019 and now leads sales and marketing.
CEO at Droplet Lab
Read More
Droplet-Lab logo
Technical Review by
Droplet Lab Team
Droplet Lab builds precision instruments and software for surface science measurement, specialising in contact angle analysis and surface tension characterisation. Used by researchers across materials science, pharmaceuticals, coatings, and advanced manufacturing, Droplet Lab's Dropometer has contributed to studies published in peer-reviewed journals including Advanced Functional Materials (Impact Factor 19). The team combines instrument engineering with deep domain knowledge in wettability science with a focus on practical accuracy.
Read More
Abhimanyu Photo
Written By

Abhimanyu Bhandankar

CEO at Droplet Lab

Holds an MBA from Schulich School of Business and a BE in IT. He joined Droplet Lab in July 2019 and now leads sales and marketing.

Droplet-Lab logo
Reviewed By

Droplet Lab Team

Droplet Lab builds precision instruments and software for surface science measurement, specialising in contact angle analysis and surface tension characterisation. Used by researchers across materials science, pharmaceuticals, coatings, and advanced manufacturing, Droplet Lab's Dropometer has contributed to studies published in peer-reviewed journals including Advanced Functional Materials (Impact Factor 19). The team combines instrument engineering with deep domain knowledge in wettability science with a focus on practical accuracy.

Featured Studies & Publications

Research Paper Contact angle measurement with a smartphone
Research Paper Surface tension measurement with a smartphone using a pendant drop
Why it matters

Why thin film surface characterization matters

Outermost 5 Å

is what the water contact angle reads on a monolayer film: polar groups buried more than about 5 Å below the surface no longer changed the angle.

Bain et al., J. Am. Chem. Soc. 111:321, 1989 (technical report version)

76.2° to 92.9°

rise in the advancing water contact angle on fresh graphene within 100 minutes in air, as airborne hydrocarbons adsorbed and the polar surface energy fell from 5.4 to 0.8 mJ/m².

Carpenter et al., ACS Appl. Mater. Interfaces 15:2429, 2023

52.7 vs 43.8 mJ/m²

total surface free energy of the same TiN coating by two different models, a gap larger than the differences the study found between coatings.

Rogowska, Maintenance Problems 2:193, 2006

Sources: Bain C.D. et al., Formation of monolayer films by the spontaneous assembly of organic thiols from solution onto gold, Journal of the American Chemical Society, 1989 (ONR technical report, 1988); Carpenter J. et al., The surface energy of hydrogenated and fluorinated graphene, ACS Applied Materials and Interfaces, 2023; Rogowska R., Surface free energy of thin layer coatings deposited by means of the arc vacuum method, Maintenance Problems, 2006. Figures come from these sources, not from Droplet Lab measurements.

Quick reference

What this thin film surface check does and what it does not

A quick reference for thin film and coating teams checking fit before reading further.

Evidence Box

Problem this solves

Film recipes and surface treatments compared by one water angle, or by surface energy numbers from different models, so results cannot be compared.

Standards

ASTM D7334 covers advancing contact angle on coatings and substrates; ISO 19403-2 covers surface free energy from contact angles.

Peer reviewed method

The Dropometer drop shape method was validated against a KRUSS DSA100E in two peer reviewed papers, in Review of Scientific Instruments and Colloids and Surfaces A.

Customer case study

The University of Toronto runs four Dropometers on two campuses, with published data on films, leaves and face mask layers.

Published research

Toronto researchers found polyserotonin films raised the surface energy of glass from about 47 to about 61 mJ/m², using three liquids (Nanomaterials, 2022).

Honest limit

Contact angle reads the top surface only. Thickness, composition, roughness and mechanical properties need their own tests.

Who this is for

What thin film question are you trying to answer?

Pick the card closest to your role. Each one points to the part of this page that answers it.

Thin film researcher

You fabricate films by RF magnetron sputtering, evaporation, ALD, plasma polymerisation or self assembly, and need a quick check that each thin-film step changed the film surface as planned. Contact angle and surface energy give that check in minutes.

Measure fresh films at a fixed time after deposition; many films age in air.

Process engineer in microelectronics or optics

You run deposition or cleaning steps for microelectronics, optical coatings or sensor surfaces, where the next layer must wet and bond and each electrical contact must stay clean. A water contact angle on each wafer or part tracks the surface between steps.

Set gates from your own yield or adhesion data, not from a generic value.

Biomaterial or nanomaterials team

You coat devices or glass with polymer, protein resistant or nanomaterial films and other advanced materials. Multi liquid surface energy separates polar and dispersive parts, as the Toronto polyserotonin study did.

Report the liquids and model with every surface energy value.
Fit check

Is this the right check for your thin film work?

It measures how liquids meet the top surface of the film. It does not measure the film in depth.

Good fit if

You compare film recipes, treatments or monolayers.
You need surface free energy with polar and dispersive parts.
You track ageing or contamination of fresh films in air.
You check surfaces between deposition and bonding steps.
You report wettability in papers on films and coatings.

Less relevant if

You need film thickness or composition.
You need hardness, modulus or fracture toughness.
You need roughness on its own; use AFM or profilometry.
You need interfacial adhesion of thin films to substrates; use scratch or peel tests.
Summary

How contact angle supports thin film characterization

The answer in under a minute.

Measure water contact angle on each film at a fixed time after deposition to see whether the surface changed as planned, and add a second and third liquid when you need surface free energy. Fix one model and one set of liquids, because the model alone can move the result more than the films differ.

The Dropometer contact angle and surface energy kit runs the measurement. Our surface energy measurement guide, surface energy components glossary entry and surface free energy calculator explain the calculation, and the ASTM D7334 and ISO 19403-2 pages cover the standards. The University of Toronto published polyserotonin film surface energy data, and our biotechnology guide covers biomaterial films.

The problem

Why thin film surface characterization is hard to compare

Thin films and coatings are made for their functional performance in a variety of applications, from electronics and automotive glass to sensor and medical surfaces: electrical and thermal conductivity, optical behaviour, corrosion protection, barrier or membrane function, or how a sensor surface binds what it should. Many of these properties depend on the outermost layer, and that layer is the one that changes most easily. Whether a film is epitaxial or polycrystalline, grown by physical vapour deposition, ion beam or wet methods, or built from layered materials, a film under 50 nm thick can change its surface with every fabrication step. A study of self assembled monolayers found water contact angle reads only the outermost few angstroms of a surface. Fresh films then age: on graphene, the advancing water contact angle rose from 76.2° to 92.9° in 100 minutes as airborne hydrocarbons adsorbed, and the same happens on many other fresh film surfaces. Many techniques are used to characterize the properties of thin films, from AFM and XPS for microstructural and chemical detail to nanoindentation for hardness, modulus and fracture toughness, but surface wetting is often reported as one number with no timing. Surface free energy adds a second problem. The same TiN coating gave 52.7 mJ/m² by one model and 43.8 mJ/m² by another, more than the difference between the coatings in that study. Without a fixed method, timing and model, thin film characterisation results cannot be compared between batches, labs or research articles.

Contact angles for the same film differ between labs or papers.
Fresh films read differently a few hours later.
Surface energy changes when you switch liquids or model.
Spots on one wafer or coupon read very differently.
Delamination of the next layer although the film looked clean.
Troubleshooting

Why thin film wetting results mislead and what to do

Why:

  • Hydrocarbons from the air adsorb on fresh, high energy films within minutes to hours.

How to detect:

  • The water angle rises with time since deposition or cleaning.

Corrective action:

  • Measure at a fixed time after deposition, store samples the same way, and record the time with every value.

Why:

OWRK, Wu, van Oss and equation of state models give different totals for the same surface. Our glossary entries on OWRK, van Oss and the equation of state explain each one.

How to detect:

  • Surface energy shifts when the liquid set or model changes.

Corrective action:

Fix one model and liquid set per project and report them. Our guide to reproducible surface energy calculation covers the choices.

Why:

  • Topography amplifies wetting: on rough hydrophilic surfaces the apparent angle falls below the flat value.

How to detect:

  • Films with the same chemistry read differently on smooth and rough substrates.

Corrective action:

  • Measure roughness by AFM alongside contact angle, and compare like with like.

Why:

  • Thickness gradients, pinholes or patchy coverage give a mixed surface.

How to detect:

  • Large spread between spots on one sample.

Corrective action:

  • Measure a set pattern of spots and report the spread, not only the mean.

Why:

  • A single static angle hides hysteresis and pinning on real films.

How to detect:

  • Static readings vary with drop placement.

Corrective action:

  • Add advancing and receding angles, as ASTM D7334 and ISO 19403-6 describe.

Why:

  • Very thin or incomplete films let the underlying substrate affect the reading.

How to detect:

  • Coated samples read close to the bare substrate.

Corrective action:

  • Measure the bare substrate as a reference and confirm coverage with XPS or ellipsometry.

Not sure which liquids and model suit your films?

Send two film samples and your current method, and we will compare them on a call.

Book a 15 minute demo
Lab records

What a thin film surface record contains

Each check produces a record you can file with the sample and the deposition run. It can sit beside your AFM, XPS and mechanical data.

Sample and process

Substrate, film, deposition method and run, and any treatment after deposition.

Timing and storage

Time from deposition or cleaning to measurement, and how the sample was stored.

Method settings

Liquids, drop volume, static or advancing and receding, and read time.

Readings

Angles at each spot, the median and spread, and surface energy with its model.

Decision

Accept the step, repeat it, or investigate with other techniques.

Drop images

Automatic edge and baseline detection gives the same reading from the same image, so a reviewer can recheck any result.

Measurements

What to measure on a thin film surface

Screen

Water contact angle at a fixed time

Why it matters: It shows whether a deposition or treatment changed the top surface.

How to interpret: Compare with the bare substrate and with the last good run; there is no universal value for a film. It turns a qualitative visual check into a quantitative one.

When it is not enough: It does not show thickness, composition or coverage.

Hysteresis

Advancing and receding angles

Why it matters: They show pinning and chemical or physical heterogeneity.

How to interpret: Report both and their spread, not only a static value.

When it is not enough: They do not separate roughness from chemistry.

Energy

Surface free energy with polar and dispersive parts

Why it matters: It is the surface property that predicts how the next layer, adhesive or biological medium will wet the film.

How to interpret: Use one model and liquid set, as in ISO 19403-2, and compare only within it.

When it is not enough: Values from different models are not interchangeable.

Ageing

Water angle over time in air

Why it matters: It shows how fast a fresh film picks up contamination.

How to interpret: Plot angle against time since deposition and set a maximum wait before the next step.

When it is not enough: It does not identify the contaminant; use XPS.

Validation

Validated measurement approach for thin film surfaces

How the Dropometer itself has been validated, and where film researchers have published with it.

Peer reviewed method

The Dropometer drop shape method is published in Review of Scientific Instruments and Colloids and Surfaces A. Contact angle was validated against a KRUSS DSA100E, with a published accuracy of 0.35°.

See the validation papers

Customer evidence on films

University of Toronto researchers measured water, glycerol and diiodomethane on polyserotonin films and calculated OWRK surface energy: coating glass raised it from about 47 to about 61 mJ/m² (Nanomaterials, 2022). In a 2025 Canadian Journal of Chemistry study of carbon nitride films, a group used the Dropometer as the reference instrument to check its own apparatus, reading 108.7 ± 2.5° on PTFE.

Read the case study
QC Protocol

How to characterize a thin film surface

Six steps for one film type. Repeat for each new film or process change.

3

Measure at a fixed time

Measure each film at the same time after deposition or cleaning, in a set pattern of spots.

4

Add liquids for energy

Measure the second and third liquids on fresh spots and calculate surface free energy with the fixed model.

5

Check ageing

For new films, repeat the water angle over hours to set a maximum wait before the next step.

We completed our gage R&R study on the unit and it performed very well.

Brandon Barbee

Corporate Quality Engineer, Zeus Industries, Polymer Manufacturing

Download the thin film surface characterization SOP

A two page SOP you can adapt for your films, with the method lock, liquid and model choice, timing after deposition, a troubleshooting table and a record sheet.

Contact angle and surface energy measurement with the Dropometer

Contact angle and surface energy measurement with the Dropometer

Example output

Example surface log for a plasma treated polymer film

Example data only. Your values will differ and must come from your own films and methods.

How to read this log

Plasma treatment lowered the water angle and raised the polar part of the surface energy. Over 24 hours in air the film partly recovered, a common ageing effect, so the next layer should go on within the wait the team set. Totals use one model only; another model would give different numbers.

Example thin film surface energy and ageing log

Sample Time after treatment Water (°) Diiodomethane (°) Surface energy (mJ/m²) Polar part (mJ/m²)
Bare film Not treated 88 48 36 2
Treated 10 min 32 40 64 25
Treated 4 h 41 42 59 21
Treated 24 h 52 44 52 15

Example data, not customer data. OWRK with water and diiodomethane; 2 µL drops, read at 5 s, median of 5 spots.

Signal order

The order to check signals on a thin film

Check these in order. Each one rules out a cause before you look at the next.

1

Method and timing

Rules out drift from liquids, drop size and ageing.

2

Bare substrate reference

Confirms the substrate reads as before.

3

Water angle on the film

Shows whether the step changed the surface.

4

Spread across spots

Shows coverage and uniformity.

5

Surface energy and other techniques

Confirm with AFM, XPS or ellipsometry; our page on plated coating wettability covers metal films.

FAQ

Common questions about thin film surface characterization

Questions thin film and coating teams ask about contact angle and surface energy.

Only the outermost few angstroms. Bain and colleagues found polar groups buried more than about 5 Å below a monolayer surface no longer changed the water angle. That makes contact angle very sensitive to the top layer and to contamination, and blind to what lies beneath. Our article on self assembled monolayers explains why.

Because each model splits the surface differently. Rogowska found the same TiN coating at 52.7 mJ/m² by one model and 43.8 mJ/m² by another. Fernandez and Khayet found two liquid methods often under or over estimate. Fix one model and liquid set per project, as ISO 19403-2 recommends, and report them.

At least one polar and one nonpolar liquid, usually water and diiodomethane, for two component models such as OWRK. Add a third, such as glycerol or formamide, for acid base models. The Toronto polyserotonin study used water, glycerol and diiodomethane. Use high purity liquids and check their surface tension.

Airborne hydrocarbons adsorb on fresh, high energy surfaces. Carpenter and colleagues saw the advancing water angle on graphene rise from 76.2° to 92.9° in 100 minutes, and Peng and colleagues saw MoS₂ rise from 69° to 89° after a day. Measure at a fixed time after deposition and record it.

Yes. On rough hydrophilic surfaces the apparent angle falls below the flat value, as Wenzel described; one study measured about 22° on smooth glass and 7° on rough glass. Measure roughness by AFM alongside contact angle, and compare films on substrates with similar roughness.

Both where you can. Huhtamäki and colleagues (Nature Protocols, 2018) note a single contact angle fails to describe solid and water interactions fully, and recommend reporting advancing and receding averages with their spread. ASTM D7334 describes advancing angle practice for coatings and substrates.

As one layer of a full picture. Nanoindentation gives hardness and modulus, XPS gives composition, AFM gives topography and ellipsometry gives thickness. Contact angle adds the quickest, cheapest comparative view of the top surface, so it suits checks between every step, with the other techniques used on selected samples.

Business impact

What changes when you characterize thin film surfaces this way

Typical changes in how teams work. Benchmarks are given only where a published source exists.

Before and with routine thin film surface checks

Metric Before Dropometer With Dropometer Indicative Benchmark
Surface check between steps Occasional, outside lab Every run, in minutes No published benchmark; track on your own process
Comparability Mixed models and liquids One fixed model and liquid set 8.9 mJ/m² spread between models on one TiN coating (Rogowska, 2006)
Ageing control Not measured Maximum wait set from angle over time Graphene 76.2° to 92.9° in 100 minutes in air (Carpenter et al., 2023)
Use of expensive techniques XPS and AFM on every sample Contact angle first, others on selected samples No published benchmark; track on your own lab

See the measurement on your own films

Send two film samples. We will show the comparison on a call.

Book a 15 minute demo

Estimate saved thin film development work

Enter your own numbers. The result is an estimate, not a Droplet Lab claim.

Thin film development estimate

Estimate saved thin film development work.

Each Dropometer unit is US$5,000; the default models one unit.
Substrate, deposition run and characterization cost for one candidate.
Deposition, contact angles with two or three liquids and analysis.
No published benchmark. Use your own estimate and start low if unsure.

Result

~0
Candidates saved per month
~0
Monthly savings
~0
Payback period
~0
First year net benefit

Monthly savings = materials saved + technician time saved from reduced iterations.

Limits

What contact angle cannot tell you about a thin film

Honest limits, so you know when to reach for another test.

It reads only the outermost few angstroms.
Fresh films age in air; fix the timing.
Surface energy depends on the model and liquids.
Roughness changes the apparent angle.
Very thin films can let the substrate show through.
It does not measure thickness or mechanical properties.

Contact angle and surface energy show how liquids meet the top surface of a film. Thickness, composition, crystal structure, roughness, hardness, modulus and adhesion to the substrate need their own characterization techniques.

Book a 15 minute demo Request a quote
Related

Standards, evidence and related coating workflows

These pages cover the contact angle and surface energy standards, the published film research and related coating checks.

Standard

ASTM D7334

Advancing contact angle on coatings, substrates and pigments.

View use case

Standard

ISO 19403-2

Surface free energy of solid surfaces from contact angles.

View use case

Case study

University of Toronto

Four Dropometers on two campuses, with published film data.

View use case

Published paper

Polyserotonin nanoparticles and films

Three liquid surface energy on polymer films.

View use case

Published paper

Carbon nitride film surface properties

The Dropometer as the reference contact angle instrument.

View use case

Instrument

Dropometer

Contact angle and surface energy by sessile drop.

View use case

Related use case

Functional, medical and electronic coatings

All coating use cases in one place.

View use case

Related use case

Dental and orthopedic implant surfaces

Surface checks on titanium and zirconia implants.

View use case

Related use case

Hydrogel and biomaterial wettability

Wetting checks for tissue engineering materials.

View use case

Guide

Biotechnology guide

Surface science for biotechnology teams.

View use case

How this page was created

Editorial and technical transparency notes for this page.

Transparency Details 4 checklist items
01

Drafting assistance

Drafted with Claude Opus 5.5 (Anthropic) using web search for sources, then edited by the Droplet Lab team.

02

Technical review

Reviewed and edited for technical accuracy by the Droplet Lab Team.

03

Verification steps

Standard identifiers, units, thresholds and key procedural claims are checked against cited sources before publication.

04

Updates

Reviewed every 12 months or when the underlying method changes.

Report a correction

Spotted an issue in this summary? Send a correction request and our team will review it.

Correction Request

We work hard to keep this page accurate and up to date. If you spot an error (wrong revision/year, missing requirement, incorrect interpretation, or broken link), tell us and we'll review it.

Contact us to report a correction
Sources

References

1.
Bain, C.D., Troughton, E.B., Tao, Y.T., Evall, J., Whitesides, G.M., Nuzzo, R.G. Formation of monolayer films by the spontaneous assembly of organic thiols from solution onto gold. Journal of the American Chemical Society 111:321 to 335, 1989 (ONR Technical Report No. 8, 1988). https://apps.dtic.mil/sti/pdfs/ADA229263.pdf
2.
Carpenter, J. et al. The surface energy of hydrogenated and fluorinated graphene. ACS Applied Materials and Interfaces 15:2429 to 2436, 2023. https://doi.org/10.1021/acsami.2c18329
3.
Peng, Z., Yang, R., Kim, M.A., Li, L., Liu, H. Influence of O2, H2O and airborne hydrocarbons on the properties of selected 2D materials. RSC Advances 7, 2017. https://pubs.rsc.org/en/content/articlehtml/2017/ra/c7ra02130e
4.
Li, Z. et al. Effect of airborne contaminants on the wettability of supported graphene and graphite. Nature Materials 12:925 to 931, 2013. https://doi.org/10.1038/nmat3709
5.
Rogowska, R. Surface free energy of thin layer coatings deposited by means of the arc vacuum method. Maintenance Problems 2:193 to 204, 2006. https://yadda.icm.edu.pl/baztech/element/bwmeta1.element.baztech-article-BAR0-0017-0107/c/httpwww_bg_utp_edu_plartpe22006pe22006193204.pdf
6.
Fernandez, V., Khayet, M. Evaluation of the surface free energy of plant surfaces: toward standardizing the procedure. Frontiers in Plant Science 6:510, 2015. https://doi.org/10.3389/fpls.2015.00510
7.
Ubuo, E.E. et al. The direct cause of amplified wettability: roughness or surface chemistry? Journal of Composites Science 5(8):213, 2021. https://doi.org/10.3390/jcs5080213
8.
Huhtamäki, T., Tian, X., Korhonen, J.T., Ras, R.H.A. Surface wetting characterization using contact angle measurements. Nature Protocols 13(7):1521 to 1538, 2018. https://doi.org/10.1038/s41596-018-0003-z
9.
Jeon, K. et al. Buffer components incorporate into the framework of polyserotonin nanoparticles and films during synthesis. Nanomaterials 12(12):2027, 2022. See our analysis of this paper. https://dropletlab.com/validation/citations/analysis/buffer-components-incorporate-into-the-framework-of-polyserotonin-nanoparticles-and-films-during-synthesis/
10.
Maley, J. et al. Fullerene like amorphous carbon nitride film surface properties and evaluating the initial adsorption kinetics of albumin and fibrinogen. Canadian Journal of Chemistry, 2025. See our analysis of this paper. https://dropletlab.com/validation/citations/analysis/fullerene-like-amorphous-carbon-nitride-film-surface-properties-and-evaluating-the-initial-adsorption-kinetics-of-albumin-and-fibrinogen/
11.
ASTM D7334-08(2022). Standard practice for surface wettability of coatings, substrates and pigments by advancing contact angle measurement. See our ASTM D7334 page. https://store.astm.org/d7334-08r22.html
12.
ISO 19403-2:2024. Paints and varnishes, wettability, part 2: determination of the surface free energy of solid surfaces by measuring the contact angle. See our ISO 19403-2 page. https://www.iso.org/standard/87262.html
13.
ASTM D5946-24. Standard test method for corona treated polymer films using water contact angle measurements. See our ASTM D5946 and ISO 15989 page. https://store.astm.org/d5946-24.html
14.
Chen, X. et al. Contact angle measurement with a smartphone. Review of Scientific Instruments 89(3):035117, 2018. https://pubs.aip.org/aip/rsi/article-abstract/89/3/035117/368179/Contact-angle-measurement-with-a-smartphone
15.
Surface tension measurement with a smartphone using a pendant drop. Colloids and Surfaces A: Physicochemical and Engineering Aspects. https://www.sciencedirect.com/science/article/abs/pii/S0927775717307744
16.
Droplet Lab validation papers
17.
Customer publications that cite the Dropometer
18.
University of Toronto case study
19.
Surface free energy calculator